• TABLE OF CONTENTS
HIDE
 Title Page
 Table of Contents
 List of Tables
 List of Figures
 Acknowledgement
 Statement of purpose
 Introduction
 Ecology of Merritt Island salt...
 Fundamentals of marsh management...
 Ecology of Merritt Island saltmarsh...
 Management options for marshes...
 Research and data needs
 Literature cited






Group Title: Florida Cooperative Fish and Wildlife Research Unit Research Work Order 15
Title: A conceptual model of salt marsh management on Merritt Island National Wildlife Refuge, Florida
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Full Citation
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Permanent Link: http://ufdc.ufl.edu/UF00073808/00001
 Material Information
Title: A conceptual model of salt marsh management on Merritt Island National Wildlife Refuge, Florida
Series Title: Technical report
Physical Description: 92 leaves : ill. ; 28 cm.
Language: English
Creator: Montague, Clay L
Zale, Alexander V
Percival, H. Franklin ( Henry Franklin )
Publisher: Cooperative Fish and Wildlife Unit, School of Forest Resources and Conservation, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville Fla
Publication Date: [1985]
 Subjects
Subject: Salt marsh ecology -- Florida -- Merritt Island   ( lcsh )
Salt marshes -- Florida -- Merritt Island   ( lcsh )
Salt marshes -- Management   ( lcsh )
Merritt Island National Wildlife Refuge (Fla.)   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographicl references (leaves: 73-92).
Statement of Responsibility: by Clay L. Montague, Alexander V. Zale, H. Franklin Percival.
General Note: " 6 August 1985."
Funding: This collection includes items related to Florida’s environments, ecosystems, and species. It includes the subcollections of Florida Cooperative Fish and Wildlife Research Unit project documents, the Sea Grant technical series, the Florida Geological Survey series, the Coastal Engineering Department series, the Howard T. Odum Center for Wetland technical reports, and other entities devoted to the study and preservation of Florida's natural resources.
 Record Information
Bibliographic ID: UF00073808
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: aleph - 001905928
oclc - 18494576
notis - AJY1326

Table of Contents
    Title Page
        Page 1
    Table of Contents
        Page 2
        Page 3
    List of Tables
        Page 4
    List of Figures
        Page 4
        Page 5
        Page 6
    Acknowledgement
        Page 7
    Statement of purpose
        Page 8
    Introduction
        Page 8
        Values of saltmarsh impoundments
            Page 9
            Page 10
        Values of natural salt marsh
            Page 11
        Concerns about impoundments and the value of Merritt Island marshes
            Page 11
            Page 12
            Page 13
        Focus of this study
            Page 14
    Ecology of Merritt Island salt marshes
        Page 15
        Theoretical basis for production
            Page 15
            Page 16
            Page 17
            Page 18
            Page 19
        Diversity of Merritt Island salt marsh
            Page 20
            Page 21
            Page 22
            Page 23
            Page 24
        Relationships between marshes and estuaries
            Page 25
            Page 26
            Page 27
            Page 28
            Page 29
        Food and cover for estuarine fish and shellfish
            Page 30
            Page 31
            Page 32
            Page 33
            Page 34
            Page 35
            Page 36
            Page 37
    Fundamentals of marsh management for mosquito control and attraction of wintering waterfowl
        Page 38
        Mosquito control
            Page 38
        Waterfowl attraction
            Page 38
            Page 39
            Page 40
    Ecology of Merritt Island saltmarsh impoundments
        Page 41
        Effects of impoundment on ecological production
            Page 41
            Page 42
            Page 43
            Page 44
            Page 45
            Page 46
            Page 47
        Effects of impoundment on overall diversity
            Page 48
        Effects of impoundment on estuarine fish and shellfish
            Page 49
            Page 50
            Page 51
            Page 52
        Analysis of commersial landings for the inshort fisheries if Brevard and Volusia counties, 1951-1982
            Page 53
            Page 54
            Page 55
            Page 56
            Page 57
            Page 58
            Page 59
            Page 60
            Page 61
            Page 62
        Effects of impoundment
            Page 63
            Page 64
            Page 65
            Page 66
            Page 67
    Management options for marshes on Merritt Island National Wildlife Refuge
        Page 68
        Options
            Page 68
            Page 69
            Page 70
            Page 71
    Research and data needs
        Page 72
    Literature cited
        Page 73
        Page 74
        Page 75
        Page 76
        Page 77
        Page 78
        Page 79
        Page 80
        Page 81
        Page 82
        Page 83
        Page 84
        Page 85
        Page 86
        Page 87
        Page 88
        Page 89
        Page 90
        Page 91
        Page 92
Full Text





TECHNICAL REPORT NO. 17


FINAL REPORT

A CONCEPTUAL MODEL OF SALT MARSH MANAGEMENT
ON
MERRITT ISLAND NATIONAL WILDLIFE REFUGE,
FLORIDA

Clay L. Montague*
Alexander V. Zale
H. Franklin Percival



Florida Cooperative Fish and Wildlife Research Unit
Newins-Ziegler Hall
School of Forest Resources and Conservation
Institute of Food and Agricultural Sciences
University of Florida, Gainesville, FL 32611

and

*Systems Ecology and Energy Analysis Program
Department of Environmental Engineering Sciences
A.P. Black Hall
University of Florida, Gainesville, FL 32611


Supported by:

The National Aeronautics and Space Administration

in cooperation with

U.S. Department of the Interior
Fish and Wildlife Service
Cooperative Agreement NO. 14-16-0009-1544
RWO #15


6 August 1985









TABLE OF CONTENTS

Page

LIST OF TABLES ........................................... ....... 4

LIST OF FIGURES .................................................... 5

ACKNOWLEDGMENTS ...................................................... 7

STATEMENT OF PURPOSE ............................................... 8

INTRODUCTION ................................................ 8

Values of Saltmarsh Impoundments .............................. 9
Values of Natural Salt Marsh .................................. 11
Concerns About Impoundments and the Value of Merritt
Island Marshes ............................................. 11
Focus of This Study ............................................. 14

ECOLOGY OF MERRITT ISLAND SALT MARSHES ............................. 15

Theoretical Basis for Production .............................. 15
The Occurrence of Biota and Environmental Stress ........... 16
Nutrient Supply ........................................ 17
Non-energy Environmental Conditions ........................ 17
Notion of Automitigation ................................. 17
Determinants of Production and the Concept of Feedback ..... 18
Ideas for Impoundment Management to Enhance
Ecological Production ................................... 20
Diversity of Merritt Island Salt Marsh ........................ 20
The Concept of Diversity ................................. 21
Importance of Diversity in Natural Areas ................... 21
Considerations in the Measurement of Diversity ............. 22
Principal Determinants of Diversity ........................ 22
Characteristics of Disturbance and Temporal Variation
That Affect Diversity .................................. 23
Characteristics of Biota That Affect Diversity ............. 24
Summary of Diversity Concepts ............................ 24
Ideas for Impoundment Management to Enhance
Ecological Diversity ................................... 25
Relationships Between Marshes and Estuaries ................... 25
Energy, Carbon, and Biota ................................ 25
Nitrogen ......................................... ...... 27
Phosphorus and Sediments ................................. 28
Sulfur, Energy, and Acid Rain .............................. 28
A Scenario of a Southeast Florida Estuary Without Marshes .. 29
Summary of Relationships and Conclusion ................... 29
Food and Cover for Estuarine Fish and Shellfish ................. 30
Foods of Estuarine Fish and Shellfish .................... 30
Food Value of Detritus ............................... 31
Vagile "Link" Organisms ............................. 33
Accessibility of Foods .............................. 34









Page

Cover for Estuarine Fish and Shellfish ..................... 35
Egress of Vagile Fish and Shellfish from Marshes ...... 36

FUNDAMENTALS OF MARSH MANAGEMENT FOR MOSQUITO CONTROL AND
ATTRACTION OF WINTERING WATERFOWL ................................ 38

Mosquito Control ................................................. 38
Waterfowl Attraction ............................................ 38

ECOLOGY OF MERRITT ISLAND SALTMARSH IMPOUNDMENTS .................... 41

Effects of Impoundment on Ecological Production ................. 41
Primary Energy (Sunlight and Turbidity) .................... 41
Water Circulation and Freshening of Water .................. 42
Whole-system Stress (Low Oxygen, Hypersalinity) ............ 47
Nutrient Supply ......................................... 47
Effects of Impoundment on-Overall Diversity .................... 48
Effects of Impoundment on Estuarine Fish and Shellfish .......... 49
Summary Diagrams of the Influence of Impoundment
on Estuarine Fish and Shellfish ......................... 49
Cover ................................................. 52
Ideas for Impoundment Management to Enhance Estuarine
Fish and Shellfish ...................................... 52
Analysis of Commercial Landings for the Inshore Fisheries
of Brevard and Volusia Counties, 1951-1982 .................... 53
Spotted Seatrout ........................................ 53
Blue Crab ............................................ 55
Spot ....................................................... 59
Mullet ........................................ ......... 59
Florida Pompano ............................................ 59
Summary ............................ .............. 63
Effects of Impoundment on Waterfowl ............................ 63

MANAGEMENT OPTIONS FOR MARSHES ON MERRITT ISLAND NATIONAL
WILDLIFE REFUGE ..................................... .. ... ... 68

Options .............................. ............... ........ 68
Permanent Flooding ....................................... 68
Impoundment Elimination ................................... 69
Vestigial Impoundments .................................... 69
Seasonal Flooding ....................................... 69
Seasonal Flooding With Added Potholes ..................... 69
Leaky Impoundments ....................................... 70
Intensive Management For Waterfowl Foods .................. 70
Integrated Marsh Management ............................... 70

RESEARCH AND DATA NEEDS ............................................. 72

LITERATURE CITED ............................................ ..... 73









LIST OF TABLES


Page

Table 1. Water Level Data for a Restored March and from Three
Impounded Marshes on Merritt Island National Wildlife
Refuge (Data from W. Leenhouts). SD = Standard Deviation,
N = Number of Observations between September 1977 and
April 1980 ..................... ....... ................ 12

Table 2. Salinity Data for a Restored March and from Three
Impounded Marshes on Merritt Island National Wildlife
Refuge (Data from W. Leenhouts). SD = Standard Deviation,
N = Number of Observations between September 1977 and
April 1980 ....................... ................... ..... 42



LIST OF FIGURES

Page

Figure 1. Features of impounded salt marsh. Note the positive
feedback loop involving economic development. ............. 10

Figure 2. Hypothetical influences on primary production in Merritt
Island salt marshes. Major sources for production are
underlined. Note the positive feedback loop between
nitrogen fixation and primary production. ................ 19

Figure 3. Conceptual model of relationships of salt marshes
to estuaries. Complex possible exchanges of elements
between salt marshes and estuarine water leads to
temporal variation and uncertainty concerning the of salt
overall influence marshes (natural or impounded) on and
biogeochemistry energetic in estuaries. ................. 26

Figure 4. Conceptual model of factors influencing egress from
natural or impounded salt marsh. Note that more access
necessitates more pumping. ............................... 37

Figure 5. Conceptual model of salt marsh management to control
mosquitos and attract wintering waterfowl. ............... 39

Figure 6. Salinity and Water Level Data from the Restored Marsh,
T-10-K, from September 1977 through April 1980 (data
courtesy of W. Leenhouts, MINWR).......................... 43

Figure 7. Salinity and Water Level Data from Black Point Impound-
ment, T-10-J, from September 1977 through April 1980
(data courtesy of W. Leenhouts, MINWR).................... 44









LIST OF TABLES


Page

Table 1. Water Level Data for a Restored March and from Three
Impounded Marshes on Merritt Island National Wildlife
Refuge (Data from W. Leenhouts). SD = Standard Deviation,
N = Number of Observations between September 1977 and
April 1980 ..................... ....... ................ 12

Table 2. Salinity Data for a Restored March and from Three
Impounded Marshes on Merritt Island National Wildlife
Refuge (Data from W. Leenhouts). SD = Standard Deviation,
N = Number of Observations between September 1977 and
April 1980 ....................... ................... ..... 42



LIST OF FIGURES

Page

Figure 1. Features of impounded salt marsh. Note the positive
feedback loop involving economic development. ............. 10

Figure 2. Hypothetical influences on primary production in Merritt
Island salt marshes. Major sources for production are
underlined. Note the positive feedback loop between
nitrogen fixation and primary production. ................ 19

Figure 3. Conceptual model of relationships of salt marshes
to estuaries. Complex possible exchanges of elements
between salt marshes and estuarine water leads to
temporal variation and uncertainty concerning the of salt
overall influence marshes (natural or impounded) on and
biogeochemistry energetic in estuaries. ................. 26

Figure 4. Conceptual model of factors influencing egress from
natural or impounded salt marsh. Note that more access
necessitates more pumping. ............................... 37

Figure 5. Conceptual model of salt marsh management to control
mosquitos and attract wintering waterfowl. ............... 39

Figure 6. Salinity and Water Level Data from the Restored Marsh,
T-10-K, from September 1977 through April 1980 (data
courtesy of W. Leenhouts, MINWR).......................... 43

Figure 7. Salinity and Water Level Data from Black Point Impound-
ment, T-10-J, from September 1977 through April 1980
(data courtesy of W. Leenhouts, MINWR).................... 44









Page


Figure 8. Salinity and Water Level Data from the Roach Hole
Impoundment, T-10-D, from September 1977 through
April 1980 (data courtesy of W. Leenhouts, MINWR)......

Figure 9. Salinity and Water Level Data from the Fresh
Impoundment, T-24-D, from September 1977 through
1980 (data courtesy of W. Leenhouts,
April MINWR)...................................... ..


Figure 10.


Figure 11.


Conceptual model of major influences on food for
estuarine fish and shellfish. Note the importance
of accessibility of food ... .........................

Conceptual model of major influences on cover for
estuarine fish and shellfish. Note the importance
of accessibility of cover ... ........................









Page


Figure 12.



Figure 13.


Figure 14.


Figure 15.




Figure 16.



Figure 17.


Figure 18.


Numbers of vessels registered for commercial use in
Brevard and Volusia counties, 1963 to 1978. Data
courtesy of Florida Department of Natural
Resources. ........................................ .... 54

Commercial landings (pounds) of spotted seatrout in
Brevard (B), Volusia (V), and both counties
combined (T), 1951 to 1982. ........................... 56

Numbers of vessels registered for recreational use in
Brevard and Volusia counties, 1963 to 1983. Data
courtesy of Florida Department of Natural Resources. ...... 57

Commercial landings (pounds) of blue crabs (hard) in
Brevard (B), Volusia (V), and both counties
combined (T), 1951 to 1982. From 1958 to 1962,
landings data for the two counties were not reported
separately. ...................................... .... 58

Commercial landings (pounds) of spot in Brevard (B),
Volusia (V), and both counties combined (T), 1951
to 1982. Note the substantial increase in landings in
Brevard County in the 1980's. ............................ 60

Commercial landings (pounds) of mullet (both white and
striped combined) in Brevard (B), Volusia (V), and both
counties combined (T), 1951 to 1982. ...................... 61

Commercial landings (pounds) of Florida pompano in
Brevard (B), Volusia (V), and both counties combined (T),
1951 to 1982. ......................................... 62









ACKNOWLEDGMENTS


This document was produced at the expense of the National Aeronautics
and Space Administration through the U.S. Fish and Wildlife Service. We
acknowledge the assistance of K. Key and M. Busacca, NASA, and S. Vehrs and
W. Leenhouts, USFWS, in pursuing the issue and securing the funds for this
investigation.

Special recognition is given to W. Leenhouts, Merritt Island National
Wildlife Refuge, and J. Salmela, Brevard County Mosquito Control District.
These individuals have provided time, encouragement and enthusiasm. Above
all they provided valuable insight into the ecology and management of the
Merritt Island salt marshes owing to their collective years of experience
on the site.

A number of other individuals have been instrumental in the technical
aspects of this task and have provided literature, citations and
discussion: we acknowledge W. Knott, M. Koller, and J. Ryan, NASA; F.
Montalbano, Florida Game and Fresh Water Fish Commission; R. Hinkle and his
staff, Biometrics Corp.; G. Gilmore, Harbor Branch Foundation Inc.

R. Gregory ably administered and Cooperative Fish and Wildlife
Research Unit throughout most of the study period and has provided
technical discussion. T. Hingtgen initially screened the coastal
impoundment and salt marsh literature making our work infinitely easier.
E. Tuggle made many trips to University of Florida libraries, drafted
figures, and made many photocopies related to this effort.

Drafts of this report were reviewed by

M. Busacca,
J. Carroll, Jr.,
F. Johnson,
K. Key,
W. Leenhouts,
F. Montalbano,
S. Vehrs.









STATEMENT OF PURPOSE

Diking and holding water on salt marshes ("impounding" the marsh) is a
management technique used on Merritt Island National Wildlife Refuge
(MINWR) and elsewhere in the Southeast to: a) prevent the reproduction of
saltmarsh mosquitos, and b) attract wintering waterfowl and other marsh,
shore, and wading birds. Because of concern that diking and holding water
may interfere with the production of estuarine fish and shellfish,
impoundment managers are being asked to consider altering management
protocol to reduce or eliminate any such negative influence. How to change
protocol and preserve effective mosquito control and wildlife management is
a decision of great complexity because: a) the relationships between
estuarine organisms and the fringing salt marshes at the land-water interface
are complex, and b) impounded marshes are currently good habitat for a
variety of species of fish and wildlife. Most data collection by scien-
tists and managers in the area has not been focused on this particular
problem. Furthermore, collection of needed data may not be possible before
changes in protocol are demanded. Therefore, the purpose of this document
is two-fold: 1) to suggest management alternatives, given existing infor-
mation, and 2) to help identify research needs that have a high probability
of leading to improved simultaneous management of mosquitos, waterfowl,
other wildlife, freshwater fish, and estuarine fish and shellfish on the
marshland of the Merritt Island National Wildlife Refuge.

INTRODUCTION

As an alternative to spraying DDT and other insecticides, nearly all
of the salt marsh in the vicinity of Merritt Island, Florida, was diked
between 1959 and 1966 (Leenhouts 1983) in order to hold water on marshland
to prevent the production of saltmarsh mosquitos. This technique works
because females of the saltmarsh mosquitos Aedes sollicitans and A.
taeniorhynchus lay eggs on the soil surface (where they hatch following
inundation by tides or rain) but not on standing water (Provost 1968,
1973b; Nielsen and Nielsen 1953). Species of mosquitos that are able to
live in the resulting standing water are not nearly as productive, so the
nuisance is considered sufficiently controlled by this method (Clements and
Rogers 1964; Provost 1968).

Early efforts to control mosquitos by impounding were effective, but
often resulted in the death of saltmarsh vegetation (e.g., black mangroves,
grasses, and succulents) because of "overflooding" (Clements and Rogers
1964; Provost 1968; Bidlingmayer 1982). Overflooding occurred primarily
because: 1) the minimum flood level and duration for effective mosquito
control were not well known, and 2) water sufficient to last the entire
season of mosquito production had to be stored early in the season as
insurance against drought (J. Salmela, pers. comm.). Concern over the loss
of vegetation was expressed notably by Dr. Maurice Provost of the Florida
Medical Entomology Laboratory in Vero Beach, who worked with the Brevard
County Mosquito Control District to develop less destructive, but effective
water level control of mosquitos (Provost 1968, 1973b, 1977). With present
knowledge and pumping capabilities, saltmarsh mosquitos can be controlled
by flooding in the vicinity of Merritt Island with far less loss of
saltmarsh and mangrove vegetation (Clements and Rogers 1964; Provost 1968,
1973b).









STATEMENT OF PURPOSE

Diking and holding water on salt marshes ("impounding" the marsh) is a
management technique used on Merritt Island National Wildlife Refuge
(MINWR) and elsewhere in the Southeast to: a) prevent the reproduction of
saltmarsh mosquitos, and b) attract wintering waterfowl and other marsh,
shore, and wading birds. Because of concern that diking and holding water
may interfere with the production of estuarine fish and shellfish,
impoundment managers are being asked to consider altering management
protocol to reduce or eliminate any such negative influence. How to change
protocol and preserve effective mosquito control and wildlife management is
a decision of great complexity because: a) the relationships between
estuarine organisms and the fringing salt marshes at the land-water interface
are complex, and b) impounded marshes are currently good habitat for a
variety of species of fish and wildlife. Most data collection by scien-
tists and managers in the area has not been focused on this particular
problem. Furthermore, collection of needed data may not be possible before
changes in protocol are demanded. Therefore, the purpose of this document
is two-fold: 1) to suggest management alternatives, given existing infor-
mation, and 2) to help identify research needs that have a high probability
of leading to improved simultaneous management of mosquitos, waterfowl,
other wildlife, freshwater fish, and estuarine fish and shellfish on the
marshland of the Merritt Island National Wildlife Refuge.

INTRODUCTION

As an alternative to spraying DDT and other insecticides, nearly all
of the salt marsh in the vicinity of Merritt Island, Florida, was diked
between 1959 and 1966 (Leenhouts 1983) in order to hold water on marshland
to prevent the production of saltmarsh mosquitos. This technique works
because females of the saltmarsh mosquitos Aedes sollicitans and A.
taeniorhynchus lay eggs on the soil surface (where they hatch following
inundation by tides or rain) but not on standing water (Provost 1968,
1973b; Nielsen and Nielsen 1953). Species of mosquitos that are able to
live in the resulting standing water are not nearly as productive, so the
nuisance is considered sufficiently controlled by this method (Clements and
Rogers 1964; Provost 1968).

Early efforts to control mosquitos by impounding were effective, but
often resulted in the death of saltmarsh vegetation (e.g., black mangroves,
grasses, and succulents) because of "overflooding" (Clements and Rogers
1964; Provost 1968; Bidlingmayer 1982). Overflooding occurred primarily
because: 1) the minimum flood level and duration for effective mosquito
control were not well known, and 2) water sufficient to last the entire
season of mosquito production had to be stored early in the season as
insurance against drought (J. Salmela, pers. comm.). Concern over the loss
of vegetation was expressed notably by Dr. Maurice Provost of the Florida
Medical Entomology Laboratory in Vero Beach, who worked with the Brevard
County Mosquito Control District to develop less destructive, but effective
water level control of mosquitos (Provost 1968, 1973b, 1977). With present
knowledge and pumping capabilities, saltmarsh mosquitos can be controlled
by flooding in the vicinity of Merritt Island with far less loss of
saltmarsh and mangrove vegetation (Clements and Rogers 1964; Provost 1968,
1973b).









Values of Saltmarsh Impoundments

A purported benefit of the continuously high water on marshes noted by
Provost (1959, 1968, 1969a, 1969b) and Trost (undated) was increased use of
marshes by waterfowl and wading birds. Waterfowl are now managed on MINWR
by holding water on the marshes at levels believed beneficial to the birds
while allowing sufficient mosquito control (W.P. Leenhouts, personal
communication), but the inundation period and water depths that are now
used for waterbirds are often in excess of that required for control of
saltmarsh mosquitos. Water level control can be terminated in fall if
mosquito control is the only objective, but on the Merritt Island National
Wildlife Refuge (MINWR) water is retained on the marsh until after
wintering waterfowl leave in about March.

Because salinity in impounded marshes often is lower than the salinity
of estuarine water (Bidlingmayer 1982; W. Leenhouts, unpubl. data) and
because water is held on the marsh longer than it would be under natural
conditions, impounded salt marsh provides habitat for a variety of fish
(especially freshwater species) and wildlife not usually found in natural
salt marshes (Provost 1968; Miglarese and Sandifer 1982; Snelson 1983).
Many of these organisms are more common to freshwater marshes of Florida
(e.g., alligators, kingfishers, centrarchids). These accumulations are
readily measurable. Not readily measurable is the effect of impoundments
on estuarine fish and shellfish populations. However, it is clear that
impoundment management strategies that preclude ingress and egress of
estuarine fish and shellfish have excluded these organisms from large
expanses of marsh which they formerly occupied (see Lewis et al. in press
for a review of this phenomenon).

Although impoundment undoubtedly results in reduced production of some
species (notably mosquitos, and perhaps other organisms as well), a variety
of values of impoundments can accrue in addition to mosquito control and
waterfowl accumulation, owing to the controllability of water levels and
salinities in separate subdivisions of marsh. Some of these values are
indicated in a conceptual model of impoundment features illustrated in
Figure 1.

At the top of Figure 1 is impounded salt marsh, which negatively
influences mosquito production and use of insecticides for mosquito con-
trol. This enhances living and working conditions in the vicinity of
Merritt Island. Such enhancement of the human environment inevitably leads
to more economic development, more by-products of development, and more
pressure to develop, to utilize, and to preserve natural areas by respec-
tive advocates of each.

Impoundment also positively influences accumulations of: 1) certain
species of waterfowl (Trost undated; Provost undated; Heitzman 1978; Wicker
et al. 1983); 2) certain wading birds (Trost undated; Provost undated,
1968, 1969a); 3) certain fish (Snelson 1983; Wicker et al. 1983); 4)
alligators (Wilkinson 1983); and 5) upland mammals that use dikes as
habitat (Miglarese and Sandifer 1982). The density and diversity of
vertebrates using these areas is undoubtedly higher than is found in








IMPOUNDED SALT MARSH

CONTROLLABILITY
+ \OF WATER LEVEL &
WATERFOWL SALINITY IN SUB-
(CERTAIN DIVISIONS OF MARSH


1e


i# i ALLIGATORS
DENSITY & '
DIVERSITY OF --- UPLA
UPLAN)+
VERTEBRATES "- __------ MAMMALS
ON DIKES
a/


/ OBSERVATION OF WASTEWATER /
NATURE MANAGEMENT

APPROPRIATE + WATER STORAGE +
NAL TECHNOLOGY /
TIES BIOMASS FOR FUEL

CONTAMINANT TRAPPING +

EXPERIMENTAL MANAGEMENT TRIALS


MANAGEMENT PRINCIPLES OF
KNOWLEDGE MARSH SYSTEMS
ECOLOGY
+ + .9.
LIVING & WORKING
CONDITIONS FOR +
,PEOPLE

+ ECONOMIC DEVELOPMENT

ADVOCACY FOR DEVELOPMENT,
SUSE, AND PRESERVATION OF
NATURAL AREAS

Figure 1. Features of Impounded Salt Marsh. Note the
positive feedback loop involving economic development.


USE OF









natural salt marsh. In addition, the dikes and access roads that accompany
impoundment enhance access by people to these marsh areas for fishing,
hunting, and observation of nature. These activities considerably enhance
the recreational opportunities in the vicinity of Merritt Island, which
also improve living conditions for people.

