• TABLE OF CONTENTS
HIDE
 Front Cover
 Title Page
 Disclaimer
 Preface
 Table of Contents
 List of Figures
 List of Tables
 Conversion table
 Acknowledgement
 Introduction
 Description of the environment
 Biological characteristics
 Ecological interrelationships
 Management
 Reference
 Back Matter
 Back Cover






Group Title: Biological report 85 (7.18)
Title: The ecology of Tampa Bay, Florida--an estuarine profile
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00000109/00001
 Material Information
Title: The ecology of Tampa Bay, Florida--an estuarine profile
Series Title: Biological report - U.S. Fish and Wildlife Service ; 85 (7.18)
Physical Description: xv, 132 p. : ill. ; 28 cm.
Language: English
Creator: Lewis, Roy R., 1944-
Estevez, Ernest D
National Wetlands Research Center (U.S.)
Publisher: Fish and Wildlife Service, U.S. Dept. of the Interior
Place of Publication: Washington, D.C,
Publication Date: 1988
 Subjects
Subject: Estuarine ecology -- Florida -- Tampa Bay   ( lcsh )
Genre: bibliography   ( marcgt )
federal government publication   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (p. 117-132).
General Note: "September 1988."
General Note: "Performed for U.S. Department of the Interior, Fish and Wildlife Service, Research and Development, National Wetlands Research Center, Washington, DC."
Statement of Responsibility: by Roy R. Lewis III and Ernest D. Estevez ; project officer, Edward C. Pendleton.
 Record Information
Bibliographic ID: UF00000109
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltqf - AAA0362
ltuf - AME7137
oclc - 17770914
alephbibnum - 002441924
lccn - 88600102

Table of Contents
    Front Cover
        Front Cover 1
        Front Cover 2
    Title Page
        Page i
    Disclaimer
        Page ii
    Preface
        Page iii
        Page iv
    Table of Contents
        Page v
        Page vi
    List of Figures
        Page vii
        Page viii
        Page ix
        Page x
        Page xi
    List of Tables
        Page xii
        Page xiii
    Conversion table
        Page xiv
    Acknowledgement
        Page xv
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
    Description of the environment
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
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        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
    Biological characteristics
        Page 55
        Page 56
        Page 57
        Page 58
        Page 59
        Page 60
        Page 61
        Page 62
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        Page 90
        Page 91
        Page 92
        Page 93
        Page 94
        Page 95
        Page 96
        Page 97
    Ecological interrelationships
        Page 98
        Page 99
        Page 100
        Page 101
    Management
        Page 102
        Page 103
        Page 104
        Page 105
        Page 106
        Page 107
        Page 108
        Page 109
        Page 110
        Page 111
        Page 112
        Page 113
        Page 114
        Page 115
        Page 116
    Reference
        Page 117
        Page 118
        Page 119
        Page 120
        Page 121
        Page 122
        Page 123
        Page 124
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        Page 131
        Page 132
    Back Matter
        Page 133
        Page 134
    Back Cover
        Page 135
        Page 136
Full Text

























.LW~


Mir




















































Cover photographs:
Upper left: Brown pelican (Pelecanus occidentalis) on a nest in mangroves in Terra Ceia Bay.
Upper right: Tampa baseball player Dazzy Vance (left) and local guide Ed Alexander (right) with reddish
(Sciaenops ocellatus), December 1931.
Lower: View of ships at the docks of the old Lee Terminal on Tampa Bay, October 13,1919.


















Biological Report 85(7.18)
September 1988





THE ECOLOGY OF TAMPA BAY, FLORIDA: AN ESTUARINE PROFILE


by


Roy R. Lewis III
Mangrove Systems, Inc.
P. 0. Box 290197
Tampa, FL 33687


and


Ernest D. Estevez
Mote Marine Laboratory
1600 City Island Park
Sarasota, FL 33577






Project Officer

Edward C. Pendleton
U.S. Fish and Wildlife Service
National Wetlands Research Center
1010 Gause Boulevard
Slidell, LA 70458





Performed for

U.S. Department of the Interior
Fish and Wildlife Service
Research and Development
National Wetlands Research Center
Washington, DC 20240




















DISCLAIMER


The mention of commercial product trade names in this report does not
constitute endorsement or recommendation for use by the Fish and Wildlife
Service, U.S. Department of the Interior.















Library of Congress Cataloging-in-Publication Data

Lewis, Roy R., 1944-
The ecology of Tampa Bay, Florida.

(Biological report 85(7.18) (May 1988))
"Performed for National Wetlands Research Center,
Research and Development, Fish and Wildlife Service,
U.S. Department of the Interior, Washington, DC."
Bibliography: p.
1. Estuarine ecology--Florida--Tampa Bay.
I. Estevez, Ernest D. II. Title. III. National
Wetlands Research Center (U.S.) IV. Series: Biological
report (Washington, D.C.) ; 85-7.18.


QH105.F6L49 1988 574.5'26365'0916364


88-600102


This report should be cited as:

Lewis, R.R., III, and E.D. Estevez. 1988. The ecology of Tampa Bay, Florida: an
estuarine profile. U.S. Fish Wildl. Serv. Biol. Rep. 85(7.18). 132 pp.

















PREFACE


The width, depth, and perimeter of;
Tampa Bay have changed over the past;
century due to natural and human causes,
and so have the numbers, kinds, and dis-!
tributions of plants and animals in the,
bay. Society's uses of the bay and atti-
tudes toward it also have been changing,
and these changes can be read in the bay s
past and present condition.


We are entering a new era in a series
of bay-management eras. At first, the bay
was a completely natural ecosystem,
affected little by the small, prehistoric-
human populations that lived along the
shore. In the second era--beginning with
Spanish fishing camps and ending with the
demise of -sturgeon late in the 19th
century--the bay s natural fertility was
exploited without harm to the underlying
ecosystem./ The bay enabled and richly
subsidized the region's settlement and
made fortunes for many poor settlers.
Exploitation of the bay's resources con-
tinued into the third era, which was a
period when projects for public and
private gain began to affect the system.
Local areas or resources of the bay were
declining in area of productivity, but the
losses were imperceptible against the
relatively limitless expanse of adjacent
bay and coastal reaches.


The third era began a period of
resource erosion that continues to the
present, but was different from modern
times because there was no basis in
science or law for understanding or con-
trolling impacts. The science of ecology
would not develop for decades and there
was no bay attitude comparable to a farm
land ethic which could foresee the long-
term, cumulative consequences of super-
ficially beneficial projects.


The fourth era arose about 25 years
ago when the overall condition of the bay
was considered to be failing or in very
poor condition. This era was significant
for signalling the treatment of the bay
as a conceptual unit and ecological entity:
a single, albeit immense, landscape
element. This era was also marked by
scientific studies of things and events in
the bay, and by the advent of rudimentary
health and environmental regulations.
Unfortunately, the fourth era has been a
period of extensive resource decline, and
recent events seem even less acceptable
given heightened awareness of the bay's
working and importance and the numerous
laws and regulations which are popularly
believed to prevent such damage.

The new era in bay management is
perhaps the most critical in the history
of human settlement in the region because
events of the new era may be irreversible,
at least compared with those of the past.
On the one hand, assaults to the bay from
physical changes, chemical wastes, or
stock depletion may occur with heretofore
unheard-of magnitudes. On the other hand,
there is widespread support for preserving
the bay and for restoring parts of it to
cause a net improvement in its existing
condition. Within liberal limits it is
entirely within our ability to make Tampa
Bay whatever we choose. Hopefully the
information in this Estuarine Profile will
help as society makes that choice. We
concur fully with a conclusion of the
Tampa Bay Area Scientific Information
Symposium (BASIS) that "with proper
management and restoration, the Bay
would become perceptibly more productive
and valuable to its users."

We are grateful to the resource
managers, environmental specialists,
regulatory agency staff, scientists, and










students who have helped to generate
information about Tampa Bay during the
past 30 years. The job of writing this
profile was simplified greatly by the
authors of BASIS reports, and by subse-
quent information produced by the Tampa
Bay Regional Planning Council, Agency on
Bay Management, and other offices of
government. For their roles in fostering
the wise stewardship of Tampa Bay we also
wish to dedicate this volume to Melvin
Anderson, John V. Betz, Sally Casper,
Betty Castor, Don Castor, William 0.
Courser Lamar Cox, Mary Grizzle, Robert
King, Plant Norton, Jan Platt, Bernard E.
Ross, Joseph L. Simon, Roger Stewart,
Sally Thompson, and William H. Taft.

In the time that has passed between
the preparation and publication of this
estuarine profile, progress has been
made on several fronts in Tampa Bay.
Although bay management has improved,
our original conclusions regarding the
shortfalls of existing programs are
still basically correct. Progress has
also been made in some areas of bay
science. For example, new and useful
studies of sediments have recently ended
(and others have begun) in Hillsborough
Bay, and a major basin-wide study of the
Little Manatee River is underway. In
addition, a major new program to assist
Tampa Bay and other Florida surface-
water management (the Surface Water
Improvement and Management or SWIM Bill)
passed and received funding during the
1987 legislative session. A NOAA
"Estuary of the Month Seminar" was held
in Washington, D.C., in December 1987 on
Tampa and Sarasota Bays, and many recent
bay projects will be summarized in the
proceedings of the seminar, scheduled
for release in 1988.


Lastly, this profile was one of
several products produced as a result of
a 3-year cooperative study by the U.S.
Fish and Wildlife Service and the Tampa
Port Authority. Other products include:

Auble, G.T., A.K. Andrews, D.B. Hamilton,
and J.E. Roelle. 1985. Fish and
wildlife mitigation options for port
development in Tampa Bay: results of a
workshop. U.S. Fish Wildl. Serv.
NCET Open File Rep. 85-2. 36 pp.
Dial R.S. and D.R. Deis. 1986. Mitiga-
tion options for fish and wildlife
resources affected by port and other
water-dependent developments in Tampa
Bay, Florida. U.S. Fish Wildl. Serv.
Biol. Rep. 86(6). 150 pp.
Fehring, W.K. 1986. Data bases for use
in fish and wildlife mitigation planning
in Tampa Bay Florida: project summary.
U.S. Fish Wildl. Serv. NWRC Open File
Rep. 86-6. 38 pp.
Kunneke, J.T., and T.F. Palik. 1984.
Tampa Bay environmental atlas. U.S.
Fish Wildl. Serv. Biol. Rep. 85(15).
78 pp + 38 maps (Al through B21).
U.S. Fish and Wildlife Service. 1986.
Tampa Bay habitat (wetland and upland)
maps and data--1950's, 1972, and 1982.
National Wetlands Research Center,
Slidell, LA.

Comments concerning or requests for
this publication should be addressed to:

Information Transfer Specialist
National Wetlands Research Center
U.S. Fish and Wildlife Service
1010 Gause Boulevard
Slidell, LA 70458
(504) 646-7287, FTS 680-7287.


















CONTENTS


Page

PREFACE ............................................ .............. iii
CONTENTS .......................................................... v
FIGURES ............................................................. vii
TABLES .............................................................. xii
CONVERSION TABLE .................................................. xiv
ACKNOWLEDGMENTS ...................................................... xv

1. INTRODUCTION ................. ................................ 1
1.1 Tampa Bay as a Natural Unit ................................ 1
1.2 Political Subunits of the Bay .............................. 1
1.3 Biological Subunits of the Bay ............................. 1
1.4 Potential Conflicts and Impacts ............................ 5

2. DESCRIPTION OF THE ENVIRONMENT ................................. 7
2.1 Geological Origin and Evolution ............................ 7
2.1.1 Geological Formations Relevant to Tampa Bay .......... 8
2.1.2 The Effects of Glaciation ............................ 10
2.1.3 Development of the Modern Bay ........................ 11
2.2 The Hydrologic Cycle ....................................... 13
2.2.1 Insolation and Cloudiness ............................ 14
2.2.2 Atmospheric Pressure and Wind ........................ 15
2.2.3 Temperature ......................................... 15
2.2.4 Evapotranspiration and Relative Humidity ............. 16
2.2.5 Fog and Rain ......................................... 16
2.2.6 Thunderstorms and Hurricanes ......................... 16
2.3 Surface and Ground Waters .................................. 18
2.3.1 Overview of Tributaries to Tampa Bay ................. 18
2.3.2 Flows .................... ....... .. ................. 18
2.3.3 Constituent Concentrations and Loads ................. 20
2.3.4 Structure of Ground -water Systems Under the Bay ..... 22
2.3.5 Ground-water Discharges to Tampa Bay .................. 23
2.4 Hydrographic Characteristics of Tampa Bay .................. 25
2.4.1 Shape and Shorelines ................................. 25
2.4.2 Depth ................................................ 26
2.4.3 Bottom Features ..................................... 26
2.4.4 Sea Level and Tides .................................. 28
2.4.5 Circulation and Flushing ............................. 30
/ 2.5 Chemistry of the Bay ...................................... 34
2.5.1 General Water Quality of Tampa Bay ................... 36
2.5.2 Hydrographic Parameters .............................. 37
2.5.3 Nutrients ............................................ 47
2.5.4 Sediments ............................................ 50
2.6 Area Summaries ............................................. 52
2.6.1 Hillsborough Bay ..................................... 52
2.6.2 Old Tampa Bay ....................................... 52










Page

2.6.3 Middle Tampa Bay ..................................... 52
2.6.4 Lower Tampa Bay ...................................... 52
2.6.5 Boca Ciega Bay ....................................... 53
2.6.6 Terra Ceia Bay and the Manatee River ................ 53
2.7 Comparison of Tampa Bay to Charlotte Harbor ................ 53

3. BIOLOGICAL CHARACTERISTICS ..................................... 55
3.1 Phytoplankton ............................................. 55
3.2 Benthic Microalgae ........................................ 56
3.3 Epiphytic Microalgae ...................................... 57
3.4 Attached and Drift Macroalgae ................... .......... 57
3.5 Seagrass Meadows .......................................... 58
3.6 Tidal Marshes ............................................ 66
3.7 Mangrove Forests .......................................... 68
3.8 Riverine Forests and Adjacent Wetlands .................... 74
3.9 Total Primary Production and Organic Material Input ....... 74
3.10 Secondary Producers ....................................... 74
3.11 Zooplankton ............................................... 75
3.12 Benthos ................................................... 81
3 .13 Fish ...................................................... 87
3.14 Reptiles .................................................. 92
3 .15 Birds ..................................................... 92
3.16 Marine Mammals ............................................ 96

4. ECOLOGICAL INTERRELATIONSHIPS
4.1 Introduction ............................................... 98
4.2 Energy Sources ............................................. 98
4.3 Abiotic Controls in Communities .................. .......... 98
4.4 Plant and Animal Interactions .............................. 99
4.5 Fisheries Habitats ......................................... 99

5. MANAGEMENT
5.1 Introduction .............. ................................ 102
5.2 Important Management Issues ................................ 106
5.2.1 Dredge and Fill ...................................... 106
5.2.2 Fisheries ........................................... 109
5.2.3 Freshwater Flow to the Bay ........................... 110
5.2.4 Eutrophication ....................................... 112
5.2.5 Other Management Considerations ...................... 114
5.3 Conclusion ......................... ...................... 114

REFERENCES .......................... .............. ............ .. 117


















FIGURES

Number Page

1 Map of Florida showing the location of Tampa Bay on the
peninsular west coast .............. .................... 2

2 The Tampa Bay area watershed extends into six counties ... 4

3 Geographic subdivisons of Tampa Bay ............ ......... 5

4 Vertical aerial photograph of the estuarine shelf
surrounding Tampa Bay .................................. 6

5 Major structural features of Florida ..................... 8

6 Hydrogeology of the Tampa Bay area ....................... 9

7 Geologic formations of the Tampa Bay area ................ 10

8 Approximate stands of Wisconsin sea level ................ 12

9 Terraces of the Tampa Bay area ......................... .. 12

10 Sea level on the southwest Florida coast ................. 13

11 Generalized hydrologic cycle for the Tampa Bay area ...... 14

12 Mean monthly pan evaporation and solar insolation near
Tampa ................................................. 14

13 Mean monthly temperature and extremes for Tampa Bay ...... 15

14 Mean monthly rainfall and extremes for Tampa Bay ......... 16

15 Mean annual rainfall in inches across the Tampa Bay
region ................................................... 17

16 Mean monthly flow in major tributaries to Tampa Bay ...... 19

17 Mean monthly flows in major and minor tributaries, and
mean annual volume delivered to Tampa Bay ................ 20

18 Mean annual constituent loads to Tampa Bay ............... 22

19 Relation of surficial and Floridan aquifers to Tampa Bay
along three axes ......................................... 23

20 Generalized flow in the surficial aquifer, September
1980 .... ................................................. 24











Number Pe

21 Generalized flow in the Floridan Aquifer, September
1980 ................................................. 24

22 Area of potential discharge from the Floridan aquifer,
September 1980 ........................................... 25

23 Areas of physical change in Tampa Bay since 1880 A:
1880-1972; B: 1972-1985 .................................. 26

24 Seasonal changes in tidal duration curves at Cockroach
Bay ...... ................................................ 29

25 Typical and extreme tides in Tampa Bay ................... 30

26 Total tide height above MSL versus return period ......... 31

27 Water movement during a typical flood tide in 1985 ....... 32

28 Residual water movement after a complete tide cycle in
1985 ..................................................... 33

29 Major circulation zones in Tampa Bay ..................... 34

30 Average tributary streamflow and tide-induced circulation
along longitudinal summary lines for 1880, 1972, and 1985
levels of development ... ................................ 35

31 Tide-induced and streamflow flushing of example
constituent along longitudinal summary line, from lower
Tampa Bay to Hillsborough Bay, for 1880, 1972, and 1985
levels of development.. ................................ 35

32 Trends in general water quality for body contact in Tampa
Bay since 1977 ........................................... 36

33 Mid depth water temperature in areas of Tampa Bay since
1975 ...... ............................................... 37

34 Typical (A), high (B), and low (C) specific-conductance
distributions in Tampa Bay ............................... 39

35 Stratification of dissolved oxygen (surface bottom
values) in Hillsborough Bay in relation to depth, 1981
through 1983 ............................................. 40

36 Mean annual dissolved oxygen near the bottom in Tampa
Bay .................................................. 40

37 Mean monthly dissolved oxygen near the bottom in Tampa
Bay ...................................................... 41

38 Mean annual effective (Secchi) light penetration in Tampa
Bay ...... ................................................ 41

39 Mean annual effective light penetration in 1982 .......... 42













40 Changes in mean seasonal light penetration in 1983 ....... 43

41 Bay-wide distributions of light-related parameters in
1982 ................... .......... .................. 44

42 Relation of organic solids to transparency in Tampa Bay .. 45

43 Average monthly turbidity and monthly dredge-spoil
production rate in (A) Hillsborough Bay, and (B) South
Tampa Bay .............................................. 46

44 Trend in phosphate concentrations in Tampa Bay, 1972
through 1981 ..................... . ...... ........... ... 47

45 Nutrient distributions in Tampa Bay ...................... 49

46 Regional trend in (A) mean sediment grain size (phi) and
(B) weight percent of carbonates in Tampa Bay ............ 51

47 Orthophosphate uptake by bay sediments ................... 51

48 Ammonia uptake by bay sediments ................. ........ 51

49 Dissolved oxygen uptake by bay sediments ................. 52

50 Typical Tampa Bay phytoplankton .......................... 55

51 Estimated total drift algae standing crops in Hillsborough
Bay during February 1983-April 1984 ...................... 58

52 Underwater photograph of flowering turtle grass (Thalassia
testudinum), off Snake Key in Lower Tampa Bay ............ 59

53 Seagrass meadow coverage in Tampa Bay, 1985 .............. 60

54 Estimated historical seagrass meadow coverage in Tampa
Bay, ca. 1879 ...................... ..................... 61

55 Seagrass meadow types in Tampa Bay ....................... 62

56 Typical seagrass meadow zonation in Tampa Bay ............ 63

57 Aerial photograph of a perennial healthy fringe seagrass
meadow offshore of Bishops Harbor, Lower Tampa Bay ....... 63

58 Aerial photograph of a perennial mid-bay shoal seagrass
meadow, Lower Tampa Bay .................. .... .......... 63

59 Aerial photograph of a perennial colonizing seagrass
meadow, south side of Courtney Campbell Causeway, Old
Tampa Bay.............................................. 64

60 Comparison of the numbers of species of fish and
invertebrates collected from dense seagrass, sparse
seagrass, and bare sand stations in Lower Tampa Bay ...... 65

ix


Page


Number












61 The generalized distribution of mangrove forests and tidal
marshes in Tampa Bay .................................... 66

62 Typical form of the five dominant plant species found in
intertidal wetlands of Tampa Bay .............. ........... 67

63 Typical tidal marsh along the shores of Tampa Bay with
dominant cover of black needlerush and a lower elevation
fringe of smooth cordgrass .............. ................. 68

64 Distribution of mangroves on an undisturbed shoreline near
Wolf Creek ............................................ 70

65 Typical view of fringing red mangroves, Lower Tampa Bay .. 71

66 Aerial photograph of view across a mangrove forest
bordering Middle Tampa Bay ............................... 71

67 Dead mangroves at Fish Creek in Old Tampa Bay ............ 72

68 Simple Tampa Bay food chain ............... ............ .. 76

69 A generalized Tampa Bay food web ......................... 77

70 Life cycle of the pink shrimp ................ ............ 80

71 Mean densities of Anchoa spp. and sciaenid drum eggs and
larvae reported in three studies of Tampa Bay
ichthyoplankton ........................................ 82

72 Trends in environmental parameters and benthic
invertebrates, Hillsborough Bay 1975-78 .................. 83

73 Underwater photograph of a natural rock reef in Lower
Tampa Bay............................................. 87

74 Stomach content analysis of juvenile Tampa Bay red drum .. 89

75 Life cycle of the red drum along Florida's Gulf coast .... 92

76 Stations and subareas of Tampa Bay sampled by the Bureau
of Commercial Fisheries (National Marine Fisheries
Service), August 1961 through June 1984 ................... 93

77 Occurrence of immature commercially important fish and
shellfish in Tampa Bay, by season and area ............... 93

78 Brown pelican with young in nest in mangroves, Lower Tampa
Bay .................................................... 96

79 Shore birds and wading birds feeding in McKay Bay ........ 96

80 Anoxic conditions in Hillsborough Bay .................... 98

81 Commercial landings of spotted seatrout and red drum ..... 101


Page


Number










Number


Page


82 If all the submerged lands dredged and filled in Tampa Bay
since 1880 were collected in one place, the area would
equal all of the Interbay Peninsula south of Ballast
Point, and surrounding shallow waters above a depth of 2
meters ................................................ 107

83 Tidal marsh creation on Tampa Bay ........................ 108

84 Tampa Bay commercial shellfish and finfish landings ....... 109

85 Florida House of Representatives Resolution 1170
recognizing the importance of Tampa Bay .................. 116

















TABLES


Number age


1 Surface-water discharge to Tampa Bay ..................... 3

2 Summary of areal measurements for subdivisions of Tampa
Bay ....................................................... 6

3 Relation of glacial periods to terraces near Tampa Bay ... 11

4 Tropical cyclones for past 50 years near Tampa Bay ....... 17

5 Land use characteristics (Area, % Total Watershed) of four
authentic rivers flowing to Tampa Bay .................... 18

6 Rank of Tampa Bay tributaries by flow and load ........... 21

7 Physical characteristics of major subareas of Tampa Bay
for 1880, 1972, and projected 1985 levels of develop-
ment .................................................. 27

