• TABLE OF CONTENTS
HIDE
 Front Cover
 Title Page
 Preface
 Frontispiece
 Table of Contents
 List of figures and tables
 Acknowledgement
 Introduction
 Autecology of mangroves
 Ecosystem structure and functi...
 Community components: Microorg...
 Community components: Plants other...
 Community components: Inverteb...
 Community components: Fishes
 Community components: Amphibians...
 Community components: Birds
 Community components: Mammals
 Value of mangrove ecosystems to...
 Management implications
 Reference
 Appendix A. Summary of site characteristics...
 Appendix B. Fishes of mangrove...
 Appendix C. Amphibians and reptiles...
 Appendix D. Avifauna of south Florida...
 Appendix E. Mammals of south Florida...
 Back Cover














Title: Ecology of the mangroves of south Florida : a community profile
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Table of Contents
    Front Cover
        Front Cover 1
        Front Cover 2
    Title Page
        Page i
        Page ii
    Preface
        Page iii
    Frontispiece
        Page iv
    Table of Contents
        Page v
        Page vi
        Page vii
    List of figures and tables
        Page viii
    Acknowledgement
        Page ix
        Page x
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
    Autecology of mangroves
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
    Ecosystem structure and function
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
    Community components: Microorganisms
        Page 40
    Community components: Plants other than mangroves
        Page 41
        Page 42
        Page 43
        Page 44
    Community components: Invertebrates
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
    Community components: Fishes
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
        Page 55
        Page 56
        Page 57
    Community components: Amphibians and reptiles
        Page 58
        Page 59
        Page 60
    Community components: Birds
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
        Page 66
        Page 67
        Page 68
        Page 69
        Page 70
        Page 71
    Community components: Mammals
        Page 72
        Page 73
    Value of mangrove ecosystems to man
        Page 74
        Page 75
        Page 76
    Management implications
        Page 77
        Page 78
        Page 79
        Page 80
        Page 81
        Page 82
        Page 83
        Page 84
        Page 85
        Page 86
        Page 87
    Reference
        Page 88
        Page 89
        Page 90
        Page 91
        Page 92
        Page 93
        Page 94
        Page 95
        Page 96
        Page 97
        Page 98
        Page 99
        Page 100
        Page 101
        Page 102
        Page 103
        Page 104
        Page 105
    Appendix A. Summary of site characteristics and sampling methodology for fishes
        Page 106
        Page 107
        Page 108
        Page 109
    Appendix B. Fishes of mangrove areas
        Page 110
        Page 111
        Page 112
        Page 113
        Page 114
        Page 115
        Page 116
        Page 117
        Page 118
        Page 119
        Page 120
        Page 121
        Page 122
        Page 123
        Page 124
        Page 125
        Page 126
    Appendix C. Amphibians and reptiles from mangrove areas
        Page 127
        Page 128
        Page 129
    Appendix D. Avifauna of south Florida mangrove swamps
        Page 130
        Page 131
        Page 132
        Page 133
        Page 134
        Page 135
        Page 136
        Page 137
        Page 138
        Page 139
        Page 140
        Page 141
    Appendix E. Mammals of south Florida mangrove swamps
        Page 142
        Page 143
        Page 144
        Page 145
    Back Cover
        Page 146
        Page 147
Full Text
89 // DOCUMOT
Biological Services Program
FWS/OBS-81/24
January 1982
STHE ECOLOGY OF THE p
MANGROVES OF SOUTH FLORIDA: A COM LE


Bureau of Land Managerrent
Fish and Wildlife Service
U.S. Department of the Interior

i ,,

















The Biological Services Program was established within the U.S. Fish
and Wildlife Service to supply scientific information and methodologies on
key environmental issues that impact fish and wildlife resources and their
supporting ecosystems. The mission of the program is as follows:

To strengthen the Fish and Wildlife Service in its role as
a primary source of information on national fish and wild-
life resources, particularly in respect to environmental
impact assessment.

To gather, analyze, and present information that will aid
decisionmakers in the identification and resolution of
problems associated with major changes in land and water
use.

To provide better ecological information and evaluation
for Department of the Interior development programs, such
as those relating to energy development.

Information developed by the Biological Services Program is intended
for use in the planning and decisionmaking process to prevent or minimize
the impact of development on fish and wildlife. Research activities and
technical assistance services are based on an analysis of the issues, a
determination of the decisionmakers involved and their information needs,
and an evaluation of the state of the art to identify information gaps
and to determine priorities. This is a strategy that will ensure that
the products produced and disseminated are timely and useful.

Projects have been initiated in the following areas: coal extraction
and conversion; power plants; geothermal, mineral and oil shale develop-
ment; water resource analysis, including stream alterations and western
water allocation; coastal ecosystems and Outer Continental Shelf develop-
ment; and systems inventory, including National Wetland Inventory,
habitat classification and analysis, and information'transfer.

The Biological Services Program consists of the Office of Biological
Services in Washington, D.C., which is responsible for overall planning and
management; National Teams, which provide the Program's central scientific
and technical expertise and arrange for contracting biological services
studies with states, universities, consulting firms, and others; Regional
Staffs, who provide a link to problems at the operating level; and staffs at
certain Fish and Wildlife Service research facilities, who conduct in-house
research studies.











FWS/OBS-81/24
January 1982





THE ECOLOGY OF THE MANGROVES OF SOUTH FLORIDA:
A COMMUNITY PROFILE



by
JAI
William E. Odum
Carole C. Mclvor
Thomas J. Smith, III

Department of Environmental Sciences
University of Virginia
Charlottesville, Virginia 22901




Project Officer

Ken Adams
National Coastal Ecosystems Team
U.S. Fish and Wildlife Service
1010 Gause Boulevard
Slidell, Louisiana 70458


Performed for
National Coastal Ecosystems Team
Office of Biological Services
Fish and Wildlife Service
U.S. Department of the Interior
Washington, D.C. 20240

and

New Orleans OCS Office
Bureau of Land Management
U.S. Department of the Interior
New Orleans, Louisiana 70130


I










DISCLAIMER


The findings in this report are not to be construed as an official
U.S. Fish and Wildlife Service position unless so designated by other
authorized documents.































Library of Congress Card Number 82-600562




This report should be cited:

Odum, W.E., C.C. McIvor, and T.J. Smith, III. 1982. The ecology
of the mangroves of south Florida: a community profile. U.S. Fish
and Wildlife Service, Office of Biological Services, Washington,
D.C. FWS/OBS-81/24. 144 pp.

















PREFACE


This profile of the mangrove commun-
ity of south Florida is one in a series
of community profiles which treat coastal
and marine habitats important to man. The
obvious work that mangrove communities do
for man includes the stabilization and
protection of shorelines; the creation and
maintenance of habitat for a great number
of animals, many of which are either
endangered or have commercial value; and
the provision of the basis of a food web
whose final products include a seafood
smorgasbord of oysters, crabs, lobsters,
shrimp, and fish. Less tangible but
equally important benefits include wilder-
ness, aesthetic and life support consider-
ations.

The information on these pages can
give a basic understanding of the mangrove
community and its role in the regional
ecosystem of south Florida. The primary
geographic area covered lies along the
coast between Cape Canaveral on the east


and Tarpon Springs on the west. Refer-
ences are provided for those seeking
in-depth treatment of a specific facet of
mangrove ecology. The format, style, and
level of presentation make this synthesis
report adaptable to a diversity of needs
such as the preparation of environmental
assessment reports, supplementary reading
in marine science courses, and the devel-
opment of a sense of the importance of
this resource to those citizens who
control its fate.

Any questions or comments about or
requests for this publication should be
directed to:


Information Transfer Specialist
National Coastal Ecosystems Team
U.S. Fish and Wildlife Service
NASA-Slidell Computer Complex
1010 Gause Boulevard
Slidell, Louisiana 70458


I rr
















CONTENTS



Page

PREFACE ................................................................. iii
FIGURES ........................................... ........................... viii
TABLES ................................................... viii
ACKNOWLEDGMENTS ......................................................... ix

CHAPTER 1. INTRODUCTION ................................................. 1

1.1 "Mangrove" Definition ............................................ 1
1.2 Factors Controlling Mangrove Distribution ......................... 1
1.3 Geographical Distribution ......................................... 2
1.4 Mangrove Species Descriptions ..................................... 5
1.5 Mangrove Community Types ................................ ..... ... 7
1.6 Substrates ................................................... 9
1.7 Water Quality ................................................. 11

CHAPTER 2. AUTECOLOGY OF MANGROVES ......................................... 12

2.1 Adaptations to Natural Stress Anaerobic Sediments ................ 12
2.2 Adaptations to Natural Stress Salinity ......................... 12
2.3 Reproductive Strategies .......................................... 14
2.4 Biomass Partitioning .......................................... 15
2.5 Primary Production ............................................ 17
2.6 Herbivory ..................................................... 23
2.7 Wood Borers ................................................... 24
2.8 Mangrove Diseases ............................................. 25

CHAPTER 3. ECOSYSTEM STRUCTURE AND FUNCTION ............................... 26

3.1 Structural Properties of Mangrove Forests ........................ 26
3.2 Zonation, Succession and "Land Building" .......................... 26
3.3 Nutrient Cycling ............................................. 30
3.4 Litter Fall and Decomposition .................................... 32
3.5 Carbon Export ............................................ .... 34
3.6 Energy Flow .................................................... 36

CHAPTER 4. COMMUNITY COMPONENTS MICROORGANISMS .......................... 40

CHAPTER 5. COMMUNITY COMPONENTS PLANTS OTHER THAN MANGROVES ............... 41

5.1 Root and Mud Algae .................................. ........... 41
5.2 Phytoplankton ................................................. 43
5.3 Associated Vascular Plants ........................................ 43












CONTENTS (continued)


Page
CHAPTER 6. COMMUNITY COMPONENTS INVERTEBRATES .......................... 45

6.1 Ecological Relationships ........................................ 45
6.2 Arboreal Arthropod Community .................................... 47
6.3 Prop Root and Associated Mud Surface Community .................... 47
6.4 Water Column Community ............................................ 49

CHAPTER 7. COMMUNITY COMPONENTS FISHES ................................. 50

7.1 Basin Mangrove Forests ............................................ 50
7.2 Riverine Forests ................................................. 52
7.3 Fringing Forests along Estuarlne Bays and Lagoons ................. 54
7.4 Fringing Forests along Oceanic Bays and Lagoons .................. 56
7.5 Overwash Mangrove Islands ......................................... 56
7.6 Gradient of Mangrove Community Interactions ...................... 57

CHAPTER 8. COMMUNITY COMPONENTS AMPHIBIANS AND REPTILES .................. 58

CHAPTER 9. COMMUNITY COMPONENTS BIRDS .................................. 61

9.1 Ecological Relationships ........................................ 61
9.2 Wading Birds ....................................... ......... 61
9.3 Probing Shorebirds .................. ..................... .... 65
9.4 Floating and Diving Water Birds ................................. 65
9.5 Aerially-searching Birds ......................................... 67
9.6 Birds of Prey .................................................... 67
9.7 Arboreal Birds ......................................... ........ 68
9.8 Associations between Mangrove Community Types and Birds ........... 70
9.9 Mangroves as Winter Habitat for North American Migrant Land Birds 71

CHAPTER 10. COMMUNITY COMPONENTS MAMMALS ............................... 72

CHAPTER 11. VALUE OF MANGROVE ECOSYSTEMS TO MAN .......................... 74

11.1 Shoreline Stabilization and Storm Protection ..................... 74
11.2 Habitat Value to Wildlife ........................................ 74
11.3 Importance to Threatened and Endangered Species ................... 75
11.4 Value to Sport and Commercial Fisheries ......................... 75
11.5 Aesthetics, Tourism and the Intangibles ......................... 75
11.6 Economic Products .............................................. 76

CHAPTER 12. MANAGEMENT IMPLICATIONS ...................................... 77

12.1 Inherent Vulnerability ............................................ 77
12.2 Man-induced Destruction ........................................... 77
12.3 Effects of Oil Spills on Mangroves .............................. 80
12.4 Man-induced Modifications ...................................... 81
12.5 Protective Measures Including Transplanting ....................... 84
12.6 Ecological Value of Black vs. Red Mangroves ...................... 85
12.7 The Importance of Inter-community Exchange ....................... 85
12.8 Management Practices: Preservation ............................. 86
vi














CONTENTS (continued)



Page
REFERENCES ................................................................ 88

APPENDIX A: SUMMARY OF SITE CHARACTERISTICS AND SAMPLING METHODOLOGY
FOR FISHES ..................................................... 106

APPENDIX B: FISHES OF MANGROVE AREAS ....................................... 110

APPENDIX C: AMPHIBIANS AND REPTILES FROM MANGROVE AREAS .................... 127

APPENDIX D: AVIFAUNA OF MANGROVE AREAS ..................................... 130

APPENDIX E: MAMMALS OF MANGROVE AREAS ..................................... 142



































vii









FIGURES
Number Page

1 Approximate northern limits for the red mangrove (R), black
mangrove (B), and white mangrove (W) in Florida ...................... 3
2a A typical intertidal profile from south Florida showing the
distribution of red and black mangroves ............................. 4
2b The pattern of annual sea level change in south Florida ............... 4
3 Three species of Florida mangroves with propagules, flowers and leaves. 6
4 The six mangrove community types .................................... 8
5a Aboveground and belowground biomass of a Puerto Rican red
mangrove forest ................................................. 16
5b Light attenuation in a mangrove canopy; canopy height is 8 m ......... 16
6 The hypothetical relationship between waterway position and
community net primary production of Florida mangrove forests .......... 22
7 The hypothetical relationship between nutrient input, biomass,
productivity, and nutrient export from mangrove ecosystems ............ 31
8 Potential pathways of energy flow in mangrove ecosystems .............. 37
9 Vertical distribution of selected algae and invertebrates on
red mangrove prop roots .......................................... 42
10 Photograph of red mangrove prop root habitat in clear shallow
water with associated animal and plant populations ................... 46
11 Gradient of mangrove-associated fish communities showing
representative species ..................................... ........ 51
12 Aerial photograph of the mangrove belt of southwest Florida
near Whitewater Bay ............................................. 53
13 The mangrove water snake, Nerodia fasciata compressicauda,
curled on a red mangrove prop root ................................. 59
14 A variety of wading birds feeding in a mangrove-lined pool
near Flamingo, Florida ................................................ 62
15 Osprey returning to its nest in a red mangrove near Whitewater Bay .... 69
16 Damaged stand of red and black mangroves near Flamingo, Florida,
as it appeared 7 years after Hurricane Donna .......................... 78
17 Mangrove forest near Key West as it appeared in 1981 after
being destroyed by diking and impounding ............................ 79
18 Mangrove islands in Florida Bay near Upper Matecumbe Key .............. 87


TABLES
Number Page

la Estimates of mangrove production in Florida ........................... 20
lb Comparative measurements of photosynthesis in gC/m2/day ............... 21
Ic Gross primary production at different salinities .................... 21
2 Aboveground biomass of mangrove forests in the Ten Thousand
Islands region of Florida ......................................... 27
3 Estimates of litter fall in mangrove forests ........................ 33
4 Estimates of particulate carbon export from mangrove forests .......... 35
5 Nesting statistics of wading birds and associated species in
south Florida, 1974-75 ........................................... 64
6 Timing of nesting by wading birds and associated species in
south Florida .................................................... 66
7 General response of mangrove ecosystems to severe oil spills .......... 82
8 Estimated impact of various stages of oil mining on mangrove ecosystems 83

















ACKNOWLEDGMENTS


Many individuals and organizations
contributed significantly to the creation
of this publication. Most notable was
Eric Heald who worked extensively with us
on the manuscript and contributed unpub-
lished data. We thank Jeffrey Carlton,
Edward Conner, Roy R. Lewis, III, Ariel
Lugo, Larry Narcisse, Steven Macko, Aaron
Mills, Michael Robblee, Martin Roessler,
Samuel Snedaker, Durbin Tabb, Mike Wein-
stein, and Joseph Zieman for information
and helpful advice.

The draft manuscript was reviewed for
its scientific content by Armando de la
Cruz, Thomas Savage, James Kushlan (bird
section), and James P. Ray. Each of these


individuals provided information as well
as critical comments. We particularly
appreciate the unselfish help of Ken Adams
and the staff of the National Coastal Eco-
systems Team of the U.S. Fish and Wildlife
Service. Janet Ryan spent many hours typ-
ing the manuscript.

Factual errors and faulty conclu-
sions are the sole responsibility of the
authors. Carole Mclvor has taken primary
responsibility for Chapter 7, Tom Smith
for Chapters 8, 9, and 10, and Bill Odum
for the remainder of the publication.
Unless otherwise noted, photographs,
figures, and the cover were produced by
the authors.


000000mr- --- __Emm









CHAPTER 1. INTRODUCTION


1.1 "MANGROVE" DEFINITION

The term "mangrove" expresses two
distinctly different concepts. One usage
refers to halophytic species of trees and
shrubs halophytee = plant growing in
saline soil). In this sense, mangrove is
a catch-all, botanically diverse, non-
taxonomic expression given to approximate-
ly 12 families and more than 50 species
(Chapman 1970) of tropical trees and
shrubs (see Waisel 1972 for a detailed
list). While not necessarily closely
related, all these plants are adapted to
(1) loose, wet soils, (2) a saline habi-
tat, (3) periodic tidal submergence, and
(4) usually have degrees of viviparity of
propagules (see section 2.3 for discussion
of "viviparity" and "propagules").

The second usage of the term mangrove
encompasses the entire plant community
including individual mangrove species.
Synonymous terms include tidal forest,
tidal swamp forest, mangrove community,
mangrove ecosystem, mangal (Macnae 1968),
and mangrove swamp.

For consistency, in this publication
we will use the word "mangrove" for indi-
vidual kinds of trees; mangrove community,
mangrove ecosystem or mangrove forest will
represent the entire assemblage of "man-
groves".


1.2 FACTORS CONTROLLING MANGROVE DISTRI-
BUTION

Four major factors appear to limit
the distribution of mangroves and deter-
mine the extent of mangrove ecosystem
development. These factors include (1)
climate, (2) salt water, (3) tidal fluc-
tuation, and (4) substrate.


Climate

Mangroves are tropical species and
do not develop satisfactorily in regions
where the annual average temperature is
below 190C or 660F (Waisel 1972).
Normally, they do not tolerate temperature
fluctuations exceeding 100C (180F) or


temperatures below freezing for any length
of time. Certain species, for example,
black mangrove, Avicennia germinans, on
the northern coast of the Gulf of Mexico,
maintain a semi-permanent shrub form by
growing back from the roots after freeze
damage.

Lugo and Zucca (1977) discuss the
impact of low temperature stress on Flori-
da mangroves. They found that mangrove
communities respond to temperature stress
by decreasing structural complexity (de-
creased tree height, decreased leaf area
index, decreased leaf size, and increased
tree density). They concluded that man-
groves growing under conditions of high
soil salinity stress are less tolerant of
low temperatures. Presumably, other types
of stress (e.g., pollutants, diking) could
reduce the temperature tolerance of man-
groves.

High water temperatures can also be
limiting. McMillan (1971) reported that
seedlings of black mangrove were killed by
temperatures of 390 to 400C (1020 to
104uF) although established seedlings and
trees were not damaged. To our knowledge,
upper temperature tolerances for adult
mangroves are not well known. We suspect
that water temperatures in the range 420
to 450C (1070 to 1130F) may be limiting.


Salt Water

Mangroves are facultative halo-
phytes, i.e., salt water is not a physical
requirement (Bowman 1917; Egler 1948). In
fact, most mangroves are capable of
growing quite well in freshwater (Teas
1979). It is important to note, however,
that mangrove ecosystems do not develop in
strictly freshwater environments; salinity
is important in reducing competition from
other vascular plant species (Kuenzler
1974). See section 2.2 about salinity
tolerance of mangrove species.


Tidal Fluctuation

While tidal influence is not a
direct physiological requirement for


_ _I ___ ~_










mangroves, it plays an important indirect
role. First, tidal stress (alternate
wetting and drying), in combination with
salinity, helps exclude most other
vascular plants and thus reduces competi-
tion. Second, in certain locations, tides
bring salt water up the estuary against
the outward flow of freshwater and allow
mangroves to become established well
inland. Third, tides may transport
nutrients and relatively clean water into
mangrove ecosystems and export accumula-
tions of organic carbon and reduced sulfur
compounds. Fourth, in areas with high
evaporation rates, the action of the tides
helps to prevent soil salinities from
reaching concentrations which might be
lethal to mangroves. Fifth, tides aid in
the dispersal of mangrove propagules and
detritus.

Because of all of these factors,
termed tidal subsidies by E.P. Odum
(1971), mangrove ecosystems tend to reach
their greatest development around the
world in low-lying regions with relatively
large tidal ranges. Other types of water
fluctuation, e.g., seasonal variation in
freshwater runoff from the Florida Ever-
glades, can provide similar subsidies.


Substrate and Wave Energy

Mangroves grow best in depositional
environments with low wave energy. High
wave energy prevents establishment of
propagules, destroys the relatively shal-
low mangrove root system and prevents the
accumulation of fine sediments. The most
productive mangrove ecosystems develop
along deltaic coasts or in estuaries that
have fine-grained muds composed of silt,
clay and a high percentage of organic
matter. Anaerobic sediments pose no
problems for mangroves (see section 2.1)
and exclude competing vascular plant
species.


1.3 GEOGRAPHICAL DISTRIBUTION

Mangroves dominate approximately 75%
of the world's tropical coastline between
250N and 250S latitude (McGill 1959). On


the east coast of Africa, in Australia and
in New Zealand, they extend 100 to 150
farther south (Kuenzler 1974) and in
Japan, Florida, Bermuda, and the Red Sea
they extend 50 to 70 farther north. These
areas of extended range generally occur
where oceanographic conditions move un-
usually warm water away from the equator.

Although certain regions such as the
tropical Indo-Pacific have as many as 30
to 40 species of mangroves present, only
three species are found in Florida: the
red mangrove, Rhizophora mangle, the black
mangrove, Avicennia germinans, and the
white mangrove, Laguncularia racemosa. A
fourth species, buttonwood, Conocarpus
erecta, is not a true mangrove (no ten-
dency to vivipary or root modification),
but is an important species in the transi-
tion zone on the upland edge of mangrove
ecosystems (Tomlinson 1980).

The ranges of mangrove species in
Florida have fluctuated over the past
several centuries in response to relative-
ly short-term climatic change. Currently,
the situation is as follows (Figure 1).
The red mangrove and the white mangrove
have been reported as far north as Cedar
Key on the west coast of Florida (Rehm
1976) and north of the Ponce de Leon Inlet
on the east coast (Teas 1977); both of
these extremes lie at approximately 29010'
N latitude. Significant stands lie south
of Cape Canaveral on the east coast and
Tarpon Springs on the west coast. The
black mangrove has been reported as far
north as 300N latitude on the east coast
of Florida (Savage 1972) and as scattered
shrubs along the north coast of the Gulf
of Mexico.


Intertidal Distribution

The generalized distribution of the
red and black mangrove in relation to the
intertidal zone is shown in Figure 2a.
Local variations and exceptions to this
pattern occur commonly in response to
localized differences in substrate type
and elevation, rates of sea level rise,
and a variety of other factors (see sec-
tion 3.2 for a full discussion of mangrove




















- 30 N


R,W----- - Ponce de Leon Inlet
Cedar Key

Cape Canaveral
Tarpon Springs Indian River


Tampa Bay




Port Charlotte Harbor/
Sanibel Island



Rookery Bay
Ten Thousand IslandsBiscayne Bay
Shark River Valley .
Whitewater Bay/North River : 25 N

Florida Keys




Figure 1. Approximate northern limits for the red mangrove (R), black mangrove
(B), and white mangrove (W) in Florida (based on Savage 1972); although not in-
dicated in the figure, the black mangrove extends along the northern Gulf of Mex-
ico as scattered shrubs.









(A)




MHW- -PEAT

MLW,--- .. / --- ^EAT


LOW HIGH
MARSH MARSH
(RED MANGROVE (BLACK MANGROVE
DOMINATED) DOMINATED)




(B)


J F M A M J J A S O N D


+10 cm


+5 cm


SEA LEVEL


-5 cm


-10 cm


Figure 2. (a) A typical intertidal profile from south Florida showing the dis-
tribution of red and black mangrove (adapted from Provost 1974). (b) The pat-
tern of annual sea level change in south Florida (Miami)(adapted from Provost
1974).










zonation). Furthermore, it is important
to recognize that the intertidal zone in
most parts of Florida changes seasonally
(Provost 1974); there is a tendency for
sea level to be higher in the fall than in
the spring (Figure 2b). As a result the
"high marsh" may remain totally dry during
the spring and be continually submerged in
the autumn. This phenomenon further com-
plicates the textbook concept of the in-
tertidal, "low marsh" red mangrove and the
infrequently flooded, "high marsh" black
mangrove.


Mangrove Acreage in Florida

Estimates of the total acreage
occupied by mangrove communities in
Fl6rida vary widely between 430,000 acres
and over 500,000 acres (174,000 ha to over
202,000 ha). Eric Heald (Tropical
Bioindustries, 9869 Fern St., Miami, Fla.;
personal communication 1981) has
identified several reasons for the lack of
agreement between estimates. These
include: (1) inclusion or exclusion in
surveys of small bays, ponds and creeks
which occur within mangrove forests, (2)
incorrect identification of mangrove areas
from aerial photography as a result of
inadequate "ground-truth" observations,
poorly controlled aerial photography, and
simple errors of planimetry caused by
photography of inadequate scale.

The two most detailed estimates of
area covered by mangroves in Florida are
provided by the Coastal Coordinating Coun-
cil, State of Florida (1974) and Birnhak
and Crowder (1974). Considerable dif-
ferences exist between the two estimates.
The estimate of Birnhak and Crowder
(1974), which is limited to certain areas
of south Florida, appears to be unrealis-
tically high, particularly for Monroe
County (Eric Heald, personal communication
1981). Coastal Coordinating Council
(1974) estimates a total of 469,000 acres
(190,000 ha) within the State and suggests
an expected margin of error of 15% (i.e.
their estimate lies between 400,000 and
540,000 acres or 162,000 and 219,000 ha).


According to this survey, ninety percent
of Florida's mangroves are located in the
four southern counties of Lee (35,000
acres or 14,000 ha), Collier (72,000 acres
or 29,000 ha), Monroe (234,000 acres or
95,000 ha), and Dade (81,000 acres or
33,000 ha).

Much of the area covered by mangroves
in Florida is presently owned by Federal,
State or County governments, or by non-
profit organizations such as the National
Audubon Society. Approximately 280,000
acres (113,000 ha) fall into this category
(Eric Heald, personal communication 1981).
Most of this acreage is held by the
Federal Government as a result of the land
being including within the Everglades
National Park.



1.4 MANGROVE SPECIES DESCRIPTIONS

The following descriptions come
largely from Carlton (1975) and Savage
(1972); see these publications for further
comments and photographs. For more
detailed descriptions of germinating seeds
(propagules) see section 2.3. The three
species are shown in Figure 3.


The Black Mangrove (Avicennia germinans)

Avicennia germinans is synonymous
with A. nitida and is a member of the
family Avicenniaceae (formerly classed
under Verbenaceae). The tree may reach a
height of 20 m (64 ft) and has dark, scaly
bark. Leaves are 5 to 10 cm (2 to 4
inches) in length, narrowly elliptic or
oblong, shiny green above and covered with
short, dense hairs below. The leaves are
frequently encrusted with salt. This tree
is characterized by long horizontal or
"cable" roots with short vertical aerating
branches (pneumatophores) that profusely
penetrate the substrate below the tree.
Propagules are lima-bean shaped, dark
green while on the tree, and several
centimeters (1 inch) long. The tree
flowers in spring and early summer.


_ I ___














Black Mangrove, Avicennia germinans


White Mangrove, Laguncularia racemosa

r"4gat Vf


Red Mangrove, Rhizophora mangle
Figure 3. Three species of Florida mangroves with propagules, flowers, and leaves.


~rb










The White Mangrove (Laguncularia racemosa)

The white mangrove is one of 450
species of plants in 18 genera of the
family Combretaceae (synonymous with
Terminaliaceae). It is a tree or shrub
reaching 15 m (49 ft) or more in height
with broad, flattened oval leaves up to 7
cm (3 inches) long and rounded at both
ends. There are two salt glands at the
apex of the petiole. The propagule is
very small (1.0 to 1.5 cm or 0.4 to 0.6
inches long) and broadest at its apex.
Flowering occurs in spring and early
summer.