The controllability of water levels and salinities in separate subdivi-
sions allows a multitude of other uses of these areas to meet particular
needs. Such needs include use of some impounded marshes for wastewater
management (tertiary treatment), for biomass fuel production, for water
storage, and for contaminant trapping. When alternative methods for
meeting these needs are even more destructive to our environment, use of
impoundments will be appropriate technology for human survival. Regardless
of the method, however, meeting these needs will result in preservation or
enhancement of living conditions for people and hence allow even more
development.

Finally, and perhaps most pertinent to management of a wildlife
refuge, the controllability and subdivision of marshes allows a variety of
experimental management regimes to be tried. As long as adequate data are
recorded to preserve continuity from manager to manager (so that what is
learned by one is adequately transferred to the next), management experi-
ments will have a high likelihood of producing a greater diversity of
desired species, including those of the estuarine fishery. In addition,
careful monitoring of the effects of a variety of management experiments
can advance the field of systems ecology, so that general principles useful
for solving a variety of environmental problems can be discovered and
validated.

Values of Natural Salt Marsh

Natural salt marshes are said to perform a variety of functions of
value to humans (OTA 1984). These include: 1) food and cover for estuarine
fish and shellfish of economic value; 2) sediment trapping and stabiliza-
tion; 3) reduction of storm surge and waves; and 4) removal of nutrients
that can produce blooms of unwanted algae in estuaries. The quality of
these functions of marshes is adequate enough to have been recognized in
numerous articles (Nixon 1980), but may not be as good as can be engi-
neered. The cost, however, of these functions is the cost of protection of
these areas, which has been relatively low in the past. As pressures of
development increase, however, the cost of natural marsh preservation
increases. State and federal agencies (e.g., USFWS Div. of Ecological
Services, U.S. EPA, Florida DNR) spend considerable effort in such habitat
preservation.

Concerns About Impoundments and the Value of Merritt Island Marshes

Of primary concern is whether natural functions of MINWR salt marsh
have been precluded by impoundment. Of particular concern is the issue of
food and cover for estuarine fish and shellfish. Elucidation of this
problem is exacerbated by differences between the natural cycle of flooding
and draining of MINWR marshes and those of tidal marshes where many of the
purported values have received the greatest study such as those of Georgia









natural salt marsh. In addition, the dikes and access roads that accompany
impoundment enhance access by people to these marsh areas for fishing,
hunting, and observation of nature. These activities considerably enhance
the recreational opportunities in the vicinity of Merritt Island, which
also improve living conditions for people.

The controllability of water levels and salinities in separate subdivi-
sions allows a multitude of other uses of these areas to meet particular
needs. Such needs include use of some impounded marshes for wastewater
management (tertiary treatment), for biomass fuel production, for water
storage, and for contaminant trapping. When alternative methods for
meeting these needs are even more destructive to our environment, use of
impoundments will be appropriate technology for human survival. Regardless
of the method, however, meeting these needs will result in preservation or
enhancement of living conditions for people and hence allow even more
development.

Finally, and perhaps most pertinent to management of a wildlife
refuge, the controllability and subdivision of marshes allows a variety of
experimental management regimes to be tried. As long as adequate data are
recorded to preserve continuity from manager to manager (so that what is
learned by one is adequately transferred to the next), management experi-
ments will have a high likelihood of producing a greater diversity of
desired species, including those of the estuarine fishery. In addition,
careful monitoring of the effects of a variety of management experiments
can advance the field of systems ecology, so that general principles useful
for solving a variety of environmental problems can be discovered and
validated.

Values of Natural Salt Marsh

Natural salt marshes are said to perform a variety of functions of
value to humans (OTA 1984). These include: 1) food and cover for estuarine
fish and shellfish of economic value; 2) sediment trapping and stabiliza-
tion; 3) reduction of storm surge and waves; and 4) removal of nutrients
that can produce blooms of unwanted algae in estuaries. The quality of
these functions of marshes is adequate enough to have been recognized in
numerous articles (Nixon 1980), but may not be as good as can be engi-
neered. The cost, however, of these functions is the cost of protection of
these areas, which has been relatively low in the past. As pressures of
development increase, however, the cost of natural marsh preservation
increases. State and federal agencies (e.g., USFWS Div. of Ecological
Services, U.S. EPA, Florida DNR) spend considerable effort in such habitat
preservation.

Concerns About Impoundments and the Value of Merritt Island Marshes

Of primary concern is whether natural functions of MINWR salt marsh
have been precluded by impoundment. Of particular concern is the issue of
food and cover for estuarine fish and shellfish. Elucidation of this
problem is exacerbated by differences between the natural cycle of flooding
and draining of MINWR marshes and those of tidal marshes where many of the
purported values have received the greatest study such as those of Georgia









(see Pomeroy and Wiegert 1981), Massachusetts (see Valiela and Teal 1979
a,b), and Louisiana (see Gosselink 1984). The well-studied marshes of
Georgia for example are flooded and drained twice per day, with short
periods (two or three days) of drought during neap tides without rains.
The average tidal range is up to 8 feet in Georgia depending on proximity
to the ocean. This tidal energy provides water motion and circulation
through these marshes as well as almost daily access of estuarine fauna to
the marsh surface. In the vicinity of Merritt Island, however, marshes are
typically dry (except for rainfall) from January to October when a general
rise in water level causes frequent and almost continuous inundation for
the remainder of the year (Provost 1973a), but wind energy rather than
tides is the primary power for water movement (Dubbelday 1975).

An important determination to be made on Merritt Island is the amount
of time unimpounded marshes are inundated. This is likely to be highly
variable not only from year to year, but also from place to place around
Merritt Island. Because topographical relief is so low in these marshes,
slight differences in elevation can affect the time of inundation of large
expanses of both impounded and unimpounded marsh. An additional
consideration is the presence of several causeways in the vicinity of
Merritt Island. These impede the flow of water and hence can create
locally higher and lower water levels for a given wind speed and direction.

Water levels have been recorded by MINWR by observing a tide-stick
approximately once per month in many Merritt Island impoundments as well as
in the restored marsh T-10-K. Data from this marsh as well as from three
of the impounded marshes are presented in Table 1. Much of the marsh area
is believed by Leenhouts (personal communication) to be inundated only when
water levels exceed one foot above mean sea level. Vegetatively, such
areas tend to consist of quantities of Spartina bakerii (Leenhouts,
personal communication). In the restored marsh, during the period from
September 1977 to April 1980, water level exceeded 1.0 ft on only 4 of 29
observations. In the adjacent Black Point impoundment (T-10-J), water
level exceeded 1.0 ft on 16 of 29 observations.

Particular effort has been spent determining inundation time of a
marsh in the southeast part of Merritt Island near the Bennett Causeway
(not part of MINWR) by the U.S. Fish and Wildlife Service, Ecological



Table 1. Water Level Data for a Restored Marsh and from Three Impounded
Marshes on Merritt Island National Wildlife Refuge (Data from W.
Leenhouts). SD = Standard Deviation, N = Number of Observations
between September 1977 and April 1980.

MARSH LOW HIGH MEAN SD N

T-10-K (Restored Marsh) 0 1.25 0.51 0.32 29
T-10-J (Black Point Imp.) 0.20 1.55 0.95 0.43 29
T-10-D (Roach Hole Imp.) 0.55 2.55 1.70 0.39 28
T-24-D (Fresh Imp.) 1.40 2.80 2.03 0.38 29









Services office in Vero Beach, Florida. Some of this marsh (exact acreage
unspecified) is believed to have been inundated for perhaps 150 or more
days per year in 1981 and 1982 (A. Banner, unp. data).

Despite the uncertainty about the time of inundation, the frequency
and duration of water level fluctuation in the vicinity of MINWR is
considerably different than in the tidal marshes of Georgia, Massachusetts,
and Louisiana, where most of the functional relationships of marshes to
estuaries have been studied. Prior to impoundment, much of the acreage of
Merritt Island marshes was inundated nearly continuously for perhaps 100
days per year (judged from unp. data of Ned Smith), with wind and rain, but
no tidal energy available to create water movement. Tidal salt marshes
elsewhere (e.g. Georgia) are inundated perhaps 300 days per year for 12
hours per day (NOAA tide tables). Water movement through tidally-flooded
marshes should be much greater and more predictable than the wind-driven
circulation of Merritt Island. Wind does not circulate shallow water very
effectively because turbulent eddies cannot usually form (H.T. Odum 1967).
Marsh vegetation will create additional resistance to wind and water
movement.

Merritt Island marshes are perhaps so different from the marshes of
greatest scientific study that results and conclusions from the majority of
the salt marsh literature have little applicability. Water movement and
inundation period, seasonal temperature fluctuations, and sediment supply
and type are considerably different from those of the major study sites of
salt marsh ecology (see Introduction of Montague et al. 1984a). The
filtering capabilities of the Merritt Island marshes are probably much less
than those of tidal marshes, because estuarine water covers the former
marshes during the winter when vegetation there is relatively senescent or
not as actively growing as at other times of year (Chynoweth 1975).
Although of the same genus, Spartina alterniflora (the principal component
of the majority of salt marsh studies) does not closely approximate
Spartina bakerii (a common plant in Merritt Island impoundments) in habitat
or presumably in physiological requirements. Vegetation of much of the
Merritt Island salt marsh includes species typical of "high marsh" (marsh
near to dry land) of the Atlantic and Gulf coasts (e.g. Salicornia spp.,
Batis maritima, Distichlis spicata, Paspalum vaginatum; see Sweet 1976;
Leenhouts and Baker 1982; Montague et al. 1984b). Differences in sediment
may result in different limiting nutrients and different effects of marsh
on chemical constituents of estuarine water (see section entitled
"Relationships Between Marshes and Estuaries"). Hence, values of Merritt
Island marshes largely remain to be determined.

Relationships between high marshes and estuaries elsewhere have not
been well-established (Nixon 1982). The studies of Byron (1968) on a North
Carolina marsh dominated by Juncus roemerianus, Blum (1969) on a
Massachusetts marsh dominated by Spartina patens, and particularly Borey et
al. (1983) on a Texas marsh co-dominatedby Spartina patens and Distichlis
spicata are perhaps indicative of the relationships between infrequently
flooded high marsh and estuarine water. Neither Byron nor Blum could
demonstrate a net export of organic matter to the estuary. Byron
demonstrated a net uptake of nitrogen on his study sites, and Blum
demonstrated a net uptake of manganese. Borey et al. demonstrated an
export of only 2.4 to 5.5% of net aerial primary production, which









consisted of refractory dissolved organic. They attributed this low value
both to the lack of twice-daily tides of a high amplitude and to the
indirect methods of measurement of export used in some of the published
studies that show considerably more export, to which they compare their
results. Their paper is a concise review of current thinking about export
of organic matter from marshes to estuaries.

Focus of This Study

A large number of issues presently occur in scientific study of salt
marshes, and also a large number of issues have been raised by a variety of
interests with regard to the potential values and damage caused by impound-
ment of salt marshes on Merritt Island and elsewhere. These issues include
not only the potential for damage to stocks of estuarine fish and shell-
fish, but also the potential for storage of contaminants from pesticides
formerly used in agriculture and mosquito control, the effects on a variety
of other wildlife including the disappearance of the dusky seaside sparrow,
wastewater application and water storage in impounded marshes, and seagrass
development in nearby estuarine waters. Our focus is primarily on the
salt marshes of Merritt Island National Wildlife Refuge and the effects of
impoundment and their management for mosquito control and waterfowl on
ecological production and diversity in general and on estuarine fish and
shellfish in particular. We will also consider briefly effects on other
wildlife. With appropriate modification, the information in these sections
should provide a general conceptual framework for considering a variety of
other concerns and problems.









ECOLOGY OF MERRITT ISLAND SALT MARSHES

Salt marshes are some of the most biologically productive lands on
earth (E.P. Odum 1971; Turner 1976; Teal 1980) and Merritt Island salt
marshes are apparently no exception, though only one study is known to us.
Chynoweth (1975) found an annual production of certain marsh 2pants in the
breached impoundment T-10-K to be approximately 2100 g(dw)'m y about
half of which is carbon. These are comparable to production values of salt
marshes elsewhere (Wiegert 1979, Teal 1980, Costanza et al. 1983). Unfor-
tunately, Chynoweth reported production from only three plant types,
Spartina bakerii, Distichlis spicata, and Sesuvium portulacastrum. Batis
maritima, several species of Salicornia, Paspalum vaginatum, and black and
white mangroves are dominant plants in many marshes in the vicinity of
Merritt Island. Production of these on Merritt Island have not been
determined.

Plant production in ecosystems is responsible for animal production.
Plants are either consumed directly by grazing insects that then become
prey for insectivorous animals, or they die and are decomposed by a variety
of bacteria, fungi, microfauna, and meiofauna. This decomposer community
then becomes food for "detritivorous" macrofauna which are food for
commercially or recreational important fish and wildlife.

Theoretical Basis for Production

To understand why salt marshes are so productive and how to manage
this production, theory of ecological production can be helpful.
Ecological production is dependent upon the availability of: 1) biota; 2)
essential nutrients; and 3) energy available to be converted into new biota
using essential nutrients. A shortage of any of these can limit
production. These three requirements are somewhat interdependent, and in
non-extreme environments (see Ocurrence of Biota and Enviromental Stress
below), where a variety of organisms can survive (see Principle
Determinants of -Diversity, w~ich follows), the magnitude of ecological
production should be proportional to the sum of primary environmental
energies and environmental energy subsidies converging on an ecosystem (see
H.T. Odum 1984 for related discussion).

Primary energies are defined here as those that are directly converted
to chemical energy of organic compounds by biota. World-wide, these
include not only sunlight, but also geothermal energy, as has been recently
demonstrated most explicitly in the case of the very rich biotic community
of the Galapagos Rift thermal vents (Ballard 1977; Levinton 1982). The
processes of photosynthesis and chemosynthesis are responsible for
conversion of these primary energies into food energy, which is utilized by
a web of consumers, including fish and wildlife of direct value to people.

Energy subsidies are flows of energy in the environment that are not
directly assimilated by plants, decomposer microbes, or animals, but are
exploited by organisms in such a way that more of the energy that they do









ECOLOGY OF MERRITT ISLAND SALT MARSHES

Salt marshes are some of the most biologically productive lands on
earth (E.P. Odum 1971; Turner 1976; Teal 1980) and Merritt Island salt
marshes are apparently no exception, though only one study is known to us.
Chynoweth (1975) found an annual production of certain marsh 2pants in the
breached impoundment T-10-K to be approximately 2100 g(dw)'m y about
half of which is carbon. These are comparable to production values of salt
marshes elsewhere (Wiegert 1979, Teal 1980, Costanza et al. 1983). Unfor-
tunately, Chynoweth reported production from only three plant types,
Spartina bakerii, Distichlis spicata, and Sesuvium portulacastrum. Batis
maritima, several species of Salicornia, Paspalum vaginatum, and black and
white mangroves are dominant plants in many marshes in the vicinity of
Merritt Island. Production of these on Merritt Island have not been
determined.

Plant production in ecosystems is responsible for animal production.
Plants are either consumed directly by grazing insects that then become
prey for insectivorous animals, or they die and are decomposed by a variety
of bacteria, fungi, microfauna, and meiofauna. This decomposer community
then becomes food for "detritivorous" macrofauna which are food for
commercially or recreational important fish and wildlife.

Theoretical Basis for Production

To understand why salt marshes are so productive and how to manage
this production, theory of ecological production can be helpful.
Ecological production is dependent upon the availability of: 1) biota; 2)
essential nutrients; and 3) energy available to be converted into new biota
using essential nutrients. A shortage of any of these can limit
production. These three requirements are somewhat interdependent, and in
non-extreme environments (see Ocurrence of Biota and Enviromental Stress
below), where a variety of organisms can survive (see Principle
Determinants of -Diversity, w~ich follows), the magnitude of ecological
production should be proportional to the sum of primary environmental
energies and environmental energy subsidies converging on an ecosystem (see
H.T. Odum 1984 for related discussion).

Primary energies are defined here as those that are directly converted
to chemical energy of organic compounds by biota. World-wide, these
include not only sunlight, but also geothermal energy, as has been recently
demonstrated most explicitly in the case of the very rich biotic community
of the Galapagos Rift thermal vents (Ballard 1977; Levinton 1982). The
processes of photosynthesis and chemosynthesis are responsible for
conversion of these primary energies into food energy, which is utilized by
a web of consumers, including fish and wildlife of direct value to people.

Energy subsidies are flows of energy in the environment that are not
directly assimilated by plants, decomposer microbes, or animals, but are
exploited by organisms in such a way that more of the energy that they do









assimilate (from sunlight in the case of plants, or from food in the case
of animals) can be allocated to production of more organisms (E.P. Odum et
al. 1979). That more productive organisms will occur in the presence of
energy subsidies in non-extreme environments (defined as above) is a
fundamental tenet of the theory of natural selection (Lotka 1922a, 1922b).

A subsidy in excess can become a stress, its value as a subsidy can
saturate (law of diminishing returns), or a perceived energy release may
not, in fact, be a subsidy. Therefore, subsidy mechanisms must be
identified and their effects on production measured before any ranking of
effectiveness of particular subsidies is possible.

Wind is an example of an environmental energy subsidy in Merritt
Island saltmarsh impoundments. It influences water circulation and wave
action, which in turn facilitate the encounter of organisms with nutrients
or foods (E.P. Odum 1974). Circulation also facilitates the separation of
organisms from their metabolic wastes (standing water does not enhance
production). Because less of an organism's directly assimilated energy
need be utilized for these functions, a natural selection occurs for
organisms that both utilize these subsidies and redirect assimilated energy
to production. Therefore, in environments where energy subsidies exist,
ecological production should be greater.

Water circulation caused by the ebb and flow of the tides has been
said to account for the very much higher aerial production of Spartina
alterniflora along the edges of tidal creeks of the southeastern United
States (E.P. Odum et al. 1983 refer to this as "tidal subsidy"; see also
Wiegert et al. -1983). In the only published study to date comparing
primary production in a natural and an adjacent impounded marsh, E.P. Odum
et al. (1983) reported 31% higher annual aboveground net production of
giant cutgrass (Zizaniopsis miliacea) in the natural marsh than in the
impounded marsh, although standing crops were almost identical (see also
the data of Morantz in Whitman 1976). The authors attributed the
difference in production to twice-daily tides in the natural marsh. On
Merritt Island, little daily tide occurs, and it seems unlikely that
impoundment would have as large a negative effect on production as in the
cutgrass marshes. Water circulation occurring for any reason, including
pumping, should provide energy subsidies with corresponding enhancement of
production.

The Occurrence of Biota and Environmental Stress

Environmental stress occurs for a species when it is exposed to an
environment that is so different from that within which its ancestors were
naturally selected that it has little or no adaptation for contending with
the stress (see also E.P. Odum et al. 1979). What is stressful for one
species, however, may not cause a change in overall ecological production
in an impoundment, though changes in species composition may result.
However, environmental conditions occasionally occur that are extreme
enough to be suboptimal for the production of any species on earth. A few
species may exist under such conditions, but overall ecological production
would be expected to be reduced. In impoundments, sustained extremely high
salinity (perhaps greater than 60 ppt) should be a sufficient stress to
greatly reduce overall ecological production, though subtle changes in
production may occur at lower salinities.









Nutrient Supply

For ecological production to be proportional to available energy
input, sufficient nutrients must be available for building new organisms.
Nutrients (primarily nitrogen and phosphorus) arrive at Merritt Island from
a variety of external sources. Stream flows, non-point source discharges,
sewage outfalls, groundwater flows, dustfall, and rainfall all contain
nutrients for ecological production. Nutrients such as nitrogen and carbon
can be fixed from atmospheric pools of nitrogen gas and carbon dioxide.
Carbon fixation requires the energy of sunlight (and is proportional to
ecological production). Nitrogen fixation requires energy of organic
compounds (fixed via photosynthesis or imported; Hanson 1977a, 1977b).

Recycling of nutrients occurs as organisms feed, egest and excrete, or
die and decompose (Johannes 1964, 1968; Pomeroy 1970). The presence of
organisms available for these processes, however, should be proportional to
available energy inputs except in extreme environments.

In all of these cases, energy supply is important in generating a
supply of nutrients as well as recycling nutrients, which themselves are
essential for ecological production, so the concept of the magnitude of
ecological production as proportional to the sum of primary environmental
energies and environmental energy subsidies converging on an ecosystem
may hold if a number of species can occur and if sufficient time has
elapsed for exploitation of available energy sources and subsidies.

Non-energy Environmental Conditions

Some environmental conditions may change without causing a significant
change in energy or nutrient supply. Nonresponsiveness to change within
some intermediate range of environmental conditions is common in both
engineered and self-organized (e.g., ecological, social, economic) systems.
This phenomenon, known as "dead zone" in systems engineering (Dransfield
1968), is a characteristic of systems with several components that have
similar function, but have slightly different environmental requirements
for maximal function. Several species of phytoplankton, for example, each
with different temperature optima for maximum photosynthesis, may cause
total photosynthesis of the water column to remain stable over small
changes in temperature. This particular phenomenon has been termed "con-
generic homotaxis" by Hill and Durham (1978). An impoundment of 5 cm water
depth may have identical ecological production to one of 25 cm depth if
energy and nutrient supplies are identical. The species comprising the
community in these two impoundments may be radically different, but a
predictable change in overall production seems impossible to rationalize.

Notion of Automitigation

If the above arguments about the causes of ecological production are
true (and the development of production theory is continually evolving),
any activity of humans that does not reduce the supply of energy and
nutrients or create environmental stress should not affect ecological
production even if non-energy conditions are changed in the environment.
When water depth is increased in an impoundent to the level of an "over-
flooded" condition, emergent vegetation often disappears (Voigts 1976), but









overall ecological production of the area may not have been reduced.
Perhaps only a shift in the types of animals and plants has occurred. As
the water level increases, abundance of emergent vegetation may decline,
while habitat for submerged vegetation is formed. With greater water level
increases, light for benthic algae may be reduced, but more habitat for
phytoplankton is produced. Since phytoplankton may further reduce light to
both benthic algae and submerged vegetation, phytoplankton may in the end
be the dominant converter of available energy and nutrient supplies to
ecological products. However, the total production of the new community
may be exactly the same as before water level was increased due to
cybernetic feedback mechanisms (Rapport et al. 1985). We refer to this
phenomenon as "automitigation" of ecological production. Of course,
production of specific species that are favored by humans may be enhanced
or reduced by any given change, whether whole-system production is affected
or not (Rapport et al. 1985).

Determinants of Production and the Concept of Feedback

A conceptual model illustrated in Figure 2 summarizes major endogenous
influences on primary production in salt marshes. Primary production in
the marsh is influenced by: 1) available light; 2) supply of plant nutri-
ents (nitrogen, phosphorus, etc.); 3) salinity; and 4) circulation of
water. A positive influence (depicted by "+") is defined as one in which
an increase of the stimulus produces an increase in response and decreased
stimulus produces decreased response. Examples are availaTle light,
nutrient supply, and water circulation below some threshold amount. A
negative influence (depicted by "-") is defined as one in which the direc-
tion of the response is opposite that of the stimulus. Salinity, for
example, is shown as a negative influence on primary production.

Water circulation and available light are positive only when not in
excess. Excessive water circulation may lead to erosion, and too much
light may cause photoinhibition (Ryther 1956). The diagram as depicted is
applicable when these factors are not excessive.

Available light is influenced both by the turbidity of water when it
covers the marsh and by the amount of incident sunlight. Turbidity is
influenced by available sediments and water turbulence (water circulation),
which in the vicinity of Merritt Island is a function of wind and rain.
Water circulation, therefore, simultaneously has a positive influence on
production by subsidizing the supply of nutrients and removing wastes, and
a negative influence by increasing turbidity. Thus the overall, or net,
influence of water circulation on production can vary over a wide range of
possibilities.

Supply of plant nutrients is influenced by nutrients in land drainage
(dissolved, suspended, and bedload transport), quantity of sewage effluent,
and nitrogen fixation. The quantity of nutrients in land drainage is
influenced by agricultural and urban development and rain. The quantity of
sewage effluent is also influenced by urban development.

Nitrogen fixation is an energy-using process that is often limited by
organic matter (Delwiche 1970; Hanson 1977a, 1977b). Because primary
production of organic matter in salt marshes is often limited by nitrogen
(Gallagher 1975; Darley et al. 1981), a reciprocal relationship, or feed-











N WIND



-WATER +
CIRCULATION


AVAILABLE
LIGHT %


SUPPLY
PLANT


OF ORGANIC
MATTER
ITS t


IN THE SALT MARSH


Hypothetical Influences on Primary Production in
Merritt Island Salt Marshes. Major sources for
production are underlined. Note the positive
feedback loop between nitrogen fixation and
primary production.


Figure 2.









back loop, is formed. Such loops can be positive or negative. The loop
shared by nitrogen fixation and primary production is positive. If a
change occurs in a component of a positive loop, the direction of change is
reinforced on every cycle of the loop. If the loop were negative, the
change would be opposed on each successive cycle and either an oscillation
or a smooth approach to a constant or steady-state would occur. Awareness
of significant loops is important because they can produce unexpected
results when changes are instituted in the environment.

Salinity of the marsh surface and interstitial (pore) waters is
influenced by the supply of fresh water, the supply of salt water, and by
evaporation. Freshwater supply is influenced by rain and saltwater supply
is influenced by flooding. Evaporation is influenced principally by
available sunlight (both through its direct excitation of water molecules
and its influence on environmental temperature). Thus, the influence of
sunlight on marsh primary production can be both positive (photosynthesis
is a function of available light) and negative (evaporation raises salini-
ty). The positive effect of sunlight should outweigh the negative effect
except at very high salinities. Because of these simultaneous positive and
negative effects of light, its overall effect on photosynthesis is non-
linear in shallow marine systems (see also H.T. Odum 1967).

Ideas for Impoundment Management to Enhance Ecological Production

Control of some of the determinants of ecological production outlined
in the previous sections is possible using structures and equipment already
in place in Merritt Island saltmarsh impoundments. Management to enhance
overall ecological production might include the following interdependent
schemes: 1) maintenance of salinity in the range of brackish water; 2)
preventing anaerobic conditions; 3) circulating water through the impound-
ments as much as possible without causing erosion and turbidity (and
perhaps increases in BOD); 4) keeping non-phytoplankton turbidity low; and
5) addition of nutrients (e.g. sewage) if nutrients are limiting. One way
to keep non-phytoplankton turbidity low is to establish submerged aquatic
vegetation. Establishment of submerged vegetation can produce a positive
feedback loop; production of submerged vegetation increases sediment
trapping which lowers turbidity and increases available light for the
production of submerged vegetation. This loop can reinforce the establish-
ment of submerged vegetation, or if started the other direction, can
quickly eliminate it. Establishing submerged vegetation requires keeping
phytoplankton low because of turbidity and competition for nutrients. It
may require wind breaks in some impoundments because of the possibility of
uprooting vegetation.