8 Tide relations in Tampa Bay ................. ............. 29

9 Dissolved oxygen concentrations for bay areas ............ 40

10 Estimated annual phytoplankton production rates in Tampa
Bay ...................................................... 57

11 Mangrove tree size by species and forest type in Tampa
Bay ...................................................... 69

12 Elevation ranges and mean elevations of 10 plant species
occurring in the control area of an undisturbed mangrove
community near Wolf Creek ................................ 71

13 Estimated annual production of primary producers based on
areal coverage in the Tampa Bay system ................... 73

14 Organic inputs to Tampa Bay from allochthonous sources ... 75

15 Holoplankton commonly found in Tampa Bay, grouped by
abundance .............................................. 78

16 Meroplankton species collected by Hopkins (1977) ......... 79

17 Dominant meroplankton species collected by Blanchet et al.
1977 and Phillips and Blanchet 1980 ...................... 80

xii










Number


Page


18 Dominant fish egg and larval taxa as percent of all eggs
or larvae collected from three ichthyoplankton surveys in
Tampa Bay ..................... ......................... 81

19 Major and minor species components for the invertebrate
assemblages identified by Bloom et al. (1972) along three
transects ....................... .................... 85

20 Summary of benthic infaunal data from three sites along a
north to south gradient in Tampa Bay ..................... 86

21 The ten dominant fish species in Tampa Bay ............... 88

22 Fish species reported as utilizing Tampa Bay as a nursery
area .................... ............................ 90

23 Birds associated with the marine environments of Tampa
Bay ...................................... ............. 94

24 Resource management issues in Tampa Bay .................. 123

25 Estimated short term pollutant loadings to Hillsborough
Bay by source ......................................... 112

26 Concentrations (pM) of nutrient nitrogen in Tampa Bay and
other estuaries ................ ......................... 113

27 Known economic benefits for selected aspects of Tampa
Bay .................................................. 115





















CONVERSION TABLE



Metric to U.S. Customary


Multiply
millimeters (mm)
centimeters (cm)
meters (m)
meters (m)
kilometers (km)
kilometers (km)

square meters (m2)
square kilometers (km2)
hectares (ha)

liters (1)
cubic meters (m3)
cubic meters (m3)

milligrams (mg)
grams (g)
kilograms (kg)
metric tons (t)
metric tons (t)

kilocalories (kcal)
Celsius degrees (C)



inches
inches
feet (ft)
fathoms
statute miles (mi)
nautical miles (nmi)

square feet (ft2)
square miles (mi2)
acres

gallons (gal)
cubic feet (ft3)
acre-feet

ounces (oz)
ounces (oz)
pounds (lb)
pounds (lb)
short tons (ton)

British thermal units (Btu]
Fahrenheit degrees (F)


By To Obtain
0.03937 inches
0.3937 inches
3.281 feet
0.5468 fathoms
0.6214 statute miles
0.5396 nautical miles

10.76 square feet
0.3861 square miles
2.471 acres

0.2642 gallons
35.31 cubic feet
0.0008110 acre-feet

0.00003527 ounces
0.03527 ounces
2.205 pounds
2205.0 pounds
1.102 short tons

3.968 British thermal units
1.8(oC) + 32 Fahrenheit degrees


U.S. Customary to Metric
25.40 millimeters
2.54 centimeters
0.3048 meters
1.829 meters
1.609 kilometers
1.852 kilometers

0.0929 square meters
2.590 square kilometers
0.4047 hectares

3.785 liters
0.02831 cubic meters
1233.0 cubic meters

28350.0 milligrams
28.35 grams
0.4536 kilograms
0.00045 metric tons
0.9072 metric tons

) 0.2520 kilocalories
0.5556 (F 32) Celsius degrees


















ACKNOWLEDGMENTS


Mary Parks and Anne Twitchell provided valuable library
assistance at Mote Marine Laboratory. Laurie Fraser processed several
drafts of text, and Denise Latulippe, Bob Whitman and Robert Dixon
produced the figures. Data and reports were provided by Carl Goodwin,
U.S. Geological Survey, Tampa; Rick Wilkins, Hillsborough County
Environmental Protection Commission, Tampa; and the Southwest Flcrida
Water Management District. Authors of review papers presented at the 1982
Tampa Bay Area Scientific Information Symposium deserve special thanks for
distilling the enormous body of original literature upon which this
profile is based. William Fehring, Benjamin McPherson, Joseph L. Simon,
Michael Heyl, Joseph Carroll, Jr., Lorna Sicarello, Millicent Quammen, and
Edward Pendleton provided constructive criticism of early drafts. Kate
Lyster and Beth Vairin edited the draft. Sue Lauritzen was responsible
for layout design and graphics assistance.


XV


















CHAPTER 1. INTRODUCTION


1.1 TAMPA BAY AS A NATURAL UNIT

Tampa Bay, Florida's largest (1,030.8
km2) open-water estuary, is a y-shaped
embayment located on the west coast of the
peninsula between latitude 27030' and
28000'N (Figure 1). The bay receives
drainage from nine named rivers or streams
(Table 1) in a watershed that covers
approximately 5,700 km (Figure 2).

Tampa Bay is subdivided into seven
named subunits: Old Tampa Bay,
Hillsborough Bay, Middle Tampa Bay, Lower
Tampa Bay, Boca Ciega Bay, Terra Ceia Bay,
and the Manatee River (Figure 3, Table 2;
Lewis and Whitman 1985). Other common
place names used in this report- are
indicated in Figure 3.

The origins of the bay, structural or
erosional, have not been clearly defined.
White (1958) hypothesized that
Hillsborough Bay and Lower Tampa Bay may
have been formed by erosion in the valley
of the Hillsborough River at a lower stand
of sea level. Old Tampa Bay has no
apparent relationship to any large stream
and may have been connected to the Gulf of
Mexico by the Lake Tarpon Trough
(Hutchinson 1983).

1.2 POLITICAL SUBUNITS OF THE BAY

The political subdivisions bordering
the bay are shown in Figures 2 and 3;
included are three major counties
(Hillsborough, Pinellas, Manatee), three
additional counties (Pasco, Polk, and
Sarasota) that lie partly in the water-
shed, and three major cities (St.
Petersburg, Tampa, and Bradenton).
Total population in the watershed is
approximately 1.7 million, located in
the three major cities and more than 45
smaller cities and towns.


The portion of the bay lying within
Hillsborough County is owned by the Tampa
Port Authority, the remainder by the State
of Florida. Various private landowners
have titles to submerged lands scattered
along the edges of the bay.



1.3 BIOLOGICAL SUBUNITS OF THE BAY

Tampa Bay is classified as a
subtropical estuary, although the northern
half, in particular, experiences low
temperatures sufficient to kill mangroves
every 10 to 20 years (Wooten 1985). McCoy
and Bell (1985) discussed this controversy
further but drew no definite conclusions.

Each of seven named subunits of the
bay consists of open water and vegetated
intertidal zones, as listed in Table 2.
Ninety-three percent of the bay is open
water (967.2 km6), and 7% is vegetated
intertidal area with mixtures of mangrove
and tidal marsh vegetation.

Around the periphery of the bay there
is a shallow shelf varying in width from
500 to 1,200 m (Figure 4), with a maximum
depth of approximately 1.5 m at its outer
edge. Upon this submerged estuarine shelf
grow the majority of the algae and
seagrasses in the bay. Outside of the
shelf, the bay drops off to natural depths
of 7 m, with dredged channels as deep as
13 m. Olson (1953) determined that the
modal depth (the depth at 50% of the total
bay area on a hypsographic curve) of the
bay was 3 m and the mean depth 3.5 m. At
the time of his measurements, the
estuarine shelf made up 33% of the
open-water area of the bay. This has
since been reduced substantially by
dredging and filling of the bay's shallows
and shorelines (Lewis 1977).

















































rE: -- W 27'30'
82"45' 82'30' 82'15'

Figure 1. Map of Florida showing the location of Tampa Bay on the peninsular west coast.










Table 1. Surface water discharge to Tampa Bay (Hutchinson 1983).


Period
of
Drainage record
Basin (years)a


Tampa Bay and
coastal areas

Rocky Creek 24
Sweetwater Creek 26
Lake Tarpon Canal 3
Tampa Bypass Canal 19
Ungaged area --

Hillsborough:

Hillsborough River 39
Sulphur Springs 18

Alafia:


Alafia River

Little Manatee:

Little Manatee
River

Manatee:


Average
discharge
Drainage during
area Mayb
(mi) (106 gal/day)


Average
annual
dischargec
(100 gal/day)


690 70 411
-- 17 27


45 420 102 297




38 211 31 155


Manatee River 11 350 57 228

Total 2,184 382 1,440

aPeriod of record includes all measurements through 1977.
Data from Conover and Leach (1975). Discharge is linearly
adjusted to include ungaged drainage area in each basin.
Discharge in ungaged basins is assumed to be directly pro-
dportional to discharge in gaged basins.
Adjusted for diversions by City of Tampa.








































































Figure 2. The Tampa Bay area watershed extends into six counties.

















































Figure 3. Geographic subdivisions of Tampa Bay (from Lewis and Whitman 1985).


1.4 POTENTIAL CONFLICTS AND IMPACTS

Tampa Bay is an urbanized estuary in
which development activities have
substantially altered natural processes
(Taylor 1973; Simon 1974; Lewis 1977;
Tampa Bay Regional Planning Council 1983,
1985). It is estimated that 44% of the
original intertidal wetlands and 81% of
the original seagrass meadow cover in the
Bay have been destroyed either by dredg-
ing and filling or pollution (Lewis 1977;
Lewis et al. 1985a). Water quality has


been degraded in much of the bay because
of the current discharge of 7.2 x 1011
1/hr (190 x 109 gal/yr) of treated sewage
and industrial wastes, and historical
discharges of untreated or poorly treated
wastes (Tampa Bay Regional Planning
Council, 1978). This figure does not
include urban stormwater discharges.
Continued expansion of the nation's 7th
largest port at Tampa is expected, and the
population is increasing by 50% per decade
(Tampa Bay Regional Planning Council,
1985).










Table 2. Summary of area measurements for subdivisions of Tampa Bay (Lewis and Whitman 1985).

Total area Open water Emergent wetland Length of Shoreline
Subdivision namea mi2 km2 mi2 km2 mi2 km2 mi2 km2

1. Old Tampa Bay 80.5 208.7 73.3 190.0 7.21 18.7 211.1 339.8
2. Hillsborough Bay 40.2 105.3 38.4 100.8 1.76 4.6 207.0 128.6
3. Middle Tampa Bay 119.7 309.9 113.1 292.9 6.55 17.0 163.3 262.8
4. Lower Tampa Bay 95.2 246.6 92.2 238.9 2.96 7.7 75.6 121.6
5. Boca Ciega Bay 35.9 93.1 34.5 89.5 1.38 3.6 180.5 290.4
6. Terra Ceia Bay 8.0 20.6 6.1 15.8 1.86 4.8 25.9 41.6
7. Manatee River 18.6 54.6 12.7 39.3 5.92 15.3 118.7 191.0
Total 398.1 1,038.8 370.3 967.2 27.64 71.7 903.7 1,454.2

a Numbers correspond to subdivisions shown in Figure 3.



With these conflicts becoming more

interests and management options for the
bay was initiated with the formation of a
Tampa Bay Study Committee. Their final
report was completed in 1983 (Tampa Bay
Regional Planning Council, 1983). The
legislatively supported committee
submitted an extensive list of management
recommendations to the Florida Legislature
in spring 1985 (Tampa Bay Regional
Planning Council, 1985) and a regional
Agency on Bay Management currently is
grappling with these complex management
issues.


Figure 4. Vertical aerial photograph of the estuarine
shelf surrounding Tampa Bay.

















CHAPTER 2. DESCRIPTION OF THE ENVIRONMENT


2.1 GEOLOGICAL ORIGIN AND EVOLUTION


Tampa Bay and Charlotte Harbor to the
south are distinctive estuaries insofar as
both are large, drowned floodplains of
subtropical rivers flowing from the
Florida peninsula to the Gulf of Mexico.
The bays owe their modern shape and
chemistry to the history of the
peninsula's formation.

The peninsula and broad Continental
Shelf extending west from the Gulf coast
make up the Florida Plateau, an
accumulation of sediment about 5,000 m
thick, over a basement of igneous and
metamorphic rocks of Jurassic and
Cretaceous age [>100 million years before
the present (myBP)] (Rainwater 1960;
Applin and Applin 1965). These deep,
thick sediments represent the persistence
over millions of years of a stable
carbonate shoal (like the modern Bahama
Banks) of temperate to subtropical nature
between the Gulf of Mexico and Atlantic
Ocean. Sediments were deposited in
shallow coastal waters, reefs formed near
old shorelines, and freshwater marshes
contributed to beds of marl, limestone,
sand, or peat.

Eustatic changes of sea level,
subsidence, and folding of the earth's
crust created the Peninsular Arch, or
"spine" of the peninsula (Figure 5). The
arch trends south-southeast and extends
from southeastern Georgia through Florida
into the Great Bahamas (Chen 1965) and is
expressed today as the topographic high
east of the Tampa Bay region. A much
younger topographic feature, the Ocala
Uplift, is a late tertiary (Miocene age,
25 myBP) swell. Tampa Bay is located
southwest of the Ocala Uplift. The arch
and uplift modify local weather conditions


and define runoff characteristics of the
watershed.

Two ancient features of negative
relief have also affected the geology of
the Tampa Bay region. To the north, the
ancient Suwanee Channel connected the
eastern gulf to the Atlantic Ocean and
effectively separated the modern peninsula
from North America from the Cretaceous
period to the Oligocene epoch (about 25
myBP). One major effect of the channel
was its interception of quartz and clay
minerals from the continent, allowing
carbonate and evaporite sediments o
accumulate on the incipient peninsula for
several million years (Chen 1965). In
places, these accumulations would become
mineable as land pebble phosphate.
Phosphate mining and shipping are major
factors in the management of Tampa Bay
today.


Another major structural influence on
the geology of west Florida persisted over
the same period and also ended in the
Eocene time. The South Florida Basin is a
downwarp in the area of southern Florida.
According to Chen (1965), the basin
plunges toward the Gulf, trends between
Cuba and the Bahamas, across to the
Florida Keys, and from Dade County
northwest to Manatee County. Sediments
have filled the basin to a depth of 4,000
m (Applin and Applin 1965). Many
sedimentary beds in peninsular Florida,
including those near the sand surface in
the Tampa Bay region, thicken and slope to
the south and west because of the
prolonged existence of the south Florida
Basin. In places, the orientation and
thickness of the beds have affected the
paths of rivers and the accumulation or
flow of underground water.














































Figure 5. Major structural features of Florida (Chen 1965).


The many thousands of feet of
sediments resting upon the basement of the
Florida Plateau are organized into
distinctive beds or formations. The
formations, which contain fossils,
minerals, or sediments of particular
characteristic sizes, have been assigned
ages and are thereby sequenced from very
old to recent. In southwest Florida,
formations vary in thickness and in the
manner of their contact with higher and
lower formations. In places, erosion or
the absence of a depositional environment
has resulted in the absence of one or more
formations.


2.1.1. Geological Formations Relevant
to Tampa Bay

None of the geological formations
bearing water or phosphate, exposed in or
near the bay, or contributing to terrace
soils are older than about 50 million
years (Eocene epoch). As mentioned,
Eocene and Oligocene formations contain
little quartz or clay minerals, but
following the Miocene closure of the
Suwanee Channel (Miocene age, 25 myBP)
quartz sand, mud, cherts, kaolin,
dolomite, phosphate, and siliceous fossils
(Ballast Point geodes) became increasingly










abundant, and it was during the Miocene
that drainage and erosion began to create
"modern" Tampa Bay (Stahl 1970).


The oldest and
formation is the Lake
150-m-thick fossilized
600-800 m (Figure 6).
the lower confining
artesian ground-water
Aquifer (Brown 1983),


deepest relevant
City Limestone, a
bed at a depth of
This formation is
bed of the major
body, the Floridan
and is of an early


Eocene age (ca. 50 myBP). A mid-Eocene
bed some 200 m thick, the Avon Park
Limestone, overlies the Lake City
Formation and is the lower water-bearing
element of the Floridan, although it is
tapped by very few wells because of its
depth (400-650 m). The Ocala Limestone is
a later Eocene bed 100 m thick and a
central aquifer formation. Only one
Oligocene Epoch (25-35 myBP) formation
occurs, the Suwanee Limestone. Like the


SERIES FORMATION HYDROGEOLOGIC LITHOLOGY


Figure 6. Hydrogeology of the Tampa Bay area (after Wehle 1978).

a










Ocala bed below it, the Suwanee may
contain highly mineralized water.

The upper confining beds of the
Floridan Aquifer are of Miocene age. The
deeper Tampa Limestone Formation (also
called the St. Marks) contains phosphatic
and silicified beds, often with fossils.
Solution cavities are common and water
yield can be good because of proximity to
the underlying Floridan Aquifer. The top
of the Tampa Limestone Formation, and the
late Miocene Hawthorn Formation, contain
quartz and clay minerals which may carry a
minor artesian aquifer containing low
mineral loads.

A youthful (late Miocene or Pliocene
epoch) Bone Valley Formation of quartz and
phosphate sand and gravel overlies the
Hawthorn. Mostly east of Tampa Bay the
Bone Valley Formation varies in thickness
up to 20 m and may be found near the
surface to a depth of 30 m. Covering
about 5,200 kmy of the Florida Coastal
Plain, this formation is a major source of
commercial phosphate. The Bone Valley
Formation, or different formations near
the surface at other places, may be
covered by as much as 40 m of
undifferentiated sand, clay, or marl of
Pleistocene (1-3 myBP) or recent age.
Along with older sediments of the
interior, the more recent coastal sands
have been extensively modified by past
stands of sea level, weathering, and
development of a karst topography and can
sustain a freshwater aquifer. The location
of formations around the bay is shown in
Figure 7. The formations generally dip
toward the south and thicken toward the
south and east following the configuration
of the ancient South Florida Basin,
because of erosion during periods of
higher sea level. The Hawthorn Formation
is a thin veneer under much of
Hillsborough County and is missing
completely from the bed of the
Hillsborough River.

2.1.2. The Effects of Glaciation

While no glaciers ever formed on the
Florida Peninsula, their effect on the
west central coast was profound. The
great glaciations (Table 3) occurred
during the Pleistocene Epoch, beginning
about 3 million years ago.


LEGEND: SERIES STAGE FORMATION
MIOCENE ALUMBLUFF HAWTHORN
7 MIOCENE TAMPA ST. MARKS
MIOCENE CHOCTAWACHEE BONE VALLEY


Figure 7. Geologic formations of the Tampa Bay area
(Roush 1985).






Sea level dropped during glaciations
and rose during interglacial periods--so
much so that the peninsula was greatly
exposed or inundated. The severity of
inundation was moderated with each
successive period, so that the peninsula
was cut into terraces by erosion during
the maximum stand of each corresponding
sea level (Figure 8). The terraces
resulting from the Sangamon interglacial
period shaped the land surface around the
bay. The terraces are most conspicuous
between the Alafia and Little Manatee
Rivers, but die out on the south valley
wall of the Alafia (White 1970); they are
still evident on the east side of Pinellas










Table 3. Relation of glacial periods to terraces near Tampa Bay (adapted from Wilhelm and Ewing
1972).


Glacial Maximum Interglacial
erosionall) advance deposition
period (years BP) period Terrace Elevation (fta)


Late Wisconsin 40,000
Silver
Bluff + 6

Peorian Pamlico + 25

Early Wisconsin 110,000 Sangamon Talbot + 42
Fenholloway + 70
Wicomico +100

Illinoian 300,000
Okeefenokee
Yarmouth Sunderland +170
Coharie +215

Kansas 660,000
Aftonian Brandywine +270

aAbove sea level.


County (Roush 1985). By the late
Wisconsin, transgressing and receding seas
had etched and filled rivers, mixed
carbonate and quartz sediments across the
coastal plain of west Florida, and cut the
Tampa Valley, which was filled in during
the Holocene (Recent) rise of the sea
(Figure 9).

In general, surface sands in terraces
above the Pamlico Terrace are regarded as
pre-Pleistocene (Brooks 1974) and terrace,
coastal, and bay sediments are Pleistocene
or later. Soils surrounding the bay are
derived from carbonate-rich siliceous
sands of marine origin rather than
phosphatic or organic mixtures with
silica. Phosphatic soils are most
prevalent in Hillsborough County,
representing about 5% of the total county
area. About one-fourth of all soils in
Hillsborough County and nearly one-half in
Manatee County are of the Leon fine sand
type. In Pinellas County, Myakka fine
sand is most abundant, making up about
one-fifth of the soils. Both these soils
are dominated by primarily 0.10- to 0.25-mm


sand, with less than 5% silt or clay.
Analyses have shown that the finest
particles have quartz, montmorillonite, and
kaolinite as their principal minerals
(Roush 1985).

The absence of fine-grained
terrestrial sediment and soils accounts
for the low sediment loads in tributaries
to the bay and for the relatively small
amount of silt-clay in bay sediment.
Sediments were delivered to the bay when
rivers were competent during lower stands
of sea level. Now, tributaries to the bay
are at grade and neither transport much
sediment nor downcut their beds (Goodell
and Gorsline 1961). Of five original
rivers, only the Hillsborough built a
delta at its entry to the bay (a marsh
displaced by Davis Island), perhaps
because of the river's relative recency
(White 1958).

2.1.3. Development of the Modern Bay

The shape of Tampa Bay is the result
of movements in the course of rivers and a







































Parnlico


Figure 8. Approximate stands of Wisconsin sea level
(Stahl 1970).


Figure 9. Terraces of the Tampa Bay area (Roush
1985).



long period of rising sea level. Doyle
(1985) reported ancient river channels
buried beneath Tampa Bay; one such channel
underlies the southern end of the Pinellas
Peninsula (Stahl 1970). When sea level
was lower, the Hillsborough, Palm, and
Alafia Rivers probably converged in a
basin now called Hillsborough Bay; the
combined streams probably flowed
southwesterly toward Egmont Key. The
Manatee River is thought to have been
independent of the ancestral Tampa Basin
Stream, flowing westerly to the gulf near
Anna Maria (Stahl 1970).

The recent geology of the upper bays
remains a puzzle. Old Tampa Bay may
represent an open passage from the bay to
the gulf located north of an island of old
terraces in Pinellas County. The upper
bay may have been etched by the Anclote










River in earlier days (Stahl 1970), or by
discharges of Lake Tarpon (Hutchinson
1983), which until recently was a brackish
tidal body connected underground to the
gulf (Hunn 1975). Equally problematic is
the relationship between the Withlacoochee
and Hillsborough Rivers (and perhaps the
Palm River). Even today, waters of the
Withlacoochee overflow into the
Hillsborough River drainage, and both
rivers are regarded as youthful geological
features (White 1958, 1970). Boca Ciega
Bay is only about 5,000 years old and
resulted primarily from longshore sediment
transport and barrier island formation
(Stahl 1970).

Sediments in Tampa Bay are quartzitic
with carbonate mixtures. Bay sediments
derive from reworking of terrace deposits,
in situ production and weathering of
shell, and inshore movement of gulf
sediment. Immense deposits of oyster
shell underlie Hillsborough Bay and have
been mined for many years for fill.