The Red Mangrove (Rhizophora mangle)

The red mangrove is one of more than
70 species in 17 genera in the family
Rhizophoraceae. This tree may reach 25 m
(80 ft) in height, has thin grey bark and
dark red wood. Leaves may be 2 to 12 cm
(1 to 5 inches) long, broad and blunt-
pointed at the apex. The leaves are
shiny, deep green above and paler below.
It is easily identified by its charac-
teristic "prop roots" arising from the
trunk and branches. The pencil-shaped
propagules are as much as 25 to 30 cm (10
to 12 inches) long after germination. It
may flower throughout the year, but in
Florida flowering occurs predominately in
the spring and early summer.


1.5 MANGROVE COMMUNITY TYPES

Mangrove forest communities exhibit
tremendous variation in form. For
example, a mixed scrub forest of black and
red mangroves at Turkey Point on Biscayne
Bay bears little resemblance to the
luxuriant forests, dominated by the same
two species, along the lower Shark River.

Lugo and Snedaker (1974) provided a
convenient classification system based on
mangrove forest physiogomy. They identi-
fied six major community types resulting
from different geological and hydrological
processes. Each type has its own charac-
teristic set of environmental variables
such as soil type and depth, soil salinity


range, and flushing rates. Each community
type has characteristic ranges of primary
production, litter decomposition and car-
bon export along with differences in
nutrient recycling rates, and community
components. The community types as shown
in Figure 4 are as follows:


(1) Overwash mangrove forests -
these islands are frequently overwashed by
tides and thus have high rates of organic
export. All species of mangroves may be
present, but red mangroves usually domi-
nate. Maximum height of the mangroves is
about 7 m (23 ft).

(2) Fringe mangrove forests man-
groves form a relatively thin fringe along
waterways. Zonation is typically as de-
scribed by Davis (1940) (see discussion in
section 3.2). These forests are best
defined along shorelines whose elevations
are higher than mean high tide. Maximum
height of the mangroves is about 10 m (32
ft).

(3) Riverine mangrove forests this
community type includes the tall flood
plain forests along flowing waters such as
tidal rivers and creeks. Although a shal-
low berm often exists along the creek
bank, the entire forest is usually flushed
by daily tides. All three species of
mangroves are present, but red mangroves
(with noticeably few, short prop roots)
predominate. Mangroves may reach heights
of 18 to 20 m (60 to 65 ft).

(4) Basin mangrove forests these
forests occur inland in depressions chan-
neling terrestrial runoff toward the
coast. Close to the coast they are in-
fluenced by daily tides and are usually
dominated by red mangroves. Moving in-
land, the tidal influence lessens and
dominance shifts to black and white man-
groves. Trees may reach 15 m (49 ft) in
height.

(5) Hammock forests hammock man-
grove communities are similar to the basin
type except that they occur on ground that
is slightly elevated (5 to 10 cm or 2 to 4
inches) relative to surrounding areas.


7


- ~------^--------DIIUIII-





















(1) OVERWASH FOREST


(3) RIVERINE FOREST


(4) BASIN FOREST


(5) HAMMOCK FOREST (6) SCRUB FOREST

Figure 4. The six mangrove community types (Lugo and Snedaker 1974).


(2) FRINGE FOREST










All species of mangroves may be present.
Trees rarely exceed 5 m (16 ft) in height.

(6) Scrub or dwarf forests this
community type is limited to the flat
coastal fringe of south Florida and the
Florida Keys. All three species are
present. Individual plants rarely exceed
1.5 m (4.9 ft) in height, except where
they grow over depressions filled with
mangrove peat. Many of these tiny trees
are 40 or more years of age. Nutrients
appear to be limiting although substrate
(usually limestone marl) must play a role.

Throughout this publication we have
attempted to refer to Lugo and Snedaker's
classification scheme wherever possible.
Without a system of this type, comparisons
between sites become virtually
meaningless.


1.6 SUBSTRATES

Understanding mangrove-substrate
relationships is complicated by the
ability of mangroves to grow on many types
of substrates and because they often alter
the substrate through peat formation and
by altering patterns of sedimentation. As
a result, mangroves are found on a wide
variety of substrates including fine,
inorganic muds, muds with a high organic
content, peat, sand, and even rock and
dead coral if there are sufficient
crevices for root attachment. Mangrove
ecosystems, however, appear to flourish
only on muds and fine-grained sands.

In Florida, the primary mangrove
soils are either calcareous marl muds or
calcareous sands in the southern part of
the State and siliceous sands farther
north (Kuenzler 1974). Sediment distribu-
tion and, hence, mangrove development, is
controlled to a considerable extent by
wave and current energy. Low energy
shorelines accumulate fine-grained sedi-
ments such as mud and silt and usually
have the best mangrove growth. Higher
energy shorelines (more wave action or
higher current velocities) are charac-
terized by sandy sediments and less pro-
ductive mangroves. If the wave energy


becomes too great, mangroves will not be
present. Of the three species of Florida
mangroves, white mangroves appear to
tolerate sandy substrates the best (per-
sonal observation), possibly because this
species may tolerate a greater depth to
the water table than the other two
species.

Mangroves in Florida often modify the
underlying substrate through peat deposi-
tion. It is not unusual to find layers of
mangrove peat several meters thick under-
lying well-established mangrove ecosystems
such as those along the southwest coast of
Florida. Cohen and Spackman (1974) pre-
sented a detailed account of peat forma-
tion within the various mangrove zones of
south Florida and also in areas dominated
by black needle rush (Juncus roemerianus),
smooth cordgrass (Spartina alterniflora)
and a variety of other macrophytes; Cohen
and Spackman (1974) also provide descrip-
tions and photography to aid in the iden-
tification of unknown peat samples.

The following descriptions come from
Cohen and Spackman (1974) and from the
personal observations of W.E. Odum and
E.J. Heald. Red mangroves produce the
most easily recognized peat. More recent
deposits are spongy, fibrous and composed
to a great extent of fine rootlets (0.2 to
3.0 mm in diameter). Also present are
larger pieces of roots (3 to 25 mm), bits
of wood and leaves, and inorganic
materials such as pyrite, carbonate
minerals, and quartz. Older deposits are
less easily differentiated although they
remain somewhat fibrous. Peat which has
recently been excavated is reddish-brown
although this changes to brown-black after
a short exposure to air. Older deposits
are mottled reddish-brown; deposits with a
high content of carbonates are greyish-
brown upon excavation.

Cohen and Spackman (1974) were unable
to find deposits of pure black mangrove or
white mangrove peat suggesting that these
two species may not form extensive depos-
its of peat while growing in pure stands.
There are, however, many examples of peats
which are mixtures of red mangrove
material and black mangrove roots. They










suggested that the black mangrove peats
identified by Davis (1946) were probably
mixtures of peat from several sources.

Throughout south Florida the sub-
strate underlying mangrove forests may
consist of complicated patterns of
calcareous muds, marls, shell, and sand
interspersed and overlain by layers of
mangrove peat and with limestone bedrock
at the bottom. Detailed descriptions of
this complex matrix and its spatial varia-
tion were given by Davis (1940, 1943,
1946), Egler (1952), Craighead (1964),
Zieman (1972) and Cohen and Spackman
(1974) among others. Scoffin (1970) dis-
cussed the ability of red mangrove to
trap and hold sediments about its prop
roots. So called "land-building" by man-
groves is discussed in section 3.2.

The long-term effect of mangrove peat
on mangrove distribution is not entirely
clear. Certainly, if there is no change
in sea level or if erosion is limited, the
accumulation of peat under stands of red
mangroves combined with deposition and
accumulation of suspended sediments will
raise the forest floor sufficiently to
lead to domination by black or white man-
groves arrd, ultimately, more terrestrial
species. Whether this is a common se-
quence of events in contemporary south
Florida is not clear. It is clear that
peat formation is a passive process and
occurs primarily where and when physical
processes such as erosion and sea level
rise are of minimal importance (Wanless
1974).

Zieman (1972) presented an inter-
esting argument suggesting that mangrove
peat may be capable of dissolving under-
lying limestone rock, since carbonates may
dissolve at pH 7.8. Through this process,
shallow depressions might become deeper
and the overlying peat layer thicker
without raising the surface of the forest
floor.

Data on chemical characteristics of
Florida mangrove soils and peat are
limited. Most investigators have found
mangrove substrates to be almost totally
anaerobic. Lee (1969) recorded typical Eh


values of -100 to -400 my in mangrove
peats. Such evidence of strongly reducing
conditions are not surprising considering
the fine-grained, high organic nature of
most mangrove sediments. Although man-
groves occur in low organic sediments
(less than 1% organic matter), typical
values for mangrove sediments are 10% to
20% organic matter.

Lee (1969) analyzed 3,000- to 3,500-
year-old mangrove peat layers underlying
Little Black Water Sound in Florida Bay
for lipid carbon content. Peat lipid
content varied between 0.6 and 2.7 mg
lipid-C/gram of peat (dry wt) or about 3%
of the total organic carbon total. These
values usually increased with depth. Long
chain fatty acids (C-16 and C-18) were the
dominant fatty acids found.

Florida mangrove peats are usually
acidic, although the presence of carbonate
materials can raise the pH above 7.0.
Zieman (1972) found red mangrove peats to
range from pH 4.9 to 6.8; the most acid
conditions were usually found in the cen-
ter of the peat layer. Lee (1969) re-
corded a pH range from 5.8 to 6.8 in red
mangrove peat at the bottom of a shallow
embayment. Although Davis (1940) found a
difference between red mangrove peat (5.0
to 5.5) and black mangrove peat (6.9 to
7.2), this observation has not been con-
firmed because of the previously mentioned
difficulty in finding pure black mangrove
peat.

Presumably, the acidic character of
mangrove peat results from release of
organic acids during anaerobic decomposi-
tion and from the oxidation of reduced
sulfur compounds if the peat is dried in
the presence of oxygen. This last point
explains why "reclaimed" mangrove areas
often develop highly acidic soils (pH 3.5
to 5.0) shortly after reclamation. This
"cat clay" problem has greatly complicated
the conversion of mangrove regions to
agricultural land in Africa and southeast
Asia (Hesse 1961; Hart 1962, 1963; Macnae
1968).

In summary, although current under-
standing of mangrove peats and soils is










fragmentary and often contradictory, we
can outline several generalizations:

(1) Mangroves can grow on a wide
variety of substrates including mud, sand,
rock, and peat.

(2) Mangrove ecosystems appear to
flourish on fine-grained sediments which
are usually anaerobic and may have a high
organic content.

(3) Mangrove ecosystems which per-
sist for some time may modify the under-
lying substrate through peat formation.
This appears to occur only in the absence
of strong physical forces.

(4) Mangrove peat is formed pri-
marily by red mangroves and consists pre-
dominantly of root material.

(5) Red mangrove peats may reach
thicknesses of several meters, have a
relatively low pH, and may be capable of
dissolving underlying layers of limestone.

(6) When drained, dried, and
aerated, mangrove soils usually experience
dramatic increases in acidity due to the
oxidation of reduced sulfur compounds.
This greatly complicates their conversion
to agriculture.


1.7 WATER QUALITY

Water quality characteristics of sur-
face waters flowing through Florida man-
grove ecosystems exhibit great variation
from one location to the next. Proximity
to terrestrial ecosystems, the ocean, and
human activities are all important in
determining overall water quality.
Equally important is the extent of the
mangrove ecosystem since drastic altera-
tions in water quality can occur within a
stand of mangroves.

In general, the surface waters
associated with mangroves are charac-
terized by (1) a wide range of salinities


from virtually fresh water to above 40 ppt
(discussed in section 2.2), (2) low macro-
nutrient concentrations (particularly
phosphorous), (3) relatively low dissolved
oxygen concentrations, and (4) frequently
increased water color and turbidity. The
last three characteristics are most pro-
nounced in extensive mangrove ecosystems
such as those adjacent to the Everglades
and least pronounced in small, scattered
forests such as the overwash islands in
the Florida Keys.

Walsh (1967), working in a mangrove
swamp in Hawaii, was one of the first to
document the tendency of mangrove eco-
systems to act as a consumer of oxygen and
a sink for nutrients such as nitrogen and
phosphorous. Carter et al. (1973) and
Lugo et al. (1976) confirmed these obser-
vations for Florida mangrove swamps. Evi-
dently, nutrients are removed and oxygen
consumed by a combination of periphyton on
mangrove prop roots, mud, organic detritus
on the sediment surface, the fine root
system of the mangroves, small inverte-
brates, benthic and epiphytic algae, and
bacteria and fungi on all these surfaces.

The results of oxygen depletion and
nutrient removal are (1) dissolved oxygen
concentrations below saturation, typically
2 to 4 ppm and often near zero in stagnant
locations and after heavy, storm-generated
runoff, (2) very low total phosphorus
values, frequently below detection limits,
and (3) moderate total nitrogen values
(0.5 to 1.5 mg/l). In addition, TOC
(total organic carbon) may range from 4 to
50 ppm or even higher after rain; Eric
Heald (personal communication 1981) has
measured DOC (dissolved organic carbon)
values as high as 110 ppm in water flowing
from mangroves to adjacent bays. Tur-
bidity usually falls in the 1 to 15 JTU
(Jackson turbity units) range. The pH of
the water column in Florida swamps is
usually between 6.5 and 8.0 and alkalinity
between 100 to 300 mg/l. Obviously, ex-
ceptions to all of these trends can occur.
Both natural and human disturbance can
raise macronutrient levels markedly.





11


III*A*IIII~IYIVIIU~.~ --









CHAPTER 2. AUTECOLOGY OF MANGROVES


2.1 ADAPTATIONS TO NATURAL STRESS -
ANAEROBIC SEDIMENTS

Mangroves have a series of remarkable
adaptations which enable them to flourish
in an environment characterized by high
temperatures, widely fluctuating salini-
ties, and shifting, anaerobic substrates.
In this section we review a few of the
most important adaptations.

The root system of mangroves provides
the key to existence upon unfriendly sub-
strates (see Gill and Tomlinson 1971 for
an anatomical review of mangrove roots).
Unlike most higher plants, mangroves
usually have highly developed aerial roots
and modest below-ground root systems. The
aerial roots allow atmospheric gases to
reach the underground roots which are
embedded in anaerobic soils. The red
mangrove has a system of stilt or prop
roots which extend a meter (3 ft) or more
above the surface of the soil and contain
many small pores (lenticels) which at low
tide allow oxygen to diffuse into the
plant and down to the underground roots by
means of open passages called aerenchyma
(Scholander et al. 1955). The lenticels
are highly hydrophobic and prevent water
penetration into the aerenchyma system
during high tide (Waisel 1972).

The black mangrove does not have prop
roots, but does have small air roots or
pneumatophores which extend vertically
upward from the underground roots to a
height of 20 to 30 cm (8 to 12 inches)
above the soil. These pneumatophores
resemble hundreds of tiny fingers sticking
up out of the mud underneath the tree
canopy. At low tide, air travels through
the pneumatophores into the aerenchyma
system and then to all living root tis-
sues. The white mangrove usually does not
have either prop roots or pneumatophores,
but utilizes lenticels in the lower trunk
to obtain oxygen for the aerenchyma sys-
tem. "Peg roots" and pneumatophores may
be present in certain situations (Jenik
1967).

Mangroves achieve structural stabili-
ty in at least two ways. Species such as
the red mangrove use the system of prop


roots to provide a more or less firm foun-
dation for the tree. Even though the prop
roots are anchored with only a modest
assemblage of underground roots, the hori-
zontal extent of the prop root system
insures considerable protection from all
but the worst of hurricanes. Other man-
grove species, including the black man-
grove, obtain stability with an extensive
system of shallow, underground "cable"
roots that radiate out from the central
trunk for a considerable distance in all
directions; the pneumatophores extend up-
ward from these cable roots. As in all
Florida mangroves, the underground root
system is shallow and a tap root is
lacking (Walsh 1974). As Zieman (1972)
found, individual roots, particularly of
red mangroves, may extend a meter or more
downward in suitable soils.

From the standpoint of effectiveness
in transporting oxygen to the underground
roots, both prop roots and cable roots
seem equally effective. From the perspec-
tive of stability, the prop roots of red
mangroves appear to offer a distinct ad-
vantage where wave and current energies
are high.

Unfortunately, as pointed out by Odum
and Johannes (1975), the same structure
which allows mangroves to thrive in an-
aerobic soil is also one of the tree's
most vulnerable components. Exposed por-
tions of the aerial root system are sus-
ceptible to clogging by fine suspended
material, attack by root borers, and pro-
longed flooding (discussed further in
section 12.1). Such extended stress on
the aerial roots can kill the entire tree.


2.2 ADAPTATIONS TO NATURAL STRESS -
SALINITY

Mangroves accommodate fluctuations and
extremes of water and soil salinity
through a variety of mechanisms, although
not all mechanisms are necessarily present
in the same species. Scholander et al.
(1962) reported experimental evidence for
two major methods of internal ion regula-
tion which they identified in two dif-
ferent groups of mangroves: (1) the salt










exclusion species and (2) the salt excre-
tion species. In addition, some mangroves
utilize succulence and the discarding of
salt-laden organs or parts (Teas 1979).

The salt-excluding species, which
include the red mangrove, separate
freshwater from sea water at the root
surface by means of a non-metabolic ultra-
filtration system (Scholander 1968). This
"reverse osmosis" process is powered by a
high negative pressure in the xylem which
results from transpiration at the leaf
surface. Salt concentration in the sap of
salt-excluding mangroves is about 1/70 the
salt concentration in sea water, although
this concentration is almost 10 times
higher than found in normal plants
(Scholander et al. 1962).

Salt-secreting species, including
black and white mangroves (Scholander
1968), use salt glands on the leaf surface
to excrete excess salt. This is probably
an enzymatic process rather than a physi-
cal process since it is markedly tempera-
ture sensitive (Atkinson et al. 1967).
The process appears to involve active
transport with a requirement for biochemi-
cal energy input. As a group, the salt
secreters tend to have sap salt concentra-
tions approximately 10 times higher (1/7
the concentration of sea water) than that
of the salt excluders.

In spite of these two general tenden-
cies, it is probably safe to say that
individual species utilize a variety of
mechanisms to maintain suitable salt
balance (Albert 1975). For example, the
red mangrove is an effective, but not
perfect, salt excluder. As a result this
species must store and ultimately dispose
of excess salt in leaves and fruit (Teas
1979). Most salt secreters, including
white and black mangroves, are capable of
limited salt exclusion at the root sur-
face. The white mangrove, when exposed to
hypersaline conditions, not only excludes
some salt and secretes excess salt through
its salt glands, but also develops
thickened succulent leaves and discards
salt during leaf fall of senescent leaves
(Teas 1979).


There appears to be some variation in
the salinity tolerance of Florida man-
groves. The red mangrove is probably
limited by soil salinities above 60 to 65
ppt. Teas (1979) recalculated Bowman's
(1917) data and concluded that transpira-
tion in red mangrove seedlings ceases
above 65 ppt. Cintron et al. (1978) found
more dead than living red mangrove trees
where interstitial soil salinities ex-
ceeded 65 ppt.

On the other hand, white and black
mangroves, which both possess salt excre-
tion and limited salt exclusion mech-
anisms, can exist under more hypersaline
conditions. Macnae (1968) reported that
black mangroves can grow at soil salini-
ties greater than 90 ppt. Teas (1979)
reported dwarfed and gnarled black and
white mangroves occurring in Florida at
soil salinities of 80 ppt.

There may be an additional factor or
factors involved in salinity tolerance of
mangroves. McMillan (1975) found that
seedlings of black and white mangroves
survived short-term exposures to 80 ppt
and 150 ppt sea water if they were grown
in a soil with a moderate clay content.
They failed to survive these salinities,
however, if they were grown in sand. A
soil with 7% to 10% clay appeared to be
adequate for increased protection from
hypersaline conditions.

Vegetation-free hypersaline lagoons
or bare sand flats in the center of man-
grove ecosystems have been described by
many authors (e.g., Davis 1940; Fosberg
1961; Bacon 1970). These features have
been variously called salitrals (-Holdridge
1940), salinas, salterns, salt flats, and
salt barrens. Evidently, a combination of
low seasonal rainfall, occasional inunda-
tion by sea water, and high evaporation
rates results in soil salinities above 100
ppt, water temperatures as high as 450C
(1130F) in any shallow, standing water,
and subsequent mangrove death (Teas 1979).
Once established, salinas tend to persist
unless regular tidal flushing is enhanced
by natural or artificial changes in tidal
circulation.



13


~F~""~~I"I"-~l~-"~111--"I










Although salinas occur frequently in
Florida, they are rarely extensive in
area. For example, between Rookery Bay
and Marco Island (south of Naples,
Florida) there are a series of salinas in
the black mangrove-dominated zone on the
upland side of the mangrove swamps. These
hypersaline lagoons occur where the normal
flow of fresh water from upland sources
has been diverted, presumably resulting in
elevated soil salinities during the dry
winter months.

In summary, salinity is a problem for
mangroves only under extreme hypersaline
conditions. These conditions occur natu-
rally in Florida in irregularly flooded
areas of the "high swamp" above the normal
high tide mark and are accompanied by high
soil salinities. Florida mangroves,
listed in order of increasing salinity
tolerance, appear to be red, white, and
black.


2.3 REPRODUCTIVE STRATEGIES

As pointed out by Rabinowitz (1978a),
virtually all mangroves share two common
reproductive strategies: dispersal by
means of water (van der Pijl 1972) and
vivipary (Macnae 1968; Gill and Tomlinson
1969). Vivipary means that the embryo
develops continuously while attached to
the parent tree and during dispersal.
Since there is uninterrupted development
from zygote through the embryo to seedling
without any intermediate resting stages,
the word "seed" is inappropriate for
viviparous species such as mangroves; the
term propagulee" is generally used in its
place.

While the phenology of black and
white mangroves remains sketchy, Gill and
Tomlinson (1971) thoroughly described the
sequence of flowering in the red mangrove.
Flowering in this species may take place
at any time of the year, at least in
extreme south Florida, but reaches a maxi-
mum in the late spring and summer. The
flowers open approximately 1 to 2 months
after the appearance of buds. The flower
remains intact only 1 to 2 days; this


probably accounts for the low fertiliza-
tion rate, estimated by Gill and Tomlinson
at 0% to 7.2%. Propagule development is
slow, ranging from 8 to 13 months. Savage
(1972) mentions that on the Florida gulf
coast, red mangrove propagules mature and
fall from the tree from July to September.
Within the Everglades National Park, black
mangroves flower from May until July and
bear fruit from August until November
while white mangroves flower from May to
August and bear fruit from July to October
(Loope 1980).

The propagules of the three species
of Florida mangroves are easy to differen-
tiate. The following descriptions all
come from Rabinowitz (1978a). White man-
grove propagules are small and flattened,
weigh less than a gram, are about 2 cm
long, are pea-green when they fall from
the parent tree, and turn mud-brown in two
days or so. The pericarp (wall of the
ripened propagule) serves as a float and
is not shed until the seedling is estab-
lished. During dispersal the radicle
(embryonic root) emerges from the propa-
gule. This germination during dispersal
has led Savage (1972) to refer to the
white mangrove as "semi-viviparous".

The propagules of the black mangrove
when dropped from the tree are oblong-
elliptical (resemble a flattened olive),
weigh about 1 g and are about 2 cm long.
The pericarp is lost within a few days
after dropping from the tree; at this
point the cotyledons (primary leaves)
unfold and the propagule resembles two
butterflies on top of one another.

Propagules of the red mangrove under-
go extensive vivipary while on the tree.
When propagules fall from the tree they
resemble large green beans. They are rod-
shaped with pointed ends, about 20 cm
long, and weigh an average of 15 g.

Propagules of all three species float
and remain viable for extended periods of
time. Apparently, there is an obligate
dispersal time for all Florida mangroves,
i.e., a certain period of time must elapse
during dispersal for germination to be











complete and after which seedling estab-
lishment can take place. Rabinowitz
(1978a) estimates the obligate dispersal
period at approximately 8 days for white
mangroves, 14 days for black, and 40 days
for red. She further estimates the addi-
tional time for root establishment at 5,
7, and 15 days for white, black, and red
mangroves, respectively. Her estimate for
viable longevity of the propagules is 35
days for white mangroves and 110 days for
black. Davis (1940) reports viable propa-
gules of red mangroves that had been kept
floating for 12 months.

Rabinowitz (1978a) also concluded
that black and white mangroves require a
stranding period of 5 days or more above
the influence of tides to take hold in the
soil. As a result, these two species are
usually restricted to the higher portions
of the mangrove ecosystem where tidal
effects are infrequent.

The elongated red mangrove propagule,
however, has the potential to become
established in shallow water with tidal
influence. This happens in at least two
ways: (1) stranding in a vertical posi-
tion (they float vertically) or (2)
stranding in a horizontal position,
rooting and then vertical erection by the
plant itself. Lawrence (1949) and Rabino-
witz (1978a) felt that the latter was the
more common method. M. Walterding (Calif.
Acad. Sci., San Francisco; personal com-
munication 1980) favors vertical estab-
lishment; based upon his observations,
surface water turbulence works the propa-
gule into the substrate during falling
tides.

Mortality of established seedlings
seems to be related to propagule size.
Working in Panama, Rabinowitz (1978b)
found that the mortality rate of mangrove
seedlings was inversely correlated with
initial propagule size. The white man-
grove, which has the smallest propagule,
has the highest rate of seedling mortal-
ity. The black mangrove has an interme-
diate mortality rate while the red man-
grove, with the largest propagule, has the
lowest seedling mortality rate. She


concluded that species with small
propagules establish new cohorts annually
but die rapidly, while species such as the
red mangroves may have long-lived and
often overlapping cohorts.

Propagule size and seedling mortality
rates are particularly important in con-
siderations of succession and replacement
in established mangrove forests. Light is
usually the most serious limiting factor
underneath existing mangrove canopies.
Rabinowitz (1978b) suggested that species
with short-lived propagules must become
established in an area which already has
adequate light levels either due to tree
fall or some other factor. In contrast,
red mangrove seedlings can become estab-
lished under an existing, dense canopy and
then, due to their superior embryonic
reserves, are able to wait for months for
tree fall to open up the canopy and pre-
sent an opportunity for growth.


2.4 BIOMASS PARTITIONING

Few investigators have partitioned
the total biomass, aboveground and below-
ground, contained in a mangrove tree. An
analysis of red mangroves in a Puerto
Rican forest by Golley et al. (1962) gives
some insight into what might be expected
in south Florida. Aboveground and below-
ground biomass existed in a ratio of 1:1
if fine roots and peat are ignored (Figure
5). In this case, peat and very fine
roots (smaller than 0.5 cm diameter) ex-
ceeded remaining biomass by 5:1. Lugo et
al. (1976) reported the following values
for a south Florida red mangrove overwash
forest. All values were reported in dry
grams per square meter, plus and minus one
standard error, and ignoring belowgr und
biomass. They found 70 + 22 g/m2 of
leaves, 12.8 15.3 g/m of propagules,
7043 + 7 g/m2 of wood, 4695 t 11 g/mi of
prop roots and 1565 + 234.5 g/m of detri-
tus on the forest floor.

Biomass partitioning between dif-
ferent species and locations must be
highly variable. The age of the forest
will influence the amount of wood biomass;


NEENSEMEMMMEMMMM











LEAVES
(778)
BRANCHES (1274)
PROP ROOTS (1437)

TRUNK (2796)


LARGE
ROOTS (997)


SMALL ROOTS (4000)


(B)


5000


10000


FOOT CANDLES


Figure 5. (a) Aboveground and belowground biomass of a Puerto Rican red mangrove
forest. Values in parentheses are dry g/m2; large roots = 2 cm+ in diameter,
small roots = 0.5 1.0 cm. (b) Vertical distribution of light intensity in the
same forest; canopy height is 8 m (26 ft) (both figures adapted from Golley et al.
1962).


(A)


SOIL
SURFACE


HEIGHT

(M)










detritus varies enormously from one site
to the next depending upon the amount of
fluvial transport. The biomass charac-
teristics of a scrub forest probably bear
little resemblance to those of a fringing
forest. At the present time, there is not
enough of this type of data available to
draw many conclusions. One intriguing
point is that red mangrove leaf bioTass
averages between 700 and 800 g/m at
various sites with very different forest
morphologies (Odum and Heald 1975a). This
may be related to the tendency of mangrove
canopies, once they have become estab-
lished, to inhibit leaf production at
lower levels through self-shading.

Golley et al. (1962) showed that the
red mangrove canopy is an extremely effi-
cient light interceptor. Ninety-five
percent of the available light had been
intercepted 4 m (13 ft) below the top of
the canopy (Figure 5). As a result, 90%
of the leaf biomass existed in the upper 4
m of the canopy. Chlorophyll followed the
same pattern of distribution.