Determination of factors limiting ecological production in impound-
ments would make for more effective management of ecological production,
should this be a desired goal of management in some or all impoundments. A
number of experimental and correlational studies (with respect to the
parameters discussed above) could be devised.

Diversity of Merritt Island Salt Marsh

Natural salt marshes typically do not contain very diverse macroflora
or macrofauna. Natural marshes in the vicinity of Merritt Island apparently









contained few species of vascular plants (Leenhouts and Baker 1982; Montague
et al 1984b). To the north and west, marshes probably consisted largely
of four to six plant species (though other species undoubtedly occurred in
smaller quantities): Distichlis spicata, Paspalum vaginatum, Batis
maritima,and one to three species of Salicornia. This assemblage is
sometimes referred to as "grassy" marsh and it is typical of marsh known as
"high" marsh that borders the upland fringe of salt marshes dominated by
Spartina alterniflora elsewhere in the southeastern United States.

Higher elevations on Merritt Island perhaps contained Spartina bakerii
and Juncus roemerianus as can presently be seen in the unimpounded area
adjacent to Turnbull Creek. A transect toward the south and east included
increasing frequency of black mangrove, Avicennia germinans and white
mangrove, Laguncularia racemosa. The denser the mangrove, the lower the
light penetration to the marsh surface, so the lower the frequency of the
grassy marsh species (and perhaps the lower the diversity as the number of
dominant species would concurrently drop from six or eight to two).

To understand why natural salt marshes are not very diverse, and to
better manage ecological diversity in marshland both require careful
consideration of the meaning, measurement and theory of diversity.

The Concept of Diversity

Species diversity is a measure of the variety of species in a given
area as indicated both by the number of different species found in the area
(called species "richness") and by the equivalence of the number of
individuals in each species (called "evenness"). Thus an area is said to
be diverse if it contains many species each represented by nearly the same
number of individuals. The relative effect of a lack of either eveness or
richness on diversity depends on how these two factors are combined into
one index of diversity. Thus, the utility of a particular index must be
evaluated with respect to the desired application.

Importance of Diversity in Natural Areas

Diversity is important both theoretically and in practice. Theoreti-
cally, following a disturbance, an area with a greater variety of plants,
animals, and protests should stand a better chance of continuing life-
processes such as photosynthesis, animal production, nutrient recycling,
and decomposition at levels more similar to those before the disturbance.
Genetic variety is believed to be the key to the survival of life during
major worldwide shifts in climate. Monocultures of an inflexible species
would be susceptible to eradication.

Pragmatically, diversity in natural areas is important in the same
sense as a diversity of crops is to the survival of a small family farm.
A diversity of commercially important fishery species allows economic
stability for fishermen. A diversity of habitats allows management for a
diversity of desired wildlife and enhances opportunity for, and may reduce
the expense of, multiple-objective biological resource management.
Appropriate evaluation of diversity in this sense should incorporate not
only the variety of species within an area, but also the variety of species
among areas.









Considerations in the Measurement of Diversity

Several methods of measuring eveness and richness and combining these
into one index of diversity exist (Fisher et al. 1943; Emlen 1973). Others
may be developed for special purposes. None, however, should be used
without an evaluation of their suitability to a particular objective.
Diversity of habitats may be more valuable than plant diversity within a
particular habitat, for example. Maximizing the diversity of endangered
species may or may not involve maximizing overall diversity.

Any given measure of diversity may be influenced by both the area
covered in the sample and by the time required to complete the sample. A
large area covered may include a variety of species, but subdivisions of
the area may be very low in diversity. An impounded area on Merritt
Island, for example, may have a large total number of plant species, each
represented by nearly the same number of individuals (or biomass), but
these species may be segregated into Tow dTversity zones according to
elevation. On Merritt Island National Wildlife Refuge, diversity is much
higher among all impoundments than is indicated by the average diversity
within impoundments (Leenhouts, pers. comm.) presumably because of differ-
ences in physical/chemical conditions among impoundments.

The time required for completing a sampling effort for determining
diversity will influence the measurement relative to the rate of change of
species composition in the sample area. If changes occur much faster than
the sample can be collected, then the resulting number of species included
in the sample may be higher than if a snap-shot of the area had been
analyzed. It is-an open question whether an area that supports 120 species
in a year, but with only an average of 20 present at any one time is more
valuable for its diversity than a system that supports only 60 species in a
year with an average of 40 present at any one time. Considerable thought
must be given both to the area sampled and the time interval of importance
before judgement about changes in diversity can be fairly evaluated.
Inconsistency in these aspects of diversity measurement promote inconclu-
siveness. There is considerable potential for error or manipulation of
sampling to achieve a particular result.

Principal Determinants of Diversity

Theorists attribute a high diversity both to biotic specialization and
to environmental variation. Given enough time for speciation, biotic
specialization can occur in environments with relatively constant physical
conditions and resource supplies such as the deep sea and the bottoms of
deep lakes (Sanders 1968, Valentine 1973, Levinton 1982; Valiela 1984).
Extreme environments, however, such as those with very high salinity
(greater than 150 ppt), have low diversity no matter how constant the
environment.

The highest species diversity seems to occur in areas that have
considerable constancy in some environmental conditions, but also contain
certain disturbances. A tropical coral reef, for example, occurs in an
area where temperature and light vary little from month to month. These
areas, however are subject to periodic storms that can topple branching
reef corals. Disturbance of the reef communities by coral-eating fishes is









also common. Such disturbances overlay a patchwork of successional stages
of the reef, thereby enhancing the overall richness and eveness of species
(Strong et al. 1984).

Whether or not a disturbance enhances diversity depends on character-
istics of the disturbance, on characteristics of affected biota, and on the
time and area over which diversity is monitored. If the disturbance
produces spatial heterogeneity within the sampled area, and sufficient time
is allowed for new niches to be occupied, the disturbance may enhance
overall diversity of the area.

Characteristics of Disturbance and Temporal Variation
That Affect Diversity

If disturbance occurs in patches, the opportunity for enhanced
diversity is present if the area sampled includes the patches. If the
disturbance is area-wide, a general reduction in diversity might be
expected at least temporarily. The time required for initial diversity to
be restored should relate to the intensity (severity, amplitude, extreme-
ness) of the disturbance. If the original richness and evenness of species
recurs, the composition of species may be different, depending on
characteristics of the species, and on the rigor of the environment. In
rigorous environments such as alpine tundras, few species can live, so
recovery after disturbance usually includes those same species. In the
tropics, however, many alternative species are available during post-
disturbance recovery, so resulting successional stages may not yield the
same species from place to place or time to time.

If the change that occurs produces an environment that is foreign to
available organisms, diversity may remain low for a very long time. If the
environment produced is so foreign or extreme that it severely interferes
with fundamental physiological processes, diversity may always be low
(Rapport et al. 1985). This may occur if the disturbance supplies
hazardous, non-biodegradable materials or produces extremes of pH, or very
high temperatures or salinities.

Periodic disturbances or temporal variation may also reduce or enhance
diversity relative to the period over which diversity is evaluated (Vogel
1980). The frequency, regularity, and abruptness of change are important.
If the change is cyclic, stimulates a cyclic change in species composition,
and a cycle of change is completed during the measurement period, then more
species will be found than under lower frequency variation. Many
ecosystems and organisms are dependent on such repetitive events which
become anticipated through selection (Vogel 1980). If the rate of environ-
mental change exceeds the rate that species composition can change, a lower
diversity might be expected. If the rate of change is very low, changes in
species composition may not be detected during the sampling period.

For example, periodic fire is now recognized to be an essential
component of a healthy boreal forest (Heinselman 1971; Rapport et al.
1985). The same may well hold true for salt marshes on Merritt Island.
Certain species are dependent upon fire for effective seed release and may
possess adaptations to survive conflagrations. Periodic burns release
minerals stored in soils and plant biomass, create space, and reduce









competition for water, nutrients, and light. Although fire may be
important in maintaining a natural system, this natural system may be
neither as productive nor as diverse as one that would replace it without
periodic fire.

Diversity may be lower under irregular than under regular periodic
change because a survival option is eliminated; survival is not possible by
regular adjustment timed to coincide with regular events. Presumably,
fewer organisms exist that can tolerate or avoid random change. Also
presumably, fewer organisms exist that can withstand abrupt change as
opposed to slower changes. If these notions are true, diversity should be
lower in an environment of random and abrupt changes of intermediate
frequency. However, in some settings, temporal variation may allow several
species to coexist, each living most of the time at suboptiomal conditions,
but each occasionally receiving optimal conditions.

Characteristics of Biota That Affect Diversity

Availability of biota for recruitment into a habitat altered by some
disturbance in time or space is an important consideration for diversity.
If the surrounding area is inhabited by a large number of species, or if a
diversity of organisms can be imported, then altered habitat may develop
higher diversity faster than would occur otherwise.

Ability to tolerate or avoid change is an important consideration in
evaluating change in diversity. Sedentary organisms must tolerate change,
whereas vagile organisms can move if altered habitat is unsuitable. By
avoidance, vagile organisms should be able to withstand more irregular and
abrupt changes than sedentary organisms.

Another characteristic of importance is genetic variability amongst
individuals of a species in a habitat undergoing change. If this
variability is high, if the number of individuals is large, and if the
production rate of individuals is high, then selection for individuals
resistant to the change may occur (e.g., insecticide-resistant strains of
mosquitos).

Thus, a given environmental change should be expected to have a
greater affect on sedentary, slowly-reproducing species represented by low
numbers of individuals of little genetic variability. If these species
compete with species of the opposite characteristics, and if such species
are available for recruitment following a change, then the effect of the
change on overall diversity may be little if any, or diversity may even
increase.

Summary of Diversity Concepts

Species diversity is a measure of the variety of species in a given
area. The notion includes the number of species found (richness) and the
relative representation of each species as compared to the others
(evenness). Measures of diversity are sensitive both to the amount of area
considered and the amount of time allowed for a measurement. Except after
an unusually intense disturbance, diversity should appear higher with
greater area and time considered.









Regular spatial and temporal variation and even some random
disturbances can enhance species diversity. Evaluation of the potential
effects of temporal variation and disturbance requires consideration of
characteristics of both the change and the affected biota. Characteristics
of the change of importance include: 1) area covered; 2) intensity; 3)
foreignness; 4) frequency; 5) regularity; and 6) abruptness.
Characteristics of biota of importance include: 1) ability to tolerate or
avoid change either by their physiological characteristics, mobility, or
genetic flexibility; and 2) availability for recolonization after a change.

Ideas for Impoundment Management to Enhance Ecological Diversity

The theoretical determinants and other considerations concerning
diversity are many, but are not contradictory and therefore may be useful
in ecosystem management. For example, to enhance diversity of any given
subgroup of animals or plants, the following may be done: 1) provide a
diversity of habitats in the area; 2) provide some patches of alternative
habitat within an area; 3) provide open access to vagile species; 4)
perhaps provide some temporal variation that is smooth, of low intensity
and foreignness, and regular; 5) avoid temporal changes that are area-wide,
abrupt, and irregular, though if these changes are highly localized (not
area-wide), they may enhance habitat variety; and 6) avoid large areas of
sustained conditions that interfere with fundamental life-processes and
thereby interfere with both production and diversity (e.g. extremely high
salinities, or temperatures, or extremes of pH, or very low dissolved
oxygen).

Relationships Between Marshes and Estuaries

Recently, the values of marshes as improvers of estuarine water
quality and exporters of organic detritus of great food value to estuarine
fish and shellfish as initially purported (Teal 1962; Gosselink et al.
1973) have been called into question (see Haines 1979b; W.E. Odum et al.
1979; Onuf et al. 1979; Nixon 1980; Borey et al. 1983; Boesch and Turner
1984; Dame and Stilwell 1984; Dankers et al. 1984). Therefore, the overall
influence of Merritt Island salt marshes on estuarine waters is unknown,
and a variety of possibilities exist. Figure 3 illustrates some principal
exchanges that occur between marshes and estuarine waters that are relevant
to energy flow in estuaries from initial conversion by photosynthetic
organisms, to the production of estuarine fish and shellfish. Principles
for determining the net influence of salt marsh on surrounding estuarine
water have not been developed and validated; the net effect of salt marsh
on estuarine water must be determined by measurement on a marsh by marsh
and estuary by estuary basis. No such studies have been conducted on
Merritt Island marshes.

Energy, Carbon, and Biota

Salt marshes convert solar energy and inorganic carbon dioxide and
carbonate into chemical energy of organic compounds, but they also harbor a
variety of organisms that utilize this chemical energy and hence return
inorganic carbon dioxide to the atmosphere and water (Figure 3).
Therefore, the net influence of the salt marsh on estuarine water may
either be to add to the organic carbon of the estuarine water (export), to





















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remove organic carbon from estuarine water (import), or to simply exchange
organic carbon atom for atom with estuarine water. In any case, biota are
produced from these processes, some of which may be estuarine biota of
economic value, or the foods of such biota (Herke and Rogers 1984).

Both production and decomposition of organic matter occur in salt
marshes, resulting in either net, import net export, or no net transport of
detritus. Marshes of each net effect have been reported in the literature,
and no consistent determinants of import or export have yet been agreed
upon, though marshes with restricted access (as through a culvert), low
tidal amplitude, and little freshwater, or groundwater inflow appear to be
unlikely exporters of significant amounts of detritus (Valiela et al. 1978;
W.E. Odum et al. 1979; Nixon 1980; Borey et al. 1983). Other determinants
of export to be considered include: 1) the resistance to decomposition of
vegetation produced in the marsh (rapid decomposition perhaps yields more
food, but with less remaining for export); 2) the density of creeks (up to
a point, more creeks per marsh area would allow better water movement); and
3) the ease with which a mass of water that comes from the marsh can
exchange with the estuary (Imberger et al. 1983). The current view is that
early estimates of export were inflated and the value of exported materials
(especially vascular plant detritus) was exaggerated (Nixon 1980; Boesch
and Turner 1984, Herke and Rogers 1984).

On the other hand, marshes on the fringes of estuaries do provide food
and cover to growing estuarine biota that live in or temporarily visit
these marshes and therefore may be very valuable as nursery grounds for
estuarine fish and shellfish. The export of biota (including commercially
important fish and shellfish) from these marshes may be their greatest
value (Haines 1979b; Montague 1980; Boesch and Turner 1984).

Nitrogen

Nitrogen is a major nutrient of plants that is in relatively short
supply in many salt marshes (Gallagher 1975; Patrick and DeLaune 1976;
Valiela et al. 1976; Valiela and Teal 1979a, 1979b; Buresh et al. 1980;
DeLaune and Patrick 1980; Darley et al. 1981) and estuarine waters (Ryther
and Dunstan 1971; Thayer 1974; Parker et al. 1975), especially those in
which phosphorus (another major plant nutrient) is in very great supply.
Phosphorus supply is great especially in turbid estuaries that have accumu-
lated iron-rich clays from erosion of uplands (Pomeroy et al. 1965, 1969,
1972; Aston 1980; Postma 1980; Meade et al. 1979). Iron in these clays
forms a complex with phosphate that can be released to slightly acidic,
anaerobic water, such as the interstitial water of salt marsh sediments
(Patrick and Khalid 1974).

Amongst the multitude of microbes in the sediments of salt marshes,
are those capable of fixing nitrogen gas as well as those capable of
denitrification. Nitrogen fixation uses organic matter (Delwiche 1970;
Hanson 1977a, 1977b). If this microbial community fixes more nitrogen than
it removes, estuarine water may receive a net input of nitrogen available
for uptake by plants and bacteria. On the other hand, nitrogen may be
removed from water more than it is supplied, or these two processes may be
in balance (Haines et al. 1977). If nitrogen supply limits production and
decomposition, as so often has been measured (numerous references indicated









above), then the net effect of this microbial community is of great impor-
tance in evaluating the function of salt marshes in estuarine production.

Phosphorus and Sediments

Because fine sediments such as clays tend to accumulate in quiet
waters, because salt marshes develop in quiet waters, and because these
clays have a great sorptive capacity (Rae and Bader 1960; Pomeroy et al.
1965, 1969, 1972) salt marshes are sites of phosphorus deposition. Georgia
salt marshes receive abundant iron-rich (red) clays from upland land
drainage (Meade et al. 1975; Postma 1980). The present accumulation of
phosphorus in the sediments of these marshes is sufficient to continue
existing primary production for several hundred years, even if all inputs
of phosphorus were discontinued (Pomeroy et al. 1972; Whitney et al. 1981).

Salt marshes are also sites of phosphate resupply to estuarine water.
Excess phosphorus in the foods of animals (especially microfauna) is
released in their metabolic wastes (Johannes 1964, 1968; Pomeroy 1970). In
addition, several workers have demonstrated a flux of phosphate from
saltmarsh cordgrass (Spartina alterniflora) to surrounding waters (Reimold
and Daiber 1970; Reimold 1972; Gardner 1975). Thus mechanisms exist for
both the removal of phosphorus from, and supply of phosphorus to, estuarine
water. Unlike the cases of carbon and nitrogen, large reservoirs of
gaseous forms of phosphorus are not available to be actively "pumped" by
organisms into marshes from the atmosphere. Hence, the overall effect of
marshes on the phosphorus content of surrounding waters is limited to net
removal or balance. In turbid estuaries such as in Georgia, the overall
effect of salt marshes on phosphorus is generally believed to be removal
(Whitney et al. 1981).

Sulfur, Energy, and Acid Rain

Aspects of the sulfur cycle are also important in energy transforma-
tions in the salt marsh that lead to estuarine fish and shellfish (Howarth
1984). Sulfate reducing bacteria are apparently very active in salt
marshes owing to both the supply of simple organic compounds (that result
from decomposition of detritus) and the abundance of sulfate (the third
most common ion in seawater) (Howarth and Teal 1979). Sulfate reducers
grow by oxidizing these simple organic compounds with sulfate when oxygen
is not available (as in the case of anaerobic sediments just beneath the
sediment surface). This energy conversion process is not as efficient as
it is with oxygen (Howarth and Teal 1980). By-products include sulfide and
elemental sulfur, both of which contain energy that can be utilized by
sulfur oxidizing bacteria if these products become juxtaposed to oxygen in
the presence of bacteria (Howarth and Teal 1980; Howarth 1984).

Some of the energy-containing by-products of sulfate reduction are
gaseous, such as hydrogen sulfide, dimethyl sulfide, and dimethyl
disulfide (Brock 1979). These gases are partially responsible for the
characteristic odor of salt marshes. The odor is indicative of both an
energy and a sulfur loss from the salt marsh. Upon entering the atmosphere
the energy is rapidly dissipated by photochemical oxidation reactions
(Cadle and Allen 1970). Thus if sulfur oxidizing bacteria do not utilize
these compounds before they escape, this energy will be eliminated from any









food chain, and the resulting atmospheric sulfur compounds will eventually
return to earth combined with water in the form of acid precipitation.

Iron-rich clays, however, are important in trapping sulfide ions at
the aerobic-anaerobic interface in sediments (Howarth 1979; Howarth and
Teal 1979; Howarth and Hobbie 1982). If sulfur oxidizing bacteria do not
convert the sulfide, and if free metal ions such as iron or manganese
(Hatton et al. 1982) ions are present (which will occur if pH is low enough
to allow any phosphate held on metals to be released), then the metal and
the sulfide will combine to make metal sulfide (Howarth 1979). The black
color of anaerobic mud in marshes is usually caused by iron sulfide. Salt
marshes with a low metal content, perhaps those in Southeast Florida
(Hoffmeister 1974), should emanate much greater quantities of sulfide to
the atmosphere. The magnitudes of sulfur emissions from salt marshes and
their possible contribution to acid precipitation is currently under study
through the consulting firm of Environmental Sciences & Engineering, Inc.,
Gainesville, Florida.

A Scenario of a Southeast Florida Estuary Without Marshes

In some estuaries, especially those without inputs of phosphate-rich
clays, phosphate supply may limit growth of estuarine seagrasses and
phytoplankton. If fringing marshes are principally removers of phosphate
(Whitney et al. 1981), then photosynthesis in estuarine water may be lower
than would occur without marshes. If this difference in photosynthesis is
not mitigated by the photosynthesis of the marshes, then it is possible
that without salt marshes, overall estuarine photosynthesis would actually
be higher (as discussed in the section on foods of estuarine fish and
shellfish, the nutritional quality of phytoplankton and benthic algae as
food may be greater than that of detritus from marsh vegetation).

The effect of this on estuarine fish and shellfish is not clear,
because, although quality food supply may be greater in such a case, the
cover afforded by marshes would be gone. Cover afforded by seagrasses
(Orth et al. 1984) may decline too, if the higher levels of phosphorus in
this scenario without marshes are utilized by phytoplankton, which increase
turbidity of the water to the point that light limits seagrass growth
(Livingston 1984).

Summary of Relationships and Conclusion

The possible net flows of energy and elements between marshes and
estuaries are many. Pathways of both production and loss of converted
energy and materials are possible. Each of the processes indicated in
Figure 3 and most if not all other biogeochemical processes in salt marshes
will respond to changes in temperature, salinity, water level, oxygen
level, and pH (Presley and Trefry 1980; Patrick and Khalid 1974). Unless
the overall effect of a marsh on estuarine water is very one-sided, consid-
erable variation of this relationship from day to day or week to week may
be expected. Assumptions about these relationships should be accompanied
by long-term data from the marsh in question until valid principles for
predicting these effects are established. Presently, insufficient data are
available for Merritt Island marshes to allow determination of their
relationships to adjacent estuarine waters.









Food and Cover for Estuarine Fish and Shellfish

Production of estuarine fish and shellfish depends on availability of
both organisms and habitat. Salient features of habitat include: available
nonstressful physiological environment (e.g. salinity, temperature, pH,
oxygen), available food, and available cover. Good habitat does not
guarantee use by organisms. Organisms may simply be unavailable because of
disruptive conditions either elsewhere, or prior to the formation of new
habitat (e.g. an usually cold winter, widespread disease, loss of habitat
for other life-history stages in the case of migratory animals).

Attraction and concentration of organisms does not guarantee enhanced
production of organisms (elaboration of tissue per unit area per unit
time), as concentration may limit growth, enhance disease transmission, or
allow over-harvest. We will be discussing habitat with the production of
the organisms in mind.

Foods of Estuarine Fish and Shellfish

Because salt, brackish, and freshwater marshes are very productive of
emergent vegetation (W.E. Odum 1970a; Teal 1980), they are often thought of
as necessarily productive of animals of commercial or recreational impor-
tance. The value of marshes to such animals depends not only on the food
value and accessibility of foods, but also on what are currently considered
species of commercial or recreational importance. The following discussion
will be limited to the food value and accessibility of foods in marshes and
the effects of impoundments on these.

Foods of estuarine fish and shellfish vary from species to species and
from stage to stage in the life cycle of each species. Most if not all of
the commercially important animals in estuaries have planktonic larvae that
survive well on a phytoplankton-based food chain consisting not only of
phytoplankton, but also of bacteria, protozoans, copepods, and other mero-
and holo-plankton. Adult filter-feeders such as clams, mussels, and
oysters also survive well on a phytoplankton-based food chain. Larval and
early juvenile fish feed almost exclusively on zooplankton, which in turn
feed on phytoplankton (W.E. Odum 1970a).

Potential foods of estuarine fish and shellfish that are found in
marshes include: 1) detritus and its accompanying community of bacteria,
fungi, microfauna, and meiofauna, 2) benthic microalgae and its accompany-
ing community of microfauna and meiofauna, 3) phytoplankton and zooplank-
ton, 4) dissolved organic compounds emanating from all organisms and
accompanying bacteria, 5) sulfur- and sulfide-oxidizing bacteria (Howarth
1984), and 6) vagile and sedentary macro-organisms that consume the above
foods and each other. At the base of this web of foods are the photosyn-
thetic organisms, the primary producers that initially convert sunlight
into chemical energy (i.e. food) (W.E. Odum 1970a). These include: 1)
phytoplankton and benthic microalgae, which are consumed directly and which
excrete dissolved organic; and 2) submerged and emergent vegetation, which
are primarily food as detritus after death but which also leak dissolved
organic and are eaten directly in small quantity (Teal 1962; E.P. Odum and
de la Cruz 1967; Pomeroy et al. 1977; Wiegert 1979; Gallagher et al. 1980).









Food Value of Detritus
Vascular plant detritus, although commonly ingested by many species of
estuarine fish and shellfish (Darnell 1958, 1961; E.P. Odum and Smalley
1959; W.E. Odum 1966, 1969; W.E. Odum and Heald 1972, 1975; Gilmore 1983),
is less valuable as food than the more easily digested and nutritional
benthic and planktonic algae. It has a lower % organic matter and
calorific value than algae (W.E. Odum 1970b). Furthermore, energy from
detritus is obtained by "detritivores" only after a community of bacteria,
fungi, and microfauna has developed on the detritus (Haines and Hanson
1979); these organisms are the actual food being assimilated rather than
the dead plant material itself (W.E. Odum 1970b; Montague et al. 1981;
Marinucci 1982; Tenore et al. 1982). Striped mullet (Mugil cephalus)
actively select small (and therefore older and more microorganism-rich)
detrital particles (W.E. Odum 1968).

The lignin and cellulose of vascular plant detritus is difficult to
decompose without special enzymes occurring in some bacteria. These
materials comprise the majority of the dry weight of vascular plants and
nearly all of the dry weight of the non-living portion of the detritus-
microbe complex (R.L. Wetzel 1975). This is important in a comparison with
algae as food because in each step of a decomposition process (detritus to
bacteria to microfauna to meiofauna to ...; Odum and Heald 1975) an esti-
mated 90% of the energy value of the food is dissipated as heat (Lindeman
1942) and is therefore unavailable to organisms in the food chain. Because
detritivores simultaneously feed on several of these levels, the loss is
usually less than 99.99%. Thus, if a detritivore feeds at an average of
one step removed from the primary producer (i.e. detritus to bacteria to
detritivore) 99% of the energy content of the detritus would be lost (see
also Pomeroy 1980; Boesch and Turner 1984). However, most phytoplankton
and benthic microalgae do not have to be broken down by a community of
microbes before their energy content can be assimilated by the estuarine
food web (see R.L. Wetzel 1977). Therefore, for microalgae only 90% is
lost in the transfer to detritivores. Thus, 10 times the detritus must be
produced to equal the energy value of algae to estuarine fish and shell-
fish.