Sea level has risen during the past
10,000 years at a diminishing, slow rate
(Figure 10). In the past 4,500 years the
sea has risen about 3 m with some
fluctuations (Brooks 1974), about 30 cm of
the rise occurring from 1550-1850, and
20-25 cm of it since 1870 (Swanson 1974).
The rising sea has etched the estuarine
shorelines of the bay, confused zonation
patterns in mangrove forests (Estevez and
Mosura 1985), structured the direction and
rate of longshore sediment movement on the
gulf beaches, and trapped sediments in the
bay. According to Brooks (1974),
backfillingg of the estuary from sediments
derived from offshore began about 8,000
years ago. Considering the fact that the
average depth of the bay is now less than


EARTH-YEAR. AGO








Figure 10. Sea level on the southwest Florida coast
(Scholl and Stuvier 1967).


ten feet, the thickness and volume of
recent sediments are astounding." Meade
suggested that weak estuaries such as
Tampa Bay export little fine sediment, a
point supported by mathematical models
(Ross et al. 1984).


2.2 THE HYDROLOGIC CYCLE

The amount of freshwater in Tampa Bay
and hence the salinity of the bay depend
at any given time on positive effects of
rainfall, runoff, and ground water efflux,
and negative effects of evapotranspira-
tion, consumptive uses, and ground water
influx (Figure 11).

The Tampa Bay Region is located in a
zone of transition between a temperate,
continental climate and a tropical,
Caribbean one. Centrally located on the
west peninsular coast, the bay area is
protected from oceanic influences by the
Peninsular Arch to the east and the broad
Continental Shelf to the west. Although
the bay area is a well-documented
biogeographic divide (Long and Lakela
1971; McCoy and Bell 1985), latitudinal
gradients of weather are gradual.
According to Jordon (1972), the only
abrupt weather changes along the entire
eastern gulf occur at the coastline where
oceanic and land-dominated forces clash.

The bay is affected by warm,
relatively humid summers resulting from
the Bermuda high pressure cell and by
mild, relatively dry winters when
continental air masses prevail. Because
moderate amounts of rain fall in the
spring, it is useful to distinguish three
categories of weather from an ecological
point of view. The warm, dry period
occurs from late April to mid-June. The
warm, wet period coincides with summer and
early fall. The cold period spans
November to April and becomes
progressively drier, although cold fronts
may cause short periods of heavy rain in
January or February.

Little is known of micro-
meteorological conditions around Tampa Bay
proper, which is protected from frontal
passages by gradual terraces around more
than 3000 of its perimeter (being open to
the gulf on the southwest). The upper




















PRECIPITATION


INTERCEPTION 4,


CONDENSATION


TRANSPIRATION


Figure 11. Generalized hydrologic cycle for the Tampa Bay area (from Culbreath et al. 1985).


bays are divided by a low peninsula and
have their longest fetches perpendicular
to one another; the whole bay is separated
from the gulf by the Pinellas Peninsula,
which has a maximum elevation of 30 m and
falls rapidly across Pleistocene terraces
into Old Tampa Bay. Land north of the bay


is mostly
east and
drained.


open and very wet. Land to the
south is also open but better


2.2.1 Insolation and Cloudiness

Tampa Bay is subject to an average of
66% of the sunshine possible in a year.
Average daily solar radiation is 444
gm-cal/cm (Langleys), with a January low
(311 gm-cal/cmc) and May high (599
gm-cal/cm2). Insolation is closely
related to evapotranspiration (Figure 12).

Mean annual cloud cover varies from
40% to 60% because of convective showers
in summer and extratropical fronts in
winter. Cumulus clouds, the most common


low-level formations, result from
sea-air temperature differences and
land-sea temperature gradients (
1954, Jordan 1972).


9.00-

8.00-

7.00-

6.00-

5.00-

4.00-

3.00


J F M A M J J A S N D


winter
summer
Leipper




o00



500 2

-450
-C 0
-400

350


Figure 12. Mean monthly pan evaporation and solar
insolation near Tampa (after Drew et al., unpubl.).


EVAPORATION


TAMPA BAY











2.2.2 Atmospheric Pressure and Wind

Pressure varies diurnally and
seasonally. A daily minimum pressure in
the early morning is followed by a late
morning maximum and evening minimum, then
by a lesser nocturnal maximum. This
atmospheric pressure cycle resembles the
mixture of diurnal and semidiurnal oceanic
tides in the bay. Superimposed over the
daily variations is a seasonal pattern,
albeit a modest one even in winter because
of the effects of the Bermuda cell. Mean
monthly pressure rises steadily from
September to January then declines through
spring. Mean annual pressure at sea level
is 1017.7 millibars.

Low pressure centers are of local,
tropical or continental origin and range
in magnitude from evanescent fronts to
tropical storms and hurricanes. Jordan
(1973) reported the occurrence of about
one low pressure center moving ashore on
the Florida gulf coast per year over a
15-year period (excluding tropical
cyclones and hurricanes). No seasonal
variation in frequency of the centers was
evident.

Rapid pressure changes accompany
northerss," periods of 1 to 3 or 4 days
when windspeeds exceed 20 knots. Between
15 and 20 northers pass Tampa Bay each
year, mostly between November and March
(Leipper 1954).

The intrusion of cold winter air into
the bay area is accompanied by
northwesterly winds, although north and
northeasterly winds prevail between
frontal passages from October to February
(NOAA 1982). Winter wind speeds do not
vary significantly from summer speeds.
The range of mean monthly windspeed varies
by only 2.2 knots; the annual mean wind
velocity (resultant vector) is 7.5 knots,
from the east. Periods of higher wind
occur during summer squalls, hurricanes,
and tornadoes. The highest official
windspeed, SE 65.2 knots, was recorded for
a 5-minute period at Tampa during the
Labor Day hurricane of 1935. Although
tornadoes are more common in the bay area
than elsewhere in Florida (mean occurrence
of 27 tornado-days/year), no data on the
speeds of winds associated with tornadoes
are available.


2.2.3. Temperature

Wooten (1985) summarized temperature
data for the Tampa Bay area. Mean annual
temperature based on four decades of
records at Tampa is 22.30C. Mean monthly
low and high temperatures are 16.0C and
27.80C in January and August,
respectively. Warming is most rapid in
March-April and cooling most rapid in
October November (Figure 13). Extreme
low and high temperatures are -7.80C
(1962) and 36.70C.

Temperature trends vary around the
bay area. Air temperatures in St.
Petersburg are moderated by proximity to
the Gulf of Mexico, whereas temperatures
become more extreme inland along the
floodplains of major rivers.







-5.0 10.1 21.4 29.4

-5.0 11.0 25.6 31.1

-0.6 13.5 24.4 33.3

3.3 16.4 28.0 33.9

9.4 19.4 30.8 36.6

15.0 22.2 32.1 36.7

17.2 23.1 32.2 36.7

18.9 23.3 32.3 36.1

122 22.5 31.7 35.6
OCT
4.4 18.6 28.9 35.0

-5.0 13.4 25.0 32.2

-7.8 10.7 22.2 30.0
-10 -5 0 5 10 15 20 25 30 35 40
TEMPERATURE C

Figure 13. Mean monthly temperature and extremes
for Tampa Bay (Wooten 1985).










2.2.4. Evapotranspiration and Relative
Humidity

Evaporative and transpirative flux
data for the actual bay are lacking, but
Simon (1974) reported 162.6 cm of Class A
pan evaporation, and Vishner and Hughes
(1969) gave lake evaporation rates of
127-132 cm/yr for the area surrounding
Tampa Bay and described a "surplus water"
gradient from 0 on the coast to about 15
cm in the upper Hillsborough River Basin.
Seasonal variations in evaporation are
given by Figure 12. Quantitative data on
evapotranspiration rates in major biotic
communities in and around the bay are
needed.

Relative humidity computed as monthly
means at Tampa range from 53% to 80%.
Lowest mean relative humidity occurs in
November, and the highest monthly average
is in August. In a typical day, mornings
are more humid than afternoons, and dew
will form in a typical evening (Wooten
1985).

2.2.5. Fog and Rain

Heavy fog occurs on 23 to 25 days/yr,
mostly from November to March. Ground
fogs are more common in basins and river
corridors, and all fogs are more common at
night than in the daytime.

Monthly rainfall patterns and the
existence of a slight peak of rainfall in
March are illustrated in Figure 14. About
60% of all rainfall occurs in the wet
season of June through September, a period
when some rain fell even in the driest of
years. Wooten (1985) noted that rainfall
was above average from the 1930's to the
1950's and has been below average since
the 1960's. Henry and Dicks (1984)
verified long-term drought patterns in the
southeastern United States but pointed out
that weather in central and south Florida
(beginning in the area of Tampa Bay) has
not correlated well with the southeast
region with respect to rainfall,
especially in the 1960-1980 period.

Light showers are more common than
heavy rains. Rainfall at Tampa averaged
123.7 cm for the period 1943-82. The
wettest and driest years were 1959 and
1956, with 194.5 cm and 73.4 cm,


JAN | | 20.4
5.7
FEB 0 20.2
7.0
MAR 32.1
7.4
I APR 16.7
5.3
SMAY 44.8
7.9

4.7 17.5
JUL =- 52.9
5.9 19.8
AUG 47.2
6.0 20.3
SEP 36.5
3.3 16.6

NOV I 18.7


4.1

5.2
0 5 10 15 20 25 30 35 40 45 50 55 60
RAINFALL
(CENTIMETERS)

Figure 14. Mean monthly rainfall and extremes for
Tampa Bay (Wooten 1985).



respectively. The lowest monthly mean
rainfall (trace amounts) occurred in
January (1950), April (1967 and 1981), and
November (1960). The highest monthly mean
rainfall was in July 1960, when 52.3 cm of
rain was recorded at Tampa. Palmer (1978)
determined that mean annual rainfall
increases concentrically from Tampa
(Figure 15).

2.2.6. Thunderstorms and Hurricanes

Thunderstorms are a common element of
bay-area weather. About 60-100 occur in
an average year, over 85-90 days, with the
largest number from June through
September. Offshore storms are more
common at night, whereas inland
thunderstorms occur more often during the









S ,day due to convective patterns in the
1' 1. 1 .oM lower atmosphere.
54 N Tropical cyclones (tropical storms
S53 and hurricanes) are much less frequent
(Table 4). Most of these storms enter the
52 bay area from the southeast to southwest.
51 From 1901 to 1971, 93 tropical cyclones
50 crossed the Florida west coast from
Apalachicola south to Venice; 70 struck
from August through October. Tampa Bay
has not been directly hit by a tropical
cyclone since 1848, when the pioneer city
of Tampa was nearly destroyed. However,
near hits have caused storm surges of more
than 3 m; the highest storm surge was
4 recorded in 1921 when a 3.2-m surge above
54 mean low water flooded coastal areas.
S 55 Today, flood zoning recognizes elevations
of 2.5-4.0 m as the limit to storm surges
with a recurrence probability of 100
years.

Ecological effects of large storms on
55 Tampa Bay and adjacent areas are not well
studied but are likely to include raising
S_ of water tables, replenishing of soil
moisture, flushing of tributaries and
Figure 15. Mean annual rainfall in inches across the redistribution of sediments, dispersal of
Tampa Bay region (Palmer 1978). propagules, export of organic matter from

Table 4. Tropical cyclones for past 50 years near Tampa Bay (H = hurricane; TS = tropical
storm) (Wooten 1985).
Type storm Month-year Path with respect to Tampa Bay

TS Sept. 1930 Moved over northern shores of Bay.
TS Aug. 1933 Moved westward 45 km south of Bay.
TS Sept. 1933 Moved northwestward 75 km NE of Bay.
H Sept. 1935 Moved northward 75 km west of Bay.
TS July 1937 Moved northeastward across Bay.

TS Sept. 1941 Moved northwestward 48 km NE of Bay.
H Oct. 1941 Moved northwestward 65 km SE of Bay.
H Oct. 1944 Moved northward through eastern Hillsborough
County.
H Sept. 1945 Moved northward 75 km E of Bay.
H Oct. 1947 Moved northward 10 km inland of Pinellas
coast.

H Sept. 1950 Moved eastward 50 km N of Bay.

H Sept. 1960 Moved northward 55 km E of Bay.
H Oct. 1968 Moved northeastward 60 km N of Bay.
H Sept. 1985 Moved northward 90 km W of Bay.










tidal marshes and forests, and the
temporary extirpation of estuarine biota.


2.3 SURFACE AND GROUND WATERS

2.3.1. Overview of Tributaries to Tampa
Bay

Four natural rivers--the Hillsbo-
rough, Alafia, Little Manatee and Manatee--
flow to Tampa Bay. Another, the Palm
River, once drained lands between the
Hillsborough and Alafia Rivers, but has
been completely channelized and controlled
since 1970 and now is called the Tampa
Bypass Canal. The Lake Tarpon outlet to
Old Tampa Bay is a significant human-made
tributary completed in 1971. The
Hillsborough and Manatee (and its
tributary, the Braden River) are impounded
as municipal reservoirs. Some of the flow
of the Little Manatee is withdrawn for
power plant cooling water, but it is
otherwise regarded to be the least
disturbed river flowing to Tampa Bay. The
Alafia has been affected by phosphate
mining and processing and is impounded at
places.

The four rivers all rise to the east
of Tampa Bay and flow 65-80 km southwest
or west, falling an average of about 10-40
cm/km. The Hillsborough watershed is
largest, L,684 km2, followed by the Alafia
(1,088 km2); Manatee (907 km ) and Little


Manatee (570 km2) (Turner 1979). From
north to south, their respective
floodplains are progressively wider and
tidally affected over longer distances.
Thus, tidal action may be detected in the
Hillsborough River at kilometer 17.7 where
the river is dammed and at kilometer 16.0
in the Alafia River (Menke et al. 1961).
The Little Manatee River is tidal to
kilometer 24.0, and the Manatee is tidal
at least to Rye Bridge (kilometer 30.0)
(Manatee Co. Utilities and Camp, Dresser &
McKee, Inc. 1984). Intertidal habitats
(e.g., oyster bars, marsh shorelines,
islands) are correspondingly more abundant
in the rivers farther south.

The northern rivers (Hillsborough,
Alafia) are more urbanized than the
southern ones, which still contain more
than 90% of their respective watersheds in
wetlands, forest, range or farmland (Table
5). The Little Manatee Watershed has been
urbanized or laid barren less than the
others.



2.3.2. Flows

Tampa Bay as a whole has a 4, 623-km2
basin and receives about 3.8 billion
liters of runoff daily, with most (77%)
flowing into Hillsborough Bay.
Approximately 85% of all flow to the bay
consist of the discharges of the four


Table 5. Land use characteristics (% total watershed area) of four authentic rivers flowing
to Tampa Bay (from FDER 1982).

Hillsborouqh Little
Land use Upper Lower Alafia Manatee Manatee


Agriculture 52.3 40.0 35.9 45.9 38.3

Range 16.1 17.1 17.1 34.9 41.3

Forest 2.8 1.0 13.5 7.4 3.6

Wetland 13.9 17.2 9.2 7.5 3.6

Urban 12.6 21.5 10.4 2.7 5.4

Barren 1.3 1.1 11.5 0.4 0.6










rivers (Figure 16). The mean annual
discharge of the Hillsborough (580 x 10
1/year) exceeds the others (Alafia: 425 x
109 1/year; Manatee: 260 x 109 1/year;


Little Manatee: 225 x 109 1/year) (Dooris
and Dooris 1985). If discharge and
watershed are compared, the Alafia and
Little Manatee Rivers yield more water


Figure 16. Mean monthly flow in major tributaries to Tampa Bay (adapted from Drew et al., unpubl.).












(1.0
area,
(0.9)


and 1.1 ratio of mean annual flow to
respectively) than the Hillsborough
or Manatee Rivers (0.7).


Numerous lesser tributaries and three
major flood control channels also drain
into Tampa Bay (Figure 17). Many unrated
creeks and streams drain 2,279 km2 of
coastal watershed between river basins;
several of these have been canalized,
filled, or modified beyond rehabilitation.
Three restorable streams are Double Branch
Creek in upper Old Tampa Bay, Bullfrog
Creek south of the Alafia River, and Piney
Point Creek near Port Manatee. Other
tidal streams entering into rivers have
not been modified as much as the urban
streams.

Of the 15% of total annual flow
attributable to other tributaries, about
two-thirds is contributed by flood-control
channels; the Tampa Bypass Canal (former
Palm River) is the largest of these
streams (about 105 x 109 1/yr). This
canal flows southwesterly from the upper
Hillsborough River Basin through Harney,
where it is connected by a control
structure to the river and continues to
McKay Bay. Part of its base flow is
ground water, since it intercepts the
Floridan Aquifer (Motz 1975). The
flood-control channels are tidal only up
to their saltwater barriers; the lesser
streams are more tidal, but urbanized.



2.3.3. Constituent Concentrations and
Loads

It does not automatically follow that
rivers with the greatest flows are the
greatest sources of material to Tampa Bay.
Table 6 illustrates the ranking of major
streams by flow, selected concentrations
of nutrients and other constituents, and
their corresponding loads (Dooris and
Dooris 1985). Flow and conductivity ranks
are correlated for most rivers except the
Lake Tarpon Outfall and Hillsborough
River, and flows are inversely related to
overall dissolved oxygen content.

Total phosphorus concentrations are
highest in the Alafia River, and that
river delivers more phosphorus to Tampa
Bay than any other (Figure 18). It is
followed in rank for both concentration


MEAN MONTHLY FLOW (CFS)


1000





100





10
10


lo


10000
5000



1000

600



100

60


_ .___ ...'i\ .____TBC


\- - S c
-- ................. .. -


_7" _LTOC


\, -*


N FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
MONTH


LEGEND:
--- TBC
SS
.... ... ... R C
- SC
--- LTOC


10
JAN FEB MAR APR MAY

LEGEND:
---- HR
-- AR
-- MR
... MR
--- BC

MI
HILLSBOROUGH RIVER
ALAFIA RIVER
MANATEE RIVER
LITTLE MANATEE RIVER
TAMPA BYPASS CANAL
BULLFROG CREEK
ROCKY CREEK/CHANNEL A
LAKE TARPON OUTFALL CANAL
SWEETWATER CREEK
TOTAL


TAMPA BYPASS CANAL
SULFUR SPRINGS
ROCKY CREEK
SWEETWATER CREEK
LAKE TARPON OUTFALL CANAL


JUN JUL AUG SEP OCT NOV DEC
MONTH

HILLSBOROUGH RIVER
ALAFIA RIVER
MANATEE RIVER
LITTLE MANATEE RIVER
BULLFROG CREEK

EAN ANNUAL VOLUME


1 10 100 1000
(L/YEAR) X109


Figure 17. Mean monthly flows in major and minor
tributaries, and mean annual volume delivered to
Tampa Bay (Dooris and Dooris 1985).










Table 6. Rank of Tampa Bay tributaries by flow and load. Conc. = concentration (Dooris and Dooris
1985).

Rank (1 highest) by


Stream


L. Tarpon
Outfall

Hillsborough
River

Tampa Bypass
Canal


Total P
Flow Cond.a D.O.b Conc. Load


Total Org N
Conc. Load


Fluoride
Conc. Load


6 2 1 6 6 2 6 N.D.c N.D.


1 4 5 3 2 5 3 3 2


5 6 3 5 5 3 4 4 5


Alafia River 2 3 4 1 1 4 2 1 1


Little Manatee
River


4 5


Manatee River 3 1 6 2

aCond.= conductivity.
bD.O. = dissolved oxygen concentrations.
cN.D. = no data.


and load by the Hillsborough and Manatee
Rivers, the Little Manatee, and the
human-made canals. Total organic nitrogen
is highest in the Manatee River (either by
concentration or load), even though its
flow rank is third; total loads of organic
nitrogen in the Alafia and Hillsborough
Rivers follow. Judging from its rank by
oxygen content, the Little Manatee River
delivers less oxygen demanding material to
Tampa Bay than any other natural river.

Fluoride concentrations and loads to
Tampa Bay reflect natural background
levels of fluoride-containing phosphate
deposits, as well as the activity of
industries that mine and process the
phosphate (Toler 1967). Mean fluoride
concentrations are uniformly low, usually
less than 2.0 mg/l as mean values, for all
streams but the Alafia. The Alafia River
has had enormously high levels of
fluoride, discharging up to 10 tonnes of
fluoride per day to Hillsborough Bay in
the 1960's. Concentrations and loads in
the river have been declining since then,


although
River is
magnitude
streams.


total loading via the Alafia
still one or two orders of
greater than loading by other


Data from Moon (1985) on loads from
permitted point sources indicate that
waste discharges to the Alafia River
render it the greatest source of
phosphorus and fluoride to the Bay. Point
discharges are also implicated by the same
data as the reason for the Manatee River's
distinction as the largest source of
organic nitrogen. On the other hand, the
Little Manatee River is distinguished as
the bay's healthiest natural river, at
least insofar as dissolved oxygen,
nutrients, and fluoride are concerned.

Moon (1985) also reported on flows
and loads from point sources directly to
waters of Tampa Bay. Although the
historic coastal basin between rivers was
small and therefore relatively unimportant
as a source of nutrients, new coastal
urbanization and anthropogenic discharges


3 4












ALAFIA RIVER
HILLSBOROUGH RIVER
MANATEE RIVER
LITTLE MANATEE RIVER
TAMPA BYPASS CANAL
ROCKY CREEK
LAKE TARPON OUTFALL CANAL
SWEETWATER CREEK








ALAFIA RIVER
MANATEE RIVER
HILLSBOROUGH RIVER
LITTLE MANATEE RIVER
SWEETWATER CREEK
TAMPA BYPASS CANAL
ROCKY CREEK
LAKE TARPON OUTFALL CANAL


PHOSPHORUS TOTAL/YEAR (KG)


NO3-N/YEAR (KG)


MANATEE RIVER
ALAFIA RIVER
HILLSBOROUGH RIVER
TAMPA BYPASS CANAL
LITTLE MANATEE RIVER
LAKE TARPON OUTFALL CANAL
SWEETWATER CREEK
ROCKY CREEK
2 103 104 105 106

TOTAL ORGANIC N /YEAR (KG)

FLUORIDE /YEAR (KG)
103 104 105 106 107
ALAFIA RIVER
HILLSBOROUGH RIVER
LITTLE MANATEE RIVER
MANATEE RIVER
ROCKY CREEK
TAMPA BYPASS CANAL
SWEETWATER CREEK

Figure 18. Mean annual constituent loads to Tampa Bay (Dooris and Dooris 1985).


from these local areas collectively
constitute a significant source of flow
and load. Moon (1985) calculated that
about one-fourth of all point-source
flows go directly into the bay, and that
such sources deliver about 839,160 kg of
phosphorus and 1,360,800 kg of nitrogen/yr
(or 78% and 85% of all anthropogenic loads
of these nutrients in the bay,
respectively).


2.3.4. Structure of Ground-water Systems
Under the Bay

The major confined aquifer below
Tampa Bay is the Floridan Aquifer. This
water-bearing series of formations (Figure
19) is approximately 300 m thick in
Hillsborough County north of the bay and
400 m thick in Manatee County south of the
bay. The Floridan is confined to varying









10 252 Ab4 over 123 Ai
A ICA,,.; _L._, AQUIFER 1 T'-':A degrees by the overlying Hawthorn
SQ R Formation, a late Miocene deposit that
100 thickens and dips toward the south under
CONFINING ER! the bay.

tooi Recharge to the Floridan Aquifer
,00o occurs primarily northeast of Tampa Bay
FLORIDAN AQUIFER where formations are at or near the
surface, as in the Green Swamp (Ryder
00 A' 1982). Upper Old Tampa Bay and
Hillsborough Bay are likely areas of
g'o vertical leakage, both upward and
downward, due to the semipermeable nature
S 'o of the confining beds of the Hawthorn.
Recharge to the Floridan in Manatee County
700 is primarily from inland areas east of the
coast.