The leaf area index (LAI) of mangrove
forests tends to be relatively low. Gol-
ley et al. (1962) found a LAI of 4.4 for a
Puerto Rican red mangrove forest. Lugo et
al. (1975) reported a LAI of 5.1 for a
Florida black mangrove forest and 3.5 for
a Florida fringe red mangrove forest. A
different black mangrove forest, in Flori-
da, was found to have values ranging from
1 to 4 and an average of 2 to 2.5 (Lugo
and Zucca 1977). These values compare
with LAI's of 10 to 20 recorded for most
tropical forests (Golley et al. 1974).
The low leaf area values of mangrove
forests can be attributed to at least
three factors: (1) effective light inter-
ception by the mangrove canopy, (2) the
inability of the lower mangrove leaves to
flourish at low light intensities, and (3)
the absence of a low-light-adapted plant
layer on the forest floor.


2.5 PRIMARY PRODUCTION

Prior to 1970 virtually no informa-
tion existed concerning the productivity


of mangroves in Florida. Since that time
knowledge has accumulated rapidly, but it
is still unrealistic to expect more than
preliminary statements about Florida man-
grove productivity. This deficiency can
be traced to (1) the difficulties asso-
ciated with measurements of mangrove pro-
ductivity and (2) the variety of factors
that affect productivity and the resulting
variations that exist from site to site.

Productivity estimates come from
three methods: (1) harvest, (2) gas ex-
change, and (3) litter fall. Harvest
methods require extensive manpower and
knowledge of the age of the forest. They
are best employed in combination with
silviculture practices. Since silvicul-
ture of south Florida mangroves is practi-
cally non-existent, this method has rarely
been used in Florida. Noakes (1955),
Macnae (1968), and Walsh (1974) should be
consulted for productivity estimates based
on this technique in other parts of the
world.

Gas exchange methods, based on
measurements of CO2 changes, have the
advantage of precision and response to
short-term changes in light, temperature,
and flooding. They include both above-
ground and belowground production. On the
negative side, the necessary equipment is
expensive and tricky to operate properly.
Moreover, extrapolations from short-term
measurements to long-term estimates offer
considerable opportunity for error.
Nevertheless, the best estimates of pro-
ductivity come from this method.

The litter fall technique (annual
litter fall x 3 = annual net primary pro-
duction) was proposed by Teas (1979) and
is based on earlier papers by Bray and
Gorham (1964) and Golley (1972) for other
types of forests. This is a quick and
dirty method although the lack of pre-
cision remains to be demonstrated for
mangroves. An even quicker and dirtier
method proposed by Teas (1979) is to (1)
estimate leaf standing crop (using various
techniques including harvesting or light
transmission relationships) and (2) multi-
ply by three. This assumes an annual leaf











turnover of one, which is supported by the
data of Heald (1969) and Pool et al.
(1977).

Mangrove productivity is affected by
many factors; some of these have been
recognized and some remain totally ob-
scure. Carter et al. (1973) propose
lumping these factors into two broad cate-
gories: tidal and water chemistry. We
believe that a number of additional cate-
gories should be considered.

A minimal, though incomplete, list of
factors controlling mangrove productivity
must include the following:

species composition of the stand

age of the stand

presence or absence of competing
species

degree of herbivory

presence or absence of disease and
parasites

*depth of substrate

substrate type

Nutrient content of substrate

*nutrient content of overlying water

salinity of soil and overlying water

transport efficiency of oxygen to root
system

amount of tidal flushing

relative wave energy

presence or absence of nesting birds

periodicity of severe stress (hurri-
canes, fire, etc.)

time since last severe stress

characteristics of ground water


inputs of toxic compounds or nutrients
from human activities

Human influences such as diking,
ditching, and altering patterns of
runoff.


In spite of the difficulties with
various methods and the interaction of
controlling factors, it is possible to
make general statements about certain
aspects of mangrove productivity. For
example, Waisel's (1972) statement that
mangroves have low transpiration rates
seems to be generally true in Florida.
Lugo et al. (1975) reported transpiration
rates of 2,500 g H20/m /day for mangrove
leaves in a fringing red mangrove forest
and 1,482 g H20/mL/day for black mangrove
leaves. This is approximately one-third
to one-half the value found in temperate
broad leaf forests on hot dry days, but
comparable to tropical rainforests (H.T.
Odum and Jordan 1970). The low transpira-
tion rates of mangroves are probably re-
lated to the energetic costs of main-
taining sap pressures of -35 to -60 atmo-
spheres (Scholander et al. 1965).

Litter fall (leaves, twigs, bark,
fruit, and flowers) of Florida mangrove
forests appears to average 2 to 3 dry
g/m day in most well-developed mangrove
stands (see discussion in section 3.4).
This can be an order of magnitude lower in
scrub forests.

Wood production of mangroves appears
to be high compared to other temperate and
tropical trees, although no measurements
from Florida are available. Noakes (1955)
estimated that the wood production of an
intensively managed Malayan forest was
39.7 metric tons/ha/year. Teas (1979)
suggested a wood production estimate of 21
metric tons/ha/year for a mature unmanaged
red mangrove forest in south Florida. His
figure was calculated from a litter/total
biomass relationship and is certainly
subject to error.

Representative estimates of gross
primary production (GPP) net primary



18


'1










production (NPP), and respiration (R) of
Florida mangroves are given in Table la.
Compared to net primary production (NPP)
estimates from other ecosystems, including
agricultural systems (E.P. Odum 1971), it
appears that mangroves are among the
world's most productive ecosystems.
Healthy mangrove ecosystems appear to be
more productive than sea grass, marsh
grass and most other coastal systems.

Further examination of Table la re-
veals several possible tendencies. The
first hypothetical tendency, as discussed
by Lugo et al. (1975),is for red mangroves
to have the highest total net production,
black to have intermediate values and
white the lowest. This conclusion assumes
that the plants occur within the zone for
which they are best adapted (see section
3.2 for discussion of zonation) and are
not existing in an area with strong limit-
ing factors. A scrub red mangrove forest,
for example, growing under stressed condi-
tions (high soil salinity or low nutrient
supply), has relatively low net produc-
tivity (Teas 1979). The pre-eminent posi-
tion of red mangroves is shown by the
comparative measurements of photosynthesis
in Table Ib; measurements were made within
canopy leaves of trees growing within
their zones of optimal growth.

A second noteworthy tendency is that
red mangrove GPP decreases with increasing
salinity while GPP of black and white
mangroves increases with increasing
salinity up to a point. Estimates of Hicks
and Burns (1975) demonstrate that this may
be a real tendency (Table Ic).

Data presented by Miller (1972),
Carter et al. (1973), Lugo and Snedaker
(1974), and Hicks and Burns (1975) sug-
gest a third hypothetical tendency,
assuming occurrence of the species within
its adapted zone. It appears that the
black mangrove typically has a much higher
respiration rate, lower net productivity,
and lower GPP/R ratio than the red man-
grove. This can be attributed at least
partially, to the greater salinity stress
under which the black mangrove usually
grows; this leads to more osmotic work.


These three apparent tendencies have
led Carter et al. (1973) and Lugo et al.
(1976) to propose a fourth tendency, an
inverted U-shaped relationship between
waterway position and net mangrove com-
munity productivity (Figure 6). This
tendency is best understood by visualizing
a typical gradient on the southwest coast
of Florida. At the landward end of the
gradient, salinities are very low,
nutrient runoff from terrestrial eco-
systems may be high and tidal amplitude is
minor. At the seaward end, salinities are
relatively high, tidal amplitude is rela-
tively great and nutrient concentrations
tend to be lower. At either end of the
gradient, the energetic costs are high and
a large percentage of GPP is used for
self-maintenance; at the landward end,
competition from freshwater plant species
is high and at the seaward end, salinity
stress may be limiting. In this scenario,
the highest NPP occurs in the middle
region of the gradient; salinity and tidal
amplitude are high enough to limit compe-
tition while tidal flushing and moderate
nutrient levels enhance productivity.
Hicks and Burns (1975) present data to
support this hypothesis.



In addition to these hypotheses
generated from field data, there have been
two significant, published attempts to
derive hypotheses from mathematical simu-
lation models of mangroves. The first
(Miller 1972) is a model of primary pro-
duction and transpiration of red mangrove
canopies and is based upon equations which
utilize field measurements of the energy
budgets of individual leaves. This model
predicts a variety of interesting trends
which need to be further field tested.
One interesting hypothesis generated by
the model is that maximum photosynthesis
of red mangrove stands should occur with a
leaf area index (LAI) of 2.5 if no accli-
mation to shade within the canopy occurs;
higher LAI's may lead to decreased produc-
tion. Another prediction is that red
mangrove production is most affected by
air temperature and humidity and, to a
lesser degree, by the amount of solar



19


-I


E










Table la. Estimates of mangrove production in Florida. All values are gC/m2/day
except annual NPP = metric tons/ha/yr. GPP = gross primary production, NPP = net
primary production, L.F. = annual litter fall X 3, R = red mangrove, W = white
mangrove, B = black mangrove. Observations 6 and 7 were on sunny days, 8 and 9
on cloudy days.



Species GPP Respiration NPP Annual NPP Method Reference


Mixed R, 24.0
W,B

B 18.0

Mature R --_a

Scrub R ---a

Basin B ---a

R (June) 12.8

R (Jan.) 9.4

R (June) 10.3

R (Jan.) 10.2

Mixed R,W, 13.9
B(riverine)

Mixed R,W, 11.8
B(basin)

B 9.0

R 6.3


11.4 12.6 46.0 Gas exchange Hicks & Burns (1975)


12.4

__ a
a


a

7.3

5.1

6.8

5.0

9.1


20.5

20.5

3.8

8.6

20.3

15.7

12.8

18.8

17.5


Gas exchange

L.F.

L.F.

L.F.

Gas exchange

Gas exchange

Gas exchange

Gas exchange

Gas exchange


Lugo & Snedaker (1974)

Teas (1979)

Teas (1979)

Teas (1979)

Miller (1972)

Miller (1972)

Miller (1972)

Miller (1972)

Carter et al. (1973)


4.3 7.5 27.4 Gas exchange Carter et al. (1973)


9.4

16.1


Gas exchange Lugo et al. (1976)

Gas exchange Lugo et al. (1976)


aMethod does not produce this data.








Table lb. Comparative measurements of photosynthesis in
gC/m2/day (Lugo et al. 1975).


Mangrove type Daytime net Nighttime P n/R
photosynthesis respiration



Red 1.38 0.23 6.0

Black 1.24 0.53 2.3

White 0.58 0.17 3.4

Red (seedling) 0.31 1.89 negative








Table Ic. Gross primary production (GPP) at different
salinities (Hicks and Burns 1975).


Mangrove type Average surface GPP
salinity (ppt) (gC/m2/day)


Red 7.8 8.0

Red 21.1 3.9

Red 26.6 1.6

Black 7.8 2.3

Black 21.1 5.7

Black 26.6 7.5

White 21.1 2.2

White 26.6 4.8


7--I

























HIGH



COMMUNITY

NET PRIMARY

PRODUCTION




LOW


LANDWARD


SEAWARD


WATERWAY POSITION




Figure 6. The hypothetical relationship between waterway position and community
net primary production of Florida mangrove forests (based on Carter et al. 1973).


_ .__










radiation within the ambient range. Gross
photosynthesis per unit leaf area was
greater at the top of the tree canopy than
at the bottom, although the middle levels
had the greatest production.

Miller (1972) concluded by suggesting
that the canopy distribution of red man-
grove leaves is nearly optimal for ef-
ficient water utilization rather than
production. This indicates that the cano-
py is adapted to maximizing production
under conditions of saturated water sup-
ply.

The mangrove ecosystem model reported
by Lugo et al. (1976) provides hypotheses
on succession, time to arrive at steady
state conditions (see section 3.2), and
several aspects of productivity. The
model output suggests that the relative
amount of tidal amplitude does not affect
GPP significantly; instead, GPP appears to
be extremely sensitive to inputs of ter-
restrial nutrients. It follows that loca-
tions with large amounts of nutrient input
from terrestrial sources riverinee man-
grove communities) have high rates of
mangrove production (see section 3.3).
All simulation model-generated hypotheses
need to be field tested with a particular-
ly critical eye, since the simplifying
assumptions that are made in constructing
the model can lead to overly simplistic
answers.

Mangrove productivity research re-
mains in an embryonic stage. Certain
preliminary tendencies or hypotheses have
been identified, but much work must be
done before we can conclude that these
hypotheses cannot be falsified.


2.6 HERBIVORY

Direct herbivory of mangrove leaves,
leaf buds, and propagules is moderately
low, but highly variable from one site to
the next. Identified grazers of living
plant parts (other than wood) include the
white-tailed deer, Odocoileus virginianus,
the mangrove tree crab, Aratus pisonii,
and insects including beetles, larvae of


lepidopterans (moths and butterflies), and
orthopterans (grasshoppers and crickets).

Heald (1969) estimated a mean grazing
effect on North River red mangrove leaves
of 5.1% of the total leaf area; values
from leaf to leaf were highly variable
ranging from 0 to 18%. Beever et al.
(1979) presented a detailed study of
grazing by the mangrove tree crab. This
arboreal grapsid crab feeds on numerous
items including beetles, crickets, cater-
pillars, littoral algae, and dead animal
matter. In Florida, red mangrove leaves
form an important component of the diet.
Beever et al. (1979) measured tree crab
grazing ranging from 0.4% of the total
leaf area for a Florida Keys overwash
forest to 7.1% for a fringing forest at
Pine Island, Lee County, Florida. The
researchers also found that tree crab
grazing rates are related t_ crab density.
Low densities (one crab/m ) resulted in
low leaf area damage (less than 1% of
total l1af area). High densities (four
crabs/m ) were accompanied by leaf area
damage ranging from 4% to 6% (see section
6.2).

Onuf et al. (1977) investigated in-
sect herbivory in fringing and overwash
red mangrove forests in the Indian River
estuary near Ft. Pierce, Florida. They
found six major herbivorous insect
species, five lepidopteran larvae and a
beetle. Comparisons were made at a high
nutrient site (input from a bird rookery)
and a low nutrient site. Both red man-
grove production and leaf nitrogen were
significantly higher at the high nutrient
site. This resulted in a four-fold
greater loss to herbivores (26% of total
leaf area lost to grazing); this increased
grazing rate more than offset the in-
creased leaf production due to nutrient
input.

Calculations of leaf area damage may
underestimate the impact of herbivores on
mangroves. For example, the larvae of the
olethreutid moth, Ecdytolopha sp.,
develops within red mangrove leaf buds and
causes the loss of entire leaves. All
stages of the beetle, Poecilips



23


"- I I~ c










rhizophorae, attack mangrove propagules
while still attached to the parent tree
(Onuf et al. 1977).


2.7 WOOD BORERS

Many people have the mistaken idea
that mangrove wood is highly resistant to
marine borers. While this may be true to
a limited extent for certain mangrove
species in other parts of the world, none
of the Florida mangroves have borer-
resistant wood. Southwell and Boltman
(1971) found that the wood of red, black,
and white mangroves has no resistance to
Teredo, Pholad and Simnorid borers; pieces
of red mangrove wood were completely de-
stroyed after immersion in ocean water for
14 months.

An interesting controversy surrounds
the ability of the wood boring isopod,
Sphaeroma terebrans, to burrow into the
living prop roots of the red mangrove.
Rehm and Humm (1973) were the first to
attribute apparently extensive damage of
red mangroves stands within the Ten
Thousand Islands area of southwestern
Florida to an isopod, Sphaeroma. They
found extensive damage throughout
southwest Florida, some infestation north
to Tarpon Springs, and a total lack of
infestation in the Florida Keys from Key
Largo south to Key West. The destruction
process was described as follows: the
adult isopod bored into the prop roots (5-
mm diameter hole); this was followed by
reproduction within the hole and develop-
ment of juveniles within the root. This
process, combined with secondary decompo-
sition from fungi and bacteria, frequently
results in prop root severance near the
mean high tide mark. These authors
attributed loss of numerous prop roots
and, in some cases, loss of entire trees
during storms to isopod damage.

The extent of damage in the Ten
Thousand Islands region led Rehm and Humm
(1973) to term the phenomenon an "eco-
catastrophe" of possibly great importance.
They further stated that shrinking of
mangrove areas appeared to be occurring as


a result of Sphaeroma infestation; this
point was not documented.

Enright (1974) produced a tongue-in-
cheek rebuttal, on behalf of Sphaeroma and
against the "terrestrial invader", red
mangroves. Snedaker (1974) contributed a
more substantial argument in which he
pointed out that the isopod infestation
might be an example of a long-term eco-
system control process.

Further arguments against the "ecoca-
tastrophe" theory were advanced by Estevez
and Simon (1975) and Estevez (1978). They
provided more life history information for
Sphaeroma and suggested a possible ex-
planation for the apparently destructive
isopod infestations. They found two
species of isopods inhabiting red mangrove
prop roots, S. terebrans and a sympatric
congener, S. quadridentatum. The latter
does not appear to be a wood borer but
utilizes S. terebrans burrows. Neither
species appeared to utilize mangrove wood
as a food source. Estevez and Simon
(1975) found extensive burrowing into
seedlings in addition to prop root damage.
In general, infestations appeared to be
patchy and limited to the periphery of
mangrove ecosystems. In areas with the
highest density of burrows, 23% of all
prop roots were infested. There appeared
to be more colonization by S. terebrans in
regions with full strength sea water (30
to 35 ppt).

The most important finding by Estevez
and Simon (1975) and Estevez (1978) was
that periods of accelerated activity by S.
terebrans were related to periods of fluc-
tuating and slightly increased salinity.
This suggests that fluctuations in isopod
burrowing may be related to the magnitude
of freshwater runoff from the Everglades.
These authors agree with Snedaker (1974)
and suggest that root and tree loss due to
Sphaeroma activity may be beneficial to
mangrove ecosystems by accelerating pro-
duction and root germination. Simberloff
et al. (1978) amplified this last sugges-
tion by showing that root branching, which
is beneficial to individual trees, is
stimulated by isopod activity.


11___










This ecocatastrophe versus beneficial
stimulus argument is not completely re-
solved. Probably, Sphaeroma root destruc-
tion, in areas of low isopod density, can
be a beneficial process to both the in-
dividual tree and to the entire mangrove
stand. Whether changes in freshwater
runoff have accelerated this process to
the point where unnatural and widespread
damage is occurring is not clear. The
data and research perspective to answer
this question do not exist. As a result,
we are reduced to providing hypotheses
which cannot be tested with available
knowledge.


2.8 MANGROVE DISEASES

Published research on mangrove
diseases is rare. The short paper by
Olexa and Freeman (1975) is the principal
reference for diseases of Florida man-
groves. They reported that black man-
groves are affected by the pathogenic


fungi, Phyllosticta hibiscina and Nigro-
spora sphaerca. These authors found that
P. hibscina caused necrotic lesions and
death of black mangrove leaves. They felt
that under conditions of high relative
humidity coupled with high temperatures,
this fungus could pose a serious threat to
individual trees, particularly if the tree
had been weakened by some other natural
agent, such as lightning or wind damage.
Nigrospora sphaerica was considered to be
of little danger to black mangroves.
Another fungus, Cylinrocarpon didymum,
appears to form galls on the prop roots
and stems of red mangroves. Olexa and
Freeman (1975) noted mortality of red
mangroves in areas of high gall infesta-
tions, although a direct causation link
was not proven.

Further research on mangrove diseases
is badly needed. Viral disease must be
Investigated. The role of pathogens in
litter production and as indicators of
mangrove stress may be very important.


-I









CHAPTER 3. ECOSYSTEM STRUCTURE AND FUNCTION


3.1 STRUCTURAL PROPERTIES OF MANGROVE
FORESTS

Published information about the
structural aspects of Florida mangrove
forests is limited; most existing data
have been published since the mid-1970's.
This lack of information is unfortunate
since quantitative structural data greatly
aid understanding of processes such as
succession and primary production. Even
more important, the response of mangrove
forests to stress, both climatic and man-
induced, can be followed quantitatively
with this type of data.

Ball (1980) contributed substantially
to understanding the role of competi-
tion in mangrove succession by measuring
structural factors such as basal area,
tree height, and tree density. Lugo and
Zucca (1977) monitored the response of
mangrove forests to freezing temperatures
by observing changes in structural proper-
ties of the trees.

Baseline studies of forest structure
have been published by Lugo and Snedaker
(1975), and Pool, Snedaker and Lugo
(1977). For example, Lugo and Snedaker
(1975) compared a fringing mangrove forest
and a basin forest at Rookery Bay, near
Naples, Florida. They found the fringing
forest, which was dominated by red man-
groves, to have a tree diversity of H =
1.48, a basal area of 15.9 m'~ha, an
aboveground biomass of 17,932 g/m and a
non-existent litter layer. The nearby
basin forest was dominated by black man-
groves, had a tree diversity of H = 0.96
and a basal area of 23.4 m /ha. The lit-
ter layer in the basin forest averaged 550
dry g/m Tree diversity in a hurricane
disturbed section of the Rookery Bay
forest was 1.62. Similar data were pre-
sented for mangrove forests in the Ten
Thousand Islands area (Table 2).

Data of this type are useful for many
purposes including impact statements, en-
vironmental surveys, and basic scientific
questions. Cintron et al. (1978) gave an
indication of the direction in which fu-
ture research might proceed. Working in a
mangrove stand in Puerto Rico, they found


tree height to be inversely proportional
(r = 0.72) to soil salinity in the range
30 to 72 ppt. Above 65 ppt salinity, dead
tree basal area was higher than live tree
basal area and above 90 ppt there was no
live tree basal area.

It should be possible to investigate
the relationship between a variety of
mangrove structural properties and factors
such as flushing frequency, soil depth,
nutrient availability, pollution stress,
and other measures of human impact. Ulti-
mately, this should lead to an ability to
predict the form and structure of mangrove
forests resulting from various physical
conditions or artificial impacts. One
example of this potential tool is Ball's
(1980) documentation of structural changes
in mangrove forests resulting from altera-
tions in the hydrological conditions of
south Florida.


3.2 ZONATION, SUCCESSION AND "LAND-
BUILDING"

Much of the world's mangrove litera-
ture consists of descriptive accounts of
zonation in mangrove forests and the spe-
cies composition within these zones. Al-
though general agreement has been lacking,
various hypotheses have been put forth
concerning the possible connection between
zonation, ecological succession, competi-
tion, and the role of physical factors
such as soil salinity and tidal amplitude.
In this section we review briefly the
dominant ideas about mangrove zonation and
succession and present our interpretation
of the current status of knowledge.

Davis (1940), working in south Flori-
da, was one of the first investigators to
describe distinct, almost monospecific,
zones within mangrove ecosystems. In what
has become the classical view, he argued
that mangrove zonation patterns were
equivalent to seral stages in succession.
The most seaward zone, dominated by red
mangroves, was regarded as the "pioneer
stage". More landward zones were
dominated by white mangrove, black
mangrove, buttonwood and, finally, the
climatic climax, a tropical forest. Since


_ ~I __~_














Table 2. Aboveground biomass of mangrove forests in the Ten Thousand Islands region
of Florida. Values are based on 25 m2 clearcuts and are expressed in dry kg/ha.
Data are from Lugo and Snedaker (1975).



Compartment Scrub Overwash Fringe Riverine
mangroves mangroves mangroves mangroves


Site A B A B C A B


Leaves 712 7,263 6,946 5,932 5,843 7,037 3,810 9,510


Fruit & flowers no data 20 236 28 210 131 148 1


Wood 3,959 70,380 70,480 57,960 84,270 128,510 79,620 161,330


Prop roots 3,197 51,980 41,920 22,270 27,200 17,190 14,640 3,060


Litter 1,140 17,310 13,990 22,730 60,250 98,410 42,950 33,930
..............................................................................................

Total above- 9,008 146,953 133,572 108,920 177,773 251,278 141,168 207,831
ground biomass










these zones were regarded as progressively
later stages in succession, the entire
mangrove ecosystem was believed to be
moving seaward through a process of sedi-
ment accumulation and colonization. Davis
based his argument primarily upon the
sequence of observed zones and cores which
showed red mangrove peat underlying black
mangrove peat which, in turn, occurred
under terestrial plant communities.

Unfortunately, this Clementsian in-
terpretation of mangrove zonation was
widely accepted, but rarely tested. For
example, Chapman (1970) expanded Davis'
original successional concept from south
Florida to explain zonation in mangrove
forests in other parts of the world.
Walsh (1974) thoroughly reviewed the man-
grove succession/zonation literature.

Fortunately, not everyone accepted
Davis' point of view. Egler (1952) and
later Thom (1967, 1975) argued that man-
grove zonation was a response to external
physical forces rather than temporal se-
quence induced by the plants themselves.
Egler (1952) showed that patterns of sedi-
ment deposition predicted by Davis' (1940)
theory did not always occur. He also
showed that in some cases mangrove zones
appeared to be moving landward rather than
seaward. Sea level has been rising in
south Florida at the rate of 1 ft (30 cm)
per 100 to 150 years (Provost 1974).
Spackman et al. (1966) emphasized the role
of sea level change in determining changes
in mangrove zonation, both through sea
level rise and land subsidence. Both
Egler (1952) and Spackman et al. (1966)
along with Wanless (1974) and Thom (1967,
1975) suggested that mangroves were
reacting passively rather than actively to
strong geomorphological processes. This
implies that mangroves should be regarded
as "land-stabilizers" rather than "land-
builders".

Furthermore, field researchers fre-
quently noted that red mangroves were not
always the only "pioneer species" on re-
cently deposited sediment. It is not
unusual to find seedlings of black, white,
and red mangroves growing together on a
new colonization site. Lewis and Dunstan


(1975) found that black mangroves and
white mangroves along with the saltmeadow
cordgrass, Spartina patens, are often the
pioneers on new dredge spoil islands in
central Florida. On the northern coast of
the Gulf of Mexico, where black mangrove
is the only mangrove species present, it
may be preceded by marsh grasses such as
saltmarsh cordgrass, S. patens, smooth
cordgrass, S. alterniflora, or the black
needle rush, Juncus roemerianus. In Puer-
to Rico, we observed that white mangrove
often pioneers and dominates sites where
oceanic overwash of beach sand has oc-
curred. All of these observations detract
from Davis' (1940) original contention
that red mangroves should be regarded as
the initial colonizer of recently de-
posited sediments. It appears that under
certain conditions, e.g., shallow water
depths, substrate type, and latitude,
white and black mangroves or marsh grasses
can be effective pioneer species.

The work of Rabinowitz (1975) added a
new perspective to the mangrove zonation
debate. Through carefully designed recip-
rocal planting experiments in Panamanian
mangrove forests using species of Rhizo-
phora, Laguncularia, Pelliciera and
Avicennia, she demonstrated that each
species could grow well within any of the
mangrove zones. In other words, physical
and chemical factors such as soil salinity
or frequency of tidal inundation, within
each zone, were not solely responsible for
excluding species from that zone. To
explain zonation, Rabinowitz proposed
tidal sorting of propagules based upon
propagule size, rather than habitat adap-
tation,as the most important mechanism for
zonation control.

The most recent piece to be added to
the zonation/succession puzzle comes from
the work of Ball (1980). Based upon re-
search of mangrove secondary succession
patterns adjacent to Biscayne Bay, Flori-
da, she made a strong case for the impor-
tance of interspecific competition in
controlling zonation. She found that
white mangroves, which grow best in
intertidal areas, do not occur consis-
tently in the intertidal zone of mature
mangrove stands. Instead, white mangroves


.I-..-.-.-r-~ ..)"V~_










dominate higher, drier locations above
mean high water where the red mangrove
does not appear to have a competitive
advantage. She suggested that competition
is not so important during the early
stages of succession but becomes critical
as individual trees reach maturity and
require more space and other resources.

Inherent in Ball's concept of zona-
tion is the differential influence of
physical factors (e.g., soil salinity,
depth to water table) on the competitive
abilities of the different mangrove
species. She concluded that succession
proceeds independently within each zone,
although breaks in the forest canopy from
lightning strikes or high winds may pro-
duce a mosaic of different successional
stages within a zone. These openings
allow species whose seedlings do not com-
pete well in shade, such as the white
mangrove, to become established, at least
temporarily, within solid zones of red
mangroves.

Zonation of mangrove species does not
appear to be controlled by physical and
chemical factors directly, but by the
interplay of these factors with interspe-
cific competition and, possibly, through
tidal sorting of propagules. Once succes-
sion in a mangrove zone reaches an equili-
brium state, change is unlikely unless an
external perturbation occurs. These per-
turbations range from small-scale distur-
bance (lightning strikes) to large-scale
perturbations (sea level change, hurricane
damage) and may cause succession within
zones to regress to an earlier stage.
There is some evidence in south Florida
that hurricane perturbations occur on a
fairly regular basis, creating a pattern
of cyclical succession.