This energetic difference can influence forage selection in faculta-
tive detritivores; in a situation where both detritus and algae were
abundant, mullet fed almost exclusively on algae (W.E. Odum 1970b). Also,
most detritivores probably cannot grow and reproduce on a diet solely
composed of vascular plant detritus (W.E. Odum 1970a). Diets of detriti-
vores invariably include at least 10-20% fresh algal cells (W.E. Odum
1969). Perhaps one of the most economically important food chains, that
ending with larval and early juvenile fishes, is based primarily on produc-
tion by phytoplankton (W.E. Odum 1970a); survival of these life history
stages (which is a primary determinant of year-class strength) is largely a
function of food supply.

Recent experiments by Lewis and Peters (1984) apparently demonstrated
that juvenile Atlantic menhaden (Brevoortia tyrannus), a facultative
detritivore, can assimilate detrital material of vascular plant origin, at
high rates of efficiency (about 75%). However, they did not demonstrate
the mechanism by which such efficiencies are achieved. As it is likely









that intestinal microbes play a part in this process, the detritus to
microbes to detritivores chain, and its attendant losses of energy as
described above, may be involved here also. Therefore, although the
assimilation efficiency of vascular plant material by the "menhaden-microbe
complex" is about 75%, assimilation by the fish itself, which they did not
report, is probably much less. Nevertheless, the efficiency of this
mechanism is probably greatly enhanced over that of organisms lacking an
intestinal microflora (but still much less efficient than direct
consumption of algae).

Nitrogen is important in the nutrition of detritivorous fish and
shellfish because it is a fundamental building block of protein. Vascular
plant detritus by itself is lower than most microalgae in nitrogen per unit
carbon (Burkholder and Bornside 1957; Gosselink and Kirby 1974). As the
decomposer community of bacteria and other organisms develops on detritus,
the relative proportion of nitrogen increases in the detritus-microbe
complex as a whole (Burkholder and Bornside 1957; E.P. Odum and de la Cruz
1967). Thus the nutritional value of the complex increases with time
(Hanson 1982). The increase in nitrogen implies that the detritus-microbe
complex collects nitrogen from the environment. Sources of nitrogen for
this complex are the same as those of microalagae. Therefore, the bacteria
of the detritus-microbe complex are competitors with microalgae for
available nitrogen (Gosselink and Kirby 1974; Thayer 1974; Parker et al.
1975), which is a major limiting nutrient in many salt marshes and coastal
zones. Actively decomposing organic detritus should not be considered the
best possible food for estuarine fish and shellfish, but rather simply one
of many utilizable foods in the estuary (Haines 1977). Stable isotope
tracer analyses show that estuarine organisms perhaps rely more heavily on
phytoplankton and benthic microalgae than on vascular plant detritus as the
ultimate source of their food (Haines 1977; Haines and Montague 1979;
Thayer et al. 1978), but location within an estuary can influence this
relationship (Fry 1981; Peterson et al. 1985). Similar analyses may
provide insight into the trophic relationships influencing estuarine fish
and shellfish in the vicinity of Merritt Island.

The reader should not infer from this discussion that vascular plant
detritus with accompanying microbes is not a valuable source of food for
estuarine organisms; it most certainly is. Although the detritus food
chain is less efficient than that of microalgae, detritus is always present
(because of its refractory nature) and may therefore serve as an important
buffer of the food supply if and when microalgal production is low (Kalber
1959). Furthermore, vascular plant detritus from present-day Merritt
Island marshes may be a better source of energy than detritus in typical
salt marshes. Because many Merritt Island marshes are now less saline than
prior to impoundment, vegetation more typical of freshwater marshes has
encroached in many areas. The detrital value of these plants is probably
greater than that of the plants they replaced because there exist indica-
tions that freshwater marsh plants are less refractory, more nutritious,
more readily attacked by detritivores, and more easily macerated than the
saltmarsh species (W.E. Odum and Heywood 1978).

The conclusion to be drawn from all of the above is that both vascular
plant detritus and microalgae produced in marshes are important ultimate
sources of food for estuarine fish and shellfish; the relative importance









of each probably varies from marsh to marsh and estuary to estuary (and
species to species). Thus, estuarine food chains should not be considered
solely detritus-based, as has often been purported, but rather should be
considered detritus/algae-based (W.E. Odum 1970b). Because it is likely
that little if any of the detrital/algal production of Merritt Island
marshes was ever, or now is, exported to the estuary (due to low tidal
amplitude, relatively low freshwater inflow, and, especially since impound-
ment, restricted access; W.E. Odum et al. 1979) the critical management
tactic to enhance estuarine fishery production would appear to be to
enhance access by these organisms to the marshes such that they can feed on
the foods (detritus, microalgae, and organisms that feed on these) produced
and present there.

Vagile "Link" Organisms
If most of the production is decomposed in place in the marsh, and
decomposing detritus is good food for many marsh residents, then unless
transient organisms venture into the marsh, much of this food will simply
decompose in place to the benefit of a multitude of microbes. Of course,
nitrogen and sulfur transformations of importance to the global atmosphere
occur because of these coastal microbes (Maclntyre 1970; Lovelock 1979), so
the decomposing material is important where it is. However, when this
material is utilized by transient organisms that venture into the marsh to
eat the detritus-microbe complex, benthic microalgae, meiofauna, or larger
organisms that eat these things (e.g. fiddler crabs, periwinkles), and if
these organisms are themselves eaten by estuarine fish and shellfish of
commercial or sports value, then the marsh can be said to be linked to this
economic value (see Sikora and Sikora 1982).

Although a few of the economically important species will venture into
the emergent vegetation of tidal marshes on occasion (e.g. redfish, blue
crabs), a far more common place to find them is in the marsh creeks. This
is especially true for juvenile estuarine fish (Zilberberg 1966; Dahlberg
1972; Burns 1974; Fritz et al. 1975; Subrahmanyam and Drake 1975; Cain and
Dean 1976; Reis 1977; Shenker and Dean 1979; Weinstein 1979; Bozeman and
Dean 1980; Reis and Dean 1981; Weinstein and Walters 1981; Crabtree and
Dean 1982; Beckman and Dean 1984; Currin et al. 1984; Rozas and Hackney
1984; Weinstein et al. 1984). They may venture into the edge occasionally,
but probably feeding is more efficient by cruising up and down the creeks.
Also many sedentary organisms of economic value (clams, oysters) are found
at the edge of the marsh in the marsh creeks much more commonly than in the
vegetation (Dame 1976, 1979; Bahr 1976; Bahr and Lanier 1981; Walker and
Tenore 1984; Mulholland 1984). However, some organisms such as grass
shrimp and killifishes (W.E. Odum and Heald 1972; Welsh 1975; Vince et al.
1976; Talbot and Able 1984) move into the marsh at high tide, where they
consume marsh organisms, and then return to the creek edge at low tide,
where they are susceptable to consumption by predatory fishes. Such "link"
organisms are important conduits between the marsh production and economi-
cally important vagile species of estuarine fish and shellfish. Other link
organisms may occur and these should also be very important in making marsh
production available to the estuarine fishery.

The situation on Merritt Island may be somewhat different, however.
Because the marshes there are inundated for several months without daily
draining, use of the vegetated marsh surface by juvenile estuarine fish may









be greater than in tidal marshes (where fish must return to the creeks
regularly to avoid stranding during ebb tides). Lewis et al. (in press)
note that ladyfish, snook, tarpon, mullet, and Irish pompano reside on the
marsh surface during the seasonal inundations in areas south of Merritt
Island. However, it is unclear whether these species actually prefer this
habitat to marsh creeks and ditches or only enter it relatively infrequent-
ly; the risks of predation by wading birds on the marsh are probably
relatively high.

Accessibility of Foods
The access to the foods of the salt marsh is as important as the
presence of foods. The creek system in the marsh is a most important part
of such access. Estuarine fish and shellfish move to the edges of marsh by
these creeks to feed on link organisms. Resident sedentary shellfish such
as clams and oysters are often found at the edges of marshes on muddy sand
either in flats or in the sediments of marsh creeks. The edges of marsh
creeks are more productive of microbes, animals, and plants than are
interior areas (Smalley 1959; Odum and Fanning 1973; Gallagher et al. 1980;
Sikora and Sikora 1982) and these edges are undoubtedly more accessible to
estuarine organisms. Thus accessibility of the foods of estuarine fish and
shellfish is enhanced near the edges of marsh creeks and ditches, as
compared with the interior. Up to a (as yet undetermined) point, marshes
with more creeks and ditches (if spoil is disposed of appropriately) per
unit of interior probably support greater production of estuarine fish and
shellfish (Browder et al., unpublished manuscript; but see Daiber 1974).

Access to marsh creeks at the marsh-estuary boundary is also impor-
tant. Natural levees and man-made dikes prevent access, but natural marsh
creeks and open water-control structures allow access. Marsh utilization
by estuarine fish and shellfish should be greater with greater submerged
cross-sectional area of open access at the marsh-estuary boundary.
However, Gilmore et al. (1982) and Gilmore (1983) found intensive use of
impoundments by estuarine fishes even though access was limited to single
culverts. Unfortunately, it is impossible to reliably assess the relative
effectiveness of culverts as access structures because quantitative esti-
mates of fish use of unmodified control marshes do not exist. However, it
is clear from Gilmore's research that even very limited access can result
in substantial use of impoundments by estuarine organisms, perhaps
equivalent to that of natural marshes. Whether this would also be true at
Merritt Island, where tidal amplitude is much less than at Gilmore's sites,
is unclear. Daily circulation of water through culverts may attract vagile
fish and shellfish and enhance their passage.

The location and dispersion of access sites may influence accessibi-
lity. Fish use of culverts appears to be variable, perhaps as a result of
their location relative to historic sites of marsh creeks (R.G. Gilmore,
pers. comm.), and data presented in Gilmore (1983) suggest (albeit tenu-
ously) that fish abundances in impoundments decrease with distance from
culverts. More recent evidence demonstrates that abundances of fishes are
enhanced in the vicinity of culverts (R.G. Gilmore, pers. comm.). These
factors suggest that a positive correlation may exist between fish use of
impoundments and number of access sites.









Exchange of marsh water with the estuary is important to the access of
planktonic stages of estuarine fish and shellfish to the foods of the
marsh. Exchange of water is not only a function of the access at the
marsh-estuary boundary, but also a function of forces capable of moving
water through the marsh. For coastal marshes, such forces include the ebb
and flood of tides, the work of the wind, and mechanical pumping. The
latter two are the most important on Merritt Island (Dubbelday 1975).

Access by vagile organisms that venture onto the marsh surface is
possible only when the water covers the marsh. Natural salt marsh on
Merritt Island is not regularly flooded by twice-daily tides, but rather
remains dry for extended periods from perhaps January through September.
It then may remain submerged for extended periods from October through
December. If the water depth were higher more of the time, access by
vagile fish and shellfish (including "link" organisms) to the foods on the
marsh would be greater, though there is perhaps a limit to this effect
also.

Cover for Estuarine Fish and Shellfish

Salt marshes contain not only foods for estuarine fish and shellfish,
but also cover. The concept that the marsh is not only a good place to
hide, but also a good place to eat (and be eaten) may seem contradictory.
However, several lines of reasoning support these two simultaneous
functions of marshes. First, some organisms clearly benefit perhaps at the
expense of others. Deposit feeding organisms, for example, that consume
organisms in deposits amongst the grasses, both eat their foods and are
protected from -their predators, though neither the predators nor the
deposit-dwelling foods may benefit. Juvenile fishes may hide from
predators in the edge of marshes, but may venture into the creeks to feed
on zooplankton. Predators may sense the presence of an accumulation of
prey and so spend more time and gain more prey per unit effort in marsh
creeks. It is entirely likely that cover allows a build-up of prey in such
a way that the area is a good place for a predator to feed, but also that
the risk for an individual prey organism is reduced. This may apply to
predatory fish as well as to wading birds. An area could not continuously
be attractive to predators without a sustained supply of accessible prey.
The simultaneous presence of food and cover can explain such a sustained
supply. Prey organisms accumulate because of food and cover to the point
where their sheer density increases the frequency of some individuals
becoming exposed to predators. Increases in food for prey organisms may
attract more prey than can be protected by existing cover, so more prey
would be exposed to predators. If food was too low, however, this
phenomenon might not be as likely to happen; prey organisms would
accumulate perhaps only as a function of the cover afforded, so the benefit
to a predator may not be as.great. If, however, the only prey were those
in the areas with cover, those areas would be good places to feed simply by
being the only places to feed.

Both emergent and submerged vegetation can provide the dual functions
of food and cover. Although some plants that become established on moist
soil can tolerate extended submergence (e.g., Eleocharis parvula: F.
Montalbano, pers. comm.), most submerged vegetation will not occur unless
water of appropriate salinity and temperature nearly continuously covers









the sediment, and unless water circulation and light penetration are
sufficient (Zieman 1982; Thayer et al. 1984). Light penetration is reduced
by phytoplankton which may grow if an excess of nutrients occurs. Excess
nutrients may arise from large accumulations of decomposing proteinaceous
matter such as dead fish, from guano and excreta from large accumulations
of birds or fish, from agricultural runoff, and from sewage outfall.

Emergent vegetation will occur if water levels are low enough to allow
aeration of roots through aerynchema tissue (Voigts 1976; Provost 1968) and
if salinity is not too high. The cover afforded to estuarine fish and
shellfish by emergent vegetation is limited to times of sufficient water
coverage. As with the case of food, accessibility to cover should be
enhanced by: 1) creek density, 2) open mouths of creeks, 3) circulation
and exchange of marsh water with the estuary, and 4) depth and duration of
inundation.

Egress of Vagile Fish and Shellfish From Marshes
A special problem of access for estuarine fish and shellfish is the
potential for egress should conditions become stressful (e.g., low
dissolved oxygen, extremes in temperature, salinity, or pH). Organisms may
be able to enter a marsh when exchange occurs, or access points are open,
but if exits are not available when stress occurs, trapped organisms may
become lethargic or die. Stressed estuarine fish and shellfish may be
quickly eaten by unstressed fish, shellfish, and wading birds. Those that
are not eaten may recover, or may die and support the everpresent community
of microbes in the marsh, whose activities may reduce the dissolved oxygen
in the water to a point where that becomes stressful to previously
unstressed organisms. This positive feedback loop can be avoided with
flushing.

Egress is also important at times of year when fish and shellfish
routinely leave the marsh to complete another phase of their life-cycle
(Provost 1968). Historically on Merritt Island, water levels were high in
October through December. At the end of this time, aquatic estuarine
organisms routinely left the marsh (Harrington and Harrington 1961).

Reproduction of historical regimes of flooding and draining may not be
essential to obtain good yields of estuarine fish and shellfish. Changed
water regimes may simply result in a selection for members of each species
that withstand the change, if the change is not outside the realm of
survival for the species, and if the species has enough genetic
variability, biotic potential, and individuals available for selection.
However, egress from marsh areas in winter is essential for cold-intolerant
species (e.g. snook, ladyfish, tarpon, shrimp).

Creek density, submerged cross-sectional area and duration of open
access at the marsh-estuary boundary, and exchange of water with the
estuary are all important for egress of vagile estuarine fish and shell-
fish although greater access at the marsh/estuary boundary may necessitate
more pumping to achieve desired water levels (see Figure 4). In addition,
harvest of species and consumption by waterbirds may be thought of as
alternative egress. Commercial and sport fishing within marshes or marsh
creeks that have limited egress directs these resources into humans rather
than into wading birds, or decomposer microbes.








EGRESS_ OF FIS AND SHELLFISH


DITCH & NATURAL
CREEK DENSITY


HARVEST


WIND TIDES & CREEK MOUTHS & DIKES &
PUMPING CROSS-SECT, AREA NATURAL
OF CULVERTS X LEVEES
TIME OPEN



\ V
+ ACCESS AT MARSH/
EXCHANGE OF ESTUARY BOUNDARY
MARSH WATER /
WITH ESTUARY


CONSUMPTION \ /
BY WATERBIRDSEGRESS OF ESTUARINE
REDAOTHERS + FISH & SHELLFISH
+ FROM MARSH


Figure 4. Conceptual Model of Factors Influencing Egress
from Natural or Impounded Salt Marsh. Note that
more access necessitates more pumping.


FGRESS OF FISH


AND SHFLFITSH









FUNDAMENTALS OF MARSH MANAGEMENT FOR MOSQUITO CONTROL AND
ATTRACTION OF WINTERING WATERFOWL

Figure 5 illustrates the relationship between various structures in
impoundments and their utilization for mosquito control and attraction of
waterfowl. Only basic concepts are presented here. A multitude of
problems may arise that supercede this conceptual model from time to time.
The information in these subsections is derived from personal interviews
and site visits with impoundment managers throughout the southeastern
United States.

Mosquito Control

Controlling mosquito breeding in salt marshes is conceptually much
simpler than attracting wintering waterfowl. Management of impoundments
now principally involves maintaining water levels of a few inches on the
surface of the marsh throughout the breeding season (March to May through
August to October; Provost 1959, 1968, 1973b; Clements and Rogers 1964);
female saltmarsh mosquitos cannot oviposit on standing water, but rather
require soil substrates (Nielsen and Nielsen 1953; Provost 1968, 1973b).
Mosquitos that replace these species are much less abundant (Clements and
Rogers 1964) and do not cause nearly the biting nuisance of saltmarsh
mosquitos. Because larvae must develop in standing water, saltmarsh
mosquitos must exist in habitats with fluctuating water levels. The
frequency of drawdown and reflooding then relates directly to the produc-
tion of saltmarsh mosquitos, although excessive fluctuation (i.e. daily
tides) will also reduce production if water does not remain on the marsh
long enough for.larvae to develop. By reducing the frequency of drawdown
and reflooding, production of saltmarsh mosquitos is also reduced.

Other methods for mosquito control have been tried. Low density
parallel ditching of the marsh during the 1930's was purported to help
drain the marsh of pools of standing water where larvae could develop.
This had little effect in the vicinity of Merritt Island, however, presum-
ably because the larvae of these mosquitos are capable of growing and
emerging very rapidly in very small depressions or cracks in marsh sedi-
ment, and low density parallel ditches did not intersect or drain all of
the breeding sites.

Many "potholes" are present in Merritt Island salt marshes. When
these are connected by ditch to the estuary, free access is established for
feeding on mosquito larvae by larvivorous fishes. In some areas this
technique ("open marsh water management", Ferrigno 1970; Ferrigno and
Jobbins 1968; Ferrigno et al. 1969) may be suitable, in which case water
would not need to be impounded for mosquito control (the presence of dikes
and water control structures can enhance the effectiveness of OMWM, how-
ever). Wading birds and other piscivores may also be attracted to the
fishes in these potholes.

Waterfowl Attraction

Management for waterfowl in salt marshes can involve more steps and
difficulties because the objectives are to enhance specific plants that
provide good food and cover for waterfowl, and to discourage undesirable









FUNDAMENTALS OF MARSH MANAGEMENT FOR MOSQUITO CONTROL AND
ATTRACTION OF WINTERING WATERFOWL

Figure 5 illustrates the relationship between various structures in
impoundments and their utilization for mosquito control and attraction of
waterfowl. Only basic concepts are presented here. A multitude of
problems may arise that supercede this conceptual model from time to time.
The information in these subsections is derived from personal interviews
and site visits with impoundment managers throughout the southeastern
United States.

Mosquito Control

Controlling mosquito breeding in salt marshes is conceptually much
simpler than attracting wintering waterfowl. Management of impoundments
now principally involves maintaining water levels of a few inches on the
surface of the marsh throughout the breeding season (March to May through
August to October; Provost 1959, 1968, 1973b; Clements and Rogers 1964);
female saltmarsh mosquitos cannot oviposit on standing water, but rather
require soil substrates (Nielsen and Nielsen 1953; Provost 1968, 1973b).
Mosquitos that replace these species are much less abundant (Clements and
Rogers 1964) and do not cause nearly the biting nuisance of saltmarsh
mosquitos. Because larvae must develop in standing water, saltmarsh
mosquitos must exist in habitats with fluctuating water levels. The
frequency of drawdown and reflooding then relates directly to the produc-
tion of saltmarsh mosquitos, although excessive fluctuation (i.e. daily
tides) will also reduce production if water does not remain on the marsh
long enough for.larvae to develop. By reducing the frequency of drawdown
and reflooding, production of saltmarsh mosquitos is also reduced.

Other methods for mosquito control have been tried. Low density
parallel ditching of the marsh during the 1930's was purported to help
drain the marsh of pools of standing water where larvae could develop.
This had little effect in the vicinity of Merritt Island, however, presum-
ably because the larvae of these mosquitos are capable of growing and
emerging very rapidly in very small depressions or cracks in marsh sedi-
ment, and low density parallel ditches did not intersect or drain all of
the breeding sites.

Many "potholes" are present in Merritt Island salt marshes. When
these are connected by ditch to the estuary, free access is established for
feeding on mosquito larvae by larvivorous fishes. In some areas this
technique ("open marsh water management", Ferrigno 1970; Ferrigno and
Jobbins 1968; Ferrigno et al. 1969) may be suitable, in which case water
would not need to be impounded for mosquito control (the presence of dikes
and water control structures can enhance the effectiveness of OMWM, how-
ever). Wading birds and other piscivores may also be attracted to the
fishes in these potholes.

Waterfowl Attraction

Management for waterfowl in salt marshes can involve more steps and
difficulties because the objectives are to enhance specific plants that
provide good food and cover for waterfowl, and to discourage undesirable









FUNDAMENTALS OF MARSH MANAGEMENT FOR MOSQUITO CONTROL AND
ATTRACTION OF WINTERING WATERFOWL

Figure 5 illustrates the relationship between various structures in
impoundments and their utilization for mosquito control and attraction of
waterfowl. Only basic concepts are presented here. A multitude of
problems may arise that supercede this conceptual model from time to time.
The information in these subsections is derived from personal interviews
and site visits with impoundment managers throughout the southeastern
United States.

Mosquito Control

Controlling mosquito breeding in salt marshes is conceptually much
simpler than attracting wintering waterfowl. Management of impoundments
now principally involves maintaining water levels of a few inches on the
surface of the marsh throughout the breeding season (March to May through
August to October; Provost 1959, 1968, 1973b; Clements and Rogers 1964);
female saltmarsh mosquitos cannot oviposit on standing water, but rather
require soil substrates (Nielsen and Nielsen 1953; Provost 1968, 1973b).
Mosquitos that replace these species are much less abundant (Clements and
Rogers 1964) and do not cause nearly the biting nuisance of saltmarsh
mosquitos. Because larvae must develop in standing water, saltmarsh
mosquitos must exist in habitats with fluctuating water levels. The
frequency of drawdown and reflooding then relates directly to the produc-
tion of saltmarsh mosquitos, although excessive fluctuation (i.e. daily
tides) will also reduce production if water does not remain on the marsh
long enough for.larvae to develop. By reducing the frequency of drawdown
and reflooding, production of saltmarsh mosquitos is also reduced.

Other methods for mosquito control have been tried. Low density
parallel ditching of the marsh during the 1930's was purported to help
drain the marsh of pools of standing water where larvae could develop.
This had little effect in the vicinity of Merritt Island, however, presum-
ably because the larvae of these mosquitos are capable of growing and
emerging very rapidly in very small depressions or cracks in marsh sedi-
ment, and low density parallel ditches did not intersect or drain all of
the breeding sites.

Many "potholes" are present in Merritt Island salt marshes. When
these are connected by ditch to the estuary, free access is established for
feeding on mosquito larvae by larvivorous fishes. In some areas this
technique ("open marsh water management", Ferrigno 1970; Ferrigno and
Jobbins 1968; Ferrigno et al. 1969) may be suitable, in which case water
would not need to be impounded for mosquito control (the presence of dikes
and water control structures can enhance the effectiveness of OMWM, how-
ever). Wading birds and other piscivores may also be attracted to the
fishes in these potholes.

Waterfowl Attraction

Management for waterfowl in salt marshes can involve more steps and
difficulties because the objectives are to enhance specific plants that
provide good food and cover for waterfowl, and to discourage undesirable












MARSH MANAGEMENT


PUMPING WATER CONTROL
STRUCTURES (DIKES
/ & TRUNKS)


OF FREQUENCY OF AMPLITUDE OF
DRAWDOWN & DRAWDOWN &
REFLOODING REFLOODING



+ EXCHANGE OF
s-MARSH WATER +


HYPOSANTY HYPERSAIITY
HYPOSALINITY HYPERSALINITY


1+ +1 \ r+
SALT MARSH LOCAL ACCUMULATION
MOSQUITOS OF WINTERING
WATERFOWL

Figure 5. Conceptual Model of Salt Marsh Management to
Control Mosquitos and Attract Wintering Waterfowl.









plants. Desirable plants include both emergent and submerged species.
Success in production of desired vegetation appears to be dependent upon
the degree of control one has over water level and the ability to circulate
water in the impoundment. A corollary to that rule is that water salinity
determines the species present.

The management of impounded coastal wetlands to attract waterfowl has
been variously discussed (e.g., Chabreck 1960; Neely 1960, 1968; Yancey
1964; Baldwin 1967; Joanen and Glasgow 1965; Morgan 1974; Morgan et al.
1975; Heitzman 1978; Prevost et al. 1978; Miglarese and Sandifer 1982;
Wicker et al. 1983). Waterfowl food management is a complex issue and
elucidation of particular nuances associated with management of each
species is beyond the scope of this report; such information can be found
in the reports cited both above and in Montague et al. (1984a). The
following synthesis is a theoretical treatment of the management principles
involved. It is based on the literature and personal communication with a
number of impoundment managers and waterfowl biologists (W. Conrad, J.
Hiers, R. Joyner, W. Leenhouts, F. Montalbano, R. Perry, J. Salmela, T.
Strange, P. Wilkinson, K. Williams) whose individual and collective experi-
ences are invaluable. At this point, we also venture to add the explicit
recommendation that anyone interested in investing in the management of
such impoundments should study the available literature, but the real,
current, and most valuable information is embodied in these (and similarly
experienced) idiviiduals. Site visits with them will provide the detail
needed to help avoid years and many dollars of error in engineering and
water management.