Undifferentiated sands, silts, and
o .... ..;.... ..._______.. B' clays of Pleistocene and Recent times
SURFICIAL AQUIFER overlie the Hawthorn and hold water
100. li II derived from local percolation. This
INIaNG LIAER 17 surficial aquifer is 7-15 m thick
200 throughout most of the bay area but is
reduced to a thin veneer or is absent
So under Tampa Bay. Consequently, the
FLORIDAN thickness and imperviousness of the
4 Hawthorn Formation controls hydrologic
AQUIFER connections between the Bay and Floridan
to0. Aquifer.
...0 2.3.5. Ground-Water Discharges to Tampa
70 Bay
.. MILES Ground waters are discharged to Tampa
Bay from the surficial (water-table) and
confined (Floridan) aquifers. Discharges
from these sources are controlled by the
u o TAMPA YS HLOROUH c' relationship of actual or potential water
C011OIRMSAL Ai surface levels and land surface, and
100 leakage. Figure 20 illustrates the
movement of surficial waters to the bay
200 FLORIDAN AQUIFER and the effect of streams on direction of
movement (Culbreath et al. 1985).
Although data from Manatee County are not
illustrated, surficial discharges to the
-00 bay are significant (Hyde 1975).

So-o Surficial discharges to the bay are
seasonal and greatest during and after the
004 Ywet season. The roles of ground water
discharge in bay ecology are poorly
understood, but for discussion purposes
can be postulated as (1) attenuating
S-000 surface flows and constituent loads; (2)
prolonging estuarine conditions along
Figure 19. Relation of surficial and Floridan aquifers shorelines and in marshes or mangrove
to Tampa Bay along three axes (Culbreath et al. 1985). forests, and (3) creating favorable







































Figure 20. Generalized flow in the surficial aquifer,
September 1980 (Culbreath et al. 1985).



refugia and nursery areas for marine life
in tidal creeks. Drainage of uplands
around the bay has concentrated the
different flows of surficial discharge,
routed it to major stormwater outlets, and
so altered the hydrology and constituent
loads of artificial tributaries that many
functions of diffuse flows have probably
been lost.

The physical interaction of the
Floridan Aquifer and Tampa Bay and its
ecological consequences also are poorly
known. Figure 21 illustrates aquifer
water moving toward and under the bay.
Ryder (1982) estimated that 8.7 billion
I/day of ground water are released from
the Floridan Aquifer in southwest Florida,
an "immense area of upward leakage."
Although 90% of the leakage is in the form
of springs, 10% occurs in the coastal area
as diffuse leakage.

There are about a dozen springs in
the Tampa Bay area, although no submarine


Figure 21. Generalized flow in the Floridan aquifer,
September 1980 (Culbreath et al. 1985).



ones are known (Rosenau et al. 1977).
Pinellas County has two dormant springs
relevant to the bay, Phillippi and
Espiritu Santo Springs. The
Hillsborough River Basin contains Purity,
Sulphur, Eureka, Lettuce Lake, and Six
Mile Springs. Buckhorn, Messer, and
Lithia Springs are located in the Alafia
River. No springs are reported in the
Little Manatee and Manatee Rivers; this is
consistent with the increased thickness of
confining layers. Together, these and
lesser springs contribute an average of
3.5 m3/s of discharge, but all of it
either is consumed or added to the flows
of their respective rivers.

On the other hand, artesian flow is
widespread around Tampa Bay and probably
was substantial prior to development of
the region (Ryder 1982). As shown in
Figure 22, artesian flow probably occurs
in eastern Pinellas County, within the
Tampa Bay Bypass Canal (formerly Palm
River), the Ruskin area, and coastal


)30 N

30





10









10
6;YN- 0


'j II P





































Figure 22. Area of potential discharge from the
Floridan aquifer, September 1980 (Culbreath et al.
1985).


Manatee County (Peek 1959; Hyde 1975;
Rosenau et al. 1977). Extensive artesian
flow has supported truck farming and
tropical fish culture from Tampa to
Bradenton. In upper Old Tampa Bay,
artesian flows into Rookery and Double
Branch Creeks were common because the
Floridan Aquifer is either poorly confined
or unconfined (Mann 1972).

Actual rates of discharge from the
Floridan Aquifer depend on potentiometric
levels (the level to which water would
rise in a confined well open at its bottom
to the aquifer) and connections to the bay
or ground surface. Long-term potentio-
metric surface projections based on
farming, new and forthcoming mining
operations, and municipal consumption are
about 9 m below existing levels; this
suggests a decreased potential for
ground-water movement to the bay (Wilson
and Gerhart 1980). Excavation of the


Tampa Bypass Canal opened the aquifer,
and ship channels probably have done so
as well, meaning that vertical fluxes are
further still from natural conditions
(Motz 1975; Hutchinson 1983).

It is apparent from the data on
surface water and ground-water hydrology
that much is known about physical
conditions relative to freshwater inputs
to Tampa Bay, but details of ground-water
dynamics and the ecological role of
freshwater in the bay are sorely
understudied. No one today probably
appreciates how wet the Tampa Bay region
once was. Until we know the "original"
hydrological conditions of the bay, it is
likely that efforts to control its
chemistry and biology will be misguided.


2.4 HYDROGRAPHIC CHARACTERISTICS OF
TAMPA BAY

Tampa Bay is Florida's largest
open-water estuary and the second largest
after the expansive network of tidal
rivers and creeks of the Everglades. The
bay covers 967 km2 and is wider than 16 km
in places. Wi h wetlands, total area is
about 1,030 km The bay has a bottom
area of 794 million m2, and a volume at
mean tide of 3.48 billion m3 (Ross et al.
1984).

2.4.1. Shape and Shorelines

The main axis of Tampa Bay is
southwest to northeast (into Hillsborough
Bay) with a northwesterly branch into Old
Tampa Bay. Historically, natural shore-
lines included estuarine sandy beaches
(found today at Piney Point), salt barrens
(Beacon Key), mangrove-dominated embay-
ments (Cockroach Bay), low river marshes
and bluffs (Little Manatee River), and
pine flatwoods (Interbay Peninsula). The
only natural rock shoreline remaining in
the bay is a coquina outcrop north of the
Alafia River near Archie Creek, although
others occurred at Ballast Point and
elsewhere (Heilprin 1887).

Goodwin (1984) computed changes in
physical characteristics within subareas
of the bay since 1885 (Figure 23; Table
7). The area of Tampa Bay has been
reduced by 3.6%, with most (3.0%)






























































Figure 23. Areas of physical change in Tampa Bay
since 1880 (Goodwin 1984).


occurring before 1972. Hillsborough Bay's
surface area was reduced by 13.6%,
primarily by residential and port-related
filling. Lower Tampa Bay has lost 1.9% of
its total area, but this figure would be
considerably higher if middle and upper
Boca Ciega Bay were included (Lindall and
Trent 1975). The loss of bay area from
filling occurred mostly along shorelines
and shallow areas of high biological
productivity. Definitive data on
shoreline loss by type are not yet
available for Tampa Bay, but a preliminary
estimate of 44% loss in total mangrove
acreage illustrates the relative
importance of the lost area (Lewis 1977).
In Charlotte Harbor to the south, Harris
et al. (1983) calculated that during
1945-1982 mangrove acreage actually
increased by 10%, so losses in Tampa Bay
have been considerable.

2.4.2. Depth

The bay contains at least three
terraces or wave-cut benches associated
with lower sea-level stands, with the
deepest water in lower Tampa Bay. Egmont
Channel at the mouth of Tampa Bay is the
deepest inlet and has a natural depth of
27.4 m. A 96-km-long ship channel
(dredged to 13 m) is the longest
bathymetric feature on the Florida west
coast.

Tampa Bay is a shallow body of water,
with a modal depth of 3.0 m and 90% of its
area shallower than 6.7 m (Olson and
Morrill 1955). Mean depths have been
reported as 4.1 m for the bay as a whole
at "mean tide," and 3.7 m (Goodwin 1984)
based on supplemental data (Rosenshein et
al. 1977). Differences in estimates are
due to definitions used in compiling data
and bay development such as the ship
channel and related spoil islands.
According to Goodwin (1984), the mean
depth of Tampa Bay has increased more than
5% during the past century with an
increase of almost 30% in Hillsborough
Bay. Most of the increased relief took
place before 1972 as a result of early
channel projects.

2.4.3. Bottom Features

The primary bottom type in Tampa Bay
is unconsolidated sediment, or so-called










Table 7. Physical characteristics of major subareas of Tampa Bay for 1880, 1972, and projected
1985 levels of development (Goodwin 1984).


Physical
Characteristics/Area


Surface area (mi2)
Lower Tampa Bay
Middle Tampa Bay
Old Tampa Bay
Hillsborough Bay
Tampa Bay

Water volume (mi2 ft)
Lower Tampa Bay
Middle Tampa Bay
Old Tampa Bay
Hillsborough Bay
Tampa Bay

Average depth (ft)
Lower Tampa Bay
Middle Tampa Bay
Old Tampa Bay
Hillsborough Bay
Tampa Bay


Year
1880 1972 1985


128.4 126.1 125.9 -
111.2 109.5 109.5 -
77.8 74.8 74.8 -
42.7 38.8 36.9 -
360.2 349.2 347.2 -


1,572 1,578 1,578 +
1,475 1,481 1,481 +
689 695 695 +
352 373 388 +
4,088 4,128 4,142 +


12.2
13.3
8.9
8.2
11.3


Tidal prism (mi2 ft) computed
at seaward end of:
Lower Tampa Bay 792
Middle Tampa Bay 570
Old Tampa Bay 205
Hillsborough Bay 116


12.2
13.5
9.3
9.6
11.8



764
548
195
105


12.5
13.5
9.3
10.5
11.9



761
541
194
98


Percent change
1880- 1972- 1880-
1972 1985 1985


+
+
+
+1
+



-


1.8
1.5
3.8
9.1
3.0


0.4
0.5
0.9
6.0
1.0


2.4
1.5
4.5
.7.1
4.4



3.5
3.8
4.9
9.5


- 0.2
0
0
- 4.9
- 0.6


0
0
0
+ 4.0
+ 0.3


1.9
- 1.5
3.8
-13.6
- 3.6


+ 0.4
+ 0.5
+ 0.9
+10.2
+ 1.3


0 + 2.4
0 + 1.5
0 + 4.5
+ 9.4 +28.0
+ 0.8 + 5.3


- 3.9
- 5.1
5.4
-15.5


soft bottom. Goodell and Gorsline (1961)
gave details on this type of bay sediment.
The actual area of soft, unvegetated
bottom is not known but in Charlotte
Harbor it represents about 80%-85% of the
total area (Estevez 1981) and is presumed
to be of similar extent in Tampa Bay.
Examples of soft bottom include expansive
tidal flats in McKay Bay, shallow basins
in Terra Ceia Bay, the undulating
flocculent substratum in Hillsborough Bay,
and the offshore bars along the lower bay.
Some soft bottom supports grassbeds.
About 30,970 ha of grassbeds once existed
in Tampa Bay, but such vegetated bottoms
have declined by 81%.

Recent estimates of oyster coverage
in the bay are limited to those by McNulty
et al. (1972), who gave a total of 3,352


ha. This value probably was much greater
a century ago before shell was harvested
for fill. Numerous earthworks around the
bay suggest intriguingly large acreages of
oysters in prehistory (Goggin and
Sturtevant 1964). Hard or live bottom
occurs in the lower bay and near Gandy
Bridge, but in unknown amounts. These
areas of rocky relief are populated by
colonial invertebrates such as sponges
and tunicates. Attached macroalgae are
diverse and plentiful, and the areas
may serve as nurseries for juvenile
fishes. Hard bottom is common where
tidal currents have removed overlying
sands from limestone, coquina, or other
rock.

The final bottom channels are either
natural or dredged. Egmont Channel is










incised into rock (Wm. H. Taft, Worcester
Polytechnic Institute, pers. comm.) and
parts of the main ship channel are cut
into limestone in middle and upper
Hillsborough Bay (Hutchinson 1983).
Smaller channels lead to docking areas and
emerge from river mouths.



2.4.4. Sea Level and Tides

Water level in Tampa Bay varies as a
function of long term oceanic change,
multiple year cycles, and solunar tidal
action. Wind and storms also affect the
level of bay waters.

Long-term trends. Sea level is
rising in Tampa Bay, although estimates of
the rates of apparent rise vary. Marmer
(1951) estimated a mean rate of 0.91 cm/yr
rise in sea level at Cedar Key. This is
equal to a rise of 91 cm/century. Bruun
(1962) estimated a rate of 0.30 cm/yr on
the west coast of Florida for 1930-60, or
a rate of 30 cm/century. Hicks and
Shofnos (1965) set the Cedar Key rate at
0.27 cm for 1939-62, the same as for Key
West over a period of 49 years. This rate
equals a rise of 27 cm/century. Hicks
(1972b) gave a rate for Cedar Key from
1940-70 of 0.03 cm/yr, for a rate of only
3.0 cm/century. Provost (1974) gave a
rate of 21 cm/century for Tampa Bay.

Not all of the observed rise in sea
level has been due to oceanic changes,
since subsidence of land contributes to a
relative transgression of the sea.
Nonetheless, the combined effect of a
rising sea and sinking coastline is
ecologically significant. In the Florida
Everglades the rise of the sea (relative
to land) has caused a dissection of the
mangrove coast in the Ten Thousand
Islands, and even today seaward islands
are drowning while the forest moves inland
(Scholl and Stuvier 1967). Shorelines of
Tampa Bay are eroding slowly, partly
because of sea-level rise (Estevez and
Mosura 1985), and the loss of bars bayward
of intertidal seagrass beds may be
declining for the same reason (Hands
1983). Over a longer period of time, sea-
level rise will cause an infilling of
Tampa Bay (Brooks 1974) and realignment of
shorelines (Bruun 1962).


During the next 50 years we foresee a
loss of seaward mangrove shorelines
similar to the loss during the past 50
years and an invasion by these trees into
lands now only inundated by the highest
tides. However, since much of the
shoreline has been bulkheaded at or above
current mean high water, there will be
little habitat for these trees to invade,
resulting in a "pinching out" of this zone
of intertidal, fringing vegetation.

A redetermination of tidal datum
planes in Tampa Bay was made during the
past 10 years by the National Ocean
Survey. Relative to the reference of the
National Geodetic Vertical Datum, these
tidal planes are higher than their
predecessors, which were derived from 1929
data. Unfortunately, these new tidal
planes are not commonly used by surveyors
or engineers (or regulatory agencies), so
that shoreline projects are being designed
too low on the shoreline and too close to
ecologically valuable intertidal areas.

Annual trends. Tides vary daily and
the cycle of tides in Tampa Bay has a
lunar period, but underlying these changes
is an annual variation of ecological
importance, particularly for intertidal
organisms. Sea level is highest in
August-October because of oceanic changes,
the movement of coastal currents, warming
of the sea, runoff, and solar and lunar
effects. It is lowest in January and
February, so the most rapid change in sea
level is in November and December. The
difference between sea level during these
extremes is about 24 cm (Marmer 1951).


Provost (1974) showed that tides of
the same amplitude inundate fixed
intertidal marsh points differently,
depending on annual sea-level changes.
Estevez (1978) presented inundation curves
for Cockroach Bay (Figure 24) and found
that organisms located at mean high water
were submerged 55% of the time in October
but only 18% of the time in February. The
range of submergence (October through
February) at mean tide was 80%-50% and
only 96%-80% at mean low water. Estevez
(1978) interpreted ecological data on red
mangrove root-borers on the basis of these
changes. Others working in the intertidal
zone should keep this variation in mind,































O .0 0 0 5,0 60o 7o 70 s o lO0O
TIME $UBMERGED (PERCENT OF TOTAL)

Figure 24. Seasonal changes in tidal duration curves
at Cockroach Bay (Estevez 1978).


Place


Egmont Key

Shell Point

Hillsborough Bay

Safety Harbor


OCTOBER

F6RA


FEBRUARY \
'\


Table 8. Tide relations in Tampa Bay.
Change relative to St. Petersburg

High tide Low tide Range
Heighta Timeb Height Time (ft)

*0.9c -2:27 *0.9 -2:24 2.1

0 +0:08 0 +0:17 2.3

+0.5 +0:07 +0.1 +0:26 2.8

+0.5 +1:38 0.0 +1:55 2.8


bRelative to mean lower low water.
Hours:minutes.
cAsterisk identifies a value to be multiplied by predicted
height at St. Petersburg.


especially when interpreting positional
data.

Tides. Tides in Tampa Bay are a
mixture of lunar (semidiurnal) and solar
(diurnal) tidal types (Goodwin and
Michaelis 1976). The average tidal range
is 0.67 m, although, as noted above,
annual sea level variation results in the
shifting of this range vertically in
relation to the shore. Tides propagate
uniformly from the Gulf of Mexico into the
bay (e.g., tidal cycles are delayed but
not distorted much at different points up
the bay). Tidal changes relative to St.
Petersburg are given in Table 8.

Typical tides in Tampa Bay are
illustrated in Figure 25 (Goodwin 1984).
When tides are mixed, a "lower" low tide
is followed by a "lower" high tide, then
by a "higher" low and "higher" high tide.
Southwesterly winds heighten tides and
northerly winds lower tides by 1.0-1.5 m,
depending on wind strength and duration.
The storm surge, although technically not
a tidal wave, is also wind driven and may
accentuate tidal variations. Figure 26
illustrates the relative frequency of
occurrence of total tide height resulting
from astronomic, barometric, and storm
surge forces for gulf beaches on the
Pinellas Peninsula. Relative to mean sea
level a 1.5-1.8 m "tide" recurs on an










METERS ST. PETERSBURG, FLORIDA


ST. PETERSBURG, FLORIDA

Extreme high caused
by strong southwesterly wind


8-17-72


*-22-72


0.3-



0.3 2-21-73
0.8 -

0.4


0 .4

1-14-72
0.4


0.8


Typical Tide


,PwA / .


2-26-73


1-19-72


\/ Extreme low caused
by strong northerly
wind

Figure 25. Typical and extreme tides in Tampa Bay (Goodwin 1984).


average of 10 years; 2.5 m heights recur
on a 25-year cycle.


2.4.5. Circulation and Flushing

Circulation refers to the paths taken
by water currents and their constituents
due to tidal forces, runoff, wind, and
other effects. Flushing is the net
retention or export of water or
waterborne material after circulation has
occurred over a period of interest.
Goodwin (1984) examined circulation and
flushing of Tampa Bay for the period
1880-1985.


Both circulation and flushing in
estuaries are determined largely by the
relationship of freshwater inflow to tidal
volume. Jotal inflow to Tampa Bay is
about 45 m /s, much less than the average
tidal flow at mid-tidal cycle of 25,500
m /s. Thus, Tampa Bay as a whole may be
considered a neutral or mildly positive
estuary which, because of bathymetry and
low inflows, is vertically well mixed and
generally unstratified with regard to
salinity (Dinardi 1978).

The tidal prism, or volume of water
in the bay between slack waters, is
greatest in Lower Tampa Bay and least in


f


METERS







































RETURN PERIOD (years)

Figure 26. Total tide height (ft) above MSL versus
return period in years (NOAA 1975). Curves applicable
to St. Petersburg Beach-Clearwater coastline.



the northern arms of the bay. In
1880, respective prisms at their seaward
ends were 1,006 km2-m for the lower bay,
724 km2-m for the mid-bay, 260 k?2-m for
Old Tampa Bay, and 147 km -m for
Hillsborough Bay. As discussed below,
these values have changed because of
dredging and filling, especially in
Hillsborough Bay, in all cases decreasing
even though bay volume has increased.

Currents. Typical current speeds
range from 1.2-1.8 m/s at the entrance to
Tampa Bay, to less than 0.14 m/s in
Hillsborough Bay. Ebb tidal current
speeds are greater than flood currents,
reflecting the faster rate of water-level
change on ebb tide. Winds and runoff may
increase current speeds under extreme
conditions.


The pattern of currents in Tampa Bay
is known for flood and ebb cycles,
although it is useful to note Goodwin's
(1984) caveat that there are no fixed
patterns of circulation in any estuary.
In general, flood tidal currents enter
Tampa Bay by the openings of the Sunshine
Skyway Causeway and separate to the east
and west shores of middle Tampa Bay
(Figure 27). Lesser speeds occur near
shorelines and in the center of the middle
bay. Water is transported at a
diminishing rate into Old Tampa Bay to,
but not much beyond, the Courtney Campbell
Causeway. Transport into Hillsborough Bay
is minimal. The pattern is basically
reversed on falling tide except that water
transport in the central part of the
midbay is greater.

Net circulation. Average flooding
and ebbing currents offset each other over
a complete tidal cycle except for a
residual movement specific to each bay
area. The residual transport is a measure
of net circulation that will occur as long
as similar tidal and other conditions
prevail. Work by Ross et al. (1984) and
Goodwin (1984) has done much to advance
our knowledge of net circulation in Tampa
Bay, and provided very interesting results
(Figure 28).

First, there is a pronounced gradient
in residual water transport (net
circulation) from the bay entrance to
upper bay areas. At the entra ce,
residual magnitu es are about 525 mq/s,
compared to 30 ml/s in Old Tampa Bay and
15 m /s in Hillsborough Bay. Second, net
circulation in Hillsborough Bay always has
been poor and, until recent channel
dredging, was attributable more to river
discharge than to other factors. Third,
at least 20 gyres are present in the bay.
The gyres are circular features of
tide-induced circulation which form when
wind and density stratification are
absent. The gyres range in diameter from
1.5 to 10.0 km and adjoin neighboring
gyres with opposite flow--much like a
series of gears.

The presence of gyres in Tampa Bay
has been known for several years, although
their actual influence remains untested .
Ross (1975) suggested a correlation
between the size and location of gyres






































h1









-- -- -- --





0


0 Location of model computation site (node)
(only 25% of nodes are shown to aid clarity)


Transport vector with node location symbol
(vector magnitude defined by length of line
0, 105 cubic feet per second; vector
direction defined from node location symbol
to end of line)



Transport vector without node location symbol


5
VILES


Figure 27. Water movement during a typical flood tide in 1985 (Goodwin 1984).


with sedimentary features and possibly
macrofauna. Several unanswered
questions regarding gyre dynamics remain:
(1) Do they develop for sufficient periods
to affect water quality, plankton
dispersion, or pollutant transport? (2)
Are their effects permanent or overwhelmed
by wind or other short-term events? and
(3) Do gyres present problems or
opportunities for resource management?


Goodwin (1984) compared tide-induced
residual transport to average tributary
inflow to identify eight significantly
different circulation zones (Figures 29
and 30). Overall, circulation is high in
Zones 1 and 4, low in Zones 3, 6, and 8,
and variable in other zones. Zone 4
(Upper Tampa Bay) is an area of naturally
high rates of exchange with Hillsborough
and Old Tampa Bays, but is separated from

































Location of model computation site (node)
(only 25% of nodes are shown to aid clarity)


Transport vector with node location symbol
(vector magnitude defined by length of line
0 5000 cubic feet per second; vector
direction defined from node location symbol
to end of line)



Transport vector without node location symbol


Figure 28. Residual water movement after a complete tide cycle in 1985 (Goodwin
1984).


Lower Tampa Bay by Zone 3, an area of
natural quiescence. The poorest circu-
lation in Tampa Bay is in Zone 6, Upper
Hillsborough Bay, despite improvements
caused by channel dredging.