Except for Ball (1980) and Taylor
(1980), the importance of fires as an
influence on mangrove succession has been
generally ignored. Most fires in the
Florida mangrove zone are initiated by
lightning and consist of small circular
openings in the mangrove canopy (Taylor
1980). These openings present an opportu-
nity for secondary succession within an
established zone. For example, we have


frequently observed white mangroves
flourishing in small lightning-created
openings in the center of red mangrove
forests. Fire may also play a role in
limiting the inland spread of mangroves.
Taylor (1981) pointed out that Everglades
fires appear to prevent the encroachment
of red and white mangroves into adjacent
herbaceous communities.

Finally, Lugo and Snedaker (1974),
Cintron et al. (1978) and Lugo (1980)
suggested that mangrove ecosystems
function as classical successional systems
in areas of rapid sediment deposition or
upon recently colonized sites such as
offshore islands. They concluded that in
most areas mangrove forests are an example
of steady-state cyclical systems. Concep-
tually, this is synonymous to E. P. Odum's
(1971) cyclic or catastrophic climax.
Chapman (1976a, b) suggested the idea of
cyclic succession for a variety of coastal
ecosystems.

If Florida mangrove ecosystems are
cyclic systems, then there should be an
identifiable perturbation capable of set-
ting succession back to an early stage.
Lugo and Snedaker (1974) suggested that
hurricanes may play this role. They
pointed out (without substantiating data)
that major hurricanes occur about every
20-25 years in south Florida. Coinci-
dently, mangrove ecosystems appear to
reach their maximum levels of productivity
in about the same period of time (Lugo and
Snedaker 1974). This hypothesis suggests
that succession within many mangrove eco-
systems may proceed on a cyclical basis
rather than in the classical fashion.
Possibly other physical perturbations may
influence mangrove succession including
incursions of freezing temperatures into
central Florida, periodic droughts causing
unusually high soil salinities (Cintron et
al. 1978), and fire spreading into the
upper zones of mangrove forests from ter-
restrial sources.

Although understanding of zonation
and succession in mangrove ecosystems
remains incomplete, a clearer picture is
emerging, at least for south Florida.
Contrary to early suggestions, mangrove


29


t











species zonation does not appear to repre-
sent seral stages of succession except,
perhaps, for locations of recent coloniza-
tion or where sediment is accumulating
rapidly. The role of mangroves in
land-building seems more passive than
active. Geomorphological and hydrological
processes appear to be the dominant forces
in determining whether mangrove shorelines
recede or grow. The role of mangroves is
to stabilize sediments which have been
deposited by physical processes.


3.3 NUTRIENT CYCLING

Current understanding of nutrient
cycles in mangrove ecosystems is far from
satisfactory. Sporadic field measurements
have been made, but a complete nutrient
budget has not been published for any
mangrove ecosystem in the world.

Several pioneering field studies were
conducted in Florida (Carter et al. 1973;
Snedaker and Lugo 1973; Onuf et al. 1977)
and one simulation model of mangrove nu-
trient cycling has been published (Lugo et
al. 1976). Preliminary measurements of
nitrogen fixation were made (Zuberer and
Silver 1975; Gotto and Taylor 1976;
Zuberer and Silver 1978; Gotto et al.
1981). Based on these studies, we present
the following preliminary conclusions.
Mangrove ecosystems tend to act as a
sink (net accumulator) for various ele-
ments including macro nutrients such as
nitrogen and phosphorus, trace elements,
and heavy metals. As we have discussed in
section 1.7, these elements are removed
from waters flowing through mangrove
swamps by the concerted action of the
mangrove prop roots, prop root algae, the
associated sediments, the fine root system
of the mangrove trees, and the host of
small invertebrates and microorganisms
attached to all of these surfaces. Al-
though the turnover times for these ele-
ments in mangrove swamps are not known, it
appears that at least a portion may be
stored or tied up in wood, sediments, and
peat for many years.


Although mangrove ecosystems may tend
to accumulate nutrients, there is a con-
tinual loss through export of particulate
and dissolved substances. If significant
nutrient storage and resultant high pri-
mary production are to occur, there must
be a continual input of nutrients to the
mangrove forest from outside the system
(Figure 7). Where nutrient influx to the
mangrove ecosystem Is approximately
balanced by nutrient loss in exported
organic matter, then nutrient storage will
be minimal and mangrove net primary pro-
duction will be low. This appears to
occur in the scrub mangrove community type
and to a lesser extent in the basin and
hammock community types.

Carter et al. (1973) and Snedaker and
Lugo (1973) have hypothesized that the
greatest natural nutrient inputs for man-
grove swamps come from upland and terres-
trial sources. Apparently for this rea-
son, the most luxuriant and productive
mangrove forests in south Florida occur in
riverine locations or adjacent to signifi-
cant upland drainage.

Localized sources of nutrients, such
as bird rookeries, can result in greater
nutrient storage and higher mangrove pro-
ductivity (Onuf et al. 1977). If however,
large bird rookeries (or artificial nu-
trient inputs) occur in poorly flushed
sections of mangrove ecosystems, resultant
high nutrient levels may inhibit mangrove
growth (R. R. Lewis, III, Hillsborough
Community College, Tampa, Fla.; personal
communication 1981).

The output from the simulation model
of Lugo et al. (1976) suggests that if
nutrient input to a mangrove ecosystem is
reduced, then nutrient storage levels
within the mangrove ecosystem will be
reduced and mangrove biomass and produc-
tivity will decline. To our knowledge
this hypothesis has not been tested in the
field.

Nitrogen fixation occurs in mangrove
swamps at rates comparable to those
measured in other shallow, tropical marine
areas (Gotto et al. 1981). Nitrogen


~I


T--














SMALL SMALL

IMPORT EXPORT
LOW STORAGE
LOW BIOMASS

LOW PRODUCTIVITY
















LARGE MODERATE

IMPORT EXPORT




HIGH STORAGE

HIGH BIOMASS

HIGH PRODUCTIVITY

Figure 7. The hypothetical relationship between nutrient input (excluding carbon),
biomass, primary productivity, and nutrient export (including carbon) from mangrove
ecosystems. Top: small nutrient import. Bottom: large nutrient import.





31


I '--~" Lm.11 ............ M---~











fixation has been found in association
with mangrove leaves, both living and
dead, mangrove sediment surfaces, the
litter layer in mangrove swamps, and man-
grove root systems (Gotto and Taylor 1976;
Zuberer and Silver 1978; Gotto et al.
1981). In virtually all cases, nitrogen
fixation appears to be limited by the
availability of labile carbon compounds.
Perhaps for this reason, the highest rates
of mangrove nitrogen fixation have been
measured in association with decaying
mangrove leaves; presumably, the decaying
leaves act as a carbon source and thus
accelerate nitrogen fixation. Macko
(1981), using stable nitrogen ratio
techniques, has indicated that as much as
25% of the nitrogen associated with black
mangrove peat in Texas is derived from
nitrogen fixation.

Zuberer and Silver (1978) speculated
that the nitrogen fixation rates observed
in Florida mangrove swamps may be suf-
ficient to supply a significant portion of
the mangrove's growth requirements. Al-
though this hypothesis is impossible to
test with present information, it might
explain why moderately productive mangrove
stands occur in waters which are severely
nitrogen depleted.

In summary, knowledge of nutrient
cycling in mangrove swamps is highly
speculative. These ecosystems appear to
act as a sink for many elements, including
nitrogen and phosphorus, as long as a
modest input occurs. Nitrogen fixation
within the swamp may provide much of the
nitrogen needed for mangrove growth.

3.4 LITTER FALL AND DECOMPOSITION

Unless otherwise stated, litter fall
refers to leaves, wood (twigs), leaf
scales, propagules, bracts, flowers, and
insect frass (excrement) which fall from
the tree. Mangrove leaves are shed con-
tinuously throughout the year although a
minor peak occurs during the early part of
the summer wet season in Florida (Heald
1969; Pool et al. 1975). Sporadic litter
fall peaks may follow periods of stress
from cold air temperatures, high soil


salinities, and pollution events. Litter
fall typically can be partitioned as 68%
to 86% leaves, 3% to 15% twigs and 8% to
21% miscellaneous; the latter includes
flowers and propagules.

Litter fall is an important ecosystem
process because it forms the energy basis
for detritus-based foodwebs in mangrove
swamps (see sections 3.5 and 3.6). The
first measurements of litter fall in man-
grove swamps were made by E.J. Heald and
W.E. Odum, working in the North River
estuary in south Florida in 1966-69.
This was subsequently published as Heald
(1969), Odum (1970), and Odum and Heald
(1975a). They estimated that litter pro-
duction from riverine red mangrove forests
averaged 2.4 dry g 9f organic
matter/m /day (or 876 g/m /year or 8.8
metric tons/ha/year).

Subsequent studies agreed with this
early estimate (Table 3), although varia-
tion clearly exists between different
types of communities. Scrub forests with
scattered, very small trees have the
smallest amount of leaf fall. Basin and
hammock forests, which appear to be
nutrient limited, have intermediate leaf
fall values. Not surprisingly, the
highest values occur in the highly produc-
tive fringing, overwash, and riverine
forests. Odum and Heald (1975a) suggested
that the relatively uniform litter fall
values from productive mangrove forests
around the world result from the shade
intolerance of the canopy leaves and the
tendency for the canopy size to remain the
same in spite of increasing height. If
detailed information is lacking, red man-
grove forests of south Florida, which are
not severely limited by lack of nutrients,
can be assumed to produce litter fall of
2.0 to 3.0 g/m /day of dry organic matter.
Pure stands of black mangroves usually
have a lower rate of 1.0 to 1.5 g/m /day
(Lugo et al. 1980).

Decomposition of fallen Florida man-
grove leaves has been investigated by a
number of researchers including Heald
(1969), Odum (1970), Odum and Heald
(1975a), Pool et al. (1975), Lugo and
Snedaker (1975), Twilley (1980) and Lugo et









Table 3. Estimates of litter fall in mangrove forests. Total litter fall in-
cludes leaves, fruits, twigs, flowers, and bark. R = red mangrove, W = white
mangrove, B = black mangrove.


Species Leaf fall Total litter Annual litter Reference
(g/m2/day) fall (g/m /day) fall (metric tons/ha/yr)


R riverinee) 1.3 2.4 8.8 Heald 1969

R riverinee) --- 3.6 12.8 Pool et al. 1975

R (overwash) --- 2.7 9.9 Pool et al. 1975

R (fringe) --- 2.7 9.9 Pool et al. 1975

R,B (basin) --- 2.0 7.3 Pool et al. 1975

R (mature) 2.2 2.9 10.6 Teas 1979

R (scrub) 0.2 0.4 1.3 Teas 1979

B (basin) 0.7 0.8 2.9 Teas 1979

B (basin) --- 2.2 8.0 Courtney 1980

B --- 1.3 4.9 Twilley 1980

B --- 1.3 4.8 Lugo et al. 1980

Mixed R,B,W --- 2.5 9.0 Lugo et al. 1980

B --- 0.8 2.9 Pool et al. 1975

Variety of --- 0.8 2.1 2.9 7.7 Heald et al. 1979
community types

26 species --- 2.4 8.8 Boto & Bunt (MS. in
(Australia) prep.)


-.-.. 1 I











al. (1980). Heald and Odum showed that
decomposition of red mangrove leaves
proceeds most rapidly under marine condi-
tions, somewhat more slowly in freshwater,
and very slowly on dry substrates. For
example, using the litter bag method, they
found that only 9% of the original dry
weight remained after 4 months in sea
water. By comparison, 39% and 54% re-
mained at the end of comparable periods in
brackish water and freshwater. Under dry
conditions, 65% remained. Higher decompo-
sition rates in sea water were related to
increased activity of shredder organisms,
such as crabs and amphipods.

Heald (1969) and Odum (1970) also
found increases in nitrogen, protein, and
caloric content as mangrove leaves pro-
gressively decayed. The nitrogen content
of leaves decaying under brackish condi-
tions (on an AFDW basis) increased from
1.5% (5.6% protein) to 3.3% (20.6%
protein) over a 6-month period. Subse-
quent information (Odum et al. 1979b)
suggested that the protein increase may
not have been this great since some of the
nitrogen increase probably included non-
protein nitrogen compounds such as amino
sugars. Fell and Master (1973), Fell et
al. (1980), Fell and Newell (1980), and
Fell et al. (1980) have provided more
detailed information on red mangrove leaf
decomposition, the role of fungi in decom-
position (see section 4), and nitrogen
changes and nitrogen immobilization during
decomposition. Fell et al. (1980)
have shown that as much as 50% of weight
loss of the leaf during decomposition is
in the form of dissolved organic matter
(DOM).

Heald et al. (1979), Lugo et al.
(1980) and Twilley (1980) discovered that
black mangrove leaves decompose more ra-
pidly than red mangrove leaves and ap-
parently produce a higher percentage of
DOM. Pool et al. (1975) have shown that
mangrove litter decomposes and is exported
most rapidly from frequently flooded
riverine and overwash forests. These
communities have little accumulation of
litter on the forest floor. Communities
which are not as well-flushed by the
tides, such as the basin and hammock


forests, have slower rates of decomposi-
tion and lower export rates.


3.5 CARBON EXPORT

Research from Florida mangrove swamps
forms a small portion of the larger con-
troversy concerned with the extent to
which coastal wetlands export particulate
organic carbon (reviewed by Odum et al.
1979a). Available evidence from Florida,
Puerto Rico and Australia (Table 4) sug-
gests that mangrove swamps tend to be net"
exporters. The values in Table 4 should
be regarded as preliminary, however, since
all five studies are based upon simplistic
assumptions and methodology.

Golley et al. (1962) based their
annual estimate of particulate carbon
export from a Puerto Rican forest upon a
few weeks of measurements. Odum and
Heald's estimates were derived from two or
three measurements a month. All investi-
gators have ignored the importance of bed
load transport and the impact of extreme
events. All investigators except Lugo et
al. (1980) have failed to measure DOC
flux.

It seems relatively clear that man-
grove forests do export organic carbon to
nearby bodies of water. The magnitude of
this export has probably been underesti-
mated due to ignoring bedload, extreme
events, and DOC.

The value of this carbon input to
secondary consumers in receiving waters is
not clear. As shown in section 3.6, food
webs based primarily upon mangrove carbon
do exist. The relative importance of
mangrove carbon to Florida coastal ecosys-
tems remains speculative. We suspect that
mangrove-based food webs are dominant in
small bays, creeks and rivers within large
mangrove ecosystems such as the North
River system studied by Heald (1969) and
Odum (1970). In intermediate-sized bodies
of water, such as Rookery Bay near Naples,
Florida, mangroves are probably important
but not dominant sources of organic car-
bon. Lugo et al. (1980) estimate that
mangroves supply 32% of the organic carbon


__I_





















Table 4. Estimates of particulate carbon export from mangrove
forests. Lugo et al. (1976) estimated export from a theoreti-
cal, steady state forest using a simulation model. Lugo et al.
(1980) measured export from an inland black mangrove forest.


Export

Investigators Location g/m2/day tonnes/ha/yr



Golley et al. (1962) Puerto Rico 1.1 4.0

Heald (1969), Odum (1970)a Florida 0.7 2.5

Lugo and Snedaker (1975) Florida 0.5 2.0

Lugo et al. (1976) Florida 1.5 1.8 5.5 6.6

Boto and Bunt (1981) Australia 1.1 4.0

Lugo et al. (1980)b Florida 0.2 0.7


aEstimate only includes carbon of mangrove origin.
Estimate includes dissolved and particulate carbon.














35


MWMM










input to Rookery Bay. In very large sys-
tems, such as Biscayne Bay near Miami,
Florida, mangroves are clearly less impor-
tant than any other sources such as algae
and sea grasses, although mangrove carbon
may be important in localized situations
such as the immediate vicinity of fringing
and overwash forests. The magnitude of
mangrove carbon export to unenclosed
coastal waters and offshore remains a
mystery.


3.6 ENERGY FLOW

At least seven sources of organic
carbon may serve as energy inputs for
consumers in mangrove ecosystems (Figure
8). The pathways by which this energy
containing material is processed and made
available to each consumer species is
indeed complex. Not surprisingly, current
understanding of energy flow In Florida
mangrove ecosystems exists largely in a
qualitative sense; quantitative data are
scarce and piecemeal. A variety of inves-
tigators have contributed information over
the past decade including, but not limited
to, Heald (1969), Odum (1970), Odum and
Heald (1972), Carter et al. (1973),
Snedaker and Lugo (1973), Heald et al.
(1974), Lugo and Snedaker (1974, 1975),
Odum and Heald (1975a, b), and Pool et al.
(1977). Probably, the most complete study
to date is the investigation of energy
flow in the black mangrove zone of Rookery
Bay by Lugo et al. (1980).

It is possible at this time to pre-
sent a series of hypotheses concerning the
relative importance of these energy
sources. First, the relative importance
of each source can vary from one location
to the next. As will be shown in the
following discussion, the consumers in
certain mangrove forests appear to depend
primarily upon mangrove-derived carbon
while in other locations inputs from phy-
toplankton and attached algae are probably
more important.

Our second hypothesis is that energy
flow based upon phytoplankton is most
important in overwash mangrove forests and
other locations associated with large


bodies of clear, relatively deep water.
Conversely, phytoplankton are hypothesized
to be relatively unimportant to the energy
budgets of the large riverine forest com-
munities along the southwest coast of
Florida. It should be remembered, how-
ever, that even where phytoplankton are
quantitatively unimportant, they poten-
tially perform an important function as
the basis of phytoplankton-zooplankton-
larval fish food webs (Odum 1970).

As a third hypothesis, Iver Brook
(Rosensteil School of Marine and Atmos-
pheric Sciences, Rickenbacker Causeway,
Miami, Fla.; personal communication 1979)
has suggested that both sea grasses and
benthic algae serve as an important energy
source for fringing mangrove communities
adjacent to large bodies of water such as
Biscayne Bay and Whitewater Bay. Although
little evidence exists to test this hypo-
thesis, observations of extensive deposits
of sea grass and macroalgal detritus with-
in mangrove forests suggest intuitively
that Brook's hypothesis may be correct.

In regions where mangrove shading of
the prop roots Is not severe, our fourth
hypothesis suggests that carbon origina-
ting from prop root epiphytes may be sig-
nificant to community energy budgets.
Lugo et al. (1975) have measured net pro-
duction of periphyton in mangroves
fringing Rookery Bay and found average
values of 1.1 gC/m /day. Hoffman and
Dawen (1980) found a lower value of 0.14
gC/m /day. Because these values are
roughly comparable to average exports of
mangrove leaf carbon (section 3.5), its
potential importance is obvious.

The fifth hypothesis states that
mangrove organic matter, particularly leaf
material, is an important energy source
for aquatic consumers. This hypothesis
was first espoused by Heald (1969) and
Odum (1970),who worked together in the
riverine mangrove communities between the
Everglades and Whitewater Bay. Clearly,
mangrove carbon is of great importance
within the riverine and basin communities
all along the southwest coast of Florida
(Odum and Heald 1975b); Carter et al.
(1973) and Snedaker and Lugo (1973)


I-. '7n






















GRASSES MANGROVES TERRESTRIAL ATMOSPHERIC
, W w SOURCES SOURCES


\[methanogenesis reduced sulfur


DIRECT GRAZING DISSOLVED PARTICULATE
ORGANIC MATTER ORGANIC MATTER /


MICROBES SULFUR OXIDIZING
BACTERIA



HIGHER
CONSUMERS



Figure 8. Potential pathways of energy flow in mangrove ecosystems. Not all possible pathways
have been drawn; for example, methanogenesis and sulfur reduction could originate from any of
the sources of organic matter. Mangrove-based pathways are enhanced for emphasis and in no way
imply relative importance.










provided subsequent supportive data. What
is not clear, is the relative importance
of mangrove carbon to consumers within
fringing, overwash, and more isolated
mangrove communities.

Our sixth hypothesis involves the
assemblage of organisms that graze man-
grove leaves directly. A variety of in-
sects (see section 6) and the mangrove
tree crab, Aratus pisonii, (Beever et al.
1979) obtain much of their energy directly
from living mangrove leaves, even though
grazing rarely exceeds 10% of net primary
production (Odum and Heald 1975b).

As a seventh hypothesis we suggest
that anaerobic decomposition of mangrove
tissue, particularly root material, may
support an extensive food web based on
bacteria associated with methanogenesis or
the processing of reduced sulfur com-
pounds. Our suggestion of the importance
of reduced sulfur comes directly from
Howarth and Teal's (1980) discovery of
this potentially important energy pathway
in temperate Spartina (cordgrass) marshes.
They found that anaerobic decomposition is
such an incomplete process that if sul-
fates are available (from sea water) as
much as 75% of the original energy in
plant tissues may be converted by sulfur
reducing bacteria to reduced sulfur com-
pounds such as hydrogen sulfide and py-
rite. Subsequently, if these reduced
sulfur compounds are moved hydrologically
to an oxidized environment (sediment sur-
face or creek bank) sulfur-oxidizing bac-
teria (e.g., Thiobacillus spp.) may convert
the chemically stored energy to bacterial-
ly stored energy with an efficiency as
great as 50% (Payne 1970). Presumably,
deposit-feeding organisms such as grass
shrimp (Palaemonetes) and mullet (Mugil)
are capable of grazing these sulfur-
oxidizing bacteria from the sediment
surface. If this hypothetical trophic
exchange does exist, it may be of con-
siderable magnitude and may cause us to
reexamine current concepts of energy pro-
cessing and export from mangrove
ecosystems. Since freshwater contains
remarkably little sulfate in comparison to
seawater, this energy pathway is probably
of little importance in mangrove forests


of very low salinity.

Carbon inputs from terrestrial
sources may be important to certain man-
grove communities. Carter et al. (1973)
have shown that terrestrial carbon can
reach coastal ecosystems particularly
where man has cut deep channels inland for
navigation or drainage purposes. The
magnitude of this influx has not been
adequately measured although Carter et al.
did find that mainland forests (including
mangroves) contributed approximately 2,100
metric tons of carbon per year to
Fahkahatchee Bay.

Atmospheric inputs from rainfall
appear to be minimal in all cases. Lugo
et al. (1980) measured throughfall (preci-
pitation passing through the tree canopy)
in Rookery Bay mangrove forests of 15 to
17 gC/m /year. This would be an overesti-
mate of atmospheric input since it con-
tains carbon leached from mangrove leaves.
The best guess of atmospheric input is
between 3 to 5 gC/m /year for south
Florida mangrove ecosystems.

Subsequent stages of energy transfer
in mangrove community food webs remain
largely hypothetical. Odum (1970) and
Odum and Heald (1975b) have outlined
several pathways whereby mangrove carbon
and energy are processed by a variety of
organisms (see Figure 8). Apparently, the
most important pathway follows the se-
quence: mangrove-leaf detritus substrate-
microbe-detritus consumer-higher consu-
mers. The critical links are provided by
the microbes such as bacteria and fungi
(see Fell et al. 1975) and by the detritus
consumers. The latter group was studied
by Odum (1970) and Odum and Heald (1975b)
and found to consist of a variety of
invertebrates (e.g., caridean shrimp,
crabs, mollusks, insect larvae, amphipods)
and a few fishes.

Stable carbon studies such as those
done by Haines (1976) in Spartina
(cordgrass) marshes have not been per-
formed in mangrove ecosystems. Mangroves
are C3 plants and have 613 values in the
range of minus 25 to minus 26 (Macko
1981). According to the same author,


38


~1131










mangrove peat has a 613 value of minus
22. Because these values are dramatically
different from the values for sea grasses
and many algae, the possibilities for
using this tool in mangrove ecosystems is
excellent. Macko (1981) also suggested
the utility of using stable nitrogen ra-
tios for future mangrove food web investi-
gations; he reported 615 values of plus
6.0 to plus 6.5 for mangrove tissue and
plus 5 for mangrove peat.

In reviewing contemporary knowledge
of energy flow in mangrove ecosystems,
three conclusions emerge.

(1) We have a hypothetical framework
of mangrove energy flow of a qualitative


nature. This framework appears to be
reasonably accurate although subsequent
developments, such as elucidation of the
reduced sulfur hypothesis, may require
some modification.

(2) Measurements of the relative
importance of various carbon sources are
generally lacking.

(3) Detailed measurements of energy
flow including the relative inputs of
different carbon sources are critically
needed. Technological difficulties, high
costs, and difficulties inherent in
transferring findings from one estuary to
the next present a major challenge to
estuarine ecologists of the future.


El1_IY










CHAPTER 4. COMMUNITY COMPONENTS MICROORGANISMS


The mycoflora (fungi) are the best
studied component of the microbial com-
munity of mangrove swamps. Much pio-
neering work has been carried out in south
Florida. Reviews of the current knowledge
of mangrove-associated fungi can be found
in Kohlmeyer and Kohlmeyer (1979) and Fell
et al. (1980).

One of the earliest studies of man-
grove mycoflora was published by Kohlmeyer
(1969). He discovered large populations
of marine fungi on the submerged parts of
aerial roots, stems, and branches and on
living and dead mangrove leaves. Exten-
sive work at the University of Miami by
Fell and his coworkers (e.g., Fell and
Master 1973; Fell et al. 1975, 1980) ex-
plored the role of fungi in the decom-
position of mangrove leaves and the im-
mobilization of nitrogen. Newell (1974)
studied the succession of mycoflora on
seedlings of red mangrove. A survey of
the aquatic yeasts occurring in the south
Florida mangrove zone was published by
Ahearn et al. (1968).

One of the most interesting pieces of
information to emerge from this extensive
mycoflora research concerns the succession
of organisms associated with decaying
leaves (summarized by Fell et al. 1975,
1980). Senescent leaves of red mangroves
are typically colonized by species of
Nigrospora, Phyllostica, and Pestalotica.
Once the leaf has fallen from the tree and
during the early stages of decay, the
fungal flora is dominated by species of
Phytophthora and, to a lesser extent,


Drechslera and Gloeosporium. In the lat-
ter stages of decay the dominant genera
are Calso, Gliocidium, and Lulworthia.

Understanding the occurrence and suc-
cession of fungi on decaying mangrove
leaves is important because of their role
in energy flow in mangrove swamps. Heald
(1969), Odum (1970) and Odum and Heald
(1975b) hypothesized that fungi and bac-
teria are important in converting mangrove
leaf organic material into a form that can
be digested and assimilated by detriti-
vores (see section 3.6).


Our understanding of the role and
occurrence of bacteria in mangrove swamps
is not as well documented as for fungi.
Casagrande and Given (1975) have suggested
that bacteria are important in the early
stages of mangrove leaf decomposition and
are replaced in the latter stages by fungi
which are better equipped to attack re-
fractive organic compounds. Unlike the
mycoflora, the bacteria are clearly impor-
tant in the anaerobic regions of mangrove
swamps. Vankatesan and Ramamurthy (unpubl.
data) found denitrifying bacteria to be
abundant and ubiquitous in mangrove soils.
Zuberer and Silver (1978) have emphasized
the importance of nitrogen-fixing bacteria
in the zone around mangrove roots. They,
in fact, were able to isolate and count a
variety of types of bacteria from mangrove
sediments including aerobic heterotrophs,
anaerobic heterotrophs, nitrogen-fixing
heterotrophs, and sulfate-reducing bac-
teria.


SI~lll~-llll









CHAPTER 5. COMMUNITY COMPONENTS PLANTS OTHER THAN MANGROVES


5.1. ROOT AND MUD ALGAE

The aerial root systems of mangroves
provide a convenient substrate for at-
tachment of algae. These root algal com-
munities are particularly noticeable on
red mangrove prop roots but also occur to
a lesser extent on black mangrove
pneumatophores located in the intertidal
zone. Productivity of prop root algal
communities can be appreciable if shading
by mangroves is not too severe; as dis-
cussed in section 3.6, Lugo et al. (1975)
found a prop root community net primary
production rate of 1.1 gC/m'/day, a level
comparable to mangrove leaf fall. Biomass
of these algae can be as high as 200 to
300 g per prop root (Burkholder and
Almodovar 1973). Of course, production of
this magnitude only occurs on the edge of
the forest and is virtually nil in the
center of the swamp. Nevertheless, this
algal carbon has considerable potential
food value either to direct grazers or
detritivores.