Desired emergent vegetation (primarily bullrushes, such as Scirpus
robustus in brackish to estuarine salinities, but a large variety of plants
as salinity approaches zero) will occur only if salinity and water depth do
not get too high. In addition, water must be drawn down to bed level in
early spring so seeds can germinate and seedlings become established prior
to reflooding. Reflooding can sometimes result in a brood of mosquitos
hatching, but if the larvae can be flushed into the estuary, consumption by
estuarine fish can prevent a serious biting nuisance. If successful,
emergent vegetation will cover much of the area. Because waterfowl require
open areas, dense stands of emergent vegetation should be burned just prior
to the arrival of wintering waterfowl. Wilkinson (pers. comm.) suggests
that the ideal ratio of open to vegetated area is about 50:50.

Establishment of extensive growth of quality submerged vegetation is
unlikely if left to chance. Both hypersaline and hyposaline water will
inhibit establishment or growth of these plants (e.g., see Heald 1970). If
water of estuarine or brackish salinity can be flushed through when
appropriate salinities are available, the risk of poor development is
greatly reduced. If the only water available is more estuarine than
brackish in salinity (i.e., more saline), then growth of appropriate
emergent vegetation seems less likely, so water levels are usually kept
deep enough to prevent undesirable emergents from establishing, and all
effort is put into submerged species that are good foods for waterfowl at
these salinities (e.g., Ruppia and Chara). As in the case for emergent
vegetation, water levels must be drawn down to achieve seed germination and
seedling establishment for Ruppia. Chara, an alga, grows best on Merritt
Island if impoundments are not drawn down, however (Leenhouts, pers.
comm.).









Additional problems occur with the growth of submerged vegetation,
however. For example, guano from accumulations of waterbirds in impound-
ments can stimulate phytoplankton which reduce light available for
submerged vegetation. Once again, water circulation can alleviate this
problem.

Thus, intensive management of waterfowl food plants requires frequent
exchange of impounded water with the estuary. Such exchange, if practiced
frequently, mitigates considerably a major possible negative influence of
impoundments on estuarine fish and shellfish (see section on Estuarine Fish
and Shellfish). Unfortunately, on Merritt Island, frequent exchange is
possible only by operating expensive mechanical pumps (which pump estuarine
water only), unless some impoundments can be set aside for water storage
that could capture runoff and gravity-feed areas of need. Elevation and
water level changes are probably insufficient on Merritt Island to allow
storage of enough head to accomplish either frequent or substantial
exchange unless the proportion of water storage area to waterfowl manage-
ment area is large. A study of surface water hydrology in impoundments is
beginning summer of 1985, funded by Florida Sea Grant College, J.P. Heaney,
W.C. Huber, and C.L. Montague, principal investigators.

ECOLOGY OF MERRITT ISLAND SALTMARSH IMPOUNDMENTS

Effects of Impoundment on Ecological Production

On Merritt Island, energy inputs that should be considered in a
hypothesis of impoundent effects on ecological production include: 1)
sunlight, which-is converted to chemical energy of organic compounds by
photosynthesis; 2) wind, which enhances both air and water circulation and
in turn subsidizes the encounter of organisms with their gaseous and
aquatic nutrients and foods, and subsidizes the separation of waste prod-
ucts from organisms; 3) rain, which enhances water circulation (directly
and by runoff), and which decreases salinity, which by itself may enhance
community production (perhaps at the expense of certain species); and 4)
human work, which results in water circulation at times of year when salt
marshes do not otherwise receive circulation.

Primary Energy (Sunlight and Turbidity)

Light penetrating to the sediment surface may be greater if over-
flooding has removed dense grassy or mangrove vegetation, or may be less if
vegetation prior to impoundment was more open and now the impoundment is
more turbid. The net effect on biota is probably a substitution of species
to more microphytes and less macrophytes (Voigts 1976), or if macrophytes,
then these would be submerged vegetation such as Ruppia or Chara. In areas
that have lost emergent vegetation, the work of the wind maybe sufficient
to uproot existing submerged vegetation and prevent establishment of
submerged vegetation via turbidity and sediment destabilization.

Initial flooding of a marsh may reduce sunlight (compared to a
periodically-dry marsh) because of light reflection (R.G. Wetzel 1975),
though once a water level is established, increases in level may not have
much further effect on overall ecological production due to automitigation.









Additional problems occur with the growth of submerged vegetation,
however. For example, guano from accumulations of waterbirds in impound-
ments can stimulate phytoplankton which reduce light available for
submerged vegetation. Once again, water circulation can alleviate this
problem.

Thus, intensive management of waterfowl food plants requires frequent
exchange of impounded water with the estuary. Such exchange, if practiced
frequently, mitigates considerably a major possible negative influence of
impoundments on estuarine fish and shellfish (see section on Estuarine Fish
and Shellfish). Unfortunately, on Merritt Island, frequent exchange is
possible only by operating expensive mechanical pumps (which pump estuarine
water only), unless some impoundments can be set aside for water storage
that could capture runoff and gravity-feed areas of need. Elevation and
water level changes are probably insufficient on Merritt Island to allow
storage of enough head to accomplish either frequent or substantial
exchange unless the proportion of water storage area to waterfowl manage-
ment area is large. A study of surface water hydrology in impoundments is
beginning summer of 1985, funded by Florida Sea Grant College, J.P. Heaney,
W.C. Huber, and C.L. Montague, principal investigators.

ECOLOGY OF MERRITT ISLAND SALTMARSH IMPOUNDMENTS

Effects of Impoundment on Ecological Production

On Merritt Island, energy inputs that should be considered in a
hypothesis of impoundent effects on ecological production include: 1)
sunlight, which-is converted to chemical energy of organic compounds by
photosynthesis; 2) wind, which enhances both air and water circulation and
in turn subsidizes the encounter of organisms with their gaseous and
aquatic nutrients and foods, and subsidizes the separation of waste prod-
ucts from organisms; 3) rain, which enhances water circulation (directly
and by runoff), and which decreases salinity, which by itself may enhance
community production (perhaps at the expense of certain species); and 4)
human work, which results in water circulation at times of year when salt
marshes do not otherwise receive circulation.

Primary Energy (Sunlight and Turbidity)

Light penetrating to the sediment surface may be greater if over-
flooding has removed dense grassy or mangrove vegetation, or may be less if
vegetation prior to impoundment was more open and now the impoundment is
more turbid. The net effect on biota is probably a substitution of species
to more microphytes and less macrophytes (Voigts 1976), or if macrophytes,
then these would be submerged vegetation such as Ruppia or Chara. In areas
that have lost emergent vegetation, the work of the wind maybe sufficient
to uproot existing submerged vegetation and prevent establishment of
submerged vegetation via turbidity and sediment destabilization.

Initial flooding of a marsh may reduce sunlight (compared to a
periodically-dry marsh) because of light reflection (R.G. Wetzel 1975),
though once a water level is established, increases in level may not have
much further effect on overall ecological production due to automitigation.









Water Circulation and Freshening of Water

It is unclear how impoundment affects any energy subsidy from water
circulation through Merritt Island salt marshes. For impoundment to reduce
such a subsidy, the overall movement of water through impounded ecosystems
would have to be lowered. Historically, water did not cover large areas of
marsh for much of the year (perhaps 100 days of inundation), and during
this time, water motion was probably determined by wind (Dubbelday 1975),
as the daily tides on Merritt Island are very low (data from Ned Smith).
Impoundments may capture and hold rainwater that would go to the estuary
and dikes may also serve as wind breaks; however, if water level increases
are sufficient to eliminate emergent vegetation, wind-baffling structure
will be reduced in the impoundment thereby increasing the effective work of
the wind, which could result in enhanced overall production at least at
times of submergence.

Salinity of water impounded on Merritt Island salt marshes is highly
variable owing primarily to variability in rainfall. Salinity and water
level data from the restored marsh T-10-K and from three impounded marshes
are plotted in Figures 6 through 9. Salinity data are summarized in Table
2. Impounded water, because it includes captured rainfall, is often
presumed to be fresher than water on natural marshland, though water from
unimpounded marsh also fluctuates with rainfall and drought. Salinity in
the restored marsh T-10-K, for example, fluctuates between 6 and 39 ppt in
the period from September 1977 and April 1980 (Table 2, Figure 6). During
the same period, salinity in the adjacent Black Point impoundment (T-10-J)
fluctuates between 5 and 39 ppt in a similar pattern (Figure 7).

Salinity in impoundments in which water levels are maintained by
pumping with salt water can be high if evaporation occurs and rainfall is
low (Bidlingmayer 1982). Impoundments that are pumped with salt water
include T-10-A, B, C, D, and F, T-10-L and M, and the impoundments on Jack
Davis Island. In the same period of reporting as above, the Jack Davis
impoundments fluctuated between 16 and 53 ppt. Impoundment T-10-D (Figure
8) fluctuated between 12 and 57 ppt, the highest salinity recorded during
this period in any of the impoundments reported.

Conversely, some impoundments have water of very low salinity. The
"fresh" impoundment T-24-D (Figure 9) holds water very well and is always
low in salinity. The ability of this marsh to retain water of low salinity
is suggestive of a groundwater flow to T-24-D.


Table 2. Salinity Data for a Restored Marsh and from Three Impounded
Marshes on Merritt Island National Wildlife Refuge (Data from W.
Leenhouts). SD = Standard Deviation, N = Number of Observations
between September 1977 and April 1980.

MARSH LOW HIGH MEAN SD N

T-10-K (Restored Marsh) 6 39 23 10 29
T-10-J (Black Point Imp.) 5 39 20 9 29
T-10-D (Roach Hole Imp.) 12 57 37 11 29
T-24-D (Fresh Imp.) 0 22 6 5 29


























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Thus, some impoundments on Merritt Island are fresher on average than
surrounding estuarine water (see Lasater 1975), and some are saltier; the
same impoundment may be fresher during the wet season and saltier during
the dry season. Probably all capture rainwater that would otherwise go to
the estuary, but we can find no evidence that the estuarine water has
increased in salinity due to impoundment. An optimal salinity for overall
production may occur in nature. Because many land and aquatic organisms
maintain a body fluid salinity of around 9 ppt (Wilson 1972, p. 574), a
salinity optimum for overall production may be somewhere in the
neighborhood of 9 ppt. Above 9 ppt many organisms may allocate energy to
excrete or exclude salts; below 9 ppt organisms may have to allocate energy
to retain salt. The variation in ecological production that can be
explained by variation in salinity in the range of 0 to 35 ppt (full
strength seawater) is unknown as is the magnitude of such an effect, but it
is subtle compared to the effects of very high salinity (e.g., greater than
60 ppt).

Whole-system Stress (Low Oxygen, Hypersalinity)

Despite the notion of a brackish salinity optimum for ecological
production, environmental extremes do not presently seem sufficient to
cause vastly lower ecological production, though clearly, species composi-
tions have radically changed in overflooded or very saline impoundements
due to a variety of stresses on individual species. It is possible that
salinities in some impoundments on Merritt Island (e.g., T-10-D) are on
occasion sufficiently high to lower whole-system production somewhat, but
no experiments have been conducted to evaluate this possibility. Oxygen
readings with time of measurement, salinity, and temperature recordings are
needed, but at a frequency not possible without a dedicated researcher or
expensive equipment.

Oxygen is probably not low enough to affect overall ecological produc-
tion, despite chronic deleterious effects on certain species that may
occur. Marshes are typically eutrophic because of their high productivity
and resultant high rates of respiration (W.E. Odum 1970a); dissolved oxygen
levels in marshes are therefore often low and it is unclear how impoundment
affects this parameter (see Estuarine Fish and Shellfish section).

Nutrient Supply

Nutrient supply to impounded salt marsh may not be affected greatly
unless trapped runoff (in those impoundments that are not back-ditched) is
exceptionally rich in nutrients, in which case nutrient supply to the
impounded marsh may be enhanced at the expense of the estuary. The
estuary, however, continues to receive ever-increasing supplies of anthro-
pogenic nutrients (East Central Florida Regional Planning Council 1975a,
1975b). In fact, addition of wastewater to an impounded marsh may enhance
ecological production within the marsh (Haines 1979a; Hardisky et al. 1983;
H.T. Odum, in press) and improve water quality in the estuary (as the
wastes would no longer be pumped directly into the estuary). The feasibi-
lity of using wetlands for sewage treatment has been examined extensively
(see references in E.P. Odum et al. 1983 and Haines 1979a) and is currently
under study at Merritt Island by Ronnie Best (Mion et al. 1985). E.P. Odum
et al. (1983) note that impounded marshes possess advantages over natural









marshes for sewage treatment because control over waste retention times,
water levels, and harvest parameters are possible. Furthermore, wastewater
management can be integrated effectively with mosquito control (Carlson
1983).

Note, however, that sewage effluent can produce subtle alterations of
considerable detriment. For example, in the Great South Bay duck farm
incident (Ryther 1954) duck-farm effluents enhanced production of micro-
algae, but the forms that prospered (Nanochloris and Stichococcus) were
unsuitable for secondary consumers. Accordingly, fish and shellfish
production declined. Marshes and estuaries are normally eutrophic, and
additional inputs of nutrients may lower dissolved oxygen concentrations to
levels deleterious to aquatic animals that cannot use atmospheric air (H.T.
Odum, in press). Enhanced ecological production generally results in
greater production of desirable organisms, but not necessarily; management
for enhanced production should therefore be considered with this caveat in
mind.

Effects of Impoundment on Overall Diversity

An evaluation of the influence of impoundment on diversity can be made
by observation, but at present, few comparative data are available (but see
Leenhouts and Baker 1982). An understanding of relevant theory of the
causes of diversity may lead to 1) a hypothesis of the effects of impound-
ment on ecological diversity, which can be tested, and 2) guidelines for
managing Merritt Island for enhanced ecological diversity (which, if
implemented, will also serve as tests of the theory).

Although the diversity of certain subgroups of interest may have
decreased, overall diversity of the area of Merritt Island that was
formerly salt marsh has undoubtedly increased (Leenhouts, pers. comm.;
personal observations). Both richness and evenness of species should now
be greater because the diversity of salinity and water level among impound-
ments is greater. Vegetation, for example, formerly included typical salt
marsh and mangrove species of this region of Florida, but now included are
all of these, as well as species common to brackish and freshwater marshes.
In addition, species of submerged marine/brackish vegetation that could
only have been found in potholes prior to impoundment are abundant in many
impoundments (e.g. Chara) and upland species inhabit dikes. Although it is
possible that some of these additional species occurred in small areas of
what is now impounded marsh, their relative prevalence has increased. It
is doubtful that the current prevalence of salt marsh species is as low as
the former prevalence of freshwater species, but even if such were the
case, diversity should be higher because diversity of salt marshes is
typically much lower than the diversity of fresher marshes.

Because vegetation is the foundation of food and cover for animals, a
diversity of vegetation should foster a diversity of animals, though this
diversity may not include all desired species. Desired species may include
organisms that occurred in greater abundance prior to the change, whether
or not the change accounts for their decline (e.g., dusky seaside sparrow).
Despite this, however, the overall diversity of the area formerly called
salt marsh has increased, and it has been replaced by a mosaic of produc-









tive brackish and freshwater marshes, and in a few cases, hypersaline areas
of perhaps lower production.

Effects of Impoundment on Estuarine Fish and Shellfish

Closed water control structures and dikes without control structures
do not allow ingress or egress of estuarine fish (Gilmore et al. 1982;
Harrington and Harrington 1982). Control structures are not closed all of
the time in most impoundments, however. When the water is held on the
marsh, access to foods by estuarine fish and shellfish is possible if water
control structures are open to allow ingress, or if fish entered while the
structures were open (Provost 1973b). Merritt Island impoundments hold
water on the marsh for much more of the year than occurred prior to im-
poundment. Perimeter ditches dug during the construction of dikes may
enhance the production of estuarine fish by increasing marsh edge (Provost
1959, 1968), which is habitat for a variety of estuarine organisms (e.g.,
young snook; Gilmore et al. 1983) and is of fundamental importance to
accessibility of foods and cover, and detrital export (a consideration of
less direct importance to fish survival). Perimeter ditches, because of
their depth, also provide refuge from predation by wading birds. Wading
birds forage poorly in such habitats (Britton and Moser 1982). However,
access to these ditches by fish is essential. Pumps can enhance the
circulation of water through marshes. Such circulation could occur natu-
rally only during the 100 or so days that the marshes were covered with
estuarine water prior to impoundment, and then only if sufficient wind
energy was available to actually move the water through the marsh. Im-
poundments that are open enough of the time to allow some ingress of
estuarine fish may not be open at times when egress is essential either for
completing life cycles or for more immediate survival.

Summary Diagrams of the Influence of Impoundment onEstuarine Fish and
Shellfish

Figures 10 and 11 summarize the relationships between impoundment
activities and production of estuarine fish with respect to food and cover,
respectively. Production of estuarine fish is at the bottom of each
diagram. In Figure 10, production of estuarine fish and shellfish is
positively related to the presence and accessibility of foods. Foods for
various species and life history stages of estuarine fish and shellfish
include: 1) vagile link organisms; 2) zooplankton; 3) resident marsh
organisms and detritus on the marsh surface; 4) phytoplankton; and 5)
detritus and its accompanying community of decomposers exported to adjacent
waters. Vagile link organisms occur, by definition, in proximity to to the
edges of marsh creeks, and themselves are consumers of the resident marsh
organisms and detritus. Zooplankton feed on phytoplankton which occur if
sufficient water is available.

Resident marsh organisms and detritus are a function of the quantity
of submerged and emergent vegetation produced in the marsh. Emergent
vegetation grows better near the edges of marsh creeks, though the causes
of this phenomenon are complex (Haines and Dunn 1976). Hypersalinity will
reduce both types of vegetation but will be prevented or alleviated by
exchange of marsh or impoundment water with the estuary. Water level can
be controlled sufficiently for both types of vegetation to coexist, but









FfODL FQR FTIRH AND SHELLFISH


DITCH & NATURAL WATER CONTROL
CREEK DENSITY WIND,TIDES & PUMPING STRUCTURES &
NATURAL LEVEES


PROXIMITY TO ACCESS AT MARSH/
MARSH/CREEK EDGE/ \ ESTUARY BOUNDARY



AVG. DEPTH OF EXCHANGE OF MARSH
MARSH WATER WATER WITH ESTUARY


HYPERSALINITY


PHYTOPLANKTON V SUBMERGED EMERGENT
VEGETATION VEGETATION
+(+
ZOOPLANKTON ACCESSIBILITY
RESIDENT MARSH OF FOOD
ORGANISMS &
S/DETRITUS

+ + DETRITAL
VAGILE "LINK" + + DECOMPOSITION
ORGANISMS EXPORTED IN MARSH
DETRITUS


FOODS



\ PRODUCTION OF +
ESTUARINE
FISH & SHELLFISH


Figure 10. Conceptual Model of Major Influences on Food
for Estuarine Fish and Shellfish. Note the
importance of accessibility of food.


D OOF FOR FI SH


D NA SHELLFISH
















COVER FOR FISH AND SHELLFISH


DITCH & NATURAL
CREEK DENSITY




PROXIMITY TO
MARSH/CREEK EDGE


WIND,TIDES & PUMPING


WATER CONTROL
STRUCTURES &
NATURAL LEVEES



ACCESS AT MARSH/
ESTUARY BOUNDARY


--- EXCHANGE 01
z 0\ \MARSH WATE
PHYTOPLANKTON &
HYPERSALINITY


SUBMERGED + EMERGENT
VEGETATION VEGETATION
(STEM DENSITY)


+ +
COVER ACCESSIBI
OF COVER




PRODUCTION OF
ESTUARINE
FISH & SHELLFISH

Figure 11. Conceptual Model of Major Influences on Cover
for Estuarine Fish and Shellfish. Note the
importance of accessibility of cover.









when too low, submerged vegetation is eliminated, and when too high,
emergent vegetation is eliminated. Submerged vegetation may also be
reduced by dense phytoplankton, which reduce light penetration to the
seagrasses. If either phytoplankton or its nutrients are greater in marsh
water than in estuarine water, exchange of marsh water with the estuary
will reduce phytoplankton growth.

Resident marsh organisms account for considerable decomposition of
detritus within the marsh itself, leaving perhaps a small fraction
available for export. Exported detritus will be greater when more has
accumulated on the marsh, and when exchange of marsh water is greater.
Export will also be greater from marsh area closer to the edges of tidal
creeks.

Accessibility of foods by estuarine fish and shellfish is enhanced by:
1) increased water depth; 2) proximity to the edge of a marsh creek; 3)
exchange of marsh water with the estuary; and 4) increased access at the
marsh-estuary boundary. The average depth of inundation of the marsh can
be higher with greater tides, wind, or pumping, or if water outlets at the
marsh-estuary boundary are sufficiently restrictive. Proximity to an edge
of a marsh creek is greater where densities of creeks or man-made ditches
are greater. Note in both Figures 10 and 11 the number of different
aspects of estuarine fish production that are enhanced by proximity to
edges of marsh creeks. Exchange of marsh water also influences several
components in the diagrams. Exchange is enhanced by tides, wind, and
pumping, and by increased access at the marsh-estuary boundary. Access is
restricted by the size of creek mouths, the size of water control struc-
tures (trunks and culverts) and the time they are open, and the extent of
natural levees and man-made dikes.

Cover

In Figure 11, production of estuarine fish and shellfish is shown as a
function of cover and accessibility of cover. Cover is dependent on the
quantity of submerged and emergent vegetation. Again, hypersalinity and
phytoplankton can reduce growth of submerged vegetation, but these effects
are reduced with greater exchange of marsh water with the estuary. Accessi-
bility of cover is enhanced by exactly the same things that enhance accessi-
bility to food and control of these is the same as in Figure 10.

Ideas for Impoundment Management to Enhance Estuarine Fish

Production of estuarine fish and shellfish should be enhanced by
allowing greater ingress and egress. The enhanced access to food and cover
within vegetated impoundments caused by perimeter ditches and flooding
should be beneficial to estuarine fish if ingress and egress are enhanced.

Possible ways to enhance food, cover, and ingress and egress to
marshes and impoundments include: 1) more submerged cross-sectional area of
open access and more time open during times of high water; 2) keeping
culverts open during the seasonal fall of water in January and letting the
marsh drain completely in as many impoundments as possible (i.e. where
mosquito control is needed, but waterfowl management is not); 3) breaching









dikes, or removing water control structures wherever possible (i.e. where
neither mosquito control nor waterfowl management is essential or where
rotary ditching provides adequate mosquito control and potholes provide
adequate waterfowl habitat); 4) adding more ditches; and 5) leaving cul-
verts at least partially open, with continuous pumping with a small pump or
occasional pumping with a large pump. Culverts can be left "partially
open" to allow egress and ingress using Neely's (1960) "leaky trunk"
technique whereby a lower riser board is replaced with chock blocks.

Analysis of Commercial Landings for the Inshore Fisheries
of Brevard and Volusia Counties, 1951-1982

Impoundment of Merritt Island marshes has been conjectured to be
detrimental to the fisheries of the Indian River lagoonal system. To
evaluate this possibility, we analyzed commercial landings statistics
(recorded by the National Marine Fisheries Service) for the five fisheries
considered by Anderson and Gehringer (1965) to be dominant in the "inside"
(i.e. lagoonal) catch of the Merritt Island area. These are spotted
seatrout (Cynoscion nebulosus), blue crab (Callinectes sapidus), spot
(Leiostomus xanthurus), mullet (Mugil curema and M. cephalus, combined for
this analysis), and Florida pompano (Trachinotus carolinus). These species
continued to be dominant components of the fishery in the 1970's (Snelson
1980).

Impoundment of Merritt Island marshes occurred primarily between 1959
and 1966 (Leenhouts 1983). Because the species considered here are rela-
tively short-lived and enter the commercial fishery at an early age,
impacts on recruitment (by alteration or removal of nursery habitat or by
trophic degradation of the estuary) should be evident in landings soon
thereafter. We examined landings of the five dominant fisheries in Brevard
and Volusia counties for sustained declines greater than normal variation
during the period following impoundment.

Landings data are easily confounded especially in the absence of
information on fishing effort expended to accrue the catches. Adequate
effort data on these fisheries do not exist. However, an indication of
trends in effort can be inferred from trends in numbers of commercial
vessels registered (Ricker 1975). Available information on numbers of
vessels registered for commercial use in Brevard and Volusia counties
(courtesy of Florida Department of Natural Resources) are shown in Figure
12. From 1963 to 1978, the number of commercial vessels registered in
Brevard county remained stable overall (with annual fluctuations), but
declined steadily in Volusia County. We readily acknowledge that the
usefulness of these data for estimating fishing effort are equivocal for a
number of reasons; e.g., varying proportions of vessels may operate off-
shore, shifts in species-specific effort are not apparent, and changes in
gear efficiency may occur. Nevertheless, their consideration is probably
more useful than their omission.

Spotted Seatrout

Juvenile spotted seatrout do not inhabit marshes and are therefore not
considered dependent on marshes for cover. However, spotted seatrout prey
on a variety of forage organisms (Moody 1950; Tabb 1966; Lorio and Perret



















COMMERCIAL


I
I
I


\ Volusia
- \


Brevard


1965


1970


1975


Figure 12.


Numbers of vessels registered for commercial use in Brevard and
Volusia counties, 1963 to 1978. Data courtesy of Florida Department
of Natural Resources.


1200





1000


800


600 -


400





200





0


1980









1980), many of which may spend part of their life cycle in marshes.
Therefore, if impoundment has any effect on their forage, this species may
be expected to decline following impoundment construction.

For both counties combined, landings of spotted seatrout declined in
the 1950's prior to impoundment but have remained stable since (Fig. 13).
However, catches increased in Volusia County whereas a gradual decline was
evident in Brevard County since the period of impoundment. As commercial
"effort" in Brevard County was stable, the declining landings suggest that
impoundment may have negatively impacted this fishery. However, Anderson
and Gehringer (1965) estimated that during the early 1960's, the recrea-
tional catch of spotted seatrout in the Merritt Island area was about twice
that of the commercial catch. As the number of pleasure boats (and there-
fore anglers) in Brevard County quadrupled from 1963 to 1983 (Fig. 14), and
the spotted seatrout is avidly sought by anglers, it is likely that the
proportion of the total spotted seatrout catch taken by anglers increased.
Therefore, the decline in commercial landings may have resulted from
increasing sportfishing pressure and harvest. That the decline was gradual
(as was the increase in sportfishing pressure) and not abrupt (as was
impoundment of the marshes) lends further credence to the hypothesis that
the decline was caused by increased sportfishing and not by impoundment.
Increased commercial landings of spotted seatrout in Volusia County,
concurrent with declining commercial "effort" and probable increased
angling pressure, offer no evidence that impoundment has affected this
fishery in Volusia County. Therefore, no clear evidence (from landings and
boat registration data) exists suggesting that impoundment of Merritt
Island marshes caused a deterioration of the spotted seatrout fishery.