Flushing. Goodwin (1984) modeled
transport of phosphorus (due to high
concentrations throughout the bay in 1975)
to assess constituent transport. The


residual transport may be treated as
"flushing" in the popular sense, since it
reflects the tendency of the bay to export
undesirable material. Tide induced
flushing, however, is the flushing of a
constituent minus transport caused by
tributary flow (Figure 31). Highest
phosphorus concentrations were 2.5 mg/l in
Hillsborough Bay and 0.8 mg/l in Old Tampa
Bay, compared to less than 0.2 mg/l at the




































Figure 29. Major circulation zones in Tampa Bay
(Goodwin 1984).



bay entrance. Flood and ebb transport
resembled tidal water transport, reaching
maximum values in the midbay and low
values in the upper arms of the bay.
Residual constituent transport vectors
assumed circular features similar to
circulation gyres, although magnitudes of
transport were affected by the
concentration gradient. The ship channel
gained importance for constituent
transport, and the importance of tributary
flows for constituent flushing from Tampa
Bay remained high.

Changes since 1880. Goodwin (1984)
concluded that historic and recent
alterations to the physical dimensions of
Tampa Bay have been responsible for the
following:

(1) decreased surface area and tidal
prism, especially in Hillsborough
Bay;
(2) increased depth and volume,
especially in Hillsborough Bay;


(3) large (more than 100%) changes in
flood and ebb tide transport caused
by causeways and filling of upper
Hillsborough Bay;
(4) large (more than 100%) changes in net
circulation in Old Tampa Bay and
Hillsborough Bay; and
(5) increased inland (trapping) and
seaward (export) exchange caused by
tidally induced flushing.

Overall, Goodwin's work underscores
three important conclusions, i.e., that
physical changes to the bay have caused
significant effects in circulation and
flushing; Hillsborough Bay was naturally
an area of poor flushing (and was thus the
worst place for municipal and industrial
waste to have been discharged); and the
continued flow of freshwater to Tampa Bay
and especially Hillsborough Bay is
essential to maintain flushing, even
though the volume is low compared to the
average tidal prism. Most of these same
conclusions regarding Hillsborough Bay
also apply to Old Tampa Bay.

2.5 CHEMISTRY OF THE BAY

Numerous studies of water chemistry
in Tampa Bay are available as reviews
(Fanning and Bell 1985), reports (Goetz
and Goodwin 1980), data presentations
(Hillsborough County Environmental
Protection Commission 1972-84), and
unpublished data. Less information is
available on sediment chemistry, but that
which is available largely corroborates
trends and patterns depicted by
water-quality data.

Selected physical and chemical
properties of bay waters and sediment are
reviewed in this section from an
ecological perspective, i.e., as a
description of the environment inhabited
by estuarine plants and animals. Readers
interested more in water quality and human
uses of the bay should realize that
subsequent comments support four
conclusions, namely:

(1) Tampa Bay is not grossly "polluted",
certainly not beyond the point of
rehabilitation;
(2) Parts of the bay are "cleaner" than
others for natural as well as
cultural reasons;


















Z 20 i


w '
S18 A8
0 \ i 1972 AND 1985
IN I 1880 6
I 16 ----- 1972 l
U .. ... .. 19 8 5 4 '

S4 CIRCULATION \
1 ----ZONE 2
1c 2 i I BOUNDARY 7
1 2 V 7 8
3I':'v" ) I ', o t *o
S0 TIDE-INDUCED
10 .CULATO A DISTANCE FROM OLD TAMPA BAY
CIRCULATION ENTRANCE, IN MILES
0 I \ i.! \ 1'iI

- : : \. I POSITION OF
S 6 f I \ \ ALAFIA RIVER MOUTH I.

-:-
4 9172 AND 1985

--V-.I i *.-.-, ., ^ ,,.".I
o . . I _
AVERAGE TRIBUTARY STRE
0 5 10 15 20 25 30 35 40
DISTANCE FROM MODEL BOUNDARY IN GULF OF MEXICO, IN MILES
Figure 30. Average tributary streamflow and tide-induced circulation along longitudinal
summary lines (see Figure 29) for 1880, 1972, and 1985 levels of development.


0 5 10 15 20 25 30 35 4C
DISTANCE FROM MODEL BOUNDARY IN GULF OF MEXICO, IN MILES

Figure 31. Tide-induced and streamflow flushing of example constituent along longitudinal
summary line (see Figure 29), from lower Tampa Bay to Hillsborough Bay, for 1880, 1972,
and 1985 levels of development.










(3) Levels of some pollutants in the bay
have been declining over the past
decade, while others have increased;
and
(4) The overall "quality" of bay zones is
the same whether judged by ecological
or human-use criteria.

2.5.1. General Water Quality of Tampa
Bay

Water quality refers to the fitness
of water for human and natural uses and
can be described by concentrations of
specific parameters (such as bacteria) or
by the relation of observed concentrations
to State standards (allowable levels of
bacteria). Several parameters are
important from the standpoint of human
uses of the bay. The Hillsborough County
Environmental Protection Commission
(HCEPC) has monitored such parameters
throughout Tampa Bay monthly since 1972.
The HCEPC summarizes monitoring data in a
series of annual reports in which a
"general water quality index" for Tampa
Bay is presented. Values of the index
range from excellent (collectively low
values) to undesirable (collectively high
values) and are based on ranked averaged
values for total coliform bacteria,
turbidity, chlorophyll _a and organic
carbon or biochemical oxygen demand
(Figure 32).

Water quality in McKay and
Hillsborough Bays has been undesirable
since monitoring began. The HCEPC
attributed low water quality in
Hillsborough Bay to domestic (City of
Tampa) and industrial wastes. The
influence of Hillsborough Bay upon Tampa
Bay extends along the eastern shore to the
area offshore from the Little Manatee
River, reflected in most years since 1978
as fair to poor water quality. General
water quality in and near the Cockroach
Bay Aquatic Preserve has been excellent or
good, except for fair to poor ratings near
the Little Manatee River due to the
seasonal influence of river discharge.

Conditions in Old Tampa Bay are mixed
because of better water exchange, but
water quality on the western and northern
shores has been deteriorating. In 1978
the western shore north of 1-275 was fair
and only the water in the northeast corner


Figure 32. Trends in general water quality for body
contact in Tampa Bay since 1977 (HCEPC 1978-1983).
E, excellent; G, good; F, fair; P, poor; U, undesirable.


of Old Tampa Bay was undesirable for human
contact and recreation. By 1983 water
quality along the entire western shore
north of 1-275 had declined to poor and
more of the open bay was only fair. The
HCEPC attributed declines in water quality
to discharge of insufficiently treated
domestic waste.











The waters of Pinellas County off the
St. Petersburg municipal waterfront have
improved from poor (1977) to fair (1978,
1981) or better in other years because of
reductions in that city's domestic waste
discharges. Water quality in the lower
bay generally is good to excellent,
although the HCEPC documented a decline to
poor in 1978 because of increased
turbidity caused by harbor deepening. In
summary, general water quality is good to
excellent for much of Tampa Bay, declining
in Old Tampa Bay, and undesirable in
Hillsborough Bay. Point sources,
especially sewage treatment plant
effluent, greatly affect water quality but
improved effluents have resulted in
improved water quality.


2.5.2. Hydrographic Parameters

Temperature. Water temperature
ranges from 110C-320C in subtidal areas
and more widely intertidally. The HCEPC
data indicate very few localized areas of
exceptionally low water temperature.
Lower Boca Ciega Bay, eastern Hillsborough
Bay, and eastern Old Tampa Bay may have
above-average maximum temperatures, but
overall the bay is thermally homogeneous.
Mean annual variation for the bay is
160C-300C.

Ten years of mean annual data are
shown in Figure 33, which illustrate the
temperature characteristics of four bay
sectors. Old Tampa Bay is usually cooler


27.0-


26.0-


25.0-







- 22.0





21.0


20.0
14 1 I I I I 1 l ,
74 75 76 77 78 70 80 81 82 83
YEAR
HILLSBOROUGH BAY ........ LOWER TAMPA BAY
- MIDDLE TAMPA BAY - OLD TAMPA BAY

Figure 33. Mid-depth water temperature in areas of Tampa Bay since 1975 (HCEPC 1984).










than Hillsborough Bay by 10C-20C, and all
bay sectors have been warming since 1976.

Localized thermal plumes near power
plants create elevated temperatures that
vary most from background water
temperatures in winter. The ecological
hazard of thermal plumes in a subtropical
estuary like Tampa Bay is greater in
summer when extra heat drives water
temperature beyond the upper thermal
tolerance of many species, usually about
320C-350C. The cumulative effect of power
plant discharges of heat to Tampa Bay has
not been studied.

Salinity. Salinity of bay waters is
determined by tides and runoff. The
extent to which oceanic salinity is
reduced by runoff and the range of
salinities observed at any place in the
bay are ecologically important for two
reasons. First, salinity gradients set up
gradients of conservative and non-
conservative constituents. Conservative
constituents are those for which observed
concentrations can be explained on the
basis of physical relationships such as
solubility, diffusion, advective
transport, or settling. Examples of
conservative constituents in the bay
include heat, color, fluoride, and
probably total phosphorus.
Nonconservative factors are biologically
alterable and vary indirectly or not at
all with salinity; some examples are
dissolved oxygen, some molecular forms of
nitrogen, and chlorophyll.

Salinity is equally important as an
ecological factor for establishing areas
within the bay which are inhabitable for
some species but not others, and as a
guide to predictable resources such as
feeding or nursery grounds. Exclusion of
oyster predators by low, varying salinity
is a well-known example (Bahr and Lanier
1981). Spawning migrations by a variety
of sport and commercial fishes and
invertebrates are another.

Salinity in the Gulf of Mexico ranges
from 22.6 to 39.0 parts per thousand (ppt)
and averages 34.1 ppt. In lower Tampa
Bay, Terra Ceia Bay to the east has an
average salinity of 24.5 ppt and the
widest range of any bay area--1.0 to
33.7 ppt (Simon 1974). Hillsborough Bay


is fresher than Old Tampa Bay (means of
20.9 and 22.5 ppt, respectively), although
the range of salinity in Old Tampa Bay is
greater by 5-10 ppt.

Vertical differences in salinity
usually are slight, although Finucane and
Dragovich (1966) reported a one time
vertical gradient of 19.6 ppt, thought by
Simon (1974) to be the greatest known
difference. The HCEPC data since 1977
reveal a mean annual vertical salinity
gradient of 2 ppt or less for most bay
areas with a range from 0.3 to 7.7 ppt in
mean annual vertical difference. East
Bay, a deep area between McKay and
Hillsborough Bays, is more stratified with
respect to salinity than most places in
the bay. Vertical salinity gradients in
East Bay are established by Tampa Bypass
Canal discharge into the shallow waters of
McKay Bay, which empties into Hillsborough
Bay as warm, brackish water and overlies
cooler, denser water transported northward
in the main ship channel.

Shipping channels have facilitated
the movement of both tidal and
freshwaters. Goetz and Goodwin (1980)
reported inland movement of isohales near
the main shipping channel during flood
tides and seaward movement during ebb
tides (Figure 34). Giovanelli (1981)
studied the influence of Alafia River
discharge on salinity in lower
Hillsborough Bay. The configuration of
the dredged channel and spoils results in
significant mixing at the river mouth. A
25% reduction in specific conductance
resulted from a 17-fold increase in river
discharge.

Dissolved oxygen. The amount of
gaseous oxygen dissolved in water depends
on temperature, salinity, degree of
physical mixing, and the consumption or
production of oxygen by organisms or
chemical processes. Cold freshwater is
physically capable of holding more oxygen
than warm salt water, for example, and
respiration by plants and animals can
depress oxygen concentrations to hazardous
levels after a long, still night when
photosynthesis has stopped and oxygenation
due to mixing is low. Anoxic conditions
occur when no oxygen is left in solution.
Anoxia may be tolerated by facultative
anaerobes (organisms with alternate
























































LEGEND


-44.0-


Line of equal specific conductance (in
millimhos per centimeter at 250C); interval,
2 millimhos


50' V 'JO 41 so o305 +46 Site of sample collection showing specific
300 0 conductancee value
3.9 \ 0 4 KILOMETERS
42.' I
45 D J3.00






.( 5 V - ?400 LOW SPECIFIC
400 CONDUCTANCE
440-- DISTRIBUTION
S 410 SEPTEMBER 1974
35' 350*


+43.5




Figure 34. Typical (A), high (B), and low (C) specific-conductance distributions in Tampa Bay
(Goetz and Goodwin 1980).











respiratory systems) but results in death
or displacement of most life. The State
of Florida considers an oxygen
concentration of 4 mg/l to be the minimum
necessary for protection of marine life.
Simon (1974) cited several documented
cases of anoxia and associated fish kills
in Tampa Bay.

Simon (1974) gave a baywide range for
dissolved oxygen of 0.9-11.6 mg/l and a
yearly mean for the entire system of 5.9
mg/l. Greater extremes have since been
documented. Vertical gradients of oxygen
are much more pronounced than salinity in
Tampa Bay, especially in deep water and in
Hillsborough Bay. Figure 35 illustrates
average differences between surface and
bottom dissolved oxygen levels in relation
to depth for HCEPC data from 1981 through
1983 at stations in Hillsborough Bay.
Strong vertical gradients are induced by
high oxygen demands of organic sediments
and by accumulations of photosynthetic
plankton near the surface, which shade
deeper waters (Ross et al. 1984).
Self-shading is known for other estuaries
but is not well studied in Tampa Bay.
More study of depth- stratified levels of
dissolved oxygen will be needed to
evaluate impacts of harbor deepening and
eutrophication.

Phytoplankton blooms are most
frequent and prolonged in Hillsborough
Bay, so dissolved oxygen extremes are
larger than in other bay sectors. Minimum


values are lower in Hillsborough Bay
because of depth (as above), reduced fetch
(Ross et al. 1984), plankton respiration
(HCEPC data) and benthic demands
(McClelland 1984). Simon (1974) gave mean
and range data for dissolved oxygen in
several bay areas (Table 9).

Goetz and Goodwin (1980) showed
higher dissolved oxygen values and lower
variability in Old Tampa Bay than
Hillsborough Bay; this agrees with HCEPC
data for 11 years of monitoring. Using
HCEPC second minimum data for dissolved
oxygen at the bottom for comparison
(Figure 36), Hillsborough Bay has the most
oxygen stress, followed by the east shore



Table 9. Dissolved oxygen concentrations for bay
areas (Simon 1974).


Section


Concentration of
dissolved oxygen
Mean (mg/1) Range (mg/1)


Old Tampa Bay

Hillsborough Bay

Upper Tampa Bay

Lower Tampa Bay

Boca Ciega Bay


6.3

6.4

5.8

5.7

5.4


2.7-10.6

0.9-11.6

1.1- 8.1

1.4- 8.5

1.6-10.6


6.0.


6.0.


1.0 2.0 3.0 4.0 5.0
DEPTH, M


6.0 7.0 8.0


Figure 35. Stratification of dissolved oxygen (surface-
bottom values) in Hillsborough Bay in relation to
depth, 1981 through 1983.


LOWER TAMPA
BAY
........


OLD TAMPA


MIDDLE TAMPA BAY .


HILLSBOROUGH BAY


74 76 70 77 78 7'9
YEAR


I I I I
80 81 82 53


Figure 36. Mean annual dissolved oxygen near the
bottom in Tampa Bay (HCEPC 1984).


5.0-

0 4.0-
Ul
0
0
o 3.0-
0

- 2.0-
0
- 1.0-


0










of upper Tampa Bay (Ruskin Apollo
Beach). The eastern shore of Old Tampa
Bay north of Interstate 275 also is
relatively low in dissolved oxygen.

Dissolved oxygen concentrations vary
diurnally (because of depth, light, and
temperature) and seasonally (because of
temperature). Bottom levels are highest
in January and lowest in June through
August (Figure 37). Bottom dissolved
oxygen levels in Hillsborough Bay violate
existing state standards 60 to 90 days
each year. Dissolved oxygen in Old Tampa
Bay covaries in range and pattern with
Tampa Bay, but Hillsborough Bay is almost
always lower. During the past decade,
bottom oxygen levels have declined
slightly and surface levels have increased
at bay areas other than Hillsborough Bay.

Bottom oxygen conditions regulate
benthic fauna composition. In
Hillsborough Bay annual anoxia affects
density and diversity patterns of benthic
invertebrates (Santos and Simon 1980a).
Anoxia in residential canals also causes
fish kills (HCEPC 1984). The extent to
which anoxic or near anoxic conditions in
Tampa Bay are natural or cultural in
origin is not known, but all
circumstantial evidence implicates
municipal wastes as the primary factor.

Light. Light regulates productivity
of phytoplankton and seagrasses in
estuaries (Odum et al. 1974), although an


140 .


120

100
lie -



X
0
I
(3
(3
40


J J
MONTH


appreciation that light is a limit to
productivity in Tampa Bay (or other
shallow, inshore waters of the Florida
gulf coast) is recent (McClelland 1984).
Much data on transparency and light-
attenuating factors are available.

Secchi disk measurements are
available from the 1950's to the present.
Unpublished studies in Sarasota Bay,
immediately south of Anna Maria Sound,
determined that 25%-30% of incident light
in the photo-synthetically active range
(PAR) of wavelengths penetrated to the
Secchi depth (0.5-10.0 m), irrespective of
water mass. The amount of light required
to sustain benthic algae and seagrass in
Tampa Bay is not known, but for
discussion's sake can be set
conservatively as light available at the
Secchi depth. This implies areas where
real depth exceeds Secchi depth would not
receive enough light to support benthic
vegetation.

Several years of HCEPC monitoring
(Figure 38) reveal that the least
transparent waters of Tampa Bay occur
regularly in Hillsborough Bay and much of
Old Tampa Bay, where mean annual light
penetration is less than 1.3 m (Figure
39). Mean depths in these bay areas are
3.2 m and 2.8 m, respectively. Light
penetration improves in Tampa Bay except
near the eastern shore in summer and is
deepest near the bay entrance (greater
than 2.8 m mean annual light penetration).


LOWER TAMPA BAY



"" ....... .............""
MOLD TAMPA SAY \


OLD TAMPA SAY "^ j *..---.- -


I NLLSONOUQIN aYl,


YEAR


0s a s


Figure 37. Mean monthly dissolved oxygen in 1982
near the bottom in Tampa Bay (HCEPC 1984).


Figure 38. Mean annual effective (Secchi) light
penetration in Tampa Bay (HECPC 1984).







































Figure 39. Mean annual effective (Secchi) light
penetration in 1982 (HCEPC 1984).


Effective light penetration varies
seasonally (Figure 40) in relation to
runoff, phytoplankton blooms, and other
factors. Transparency was greatest in
January through March and decayed during
April-September, so that by the fourth
quarter of the year mean Secchi depths
were less than 2.0 m everywhere north of
the Sunshine Skyway Bridge.

Attenuation of light is caused by
scattering and absorption. Color,
chlorophyll, turbidity, and organic carbon
are parameters useful in identifying
causes of attenuation. Color is caused
primarily by discharge of natural metallic
ions, tannins, lignins, and other organic
molecules from rivers and forested
embayments such as Cockroach Bay. Color
is greatest during the wet season.
Patterns and trends of color in areas of


Tampa Bay resemble those described for
Secchi data, indicating the importance of
color as a factor in transparency (Figure
41).

Chlorophyll in phytoplankton absorbs
light, and the cells containing it scatter
light. Chlorophyll a has been measured
at middepth by the HCEPC. Pigment
concentrations are highest (greater than
20 pg/i) in Hillsborough Bay and along the
eastern shoreline south to Ruskin. Low
values (less than 5 pg/1) are typical in
lower Tampa Bay. Mean annual pigment
concentrations in Old Tampa Bay vary and
are usually highest near the Largo Inlet.
The contribution of phytoplankton to light
attenuation is probably understated by
concentrations measured at middepth, since
all HCEPC collections are made in
daylight, when more plankton usually is
near the surface. A complete
understanding of light dynamics in the bay
will require synoptic Secchi disk,
transmissivity, and surface chemistry data
(including chlorophyll), since only the
water column above the Secchi depth is
photically relevant.

Chlorophyll is a partial indicator of
overall turbidity. Another indicator is
total suspended solids, which are usually
quantified as the weight of all filterable
material in suspension (total solids) or
the weight of organic material in
suspension (volatile solids). Turbidity
may also be measured as the loss of light
through a water column (Jackson Turbidity
Units or JTU) or normal scattering of
light (nephelometric turbidity units or
NTU). The latter units are roughly
equivalent. Goodwin and Michaelis (1981)
related these turbidity measures for Tampa
Bay (Figure 42) by the expressions:

Volatile solids = 0.456 (suspended solids)

Nephelometric turbidity = 0.265 (suspended solids)1-155

(Cm. Transparency-10) x Nephelometric turbidity = 500.


It follows from these relations that
suspended solids in the bay are (a)
largely organic; and (b) contribute to
variation in nephelometric turbidity,
which in turn varies as the hyperbolic
inverse of transparency (Secchi depth).








































_>!2.8 m 2.3 m-2.8 m @ 1.8 m-2.3 m 1.3 m-1.8 m <1.3 m

Figure 40. Changes in mean seasonal (Secchi) light penetration in 1983 (HCEPC 1984).



43
































A COLOR
(Platinum-Cobalt Units)


(pg/I)


(mg/1)


Figure 41. Bay-wide distributions of light related parameters in 1982 (HCEPC 1984).











10,000


1,000

o,
E
S100
-I
0
()
UJ
_J
S10
0


1 10 100 1,000 10,000 100,000
SUSPENDED SOLIDS (mg/I)


.Hillsborough Bay
South Tampa Bay

Least-squares regression line
between turbidity (T) and. /
suspended solids (ss)
T 0.265ss1.1551 standard
-/ deviation
/ /


:.. : / "







SUSPENDED SOLIDS (mg/1)

Hillsborough Bay
*South Tampa Bay




Empirical hyperbolic relation
between transparency (TR)
and turbidity (T)
(TR-10) x T = 500
(Transparency 10) x Turbidity = 500
..


0 20 40 60 80 100 1
TURBIDITY (Nephelometric turbidity units)


Figure 42. Relation of organic solids to transparency
in Tampa Bay (Goodwin and Michaelis 1981).


Based on HCEPC data, nephelometric
turbidity usually is greatest in
Hillsborough Bay and Largo Inlet (Figure
41C), although relatively high values are
possible near Mullet Key. Otherwise, mean
annual turbidity for bay waters is 3-5
NTU. For the past decade, mean annual
turbidity has ranged from 3.3 to 7.3 NTU
for all bay sectors. The year 1980 was
exceptional for low turbidity throughout
the bay. Mean annual Secchi depths were
about 1 m, mean annual color and turbidity
were lower than for any other year on
record. Chlorophyll was lower than
previous years but still greater than 20.0
pg/l.

The 1980 data and 10-year trends
suggest that transparency in lower Tampa
Bay is controlled by nonplanktonic
turbidity, whereas plankton (as chloro-
phyll a ) controls transparency in
Hillsborough Bay. Lower Tampa Bay mean
annual transparency declined during
1975-79 and rose thereafter (HCEPC 1984).
Chlorophyll a and color were relatively
constant for the same period, whereas
turbidity rose from a 1975 low and peaked
in 1978. We conclude that turbidity in
the lower bay was either mineral or
nonliving organic matter. In Hillsborough
Bay transparency has been low and annual
means have increased slightly. Trans-
parency and chlorophyll data are rela-
tively high and steady compared to color
and turbidity, indicating that phyto-
plankton is the major factor controlling
light penetration.