Vertical distribution of prop root
algae has been studied by many researchers
(Gerlach 1958; Almodovar and Biebl 1962;
Biebl 1962; Post 1963; Rutzler 1969;
Burkholder and Almodovar 1973; Rehm 1974;
Yoshioka 1975); only one of these studies
(Rehm 1974) was conducted in Florida.
There is a tendency for certain genera of
algae to form a characteristic association
on mangrove roots around the world (Post
1963). Four phyla tend to dominate:
Chlorophyta, Cyanophyta, Phaeophyta, and
Rhodophyta; the last is usually the most
important in terms of biomass. Of 74
species of marine algae recorded as prop
root epiphytes between Tampa and Key
Largo, 38 were Rhodophyta, 29 Chlorophyta,
4 Phaeophyta and 3 Cyanophyta (Rehm 1974).

Zonation to be expected on Florida
mangroves is shown in Figure 9; this se-
quence comes largely from Taylor (1960).
Near the high water mark, a green band
usually exists which is dominated by spe-
cies of Rhizoclonium. Below this is a
zone dominated by species of Bostrychia,
Catenella, and Caloglossa. It is this
association that most people think of when
mangrove prop root algae are mentioned.


Because much mud is often deposited on the
Bostrychia-Catenella-Caloglossa complex,
it often has a dingy, gray appearance.
There are many other algae found in this
zone, but these three genera usually domi-
nate. At brackish or nearly freshwater
locations, they are replaced by species of
Batophora, Chaetomorpha, Cladophora, and
Penicillus. The pneumatophores of
Avicennia, when colonized, are often
covered with species of Rhizoclonium,
Bostrychia and Monostroma (Taylor 1960).
Hoffman and Dawes (1980) found that the
Bostrychia binderi-dominated community on
the pneumatophores of black mangroyes had
a standing crop of 22 g dry wt/m' and a
net production of 0.14 gC/m /day.

If there is a permanently submerged
portion of the prop root, it may be
covered with rich growths of Acanthophora,
Spyrida, Hypnea, Laurencia, Wrangelia,
Valonia, and Caulerpa (Almodovar and Biebl
1962). Additional genera which may be
present below mean high water are:
Murrayella, Polysiphonia, Centroceras,
Wurdemannia, Dictyota, Halimeda,
Laurencia, and Dasya (Tayor 1960;
Burkholder and Almodovar 1973; Yoshioka
1975). In addition, anywhere on the moist
sections of the prop roots there are
usually epiphytic diatoms and filamentous
green and blue-green algae of many genera.

Rehm (1974) found a significant dif-
ference in the prop root algae between
south and central Florida. South of Tampa
Bay the standard Bostrychia-Catenella-
Caloglossa dominates. In the Tampa Bay
area, species of the orders Ulotrichales
and Cladophorales are dominant.

The mud adjacent to the mangrove root
community is often richly populated with a
variety of algae. These can include
species of Cladophoropsis, Enteromorpha,
Vaucheria, and Boodleopsis (Taylor 1960)
in addition to a whole host of benthic
diatoms and dinoflagellates (Wood 1965)
and other filamentous green and blue-green
algae (Marathe 1965).

Adjacent to mangrove areas, on the
bottoms of shoals, shallow bays and
creeks, there is often a variety of


ml -----


























PLANTS


ANIMALS


Rhlzoclonlum sr
MHW-----


Bostrychla spp.
Catenella spp.
Caloglossa spp.



MLW ----
Acanthophora spp. <
Caulerpa spp.
Wranglela spp.


LIgea exotica

Littorina angulifera

Balanus eburneus
Brachldontes spp.
Nerels spp.
SBulla spp.
Ascidla niger
Crassostree
virginica

Sphaeroma
terebrans


Figure 9. Vertical distribution of selected algae and Invertebrates on red
mangrove prop roots (compiled from Taylor 1960 and our own observations).


__I











tropical algae including species of
Caulerpa, Acetabularia, Penicillus,
Gracilaria, Halimeda, Sargassum,
Batophora, Udotea, and Dasya. These are
discussed at length by Zieman (in prep.).
Other pertinent references for mangrove
regions include Davis (1940), Taylor
(1960), Tabb and Manning (1961), and Tabb
et al. (1962).


5.2 PHYTOPLANKTON

All aspects of phytoplankton, from
seasonal occurrence to productivity
studies, are poorly studied in mangrove
ecosystems. This is particularly true in
Florida.

Evidence from Brazil (Teixeira et al.
1965, 1967, 1969; Tundisi 1969) indicates
that phytoplankton can be an important
component of the total primary production
in mangrove ecosystems; just how important
is not clear. Generally, standing crops
of net phytoplankton in mangrove areas are
low (personal observation). The nanno-
plankton, which have not been studied at
all, appear to be most important in terms
of total metabolism (Tundisi 1969). The
net plankton are usually dominated by
diatoms such as Thalassothrix spp.,
Chaetoceras spp., Nitzschia spp.,
Skeletonema spp., and Rhizosolenia spp.
(Mattox 1949; Wood 1965; Walsh 1967; Bacon
1970). At times, blooms of dinoflagel-
lates such as Peridinium spp. and
Gymnodinium spp. may dominate (personal
observation). In many locations, particu-
larly in shallow waters with some turbu-
lence, benthic diatoms such as Pleurosigma
spp., Mastogloia spp., and Disploneis may
be numerically important in the net plank-
ton (Wood 1965).

Understanding the mangrove-associated
phytoplankton community is complicated by
the constant mixing of water masses in
mangrove regions. Depending upon the
location, the phytoplankton may be domi-
nated by oceanic and neritic forms, by
true estuarine plankton, and by freshwater
plankton. The pattern of dominance may
change daily or seasonally depending upon
the source of the principal water mass.


Before we can understand the impor-
tance (or lack of importance) of phyto-
plankton in mangrove regions, some ques-
tions must be answered. How productive
are the nannoplankton? How does the daily
and seasonal shift in phytoplankton domi-
nance affect community productivity? Does
the generally low standing crop of phyto-
plankton represent low productivity or a
high grazing rate?


5.3 ASSOCIATED VASCULAR PLANTS

Four species of aquatic grasses occur
on bay and creek bottoms adjacent to man-
grove forests. Turtle grass, Thalassia
testudinum, and manatee grass, Syringodium
filliforme, are two tropical sea grasses
which occur in waters with average salini-
ties above about 20 ppt. Shoal grass,
Halodule wrightii, is found at somewhat
lower salinities and widgeongrass, Ruppia
maritima, is a freshwater grass which can
tolerate low salinities. These grasses
occur throughout south Florida, often in
close juxtaposition to mangroves. Zieman
(in prep.) presents a thorough review of
sea grasses along with comments about
possible energy flow linkages with
mangrove ecosystems.

There are extensive areas of man-
groves in south Florida which are closely
associated with marshes dominated by a
variety of other salt-tolerant plants.
For example, along the southwest coast
between Flamingo and Naples, marshes are
scattered throughout the mangrove belt and
also border the mangroves on the upland
side. The estuarine marshes within the
mangrove swamps have been extensively
described by Egler (1952), Carter et al.
(1973), and Olmstead et al. (1981). They
contain various salt-tolerant marsh
species including: salt grass, Distichlis
spicata, black needle rush, Juncus
roemerianus, spike rush, Eleocharis
cellulosa, glass wort, Salicornia spp.,
Gulf cordgrass, Spartina spartinae, sea
purslane, Sesuvium portulacastrum, salt
wort, Batis maritima, and sea ox-eye,
Borrichia frutescens. Farther north,
above Tampa on the west coast of Florida,
marshes populated by smooth cordgrass,


43


I. _











Spartina alterniflora, and black needle
rush, Juncus roemerianus, become more
extensive and eventually replace mangrove
swamps. Even in the Everglades region,
the saline marshes are comparable to man-
groves in areal extent, although they
tend to be some distance from open water.
Studies of these marshes, including as-
sessment of their ecological value, are
almost non-existent. Certainly, they have
considerable importance as habitat for
small fishes which, in turn, support many
of the nesting wading birds in south
Florida (see section 9).

Tropical hardwood forests may occur
within the mangrove zone in south Florida,
particularly where old shorelines or areas
of storm sedimentation have created ridges
1 m or more above MSL (mean sea level)
(Olmstead et al. 1981). Similar forests
or "hammocks" occur to the rear of the
mangrove zone on higher ground. Typical
trees in both forest types include the fan
palm, Thrinax radiata, buttonwood,
Conocarpus erecta, manchineel, Hippomane
mancinella, and, in the past, mahogany,
Swietenia mahagoni. Olmstead et al.
(1981) provide a description of these
communities.

Freshwater marsh plants, such as the
grasses, rushes and sedges that dominate
the freshwater Everglades, are not
mentioned here, although they are
occasionally mixed in with small mangroves


that have become established well inland.
See Hofstetter (1974) for a review of
literature dealing with these plants.

Finally, a group of somewhat salt-
tolerant herbaceous plants is found
within stands of mangroves. They usually
occur where slight increases in elevation
exist and where sufficient light filters
through the mangrove canopy. Carter et
al. (1973) list the following as examples
of members of the mangrove community:
leather ferns, Acrostichum aureum and A.
danaeifolium; spanish bayonet, Yucca
aloifolia; spider lily, Hymenocallis
latifolia; sea blite, Suaeda linearis;
chaff flower, Alternanthera ramosissima;
samphire, Philoxerus vermicularis; blood-
leaf, Iresine celosia; pricklypear cactus,
Opuntia strict; marsh elder, Iva
frutescens; the rubber vine, Rhabdadenia
biflora; the lianas, Ipomoea tuba and
Hippocratea volubilis; and a variety of
bromeliads (Bromeli aceae).

Although the lists of vascular plants
which occur in mangrove swamps may seem
extensive, the actual number of species in
any given location tends to be low
compared to totally freshwater environ-
ments (see Carlton 1977). Analogous to
temperate salt marshes, mangrove swamps
possess too many sources of stress,
particularly from tidal salt water, to
have a high diversity of vascular plant
species.


_1~1









CHAPTER 6. COMMUNITY COMPONENTS INVERTEBRATES


6.1 ECOLOGICAL RELATIONSHIPS

The mangrove ecosystem, with its tree
canopies, masses of aerial roots, muddy
substrates, and associated creeks and
small embayments, offers many habitat
opportunities for a wide variety of inver-
tebrates. While there are few comparisons
of species richness with other types of
coastal ecosystems, mangrove swamps appear
to be characterized by moderately high
invertebrate species diversity. Abele
(1974) compared H' (Shannon Weaver) diver-
sity of decapod crustaceans between
various littoral marine communities and
found mangrove swamps in an intermediate
position with more decapod species than
Spartina marshes but considerably less
than were associated with rocky substrate
communities.

There is little doubt that the maze
of prop roots and muddy substrates under
intertidal mangrove trees provides habitat
for a wide range of invertebrates and
fishes (Figure 10) (see section 7 for the
latter). The nursery value of the prop
root complex for juvenile spiny lobsters,
Panulirus argus, is well established
(Olsen et al. 175; Olsen and Koblic 1975;
Little 1977; Witham et al. 1968). Ac-
cording to these researchers, the phyl-
losome larvae of spiny lobsters often
settle among the prop roots and remain
there for much of their juvenile lives.
The prop roots provide protection from
predators and a possible source of food in
the associated populations of small inver-
tebrates. To provide the best habitat, a
section of the prop roots should extend
below mean low tide. If conditions are
suitable, the juveniles may remain in
close association with the prop root com-
munity for as much as 2 years until they
reach a carapace length of 60 to 70 mm.

In addition to its value as spiny
lobster habitat, mangrove ecosystems also
harbor the following invertebrates: bar-
nacles, sponges, polychaete worms, gastro-
pod mollusks, pelecypod mollusks, isopods,
amphipods, mysids, crabs, caridean shrimp,
penaeid shrimp, harpacticoid copepods,
snapping shrimp, ostracods, coelenterates,
nematodes, a wide variety of insects,


bryozoans, and tunicates. The most ob-
vious and dominant organisms are usually
barnacles, crabs, oysters, mussels, iso-
pods, polychaetes, gastropods and, tuni-
cates.

A striking characteristic of most
mangrove swamps is the pattern of horizon-
tal and vertical zonation of invertebrates
(Figure 9). Characteristic vertical zona-
tion patterns are found on the prop roots
(Rutzler 1969) and not so obvious horizon-
tal distributions occur as you move back
into the center of the swamp (Warner
1969). Invertebrate biomass in the red
mangrove zone on the edge of the swamp may
be pery high, often in excess of 100 dry
g/m of organic matter in many locations
(personal observation). In the center of
the swamp, particularly where there is
little flooding, biomass is usually an
order of magnitude less; Golley et al.
(1962) found an average of 6.4 g/m2 of
invertebrates in the center of a Puerto
Rican mangrove swamp.

Mangrove-associated invertebrates can
be placed in four major categories based
on trophic position:

(1) direct grazers limited to

(a) insects and the mangrove tree
crab, Aratus pisonii, all of which feed on
leaves in the mangrove canopy and

(b) a group of small invertebrates
which graze the prop root and mud algae
directly;

(2) filter feeders largely sessile
prop root invertebrates which filter phy-
toplankton and detritus from the water;

(3) deposit feeders mobile inverte-
brates which skim detritus, algae and
occasional small animals from the surface
of the mud and forest floor;

(4) carnivores highly mobile inverte-
brates which feed upon the three preceding
groups in all locations from the tree
canopy (largely insects) to the mud sur-
face. Food sources in mangrove swamps and
energy flow are discussed in section 3.6.
45


I.


1U~Y'Y~-"--I--- Il- l













6.2. ARBOREAL ARTHROPOD COMMUNITY

A surprising variety of arthropods
inhabit the mangrove canopy. Because they
are frequently secretive or possess
camouflage coloration, their numerical
importance often has been overlooked.
Beever et al. (1979) pointed out that
arboreal arthropods have a variety of
ecological roles: (1) direct herbivory on
mangrove leaves, (2) predator-prey inter-
actions, and (3) biomass export through
frass production and leaf defoliation.
Direct grazing is typically patchy in
distribution. It is not unusual to find
extensive stretches of mangroves that have
scarcely been grazed. In nearby areas, as
much as 80% of the leaves may have some
damage (Beever et al. 1979). As a general
rule, it is probably safe to state that
healthy, unstressed mangrove stands nor-
mally have less than 10% of their total
leaf area grazed (Heald 1969). In many
locations, percent leaf area damaged is on
the order of 1% to 2% (Beever et al.
1979). There are exceptions. Onuf et al.
(1977) reported biomass loss to arthropod
grazers as high as 26% in a mangrove stand
where growth and nitrogen content of the
leaves had been enhanced by input of nu-
trients from a bird rookery.

In terms of numbers of species, the
dominant group of arboreal arthropods is
insects. The most thorough inventory of
mangrove-associated insects was conducted
by Simberloff and Wilson to obtain the raw
data for their papers on island bio-
geography (Simberloff and Wilson 1969;
Simberloff 1976). These papers list over
200 species of insects associated with
overwash mangrove islands in the Florida
Keys. There is no reason to expect lesser
numbers in other types of mangrove com-
munities, except for the mangrove scrub
forests. The most thorough study of in-
sect grazing on mangrove leaves is that of
Onuf et al. (1977) (see section 2.6).

Although not as numerically impres-
sive as the insects, the mangrove tree
crab, Aratus pisonii, appears to be poten-
tially as important in terms of grazing
impact (Beever et al. 1979). The life
history of this secretive little crab has


been described by Warner (1967). Iq
Jamaica its numbers range from 11 to 1P/m
at the edge of fringing swamps to 6/m in
the center of large swamps. Beever et al.
(1979) reported typical densities for a
variety o sites in south Florida of 1 to
4 crabs/m These same authors reported
some interesting details about the crab:
(1) the diet is omnivorous ranging from
fresh mangrove leaves to caterpillars,
beetles, and various insects; (2) the crab
suffers highest predation pressure while
in the planktonic larval stage; (3) preda-
tion on the crabs while in the arboreal
community is low and comes from birds such
as the white ibis, raccoons, other man-
grove tree crabs and, if the crabs fall in
the water, fishes such as the mangrove
snapper; and (4) in one location in south
Florida (Pine Island Sound) they found in
accordance with normal biogeographical
theory, the highest densities of crabs
associated with fringing forests and the
lowest densities on distant islands, but
at Sugar Loaf Key the unexplainable
reverse distribution was found.

Other invertebrates may visit the
canopy from below either for purposes of
feeding or for protection from high tides.
Included in this group are the pulmonate
gastropods, Littorina angulifera,
Cerithidea scalariformis, and Melampus
coffeus, the isopod, Ligea exotica, and a
host of small crabs.

In summary, with the exception of a
half dozen key papers, the arboreal man-
grove community has been generally ig-
nored. Both insects and the mangrove tree
crab play significant ecological roles and
may affect mangrove productivity to a
greater extent than has been recognized.

6.3 PROP ROOT AND ASSOCIATED MUD SURFACE
COMMUNITY

These two somewhat distinct com-
munities have been lumped together because
of the large number of mobile organisms
which move back and forth between tidal
cycles. The aerial roots are used as
protective habitat and to some extent for
feeding while the nearby mud substrates
are used principally for feeding.










The prop roots support an abundance
of sessile organisms. The vertical
zonation of both mobile and sessile inver-
tebrates has been studied extensively in
other parts of the world (Goodbody 1961;
Macnae 1968; Rutzler 1969; Coomans 1969;
Bacon 1970; Kolehmainen 1973; Sasekumar
1974; Yoshioka 1975). Vertical zonation
certainly exists on Florida red mangrove
roots. The generalized scheme shown in
Figure 9 essentially contains two zones:
an upper zone dominated by barnacles and
a lower zone dominated by mussels, oysters
and ascidians. Between mean high tide and
mean tide, the wood boring isopod,
Sphaeroma terebrans (discussed at length
in section 2.7) is important, both numeri-
cally and through the provision of
numerous holes for use by other organisms
(Estevez 1978).

The most complete study of the
Florida mangrove prop root community is
Courtney's (1975) comparison of seawall
and mangrove associations. He reported an
extensive list of invertebrates from man-
grove prop roots at Marco Island, Florida,
including: Crassostrea virginica,
Littorina angulifera, Crepidula plana,
Diodora cayenensis, Urosalpinx perrugata,
Pisania tincta, Brachidontes exustus,
nine species of polychaetes, Sphaeroma
terebrans, Palaemon floridanus,
Periclimenes longicaudatus, Synalpheus
fritzmuelleri, Thor floridanus,
Petrolisthes armatus, and at least eight
species of crabs. The following species
were found only on mangrove roots and not
on seawalls: Turitella sp., Melongena
corona, Anachis semiplicata, Bulla
striata, Hypselodoris sp., Arca imbricata,
Carditamera floridana, Pseudoirus typical,
and Martesia striata.

Tabb et al. (1962) and Odum and Heald
(1972) reported a variety of invertebrates
associated with prop roots in the White-
water Bay region. Although many species
coincide with Courtney's (1975) list,
there are also significant differences due
to the lower salinities in this region.
It is probably safe to conclude that prop
root communities vary somewhat from site
to site in response to a number of factors


including latitude, salinity, and proxi-
mity to other communities such as sea
grass beds and coral reefs.

Sutherland (1980), working on red
mangrove prop root communities in
Venezuela, found little change in the
invertebrate species composition on indi-
vidual prop roots during an 18-month
period. The species composition varied
greatly, however, between adjacent prop
roots, presumably in response to stochas-
tic (chance) processes.

The mud flats adjacent to mangroves
provide feeding areas for a range of in-
vertebrates that scuttle, crawl, and swim
out from the cover of the mangrove roots.
Some emerge at low tide and feed on algae,
detritus, and small invertebrates on the
mud flats while they are high and dry.
Others emerge while the tide is in, parti-
cularly at night, and forage across the
flooded flats in search of the same foods
plus other invertebrates which have
emerged from the mud. In many ways the
mangrove-mud flat relationship is analo-
gous to the coral reef (refuge) sea grass
(feeding area) relationship reviewed by
Zieman (in prep.). The net effect is that
the impact of the mangrove community may
extend some distance beyond the boundaries
of the mangrove forest.

In addition to the organisms which
move from the mangroves to the mud flats,
there is a small group which uses the
substrate adjacent to mangroves for both
habitat and feeding. In the Whitewater
Bay region, four crabs exploit the inter-
tidal muds from the safety of burrows:
Uca pugilator, U. speciosa, U. thayeri,
and Eurytium limosum (Tabb et al. 1962).
In low salinity mangrove forests of south
Florida, the crayfish, Procambarus alleni,
is a dominant member of the burrowing,
benthic community (Hobbs 1942) as is the
crab, Rhithropanopeus harrisii (Odum and
Heald 1972). Both organisms are found in
a remarkable number of fish stomachs.

The benthic fauna and infauna of
creek and bay bottoms near mangrove
forests are highly variable from one



48










location to the next. Many of these
organisms, particularly the deposit and
filter feeders, benefit from particulate
organic matter originating from mangrove
litter fall (Odum and Heald 1972, 1975b).
Tabb and Manning (1961) and Tabb et al.
(1962) present lists and discussions of
many of the benthic invertebrates adjacent
to mangrove areas of Whitewater Bay.
Weinstein et al. (1977) compared the ben-
thic fauna of a mangrove-lined creek and a
nearby man-made canal on Marco Island.
They found (1) the mangrove fauna to be
more diverse than the canal fauna and (2)
a higher diversity of organisms at the
mouths of mangrove creeks than in the
"heads" or upstream ends. Courtney (1975)
found the same pattern of upstream
decreases in diversity, presumably in
response to decreasing oxygen concentra-
tions and increasingly finer sediments.

Finally, the irregularly flooded sub-
strates in the center of mangrove forests
contain a small but interesting assemblage
of invertebrates. The litter layer,
composed largely of mangrove leaves, evi-
dently includes a variety of nematodes.
Due to the usual taxonomic difficulties in
identifying nematodes, complete species
lists do not exist for mangrove forests;
however, many species and individuals are
associated with the decaying leaves
(Hopper et al. 1973). In addition to
nematodes, the wetter sections of the
swamp floor can contain mosquito and other
insect larvae, polychaetes, harpacticoid
copepods, isopods, and amphipods.
Simberloff (1976) lists 16 species of
insects associated with the muddy floor of
mangrove forests. Roaming across the
forest floor during low tide are several
crustaceans including the mangrove tree
crab, Aratus pisonil, crabs of the genus
Sesarma, and the pulmonate gastropods,
Melampus coeffeus and Cerithidea
scalariformis. Both snails clearly have
the ability to graze and consume recently
fallen leaves (personal observation).
With favorable conditions (relatively fre-
quent tidal inundation plus the presence
of red mangroves) Melampus populations can


exceed 500/m2 and average 100 to 200/m2
(Heald, unpublished dat4. Cerithidea is
found largely in association with black
mangroves aid can reach densities of at
least 400/mt.


6.4 WATER COLUMN COMMUNITY

This section is embarrassingly short;
the reasons for this brevity are (1) the
paucity of research on zooplankton in
Florida mangrove-dominated areas and (2)
our inability to discover some of the work
which undoubtedly has been done. Davis
and Williams (1950) are usually quoted as
the primary reference on Florida mangrove-
associated zooplankton, but their paper
only lists zooplankters collected in two
areas. Zooplankton near mangroves are
probably no different from those found in
other shallow, inshore areas in south
Florida. Based on Davis and Williams
(1950) and Reeve (1964), we can hypothe-
size that the community is dominated by
copepod species of genus Acartia, particu-
larly Acartia tonsa. In addition, we
could expect a few other calanoid cope-
pods, arrow worms (Sagitta spp.), many
fish, polychaete and crustacean larvae and
eggs. Another component of the "plankton;'
particularly at night, are benthic
amphipods, mysids, and isopods which leave
the bottom to feed (personal observation).

Plankton are not the only inverte-
brates in the water column. Swimming
crabs, such as the blue crab, Callinectes
sapidus, are plentiful in most estuarine
mangrove regions of south Florida. Other
swimming crustaceans include the caridean
shrimp (Palaemonetes spp. and Peri-
climenes spp.), the snapping shrimp
(Alpheus spp.), and the penaeid shrimp
(Penaeus spp). All of these swimming
crustaceans spend considerable time on or
in the benthos and around mangrove prop
roots. From the economic point of view,
the pink shrimp, Penaeus duorarum, is
probably the most important species asso-
ciated with mangrove areas (see discussion
in section 11).









CHAPTER 7. COMMUNITY COMPONENTS FISHES


Of the six mangrove community types
discussed in section 1.5, fishes are an
important component of four: (1) basin
forests, (2) riverine forests, (3) fringe
forests, and (4) overwash island forests.
For convenience we have divided fringe
forests into two sub-components: (a)
forests which fringe estuarine bays and
lagoons and (b) forests which fringe
oceanic bays and lagoons. This division
is necessary because the fish communities
differ markedly.

Mangroves serve two distinct roles
for fishes and it is conceptually impor-
tant to distinguish between them. First,
the mangrove-water interface, generally
red mangrove prop roots, afford a rela-
tively protected habitat which is particu-
larly suitable for juvenile fishes.
Secondly, mangrove leaves, as discussed in
section 3.6, are the basic energy source
of a detritus-based food web on which many
fishes are dependent. The habitat value
of mangroves can be considered strictly a
function of the area of interface between
the water and the mangrove prop roots; it
is an attribute shared by all four types
of mangrove communities. The importance
of the mangrove detritus-based food web is
dependent on the relative contribution of
other forms of energy in a given environ-
ment, including phytoplankton, benthic
algae, sea grass detritus, and terrestrial
carbon sources. Figure 11 provides a
diagrammatic representation of the rela-
tive positions along a food web continuum
of the four mangrove communities.

Fishes recorded from mangrove habi-
tats in south Florida are listed in Appen-
dix B. Although the fish communities are
discussed separately below, they have been
combined into certain categories in Appen-
dix B; fishes from mangrove basins and
riverine forests have been combined under
the heading of tidal streams; fishes from
fringing forests along estuarine bays and
lagoons are listed under the heading of
estuarine bays; fishes from oceanic bays
and lagoons have been listed under oceanic
bays. Since no surveys have been
published specifically relating to over-
wash island forests, there is no listing
for this community type in Appendix B.


Site characteristics and sampling methods
for these community types are summarized
in Appendix A. Nomenclature and taxonomic
order follow Bailey et al. (1970).


7.1 BASIN MANGROVE FORESTS

The infrequently flooded pools in the
black mangrove-dominated zone provide an
extreme habitat which few species of
fishes can tolerate. The waters are
darkly stained with organic acids and
tannins leached from the thick layer of
leaf litter. Dissolved oxygen is
frequently low (1-2 ppm) and hydrogen
sulfide is released from the sediments
following physical disturbance. Salini-
ties are highly variable ranging from
totally fresh to hypersaline. The fish
families best adapted to this habitat are
the euryhaline cyprinodonts (killifishes)
and the poeciliids (livebearers). The
killifishes include Fundulus confluentus
(Heald et al. 1974), Rivulus marmoratus
(M. P. Weinstein, Va. Commonwealth Uni v.,
Richmond, Va.; personal communication
1981), Floridichthys carpio, and
Cyprinodon variegatus (Odum 1970). The
poecillids include Poecilia latipinna
(Odum 1970) and, the most common, Gambusia
affinis (Heald et al. 1974). While the
species richness of fishes in this habitat
is low, the densities of fish are often
very high. Weinstein (pers. comm.) has
recorded up to 38 fish/m.

All of these fishes are permanent
residents, completing their life cycles in
this habitat. They feed primarily on
mosquito larvae and small crustaceans such
as amphipods which, in turn, feed on man-
grove detritus and algae. These small
fishes enter coastal food webs when they
are flushed into the main watercourses
during high spring tides or following
seasonally heavy rains. Here they are
eaten by numerous piscivorous fishes in-
cluding snook, ladyfish, tarpon, gars, and
mangrove snappers. The alternate energy
pathway for fishes of the black mangrove
basin wetlands occurs when the pools
shrink during dry weather, the fishes are
concentrated into smaller areas, and are
fed-upon by various wading birds including


~b=i------~-----


--



















0 k/ 4
Z



0
Ow
U




-J
Q






u, ,.