Blue Crab

Blue crabs reside in or near salt marshes throughout much of their
life cycle (Weinstein 1979; Van Den Avyle and Fowler 1984) and could be
expected to be deleteriously affected by loss or degradation of marsh
habitats. Landings analysis for this species was hindered by the lack of
differentiation between landings in the two counties between 1958 and 1962
(Fig. 15).

The blue crab fishery in Volusia County has apparently never been very
large compared to that in Brevard County (Fig. 15), or crabs taken there
are brought to fish houses elsewhere. Crab landings in Volusia County
during the 1970's and 1980's appear to be somewhat lower than landings
reported in the 1950's.

Beginning in the mid-1960's, blue crab landings in Brevard County
oscillated regularly (perhaps as a density-dependent response) but were
considerably greater than during the 1950's and early 1960's. The
increased landings perhaps resulted from a shift in local effort to this
fishery, or perhaps impoundment enhanced this fishery by unknown means.
Because landings improved so markedly during the 1960's, following the
period of impoundment, it is unlikely that impoundment of Merritt Island
marshes negatively impacted this fishery. Increased landings could be due
to increased demand or increased production. Demand could be greater
because of increased development concurrent with impoundment of the
marshes.



























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Spot

Along the Atlantic coast north of Florida and the Gulf coast of
northern Florida, juvenile spot are one of the most common components of
salt marsh tidal creek fish assemblages (Subrahmanyam and Drake 1975;
Weinstein 1979; Weinstein et al. 1980). However, they are notably absent
from marshes in the southern part of the Indian River system (Harrington
and Harrington 1961; Gilmore 1983). Consequently, the degree of their
dependence on marshes in the vicinity of Merritt Island (or perhaps any-
where) is unclear. Stickney and Cuenco (1982) suggest that juvenile spot
are "adapted to, and live in virtually all portions of estuaries", with
habitat suitability decreasing with increasing depth.

The spot fishery in Volusia County remained small and stable from the
1950's to the 1980's (Fig. 16). Landings in Brevard County generally
increased through the 1960's and declined in the 1970's but skyrocketed
dramatically in the early 1980's (Fig. 16). The astronomical landings
reported in 1982 were checked and confirmed by Ernie Snell of the National
Marine Fisheries Service. Apparently, this species was underfished histor-
ically in the Merritt Island area and recently became more marketable. No
evidence exists in these data to suggest that this fishery has been nega-
tively impacted by impoundment of Merritt Island marshes.

Mullet

Juvenile mullet commonly inhabit salt marsh creeks and were selected
as the indicator species for the transient fish guild in the WELUT AEA
Workshop (Hamilton et al. 1985). Gilmore (1983) considered the striped
mullet, Mugil cephalus (landings of which greatly exceeded those of white
mullet, Mugl curema) a marsh dependent species.

Since the late 1950's, mullet landings in both counties were equiva-
lent and constant (Fig. 17). Supply exceeds demand in this fishery (Cato
et al. 1976) and fish house operators limit landings by assigning fishermen
quotas (Anderson and Gehringer 1965; Snelson 1980). Therefore, the land-
ings data do not reflect abundances of mullet in the Indian River system
and offer no insight into the effects of impoundment on this fishery.
However, it is apparent that current conditions in the system are adequate
to maintain mullet stocks at levels resistant to overexploitation given
current demand.

Florida pompano

Florida pompano do not regularly inhabit marshes, but do feed on
organisms which commonly spend part of their life cycle in the marsh.
Florida pompano command a high price (Anderson and Gehringer 1965) and are
regularly sought by commercial fishermen. Because of this high demand,
landings of Florida pompano (Fig. 18) probably reflect the relative abun-
dances of this species in the Merritt Island area.









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Until the mid-1970's, very few Florida pompano were landed in Volusia
County, the bulk of landings in this area taking place in Brevard County.
Since the 1950's, landings of Florida pompano oscillated regularly every
few years, probably in response to density-dependent factors. No decline
in the fishery following the 1959-1966 impoundment period is apparent. In
fact, the fishery appears to have improved since this period.

Summary

With the exception of spotted seatrout in Brevard County, commercial
landings data for the five dominant inshore fisheries of the Merritt Island
area show no evidence of significant declines in these fisheries despite
the impoundment of virtually all marshes in the area between 1959 and 1966.
The spotted seatrout commercial landings may have declined because of
increased recreational catch as suggested by the four-fold increase in
registered pleasure boats between 1963 and 1984.

These findings are perhaps as much a reflection of the confounding of
these data as they are an indication of the lack of effect of impoundments,
but in any case the concern over fishery effects is not apparent in the
actual commercial landings records. Confounding arises from concomitant
changes in development, sportfishing pressure, climatic abnormalities, gear
efficiency, market value, and regulations. However, the absence of drama-
tic declines and the presence of increases in some of these fisheries
suggest that any effects of impoundment may be much more subtle or even
different from the declines speculated.

Effects of Impoundments on Waterfowl

Demographically, two major factors births and deaths control
population growth. In waterfowl management, the historical approach has
been to provide and protect suitable breeding habitat, protect key
wintering habitat, and regulate harvest. Increasing pressures on both
breeding and wintering habitats, maintenance of hunter demand, and the
realities of involvement with at least three nations and numerous state and
provincial governments complicate continental management of waterfowl.
Until Anderson and Burnhan's (1976) classic publication on the subject,
harvest of waterfowl was managed largely on the assumption that hunting
mortality was additive to natural mortality and thus was negatively
correlated with survival. The notion that hunting mortality of mallards is
compensatory but may exceed some threshold and actually become additive to
total annual mortality (Anderson and Burnham 1976) revolutionized waterfowl
management. That notion was important in prompting increased attention to
wintering waterfowl ecology and management and habitat preservation both in
breeding and wintering habitats. The debate has now shifted (e.g. Nichols,
et al. 1984) to examination of the reliability of the current evidence of
compensatory mortality and its applicability to species other than the
mallard.

Management to enhance waterfowl food plants has been described most
extensively for such areas as Louisiana (e.g., Chabreck 1960; Yancey 1964;
Joanen and Glasgow 1965; Baldwin 1967; Wicker et al. 1983) and the
Carolinas (e.g., Neely 1960, 1968; Yancey 1964; Morgan 1974; Morgan et al.
1975; Heitzman 1978; Prevost et al. 1979; Miglarese and Sandifer 1982;









Swiderek et al. 1985). Techniques described as "moist soil management" are
similar to the management of freshwater coastal impoundments and are
currently being employed in inland impoundments (Green et al. 1964;
Fredrickson et al. 1984; Fredrickson, pers. comm.). Managed impoundments
provide food, cover, and security for waterfowl and are definitely
attractive to them. Impoundment management is being used as a tool on
refuges, wildlife management areas, and private hunting areas. In many
cases we know the foods being used by waterfowl and they are generally the
plants targeted for management. Fredrickson et al. (1984) calculated
nutritional values of many of the native food plants encouraged by moist
soil management and concluded (Fredrickson, pers. comm.) that such impound-
ments may provide more beneficial nutrition than grain crops which hereto-
fore had been recommended for such situations. In addition, these natural
foods can be produced in adequate supply much less expensively than by
flooding grain crops. The water management techniques being employed for
moist soil management are not unlike those long in use along the south
Atlantic Seaboard in coastal impoundments. Frederickson is providing a
link between waterfowl management and waterfowl ecology.

Attractiveness of impoundments to waterfowl has beneficial aspects
such as public viewing, control of hunting opportunity (and perhaps
harvest), and possible energetic/nutritional benefits. Negative aspects
include possible increases in harvest, increases in exposure to spent lead
shot (Shillinger and Cottam 1937; Bellrose 1975; Baker and Thompson 1975;
Feierabend 1983), and increased probability of disease. We know that
waterfowl are attracted to Merritt Island National Wildlife Refuge. We do
not have strong data to demonstrate a net gain of current populations over
past populations, though Chamberlain (1960) and local authorities (e.g., J.
Salmela, pers. comm.) suggest a positive response. Likewise, we do not
know if the attractiveness of MINWR is actually competitive with other
wetlands in the surrounding region nor, especially, whether we have
actually enhanced continental populations.

For an individual area one may be able to demonstrate positive popula-
tion responses. However, for the immediate regional population or the
continental population we do not have the ability to determine impact. For
the numbers attracted to a specific location there are areas from which an
equal number were subtracted. Only when winter survival is enhanced has
population growth been positively affected. Evidence exists for increasing
populations of some Canada geese and snow geese populations which were
attracted to more northern wintering habitats because of easy access to
high energy foods and security of refuges. Obviously, those migrational
shifts, referred to by some as "short-stopping", were advantageous to
survival in these populations (see e.g., Crider 1967; Hankla and Rudolph
1967; Reeves et al. 1968). Geese are large, gregarious, visible, and
limited in distribution; these factors allow ease of monitoring by aerial
counts. Characteristics of most ducks are considerably different, and
changes in population sizes or demography are much more difficult to
detect.

Aspects surrounding effects on regional or continental populations are
extremely elusive but nevertheless an important future research objective.
For example, much effort has been expended on the question of compensatory
mortality in waterfowl populations. This work has been done principally









using some of the largest and best banding and recovery data sets available
for continental populations of waterfowl, yet even the foremost researchers
in this area (Nichols et al. 1984) exercise caution in interpreting the
results.

In the case of a private waterfowl hunting area, the latter concerns
may not be, nor must they be, an issue to the owner and manager. For
public areas, impacts on populations should be considered. At this point
such consideration would be speculative but management decisions must often
be made on speculation hopefully well spiced with intuition and logic.

Most waterfowl management of impoundments has been directed at
wintering waterfowl. Limited opportunities exist for management of locally
breeding species, notably the wood duck and mottled duck. In the case of
Merritt Island, those opportunities are probably limited to the mottled
duck. Montalbano (pers. comm.) suggests that nesting densities for this
species is low throughout its range and suspects above range-wide average
nesting densities on MINWR. Potential exists for successful management of
breeding habitat for mottled ducks on MINWR (Johnson, pers. comm.) and
efforts to enhance breeding success should be encouraged. More information
is needed on breeding habitat requirements, brood ecology, and survival of
locally produced birds to recommend breeding habitat management procedures.

Earlier studies of mottled ducks on MINWR indicated rather high
nesting densities on spoil islands in the Indian River. Management of the
islands to enhance mottled duck production was recommended (Stieglitz and
Wilson 1968). Estimates of nesting densities for Merritt Island itself are
not available, but most assuredly are low compared to the islands (W.
Leenhouts, pers. comm.). Even in the case of known nesting on the spoil
islands, estimates of recruitment are unavailable and are suspected to be
low (F. Montalbano, pers. comm.). Any efforts to enhance breeding habitats
for mottled ducks should be directed toward more freshwater areas until
more information is available on brood survival in more saline habitats.
Swanson et al. (1984) found that young ducklings could not survive at
conductivities above 20 mmhos/cm in prairie lakes without access to fresh
water. The lack of survival of ducklings produced on the islands could be
due to salinity as well as a number of other factors all of which should
be investigated further before committing to their intensive management for
mottled duck production.

Thomas (1982) suggests that wintering mottled ducks use different
habitat types than do other waterfowl. Though these observations were
inconclusive, the hypothesis that mottled ducks have special wintering
habitat requirements is certainly worth investigation if this species
became the subject of intensive management on Merritt Island.

Research information on wintering waterfowl and other migratory birds
is seriously lacking. Anderson (1976) and Fretwell (1972) both indicated
the need for such data and Rogers (1979) emphasized the importance of an
understanding of total annual mortality. The reasons for this void of
knowledge are attributable to the past philosophy of migratory bird manage-
ment which was centered on the reproductive cycle (Pospahala et al. 1974).
That focus probably was engendered because of serious, rapid, and con-
spicuous alteration of surrounding habitat that was occurring in the 1930's
- 50's, particularly within the prairie pothole regions of the mid-western









U.S. and south-central Canada. Any changes within the wintering range at
that time were small in scale, isolated, and resultingly inconspicuous.
However, in the late '60's and '70's, technology allowed significant and
large scale alteration of wintering range habitats such as coastal eco-
systems (Tiner 1984) and bottomland hardwoods (Harris et al. 1984).

These changes precipitated accelerated research beginning circa 1975.
Only 8 percent of over 2500 titles of publications on waterfowl and
wetlands reviewed by Reinecke (1981) involved study within the wintering
range of waterfowl. Our own experience with that small volume of
literature indicates that the majority relate to habitat management
techniques to attract wintering waterfowl. Those studies which concerned
waterfowl biology were generally on wood ducks and mottled ducks and these
principally involved the reproductive cycle as well. In the recent
symposium, Waterfowl in Winter, held in January 1985, in Galveston, TX, a
wealth of papers were presented. In a 10 year span, considerable progress
has been made toward filling the void, though not sufficiently to elucidate
many of the arguments surrounding coastal impoundments.

This surging interest in avian wintering ecology indicates that birds
have special requirements in wintering habitats as well as those that have
been identified for the breeding season. Jeske and Percival (1985) suggest
that waterfowl have evolved "wintering strategies" that are expressed in a
complex combination of characteristics such as anatomy, migration distance,
and survival rates. White and James (1978) and Thomas (1982) have shown
that waterfowl species are spatially distributed within specific wintering
habitats and probably have varying habitat requirements. Alexander and
Hair (1979) and- Alexander (1983) have shown that even sexes of the same
species may vary in geographical distribution and habitat use. More recent
evidence for niche separation among species and between sexes have been
based on morphometric variation (Livezey and Humphrey 1984; Nudds and
Bowlby 1984; Nudds and Kaminsky 1984).

Three geographic areas and impoundments specific to these areas can be
defined: the coastal deltaic marshes of Louisiana; coastal marshes and
abandoned rice fields of Georgia and the Carolinas; and impounded high
marsh and mangrove of eastern Florida. Whereas impoundments of the former
two areas have been managed specifically for wildlife namely waterfowl,
furbearers, and crayfish the latter were designed to control nuisance
salt marsh mosquitos. In these situations, attractiveness to wildlife has
been a serendipity to mosquito control objectives and impoundment manage-
ment has been opportunistic around the schedule designed for effective
mosquito control rather than specifically managed for waterfowl.

Effective management of wetlands depends on control of salinity and
water levels. In the absence of control over salinity, water level manage-
ment is essential for intensive management of desired waterfowl food
plants. In the case of MINWR, most of the impoundments were previously
"grassy" marshes which are high elevation, infrequently flooded wetlands.
In this area, "lunar tidal action is negligible" (Stieglitz and









Wilson 1968) and these marshes are usually flooded only on storm tides and
in the fall when water levels are normally higher. As such, water control
is expensive to attain (compared to many of the coastal impoundments in
Georgia, Louisiana, and the Carolinas, for example) since pumping or
distribution of stored rain water are required for flooding. In addition,
many of the impoundments are extremely large which complicates the ability
to manage water for most effective plant management. Nevertheless, MINWR
impoundments have provided an immense amount of waterfowl habitat when, in
other areas of the State, some waterfowl habitat has been degraded.

The ecological value of impoundments is currently being debated.
Obviously, for any management action, one is faced with acceptance of the
consequences as well as the rewards for those actions. In many cases
consequences may be mitigated to some degree but never fully mitigated at
least not until they are identified. We can identify some of these trade-
offs, but in most cases we cannot determine the magnitude. Based on the
options available a number of consequences and alternatives are possible.
Management alternatives which provide positive benefits for mosquito
control, wildlife, and fisheries are possible but will require innovation
and commitment.









MANAGEMENT OPTIONS FOR MARSHES ON
MERRITT ISLAND NATIONAL WILDLIFE REFUGE

The current objectives of marsh management on MINWR are to preserve,
maintain, enhance, and restore marsh and aquatic wildlife habitat and
populations and to provide opportunity for wildlife-oriented recreation
while maintaining established mosquito-control health and safety standards
(Leenhouts 1983).

Specific objectives listed by Leenhouts (1983) are: 1) to maintain
saltmarsh mosquito populations at levels which do not pose health or safety
dangers to populated areas of Brevard and Volusia counties or to work areas
of the Kennedy Space Center; 2) to maintain wildlife productivity and
diversity within marine communities at 1980 levels; 3) to provide habitat
for endangered and threatened species of plants and animals and migratory
and resident wildlife according to established USFWS policy; 4) to optimize
wildlife and wildlife habitat productivity and diversity within the mosqui-
to control impoundments; and 5) to provide opportunities for wildlife
oriented recreation and interpretation in marsh and aquatic habitats open
to public access.

To date, the primary objective of marsh management on MINWR has been
mosquito control. Its successful achievement by impoundment of marshlands
has eliminated the use of insecticides (only mosquito-specific hormonal
larvicides are used currently). Impoundment has been considered the best
mosquito-control strategy to date (Brevard Mosquito Control District 1951;
Florida Anti-mosquito Association 1970; correspondence from J. Salmela to
D. Carlson, 23 July 1984). In addition, the impoundments provide habitat
for a variety of fish and wildlife and provide distinct areas of marsh that
may be used for other purposes (e.g., wastewater treatment, controlled
access and observation points for hunters, anglers, and wildlife
observers).

With a wide range of management objectives in mind, the following
management alternatives are identified and discussed. The first four
alternatives are currently practiced on some of more than 20,000 acres of
MINWR marshes. The remainder are suggested in addition to these. These
alternatives should promote discussion resulting in research and management
trials leading to satisfactory multiple-objective management of marshes on
MINWR.

Options

Permanent Flooding

This option entails closure of water-contol structures throughout the
year, except when water levels in the estuary exceed those in the impound-
ment. Flooding of the marsh is maintained at all times (via rainfall-
capture, pumping, and passive estuarine inflow) to control saltmarsh
mosquitos and provide habitat and foods (especially Chara) for wintering
waterfowl. Chara grows best with constant inundation (Leenhouts pers.
comm.). This option corresponds to that exercised on most MINWR marshes in
the past. Currently, over 16,000 acres of MINWR improvements are scheduled
for this type of management (MINWR Annual Water Management Program 1985).









MANAGEMENT OPTIONS FOR MARSHES ON
MERRITT ISLAND NATIONAL WILDLIFE REFUGE

The current objectives of marsh management on MINWR are to preserve,
maintain, enhance, and restore marsh and aquatic wildlife habitat and
populations and to provide opportunity for wildlife-oriented recreation
while maintaining established mosquito-control health and safety standards
(Leenhouts 1983).

Specific objectives listed by Leenhouts (1983) are: 1) to maintain
saltmarsh mosquito populations at levels which do not pose health or safety
dangers to populated areas of Brevard and Volusia counties or to work areas
of the Kennedy Space Center; 2) to maintain wildlife productivity and
diversity within marine communities at 1980 levels; 3) to provide habitat
for endangered and threatened species of plants and animals and migratory
and resident wildlife according to established USFWS policy; 4) to optimize
wildlife and wildlife habitat productivity and diversity within the mosqui-
to control impoundments; and 5) to provide opportunities for wildlife
oriented recreation and interpretation in marsh and aquatic habitats open
to public access.

To date, the primary objective of marsh management on MINWR has been
mosquito control. Its successful achievement by impoundment of marshlands
has eliminated the use of insecticides (only mosquito-specific hormonal
larvicides are used currently). Impoundment has been considered the best
mosquito-control strategy to date (Brevard Mosquito Control District 1951;
Florida Anti-mosquito Association 1970; correspondence from J. Salmela to
D. Carlson, 23 July 1984). In addition, the impoundments provide habitat
for a variety of fish and wildlife and provide distinct areas of marsh that
may be used for other purposes (e.g., wastewater treatment, controlled
access and observation points for hunters, anglers, and wildlife
observers).

With a wide range of management objectives in mind, the following
management alternatives are identified and discussed. The first four
alternatives are currently practiced on some of more than 20,000 acres of
MINWR marshes. The remainder are suggested in addition to these. These
alternatives should promote discussion resulting in research and management
trials leading to satisfactory multiple-objective management of marshes on
MINWR.

Options

Permanent Flooding

This option entails closure of water-contol structures throughout the
year, except when water levels in the estuary exceed those in the impound-
ment. Flooding of the marsh is maintained at all times (via rainfall-
capture, pumping, and passive estuarine inflow) to control saltmarsh
mosquitos and provide habitat and foods (especially Chara) for wintering
waterfowl. Chara grows best with constant inundation (Leenhouts pers.
comm.). This option corresponds to that exercised on most MINWR marshes in
the past. Currently, over 16,000 acres of MINWR improvements are scheduled
for this type of management (MINWR Annual Water Management Program 1985).









There include several very large impoundments (T-16, 17, 18, and T-24-D).
Although effective for mosquito control, waterfowl attraction, and
freshwater fish management (in low salinity impoundments), it severely
limits the accessibility of the marshes to estuarine fish and shellfish and
inhibits or precludes growth of natural saltmarsh vegetation.

Impoundment Elimination

Removal of all dikes as was done in T-10-K would come closest to
restoring MINWR marshes to a natural state, allowing growth of natural
saltmarsh vegetation and access by estuarine fish and shellfish. However,
it would also restore natural abundances of saltmarsh mosquitos and
decrease habitat for wintering waterfowl and freshwater sportfish. Open
marsh water management techniques could be instituted to negate the
resultant mosquito problem, but perhaps not nearly as effectively as did
impoundment (letter from J. Salmela to D. Carlson, 23 July 1984).

Vestigial Impoundments

By removing portions of dikes, or leaving all water-control structures
open at all times, an effect similar to that brought about by impoundment
elimination could be produced, but perimeter ditches would remain intact.
These would serve as additional habitat for estuarine fish and shellfish
and also would provide some protected, albeit minimal, aquatic habitat for
wintering waterfowl. This option would also facilitate restoration of
water control in the future if desired. The beach impoundments T-38, T-39,
T-39-South and the "salt cell" (T-10-H) are currently of this type on
Merritt Island.

Seasonal Flooding

In this option (proposed by Clements and Rogers 1964; Provost 1973b,
and Lewis et al. in press), water-control structures are kept closed during
the mosquito breeding season (about May to October) whenever estuarine
water levels are below those in impoundments to ensure adequate mosquito
control by keeping the marshes flooded. Estuarine inflows, pumping, and
rainwater capture are used to maintain impoundment water levels. At the
end of the mosquito breeding season (October), water-control structures are
opened and remain so until the following May (or later if adequate pumping
is available so that water does not have to be stockpiled in anticipation
of later needs; J. Salmela, pers. comm.) thereby allowing water levels to
fluctuate naturally. During this period, estuarine organisms can enter the
marshes with the fall rise in water levels and use the cover and food found
therein (though the marsh will generally be dry). Egress is possible when
water levels decline or during cold weather. This option provides adequate
mosquito control, restores the nursery value of the marsh, and allows
perpetuation of natural saltmarsh vegetation. However, it results in less
flooded area for both fish and wintering waterfowl, precludes development
of Chara, and, by increasing salinity, renders the habitat unsuitable for
freshwater sportfish.

Seasonal Flooding With Added Potholes

This option modifies the seasonal flooding strategy via the addition
of man-made potholes (e.g., by blasting; Provost 1948). It offers the same









advantages of seasonal flooding but mitigates the deleterious effect on
wintering waterfowl by producing more potential waterfowl habitat and
Chara-producing areas. None of the MINWR marshes are currently managed in
this way.

Leaky Impoundments

In this option, water-control structures are modified to allow con-
stant, but limited, water exchange with the estuary by replacement of a
lower riser board with chock blocks. A prescribed water level in the
impoundment is maintained by constant pumping with a small pump, or the
level is allowed to fluctuate between limits by intermittent pumping with a
large pump. All riser boards can be removed during the peak of the fall
inundation. This option provides mosquito control, acceptable habitat for
wintering waterfowl and Chara production, and at least some opportunity for
ingress and egress by estuarine fish and shellfish. However, it would
result in the removal of habitat for freshwater sportfish and would most
likely impair production of natural saltmarsh vegetation. This management
strategy would be expensive and time-consuming, but would satisfy, at least
in part, demand for the three major uses of MINWR marsh areas impacted by
impoundments: mosquito control, wintering waterfowl attraction, and estua-
rine fish and shellfish nursery habitat. Although continuous free access
by estuarine fish and shellfish would perhaps be at most times less than in
a natural marsh, the availability of aquatic habitat in the marsh through-
out the year might mitigate this difference.

Intensive Management For Waterfowl Foods

In this option, small impoundments, or diked-off sections of large
impoundments (subimpoundments), would be intensively managed for preferred
duck foods such as Ruppia, Chara, Sesuvium, or Scirpus robustus. Current-
ly, waterfowl food management in MINWR marshes is largely a serendipity of
mosquito control, and is relatively ineffective compared to impoundments
elsewhere managed specifically for waterfowl foods. Intensive management
of small areas may provide amounts of duck food comparable to those
currently produced throughout the refuge. Concentration of waterfowl in
such areas might also enhance recreational opportunities. Because only a
small acreage of marsh would be managed in this fashion, deleterious
impacts on other uses would be negligible. This option is particularly
attractive if modifications in the management of other impoundments results
in decreased waterfowl food production there.

Integrated Marsh Management

This option requires: 1) determination of the desired uses of marshes
on MINWR (e.g., mosquito control, attraction of wintering waterfowl,
nursery areas for estuarine fish and shellfish, maintenance of depleted or
scarce habitat wildlife observation, sportfishing, endangered and
threatened species management, wastewater treatment); 2) determination of
the relative importance of each of these uses; 3) allocation of areas of
marsh to each of these uses by their perceived importance; and 4)
appropriate management of these areas, possibly by the options listed
above. For example, areas within 4 miles of human activity centers could
be managed primarily for mosquito control, areas frequented by refuge





71



visitors could be managed for waterfowl or other wildlife, etc. Management
of each impoundment, or formerly impounded area, would be tailored to the
specific use or combination of uses dictated for that area. Determination
of the best areas for some uses (e.g., best nursery areas for estuarine
fish and shellfish) would be difficult to predict a priori and would
require monitoring and comparisons. Integrated marsh management would
result in multiple-objective management of MINWR marshes for all uses
deemed desirable or necessary. Both simultaneous multiple-objective
management within marshes and multiple objective management among marshes
for specialized purposes are possible.









RESEARCH AND DATA NEEDS

The paucity of scientifically collected data on impoundments and
natural marshes in the Merritt Island area, together with the singularities
of Merritt Island marshes (regime of inundation, sediments, climate,
vegetation, lack of water movement) necessitate original data collection
and analysis before any speculations and deductions (including those
presented in this report) can be reliably applied. Below is a brief list
of experiments and correlation analyses that if performed would consider-
ably enhance understanding of the energetic, biogeochemistry, fish and
wildlife use, and effects of various perturbations and management schemes
in Merritt Island marshes (natural and impounded), and the relationship of
these marshes to adjacent estuarine water.