Turbidity is caused by ship traffic
(Goetz and Goodwin 1980), suspension of
bottom sediments by currents and runoff,
sewage outfalls and dredging (HCEPC
1977-84). The extent to which dredging
changes turbidity levels is much disputed.
Using HCEPC and other data, Goodwin and
Michaelis (1981) concluded that harbor
deepening did not raise mean turbidity
levels in Hillsborough Bay or lower Tampa
Bay, but that seasonal turbidity minima
may have been slightly raised (Figure 43).
Scientists at HCEPC interpret their data
much differently:

Relatively high values [of
turbidity] in the vicinity of Mullet
Key were the result of dredging
operations occurring in that area as


100,000


10,000


1,000


100


1001



















0
E
1.4
1.2 C
0
1.0 =
0.8 u
I-
0.6 <
0.4 2
0
0.2







0.8
0




10.4


0.6
0.4
0.2


1976 1977 1978 1979 1980
TIME (yr)


*--- Average turbidity


I Standard error of the mean


---- Trend of turbidity minima


Figure 43. Average monthly turbidity and monthly dredge-spoil production rate in (A) Hillsborough Bay, and
(B) South Tampa Bay (Goodwin and Michaelis 1981).


part of the Tampa Harbor Deepening
Project. (1977);

Turbidity patterns throughout
the Tampa Bay Basin were affected by
dredging activities associated with
harbor deepening. The Bay will
continue to be affected to varying
degrees as the project continues.
(1978, 1979);


During 1980 and 1981 [another
bay section] was dredged, adversely
affecting light climate in upper
Tampa Bay and lower Hillsborough
Bay. (1981);

No dredging occurred in the
area during 1982 and 1983 which may
account for the improvement in light
climate. (1984)










Disagreement on the effects of
dredging results in part from the
different time frames used in each
investigation, and also because neither
study was designed nor executed to monitor
dredging effects over local areas within
the bay.

2.5.3. Nutrients

Phosphorus and nitrogen in elemental
form and in molecular combination with
other common elements are taken up by
estuarine plants and animals for use in
metabolism, structural growth, and
reproduction. When an increase in
availability of these substances stim-
ulates biological activity, they are
inferred to be limiting nutrients. In
some cases silica can limit phytoplankton
growth and organic carbon may limit
secondary production.

Forms and amounts of phosphorus and
nitrogen in Tampa Bay have received the
most study due to their role in
stimulating excessive algal growth. In
1967, the Federal Water Pollution Control
Administration (FWPCA 1969) studied odor
in Hillsborough Bay and concluded the
following:

(1) Massive amounts of carbonaceous
organic material, phosphorus, and
nitrogen were discharged by the
Alafia and Hillsborough Rivers, Tampa
and MacDill Air Force Base sewage
treatment plants, and phosphate
chemical plants.

(2) Phosphorus, nitrogen, and chlorophyll
levels indicated rapid
eutrophication, including changes to
sediment chemistry in Hillsborough
Bay.

(3) Eutrophic conditions stimulated
blooms of the macroalgae Gracilaria,
which decomposed along residential
shorelines.

(4) Nitrogen availability was limiting
still greater production of
phytoplankton and Gracilaria.


coastal waters, Tampa Bay is considerably
enriched in phosphate. In fact, no other
major estuarine or coastal area we know of
even comes close to having as high a
phosphate concentration." Their analysis
confirmed the ranking of Hillsborough Bay
as highest in phosphate concentration,
followed by upper Tampa Bay, Old Tampa
Bay, lower Tampa Bay, and Boca Ciega Bay.
Fanning and Bell (1985) detected little
evidence for seasonality in phosphate
trends except for the possibility of a
minor winter minimum. Simon (1974) cited
Taylor and Saloman (1968), Saloman and
Taylor (1972) and data from the
Hillsborough County Environmental
Protection Commission to document a
progressive enrichment of total phosphorus
from 1952 to 1972. There has been a
reduction in mean annual phosphate
concentration in Hillsborough Bay and
other bay segments since 1972 (Figure 44).


The Alafia River is regarded as the
primary source of phosphorus to
Hillsborough Bay, due to naturally high
background levels, upstream discharges of
mining and beneficiation operations,
phosphate chemical processing at the river
mouth, and leaking during loading of
ships. There is, however, not much
evidence supporting the view that
naturally high levels of phosphate in the
Alafia River basin cause elevated levels


1972


'-----r
ACE SEAWATER B
1974 1976 1978
YEAR


1980 1982


Phosphorus. Fanning and Bell (1985) Figure 44. Trend in phosphate concentrations in
stated "Compared to other estuaries and Tampa Bay, 1972-1981 (Fanning and Bell 1985).










of the nutrient in Tampa Bay as opposed to
Hillsborough Bay. The Little Manatee
River drains similar geological formations
but concentrations and loads of phosphorus
are very much lower (Florida Department of
Environmental Regulation 1982; Dooris and
Dooris 1985). The primary sources of
phosphorus to Hillsborough Bay have been
discharges by the phosphate industry
(Toler 1967). Recycling of process and
nonprocess wastewater by the industry has
resulted in a decline in total phosphorus
loading to the Alafia River for the past
decade, a trend also reflected in fluoride
concentrations.

Ross et al. (1984) suggested a mas5
balance for phosphate in which 1.07 x 10'
kg are in storage (plants, animals,
sediments, and waters); inputs result from
rain (45 kg/day), point and nonpoint
sources (11,110 kg/day) and benthic flux
(9,300 kg/day); and exports result from
tidal exchange (-19,960 kg/day), benthic
flux (-22,120 kg/day) and other routes
(-1,510 kg/day). Interesting aspects of
this proposal are the ratio of storage to
exchange, the relative balance of imports
and exports, and the net loading of
phosphate to sediments. Fanning and Bell
(1985) speculated that tributary loads of
phosphorus to the bay may be able to
replace phosphate in the water column of
the bay in about 1 month or less, and that
sedimentary sources could cause the same
replacement in 30-300 days. They conclude
that the input and flow of phosphorus
through the biological system of the bay
could be tremendous, and they urge more
study on the subject.

Nitrogen. Nitrogen is generally
regarded as the limiting macronutrient for
primary production in Tampa Bay. Nitrogen
occurs in seawater as a dissolved gas and
as complex organic molecules such as
protein. Organically bound nitrogen is a
source for animals and large amounts can
occur in municipal effluents. Ammonia
(NH and NH4+), made in the breakdown of
organic nitrogen and by fixation of
gaseous nitrogen, is a preferred nitrogen
source for algae. Both ammonia and
organic nitrogen can be transformed
by bacteria into nitrate (NO3-) via the
intermediate nitrite (NO2-). Aerobic
decomposition of organic nitrogen ends
with nitrate. Concentrations of nitrogen


may be presented as the sum of endpoint
forms, e.g., total Kjeldahl nitrogen
equals ammonia plus organic nitrogen.
Also, nitrate alone or with nitrite has
been reported by some investigators.

Simon (1974) identified municipal
sewage treatment plants as the primary
source of nitrogen to Tampa Bay. Mean
annual loading of nitrate to Tampa Bay is
greatest from the Alafia River (about 3.9
x 10 kg/yr) followed by the Manatee and
Hillsborough Rivers (each about 9 x 104
kg/yr). On the other hand, the Manatee
and Alafia Rivers contribute nearly the
same amount of organic nitrogen, 2.5 x 10-
kg/yr, followed by the Hillsborough River
(2 x 10 kg/yr) (Dooris and Dooris 1985).
High levels of organic nitrogen in the
Manatee River have been caused by the
Bradenton sewage treatment plant and pulp
effluent from a citrus processing plant
(DeGrove 1984). Municipal sewage
treatment plants elsewhere around the bay
are significant nitrogen sources
(McClelland 1984).

A careful geographic comparison of
nitrogen species from 1972 to 1976 was
made by Goetz and Goodwin (1980). Mean
organic nitrogen ranged from 0.5-1.0 mg/l
in Old Tampa Bay, around 0.5 mg/l in upper
Tampa Bay and at or below the same level
in the lower bay (Figure 45). In all
three areas, seasonal and year-to-year
variation was low. On the other hand,
mean organic nitrogen concentration in
Hillsborough Bay ranged from 0.75 to 1.25
mg/l, and temporal variation was greater.
Nitrite and nitrate concentrations were
similarly low and steady everywhere in the
bay, except in Hillsborough Bay. Ammonia
levels were variable in all zones.
Seasonal minima were less than 0.1 mg/l in
most places but more than 0.1 mg/l in
Hillsborough Bay. Seasonality was evident
for total inorganic nitrogen, which
decreases substantially after rainy
seasons; reasons for this trend are
unclear (Fanning and Bell 1985).

Past nitrogen levels in Hillsborough
Bay were greater than in other estuaries
(FWPCA 1969) but inorganic nitrogen for
the bay as a whole is only slightly higher
than reported elsewhere (Fanning and Bell
1985). However, ammonia is more abundant
relative to other inorganic forms than in
























































C D
82 45 40' 35' 30' 82 25' S2*45' 40' 35' 30' S2*25'




.474
0 +0 + +4 0

020 21+ 32 0.


5" + 55' +
37 1








I5 1C 23 44
40 25 n 1 o 0















Figure 45. Nutrient distributions (mg/I) in Tampa Bay. (A) Ortho-P, Sept. 1972; (B) NH4, Dec. 1973;
(C) NO3, Dec. 1972; (D) Organic-N, Dec. 1973 (Goetz and Goodwin 1980).










many other estuaries. Fanning and Bell
reported a mean ratio of NH3 to total
inorganic nitrogen of 0.84 (range
0.54-0.99).

Ross et al. (1984) outlined the
dimensions of a preliminary nitrogen
budget for Tampa Bay. They suggested a
nitrogen storage of 3.87 x 107 kg, inputs
from rain and cultural sources, (21,470
kg/day) and benthic releases (55,750
kg/day). Exports occur in tidal exchange
(-16,100 kg/day), biological losses
(-8,140 kg/day), and benthic uptake
(-53,000 kg/day). By these estimates the
benthos is a net source of nitrogen and is
acting as a sink for phosphorus. Fanning
and Bell (1985) computed a rapid turnover
rate for nitrite and nitrate through Tampa
Bay of about 1.4 months, due to runoff.
They also estimated that benthic releases
of ammonia could replace the overlying
ammonia in 14 days.

Nutrient relationships. Fanning and
Bell (1985) calculated a ratio of nitrogen
to phosphorus of 0.3 in 1972 and 1.3 in
1981 and concluded that phytoplankton have
been nitrogen-limited since 1972. They
cautioned against an interpretation that
nitrogen limitation has declined; rather,
lower phosphate levels indicate that
plants may be consuming more of the
available phosphate. McClelland (1984)
found correlations of organic and total
nitrogen, ortho and total phosphorus, and
orthophosphorus and chlorophyll a but
concluded that all were trivial
relationships.

2.5.4. Sediments

Despite the fact that since the
1950's sediment composition and chemistry
have been known to influence ecological
conditions in Tampa Bay (Dawson 1953,
Hutton et al. 1956) comparatively little
is known of sediment structure or
dynamics. The most authoritative,
descriptive work, by Goodell and Gorsline
(1961), is 25 years old. Methods for
sediment-water nutrient exchange are
recent and have been used only in small
areas of the bay during the past few
years.

Granulometry. Sedimentary types
correspond with bathymetric features of


Tampa Bay (Goodell and Gorsline 1961). In
sand and grass flats less than 2 m deep,
mean grain size was 2.92 phi and sediment
was 2.7% carbonate. In deeper natural
channels more than 6 m deep, mean grain
size was 2.05 phi and sediment was 25.2%
carbonate. Lagoonal beaches were about
28% carbonate, whereas mangrove beaches
contained no carbonate.

Mean grain size decreased from 2.2
phi at the entrance to Tampa Bay to 3.20
phi at its head (Figure 46). Mean
carbonate content decreased from 16% to 2%
over the same distance. Deeper waters in
lower Tampa Bay had coarser sediments that
contained more carbonate than average.
Hillsborough Bay had finer sediment than
average (mostly silt), and sediments
between Interbay Peninsula and Big Bend
had above-average amounts of carbonate.
Organic content and sorting increased from
the southeast side of lower Tampa Bay to
the northwest corner of Old Tampa Bay, in
a pattern almost 900 to the plane of mean
grain size. These results were
interpreted as evidence for two
sedimentary populations, terrigenous and
biogenic, which are of similar density and
travel together.

Chemistry. Organic carbon and
nitrogen and total phosphate distributions
in Hillsborough Bay sediments were
determined in 1968 by FWPCA (1969). All
three constituents were in greatest
concentration at the mouth of the Alafia
River. Organic carbon and nitrogen
concentrations were also high at Hookers
Point and south of Long Shoal, east of the
MacDill Air Force Base sewage treatment
plant outfall. These distributions may be
different in 1985, because of extensive
dredging and filling by the U.S. Army
Corps of Engineers and improved municipal
effluent quality, but Hillsborough Bay is
still an area of exceptional oxygen demand
and uptake of ammonia and orthophosphate
(McClelland 1984). Shoreline areas of Old
Tampa Bay also have rapid flux rates with
regard to these parameters (Figures 47
through 49).


McClelland (1984) gave rates for
constituent release from sediments in
Hillsborough Bay as 58.75 mg/mi/day
(ammonia), 40.43 mg/m2/day (total










































Figure 47. Orthophosphate uptake by bay sediments
(McClelland 1984).


Figure 48. Ammonia uptake by bay sediments
(McClelland 1984).


Figure 46. Regional trend in (A) mean sediment grain
size (phi) and (B) weight percent of carbonates in
Tampa Bay (Goodell and Gorsline 1961).




































Figure 49. Dissolved oxygen uptake by bay sediments
(McClelland 1984).


phosphate), and 10.88 mg/m2/day (total
nitrogen). Constituent uptake rates
characteristic of the sediments in
Hillsborough Bay were 699.12 mg/m2/day
(total organic carbon); 6.8 mg/m2/day
(nitrites and nitrates) and 0.54-9.10
g/m /day (oxygen). Ross et al. (1984)
used the same data to compute a baywide
net flux of 2,750 kg nitrogen/day from
sediments, and an incorporation of 12,823
kg phosphorus/day into sediments.


2.6 AREA SUMMARIES

2.6.1. Hillsborough Bay

Hillsborough Bay is the best studied
area of Tampa Bay. This area is the
deepest, most poorly flushed area; it has
lowest average salinities and is affected
most by freshwater input (from 3 rivers).
As a result, salinity stratification
occurs more often in Hillsborough Bay than
elsewhere, but such conditions are not


0 6 ___ 10 ILE S
a 0 a 10 16 ,(ILOuETERS
Explanation of Rates
V = Very high rate (0.203 gm O2/hr/m2)
H = High rate (0.131 gm 02/hr/m2)
M = Medium rate (0.111 gm O2/hr/m2)
All other areas low rate
1,. (0.040 gm O2/hr/m2)


extreme. On the other hand, vertical
gradients in dissolved oxygen are strong;
oxygen levels vary greatly due to
phytoplankton blooms and sediment demands;
and long periods of anoxia are common.
Benthic faunal communities reflect oxygen
stress. Benthic nutrient fluxes are
probably important in regulating
water-column dynamics. Phosphate and
fluoride levels have been very high in the
past but are declining. Harbor projects
may have improved circulation but flushing
remains poor.

2.6.2 Old Tampa Bay

This area is cooler than Hillsborough
Bay but not as brackish. Inflows of
freshwater have been modified extensively
and shoreline areas are rapidly being
urbanized. Old Tampa Bay is relatively
shallow, and waters south of the Courtney
Campbell Causeway are moderately well
flushed. Waters north of the causeway and
in the Largo Inlet area have exhibited
signs of eutrophication during the past
decade. Because of development in the
area and water quality projections by
McClelland (1984) there is great concern
that sediment conditions and water quality
will deteriorate rapidly by the year 2000.

2.6.3 Middle Tampa Bay

This area of geographical transition
is also where physical and chemical
gradients between the lower and upper bays
are pronounced. Circulation is good,
although flushing is variable depending on
location. The eastern shore is not as
highly developed as the western shore but
is influenced in wet years by Hillsborough
Bay and inadequate sewage treatment.
General water quality off St. Petersburg
has been erratic and may foreshadow
deterioration. Loss of transparency is a
particular threat to this area, because
seagrass loss has not been severe but may
increase as light declines.

2.6.4 Lower Tampa Bay

Because of its proximity to the Gulf
of Mexico, this area continues to be least
affected by cultural influences.
Circulation and flushing are comparatively
good. Temperature and salinity ranges are
lower than in upper bay areas. Oxygen and










transparency levels are high. Overall
water quality is high and better where the
area meets all other areas, except Boca
Ciega Bay. The waters of lower Tampa Bay
are threatened most by maintenance and
deepening of channels in the north and
nutrient enrichment in the south.

2.6.5 Boca Ciega Bay

This area was investigated by the
U.S. Bureau of Commercial Fisheries in the
1950's and 1960's, when it was subject to
extensive dredging and filling for
residential waterfront property
development. Simon (1974) summarized the
early studies, but except for Geo-Marine,
Inc. (1973) few recent data are reported.
The bay has been channelized and filled
extensively. Anaerobic sediments are
found in poorly flushed canals and other
areas. Nutrient concentrations are high
and increased during the past decade
because of sewage plant effluents and
stormwaters. Light penetration is poor
much of the time and phytoplankton blooms
cause erratic oxygen variations.


2.6.6. Terra Ceia Bay and the Manatee
River

These areas have warmer winter air
temperatures and as a result have the
largest mangroves in Tampa Bay. Terra
Ceia Bay and surrounding waters (including
Bishop Harbor) were declared an aquatic
preserve by the State of Florida in 1984
because of high overall environmental
quality. The bay is subject to oxygen and
transparency depressions in the wet season
due to runoff, but in this area such
trends are natural. Conditions in the
Manatee River are poorer than Terra Ceia
Bay but the river as a whole is in good
condition. Sediments near Bradenton are
organic and anoxic because of municipal
and industrial effluent; nutrients in the
middle river are consequently high and
phytoplankton blooms reduce oxygen levels
to lower than State standards. Withdrawal
of freshwater from the Manatee River and
its tributary, the Braden River, pose
serious threats to the integrity of this
environment by eliminating dry-season
flows and reducing wet-season flows. The
Manatee River delivers more organic
nitrogen to Tampa Bay than any other


river, and additional loading is likely to
occur.


2.7 COMPARISON OF TAMPA BAY TO
CHARLOTTE HARBOR

The natural history of Charlotte
Harbor was reviewed by Taylor (1974) and
Estevez (1981). Comparisons to Tampa Bay
are based on these reviews, which should
be consulted for references to original
literature.

Charlotte Harbor and its adjacent
estuarine waters are about 70 square miles
smaller than Tampa Bay. The harbor has
nearly the same original shoreline. Like
the bay, the harbor is Y-shaped, but its
upper reaches are much narrower. Their
mean depths are comparable, as are their
relative depth distributions. The harbor
has a more extensive lagoonal system than
Tampa Bay (and for that reason had about
two to three times more original seagrass
acreage). Sediment composition is very
similar in the two estuaries.

The climate around Charlotte Harbor
is warmer but only slightly wetter than
Tampa Bay. However, runoff to the harbor
and adjacent inshore waters is about one-
third greater, or twice as great if the
Caloosahatchee River is considered. The
Myakka River resembles the Little Manatee
River in Tampa Bay, because both have low
flows and periods of no flow, but no bay
counterpart exists for the Peace River.
Discharges from the Peace River cause a
pronounced density stratification
throughout much of the harbor, which is
accompanied by vertical oxygen gradients
and anoxia. Density stratification
distinguishes Charlotte Harbor from Tampa
Bay, and oxygen dynamics in the harbor
resemble that seen in Hillsborough Bay.
The latter area's dominant and
characteristic phytoplankton blooms are
also shared by the upper and middle
portions of Charlotte Harbor.

Dissolved oxygen levels are similar
in Charlotte Harbor and Tampa Bay, a fact
which deserves considerable investigation
insofar as ecological consequences are
concerned because the bays have much
different salinity structures. In
addition, low oxygen levels in Tampa Bay










are thought to be caused by human
activities rather than natural forces, but
it may be that biota in the two bays
respond to reduced oxygen in comparable
ways. Total nitrogen levels are roughly
comparable, but total phosphorus is many
times higher in Tampa Bay than in
Charlotte Harbor.

It follows from this brief comparison
that Tampa Bay is not physically unlike a
nearby estuary except for different


salinity structure. Moreover, dissolved
oxygen and nutrient data for the two
systems are intriguing both where they
agree and differ. Additional comparative
studies are needed to understand the
extent to which undesirable conditions in
Tampa Bay are ecologically relevant,
significant, or reversible. It may be
that widely held views about the two
systems --or even the definition of
pollution in subtropical estuaries--need
to be revised.

















CHAPTER 3. BIOLOGICAL CHARACTERISTICS


3.1 PHYTOPLANKTON


Phytoplankton are microscopic
floating plants which are classified by
size or taxonomic group. The smallest
phytoplankton (ultraplankton) are less
than 5 pm in diameter; some of the larger
forms in Tampa Bay may be up to 2 mm in
diameter. There are four principal groups
of phytoplankton in Tampa Bay (Steidinger
and Gardiner 1985): phytomicroflagellates,
diatoms (Figure 50), dinoflagellates, and
blue-green algae. The early studies of
phytoplankton in Tampa Bay (Marshall 1956,
Pomeroy 1960, Dragovich and Kelly 1964,
1966, Taylor 1970, Turner 1972) have been
summarized by Steidinger and Gardiner
(1985). These studies were initiated in
response to the problem of blooms (cell
counts usually greater than 50,000 per
liter) of toxic dinoflagellates
(Ptychodiscus brevis), known as "red
tides," particularly the massive blooms of
1946-1947. The findings of all studies to
date can be summarized as follows:


(1) A north-to-south, or head-to-mouth,
gradient exists in phytoplankton
species numbers. In general as one
moves from the less saline upper
portions of the bay to the more
saline, lower portions of the bay,
water clarity and phytoplankton
species numbers (or "diversity")
increase, while nutrient levels,
chlorophyll _a., and total
phytoplankton cell counts decrease.
The frequency of phytoplankton blooms
and the eutrophic and turbid nature
of the upper bay, particularly Hills-
borough Bay, have been a common
observation in recent years (Federal
Water Pollution Control
Administration 1969; Simon 1974).


Skeletonema costatum (Greville)Cleve




10 l
& io
C


25 j
Ptychodiscus brevis (Davis)Steidinger

Figure 50. Typical Tampa Bay phytoplankton.
Skeletonema costatum is a diatom and Ptychodiscus
brevis a dinoflagellate.


(2) Nanoplankton (5-20 pm) are generally
the dominant size class of the
phytoplankton. Small diatoms and
microflagellates predominate, except
when certain seasonal, monospecific
blooms of species of blue-green algae
(Schizothrix) or dinoflagellates
(Gymnodinium nelsonii, Ceratium










hircus, Procentrum micans, Gonyaulax
spp. and others) dominate in
Hillsborough Bay and Middle Tampa
Bay.

(3) At least 272 species of phytoplankton
occur in the bay; the majority (167
of 272) are diatoms (Steidinger and
Gardiner 1985). The species fall
into two cosmopolitan classes: those
characteristic of temperate and warm
waters and those characteristic of
warm water only. The most dominant
planktonic species is the diatom
Skeletonema costatum. Numerically,
it dominates samples taken between
January and May and again in the
fall. Other diatoms (Rhizosolenia
spp., Chaetoceros spp.) are dominant
during late spring and summer.
Localized blooms of the blue-green
alga Schizothrix calcicola and some
dinoflagellate species (Gonyaulax
monilata) can complicate this general
pattern.

(4) Short-term fluctuations in species
composition and standing crop are
common. Seven-fold to ten-fold
differences in biomass are reported
within one tidal cycle.