BLACK MANGROVE RIVERINE FRINGING ESTUARINE BAY OCEANIC BAY OVERWASH ISLAND.
BASIN FOREST COMMUNITY FRINGING COMMUNITY FRINGING COMMUNITY FLORIDA KEYS


HIGH SALINITY VARIABILITY LOW

HIGH RELATIVE IMPORTANCE of MANGROVE DETRITUS in FOOD WEB LOW

MUDDY, HIGH ORGANIC SUBSTRATE LARGELY SANDY


GRADIENTS

Figure 11. Gradient of mangrove-associated fish communities showing representative species. Fish are not
drawn to scale. 1 = rivulus, 2 = mosquitofish, 3 = marsh killifish, 4 = ladyfish, 5 = striped mullet, 6 =
yellowfin mojarra, 7 = juvenile sheepshead, 8 = tidewater silversides, 9 = sheepshead minnow, 10 = silver
perch, 11 = pigfish, 12 = blackcheek tonguefish, 13 = scrawled cowfish, 14 = fringed pipefish, 15 = fringed
filefish, 16 = lemon shark, 17 = goldspotted killifish, 18 = southern stingray, 19 = juvenile schoolmaster,
20 = juvenile tomtate, 21 = juvenile sergent major. See Appendix B for scientific names.


~---~--I - -- -- I .1......1-. .


--- -- 1. ---- ra~











herons, ibis and the wood stork (Heald et
al. 1974).


7.2 RIVERINE FORESTS

Tidal streams and rivers, fringed
largely by red mangroves, connect the
freshwater marshes of south Florida with
the shallow estuarine bays and lagoons
(Figure 12). Few of these streams have
been studied thoroughly. The exception is
the North River which flows into White-
water Bay and was studied by Tabb (1966)
and Odum (1970). Springer and Woodburn
(1960) collected fishes in a bayou or
tidal pass connecting Boca Ciega Bay and
Old Tampa Bay. Carter et al. (1973)
reported on the fishes of two tidal
streams entering Fahkahatchee and Fahka
Union Bays. Nugent (1970) sampled fishes
in two streams on the western shore of
Biscayne Bay. Characteristics of these
areas and sampling gear used by the inves-
tigators are summarized in Appendix A.

These tidal streams and associated
riverine mangrove forests exhibit extreme
seasonal variability in both physical
characteristics and fish community compo-
sition. Salinity variations are directly
related to changes in the make-up of the
fish assemblage. During the wet season
(June November), salinities fall
throughout the water courses and, at some
locations in certain heavy runoff years,
become fresh all of the way to the mouth
(Odum 1970). Opportunistic freshwater
species, which are normally restricted to
the sawgrass and black needle rush marshes
of the headwaters, invade the mangrove
zone. These include the Florida gar,
Lepisosteus platyrhincus; several
centrarchid sunfishes of the genus Lepomis
and the largemouth bass, Micropterus
salmoides; the freshwater catfishes,
Ictalurus natalis and Noturus gyrinus and
the killffishes normally considered
freshwater inhabitants such as Lucania
goodei and Rivulus marmoratus.

During the dry season (December to
early May) salinities rise as a result of
decreased freshwater runoff and continuing
evaporation. Marine species invade the


tidal streams primarily on feeding forays.
Examples include the jewfish, Epinephelus
itajara, the stingrays (Dasyatidae), the
needlefishes (Belonidae), the jacks
(Carangidae), and the barracuda, Sphyraena
barracuda. Other seasonal movements of
fishes appear to be temperature related.
Tabb and Manning (1961) documented move-
ments of a number of species from shallow
inshore waters to deeper water during
times of low temperature stress. The
lined sole, the hogchoker, the bighead
searobin, and the striped mullet, for
example, are much less frequently caught
in winter in shallow inshore waters.

A third type of seasonality of fish
populations in the tidal rivers is related
to life cycles. Many of the fish which
utilize the tidal stream habitat do so
only as juveniles. Thus, there are peaks
of abundance of these species following
offshore spawning when larval or juvenile
forms are recruited to the mangrove stream
habitat. In general, recruitment occurs
in the late spring or early summer fol-
lowing late winter and spring spawning
offshore or in tidal passes (Reid 1954).
Numerous species are involved in this life
cycle phenomenon including striped mullet,
grey snapper, sheepshead, spotted sea
trout, red drum, and silver perch.

The only estimate of fish standing
crop from tidal stream habitats is that of
Carter et al. (1973). They recorded 27
species weighing 65,891 g (wet w .) from
an area of 734 m or about 90 g/m This
is probably an overestimate since an un-
known portion of the fish community had
moved from the flooded lowlands to the
stream on the ebb tide; sampling occurred
at low tide in October. Nonetheless, this
is an indication of the high fish standing
crop which this mangrove-associated habi-
tat can support. The number of species
reported from individual tidal streams
annually ranges from 47 to 60 and the
total from all tidal streams in southwest
Florida is 111 species (Appendix B).

The food webs in these riverine man-
grove ecosystems appear to be predomi-
nantly mangrove detritus-based, although
the Biscayne Bay stream studied by Nugent


X__L lmli_



























































Figure 12. Aerial photograph of the mangrove belt of southwest Florida near
Whitewater Bay. Note the complex system of pools and small creeks which connect
with the tidal river system.



53


_











(1970) may be an exception. The basic
link between the mangrove leaf and higher
order consumers is provided by micro-
organisms (fungi, bacteria, Protozoa)
which colonize the decaying leaf and con-
vert them into a relatively rich protein
source (Odum 1970; Odum and Heald 1975a).
These decaying leaf fragments with asso-
ciated microorganisms are fed upon by a
group of omnivorous detritivores including
amphipods, mysids, cumaceans, ostracods,
chironomid larvae, harpacticoid and
calanoid copepods, snapping shrimp,
caridean and penaeid shrimp, a variety of
crabs, filter-feeding bivalves, and a few
species of fishes (Odum 1970; Odum and
Heald 1972; Odum and Heald 1975b). These
detritivores, in turn, are consumed by a
number of small carnivorous fishes, which
in turn, are consumed by larger
piscivorous fishes. The concept of man-
grove trophic structure is also discussed
in section 3.6. See Appendix B for
species specific dietary information.

The tidal creeks studied by Nugent
(1970) on the western shore of Biscayne
Bay differ from the previously discussed
streams in the Everglades estuary. The
mouths of the Biscayne Bay creeks have
dense growths of sea grasses which con-
tribute sea grass detritus. The salini-
ties are considerably greater and the
streams are located only a few kilometers
from coral reefs, which are largely absent
on Florida's west coast, at least close to
shore. As a result, 23 species listed in
Appendix B were captured by Nugent (1970)
and are not recorded from riverine man-
grove habitat on the west coast of
Florida. Examples include several of the
grunts (Pomadasyidae), the gray trigger-
fish, Balistes capriscus, the barbfish,
Scorpaena brasiliensis, the scrawled box-
fish, Lactophrys quadricornis, and the
snappers, Lutjanus apodus and L. synagrs.

Riverine mangrove communities and
associated tidal streams and rivers are
typified by the following families of
fishes: killifishes (Cyprinodontidae),
livebearers (Poeciliidae), silversides
(Atherinidae), mojarras (Gerreidae), tar-
pon (Elopidae), snook (Centropomidae),
snappers (Lutjanidae), sea catfishes


(Ariidae), gobies (Gobiidae), porgys
(Sparidae), mullets (Mugilidae), drums
(Sciaenidae), and anchovies (Engraulidae).
The mangrove-lined streams and associated
pools are important nursery areas for
several marine and estuarine species of
gamefish. The tarpon, Megalops atlantica,
snook, Centropomus undecimalis, and lady-
fish, Elo saurus, utilize these areas
from the time they reach the estuary as
post-larvae, having been spawned offshore.
Gray snapper, Lutjanus griseus,
sheepshead, Archosargus probatocephalus,
spotted seatrout, Cynoscion nebulosus, and
red drum, Sciaenops ocellata, are re-
cruited to grass beds of shallow bays and
lagoons as post-larvae and enter the
mangrove-lined streams for the next sever-
al years (Heald and Odum 1970). Of these
species, only the spotted seatrout prob-
ably spawns in the estuary (Tabb 1966).
Other species of commercial or game impor-
tance which use the riverine fringing
habitat include crevalle jack, gafftopsail
catfish, jewfish, striped mojarra, barra-
cuda, Atlantic thread herring, and yellow-
fin menhaden (Odum 1970).


7.3 FRINGING FORESTS ALONG ESTUARINE BAYS
AND LAGOONS

Mangrove-fringed estuarine bays and
lagoons are exemplified by the Ten
Thousand Islands area and Whitewater Bay.
Quantitative fish data are available from
Fahkahatchee Bay (Carter et al. 1973;
Yokel 1975b; Seaman et al. 1973), Fahka
Union Bay (Carter et al. 1973), Rookery
Bay (Yokel 1975a), the Marco Island
Estuary (Weinstein et al. 1977; Yokel
1975a), and Whitewater Bay (Clark 1970).
Individual site characteristics are
summarized in Appendix A. All except
Fahka Union Bay contain significant
amounts of sea grasses. Macroalgae domi-
nate the benthic producers of Fahka Union
Bay. Studies by Reid (1954) and Kilby
(1955) near Cedar Key, Florida,were not
included in our summary because mangroves
are sparse in this area and no mention of
mangrove collecting sites were made by
these authors. Studies of Caloosahatchee
Bay (Gunter and Hall 1965) and of
Charlotte Harbor (Wang and Raney 1971)










were omitted because the areas studied
have been highly modified and because data
from many habitats were pooled in the
final presentation.

All of the bays reviewed in our sum-
maries are fringed by dense growths of red
mangroves and all contain small mangrove
islets. Carter et al. (1973), in their
studies of Fahkahatchee and Fahka Union
bays, estimated that 57% to 80% of the
total energy budget of these two bays is
supported by exports of particulate and
dissolved organic matter from the man-
groves within the bays and inflowing tidal
streams. Lugo et al. (1980) estimated
that the mangroves surrounding Rookery Bay
provide 32% of the energy base of the
heterotrophic community found in the bay.

Salinities in these bays tend to be
higher than in the tidal streams and
rivers and the fish assemblages reflect
both this feature and the added habitat
dimension of sea grass and macro algae
beds. Truly freshwater species are rare
in these communities and a proportionally
greater percentage of marine visitors is
present. The dominant fish families of
the benthic habitat include drums
(Sciaenidae), porgys (Sparidae), grunts
(Pomadasyidae), mojarras (Gerreidae),
snappers (Lutjanidae), and mullet (Mugill-
dae). Other families with sizeable contri-
butions to the benthic fauna include pipe-
fishes (Syngnathidae), flounder (Bothi-
dae), sole (Soleidae), searobins (Trigli-
dae), and toadfishes (Batrachoididae).

Numerically abundant fishes of the
mid and upper waters include anchovies
(Engraulidae), herrings (Clupeidae) and
needlefishes (Belonidae). At all loca-
tions studied, the benthic fauna was domi-
nated by the pinfish, Lagodon rhomboides,
the silver perch, Bairdiella chrysura, the
pigfish, Orthopristis chrysoptera. and the
mojarras, Eucinostomus gula and E.
argenteus. The most common midwater and
surface species include the two anchovies,
Anchoa mitchilli and A. hepsetus, and two
Tclupeds, Brevoortia smith and Harengula
pensacolae. The total number of species
recorded in the individual studies ranged
from 47 to 89; a total of 117 species was


collected in these mangrove-fringed bays
and lagoons (Appendix B).

In none of these studies were the
fishes specifically utilizing the fringing
mangrove habitat enumerated separately
from those collected in the bay as a
whole. The collections were most often at
open water stations easily sampled by
otter trawl. Carter et al. (1973) had two
shore seine stations adjacent to mangroves
but the data were pooled for publication.
Of the four stations in Rookery Bay sam-
pled by Yokel (1975a), one was immediately
adjacent to the fringing mangrove shore-
line and had moderate amounts of sea
grasses.

The typical pattern which emerges
from many estuarine studies is that rela-
tively few fish species numerically domi-
nate the catch. This is certainly true in
mangrove-fringed estuaries. In Rookery
Bay (Yokel 1975a) six species comprised
88% of the trawl-catchable fishes, in
Fahkahatchee Bay seven species comprised
97% of the catch from three capture
techniques (Carter et al. 1973), and in
the Marco Island estuary 25 species com-
prised 97% of the trawl-catchable fishes
(Weinstein et al. 1977).

Like tidal river and stream communi-
ties, these shallow bays serve as nur-
series for numerous species of estuarine-
dependent fishes that are spawned off-
shore. Based on the distribution and
abundance of juvenile fishes of all spe-
cies in six habitats, Carter et al. (1973)
ranked the mangrove-fringed bays as the
most important nursery grounds; the tidal
streams were a close second. Shallow bays
and tidal streams provide safe nurseries
due to seasonally abundant food resources
and the low frequency of large predators
(Carter et al. 1973; Thayer et al. 1978).
The relative lack of large predaceous
fishes is probably due to their general
inability to osmoregulate in waters of low
and/or fluctuating salinity.

As in tidal streams, the peak abun-
dance of juvenile and larval fishes in the
bays is in spring and early summer (Reid
1954). In general, the highest standing


II....;.










crops and the greatest species richness of
fishes occur in the late summer and early
fall (Clark 1970). Fish densities decline
in the autumn and winter as many fishes
move to deeper waters.


7.4 FRINGING FORESTS ALONG OCEANIC BAYS
AND LAGOONS

Mangrove-fringed "oceanic" bays and
lagoons are exemplified by Porpoise Lake
in eastern Florida Bay (Hudson et al.
1970), western Florida Bay (Schmidt 1979),
southern Biscayne Bay (Bader and Roessler
1971), and Old Rhodes Key Lagoon in
eastern Biscayne Bay (Holm 1977). Charac-
teristics of these sites are summarized in
Appendix A. Compared to the mangrove-
fringed bays discussed in the previous
section, these environments generally ex-
hibit clearer water, sandier substrates,
and higher and less variable salinities.
Closer proximity to the Florida reef
tract, the Atlantic Ocean, and the Gulf of
Mexico results in a larger potential pool
of fish species. These four locations
have produced reports of 156 fish species
(Appendix B).

Mangrove fringes make up a relatively
small proportion of these environments;
accordingly, their contribution to the bay
food webs is probably not very large.
Bader and Roessler (1972) estimated that
the fringing mangrove community contrib-
utes approximately 1% of the total energy
budget of southern Biscayne Bay; they
considered only mainland mangroves and did
not include the small area of mangrove
islands. The main ecological role of the
fringing mangroves in this type of en-
vironment is probably twofold. First,
they increase the habitat diversity within
an otherwise relatively homogeneous bay
system. Second, they provide a relatively
protected habitat for juvenile fishes (and
certain invertebrates) that later move to
more open water or coral reef communities.
The second role is analogous to one of the
ecological roles of sea grass communities
(see Zieman, in prep.) although the fish
species involved may be different.


Based primarily on habitat designa-
tions of Voss et al. (1969), the fishes of
Biscayne Bay can be characterized as to
preferred habitat. Of the three main
habitat types, (1) rock/coral/seawall, (2)
grassbed/tidal flat, and (3) mangrove, the
grassbed/tidal flat ranked first in fish
species occurrences. One hundred and
twenty-two of 156 species (79%) are known
to occur in this environment.
Rock/coral/seawall habitats were fre-
quented by 49 species (32%) and mangroves
are known to be utilized by 54 species
(35%) of the total fish species recorded
from this bay.


7.5 OVERWASH MANGROVE ISLANDS

In terms of fish-related research,
these communities are the least studied of
all mangrove community types in south
Florida. They are typified by the low-
lying mangrove-covered islands that occur
in the Florida Keys and Florida Bay and
may be overwashed periodically by the
tides. Examples include Shell Key, Cotton
Key, and the Cowpens. Islands of this
type extend southwest from the Florida
mainland through the Marquesas. The Dry
Tortugas lack well-developed mangrove com-
munities although stunted trees are found
(Davis 1942).

These islands are the most oceanic of
any of the mangrove communities discussed.
They are characterized by relatively clear
water (Gore 1977) and are largely free of
the freshwater inflow and salinity varia-
tions which characterize other Florida
mangrove communities to varying degrees.
Numerous statements exist in the litera-
ture acknowledging the frequent proximity
of mangrove islands to coral reefs and sea
grass beds (McCoy and Heck 1976; Thayer et
al. 1978). Olsen et al. (1973) working in
the U.S. Virgin Islands, found 74% to 93%
overlap in the fish species composition of
fringing coral reefs and shallow mangrove-
fringed oceanic bays. Voss et al. (1969)
listed fish species that were collected
from all three types of communities:
fringing mangroves, coral reefs and sea










grass beds in Biscayne Bay, but there
appears to have been no systematic survey
of the fish assemblage characteristic of
the mangrove-covered or mangrove-fringed
Florida Keys. No one has quantified the
faunal connections which we hypothesize
exist between the mangroves and sea
grasses and between the mangroves and
coral reefs.

In the absence of published data from
the mangrove key communities, only tenta-
tive statements can be made. In general,
we expect that while mangrove islands
serve as a nursery area for juvenile
fishes, this function is limited largely
to coral reef and marine inshore fishes
and not the estuarine-dependent species
that we have discussed previously. The
latter (juvenile snook, red drum, spotted
seatrout) appear to require relatively low
salinities not found in association with
most of the overwash islands. Casual
observation around the edges of these
islands suggests that characteristic
fishes include the sea bass family (Ser-
ranidae), triggerfishes (Balistidae),
snappers (Lutjanidae), grunts (Poma-
dasyidae), porgies (Sparidae) parrotfishes
(Scaridae), wrasses (Labridae), bonefishes
(Albulidae), jacks (Carangidae), damsel-
fishes (Pomacentridae), and surgeonfishes
(Acanthuridae); many of these fishes occur
on or are associated with coral reefs. We
also suspect that considerable overlap
occurs in the fish assemblage of these
mangrove islands and sea grass communi-
ties; examples include puffers (Tetrao-
dontidae), pipefishes (Syngnathidae), go-
bies (Gobiidae) and scorpionfishes (Scor-
paenidae). Stark and Schroeder (1971)
suggested that juvenile gray snapper,
which use the fringing mangroves of the
keys as shelter during the day, forage in
adjacent sea grass beds at night. In the
absence of salinity barriers, predatory
fishes probably enter the fringes of these


mangrove islands on the rising tide.
Included in this group are sharks, tarpon,
jacks, snook, bonefish and barracuda.


7.6 GRADIENT OF MANGROVE COMMUNITY
INTERACTIONS

Mangrove communities occur under a
wide range of conditions from virtually
freshwater at the headwaters of tidal
streams to nearly oceanic conditions in
the Florida Keys. Attempting to present a
single list of fish characteristic of
mangrove environments (Appendix B) can be
misleading. For this reason we presented
the concept of a continuum or complex
gradient in Figure 11 and have followed
that scheme throughout section 7. The
gradient stretches from seasonally fresh
to oceanic conditions, from highly varia-
ble salinities to nearly constant salini-
ty, from muddy and limestone substrates to
sandy substrates, from dark-stained and
sometimes turbid waters to clear waters,
and from food webs that are predominantly
mangrove detritus-based to food webs based
primarily on other energy sources. Clear-
ly, there are other gradients as one moves
from north to south in the State of
Florida. At the northern end of the
State, temperatures are more variable and
seasonally lower than in the south. Sedi-
ments change from predominantly silicious
in central and north Florida to predomi-
nantly carbonate in extreme south Florida.
Nevertheless, the complex gradient shown
in Figure 11, while greatly simplified for
graphic purposes, suggests that charac-
teristic fish assemblages replace one
another along a gradient of changing
physical and biogeographic conditions.
Such a concept is useful in understanding
the factors controlling the composition of
fish assemblages associated with mangroves
of the four major community types in south
Florida.


_I__F1









CHAPTER 8. COMMUNITY COMPONENTS AMPHIBIANS AND REPTILES


Food habits and status of 24 species
of turtles, snakes, lizards, and frogs of
the Florida mangrove region are given in
Appendix C. Any of three criteria had to
be met before a species was included in
this table: (1) a direct reference in
the literature to mangrove use by the
species, (2) reference to a species as
being present at a particular geographical
location within the mangrove zone of
Florida, and (3) North American species
recorded from mangroves in the West Indies
or South America, but not from Florida.
This last criterion assumes that a species
which can utilize mangroves outside of
Florida will be able to use them in
Florida. Ten turtles are listed of which
four (striped mud turtle, chicken turtle,
Florida red-bellied turtle, and softshell
turtle) are typical of freshwater. Two
(mud turtle and the ornate diamondback
terrapin) are found in brackish water and
the remainder (hawksbill, green, logger-
head, and Atlantic ridley) are found in
marine waters.

Freshwater species usually occur in
the headwater regions of mangrove-lined
river systems. All four freshwater
species are found in habitats other than
mangrove swamps including streams, ponds,
and freshwater marshes. The brackish
water species are found in salt marshes in
addition to mangrove swamps. Mangroves,
however, are the principal habitat for the
ornate diamondback terrapin (Ernst and
Barbour 1972). Carr and Goin (1955)
listed two subspecies of the diamondback:
Malaclemys terrapin macrospilota and M. t.
rhizophorarum. Malaclemys terrapin macro-
spilota inhabits the southwest and south-
ern coasts, and M. t. rhizophorarum is
found in the Florida Keys. The two sub-
species intergrade in the region of north-
ern Florida Bay.

All four of the marine turtles are
associated with mangrove vegetation at
some stage of their lives. Loggerhead and
green turtles are apparently much less
dependent on mangroves than the remaining
two, although we strongly suspect that
recently hatched loggerheads may use man-
grove estuaries as nursery areas. Green
turtles are generally believed to feed on


a variety of submerged aquatic plants and
sea grasses; recent evidence has shown
that they also feed on mangrove roots and
leaves (Ernst and Barbour 1972). The
Atlantic ridley's preferred habitat is
"shallow coastal waters, especially the
mangrove-bordered bays of the southern
half of the peninsula of Florida" (Carr
and Goin 1955). Hawksbill turtles feed on
a variety of plant materials including
mangrove (especially red mangrove),
fruits, leaves, wood, and bark (Ernst and
Barbour 1972).

Three species in the genus Anolis
have been reported from Florida mangroves:
the green anole, the cuban brown anole,
and the Bahaman bank anole. All are
arboreal lizards that feed on insects.
The green anole is widespread throughout
the Southeastern United States and is not
at all dependent on mangrove swamps. The
other two species have much more
restricted distributions in the United
States and are found only in south
Florida. They also are not restricted
to mangrove ecosystems. Of the six
species of snakes listed, the mangrove
water snake (Figure 13) is most dependent
upon mangrove habitats.

Two important species of reptiles
found in mangrove swamps are the American
alligator and the American crocodile. The
alligator is widespread throughout the
Southeastern United States and is only
incidentally found in low salinity sec-
tions of Florida mangrove areas (Kushlan
1980). The American crocodile is rare;
historically its distribution was centered
in the mangrove-dominated areas of the
upper and lower Florida Keys (particularly
Key Largo) and the mangrove-lined shore-
lines and mud flats along the northern
edge of Florida and Whitewater Bays
(Kushlan 1980). Mangroves appear to be
critical habitat for this species. Its
range has shrunk considerably in south
Florida since the 1930's, even though
Florida Bay was added to Everglades
National Park in 1950 (Moore 1953; Ogden
1978). Much of the decrease in range is
due to increased human activity in the
Florida Keys. The remaining population
centers of the American crocodile are in
58


-~-----~l~nri~ -























































Figure 13. The mongrve *aver srve. Nerbdllfaclta cdngresjcauda, arted n










northern Florida Bay and adjacent coastal
swamps and the northern end of Key Largo
(Ogden 1978; Kushlan 1980). The species
uses a variety of habitats for nesting in
the Florida Bay region including open
hardwood thickets along creek banks,
hardwood-shrub thickets at the heads of
sand-shell beaches, and thickets of black
mangroves behind marl banks (Ogden 1978).
On Key Largo the crocodile locates its
nests on creek and canal banks in red and
black mangrove swamps (Ogden 1978). Man-
grove areas thus appear to be important in
the breeding biology of this endangered
species.

Interestingly, only three species of


amphibians, to our knowledge, have been
recorded in Florida mangrove swamps (Ap-
pendix C). This is due to two factors:
(1) lack of detailed surveys in low sa-
linity swamps and (2) the inability of
most amphibians to osmoregulate in salt
water. No doubt, several additional
species occur in the freshwater-dominated
hammock and basin mangrove communities
inland from the coast. Possible addi-
tional species include: the eastern
narrow-mouthed toad, Gastrophryne caro-
linensis, the eastern spadefoot toad,
Scaphiopus holbrooki, the cricket frog,
Acris gryllus, the green tree frog, Hyla
cinerea, and the southern leopard frog,
Rana utricularia.






































60


_____. __









CHAPTER 9. COMMUNITY COMPONENTS BIRDS


9.1 ECOLOGICAL RELATIONSHIPS

Because mangroves present a more
diverse structural habitat than most
coastal ecosystems, they should harbor a
greater variety of birdlife than areas
such as salt marshes, mud flats, and
beaches (MacArthur and MacArthur 1961).
The shallow water and exposed sediments
below mangroves are available for probing
shorebirds. Longer-legged wading birds
utilize these shallow areas as well as
deeper waters along mangrove-lined pools
and waterways. Surface-feeding and diving
birds would be expected in similar areas
as the wading birds. The major difference
between mangrove swamps and other coastal
ecosystems is the availability of the
trunks, limbs, and foliage comprising the
tree canopy. This enables a variety of
passerine and non-passerine birds, which
are not found commonly in other wetland
areas, to use mangrove swamps. It also
allows extensive breeding activity by a
number of tree-nesting birds.

The composition of the avifauna com-
munity in mangrove ecosystems is, in fact,
highly diverse. Cawkell (1964) recorded
45 species from the mangroves of Gambia
(Africa). Haverschmidt (1965) reported 87
species of birds which utilized mangroves
in Surinam (S. America). Ffrench (1966)
listed 94 species from the Caroni mangrove
swamp in Trinidad while Bacon (1970) found
137 in the same swamp. In Malaya, Nisbet
(1968) reported 121 species in mangrove
swamps and Field (1968) observed 76 from
the mangroves of Sierra Leone (Africa).

Use of mangrove ecosystems by birds
in Florida has not been recorded in de-
tail. Ninety-two species have been ob-
served in the mangrove habitat of Sanibel
Island, Florida (L. Narcisse, J.N. "Ding"
Darling Natl. Wildlife Refuge, Sanibel
Is., Fla.; personal communication 1981).
Robertson (1955) and Robertson and Kushlan
(1974) reported on the entire breeding
bird fauna of peninsular south Florida,
including mangrove regions. Based on
limited surveys, these authors reported
only 17 species as utilizing mangroves for
breeding purposes. Because their studies
did not consider migrants or non-breeding


residents, a significant fraction of the
avifauna community was omitted.

Based on information gleaned from the
literature, we have compiled a list of 181
species of birds that use Florida mangrove
areas for feeding, nesting, roosting, or
other activities (Appendix D). Criteria
for listing these species is the same as
that used for listing reptiles and amphi-
bians (see Chapter 8 of this volume).

Often references were found stating
that a given species in Florida occurred
in "wet coastal hammocks", "coastal wet
forests" or the like, without a specific
reference to mangroves. These species
were not included in Appendix D. Thus,
this list is a conservative estimate of
the avifauna associated with Florida man-
grove swamps. Sources for each listing
are provided even though many are redun-
dant. Food habit data are based on Howell
(1932) and Martin et al. (1951). Esti-
mates of abundance were derived from bird
lists published by the U.S. Fish and
Wildlife Service for the J.N. "Ding"
Darling National Wildlife Refuge at
Sanibel Island, Florida, and by the Ever-
glades Natural History Association for
Everglades National Park. Frequently,
species were recorded from mangrove swamps
at one location, but not the other.

We have divided the mangrove avifauna
into six groups based on similarities in
methods of procuring food. These groups
(guilds) are the wading birds, probing
shorebirds, floating and diving water-
birds, aerially-searching birds, birds of
prey, and arboreal birds. This last group
is something of a catch-all group, but is
composed mainly of birds that feed and/or
nest in the mangrove canopy.


9.2 WADING BIRDS

Herons, egrets, ibises, bitterns, and
spoonbills are the most conspicuous group
of birds found in mangroves (Figure 14)
and are by far the most studied and best
understood. Eighteen species (and one
important subspecies) are reported from
south Florida mangroves.
61



























































Figure 14. A variety of wading birds feeding n a mangrove-lned poo near
Flamlngo, Florlda. Photograph by Daid Scott.