1. Understand impounded salt marsh under different management regimes:

a) fish and wildlife use, including estuarine fish and shellfish
b) overall primary production
c) macrophyte diversity
d) relationship to estuary (import/export of biota, chemical
constituents, detritus).

2. Comparison of impounded and unimpounded marsh with respect to above.

3. Quantitative determination of limiting nutrients and assessment of
potential energy subsidies (wind, water movement) and stresses
(salinity) on overall primary production.

4. Assessment of the influences of degree of temporal and spatial
variability in water level and salinity on diversity of macrophytes.

5. Determine pump-passage mortality of estuarine biota.

6. Determine the optimal ditch density or edge per unit area of marsh.

7. Assess the use of man-made (blasted) potholes in natural marsh as a
water and marsh bird management technique.

8. Track crude vegetative changes with an annual fly-over and correlate
changes to management and environment. The level of detail included
in such fly-overs must be chosen by considering the need for a time
frame that can allow efficient adjustments in management. Detailed
mapping of vegetation, while useful, is not essential for this pur-
pose; rapid promulgation of results is.
9. Management trials should be accompanied by record keeping of what was
done. Minimize confounding so that the effects of particular tech-
niques can be evaluated. Response variables ideally should include:

a) water level
b) salinity
c) diurnal dissolved oxygen (or possibly dusk-dawn)
d) fish and wildlife use including estuarine biota
e) macrophyte diversity (number of species, % cover of each)
f) flux of chemical constituents and detritus to and from estuary.









LITERATURE CITED


Alexander, W.C. 1983. Differential sex distributions of wintering
diving ducks (Aythyini) in North Ameria. American Birds
37:26-29.

Alexander, W.C., and J.D. Hair. 1979. Winter foraging behavior and
aggression of diving ducks in South Carolina. Proc. Annu. Conf.
S.E. Assoc. Fish and Wildl. Agencies 31:226-232.

Anderson, D.R., and K.P. Burnham. 1976. Population ecology of the
mallard. VI. The effect of exploitation on survival. U.S. Fish
and Wildlife Service Resource Publ. 128. Washington, D.C. 66 pp.

Anderson, W.W., and J.W. Gehringer. 1965. Biological-statistical
census of the species entering fisheries in the Cape Canaveral
area. U.S. Fish and Wildlife Service Special Scientific Report -
Fisheries No. 514. 79 pp.

Aston, S.R. 1980. Nutrients, dissolved gases, and general biogeo-
chemistry in estuaries. Pages 233-262 in E. Olausson and I. Cato
(eds.). Chemistry and Biogeochemistry of Estuaries. John Wiley and
Sons, New York, NY.

Bahr, L.M. 1976. Energetic aspects of the intertidal oyster reef
community at Sapelo Island, Georgia. Ecology 57:121-131.

Bahr, L.M, and W.P. Lanier. 1981. The ecology of intertidal oyster
reefs of the South Atlantic coast: a community profile. U.S. Fish
and Wildlife Service, Office of Biological Services, Washington,
D.C. FWS/OBS-81/15. 105 pp.

Baldwin, W.P. 1967. Impoundments for waterfowl on south Atlantic and
Gulf coastal marshes. Pages 127-133 in J.D. Newsom, ed., Proceed-
ings of the marsh and estuary management symposium. Louisiana
State Univ., Baton Rouge.

Ballard, R.W. 1977. Notes on a major oceanographic find. Oceanus 20:
35-44.

Beckman, D.W., and J.M. Dean. 1984. The age and growth of young-of-
the-year spot, Leiostomus xanthurus Lacepede, in South Carolina.
Estuaries 7:487-496.

Bellrose, F. 1975. Impact of ingested lead pellets on waterfowl.
Pages 163-167 in Proc. 1st Int. Waterfowl Symp., Ducks Unlimited,
St. Louis, MO.

Bidlingmayer, W.L. 1982. Surveying salt marsh mosquito control
impoundments in central Florida. J. Florida Anti-mosquito Assoc.
53(1):4-7.









Blum, J.L. 1969. Nutrient changes in water flooding the high salt
marsh. Hydrobiologia 34: 95-99.

Boesch, D.F., and R.E. Turner. 1984. Dependence of fishery species on
salt marshes: the role of food and refuge. Estuaries 7:460-468.

Borey, R.B., P.A. Harcombe, and F.M. Fisher. 1983. Water and organic
carbon fluxes from an irregularly flooded brackish marsh on the
upper Texas coast, U.S.A. Estuarine, Coastal and Shelf Science
16:379-402.

Bozeman, E.L., Jr., and J.M. Dean. 1980. The abundance of estuarine
larval and juvenile fish in a South Carolina intertidal creek.
Estuaries 3:89-97.

Brevard Mosquito Control District. 1951. Policy of the Florida State
Board of Health pertaining to present mosquito control practices
and recommendations for a long-range plan to bring about more
effective control in the state. Adopted by Florida State Board of
Health 18 November 1951. 12 pp.

Britton, R.H., and M.E. Moser. 1982. Size specific predation by herons
and its effect on the sex-ratio of natural populations of the
mosquito fish Gambusia affinis Baird and Girard. Oecologia 53:
146-151.

Brock, T.D. 1979. Biology of microorganisms. Prentice-Hall, Inc.
Englewood Cliffs, NJ.

Browder, J.A., H.A. Bartley, and K.S. Davis. Unpublished manuscript. A
probabilistic model of the relationship between marshland-water
interface and marsh disintegration. 18 pp.

Buresh, R.J., R.D. DeLaune, and W.H. Patrick, Jr. 1980. Nitrogen and
phosphorus distribution and utilization by Spartina alterniflora in
a Louisiana Gulf coast marsh. Estuaries 3:111-121.

Burkholder, P.R., and G.H. Bornside. 1957. Decomposition of marsh
grass by aerobic marine bacteria. Bull. Torrey. Bot. Club 84:
366-383.

Burns, R.W. 1974. Species abundance and diversity of larval fishes in
a high-marsh tidal creek. MS Thesis, Univ. of South Carolina,
Columbia, SC.

Byron, M.M 1968. Net nutrient exchange between high marsh areas and an
estuary. M.S. Thesis, North Carolina State University, Raleigh,
North Carolina. 22 p.

Cadle, R.D., and E.R. Allen. 1970. Atmospheric photochemistry.
Science 167:243-249.









Cain, R.L., and J.M. Dean. 1976. Annual occurrence, abundance, and
diversity of fish in a South Carolina tidal creek. Mar. Biol.
36:369-379.

Carlson, D.B. 1983. The use of salt-marsh mosquito control impound-
ments as wastewater retention areas. Mosquito News 43:1-6.

Cato, J.C., P.B. Youngberg, and R. Raulerson. 1976. Production,
prices, and marketing: an economic analysis of the Florida mullet
fishery. Pages 15-62 in J.C. Cato and W.E. McCullough (eds.).
Economics, biology, and food technology of mullet. Florida Sea
Grant Progress Report No. 15.

Chabreck, R.H. 1960. Coastal marsh impoundments for ducks in
Louisiana. Proc. Ann. Conf. S.E. Assoc. Game Fish Comm. 14:24-29.

Chamberlain, E.B., Jr. 1960. Florida waterfowl populations, habitats,
and management. Fla. Game and Fresh Water Fish Comm. Tech. Bull.
No. 7, 62 p.

Chynoweth, L.A. 1975. Net primary production of Spartina and species
diversity of associated macroinvertebrates of a semi-impounded salt
marsh. Tech. Rep. No. 1, Grant No. NGR 10-019-009. National
Aeronautics and Space Administration, Kennedy Space Center,
Florida. 147 pp.

Clements, B.W., Jr., and A.J. Rogers. 1964. Studies of impounding for
the control of salt marsh mosquitos in Florida, 1958-1963.
Mosquito News 24:265-276.

Costanza, R., C. Neill, S.G. Leibowitz, J.R. Fruci, L.M. Bahr, Jr., and
J.W. Day, Jr. 1983. Ecological models of the Mississippi Deltaic
Plain Region: data collection and presentation. U.S. Fish and
Wildlife Service, Division of Biological Services, Washington, DC
FWS/OBS-82/68. 342 pp.

Crabtree, R.E., and J.M. Dean. 1982. The structure of two South
Carolina estuarine tidal pool fish assemblages. Estuaries 5:2-9.

Currin, B.M., J.P. Reed, and J.M. Miller. 1984. Growth, production,
food consumption, and mortality of juvenile spot and croaker: a
comparison of tidal and nontidal nursery areas. Estuaries
7:451-459.

Dahlberg, M.D. 1972. An ecological study of Georgia coastal fishes.
Fish. Bull. 70:323-353.

Daiber, F.C. 1974. Salt marsh plants and future coastal salt marshes
in relation to animals. Pages 475-508 in R.J. Reimold and W.H.
Queen (eds.). Ecology of halophytes. Academic Press, Inc., New
York, NY.

Dame, R.F. 1976. Energy flow in an intertidal oyster population.
Estuarine and Coastal Marine Science. 4:243-283.









Dame, R.F. 1979. The abundance, diversity and biomass of macrobenthos
on tidal oyster reefs. Proc. Natl. Shellfish. Assoc. 69:6-10.

Dame, R.F., and D. Stilwell. 1984. Environmental factors influencing
macrodetritus flux in North Inlet Estuary. Estuarine, Coastal and
Shelf Science 18:721-726.

Dankers, N., M. Binsbergen, K. Zegers, R. Laane, and M.R. van der Loeff.
1984. Transportation of water, particulate and dissolved organic
and inorganic matter between a salt marsh and the Ems-Dollard
Estuary, the Netherlands. Estuarine and Coastal Shelf Science
19:143-165.

Darley, W.M., C.L. Montague, F.G. Plumley, W.W. Sage, and A.T. Psalidas.
1981. Factors limiting edaphic algal biomass and productivity in a
Georgia salt marsh. J. Phycol. 17:122-128.

Darnell, R. 1958. Food habits of fishes and larger invertebates of
Lake Pontchartrain, Louisiana, an estuarine community. Publ. Inst.
Mar. Sci. Univ. Tex. 5:353-416.

Darnell, R. 1961. Trophic spectrum of an estuarine community, based on
studies of Lake Pontchartrain, Louisiana. Ecology 42:553-568.

DeLaune, R.D., and W.H. Patrick, Jr. 1980. Rate of sedimentation and
its role in nutrient cycling in a Louisiana salt marsh. Pages
401-412 in P. Hamilton and K.B. MacDonald (eds.). Estuarine and
wetland processes with emphasis on modeling. Marine science
series, Vol. 11. Plenum Press, New York, NY.

Delwiche, C.C. 1970. The nitrogen cycle. Pages 71-80 in The bio-
sphere, a collection of reprints from Scientific American. W.H.
Freeman, San Francisco.

Dransfield, P. 1968. Engineering systems and automatic control.
Prentice-Hall, Inc. Englewood Cliffs, NJ. 429 pp.

Dubbelday, P.S. 1975. Lagoonal circulation. Ch. 3 in An ecological
study of the lagoons surrounding the John F. Kennedy Space Center
Brevard County, Florida, April 1972 to September 1975. Volume I.
Experimental results and conclusions. December 31, 1975. Final
report to NASA from Florida Institute of Technology, Project #NGR
10-015-008.

East Central Florida Regional Planning Council. 1975a. Florida
Regional Coastal Zone Management Atlas, Region 6, East Central
Florida. Bureau of Coastal Zone Planning, Division of Resource
Management, Florida Department of Natural Resources.

East Central Florida Regional Planning Council. 1975b. Florida
Regional Coastal Zone Environmental Quality Assessment. Region 6,
East Central Florida. Bureau of Coastal Zone Planning, Division of
Resource Management, Florida Department of Natural Resources.









Emlen, J.M. 1973. Ecology: an evolutionary approach. Addison-Wesley,
Reading, Mass. 493 pp.

Feierabend, J.S. 1983. Steel shot and lead poisoning in waterfowl.
National Wildlife Federation Scientific and Technical Services No.
8. 62 pp.

Ferrigno, F. 1970. Preliminary effects of open marsh water management
on the vegetation and organisms of the salt marsh. Proc. Ann. Mtg.
N.J. Mosq. Exterm. Assoc. 57:79-94

Ferrigno, F., and D.M. Jobbins. 1968. Open marsh water management.
Proc. Ann. Mtg. N.J. Mosq. Exterm. Assoc. 55:104-115.

Ferrigno, F., L.G. MacNamara, and D.M. Jobbins. 1969. Ecological
approach for improved management of coastal meadowlands. Proc.
Ann. Mtg. N.J. Mosq. Exterm. Assoc. 56:188-202.

Fisher, R.A., A.S. Corbet, and C.B. Williams. 1943. The relation
between the number of species and the number of individuals in a
random sample of an animal population. J. Anim. Ecol. 12:42-58.

Florida Anti-mosquito Association. 1970. Statement of policy on
mosquito control in Florida. Concurred in by the Bureau of
Entomology, Division of Health, Department of Health and Rehabili-
tative Services. 3 pp.

Fredrickson,-L., M. Heitmeyer, and F. Reid. 1984. Applications of
moist-soil management techniques for waterfowl management.
Information Transfer Update, Office of Information Transfer, U.S.
Fish and Wild. Serv., Ft. Collins, CO. 79 pp.

Fretwell, S.D. 1972. Populations in a seasonal environment. Princeton
Univ. Press. Princeton, NJ. 217 pp.

Fritz, E.S., W.H. Meredith, and V.A. Lotrich. 1975. Fall and winter
movements and activity level of the mummichog, Fundulus
heteroclitus, in a tidal creek. Chesapeake Science 16:211-214.

Fry, B. 1981. Natural stable carbon isotope tag traces Texas shrimp
migrations. Fish. Bull. 79:337-345.

Gallagher, J.L. 1975. Effect of an ammonium nitrate pulse on the
growth and elemental composition of natural stands of Spartina
alterniflora and Juncus roemerianus. Amer. J. Bot. 62:644-648.

Gallagher, J.L., R.J. Reimold, R.A. Linthurst, and W.J. Pfeiffer. 1980.
Aerial production, mortality, and mineral accumulation-export
dynamics in Spartina alterniflora and Juncus roemerianus plant
stands. Ecology 61:303-312.

Gardner, L.R. 1975. Runoff from an intertidal marsh during tidal
exposure: regression curves and chemical characteristics. Limnol.
Oceanogr. 20:81-89.









Gilmore, R.G. 1983. Fishes and macrocrustacean population dynamics in
a tidally influenced impounded sub-tropical marsh, in D.B.
Carlson, R.G. Gilmore, and J. Rey. Impoundment management. Final
Report: CM-47 and CM-73. unpublished report to Florida Department
of Environmental Regulation, Coastal Zone Management Department.

Gilmore, R.G., D.W. Cooke, and C.J. Donohoe. 1982. A comparison of the
fish populations and habitat in open and closed salt marsh
impoundments in east-central Florida. Northeast Gulf Science
5:25-37.

Gilmore, R.G., C.J. Donohoe, and D.W. Cooke. 1983. Observations on the
distribution and biology of east-central Florida populations of the
common snook, Centropomus undecimalis (Bloch). Fla. Sci. 46:
313-336.

Gosselink, J.G. and C.J. Kirby. 1974. Decomposition of salt marsh
grass Spartina alterniflora Loisel. Limnol. Oceanogr. 19:825-832.

Gosselink, J.G., E.P. Odum, and R.M. Pope. 1973. The value of the
tidal marsh. Center for Wetland Resources, Louisiana State
University, Baton Rouge, LA. 30 pp.

Green, W.E., L.G. MacNamara, and F.M. Uhler. 1964. Water off and on.
Pages 557-568 in J.P. Linduska (ed.). Waterfowl tomorrow. U.S.
Dept. of Interior, Washington, D.C. 770 pp.

Haines, B.L., and E.L. Dunn. 1976. Growth and resource allocation
responses of Spartina alterniflora Loisel to three levels of NH4-N,
Fe, and NaCl in solution culture. Bot. Gaz. 137:224-230.

Haines, E.B. 1977. The origins of detritus in Georgia salt marsh
estuaries. Oikos 29:254-260.

Haines, E.B. 1979a. Growth dynamics of cordgrass, Spartina
alterniflora Loisel., on control and sewage sludge fertilized plots
in a Georgia salt marsh. Estuaries 2:50-53.

Haines, E.B. 1979b. Interactions between Georgia salt marshes and
coastal waters: a changing paradigm. Pages 35-46 in R.J.
Livingston (ed.). Ecological processes in coastal and marine
systems, Plenum, New York, NY.

Haines, E.B., A. Chalmers, R. Hanson, and B. Sherr. 1977. Nitrogen
pools and fluxes in a Georgia salt marsh. Pages 241-254 in M.
Wiley (ed.). Estuarine processes, Vol. II, Academic Press, New
York, NY.

Haines, E.B., and R.B. Hanson. 1979. Experimental degradation of
detritus made from the salt marsh plants Spartina alterniflora
Loisel, Salicornia virginica L. and Juncus roemerianus Scheele. J.
Exp. Mar. Biol. Ecol. 40:27-40.









Haines, E.B., and C.L. Montague. 1979. Food sources of estuarine
invertebrates analyzed using 13C/12C ratios. Ecology 60: 48-56.

Hamilton, D.B., A.K. Andrews, G.T. Auble, R.A. Ellison, A.H. Farmer, and
J.E. Roelle. 1985. Environmental systems and management
activities on the Kennedy space Center, Merritt Island, Florida:
results of a modeling workshop. USFWS, Western Energy and Land Use
Team, WELUT-85/W05, 130 pp.

Hanson, R.B. 1977a. Comparison of nitrogen fixation activity in tall
and short Spartina alterniflora salt marsh soils. Appl. Environ.
Microbiol. 33:596-602.

Hanson, R.B. 1977b. Nitrogen fixation (acetylene reduction) in a salt
marsh amended with sewage sludge and organic carbon and nitrogen
compounds. Appl. Environ. Microbiol. 33:846-852.

Hanson, R.B. 1982. Organic nitrogen and caloric content of detritus
II. Microbial biomass-and activity. Est. Coast. Shelf Sci. 14:
325-336.

Hardisky, M.A., R.M. Smart, and V. Klemas. 1983. Growth response and
special characteristics of a short Spartina alterniflora salt
marsh irrigated with freshwater and sewage effluent. Remote
sensing of Environment 13:57-67.

Harrington, R.W., Jr., and E.S. Harrington. 1961. Food selection among
fishes invading a high subtropical salt marsh: from onset of
flooding through progress of a mosquito brood. Ecology 42:646-666.

Harrington, R.W., Jr., and E.S. Harrington. 1982. Effects on fishes
and their forage organisms of impounding a Florida salt marsh to
prevent breeding by salt marsh mosquitos. Bull. Mar. Sci.
32:523-531.

Harris, L.D., R. Sullivan, and L. Badger. 1984. Bottomland hardwoods:
valuable, vanishing, vulnerable. Florida Cooperative Extension
Service, Gainesville, FL 18 pp.

Hatton, R.S., W.H. Patrick, and R.D. DeLaune. 1982. Sedimentation,
nutrient accumulation, and early diagenesis in Louisiana Barataria
basin coastal marshes. Pages 255-267 in V.S. Kennedy (ed.).
Estuarine Comparisons. Academic Press, New York, NY.

Heitzman, B. 1978. Management of salt marsh impoundments for waterfowl
in North Carolina. North Carolina Wildlife Resources Commission.
35 pp.

Heald, E.J. 1970. The Everglades estuary: an example of seriously
reduced inflow of freshwater. Trans. Am. Fish. Soc. 99:847-848.

Heinselman, M.L. 1971. The natural role of fire in conifer forests.
Pages 61-72 in C.W. Slaughter, R.J. Barney, and G.M. Hansen (eds.).
Fire in the northern environment. U.S. Forest Service, Pacific
Northwest Forest and Range Experiment Station, Portland, Oregon.









Herke, W.H. and B.D. Rogers. 1984. Comprehensive estuarine nursery
study completed. Fisheries (Bethesda) 9(6):12-16.

Hill, J., IV, and S.L. Durham. 1978. Input, signals and control in
ecosystems. Pages 1-6 in Proc. 1978 IEEE Intl. Conf. on Acoustics,
Speech, and Signal Processing. April 1978. Tulsa, OK.

Hoffmeister, J.E. 1974. Land from the sea: the geologic story of
south Florida. University of Miami Press, Coral Gables, Florida.
143 pp.

Howarth, R.W. 1979. Pyrite: its rapid formation in a salt marsh and
its importance to ecosystem metabolism. Science 203:49-51.


Howarth, R.W. 1984.
energy dynamics
Biogeochemistry


The ecological significance of sulfur in the
of salt marsh and coastal marine sediments.
1:5-27.


Howarth, R.W., and J.E. Hobbie. 1982. The regulation of decomposition
and heterotrophic microbial activity in salt marsh soils: a review.
Pages 183-207 in V.S. Kennedy (ed.). Estuarine comparisons.
Academic Press, New York, NY.

Howarth, R.W., and J.M. Teal. 1979. Sulfate reduction in a New England
salt marsh. Limnol. Oceanogr. 24:999-1013.

Howarth, R.W., and J.M. Teal. 1980. Energy flow in a salt marsh
ecosystem: the role of reduced inorganic sulfur compounds. Am.
Nat. 116:862-872.

Imberger, J., T. Berman, R.R. Christian, E.B. Sherr, D.C. Whitney, L.R.
Pomeroy, R.G., Wiegert, and W.J. Wiebe. 1983. The influence of
water motion on the distribution and transport of materials in a
salt marsh estuary. Limnol. Oceanogr. 28: 201-214.

Jeske, C.W., and H.F. Percival. 1985. Wintering strategies of
Anatinae. Presented at the Waterfowl in Winter symposium, 7-10
January 1985, Galveston, TX.

Joanen, T., and L.L. Glasgow. 1965. Factors influencing the
establishment of widgeongrass stands in Louisiana. Proc. Ann.
Conf. S.E. Assoc. Game Fish Comm. 19:78-92.

Johannes, R.E. 1964. Phosphorus excretion and body size in marine
animals: microzooplankton and nutrient regeneration. Science 146:
923-924.


Johannes, R.E.
203-213 in
biology of


1968. Nutrient regeneration in lakes and oceans. Pages
M.R. Droop and E.J.F. Wood (eds.). Advances in micro-
the sea. Academic Press, New York, NY.


Kalber, F.A., Jr. 1959. A hypothesis of the role of tide-marshes in
estuarine productivity. Estuarine Bulletin 4(1):3.









Lasater, J.A. 1975. Water chemistry studies of the Indian River
Lagoons. Chapter 6 in An ecological study of the lagoons
surrounding the John F. Kennedy Space Center, Brevard County,
Florida, April 1972 to September 1975. Volume I. Experimental
results and conclusions. December 31, 1975. Final report to NASA
from Florida Institute of Technology, Project #NGR 10-015-008.

Leenhouts, W.P. 1983. Marsh and water management plan, Merritt Island
National Wildlife Refuge. Titusville, FL.

Leenhouts, W.P., and J.L. Baker. 1982. Vegetation dynamics in dusky
seaside sparrow habitat on Merritt Island National Wildlife Refuge.
Wildl. Soc. Bull. 10:127-132.

Levinton, J.S. 1982. Marine ecology. Prentice-Hall, Inc., Englewood
Cliffs, NJ. 526 pp.

Lewis III, R.R., R.G. Gilmore, Jr., D.W. Crewz, and W.E. Odum. In
press. Mangrove habitat and fishery resources of Florida. in
Proceedings of the Florida Fishery Habitat Symposium. Florida
Chapter American Fisheries Society, Gainesville, FL.

Lewis, V.P., and D.S. Peters. 1984. Menhaden a single step from
vascular plant to fishery harvest. J. Exp. Mar. Biol. Ecol.
84:95-100.

Lindeman, R.L. 1942. The trophic-dynamic aspect of ecology. Ecology
23:399-418.

Livezey, B.C., and P.S. Humphrey. 1984. Sexual dimorphism in
continental steamer-ducks. Condor 86:368-377.

Livingston, R.J. 1984. Trophic response of fishes to habitat
variability in coastal seagrass systems. Ecology 75:1258-1275.

Lorio, W.J., and W.S. Perret. 1980. Biology and ecology of the
spotted seatrout (Cynoscion nebulosus Cuvier). Pages 7-13 in R.O.
Williams, J.E. Weaver, and F.A. Kalber (eds.). Proceedings: a
colloquium on the biology and management of the red drum and
seatrout. Gulf States Mar. Fish. Comm. No. 5.

Lotka, A.J. 1922a. Contribution to the energetic of evolution. Proc.
Nat. Acad. Sci. 8:147-151.

Lotka, A.J. 1922b. Natural selection as a physical principle. Proc.
Nat. Acad. Sci. 8:151-154.

Lovelock, J.E. 1979. Gaia: a new look at life on earth. Oxford
University Press, New York, NY. 157pp.

MacIntyre, F. 1970. Why the sea is salt. Pages 104-115 in Ocean
science: readings from Scientific American. W.H. Freedman and Co.,
San Francisco, CA.









Marinucci, A.C. 1982. Trophic importance of Spartina alterniflora
production and decomposition to the marsh-estuarine ecosystem.
Biol. Conserv. 22:35-58.

Meade, R.H., P.L. Sachs, T.T. Manheim, J.C. Hathaway, and D.W. Spencer.
1975. Sources of suspended matter in water of the middle Atlantic
Bight. J. Sed. Petrol. 45:171-188.

Miglarese, J.V., and P.A. Sandifer (eds.). 1982. An ecological
characterization of South Carolina wetland impoundments. South
Carolina Marine Resources Center Tech. Rep. No. 51. 132 pp.

Mion, P., G.R. Best, and C.R. Hinkle. 1985. Low-energy wastewater
recycling through wetland ecosystems: experimental use of a marsh
ecosystem at Kennedy Space Center. Abstract in Ecol. Bull.
66(2):233.

Montague, C.L. 1980. The net influence of the mud fiddler crab, Uca
pugnax, on carbon flow through a Georgia salt marsh: the
importance of work by macroorganisms to the metabolism of
ecosystems. Ph.D. Diss., Univ. of Georgia, Athens, GA. 157 pp.


Montague, C.L., S.M. Bunker, E.B. Haines, M.L. Pace, and
1981. Aquatic macroconsumers. Pages 69-85 in L.R.
R.G. Wiegert (eds.). The ecology of a salt marsh.
Verlag, New York, NY.