(5) The majority of the bloom species are
resident in the bay autochthonouss)
but significant blooms occasionally
occur due to species which invade
from the Gulf of Mexico
(allochthonous). Blooms of the toxic
Ptvchodiscus brevis originate 16-60
km offshore of the mouth of the bay
for reasons as yet unclear, and are
carried into the bay. Between 1946
and 1982, such invasions occurred at
least 12 times (Steidinger and
Gardiner 1985). In 1963 and 1971 the
bloom extended into the upper reaches
of the bay and resulted in massive
fish kills. Many factors are
implicated in algal blooms including
salinity regimes, availability of an
inoculum, and low rates of mixing of
bay waters. For example, higher than
normal salinities in the upper bay
(up to 31 ppt) during 1963, and 1971
allowed P. brevis to survive and
bloom after invasion from the ocean
(Steidinger and Gardiner 1985). For
the blue-green algae Schizothrix,


temperature and high light tolerance
are also important. Johansson et al.
(1985) noted that Schizothrix
displaced Skeletonema and other
diatoms at peak summer water
temperatures above 300C, but was
virtually absent between late winter
and early summer.

(6) Many of the previous studies utilized
analytical procedures which limit the
quantitative comparison of all data;
some uniform sampling strategy and
analytical procedures are needed to
make future data more usable
(Steidinger and Gardiner 1985).
Quarterly sampling and ignoring the
nanoplankton in taxonomic and
production studies are two of the
problem areas.

Primary production studies on
phytoplankton in Tampa Bay have been
summarized by Johansson et al. (1985).
Table 10 lists the annual rates reported
in several studies using three different
methods. Whether the different values
over time reflect a real increase in
primary production by phytoplankton or
simply the results of different
methodologies cannot be determined at
present. Earlier data may be of limited
value due to the methodology used (lack of
grinding), which produces a probable
underestimation of chlorophyll a in
eutrophic waters; however, it is reason-
able to assume a real increase in phyto-
plankton production due to eutrophication
(Johansson et al. 1985). Annual produc-
tion of 340 g C/m2 is suggested as a
reasonable estimate for phytoplankton
primary production in the deeper portions
of Tampa Bay and 50 g C/m2 for shallower
portions based upon the available data
(Johansson et al. 1985).


3.2 BENTHIC MICROALGAE

Benthic microalgae are species of
algae, similar to the phytoplankton, that
live on surfaces (sediment, seagrass
blades, rocks) instead of being suspended
in the water column. Steidinger and
Gardiner (1985) noted that benthic
microalgae have received very little
attention in Tampa Bay, even though they
may be a significant source of food for










Table 10. Estimated annual phytoplankton production rates in the Tampa Bay system
(g C/m2/yr) (Johansson et al. 1985).


Old
Dates and methods Tampa Bay


Hillsborough


Middle


Bay Tampa Bay


1968
Chlorophyll + light 170 270

1965-67
Oxygen 430 610

1969-72
Chlorophyll + light 290 580


1973-83
Carbon isotope -- 620 620


many organisms. Primary production rates
of 100-200 g C/m2 have been reported for
benthic microalgal communities on shallow
mudflats (Steidinger and Gardiner 1985).
In addition, bacteria and microalgae are
commonly the first colonizers on newly
produced seagrass leaves and are grazed by
organisms living on seagrass blades
(Zieman 1982).

Benthic dinoflagellates (Amphidin-
ium, Thecadinium, Polvkrikos, Scrippsi-
ella) can be numerous in sediments.
Durako et al. (1982) demonstrated high
rates of oxygen production by such benthic
dinoflagellates in a Tampa Bay seagrass
bed.


3.3 EPIPHYTIC MICROALGAE

Epiphytic (living on plants)
microalgae are treated here as a group
separate from the other benthic algae
because of their apparent importance in
food webs in other Florida estuarine
systems (Fry 1984), and because those
found growing on seagrass leaves in Tampa
Bay have received some study (Dawes 1985).
The most common epiphytes are species of
Champia, Lomentaria, Polysiphonia,
Acrochaetium, Fosliella, Hypnea, Spyridia,
Cladosiphon, Ectocarpus, and Cladophora.
The epiphytic brown algae are typically
more common in winter. Although no


detailed seasonal and taxonomic studies
have been made on the algal epiphytic
community in Tampa Bay, studies elsewhere
in Florida (Humm 1964; Ballantine and Humm
1975; Hall and Eiseman 1981) have revealed
a diverse population of these algae on
seagrass blades; up to 113 species have
been identified during a 1 year study.
The possible importance of epiphytic algae
in the food web and the general health of
seagrasses in a eutrophic estuary like
Tampa Bay will be discussed later. It is
enough to note here that the abundant
caridean shrimp and amphipods found in
Tampa Bay seagrass meadows have been shown
elsewhere to depend heavily upon seagrass
algal epiphytes as a source of food (Ewald
1969; Zimmerman et al. 1979; Van Montfrans
et al. 1982; Orth and Van Montfrans 1984).
It is likely that the same dependence will
be found here.


3.4 ATTACHED AND DRIFT MACROALGAE

Macroalgae are abundant in Tampa Bay
and the 221 identified species from the
bay represent a greater diversity than
that reported for any other estuary in
Florida (Dawes 1985). Red and green algae
predominate, with brown algae being more
abundant in the winter and early spring,
though still not predominant.
Ninety-nine species of red algae, 68
species of green algae, 30 species of


Lower
Tampa Bay










brown algae, and 1 Xanthophycean alga are
listed by Dawes. Dominant genera include
Gracilaria, Ulva, Hypnea, and
Acanthophora. Although blue-green algae
have not been extensively studied, about
30 species are believed to occur.

The ecological role of macroalgae in
the bay has not been studied. In other
parts of Florida, the drift algal
assemblage (Ulva spp., Gracilaria
tikvahiae, Hypnea spp., Acanthophora
spicifera) commonly seen in the bay has
been reported to provide fish and
invertebrate habitat (Kulczycki et al.
1981) and possibly food, both by being
directly consumed and as attachment sites
for epiphytic algae that also are directly
consumed (Zimmerman et al. 1979; Lewis
1982b).

Most studies of macroalgae in the bay
have been taxonomic or physiological in
nature (Dawes 1985); have focused on the
overabundance of certain pollution
indicator species (Ulva spp., Gracilaria
spp.) which cause aesthetic problems
(Federal Water Pollution Control
Administration 1969); have been implicated
in the elimination of seagrass meadows
from certain parts of the bay (Guist and
Humm 1976); or have anecdotally reported
consumption of macroalgae by manatees
(Lewis et al. 1984). The Federal Water
Pollution Control Administration (1969)
studied the abundance and distribution of
macroalgae in Hillsborough and Old Tampa
Bay to determine the source of odor
problems reported by residents along the
western shore of Hillsborough Bay. The
study concluded that the odors were caused
by excessive nutrient concentrations which
led to massive blooms of the macroalga
Gracilaria tikvahiae. This species, in
turn, was killed by normal salinity
reductions during times of heavy rainfall
and decayed to produce the odor.

More recently, after a period when a
relatively low standing crop of macroalgae
was observed--in conjunction with the
upgrading of treatments by major
dischargers--a bloom of algae occurred in
1982. As a result, a 1-year study of the
distribution and abundance of macroalgae
in Hillsborough Bay was funded by the City
of Tampa (Mangrove Systems, Inc. 1985).
The results of that study indicated that


large blooms of macroalgae still are
occurring in Hillsborough Bay, and that
seasonal and large-scale, year-to-year
variations may occur for reasons not well
understood. Figure 51 shows the total
estimated dry weight standing crop of
macroalgae in Hillsborough Bay based upon
quantitative sampling at eight permanent
and three to four floating stations
sampled monthly between February 1983 and
April 1984. Normal year-to-year water
temperature variations may be important.
In any case, nutrient concentrations in
the upper portions of the bay do not
appear to have been reduced enough to
limit the macroalgal blooms.

Rates of primary production by Tampa
Bay macroalgae of approximately 70 g
C/m2/yr have been measured in both
laboratory and field experiments (Hoffman
and Dawes 1980, Dawes 1985). The data are
very sparse, and much additional work,
particularly seasonal field measurements,
is needed.


3.5 SEAGRASS MEADOWS

Seagrasses are submerged flowering
plants with true roots and stems (Figure
52) and are quite different from
"seaweeds" (macroalgae), nonflowering
algal species without true roots. Lewis


24
22-
20-
o 18
S16-
- 14-
I-
S12-
10-
>- 8
6-
8-
0 6-
N 4-
2-
0


W SHALLOW WATER
(depth less than 1 fathom MLW)
DEEP WATER
(depth greater than 1 fathom MLW)


F M A M J J A S O N D J F M A
E A
B 1983 MONTH N 1984


Figure 51. Estimated total drift algae standing crops
in Hillsborough Bay during February 1983-April 1984
(Mangrove Systems, Inc. 1985).


FA


0 Fl;7-q L]


"eA I "/11 IVVZA LZ.U


If/Jl


























Figure52. Underwater photograph offlowering turtle
grass IThalassia testudlnum), off Snake Key in Lower
Tampa Bay.


et al. 1985a) reported that five of the
seven species of seagrasses known from
Florida are found in Tampa Bay: Thalassia
testudinum (turtle grass); Syringodiue
filiforme (manatee grass); Halodule
wrightii (shoal grass); Ruppia maritime
(widgeon grass); and Halophila engelmannii
(star grass).

Seagrass meadows now cover 5,750 ha
of the bottom of the bay (Figure 53).
Based upon historical aerial photography
and maps, it is estimated that seagrasses
once covered 30,970 ha of the bay (Figure
54). This 81% loss has had severe effects
on the bay's fisheries (Lombardo and Lewis
1985).

Box cores taken at 18 stations in the
bay over a 1-year period (Lewis et al.
1985a) showed that seagrass meadows in
Tampa Bay are largely monospecific, with
approximately 40% being turtle grass, 35%
shoal grass, 15% manatee grass, and 10%
widgeon grass. Star grass was seen
infrequently. Lewis et al. (1985a) defined
five types of seagrass meadows in the bay
based on location, form, and species
composition (Figure 55): (1) mid-bay shoal
perennial MBS(P); (2) healthy fringe
perennial HF(P); (3) stressed fringe
perennial SF(P); (4) ephemeral E; and
(5) colonizing perennial C(P). The
idealized cross sections in Figure 56 are


derived from actual transects established
during 1979-80 (Lewis and Phillips 1980).
It is hypothesized that Types 2-4 are
stages in the eventual disappearance of a
seagrass meadow due to human-induced
stress, as illustrated by the arrows in
Figure 55. A brief description of each
seagrass meadow type follows.

Mid-bay shoal perennial (Figure 55
and 57). These meadows are generally
composed of Halodule, Thalassia and
Syringodimm. Ruppia rarely is observed,
which may be attributed to the generally
high current regime and/or higher
salinities not typically found in meadows
closer to shore. These meadows are
located on natural shoals existing in the
middle portion of the bay. They are
present year round (perennial), although
variations in cover by the different
species occur seasonally.

Healthy fringe perennial (Figures 55
and 58). These meadows are the most
common meadow type in the bay and extend
from around the mean low water mark into
water depths of approximately -2 m MSL.
All five species of seagrasses found in
the bay occur in this meadow type.
Zonation begins with ARuppa in the
shallowest water close to shore and grades
with increasing depth through nearly pure
patches of Halodule, followed by Thalassia
and then Syringndium. Healthy fringe
meadows in Tampa Bay normally have an
offshore, unvegetated sand bar separating
the main portion of the meadow from open
bay waters and creating a "basin" behind
the bar. This basin was described by
Phillips (1950b) as a "central
declivity." Similar sand bars have been
observed offshore of seagrass meadows in
Charlotte Harbor and are plainly visible
in aerial and satellite photography of
that area. The offshore bar may be
critical in intercepting waves and
reducing storm and boat wake damage to
these seagrass meadows. Its complete loss
may make replanting of seagrasses and the
restoration of the fringe meadows very
difficult. A typical cross section
through a healthy fringe perennial
seagrass meadow is diagrammed in Figure
57.

Stressed fringe Perennial (Figure
55). These meadows are similar to healthy




























gULF


cE EX I CO


Tampa


* = SEAGRASS
H = HARD BOTTOM
U = UNCLASSIFIED


Figure 53. Seagrass meadow coverage In Tampa Bay, 1985 (from Lewis et al. 1985a).



































Figure 54. Estimated historical seagrass meadow
coverage in Tampa Bay, c. 1879 (from Lewis et al.
1985a).


fringe perennial meadows except that total
cover is reduced within the basin behind
the offshore bar. Destabilization of the
offshore sand bar apparently leads to its
inshore migration and eventual
disappearance. This type of meadow
generally occurs in areas closer to
Hillsborough Bay where a tenfold increase
in average chlorophyll a values (compared
to Tampa Bay) is typical.

Ephemeral (Figure 55). These meadows
are composed almost entirely of Ruppia
with occasional sprigs of Halodule. They
are not present year round and their
locations often vary from year to year.
Phillips (1962) noted the unusual
appearance of Ruppia patches in
Hillsborough Bay along Bayshore Boulevard
and at the mouth of Delaney Creek in the
winter of 1961. No other seagrass was
seen in these areas. Mangrove Systems,
Inc. (1978) also noted the cyclic
appearance and disappearance of a


monospecific Ruopia meadow near the Big
Bend power plant in Hillsborough Bay
during 1976-78. These meadows probably
represent the final stage of seagrass
meadow degradation in Tampa Bay and would
be followed by the complete absence of
meadows which presently is the case in
most of Hillsborough Bay.

Colonizing perennial (Figures 55 and
59). This meadow type commonly is found
in a narrow band in the euphotic zone of
human-made fills such as Courtney Campbell
Causeway (Figure 59), Howard Frankland
Bridge Causeway, and the Picnic Island
fill. It is believed to represent a
meadow type dominated by those species
that can produce abundant propagules that
disperse and colonize appropriate shallow
substrates. Only Ruppia shows large-scale
sexual reproduction and seed production in
Tampa Bay (Lewis et al. 1985a). Seed
production by the other four species is
rare to nonexistent, and therefore, these
seagrasses colonize by dispersal of shoots
or rhizomes produced asexually through
fragmentation. Because of the exposed
nature of the human-made fills and their
generally coarser sediments, Ruppia is not
as common as in the inshore portions of
the fringe meadows. Both Halodule and
Syrinqodium produce large amounts of
detached rhizomes, particularly during
storms, and it is possible that these
float into unvegetated areas, attach
through new root formation, and establish
new meadows. Thalassia produces
relatively fewer detached shoots and
rhizomes, and, due to their increased
buoyancy, these are less likely to sink
into an area appropriate for meadow
establishment. Even if sinking and
attachment occur, slower root and rhizome
growth rates would make establishment of a
new meadow by asexual means less likely.
This may explain why Halodule and
Syrinqgodium are the dominant species in
this meadow type.

As noted by Lewis et al.(1985a), most
of the work to date on seagrass meadows in
Tampa Bay has concentrated on descriptive
biology (distribution, reproduction,
infaunal communities). The elucidation of
the functional role of seagrass meadows in
the bay in terms of value as a food source
(direct herbivory, detrital, drift and
epiphytic algal component) and habitat is






























,,-"-. OR
"_ * R ( H )

RIH -
9r1



F ,),---''- ,(. -. -

R(H) ~~ ~ -- -___ ___


H. HALODULE R RUPPIA S SYRINGODIUM T THALASSIA

Figure 55. Seagrass meadow types in Tampa Bay as described in Lewis et al. 1985a.


MBS(P)





HF(P)





SF(P)


(E)





C(P)











A S T/S 0 H/T H/R R O/A


SHORE 1



.^ MH A ALGAE
MMMW MEAN HIGHER HIGH WATER / H. L2E
MLHW MEAN LOWER HIGH WATER R. U-PPIA
M/ HLW MEAN HIGHER LOW WATER . 8 .IN.oo
MLLW MEAN LOWER LOW WATER T T TLASA
Fg0 UNVEGETATED


Figure 56. Typical seagrass meadow zonation in Tampa Bay (from Lewis et al. 1985a).


Figure 57. Aerial photograph of a perennial healthy Figure 58. Aerial photograph of a perennial mid-bay
fringe seagrass meadow offshore of Bishops Harbor, shoal seagrass meadow, Lower Tampa Bay.
Lower Tampa Bay.


being initiated only now, primarily in
relation to larval fish use. Even
estimates of total primary production by
seagrasses are hampered by the lack of
comprehensive baywide seasonal data.

Using oxygen production measurements,
Pomeroy (1960) calculated that turtle
grass and manatee grass production in
lower Tampa Bay was 500 g C/m2/yr. This
technique is no longer considered to be
accurate because recycling of oxygen in


the lacunal spaces of seagrasses
introduces error (Hartman and Brown 1966).
For purposes of calculating baywide
seagrass production, a mean value of 2 g
C/mo/day (730 g C/m/yr) may be used based
upon Zieman's (1982) commonly used
seagrass production range of 1-4 g
C/m'/day.

Heffernan and Gibson (1985), using
the 14C technique and a special chamber
(Heffernan and Gibson 1983) reported

























Figure 59. Aerial photograph of a perennial coloniz-
Ing seagrass meadow, south side of Courtney Camp-
bell Causeway, Old Tampa Bay.


productivity rates for two sampling
periods (October and February 1982).
Gravimetric rates (g C/g dry wt/hr) ranged
from 72.6 to 95.0 in October and from 3.0
to 9.6 in February. Areal rates (g
C/m2/hr) ranged from a high of 5.2 in
October to as low as 0.004 in February.
Significantly, they noted that Tampa Bay
seagrasses had more epiphytic biomass than
seagrass in the Bahamas or the Indian
River Lagoon. For example, in February an
average of 76% of the weight of a seagrass
blade in Tampa Bay was composed of
epiphytes, while only 29% and 26% of leaf
weights in the Indian River Lagoon and the
Bahamas, respectively, were composed of
epiphytes. These preliminary data may
indicate significant stress on seagrasses
in Tampa Bay due to eutrophication and
competition for light similar to that
previously reported for the Indian River
(Rice et al. 1983), Rhode Island (Harlin
and Thorne-Miller 1981) and Australia
(Cambridge 1975, 1979).

It is likely that seagrass meadows in
Tampa Bay are important habitat for
benthic invertebrates and certain species
of juvenile fish. Virnstein et al. (1983)
noted in their studies in the Indian River
that seagrass meadows had a density of
infaunal invertebrates three times that of
unvegetated sediments, and that epifaunal
organisms were 13 times as abundant in
seagrass as in sandy areas. Zieman (1982)


noted that eight sciaenid species have
been associated with seagrass meadows in
southwestern Florida and that the spotted
seatrout (Cynoscion nebulouss, the spot
(Leiostomus xanthurus), and the silver
perch airdiela2 chrysoura) are commonly
found in seagrass beds as juveniles. The
sheepshead (Archosarus robatocehalus)
and the snook (Centrooomus undecimalis)
also use seagrass meadows as habitat
during their life cycles (Odum and Heald
1970; Gilmore et al. 1983).

Similar data for seagrass meadows in
Tampa Bay are sparse, but the existing
data support the importance of seagrass
meadows as habitat for fish and
invertebrates. Studies of fish
populations in Tampa indicate that
seagrass meadows are one of several
important nursery habitats for juvenile
fish species (Springer and Woodburn 1960;
Comp 1985). Collections by Springer and
Woodburn (1960) at two areas containing
mixed seagrass and algae had the highest
number of species (108 and 93,
respectively, of a total of 253 species).
The lowest species numbers (48) were
reported for a sandy beach (unvegetated)
station.

Taylor and Saloman (1968) (in
documenting the filling of 1,400 ha of bay
bottom in Boca Ciega Bay and the loss of
1,133 t of annual standing crop of
seagrasses) estimated infaunal biomass for
well-vegetated bay bottoms to be 137 g dry
wt/m2 in comparison to 12 g dry wt/mn for
unvegetated bay bottoms. Godcharles
(1971) reported the results of testing a
commercial hydraulic soft-shell clam
dredge at six experimental sites in Middle
and Lower Tampa Bay, Boca Ciega Bay, and
just offshore of Mullet and Egmont Keys.
He listed 142 species of macro-
invertebrates and 47 species of fish
collected from these sites using the
dredge, a trynet, and a benthic plug
sampler. Figure 60 summarizes the numbers
of species in each group and the
percentage of the total number of species
found at each site. Three of the sites
were heavily vegetated with seagrass, a
fourth had a mixture of algae (Caulerna)
and seagrass, and two were unvegetated.
It is apparent from Figure 60 that four to
five times more invertebrate species and
ten times as many fish species were found










% TOTAL NUMBER OF SPECIES
25 50 75


STATION 7

HEAVY SEAGRASS

Thalassia dominant

STATION 11
HEAVY SEAGRASS

Syringodium dominant

STATION 27
HEAVY ALGAE
THIN SEAGRASS
Caulerpa dominant


25 50 75 100

Figure 60. Comparison of the numbers of species (crude diversity) of fish and invertebrates
collected from dense seagrass, sparse seagrass, and bare sand stations in Lower Tampa
Bay (original data from Godcharles and Jaap 1973).


at the sites dominated by turtle grass as
were collected in the unvegetated areas.
Even the manatee grass-dominated site and
the mixed algae and seagrass site commonly
had three times as many invertebrate
species and nine times as many fish
species as the unvegetated sites.


Godcharles (1971) and Godcharles and
Jaap (1973) also noted that the areas of
seagrass that were dredged did not recover
during the study. One of the sites had
shown no natural seagrass recolonization
36 months after the original seagrass
cover was removed by the clam dredge.










This observation confirms that of Phillips
(1960a), Zieman (1976), and Phillips and
Lewis (1983) that natural recolonization
of excavated areas in existing seagrass
meadows is slow. It is not unusual for
3-5 years to elapse before recovery is
visible in a turtle grass meadow; complete
recovery might take 10 years or more,
depending on the size of the denuded site.
This assumes the area is undisturbed
during the recovery period. Repeated
scarring by boat propellers, for example,
can delay recovery or lead to the loss of
an even larger area of seagrasss.

3.6 TIDAL MARSHES

About 7,200 ha of emergent wetlands
border Tampa Bay (Lewis and Whitman 1985).
They are located at 14 major sites as
mapped by Estevez and Mosura (1985)
(Figure 61). These sites are: (1) Upper


Figure 61. The generalized distribution of mangrove
forests and tidal marshes in Tampa Bay. Names of
numbered areas are listed in text (from Estevez and
Mosura 1985).


Boca Ciega; (2) Lower Boca Ciega; (3)
Weedon Island Complex; (4) Gateway; (5)
Upper Old Tampa Bay; (6) Interbay; (7)
McKay Bay; (8) Archie Creek; (9) Alafia to
Kitchen Complex; (10) Wolf Creek; (11)
Little Manatee and Cockroach Bay; (12)
Bishop Harbor; (13) Terra Ceia; and (14)
Perico units. The vegetation of these
emergent wetlands consists of various
mixtures of five major plant species
(Figure 62), two of which are tidal marsh
species: black needlerush (Juncus
roemerianus) and smooth cordgrass
(Spartina al terniflora). Minor species in
these tidal marshes include leather fern
(Acrostichum danaeofolium) and the
brackish water cattail (Tvpha
domingensis). A typical Tampa Bay tidal
marsh is shown in Figure 63.