62










Mangrove swamps provide two functions
for wading birds. First, they function as
feeding grounds. Two-thirds of these
species feed almost exclusively on fishes.
Although much of their diet is provided by
freshwater and non-mangrove marine areas,
all of them feed frequently in mangrove
swamps. White ibis feed predominantly on
crabs of the genus Uca when feeding in
mangroves (Kushlan and Kushlan 1975;
Kushlan 1979). Mollusks and invertebrates
of the sediments are principal foods of
the roseate spoonbill although some fish
are eaten (Allen 1942). Yellow-crowned
night herons and American bitterns eat
crabs, crayfish, frogs, and mice in addi-
tion to fishes. Snails of the genus
Pomacea are fed upon almost exclusively by
the limpkin. The sandhill crane is an
anomaly in this group since a majority of
its food is vegetable matter, especially
roots and rhizomes of Cyperus and
Sagittaria. Its use of mangroves is
probably minimal, occurring where inland
coastal marshes adjoin mangroves (Kushlan,
unpubl. data). The remaining 12 species
are essentially piscivorous although they
differ somewhat in the species and sizes
of fishes that they consume.

Mangrove swamps also serve as
breeding habitat for wading birds. With
the exception of the limpkin, sandhill
crane, and the two bitterns, all wading
bird species in Appendix D build their
nests in all three species of mangrove
trees (Maxwell and Kale 1977; Girard and
Taylor 1979). The species often aggregate
in large breeding colonies with several
thousand nesting pairs (Kushlan and White
1977a). The Louisiana heron, snowy egret,
and cattle egret are the most numerous
breeders in south Florida mangroves (based
on data in Kushlan and White 1977a).

In wet years over 90% of the south
Florida population of white ibis breed in
the interior, freshwater wetlands of the
Everglades; during these times the man-
groves are apparently unimportant, sup-
porting less than 10% of the population
(Kushlan 1976, 1977a, b). During drought
years, however, production is sustained
solely by breeding colonies located in
mangroves near the coast (Kushlan 1977a,


b). Mangroves are critically important
for the survival of the white ibis popula-
tion even though they appear to be
utilized to a lesser extent than fresh-
water habitats. This pattern of larger
but less stable breeding colonies using
inland marshes and smaller but more stable
colonies using mangroves is also charac-
teristic of heron populations (Kushlan and
Frohring, in prep.).

Table 5 gives the number of active
nests observed in mangrove regions during
the 1974-75 nesting season and the percen-
tage this represents of the entire south
Florida breeding population for the nine
most abundant species of waders and three
associated species. The dependence of
roseate spoonbills, great blue herons,
Louisiana herons, brown pelicans, and
double-crested cormorants on mangrove
regions is evident. Nesting by the red-
dish egret was not quantified during this
study although Kushlan and White (1977a)
indicated that the only nests of this
species which they saw were, in fact, in
mangroves. Further observations indicate
that this species nests in mangroves ex-
clusively (Kushlan,pers. comm.). Similar-
ly, the great white heron is highly depen-
dent upon mangroves for nesting; they use
the tiny mangrove islets which abound
along the Florida Keys and in Florida Bay
(Howell 1932).

During many years the Everglades
population of wood storks is known to nest
almost solely in mangroves (Ogden et al.
1976); this population comprises approxi-
mately one-third of the total south
Florida population. Successful breeding
of all these mangrove nesters is un-
doubtedly correlated with the abundant
supply of fishes associated with man-
groves. Meeting the energetic demands of
growing young is somewhat easier in habi-
tats with abundant prey. This is
especially important for the wood stork
which requires that its prey be concen-
trated into small pools by falling water
levels during the dry season before it can
nest successfully (Kahl 1964; Kushlan et
al. 1975; Odgen et al. 1978). Breeding
activity by wading birds in mangroves
along the southwest and southern Florida


m





















Table 5. Nesting statistics of wading birds and associated
species in south Florida, 1974-1975 (based on data in
Kushlan and White 1977a).

% of total active
Active nests in nests in south
Species mangroves Florida


White ibis 1914 7

Roseate spoonbill 500 100

Wood stork 1335 31

Great blue heron 458 92

Great egret 1812 39

Snowy egret 2377 46

Little blue heron 71 15

Louisiana heron 3410 70

Cattle egret 2180 13

Brown pelican 741 100

Double-crested
cormorant 1744 83










coasts takes place throughout the year
(Table 6); at least one species of wader
breeds during every month. Colonies on
the mangrove islands in Florida Bay were
noted to be active nesting sites during
all months of the year except September
and October (Kushlan and White 1977a).

The seasonal movements of wood storks
and white ibises between the various south
Florida ecosystems were described by
Ogden et al. (1978) and Kushlan (1979).
Mangrove ecosystems appear to be most
heavily used for feeding in summer (white
ibis) and early winter (white ibis and
wood stork). The remaining species of
wading birds appear to use mangrove areas
most heavily in the winter months,reflec-
ting the influx of migrants from farther
north.

Wading birds play an important role
in nutrient cycling in the coastal man-
grove zone. McIvor (pers. observe ) has
noted increased turbidity, greater algal
biomass, and decreased fish abundance
around red mangrove islets with nesting
frigate birds and cormorants. Onuf et al.
(1977) reported results from a small (100
bird) rookery on a mangrove islet on the
east coast of Florida. Additions of
ammonium-nitrogen from the bird's
droppings exceeded 1 g/m /day. Water
beneath the mangroves contained five times
more ammonium and phosphate than water
beneath mangroves without rookeries.
Although the wading birds were shown to be
a vector for concentrating nutrients, it
must be noted that this is a localized
phenomenon restricted to the areas around
rookeries in the mangrove zone. The
effect would be larger around larger
rookeries. Onuf et al. (1977) also
reported that mangroves in the area of the
rookery had increased levels of primary
production, higher stem and foliar nitro-
gen levels, and higher herbivore grazing
impact than mangroves without rookeries.
Lewis and Lewis (1978) stated that man-
groves in large rookeries may eventually
be killed due to stripping of leaves and
branches for nesting material and by
poisoning due to large volumes of urea and
ammonia that are deposited in bird guano.
This latter effect would be more


pronounced in rookeries within mangrove
regions subject to infrequent tidal flush-
ing.

9.3 PROBING SHOREBIRDS

Birds in this group are commonly
found associated with intertidal and shal-
low water habitats. Wolff (1969) and
Schneider (1978) have shown that plovers
and sandpipers are opportunistic feeders,
taking the most abundant, proper-sized
invertebrates present in whatever habitat
the birds happen to occupy.

Of the 25 species included in this
guild (Appendix D), two are year-round
residents (clapper rail and willet), two
breed in mangrove areas (clapper rail and
black-necked stilt), and the remainder are
transients or winter residents. Baker and
Baker (1973) indicated that winter was the
most crucial time for shorebirds, in terms
of survival. Coincidentally, winter is
the time when most shorebirds use mangrove
areas. The invertebrate fauna (mollusks,
crustaceans, and aquatic insects) which
occur on the sediments under intertidal
mangroves forms the principal diet of
these species. Willets and greater
yellowlegs eat a large amount of fishes,
especially Fundulus, in addition to inver-
tebrates. Many of the species listed in
this guild obtain a significant portion of
their energy requirements from other habi-
tats, particularly sandy beaches, marshes,
and freshwater prairies. Of the species
in this guild, the clapper rail is prob-
ably most dependent on mangroves for
survival in south Florida (Robertson
1955), although in other geographical
locations they frequent salt and brackish
marshes.


9.4 FLOATING AND DIVING WATER BIRDS

Twenty-nine species of ducks, grebes,
loons, cormorants, and gallinules were
identified as populating mangrove areas in
south Florida (Appendix D). Eight species
are year-round residents while the
remainder are present only during migra-
tion or as winter visitors.


I




















Table 6. Timing of nesting by wading birds and associated
species in south Florida. Adapted from data in Kushlan and
White (1977a), Kushlan and McEwan (in press).


Months
S ND J F M A M J J A


Species


White ibis

Wood stork

Roseate spoonbill

Great blue/white
heron

Great egret

Little blue heron

Cattle egret

Double-crested
cormorant

Brown pelican


1 -3










From the standpoint of feeding, mem-
bers of this guild are highly hetero-
geneous. Piscivorous species include the
cormorant, anhinga, pelicans, and mergan-
sers. Herbivorous species include the
pintail, mallard, wigeon, mottled duck,
and teals. A third group feeds primarily
on benthic mollusks and invertebrates.
Scaup, canvasback, redhead, and gallinules
belong to this group. The ducks in this
last group also consume a significant
fraction of plant material.

Species of this guild are permanent
residents and usually breed in mangrove
swamps. As shown in Table 5, the brown
pelican and double-crested cormorant are
highly dependent upon mangroves for
nesting in south Florida even though both
will build nests in any available tree in
other geographical regions. It seems that
when mangroves are available, they are the
preferred nesting site. The anhinga
breeds in mangrove regions but is more
commonly found inland near freshwater (J.
A. Kushlan, So. Fla. Res. Ctr., Everglades
Natl. Park, Homestead, Fla.; 'personal
communication 1981). For the other species
listed in this guild, mangrove swamps
provide a common but not a required habi-
tat; all of these species utilize a
variety of aquatic environments.

Kushlan et al. (in prep.) provide
recent data on the abundance and distribu-
tion of 22 species of waterfowl and the
American coot in south Florida estuaries.
The American coot is by far the most abun-
dant species, accounting for just over 50%
of the total population. Six species of
ducks were responsible for more than 99%
of the individuals seen: blue-winged teal
(41%), lesser scaup (24%), pintail (18%),
American wigeon (9%), ring-necked duck
(5%), and shoveler (3%). The major habi-
tats included in these authors' surveys
were coastal prairie and marshes, mangrove
forests, and mangrove-lined bays and
waterways of the Everglades National Park.

From these data it appears that
waterfowl and coots are most abundant in
regions where mangrove, wet coastal
prairies, marshes, and open water are
interspersed. Overall, the Everglades


estuaries support from 5% to 10% of the
total wintering waterfowl population in
Florida (Goodwin 1979; Kushlan et al. in
prep.). As Kushlan et al. point out,
however, the Everglades are not managed
for single species or groups of species as
are areas of Florida supporting larger
waterfowl populations. Although the
importance of south Florida's mangrove
estuaries to continental waterfowl popula-
tions may be small, the effect of 70,000
ducks and coots on these estuaries
probably is not (Kushlan et al. in prep.).

Kushlan (personal communication)
thinks that the estuaries of the Ever-
glades have an important survival value
for some segments of the American white
pelican population. In winter, approxi-
mately 25% of the white pelicans are found
in Florida Bay and 75% in the Cape Sable
region. They feed primarily in freshwater
regions of coastal marshes and prairies
and use mangroves where they adjoin this
type of habitat.

9.5 AERIALLY-SEARCHING BIRDS

Gulls, terns, the kingfisher, the
black skimmer, and the fish crow comprise
this guild of omnivorous and piscivorous
species (Appendix D). These birds hunt in
ponds, creeks, and waterways adjacent to
mangrove stands. Many fishes and inverte-
brates upon which they feed come from
mangrove-based food webs. Only six of the
14 species are year-round residents of
south Florida. The least tern is an abun-
dant summer resident and the remainder are
winter residents or transients.

Only the fish crow actually nests in
mangroves. Gulls and terns prefer open
sandy areas for nesting (Kushlan and White
1977b) and use mangrove ecosystems only
for feeding. All of the species in this
guild are recorded from a variety of
coastal and inland wetland habitats.

9.6 BIRDS OF PREY

This guild is composed of 20 species
of hawks, falcons, vultures, and owls


hL-~










which utilize mangrove swamps in south
Florida (Appendix D). The magnificent
frigatebird has been included in this
group because of its habit of robbing many
of these birds of their prey. Prey con-
sumed by this guild includes snakes,
lizards, frogs (red-shouldered hawk,
swallow-tailed kite), small birds (short-
tailed hawk), waterfowl (peregrine falcon,
great-horned owl), fishes (osprey, bald
eagle), and carrion (black and turkey
vultures).

Eleven of these species are permanent
residents, one a summer resident, and the
remainder are winter residents. Their use
of mangrove areas varies greatly. The
magnificent frigatebird, which occurs
principally in extreme southern Florida
and the Florida Keys, utilizes small over-
wash mangrove islands for both roosts and
nesting colonies. Both species of vul-
tures are widely distributed in south
Florida mangrove regions; large colonial
roosts can be found in mangrove swamps
near the coast. Swallow-tailed kites are
common over the entire Florida mangrove
region (Robertson 1955; Snyder 1974).
Snyder (1974) reports extensively on the
breeding biology of the swallow-tailed
kites in south Florida. The nests he
observed were all located in black man-
groves although they do nest in other
habitats.

The bald eagle, osprey (Figure 15),
and peregrine falcon are dependent upon
mangrove ecosystems for their continued
existence in south Florida. Both the bald
eagle and osprey feed extensively on the
wealth of fishes found associated with
mangrove ecosystems. Additionally, man-
groves are used as roosts and support
structures for nests. Nisbet (1968) indi-
cated that in Malaysia the most important
role of mangroves for birds may be as
wintering habitat for palaearctic mi-
grants, of which the peregrine falcon is
one. Kushlan (pers. comm.) stated that
recent surveys have shown falcons to
winter in mangroves, particularly along
the shore of Florida Bay where they estab-
lish feeding territories. They forage on
concentrations of shorebirds and water-
fowl. These prey species of the peregrine


are common inhabitants of mangrove areas.
This could also be true for the merlin,
which like the peregrine falcon, feeds on
waterfowl and shorebirds. The remaining
species in this guild are probably not so
dependent on mangroves; although they may
be common in mangrove ecosystems, they
utilize other habitats as well.


9.7 ARBOREAL BIRDS

This guild is the largest (71
species) and most diverse group inhabiting
mangrove forests. Included are pigeons,
cuckoos, woodpeckers, flycatchers,
thrushes, vireos, warblers, blackbirds,
and sparrows. We have lumped this diverse
group together because they utilize man-
grove ecosystems in remarkably similar
ways. Invertebrates, particularly
insects, make up a significant portion of
most of these birds' diets, although the
white-crowned pigeon, mourning dove, and
many of the fringilids (cardinal, towhee)
eat a variety of seeds, berries, and
fruits.

As the name given this guild implies,
these birds use the habitat provided by
the mangrove canopy. Many birds also use
the trunk, branches, and aerial roots for
feeding. Several different types of
searching patterns are used. Hawking of
insects is the primary mode of feeding by
the cuckoos, chuck-wills-widows,the
kingbirds, and the flycatchers. Gleaning
is employed by most of the warblers.
Woodpeckers and the prothonotary warbler
are classic probers.

Several of the birds in this guild
are heavily dependent upon mangrove areas.
The prairie warbler and the yellow warbler
are subspecies of more widespread North
American species (see Appendix D for
scientific names). They are found largely
within mangrove areas (Robertson and
Kushlan 1974). The white-crowned pigeon,
mangrove cuckoo, gray kingbird, and black-
whiskered vireo are of recent West Indian
origin. They first moved into the
mangrove-covered regions of south Florida
from source areas in the islands of the
Caribbean. Confined at first to mangrove


68


I I "" 4m































































RIYr~ II OIP"I r.tulnlnl to Ifr nif in a rpd ~m~ForP fr~~ Dl~r Uhit~nt~r
Bay. Photogr~~h ly D~r~e Ir~tt.






61










swamps, all but the mangrove cuckoo have
expanded their range in peninsular Florida
by using non-mangrove habitat. In this
vein it is interesting to note that many
species of rare and/or irregular occur-
rence in south Florida are of West Indian
origin and use mangroves to a considerable
extent. These include the Bahama pintail,
masked duck, Caribbean coot, loggerhead
kingbird, thick-billed vireo, and stripe-
headed tanager (Robertson and Kushlan
1974).

Twenty-four of the species in this
guild are permanent residents, 27 are win-
ter, and 6 are summer residents. Fourteen
species are seen only during migrations.


9.8 ASSOCIATIONS BETWEEN MANGROVE
COMMUNITY TYPES AND BIRDS

Estimating the degree of use of
mangrove swamps by birds as we have done
(Appendix D) is open to criticism because
of the paucity of information upon which
to base judgements. Estimating which
mangrove community types (see section 1,
Figure 4) are used by which birds is open
to even more severe criticism. For this
reason the following comments should be
regarded as general and preliminary.

In terms of utilization by avifauna,
the scrub mangrove swamps are probably the
least utilized mangrove community type.
Because the canopy is poorly developed,
most of the arboreal species are absent,
although Emlen (1977) recorded the red-
winged blackbird, hairy woodpecker, north-
ern waterthrush, yellow-rumped warbler,
common yellowthroat, orange-crowned
warbler, palm warbler, yellow warbler,
mourning dove, and gray kingbird in scrub
mangroves on Grand Bahama Island. Of 25
different habitats surveyed by Emlen
(1977), the yellow warbler and gray
kingbird were found in the scrub mangroves
only. Aerially-searching and wading birds
might use scrub mangroves if fishes are
present.

Overwash mangrove islands are
utilized in a variety of ways by all of
the bird guilds. Most of the wading birds


plus the magnificent frigatebird, the
anhinga, the cormorant, and the brown
pelican use overwash islands for nesting
(Kushlan and White 1977a). Wading and
aerially-searching birds commonly feed in
close proximity to overwash islands. A
variety of migrating arboreal and probing
species use the islands for feeding and
roosting. Yellow and palm warblers are
common around mangrove islands in Florida
Bay as are the black-bellied plover, ruddy
turnstone, willet, dunlin, and short-
billed dowitcher. Rafts of ducks are
common near the inshore islands and birds
of prey such as the osprey, the bald
eagle, and both vultures use mangrove
islands for roosting and nesting.

Fringe and riverine mangrove com-
munities are important feeding areas for
wading and probing birds. Floating and
diving and aerially-searching birds use
the lakes and waterways adjacent to these
mangrove communities for feeding. Many of
the wading birds nest in fringe and
riverine forests. For example, when the
wood ibis nests in coastal areas, it uses
these mangrove communities almost exclu-
sively (Kushlan, personal communication).
Most of the arboreal birds and birds of
prey associated with mangroves are found
in these two types of communities. This
is not surprising since the tree canopy is
extremely well-developed and offers
roosting, feeding and nesting opportuni-
ties.

Hammock and basin mangrove communi-
ties are so diverse in size, location, and
proximity to other communities that it is
difficult to make many general statements
about their avifauna. Since there often
is little standing water in hammock
forests, wading and diving birds probably
are not common. Proximity to terrestrial
communities in some cases may increase the
diversity of arboreal species in both
hammock and basin forests; proximity to
open areas may increase the likelihood of
birds of prey.

It seems safe to conclude that each
of the six mangrove community types has
some value to the avifauna. This value
differs according to community type and










kind of bird group under consideration.
Certainly, more information is needed,
particularly concerning the dependence of
rare or endangered species on specific
community types.



9.9 MANGROVES AS WINTER HABITAT FOR NORTH
AMERICAN MIGRANT LAND BIRDS

An interesting observation based on
the data in this chapter is the seemingly
important role that mangrove ecosystems
play in providing wintering habitat for
migrants of North American origin. Lack
and Lack (1972) studied the wintering
warbler community in Jamaica. In four
natural habitats including mangrove
forest, lowland dry limestone forest, mid-
level wet limestone forest, and montane
cloud forest,a total of 174, 131, 61, and
49 warblers (individuals) were seen,
respectively. When computed on a per hour
of observation basis, the difference is
more striking with 22 warblers per hour
seen in mangroves and only 1, 2, and 1
seen in the other forest habitats, respec-
tively. For all passerines considered
together, 26 passerines/hour were seen in
mangroves with 5, 13, and 3 respectively
in the other forest habitats. On a


species basis only 9 were recorded from
mangroves whereas 19, 13, and 16 species,
respectively, were seen in the other habi-
tats. This large number of species from
the other habitats appears to result from
the sighting of rare species after many
hours of observation. Only 9 hours were
spent by Lack and Lack (1972) in the man-
groves whereas between 30 and 86 hours
were spent in other habitats. More time
in the mangrove zone would have undoubted-
ly resulted in more species (and in-
dividuals) observed (Preston 1979).

Hutto (1980) presented extensive data
concerning the composition of migratory
land bird communities in Mexico in winter
for 13 habitat types. Mangrove areas
tended to have more migrant species than
most natural habitats (except gallery
forests) and also had a greater density of
individuals than other habitats (again
except for gallery forests). In both Lack
and Lack's and Hutto's studies, disturbed
and edge habitats had the highest number
of species and greatest density of
individuals. The percentage of the
avifauna community composed of migrants
was highest in mangrove habitats, however.
From this we can infer the importance of
mangroves in the maintenance of North
American migrant land birds.









CHAPTER 10. COMMUNITY COMPONENTS MAMMALS


Thirty-six native and nine introduced
species of land mammals occur in the south
Florida region (Layne 1974; Hamilton and
Whittaker 1979). Of these, almost 50% (18
species) are found in the mangrove zone
(Layne 1974). In addition, two species of
marine mammals are known from mangrove
areas. Data on the abundance and food
habits of these 20 species are summarized
in Appendix E. All are permanent resi-
dents. The criteria for inclusion in this
table are similar to those used for the
avifauna. Sight records in mangroves or
locality data from known mangrove areas
were required before a species was in-
cluded. This has produced a conservative
estimate of the mammal species that uti-
lize mangrove areas.

Several mammals do not appear in
Appendix E because they have not been
recorded from mangrove swamps in south
Florida; however, they occur so widely
that we suspect they will be found in this
habitat in the future. This group
includes the cotton mouse, Peromyscus
gossypinus, the hispid cotton rat, Sig-
modon hispidus, the round-tailed muskrat,
Neofiber alleni, the house mouse, Mus
musculus, theleast shrew, Cryptotis
parva, and the short-tailed shrew, Blarina
brevicauda.

Few rodents and no bats are included
in Appendix E. Compared to the rest of
the State, the south Florida region is
deficient in these two groups (Layne
1974). Although we have no confirmative
field data, we suspect that mangrove
swamps along the central and north Florida
coasts contain more mammal species, par-
ticularly rodents and bats.

A number of medium-sized and large
carnivores, including panther, gray fox,
bobcat, striped skunk, raccoon, mink,
river otter, and black bear, appear to
utilize south Florida mangrove areas.
Only three of these species (striped
skunk, raccoon, and bobcat) are common in
mangroves, but several of the rarer
species seem to be highly dependent on
mangrove swamps. Of 18 recent sightings
of the panther in Everglades National
Park, 15 were from mangrove ecosystems


(Layne 1974). Hamilton and Whittaker
(1979) state that it is the coastal ham-
mocks of south Florida, including mangrove
areas, which serve to preserve this
species in the Eastern United States.
Shemnitz (1974) reported that most of the
remaining panthers were found in the
southwest portion of Florida along the
coast and in the interior Everglades
regions.

The extent to which other carnivores
use mangrove areas varies widely among
species. Schwartz (1949) states that
mink, although rare, prefer mangroves to
other coastal habitats in Florida. Layne
(1974, see his figure 1) gives a disjunct
distribution for this species in Florida,
with the major geographical range being
the southwest coast. River otters also
utilize mangrove habitat heavily. Otters
have been found even far from shore on
small mangrove overwash islands in Florida
Bay (Layne 1974). Gray fox are not depen-
dent upon mangroves, although they occa-
sionally use this habitat. Less than 20%
of all sightings of this species in Ever-
glades National Park were from mangroves
(Layne 1974). Bobcat are found in almost
all habitats in south Florida from pine-
lands to dense mangrove forests. The
preponderance of recent sightings, how-
ever, has been made from the mangrove
zone, particularly on offshore mangrove
overwash islands (Layne 1974). Black bear
are apparently most abundant in the Big
Cypress Swamp of Collier County (Shemnitz
1974) and are rare in the remainder of
south Florida.


The small mammal fauna of the man-
grove zone of south Florida are predomi-
nately arboreal and terrestrial species
which are adapted to periodic flooding.
Opossum, marsh rabbits, cotton rats, and
rice rats are commonly found in mangrove
swamps. The Cudjoe Key rice rat is a
newly described species found only on
Cudjoe Key in the Florida Keys. This
species appears to be closely associated
with stands of white mangroves (Hamilton
and Whittaker 1979).

White-tailed deer are common in










Florida mangrove swamps, although they
utilize many other habitats. The key
deer, a rare and endangered subspecies, is
restricted to the Big Pine Key group in
the Florida Keys, although it ranged onto
the mainland in historical times. Al-
though this little deer makes use of pine
uplands and oak hammocks, it extensively
exploits mangrove swamps for food and
cover.

Two marine mammals, the bottlenose
porpoise and the manatee, frequent
mangrove-lined waterways. The bottlenose
porpoise feeds on mangrove-associated
fishes such as the striped mullet, Mugi
cephalus. Although the manatee feeds


primarily upon sea grasses and other
submerged aquatic plants, it is commonly
found in canals, coastal rivers, and
embayments close to mangrove swamps.

Except for the Cudjoe Key rice rat,
none of the mammals found in Florida man-
groves are solely dependent upon mangrove
ecosystems; all of these species can
utilize other habitats. The destruction
of extensive mangrove swamps would, how-
ever, have deleterious effects on almost
all of these species. Populations of
panther, key deer, and the river otter
would probably be the most seriously
affected, because they use mangrove habi-
tat extensively.









CHAPTER 11. VALUE OF MANGROVE ECOSYSTEMS TO MAN


Mangrove swamps are often hot, fetid,
mosquito-ridden, and almost impenetrable.
As a consequence, they are frequently held
in low regard. It is possible that more
acres of mangrove, worldwide, have been
obliterated by man in the name of "recla-
mation" than any other type of coastal
environment. Reclamation, according to
Webster's, means "to claim back, as of
wasteland". Mangrove swamps are anything
but wasteland, however, and it is impor-
tant to establish this fact before a
valuable resource is lost. We can think
of six major categories of mangrove values
to man; no doubt, there are more.


11.1 SHORELINE STABILIZATION AND STORM
PROTECTION

The ability of all three Florida
mangroves to trap, hold and, to some
extent, stabilize intertidal sediments has
been demonstrated repeatedly (reviewed by
Scoffin 1970; Carlton 1974). The contem-
porary view of mangroves is that they
function not as "land builders" as hypo-
thesized by Davis (1940) and others, but
as "stabilizers" of sediments that have
been deposited largely by geomorphological
processes (see section 3.2).

Gill (1970), Savaqe (1972), Teas
(1977), and others have emphasized that
land stabilization by mangroves is pos-
sible only where conditions are relatively
quiescent and strong wave action and/or
currents do not occur. Unfortunately, no
one has devised a method to predict the
threshold of physical conditions above
which mangroves are unable to survive and
stabilize the sediments. Certainly, this
depends to some extent on substrate type;
mangroves appear to withstand wave energy
best on solid rock substrates with many
cracks and crevices for root penetration.
From our own experience, we suspect that
mangroves on sandy and muddy substrates
cannot tolerate any but the lowest wave
energies, tidal currents much above 25
cm/s, or heavy, regular boat wakes.

The concept that the red mangrove is
the best land stabilizer has been ques-


tioned by Savage (1972), Carlton (1974),
and Teas (1977). These authors argue that
the black mangrove (1) is easier to
transplant as a seedling, (2) establishes
its pneumatophore system more rapidly than
the red mangrove develops prop roots, (3)
has an underground root system that is
better adapted to holding sediments (Teas
1977), (4) is more cold-hardy, and (5) can
better tolerate "artificial" substrates
such as dredge-spoil, finger fills, and
causeways. Generally, the white mangrove
is regarded as the poorest land stabilizer
of the Florida mangroves (Hanlon et al.
1975).

Although mangroves are susceptible to
hurricane damage (see section 12.1), they
provide considerable protection to areas
on their landward side. They cannot
prevent all flooding damage, but they do
mitigate the effects of waves and
breakers. The degree of this protection
is roughly proportional to the width of
the mangrove zone. Very narrow fringing
forests offer minimal protection while
extensive stands of mangroves not only
prevent wave damage, but reduce much of
the flooding damage by damping and holding
flood waters. Fosberg (1971) suggested
that the November 1970 typhoon and accom-
panying storm surge that claimed between
300,000 and 500,000 human lives in
Bangladesh might not have been so destruc-
tive if thousands of hectares of mangrove
swamps had not been replaced with rice
paddies.



11.2 HABITAT VALUE TO WILDLIFE

Florida mangrove ecosystems are
important habitat for a wide variety of
reptiles, amphibians, birds, and mammals
(see sections 8, 9, and 10). Some of
these animals are of commercial and sport
importance (e.g., white-tailed deer, sea
turtles, pink shrimp, spiny lobster,
snook, grey snapper). Many of these are
important to the south Florida tourist
industry including the wading birds (e.g.,
egrets, wood stork, white ibis, herons)
which nest in the mangrove zone.