R.L. Wetzel.
Pomeroy and
Springer-


Montague, C.L., A.V. Zale, H.F. Percival, and T. Hingtgen. 1984a. A
categorized bibliography for a conceptual model of salt marsh
management on Merritt Island, Florida. Florida Cooperative Fish
and Wildlife Research Unit Technical Report No. 9. 98 pp.

Montague, C.L., A.V. Zale, and H.F. Percival. 1984b. Photographic
analysis of natural and impounded salt marsh in the vicinity of
Merritt Island, Florida. Florida Cooperative Fish and Wildlife
Research Unit Technical Report No. 11. 23 pp.

Moody, W.D. 1950. A study of the natural history of the spotted
seatrout, Cynoscion nebulosus, in the Cedar Key, Florida area.
Q. J. Fla. Acad. Sci. 12:147-171.


Morgan, P.H. 1974. A study of
three-river delta system -
rivers of South Carolina.
92 pp.


tidelands and impoundments within a
the South Edisto, Ashepoo and Combahee
MS Thesis, Univ. of Georgia, Athens, GA.


Morgan, P.H., A.S. Johnson, W.P. Baldwin, and J.L. Landers. 1975.
Characteristics and management of tidal impoundments for wildlife
in a South Carolina estuary. Proc. Ann. Conf. S.E. Assoc. Game
Fish Comm. 29:526-539.

Mulholland, R. 1984. Habitat suitability index models: hard clam.
U.S. Fish Wildl. Serv. FWS/OBS-82/10.77. 21 pp.









Neely, W.W. 1960. Managing Scirpus robustus for ducks. Proc. S.E.
Assoc. Game Fish Comm. 14:30-34.

Neely, W.W. 1968. Planting, disking, mowing, and grazing. Pages
212-221 in J.D. Newsom (ed.). Proc. LSU Marsh and Estuary
Management Symposium, Louisiana State University Division of
Continuing Education, Baton Rouge, LA.

Nichols, J.D., M.J. Conroy, D.R. Anderson, and K.P. Burnham. 1984.
Compensatory mortality in waterfowl populations: a review of the
evidence and implications for research and management. Trans. N.
Amer. Wildl. Nat. Res. Conf. 49:535-554.

Nielsen, E.T., and A.T. Nielsen. 1953. Field observations on the
habits of Aedes taeniorhynchus. Ecology 34:141-156.

Nixon, S.W. 1980. Between coastal marshes and coastal waters a
review of twenty years of speculation and research on the role of
salt marshes in estuarine productivity and water chemistry. Pages
437-525 in P. Hamilton and K.B. MacDonald (eds.). Estuarine and
wetland processes, Plenum, New York, NY.

Nixon, S.W. 1982. The ecology of New England high salt marshes: a
community profile. U.S. Fish and Wildlife Service, Office of
Biological Services, Washington, D.C. FWS/OBS-81/55. 70 pp.

Nudds, T.D., and J.N. Bowlby. 1984. Predator-prey size relationships
in North American dabbling ducks. Can. J. Zool. 62:2002-2008.

Nudds, T.D., and R.M. Kaminski. 1984. Sexual size dimorphism in
relation to resource partitioning in North American dabbling ducks.
Can. J. Zool. 62:2009-2012.

Odum, E.P. 1971. Fundamentals of ecology. W.B. Saunders, New York,
NY.

Odum, E.P. 1974. Halophytes, energetic and ecosystems. Pages 599-602
in R.J. Reimold and W.H. Queen (eds.). Ecology of halophytes.
Academic Press, Inc., New York, NY.

Odum, E.P., J.B. Birch, and J.L. Cooley. 1983. Comparison of giant
cutgrass productivity in tidal and impounded marshes with special
reference to tidal subsidy and waste assimilation. Estuaries 6:
88-94.

Odum, E.P., and A.A. de la Cruz. 1967. Particulate organic detritus in
a Georgia salt marsh estuarine ecosystem. Pages 383-388 in G.H.
Lauff (ed.). Estuaries. AAAS Publ. No. 83.

Odum, E.P., and M.E. Fanning. 1973. Comparison of the productivity of
Spartina alterniflora and Spartina cynosuroides in Georgia coastal
marshes. Bull. Georgia Acad. Sci. 31:1-12.









Odum, E.P., J.T. Finn, and E.H. Franz. 1979. Peturbation theory and
the subsidy-stress gradient. BioScience 29:349-352.

Odum, E.P., and A.E. Smalley. 1959. Comparison of population energy
flow of a herbivorous and a deposit-feeding invertebrate in a salt
marsh ecosystem. Proc. Nat. Acad. Sci. 45:617-622.

Odum, H.T. 1967. Biological circuits and the marine systems of Texas.
Pages 99-157 in Burgess and Olson (eds.). Pollution and marine
ecology. John Wiley and Sons, New York, NY.

Odum, H.T. 1984. Systems ecology. John Wiley and Sons, New York, NY.
744 pp.

Odum, H.T. In press. Self organization of estuarine ecosystems in
marine ponds receiving treated sewage. North Carolina Sea Grant
No. GH103, Project UNC-10. Data from experimental pond studies at
Morehead City, NC, 1968-72.

Odum, W.E. 1966. The food and feeding of the striped mullet, Mugil
cephalus, in relation to the environment. MS Thesis, Univ. of
Miami, Miami, FL. 118 pp.

Odum, W.E. 1968. The ecological significance of fine particle
selection by the striped mullet, Mugil cephalus. Limnol. Oceanogr.
133:92-98.

Odum, W.E. 1-969. The structure of detritus based food chains in a
south Florida mangrove system. Ph.D. Diss., Univ. of Miami, Miami,
FL.
Odum, W.E. 1970a. Insidious alteration of the estuarine environment.
Trans. Am. Fish. Soc. 99:836-847.

Odum, W.E. 1970b. Utilization of the direct grazing and plant detritus
food chain by the striped mullet Mugil cephalus. Pages 222-240 in
J.H. Steele (ed.). Marine food chains, a symposium. Oliver and
Boyd, Edinburgh.

Odum, W.E., J.S. Fisher, and J.C. Pickral. 1979. Factors controlling
the flux of particulate organic carbon from estuarine wetlands.
Pages 69-80 in R.J. Livingston (ed.). Ecological processes in
coastal and marine systems. Plenum, New York, NY.

Odum, W.E., and E.J. Heald. 1972. Trophic analyses of an estuarine
mangrove community. Bull. Mar. Sci. 22:671-738.

Odum, W.E., and E.J. Heald. 1975. The detritus based food web of an
estuarine mangrove community. Pages 265-286 in Estuarine research.
Academic Press, New York, NY.

Odum, W.E., and M.A. Heywood. 1978. Decomposition of intertidal
freshwater marsh plants. Pages 89-97 in R.E. Good, D.F. Whigham
and R.L. Simpson (eds.). Freshwater wetlands: ecological processes
and management potential. Academic Press, Inc., New York, NY.









OTA (Office of Technology Assessment) 1984. Wetlands: their use and
regulations. U.S. Congress OTA-0-206. 208 pp.

Onuf, C.P., M.L. Quammen, G.P. Shaffer, C.H. Peterson, J.W. Chapman,
J. Cermak, and R.W. Holmes. 1979. An analysis of the values of
central and southern California coastal wetlands. Pages 186-199 in
P.E. Greeson, J.R. Clark, and J.E. Clark (eds.). Wetland functions
and values: the state of our understanding. Proceedings of the
National Symposium on Wetlands, 7-10 November 1978, Lake Buena
Vista, FL.

Orth, R.J., K.L. Heck, Jr., and J. van Montfrans. 1984. Faunal com-
munities in seagrass beds: a review of the influence of plant
structure and prey characteristics on predator prey relation-
ships. Estuaries 7:339-350.

Parker, R.R., J. Sibert, and T.J. Brown. 1975. Inhibition of primary
productivity through heterotrophic competition for nitrate in a
stratified estuary. J; Fish Res. Board Can. 32:72-77.

Patrick, W.H., Jr., and R.D. DeLaune. 1976. Nitrogen and phosphorus
utilization by Spartina alterniflora in a salt marsh in Barataria
Bay, Louisiana. Est. Coast. Mar. Sci. 4:59-64.

Patrick, W.H., Jr., and R.A. Khalid. 1974. Phosphate release and
absorption by soils and sediments: effect of aerobic and anaerobic
conditions. Science 186:53-55.

Peterson, B.J., R.W. Howarth, and R.H. Garritt. 1985. Multiple stable
isotopes used to trace the flow of organic matter in estuarine food
webs. Science 227:1361-1363.

Pomeroy, L.R. 1970. The strategy of mineral cycling. Ann. Rev. Ecol.
Syst. 1:171-190.

Pomeroy, L.R. 1980. Detritus and its role as a food source. Pages
84-102 in R.K. Barnes and K.H. Mann (eds.). Fundamentals of
aquatic ecosystems. Blackwell Scientific Publications, Oxford.

Pomeroy, L.R. and R.G. Wiegert (eds.). 1981. The Ecology of a Salt
Marsh. Ecological Studies 38, Springer-Verlag, New York 271 pp.

Pomeroy, L.R., E.E. Smith, and C.M. Grant. 1965. The exchange of
phosphate between estuarine water and sediments. Limnol. Oceanogr.
10:167-172.

Pomeroy, L.R., R.E. Johannes, E.P. Odum, and B. Roffman. 1969. The
phosphorus and zinc cycles and productivity of a salt marsh. Pages
412-419 in D.J. Nelson and F.C. Evans (eds.). Symposium on radio-
ecology. U.S. Atomic Energy Comm., Washington, DC.

Pomeroy, L.R., L.R. Shenton, R.D. Jones, and R.J. Reimold. 1972.
Nutrient flux in estuaries. Amer. Soc. Limnol. Oceanogr. Spec.
Symp. 1:274-291.









Pomeroy, L.R., K. Bancroft, J. Breed, R.R. Christian, D. Frankenberg,
J.R. Hall, L.G. Maurer, W.J. Wiebe, R.G. Wiegert, and R.L. Wetzel.
1977. Flux of organic matter through a salt marsh. Pages 270-279
in M. Wiley (ed.). Estuarine processes, Vol. II. Academic Press,
New York, NY.

Pospahala, R.S., D.R. Anderson, and C.J. Henry. 1974. Population
ecology of the mallard. II. Breeding habitat conditions, size of
the breeding populations and population indices. U.S. Fish &
Wildl. Serv. Res. Publ. 115. Washington, DC. 73 pp.

Postma, H. 1980. Sediment transport and sedimentation. Pages 153-186
in E. Olausson and I. Cato (eds). Chemistry and biogeochemistry of
estuaries. John Wiley and Sons, New York, NY.

Presley, B.J., and J.H. Trefry. 1980. Sediment-water interactions and
the geochemistry of interstitial waters. Pages 187-232 in E.
Olausson and I. Cato (eds.). Chemistry and biogeochemistry of
estuaries. John Wiley-and Sons, New York, NY.

Prevost, M.B., A.S. Johnson, and J.L. Landers. 1978. Production and
utilization of waterfowl foods in brackish impoundments in South
Carolina. Proc. Ann. Conf. S.E. Assoc. Fish Wildl. Agencies
32:60-70.

Provost, M.W. Undated. Charles H. Trost's study of wildlife usage of
salt marsh on the east coast of Florida before and after impound-
ment for mosquito and sandfly control. Appendix: analysis by
marsh and by species. Bureau of Sport Fisheries and Wildlife,
Contract No. 14-16-0008-623. 26 pp.

Provost, M.W. 1948. Marsh-blasting as a wildlife management technique.
J. Wildl. Manage. 12:350-387.

Provost, M.W. 1959. Impounding salt marshes for mosquito control and
its effects on bird life. Fla. Nat. 32:163-169.

Provost, M.W. 1968. Managing impounded salt marsh for mosquito
control and estuarine resource conservation. Pages 163-171 in J.D.
Newsom (ed.). Proc. L.S.U. Marsh and Estuary Management Symposium,
Louisiana State University Division of Continuing Education, Baton
Rouge, LA.

Provost, M.W. 1969a. Ecological control of salt marsh mosquitoes with
side benefits to birds. Proc. Tall Timbers Conf. on Ecological
Animal Control by Habitat Management 1:193-206.

Provost, M.W. 1969b. Man mosquitos and birds. Fla. Nat. April 1969:
63-67.

Provost, M.W. 1973a. Mean high water mark and use of tidelands in
Florida. Fla. Sci. 36:50-66.









Provost, M.W. 1973b. Salt marsh management in Florida. Proc. Tall
Timbers Conf. on Ecological Animal Control by Habitat Management
5:5-17.

Provost, M.W. 1977. Source reduction in salt-marsh mosquito control:
past and future. Mosquito News 37:689-698.

Rae, K.M., and R.G. Bader. 1960. Clay-mineral sediments as a reservoir
for radioactive materials in the sea. Proc. Gulf Carib. Fish.
Inst. 12:55-61.

Rapport, D.J., H.A. Regier, and T.C. Hutchinson. 1985. Ecosystem
behavior under stress. Am. Nat. 125:617-640.

Reeves, H.M., H.D. Dill, and A.S. Hawkins. 1968. A case study in
Canada goose management: the Mississippi valley population. Pages
701-722 in R. L. Hine and C. Schoenfeld (eds). Dembar Educational
Research Services, Madison, WI.

Reimold, R.J. 1972. The movement of phosphorus through the salt marsh
cord grass, Spartina alterniflora Loisel. Limnol. Oceanogr. 17:
606-611.

Reimold, R.J., and F.C. Daiber. 1970. Dissolved phosphorus concentra-
tions in a natural salt-marsh of Delaware. Hydrobiologia 36:
361-371.

Reinecke, K.J. 1981. Winter waterfowl research needs and efforts in
the Mississippi Delta. Pages 231-235 in Fourth international
waterfowl symposium, 30 January 1 February 1981, New Orleans, LA.
Ducks Unlimited.

Reis, R.R. 1977. Temporal variation in utilization of a high marsh
intertidal creek by larval and juvenile fish. MS Thesis, Univ. of
South Carolina, Columbia, SC. 68 pp.

Reis, R.R., and J.M. Dean. 1981. Temporal variation in the utilization
of an intertidal creek by the bay anchovy (Anchoa mitchilli).
Estuaries 4:16-23.

Ricker, W.E. 1975. Computation and interpretation of biological
statistics of fish populations. Bull. Fish. Res. Board Can. No.
191. 382 pp.

Rogers, J.P. 1979. Symposium summary and comments on the future of
waterfowl and wetlands. Pages 143-147 in T.A. Bookhout (ed.).
Waterfowl and wetlands: an integrated review. Proc. 1977 Symp.,
Madison, WI. N. Cent. Sect., The Wildlife Society.

Rozas, L.P., and C.T. Hackney. 1984. Use of oligohaline marshes by
fishes and macrofaunal crustaceans in North Carolina. Estuaries
7:213-224.









Ryther, J.H. 1954. The ecology of phytoplankton blooms in Moriches
Bay and Great South Bay, Long Island, New York. Biol. Bull.
106:198-209.

Ryther, J.H. 1956. Photosynthesis in the ocean as a function of light
intensity. Limnol. Oceanogr. 1:61-70.

Ryther, J.H., and W.M. Dunstan. 1971. Nitrogen, phosphorus, and
eutrophication in the coastal marine environment. Science 171:
1008-1013.

Sanders, H.L. 1968. Marine benthic diversity: a comparative study.
Am. Nat. 102:243-282.

Shenker, J., and J.M. Dean. 1979. The utilization of an intertidal
salt marsh creek by larval and juvenile fishes: abundance,
diversity and temporal variations. Estuaries 2:154-163.

Shillinger, J.E., and C.S. Cottam. 1937. The importance of lead
poisoning in waterfowl. Trans. N. Am. Wildl. Conf. 2:398-403.

Sikora, W.B., and J.P. Sikora. 1982. Ecological implications of the
vertical distribution of meiofauna in salt marsh sediments. Pages
269-282 in V.S. Kennedy (ed.). Estuarine comparisons. Academic
Press, New York, NY.

Smalley, A.E. 1959. The growth cycle of Spartina and its relation to
the insect population in the marsh. Pages 96-100 in Proc. Salt
Marsh Conf., Marine Inst., University of Georgia, Athens, GA.

Snelson, F.F., Jr. 1980. Volume III of IV: Part I Ichthyological
studies; ichthyological survey of lagoonal waters. A continuation
of base-line studies for environmentally monitoring space transpor-
tation systems (STS) at John F. Kennedy Space Center. 119 pp.

Snelson, F.F., Jr. 1983. Ichthyofauna of the northern part of the
Indian River lagoon system, Florida. Fla. Sci. 46:187-206.

Stickney, R.R., and M.L. Cuenco. 1982. Habitat suitability index
models: juvenile spot. U.S. Dept. Int. Fish Wildl. Serv.
FWS/OBS-82/10.20. 12 p.

Stieglitz, W.O., and C.T. Wilson. 1968. Breeding biology of the
Florida duck. J. Wildl. Manage. 32:921-934.

Strong, D.R., Jr., D. Simberloff, L.G. Abele, and A.B. Thistle. 1984.
Ecological communities: conceptual issues and the evidence.
Princeton Univ. Press, Princeton, NJ. 614 pp.

Subrahmanyam, C.B., and S.H. Drake. 1975. Studies on the animal
communities in two north Florida salt marshes. Bull. Mar. Sci. 25:
445-465.









Sweet, H.C. 1976. Botanical studies of Merritt Island. Final report
NGR10.019 004 to NASA from Florida Technological University,
Orlando, Florida. 258 p.

Swiderek, P.K., A.S. Johnson, P.E. Hale, and R.L. Joyner. 1985. Sea
purslane, gulf coast muskgrass, and widgeongrass in brackish
impoundments. draft manuscript presented at Waterfowl in Winter
symposium and workshop, 7-10 January 1985, Galveston, TX.

Tabb, D.C. 1966. The estuary as a habitat for spotted seatrout
(Cynoscion nebulosus). Pages 59-67 in R.S. Smith (chairman). A
symposium on estuarine fishes. Am. Fish. Soc. Spec. Publ. No. 3.

Talbot, C.W., and K.W. Able. 1984. Composition and distribution of
larval fishes in New Jersey high marshes. Estuaries 7:434-443.

Teal, J.M. 1962. Energy flow in the salt marsh ecosystem of Georgia.
Ecology 43:614-624.

Teal, J.M. 1980. Primary production of benthic and fringing plant
communities. Pages 67-83 in R.K. Barnes and K.H. Mann (eds.).
Fundamentals of aquatic ecosystems. Blackwell Scientific Publica-
tions, Oxford.

Tenore, K.R., L. Cammen, S.E.G. Findlay, and N. Phillips. 1982.
Perspectives of research on detritus: do factors controlling the
availability of detritus to macroconsumers depend on its source?
J. Mar. Res. 40:473-490.

Thayer, G.W. 1974. Identity and regulation of nutrients limiting
phytoplankton production in the shallow estuaries near Beaufort,
N.C. Oecologia 14:75-92.


Thayer, G.W., W.J. Kenworthy, and M.S. Fonseca.
eelgrass meadows of the Atlantic coast: a
Fish Wildl. Serv. FWS/OBS-84/02. 147 pp.

Thayer, G.W., P.L. Parker, M.W. LaCroix, and B.
carbon isotope ratio of some components of
marina, bed. Oecologia 35:1-12.


1984. The ecology of
community profile. U.S.


Fry. 1978. Stable
an eelgrass, Zostera


Thomas, C. 1982. Winter ecology of dabbling ducks in central Florida.
MS Thesis, Univ. of Missouri, Columbia, MO. 60 pp.


Tiner, R.W., Jr. 1984.
and recent trends.
Wetlands Inventory.


Wetlands of the United States: current status
U.S. Fish and Wildlife Service, National
59 pp.


Trost, C.H. Undated. Study of wildlife usage of salt marsh on the east
coast of Florida before and after impoundment for mosquito and
sandfly control. Final report. Bureau of Sport Fisheries and
Wildlife, Contract No. 14-16-0008-623. 30 pp.

Turner, R.E. 1976. Geographic variation in salt marsh macrophyte
production: a review. Contrib. Mar. Sci. 20:47-68.










Valentine, J.W. 1973. Evolutionary ecology of the marine biosphere.
Prentice-Hall, Inc. Englewood Cliffs, N.J. 511 pp.

Valiela, I. 1984. Marine ecological processes. Springer-Verlag, New
York, NY.

Valiela, I., J.M. Teal, and N.Y. Persson. 1976. Production and
dynamics of experimentally enriched salt marsh vegetation:
belowground biomass. Limnol. Ocanogr. 21:245-252.

Valiela, I., and J.M. Teal. 1979a. Inputs, outputs and interconver-
sions of nitrogen in a salt marsh ecosystem. Pages 399-414 in R.L.
Jefferies and A.J. Davy (eds.). Ecological processes in coastal
environments. Blackwell, London.

Valiela, I., J.M. Teal, S. Volkmann, D. Shafer, and E.J. Carpenter.
1978. Nutrient and particulate fluxes in a salt marsh ecosystem:
Tidal exchanges and inputs by precipitation and groundwater.
Limnol. Oceanogr. 23: 798-812.

Valiela, I., and J.M. Teal. 1979b. The nitrogen budget of a salt marsh
ecosystem. Nature 280:652-656.

Valiela, I., S. Vince, and J.M. Teal. 1976b. Assimilation of sewage by
wetlands. Pages 234-253 in M. Wiley (ed.). Estuarine processes.

Van Den Avyle, M.J., and D.L. Fowler. 1984. Species profiles: life
histories and environmental requirements of coastal fishes and
invertebrates (South Atlantic) -- blue crab. U.S. Fish Wildl. Serv.
FWS/OBS-82/11.19. U.S. Army Corps of Engineers TR EL-82-4. 16 pp.

Vince, S., I. Valiela, N. Backus, and J.M. Teal. 1976. Predation by
the salt marsh killifish Fundulus heteroclitus (L.) in relation to
prey size and habitat structure: consequences for prey distribu-
tion and abundance. J. Exp. Mar. Biol. Ecol. 23:255-266.

Voigts, D.K. 1976. Aquatic invertebrate abundance in relation to
changing marsh vegetation. Am. Midi. Nat. 95:313-322.

Vogal, R.J. 1980. The ecological factors that produce perturbation-
dependent ecosystems. Pages 63-94 in J. Cairns, Jr. (ed.). The
recovery process in damaged ecosystems. Ann Arbor Science, Ann
Arbor, MI.

Walker, R.L. and K.R. Tenore. 1984. The distribution and production of
the hard clam, Mercenaria mercenaria, in Wassaw Sound, Georgia.
Estuaries 7:19-27.

Weinstein, M.P. 1979. Shallow marsh habitats as primary nurseries for
fishes and shellfish, Cape Fear River, North Carolina. U.S. Fish.
Bull. 77:339-357.









Weinstein, M.P., L.S. Scott, S.P. O'Neil, R.C. Siegfried II, and S.T.
Szedlmayer. 1984. Population dynamics of the spot, Leiostomus
xanthurus, in polyhaline tidal creeks of the York River Estuary,
Virginia. Estuaries 7:444-450.

Weinstein, M.P., and M.P. Walters. 1981. Growth, survival and
production in young-of-year populations of Leiostomus xanthurus
Lacepede residing in tidal creeks. Estuaries 4:185-197.

Weinstein, M.P., S.L. Weiss, and M.F. Walters. 1980. Multiple determi-
nants of community structure in shallow marsh habitats, Cape Fear
River Estuary, North Carolina, USA. Mar. Biol. 58:227-243.

Welsh, B. 1975. The role of grass shrimp, Palaemonetes pugio, in a
tidal marsh ecosystem. Ecology 56:513-530.

Wetzel, R.G. 1975. Limnology. W.B. Saunders, Co., Philadelphia, PA.
743 pp.

Wetzel, R.L. 1975. An experimental study of detrital carbon
utilization in a Georgia salt marsh. Ph.D. Diss., Univ. of
Georgia, Athens, GA.

Wetzel, R.L. 1977. Carbon resources of a benthic salt marsh
invertebrate, Nassarius obsoletus Say (Mollusca: Nassaridae).
Estuarine processes. Vol. 2:293-308. Academic Press, New York,
NY.

White, D.H., and D. James. 1978. Differential use of freshwater
environments by wintering waterfowl of coastal Texas. Wilson Bull.
90:99-111.

Whitman, W.R. 1976. Impoundments for waterfowl. Occas. Pap. No. 22,
Canadian Wildl. Serv. 22 pp.

Whitney, D.E., A.G. Chalmers, E.B. Haines, R.B. Hanson, L.R. Pomeroy,
and B. Sherr. 1981. The cycles of nitrogen and phosphorus. Pages
163-182 in L.R. Pomeroy and R.G. Wiegert (eds.). The ecology of a
salt marsh. Ecological Studies 38, Springer-Verlag, New York, NY.

Wicker, K.M., D. Davis, and D. Roberts. 1983. Rockefeller State
Wildlife Refuge and Game Preserve: evaluation of wetland management
techniques. Louisiana Dept. Nat. Res., Baton Rouge, LA.

Wiegert, R.G. 1979. Ecological processes characteristic of coastal
Spartina marshes of the south-eastern U.S.A. Pages 467-490 in R.L.
Jefferies and A.J. Davy (eds.). Ecological processes in coastal
environments. Blackwell, London.

Wiegert, R.G., A.G. Chalmers, and P.F. Randerson. 1983. Productivity
gradients in salt marshes: the response of Spartina alterniflora to
experimentally manipulated soil water movement. Oikos 41:1-6.









Wilkinson, P.M. 1983. Nesting ecology of the American alligator in
coastal South Carolina. Study completion report, August 1978 -
September 1983. South Carolina Wildlife and Marine Resources
Department. 113 pp.


Wilson, J.A. 1972. Principles of animal physiology.
Publishing Co., New York, NY. 842 pp.


MacMillan


Yancey, R.K.
Linduska
DC. 770


1964.
(ed.).
pp.


Matches and marshes.
Waterfowl tomorrow.


Pages 619-626 in J.P.
U.S. Dept. Int. Washington,


Zieman, J.C. 1982. The ecology of the seagrasses of south Florida: a
community profile. U.S. Fish and Wildlife Services, Office of
Biological Services, Washington, D.C. FWS/OBS-82/85. 158 pp.


Zilberberg, M.H. 1966. Seasonal
marsh of northwest Florida.


occurrence of fishes in a coastal
Contrib. Mar. Sci. 11:126-134.




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