11.3 IMPORTANCE TO THREATENED AND ENDAN-
GERED SPECIES

The mangrove forests of south Florida
are important habitat for at least seven
endangered species, five endangered sub-
species, and three threatened species
(Federal Register 1980). The endangered
species include the American crocodile,
the hawksbill sea turtle, the Atlantic
ridley sea turtle, the Florida manatee,
the bald eagle, the American peregrine
falcon, and the brown pelican. The endan-
gered subspecies are the key deer
(Odocoileus virginianus clavium), the
Florida panther (Felis cocolor coryi),
the Barbados yellow warbler (Dendroica
etechia petechia), the Atlantic saltmarsh
snake Nerodia fasciata taeniata) and the
eastern indigo snae Drmarcon corais
couperi). Threatened species include the
American alligator, the green sea turtle
and the loggerhead sea turtle. Although
all of these animals utilize mangrove
habitat at times in their life histories,
species that would be most adversely
affected by widespread mangrove destruc-
tion are the American crocodile, the
Florida panther, the American peregrine
falcon, the brown pelican, and the
Atlantic ridley sea turtle. The so-called
mangrove fox squirrel (Sciurus niger
avicennia) is widely believed to be a
mangrove-dependent endangered species.
This is not the case since it is currently
regarded as "rare", not endangered, and,
further, there is some question whether
or not this is a legitimate sub-species
(Hall 1981). As a final note, we should
point out that the red wolf (Canis rufus),
which is believed to be extinct in
Florida, at one time used mangrove habitat
in addition to other areas in south
Florida.


11.4 VALUE TO SPORT AND COMMERCIAL
FISHERIES

The fish and invertebrate fauna of
mangrove waterways are closely linked to
mangrove trees through (a) the habitat
value of the aerial root structure and (b)
the mangrove leaf detritus-based food web
(see sections 6 and 7). The implications


of these connections were discussed by
Heald (1969), Odum (1970), Heald and Odum
(1970), and Odum and Heald (1975b) in
terms of support for commercial and sport
fisheries.

A minimal list of mangrove-associated
organisms of commercial or sport value
includes oysters, blue crabs, spiny
lobsters, pink shrimp, snook, mullet,
menhaden, red drum, spotted sea trout,
gray and other snapper, tarpon,
sheepshead, ladyfish, jacks, gafftopsail
catfish, and the jewfish. Heald and Odum
(1970) pointed out that the commercial
fisheries catch, excluding shrimp, in the
area from Naples to Florida Bay was 2.7
million pounds in 1965. Almost all of the
fish and shellfish which make up this
catch utilize the mangrove habitat at some
point during their life cycles. In addi-
tion, the Tortugas pink shrimp fishery,
which produces in excess of 11 million
pounds of shrimp a year (Idyll 1965a), is
closely associated with the Everglades
estuary and its mangrove-lined bays and
rivers.


11.5 AESTHETICS, TOURISM AND THE
INTANGIBLES

One value of the mangrove ecosystem,
which is difficult to document in dollars
or pounds of meat, is the aesthetic value
to man. Admittedly, not all individuals
find visits to mangrove swamps a pleasant
experience. There are many others, how-
ever, who place a great deal of value on
the extensive vistas of mangrove canopies,
waterways, and associated wildlife and
fishes of south Florida. In a sense, this
mangrove belt along with the remaining
sections of the freshwater Everglades and
Big Cypress Swamp are the only remaining
wilderness areas in this part of the
United States.

Hundreds of thousands of visitors
each year visit the Everglades National
Park; part of the reason for many of these
visits includes hopes of catching snook or
gray snappers in the mangrove-lined water-
ways, seeing exotic wading birds, croco-
diles, or panthers, or simply discovering










what a tropical mangrove forest looks
like. The National Park Service,in an
attempt to accommodate this last wish,
maintains extensive boardwalks and canoe
trails through the mangrove forests near
Flamingo, Florida. In other, more
developed parts of the State, small stands
of mangroves or mangrove islands provide a
feeling of wilderness in proximity to the
rapidly burgeoning urban areas. A variety
of tourist attractions including Fairchild
Tropical Gardens near Miami and Tiki
Gardens near St. Petersburg utilizes the
exotic appearance of mangroves as a key
ingredient in an attractive landscape.
Clearly, mangroves contribute intangibly
by diversifying the appearance of south
Florida.


11.6 ECONOMIC PRODUCTS

Elsewhere in the world, mangrove
forests serve as a renewable resource for
many valuable products. For a full dis-
cussion of the potential uses of mangrove
products, see de la Cruz (in press a),
Morton (1965) for red mangrove products,
and Moldenke (1967) for black mangrove
products.

In many countries the bark of man-
groves is used as a source of tannins and
dyes. Since the bark is 20% to 30% tannin
on a dry weight basis, it is an excellent
source (Hanlon et al. 1975). Silviculture
(forestry) of mangrove forests has been
practiced extensively in Africa, Puerto
Rico, and many parts of Southeast Asia
(Holdridge 1940; Noakes 1955; Macnae 1968;
Walsh 1974; Teas 1977). Mangrove wood


makes a durable and water resistant timber
which has been used successfully for resi-
dential buildings, boats, pilings,
hogsheads, fence posts, and furniture
(Kuenzler 1974; Hanlon et al. 1975). In
Southeast Asia mangrove wood is widely
used for high quality charcoal.

Morton (1965) mentions that red man-
grove fruits are sometimes eaten by humans
in Central America, but only by popula-
tions under duress and subject to starva-
tion. Mangrove leaves have variously been
used for teas, medicinal purposes, and
livestock feeds. Mangrove teas must be
drunk in small quantities and mixed with
milk because of the high tannin content
(Morton 1962); the milk binds the tannins
and makes the beverage more palatable.

As a final note, we should point out
that mangrove trees are responsible for
contributing directly to one commercial
product in Florida. The flowers of black
mangroves are of considerable importance
to the three million dollar (1965 figures)
Florida honey industry (Morton 1964).

Other than the honey industry, most
of these economic uses are somewhat
destructive. There are many cases in
which clear-cut mangrove forests have
failed to regenerate successfully for many
years because of lack of propagule
dispersal or increased soil salinities
(Teas 1979). We believe that the best use
of Florida mangrove swamps will continue
to be as preserved areas to support
wildlife, fishing, shoreline stabiliza-
tion, endangered species, and aesthetic
values.









CHAPTER 12. MANAGEMENT IMPLICATIONS


12.1 INHERENT VULNERABILITY

Mangroves have evolved remarkable
physiological and anatomical adaptations
enabling them to flourish under conditions
of high temperatures, widely fluctuating
salinities, high concentrations of heavy
metals (Walsh et al. 1979), and anaerobic
soils. Unfortunately, one of these adap-
tations, the aerial root system, is also
one of the plant's most vulnerable compo-
nents. Odum and Johannes (1975) have
referred to the aerial roots as the man-
grove's Achilles'heel because of their
susceptibility to clogging, prolonged
flooding, and boring damage from isopods
and other invertebrates (see section 6 for
a discussion of the latter). This means
that any process, natural or man-induced,
which coats the aerial roots with fine
sediments or covers them with water for
extended periods has the potential for
mangrove destruction. Bacon (1970) men-
tions a case in Trinidad where the Caroni
River inundated the adjacent Caroni
Mangrove Swamp during a flood and
deposited a layer of fine red marl in a
large stand of black mangroves which sub-
sequently died. Many examples of damage
to mangrove swamps from human activities
have been documented (see section 12.2).

One of the few natural processes that
causes periodic and extensive damage to
mangrove ecosystems is large hurricanes
(Figure 16). Craighead and Gilbert (1962)
and Tabb and Jones (1962) have documented
the impact of Hurricane Donna in 1960 on
parts of the mangrove zone of south
Florida. Craighead and Gilbert (1962)
found extensive damage over an area of
100,000 acres (40,000 ha). Loss of trees
ranged from 25% to 100%. Damage occurred
in three ways: (1) wind shearing of the
trunk 6 to 10 ft (2 to 3 m) above ground,
(2) overwash mangrove islands being swept
clean, and (3) trees dying months after
the storm, apparently in response to
damage to the prop roots from coatings by
marl and fine organic matter. The latter
type of damage was most widespread, but
rarely occurred in intertidal forests,
presumably because the aerial roots were
flushed and cleaned by tidal action. Fish
and invertebrates were adversely affected


by oxygen depletion due to accumulations
of decomposing organic matter (Tabb and
Jones 1962).

Hurricane Betsy in 1965 did little
damage to mangroves in south Florida;
there was also little deposition of silt
and marl within mangrove stands from this
minimal storm (Alexander 1967). Lugo et
al. (1976) have hypothesized that severe
hurricanes occur in south Florida and
Puerto Rico on a time interval of 25 to 30
years and that mangrove ecosystems are
adapted to reach maximum biomass and pro-
ductivity on the same time cycle.


(12.2 MAN-INDUCED DESTRUCTION

Destruction of mangrove forests in
Florida has occurred in various ways
including outright destruction and land
filling, diking and flooding (Figure 17),
through introduction of fine particulate
material, and pollution damage, par-
ticularly oil spills. To our knowledge
there are no complete, published docu-
mented estimates of the amount of mangrove
forests in Florida which have been
destroyed by man in this century. Our
conclusion is that total loss statewide is
not too great, probably in the range of 3
to 5% of the original area covered by
mangroves in the 19th century, but that
losses in specific areas, particularly
urban areas, are appreciable. This con-
clusion is based on four pieces of infor-
mation. (1) Lindall and Saloman (1977)
have estimated that the total loss of
vegetated intertidal marshes and mangrove
swamps in Florida due to dredge and fill
is 23,521 acres (9,522 ha); remember that
there are between 430,000 and 500,000
acres (174,000 to 202,000 ha) of mangroves
in Florida (see section 1.3). (2)
Birnhak and Crowder (1974) estimate a loss
of approximately 11,000 acres (4,453 ha)
of mangroves between 1943 and 1970 in
three counties (Collier, Monroe, and
Dade). (3) An obvious loss of mangrove
forests has occurred in Tampa Bay, around
Marco Island, in the Florida Keys, and
along the lower east coast of Florida.
For example, Lewis et al. (1979) estimated
that 44% of the intertidal vegetation
77























































Figure 16. Damaged stand of red and black mangroves near Flamingo, Florida, as
It appeared 7 years after Hurricane Donna.





78


























































Figure 17. Mangrove forest near Key West as it appeared in 1981 after being
destroyed by diking and impounding.





79










including mangroves in the Tampa Bay
estuary has been destroyed during the past
100 years. (4) Heald (unpublished MS.)
has estimated a loss of 2,000 acres (810
ha) of mangroves within the Florida Keys
(not considered by Birnhak and Crowder
1974). So while loss of mangrove ecosys-
tems throughout Florida is not over-
whelming, losses at specific locations
have been substantial.

Diking, impounding, and long-term
flooding of mangroves with standing water
can cause mass mortality, especially when
prop roots and pneumatophores are covered
(Breen and Hill 1969; Odum and Johannes
1975; Patterson-Zucca 1978; Lugo 1981).
In south Florida, E. Heald (pers. comm.)
has observed that permanent impoundment by
diking which prevents any tidal exchange
and raises water levels significantly
during the wet season will kill all adult
red and black mangrove trees. If condi-
tions behind the dike remain relatively
dry, the mangroves may survive for many
years until replaced by terrestrial vege-
tation.


Mangroves are unusually susceptible
to herbicides (Walsh et al. 1973). At
least 250,000 acres (100,000 ha) of man-
grove forests were defoliated and killed
in South Viet Nam by the U.S. military.
This widespread destruction has been docu-
mented by Tschirley (1969), Orians and
Pfeiffer (1970), Westing (1971), and a
committee of the U.S. Academy of Sciences
(Odum et al. 1974). In many cases these
forests were slow to regenerate; observa-
tions by de Sylva and Michel (1974) indi-
cated higher rates of siltation, greater
water turbidity, and possibly lower dis-
solved oxygen concentrations in swamps
which sustained the most damage. Teas and
Kelly (1975) reported that in Florida the
black mangrove is somewhat resistant to
most herbicides but the red mangrove is
extremely sensitive to herbicide damage.
He hypothesized that the vulnerability of
the red mangrove is related to the small
reserves of viable leaf buds in this tree.
Following his reasoning, the stress of a
single defoliation is sufficient to kill
the entire tree.


Although mangroves commonly occur in
areas of rapid sedimentation, they cannot
survive heavy loads of fine, floculent
materials which coat the prop roots. The
instances of mangrove death from these
substances have been briefly reviewed by
Odum and Johannes (1975). Mangrove deaths
from fine muds and marl, ground bauxite
and other ore wastes, sugar cane wastes,
pulp mill effluent, sodium hydroxide
wastes from bauxite processing, and from
intrusion of large quantities of beach
sand have been documented from various
areas of the world.

12.3 EFFECTS OF OIL SPILLS ON MANGROVES

There is little doubt that petroleum
and petroleum byproducts can be extremely
harmful to mangroves. Damage from oil
spills has been reviewed by Odum and
Johannes (1975), Carlberg (1980), Ray (in
press), and de la Cruz (in press, b).
Over 100 references detailing the effects
of oil spills on mangroves and mangrove-
associated biota are included in these
reviews.

Petroleum and its byproducts injure
and kill mangroves in a variety of ways.
Crude oil coats roots, rhizomes, and pneu-
matophores and disrupts oxygen transport
to underground roots (Baker 1971).
Various reports suggest that the critical
concentration for crude oil spills which
may cause extensive damage is between 100
and 200 ml/m of swamp surface (Odum and
Johannes 1975). Petroleum is readily
absorbed by lipophylic substances on sur-
faces of mangroves. This leads to severe
metabolic alterations such as displacement
of fatty molecules by oil hydrocarbons
leading to destruction of cellular permea-
bility and/or dissolution of hydrocarbons
in lipid components of chloroplasts (Baker
1971).

As with other intertidal communities,
many of the invertebrates, fishes, and
plants associated with the mangrove com-
munity are highly susceptible to petroleum
products. Widespread destruction of
organisms such as attached algae, oysters,
tunicates, crabs, and gobies have been
reported in the literature (reviewed by de










la Cruz in press, b; Ray in press).

Damage from oil spills follows a
predictable pattern (Table 7) which may
require years to complete. It is impor-
tant to recognize that many of the most
severe responses, including tree death,
may not appear for months or even years
after the spill.

In Florida, Chan (1977) reported that
red mangrove seedlings and black mangrove
pneumatophores were particularly sensitive
to an oil spill which occurred in the
Florida Keys. Lewis (1979a, 1980b) has
followed the long-term effects of a spill
of 150,000 liters (39,000 gal) of bunker C
and diesel oil in Tampa Bay. He observed
short-term (72-hour) mortality of inverte-
brates such as the gastropod Melongena
corona and the polychaete Laeonereis
culveri. Mortality of all three species
of mangroves began after three weeks and
continued for more than a year. Sub-
lethal damage included partial defoliation
of all species and necrosis of black
mangrove pneumatophores; death depended
upon the percentage of pneumatophores
affected.

In addition to the damage from oil
spills, there are many adverse impacts on
mangrove forests from the process of oil
exploration and drilling (Table 8). This
type of damage can often be reduced
through careful management and monitoring
of drilling sites.

Although little is known concerning
ways to prevent damage to mangroves once a
spill has occurred, protection of aerial
roots seems essential. Prop roots and
pneumatophores must be cleaned with com-
pounds which will not damage the plant
tissues. Dispersants commonly used to
combat oil spills are, in general, toxic
to vascular plants (Baker 1971). If pos-
sible, oil laden spray should not be
allowed to reach leaf surfaces. Damage
during clean-up (e.g., trampling, compac-
tion, bulldozing) may be more destructive
than the untreated effects of the oil
spill (de la Cruz in press,b).


12.4 MAN-INDUCED MODIFICATIONS

In south Florida, man has been re-
sponsible for modifications which, while
not killing mangroves outright, have al-
tered components of the mangrove ecosys-
tem. One of the most widespread changes
involves the alteration of freshwater
runoff. Much of the freshwater runoff of
the Florida Everglades has been diverted
elsewhere with the result that salinities
in the Everglades estuary are generally
higher than at the turn of the century.
Teas (1977) points out that drainage in
the Miami area has lowered the water table
as much as 2 m (6 ft).

Interference with freshwater inflow
has extensive effects on estuaries (Odum
1970). Florida estuaries are no excep-
tion; the effects on fish and invertebrate
species along the edge of Biscayne and
Florida Bays have been striking. The
mismanagement of freshwater and its
effects on aquatic organisms have been
discussed by Tabb (1963); Idyll (1965a,b);
Tabb and Yokel (1968) and Idyll et al.
(1968). In addition, Estevez and Simon
(1975) have hypothesized that the impact
of the boring isopod, Sphaeroma terebrans,
may be more severe when reswiater f
from the Everglades are altered.

One generally unrecognized side
effect of lowered freshwater flow and salt
water intrusion has been the inland expan-
sion of mangrove forests in many areas of
south Florida. There is documented evi-
dence that the mangrove borders of
Biscayne Bay and much of the Everglades
estuary have expanded inland during the
past 30 to 40 years (Reark 1975; Teas
1979; Ball 1980).

Sections of many mangrove forests in
south Florida have been replaced by filled
residential lots and navigation canals.
Although these canal systems have not been
studied extensively, there is some evi-
dence, mostly unpublished, that canals are
not as productive in terms of fishes and
invertebrates as the natural mangrove-
lined waterways which they replaced.















Table 7. General response of mangrove ecosystems to
severe oil spills (from Lewis 1980b)


Observed Impact


Acute

0 to 15 days


15 to 30 days


Chronic

30 days to 1 year



1 year to 5 years





1 year to 10 years (?)







10 to 50 years (?)


Deaths of birds, turtles, fishes, and
invertebrates

Defoliation and death of small mangroves,
loss of aerial root community



Defoliation and death of medium-sized
mangroves (1 3 m), tissue damage to
aerial roots

Death of large mangroves (greater than
3 m), loss of oiled aerial roots, and
regrowth of new roots (often deformed)

Recolonization of oil-damaged areas by
new seedlings

Reduction in litter fall, reduced re-
production, and reduced survival of
seedlings

Death or reduced growth of young trees
colonizing spill site (?)

Increased insect damage (?)

Complete recovery


Stage










Table 8. Estimated impact of various stages of oil mining on mangrove ecosystems
(modified from Longley et al. 1978 and de la Cruz in press,b).



Stage Activity Impacts


Seismic surveys
Clearing of survey lines
Drilling "shot lines"

Canal excavation
Dredge spoil deposition
Road construction



Increased activity at site
related to drilling


Construction of platforms
Construction of pipelines
Maintenance dredging
Placement of tanks and
other equipment


Oil leaks and spills due
to well blow-out, pipe-
line breakage, careless-
ness, and barge rupture
Clean-up activities


Crushing and clearing vegetation
Vehicle track compaction
Damage to natural levees

Loss of habitat in disturbed areas
Alteration of water flow pathways
Increased turbidity, higher rates of sed-
imentation, and lowered dissolved oxy-
gen in nearby waters

Continued high turbidity
Release of toxic substances
Displacement of wildlife

Continued high turbidity
Loss of additional habitat
Further changes in wetland drainage pat-
terns from pipeline construction
Release of toxic substances
Oil spills

Destruction of plant and animal popula-
tions
Alteration of ecosystem processes such
as primary production and decomposition
Introduction of persistent toxic substan-
ces into soils


Pre-exploration



Site preparation





Drilling



Production






Oil spills










Weinstein et al. (1977) found that artifi-
cial canals had lower species diversity of
benthic infauna and trawl-captured fishes
and generally finer sediments than the
natural communities. Courtney (1975)
reported a number of mangrove-associated
invertebrates which did not occur in the
artificial channels.

Mosquito production is a serious
problem in black mangrove-dominated swamps
in Florida (Provost 1969). The salt marsh
mosquitos, Aedes taeniorhynchus and A.
sollicitans, do not reproduce below the
mean high tide mark and for this reason
are not a serious problem in the inter-
tidal red mangrove swamps. Mosquitos lay
their eggs on the damp soil of the irregu-
larly flooded black mangrove zone; these
eggs hatch and develop when flooded by
spring tides, storm tides or heavy rains.
As with the "high marsh" of temperate
latitudes, there have been some attempts
to ditch the black mangrove zone so that
it drains rapidly after flooding.
Although properly designed ditching does
not appear to be particularly harmful to
mangrove swamps (other than the area
destroyed to dig the ditch and receive the
spoil), it is an expensive practice and
for this reason is not widely practiced.
Properly managed diking can be an effec-
tive mosquito control approach with mini-
mal side effects to black mangroves
(Provost 1969). Generally, ditching or
diking of the intertidal red mangrove zone
is a waste of money.

Mangrove swamps have been proposed as
possible tertiary treatment areas for
sewage (see discussion by Odum and
Johannes 1975). To our knowledge, this
alternate use is not currently practiced
in south Florida. Until more experimental
results are available on the assimilative
capacities and long-term changes to be
expected in mangrove forests receiving
heavy loads of secondary treated sewage,
it would be an environmental risk to use
mangrove forests for this purpose.

In many areas of the world mangrove
swamps have been converted to other uses
such as aquaculture and agriculture (see
de la Cruz, in press, a). Although some


of the most productive aquaculture ponds
in Indonesia and the Philippines are
located in former mangrove swamps, there
is some question whether the original
natural system was not equally productive
in terms of fisheries products at no cost
to man (Odum 1974). Conversion to
aquaculture and agriculture is cursed with
a variety of problems including subsequent
land subsidence and the "cat clay"
problem. The latter refers to the
drastically lowered soil pH which often
occurs after drainage and has been traced
to oxidation of reduced sulfur compounds
(Dent 1947; Tomlinson 1957; Hesse 1961;
Hart 1962, 1963; Moorman and Pons 1975).
Experience in Africa, Puerto Rico, and
Southeast Asia confirms that mangrove
forests in their natural state are more
valuable than the "reclaimed" land.

12.5 PROTECTIVE MEASURES INCLUDING
TRANSPLANTING

Protection of mangroves includes (1)
prevention of outright destruction from
dredging and filling; (2) prevention of
drainage, diking and flooding (except for
carefully managed mosquito control); (3)
prevention of any alteration of hydrologi-
cal circulation patterns, particularly
involving tidal exchange; (4) prevention
of introduction of fine-grained materials
which might clog the aerial roots, such as
clay, and sugar cane wastes; (5) preven-
tion of oil spills and herbicide spray
driftage; and (6) prevention of increased
wave action or current velocities from
boat wakes, and sea walls.

Where mangroves have been destroyed,
they can be replanted or suitable alter-
nate areas can be planted, acre for acre,
through mitigation procedures (see Lewis
et al. 1979). An extensive body of
literature exists concerning mangrove
planting techniques in Florida (Savage
1972; Carlton 1974; Pulver 1976; Teas
1977; Goforth and Thomas 1979; Lewis
1979b). Mangroves were initially planted
in Florida at least as early as 1917 to
protect the overseas railway in the
Florida Keys (Teas 1977).

Both red and black mangroves have










been used in transplanting. As we men-
tioned in section 11, black mangroves seem
to have certain advantages over red man-
groves. Properly designed plantings are
usually 75% to 90% successful, although
the larger the transplanted tree, the
lower its survival rate (Teas 1977).
Pruning probably enhances survival of
trees other than seedlings (Carlton 1974).
Important considerations (Lewis 1979b;
Teas 1977) in transplanting mangroves are:
(1) to plant in the intertidal zone and
avoid planting at too high or too low an
elevation, (2) to avoid planting where the
shoreline energy is too great, (3) to
avoid human vandalism, and (4) to avoid
accumulations of dead sea grass and other
wrack.

Costs of transplanting have been
variously estimated. Teas (1977) suggests
$462 an acre ($1,140/ha) for unrooted
propagules planted 3 ft (0.9 m) apart,
$1,017 an acre ($2,500/ha) for established
seedlings planted 3 ft (0.9 m) apart and
$87,500 ($216,130/ha) for 3 year-old nur-
sery trees planted 4 ft (1.2 m) apart.
Lewis (1979b) criticized Teas' costs as
unrealistically low and reported a project
in Puerto Rico which used established
seedlings at a cost of $5,060 an acre
($12,500/ha); he did suggest that this
cost could be cut in half for larger
projects.


12.6 ECOLOGICAL VALUE OF BLACK VS. RED
MANGROVES

One unanswered question of current
interest in Florida concerns the ecologi-
cal value of black mangrove forests com-
pared to intertidal red mangrove forests.
In many respects, this is identical to the
"high marsh" versus "low marsh" debate in
temperate wetlands. One hypothetical
argument which has been presented fre-
quently in court cases during the past
decade suggests that black mangrove
forests have less ecological value than
red mangrove forests to both man and
coastal ecosystems. This argument is
based on an apparent lack of substantial
particulate detritus export from black
mangrove forests above mean high tide and


the generally perceived lack of organisms,
particularly gamefishes, which use black
mangrove forests as habitat.

The counter argument states that
black mangrove forests are important for
the support of wildlife and the export of
substantial quantities of dissolved
organic matter (DOM). Lugo et al. (1980)
provide evidence that black mangrove
forests do, in fact, export large quanti-
ties of DOM. They point out that (1)
black mangrove leaves decompose more
rapidly than red mangrove leaves and thus
produce relatively more DOM and (2) abso-
lute export of carbon from these forests,
on a statewide scale, is equal or greater
than from red mangrove forests.


12.7 THE IMPORTANCE OF INTER-COMMUNITY
EXCHANGE

From previous discussions (sections 6
and 7.5 and Appendices B, C, D and E) it
is clear that many species of fishes,
invertebrates, birds, and mammals move
between mangrove forest communities and
other habitats including sea grass beds,
coral reefs, terrestrial forests, and the
freshwater Everglades. For example, the
gray snapper, Lutjanus griseus, spends
part of its juvenile life in sea grass
beds, moves to mangrove-lined bays and
rivers, and then migrates to deeper water
and coral reefs as an adult (Croaker 1962;
Starck and Schroeder 1971). The pink
shrimp, Penaeus duorarum, spends its juve-
nile life in mangrove-lined bays and
rivers before moving offshore to the
Tortugas grounds as an adult. During its
juvenile period it appears to move back
and forth from mangrove-dominated areas to
sea grass beds. The spiny lobster,
Panulirus argus, s a juvenile frequently
uses mangrove prop root communities as a
refuge; when nearing maturity this species
moves to deeper water in sea grass and
coral reef communities (see discussion
section 6.1). Many of the mammals (sec-
tion 10) and birds (section 9) move back
and forth between mangrove communities and
a variety of other environments.

These are only a few of many










examples. Clearly, mangrove ecosystems
are linked functionally to other south
Florida ecosystems through physical pro-
cesses such as water flow and organic
carbon flux. As a result, the successful
management and/or preservation of many
fishes, mammals, birds, reptiles, and
amphibians depends on proper understanding
and management of a variety of ecosystems
and the processes that link them. Saving
mangrove stands may do the gray snapper
little good if sea grass beds are
destroyed. Pink shrimp populations will
be enhanced by the preservation of sea
grass beds and mangrove-lined waters, but
shrimp catches on the Tortugas grounds
will decline if freshwater flow from the
Everglades is not managed carefully (Idyll
et al. 1968). Successful management of
south Florida mangrove ecosystems,
including their valuable resources, will
depend on knowledgeable management of a
number of other ecosystems and the
processes which link them.


12.8 MANAGEMENT PRACTICES: PRESERVATION

Based on years of research in south
Florida and based on the information


reviewed for this publication, we have
concluded that the best management prac-
tice for all types of Florida mangrove
ecosystems is preservation. Central to
this concept is the preservation of
adjacent ecosystems that are linked signi-
ficantly by functional processes. The
continued successful functioning of the
mangrove belt of southwest Florida is
highly dependent on the continual exis-
tence of the Everglades and Big Cypress
Swamp in an ecologically healthy condi-
tion.

At no cost to man, mangrove forests
provide habitat for valuable birds, mam-
mals, amphibians, reptiles, fishes, and
invertebrates and protect endangered
species, at least partially support exten-
sive coastal food webs, provide shoreline
stability and storm protection, and
generate aesthetically pleasing experi-
ences (Figure 18). In situations where
overwhelming economic pressures dictate
mangrove destruction, every effort should
be made to ameliorate any losses either
through mitigation or through modified
development as described by Voss (1969)
and Tabb and Heald (1973) in which canals
and seawalls are placed as far to the rear
of the swamp as possible.























































Figure 18. alngrove islands In Florida Bay near Upper Matecumbe Key. Note the
extensive stands of seedling red mangroves which have become established (1981)
after l period without major hurricanes. Angve islands n the Florida
Keys tend to expand during storm-free intervals.




87
















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