Estimates of the percentage of the
total emergent wetlands which are tidal
marsh vary from 10% to 18% (Estevez and
Mosura 1985; Ed Pendleton, U.S. Fish and
Wildlife Service, Slidell, Louisiana; pers.
comm.). Mangroves are the dominant
vegetation, but periodic freezes allow
substantial areas of tidal marsh to
persist as cold-sensitive mangroves are
pruned or killed (Estevez and Mosura
1985).

Estevez and Mosura (1985) noted that
"regrettably little is known of the
organization or functioning of tidal
marshes in Tampa Bay." Decomposed marsh
plant fragments, known as deAtrttur,-iave
been shown to be important in some
estuarine food webs, although considerable
controversy exists as to the magnitude of
that role (Haines 1976; Nixon 1980; Stout
1984; Durako et al. 1985). The
controversy arises from the ambiguous
results from isotope studies designed to
pinpoint the source of carbon in the diet
of specific marsh animals. A diet that
includes a mixture of benthic microflora
and vascular plant detritus, for example,
could give a value halfway in between
those expected if only a single carbon
source was utilized.

The role of marsh surfaces and creeks
as habitat for juvenile and adult fishes,
invertebrates, and birds is less
controversial, though not well studied
(Durako et al. 1985). Subrahmanyam et al.
(1976) reported 55 species of






























































Figure 62. Typical form of the five dominant plant species found in intertidal wetlands of
Tampa Bay. A: Juncus roemerianus, black needlerush; B: Spartina alterniflora, smooth cord-
grass; C: Laguncularia racemosa, white mangrove; D: Rhizophora mangle, red mangrove;
E: Avicennia germinans, black mangrove (from Estevez and Mosura 1985).









67






































Figure 63. Typical tidal marsh along the shores of
Tampa Bay with dominant cover of black needlerush
(Juncus roamerlanus) and a lower elevation fringe of
smooth cordgrass (Spartina alterniflora).


invertebrates from north Florida tidal
marshes. Fish and shellfish species
important to Florida's commercial and
recreational fisheries, including shrimp,
menhaden, blue crabs, and mullet, commonly
inhabit tidal marsh creeks (Durako et al.
1985). Fifty-three species of fish,
dominated by the killifishes (Fundulus
similis, F. grandis, and Cyprinodon
variegatus), are present in these marshes
(Subrahmanyam and Drake 1975).

Kruczynski et al. (1978) reported
primary production values ranging from 390
to 1,140 g dry wt/m /yr for needlerush,
and 130-700 g dry wt/m2/yr for smooth
cordgrass in north Florida. The overall
mean value would be around 600 g dry
wt/m2/yr. No similar productivity data or
the previously mentioned habitat data are
available for Tampa Bay marshes. This
information is particularly important


since emergent wetlands restoration and
creation efforts in the bay are
concentrating on the use of smooth
cordgrass (Hoffman et al. 1985).

The reasons for this, discussed by
Lewis (1982a, 1982b), include the fact
that smooth cordgrass, although not a
dominant plant in the bay, has been
observed to be a pioneer species on spoil
islands in the bay. Smooth cordgrass, in
turn, facilitates the invasion of mangrove
seeds by stabilizing the substrate and
reducing wave energy and is eventually
replaced by these mangroves (Lewis and
Dunstan 1975a).

Because the frequency of cold weather
can cause dieback or kill mangroves on
Tampa Bay (Estevez and Mosura 1985),
direct planting of mangroves only is not
encouraged (Lewis 1982b, Hoffman et al.
1985). The functional roles of both
natural and created marshes as sources of
energy and as fish and wildlife habitat is
thus a high priority research item.


3.7 MANGROVE FORESTS

In contrast to tidal marshes,
mangrove forests on the bay have received
some study (Estevez and Mosura 1985),
although it is primarily descriptive in
nature. The forests are composed of three
species, red mangrove (Rhizoohora mangle);
black mangrove (Avicennia germinans); and
white mangrove (Laquncularia racemosa)
(Figure 62). Unlike mangrove forests
further south (Odum and Heald 1972),
mangrove forests on Tampa Bay are composed
of a mixture of all three species, and
while exhibiting natural zonation similar
to that described by Davis (1940), have
some unique features (Estevez and Mosura
1985, Lewis et al. 1985b).

Lugo and Snedaker (1974) have
classified mangrove assemblages into six
forest "types" based on the influence of
environmental factors, appearance of the
vegetation, and community energetic. Not
all mangrove stands in Tampa Bay are
easily categorized by this system, but in
general most forests resemble the "fringe"
forest type of Lugo and Snedaker (1974)
wherein the plant assemblages:










(1) grow on mainland shorelines of
gradual slope;
(2) are exposed to tides but are not
daily overwashed;
(3) have sluggish internal water flow on
high tides, and minor to no scouring;
and
(4) export particulate as well as labile
organic matter.

The "overwash" mangrove forest type is
well developed along the north shore of
upper Old Tampa Bay and the east shore of
Lower Tampa Bay, especially in Cockroach
Bay. The salinity and velocity of water in
overwash forests are higher than in fringe
forests, and islands are completely
inundated by daily tides. Overwash
islands are often uniform stands of red
mangrove, although some black mangroves
may be present.

Mangroves grow on banks along the
mouths of rivers, but we regard these as
extensions of the fringe form rather than
the riverinee" forest type and are termed
"tributary" forests (Table 11). Where
upriver, but tidal, habitat is available
for the development of the riverine forest
one instead finds Juncus marshes.


One new forest type may be
appropriate for mangrove assemblages in
Tampa Bay, the "shrub" form created by
repetitive freezes, water stress, and
other factors (Estevez and Mosura 1985).
Provost (1967) described this type as
"scrub-marsh" and noted its occurrence
around Tampa.



The shrub forest grows primarily on
mainland shorelines, like fringing
forests. It is composed of a mixture of
red and black mangrove, the reds being
shorter and denser in aspect. The forests
are low, often averaging 2-3 m. Lugo and
Zucca (1977) related temperature stress to
decreased leaf size and number, and
increased tree density. These features
are typical of shrub forests in the bay.
Limbs of red and black mangroves killed by
previous frosts are frequently evident
above the live canopy. The shrub forest
may support epiphytes or fungal galls, or
both. Examples of shrub forests are on
the eastern shore of Tampa Bay north of
Wolf Creek, including the stands in McKay
Bay, and the Bower tract in Upper Old
Tampa Bay.


Table 11. Mangrove tree size by species and forest type in Tampa
Bay (Williamson and Mosura 1979).

Cumulative mean D.B.H.d (cm)

Forest type Rhizophora Avicennia Laguncularia

Fringe 2.69 + 2.26 4.59 + 3.16 2.31 + 2.64

(139)b (186) (203)

Overwash 3.37 + 2.04 5.27 + 1.37

(90) (7)


Tributary 2.91 + 2.01 1.85 + 0.99 2.57 + 0.38

(50) (17) (10)

aDiameter at breast height.
bNumbers in parentheses are sample sizes.










The typical zonation pattern and
species makeup along a transect through an
undisturbed mangrove forest located on the
east side of Middle Tampa Bay (Wolf
Branch) are shown in Figure 64 and Table
12. Table 11 gives data for cumulative
size expressed as diameter at breast
height for three mangrove forest types on
the bay. The data for the fringe type are
applicable to the Wolf Branch transect.
These data indicate that the forests occur
over a range of elevations from 0.06 to
0.76 m above mean sea level (MSL), and the
lower elevation zones are occupied by red
mangroves (Figure 65), which are gradually
replaced by black and white mangroves as
the elevation increases. There is not a
distinct zonation between the black and
white mangroves; they intergrade over much
of the area of the forest, although the
black mangroves extend to a somewhat lower
elevation. At the higher elevations
normally reached by tides only once or
twice a month, only stunted and scattered


ELEVATION
5.0-
4.0
3.0-
MHW 2.0
1.0-
SLD-0--
MLW--0.5-


100 RHIZOPHORA


cc
LIJ
>


U
u"
IT*


black mangroves are found; soil salinities
can be over 100 ppt due to the evaporation
of seawater and residual salt
accumulation. In this area of the forest
a salt barren, or salina, is found with
areas of very salt-tolerant, low-growing
vegetation interspersed with barren
patches devoid of all vegetation (Figure
66). These plant assemblages are
dominated by sea purslane (Sesuvium
portulacastrum), glasswort (Salicornia
virginica), saltwort (Batis maritima), sea
oxeye daisy (Borrichia frutescens), sea
lavender (Limonium carolinianum), and
various salt-tolerant grasses.
The latitude of Tampa Bay is near the
northern limit of mangroves and
low-temperature stress is common in the
mangrove forests. Repetitive freezes can
intensify temperature effects on the
structure of the forest. Initially the
canopy is partially destroyed. If another
freeze quickly follows, the damaged trees


~JL i ~JLM.H.W.

M.L.W.


I 0 -


Li


SI LAGUNCULARIA



I0 5 10 15 20 25 30 35 40 45 50 55 60 5 70
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70


CONTROL AREA TRANSECT

Figure 64. Distribution of mangroves on an undisturbed (control) shoreline near Wolf Creek
(20-m sampling intervals). Elevations are shown in feet (from Detwiler et al. 1975).


U*"""" -----"**"*-------------. 1,1...---------.-----..1------1-------- !* *











Table 12. Elevation ranges and mean elevations of 10 plant species
found in the control area of an undisturbed mangrove community near
Wolf Creek (Detweiler et at. 1975). Elevation in ft above mean sea level.

No. of Mean
Species quadrats Range elevation


Rhizophora mangle 35 +1.6 +0.2 +1.0

Avicennia germinans 49 +2.5 +0.4 +1.5

Laguncularia racemosa 47 +2.5 +0.7 +1.5

Soartina alterniflora 4 +1.7 +1.6 +1.7

Salicornia viroica 10 +1.9 +1.6 +1.7

Sesuvlum portulacastrum 2 +1.7 +1.7

Limonium carolinianum 6 +1.7 +1.6 +1,7

Batlis maritima 14 +2.2 +1.6 +1.8

Borrichia frutescens 2 +1.9 +1.9

Philoxerus vermicularis 5 +2.2 +1.6 +1.9





















Figure 65. Typical view of fringing red mangroves, Figure 66 Aerial photograph of view across a man-
Lower Tampa Bay. grove forest bordering Middle Tampa Bay. The pale
areas at the bottom are salt barrens.










are killed. In recent years two freezes
have occurred relatively close together
(1977 and 1983). During January 1977, a
minimum temperature of -50C was reached
and snow fell for the first time in over
100 years. The Christmas freeze of 1983
involved 2 days during which the
temperature in Tampa fell to -6.70C
followed by a -7.2C reading the next day.
Such low temperatures had not occurred in
Tampa since the historical freeze of
1894-95 which dealt a serious blow to the
then flourishing citrus industry in
Florida (Sanders 1980). These freezes
caused significant losses of mangroves and
the total area o-tidaTi marsTion the bay
may increase as more low temperature
tolerant marsh plants .r. i areas left
barren by the death r -i. _mangroves
(Figure 67). During a less severe frost
or freeze selective survival of mangroves
has been observed, with the black mangrove
having the greatest resistance to freeze
damage and the white mangrove the least.
The black mangrove is typically the











I.5


Figure 67. Dead mangroves at Fish Creek in Old
Tampa Bay. Low temperatures in 1983 killed this forest
of predominantly black and white mangroves.


largest-diameter tree in the forest (Table
13), particularly in the fringe and
overwash forests which are the dominant
types in the bay.

This size difference is believed to
exist because these trees are older,
having survived some freezes that killed
red and white mangroves. The 1983 freeze
was significant in that even some of the
large black mangroves which survived
earlier freezes were killed or frozen back
to the ground. It is likely that the
structure of forests on the bay has been
significantly altered by these freezes,
particularly those in the northern third
of the bay, where air temperatures can be
as much as 40C lower than in the southern
portion of the bay (Estevez and Mosura
1985). It is not surprising, then, to see
a north-to-south gradient in the bay with
the better developed mangrove forests in
the southern half and the more
freeze-damaged forests mixed with tidal
marsh species in the northern half.

Primary production rates as measured
by litter fall are reported by Estevez and
Mosura (1985) to have a mean value of 3.1
g C/m2/day (11.3 t C/ha/yr) for three
sites in Tampa Bay. These values are
conservative, since they do not include
biomass added to the structure of the
forest as the trees grow or metabolic
energy losses.

As with tidal marsh research in the
bay, functional studies of the role of
mangroves as sources of carbon or as
habitat are rare. The only functional
value that has received some stu-yTs the
role of maigovesae- o~h T fr
colonial sea birds and wading birds (Lewis
and Dunstan1975b; SchreTIber and Schreiber
1978; Lewis and Lewis 1978; Paul and
Woolfenden 1985). Woolfenden and
Schreiber (1973) stated that mangrove
forests:
. are absolutely-essential to the
existence of a large number of water
birds that breed In FTorida, for
essentially all of the breeding
colonies of pelicans, cormorants,
herons, and ibises of saline environs
are in mangrove. Not only does
mangrove supply breeding sites, but
also the nutrients necessary early in










Table 13. Estimated annual production of primary producers based on areal coverage in the
Tampa Bay system (modified from Johansson et al. 1985).
Total Percent
Production Area Production of
Primary producer (g C/m /yr) (km2) (g C/yr x 106) Total

Seagrass and
epiphytes 730 57.5 42.0 8.5

Macroalgae 70 100.0 7.0 1.4

Benthic
microalgae 150 200.0 30.0 6.0

Mangrove forests 1,132a 64.5b 73.0 14.7

Tidal marshes 300 10.5b 3.2 0.6

Phytoplanktonc 340 864.0 293.8 59.1

Phytoplanktond 50 96.0 48.0 9.7

Riverine forests NDe ND ND ND


aEstevez and Mosura 1985.
bAssuming 14% of the bays emergent
cFor bay areas deeper than 2 m.
dFor bay areas shallower than 2 m.
eNo data available.


the food webs that lead to the items
taken as prey by birds.

Although the necessary habitat
utilization studies have not been
conducted for Tampa Bay, the value of
mangroves to Florida's fisheries is well
documented (Lewis et al. 1985b). _Man-
groves are known to serve as one of
several critical habitats in the life
history of many fish and shellfish
species important in commercial and
recreational fisheries, including the
pink shrimp (Penaeus duorarum), redfish
or red drum (Sciaenops ocellatus), tarpon
(Megalops atlanticus), and snook
(Centropomus undecimalis) (Odum et al.
1982; Lewis et al. 1985b).

While the frequently flooded lower
portions of mangrove forests and tidal
marshes are documented to be valuable
habitat, the roles of the higher marsh and
mangrove forest and tidal salt flats


wetlands are tidal marsh.





behind the lower elevation habitats are
less well understood. Heald et al. (1974)
noted that:

. during the dry season, when the
high marsh areas are drying rapidly,
the deeper, more permanent, ponds
within the impoundment provide
temporary refuge for retreating
fishes. At this point wading bird
populations are able to efficiently
exploit them.

Richard T. Paul (National Audubon
Society, Tampa; pers. comm.) observed the
salt flat habitat on Tampa Bay being
extensively utilized as foraging and
breeding habitat by a variety of forage
fish species including Cyprinodon,
Fundulus, and Poecilia. In turn, these
fish became important food sources for a
variety of herons and egrets during times
of high tides when the flats were flooded.
Paul stated that the reddish egret










(Egretta rufescens), the rarest egret in
Florida, is uniquely suited to feed in
this habitat because of its active feeding
behavior. Further documentation of this
habitat value is important.


3.8 RIVERINE FORESTS AND ADJACENT
WETLANDS

All major rivers and streams entering
the bay have floodplain forests and
adjacent wetlands that drain eventually
into the bay. These freshwater wetlands
serve as the first of a series of filters
to cleanse upland drainage before it
enters the bay and also act as
contributors of dissolved and particulate
organic matter and nutrients.

Typical of these wetlands are those
bordering the Alafia River. Clewell et
al. (1983) described these wetlands as
supporting 409 plant species including 84
tree species dominated by red maple (Acer
rubrum) and swamp tupelo (Nyssa biflora).

Sipe and Swaney (1974) noted that the
acreage of freshwater wetlands of
Hillsborough County has declined
significantly since historical times.
Losses would be expected to reduce the
ability of these systems to filter upland
runoff, allowing more turbid water to
reach the bay.. Particulate organic matter
inputs to the bay from litter fall in
adjacent wetland and terrestrial habitats
would also be expected to decline, and
nutrient inputs would probably increase as
filtration capacity declined. In
addition, many streams have been
channelized, and even if the wetlands are
intact hydraulic exchange with the
adjacent water body may be impaired.

Total streamflow input to Tampa Bay
is estimated to average 2 x 1012 1/yr
(Hutchinson 1983). If it can be assumed
that total organic carbon concentration
(TOC) averages 10 mg C/1 (Dooris and
Dooris 1985), then TO1 input via
streamflow would be 2 x 10 kg C/yr. TOC
measurements of this sort are typically
made on unfiltered water samples, but do
not take into account bedload transport of
organic material derived from adjacent
wetlands and uplands or pulse events when
large amounts of organic matter may be


moved
time.
value


in a relatively short period of
For this reason, the above input
should be considered conservative.


3.9 TOTAL PRIMARY PRODUCTION AND
ORGANIC MATERIAL INPUT

Total net primary production (carbon
reduced by photosynthesis) by natural
plant communities in Tampa Bay (listed by
category in Table 13) is estimated at
478.2 x 106 kg/yr. These figures indicate
that Tampa Bay can be characterized as a
phytoplankton-based system when compared
to other sources of net primary
production. By virtue of their high
annual production, mangroves are the
second most important primary producer in
the estuary.

In addition to primary production,
organic material can be transported to the
bay from outside sources by streamflow,
sewage discharges, urban runoff from
streets, rainfall, and ground-water
discharge. These values (listed in Table
14) account for a tgtal input of organic
carbon of 92.7 x 10 kg/yr, or about 25%
of the amount produced by photosynthesis
(or marine plants) in the bay. This
figure was probably much higher prior to
recent improvements in industrial and
municipal discharges, and substantial
deposits of residual organic matter are
still present in bay sediments (Ross et
al. 1984). The estimate of Ross et al.
for current allochthonous sources of
organic carbon is somewhat less than ours
(66.7 vs. 92.7 x 106 kg/yr).


3.10 SECONDARY PRODUCERS

Secondary producers are the animal
communities, either herbivorous or
carnivorous, that consume the organic
carbon in an area. A very simple Tampa
Bay food chain is illustrated in Figure
68. A simplified food web for the bay is
shown in Figure 69. Ideally, one should
be able to measure the amount of fish or
crab biomass produced over a period of
time. This is total secondary production.
From studies with simpler systems, we know
that total secondary production typically
cannot exceed 10% of primary production
because of inefficiencies in energy










Table 14. Organic inputs to Tampa Bay from allochthonous sources.

Source 106 gal/yr 1/yr mg/l TOC kg C/yr


Streamflowa 1,447 2 x 1012 10 20.0 x 106

Ground water 100 1.4 x 1011 0.1 0.014 x 106

Rainfallb 1,048 1.5 x 1012 1.0 1.5 x 106

Municipal and
industrial
discharge 520 7.1 x 1011 100 71.2 x 106

Urban runoffd .

Total 92.7 x 106e
aModified from Hutchinson 1983.
bHutchinson 1983.
CMoon 1985.
dData unavailable.
eWithout urban runoff data.


transfer and the use of consumed energy to
fuel life processes (Odum and Odum 1981).
As noted in the section on total primary
production and organic carbon input, the
available data allow only an approximation
of the amount of organic material produced
or delivered to the bay. Data on
secondary production have not been
generated accurately. Ross et al. (1984)
estimated fish standing crop in the bay at
271 x 10 kg by multiplying the commercial
landing data by a factor of 10. The
accuracy of this figure is unknown.

In order to understand how the bay
works it will be important to quantify
both the types and amounts of primary and
secondary production. Simply having large
amounts of both may not necessarily be
ideal. A bay ecosystem with a large
variety of plant and animal species
actually may require less organic material
input. The typical "green pea soup"
appearance in a polluted pond or sewage
treatment plant lagoon is an example of
high primary production that also
indicates an imbalanced system. Proper
management of Tampa Bay to provide stable,
balanced populations without abnormal
algal blooms and fish kills will require a


better understanding
secondary production.


of both primary and


3.11 ZOOPLANKTON

Zooplankton in Tampa Bay are divided
into holoplankton (animals who spend their
entire lives as plankton) and meroplankton
(temporarily planktonic). Copepods are
typical holoplankton. Barnacles and
oysters are typical meroplankton, spending
their early lives floating in the bay
until they find a suitable point of
attachment (e.g., a mangrove prop root, a
boat hull), at which time they
metamorphose into their more familiar
attached forms. Other meroplankton, e.g.,
pink shrimp, blue crabs, larval fish and
some marine snails, metamorphose into
mobile forms.

The most extensive study of
zooplankton to date (Hopkins 1977)
provides much useful data, but the author
emphasized that collections were only
taken at the surface of the bay once every
3 months (quarterly) for one year. The
data are of limited value in describing
long term cycles but are essential as a



































________ *-.


~-.-...- ~-
----,' -- -




%.~..
Sg




K


Figure 68. Simple Tampa Bay food chain illustrating energy flow through seagrass epiphytes,
caridean shrimp, and spotted seatrout.










































Figure 69. A generalized Tampa Bay food web.


first step in describing the general
characteristics of bay zooplankton.
Thirty-seven species of holoplankton were
identified in the study and were grouped
into three categories based upon abundance
(Table 15). Mean biomass for all
zooplankton was 39.6 mg dry wt/m3. The
dominant species were three copepods
(Oithona colcarva, Acartia tonsa,
Paracalanus crassirostris), which made up
56% of the zooplankton biomass. The
cosmopolitan species Acartia tonsa alone
accounted for 30% of total zooplankton
biomass. Although no feeding studies for
this species have been done in Tampa Bay
Conover (1956) and Reeve and Walter (1977)
indicated that it is an omnivore,
consuming phytoplankton, zooplankton, and
detritus.


Researchers have been unable to find
a significant relationship between
chlorophyll concentration (as a measure of
phytoplankton abundance) and numbers of
the 10 most abundant holoplankton species
(Hopkins 1977). This indicates that
phytoplankton occur in numbers greater
than those needed to feed the existing
population of zooplankton, and that other
factors control the maximum population
densities of zooplankton, or that other
food sources are being utilized.

Holoplankton are important in the
diet of larval fish in Tampa Bay, as is
further described in the section on fish.
For this reason and others, the population
dynamics of holoplankton need additional
study.







Table 15. Holoplankton commonly found in
(Turner and Hopkins 1985).


Tampa Bay grouped by abundance


Group Family Species


Greater than 1,000/m3;
60% of total biomass


Copepods


Oithona colcarva
Acartia tonsa
Paracalanus crassirostris


Tunicates 0 Oikopleura dioica


100-1,000/m3;
5% of total biomass


Less than 100/m3


Copepods


Cladoceran

Copepods


Cladocerans


Decapods

Chaetognaths


Tunicates


Oithona nana
Pseudodiaptomus coronatus
Othonia simplex
Labidocera aestiva
Euterpina acutifrons

Evadne terqestina

Eucalanus pileatus
Paracalanus quasimodo
Temora turbinata
Centropaqes hamatus
Centropages velificatus
Oncaea curta
Oncaea venusta
Corycaeus amozonicus
Corycaeus americanus
Corycaeus giesbrechtii
Microstella rosea

Penilia avirostris
Podon polyphemoides

Lucifer faxoni

Saqitta tenuis
Saqitta hispida

Oikopleura lonqicaudata
Oikopleura fusiformis
Appendicularia sicula
Doliolum qegenbauri


Siphonophores Muqqiaea kochi

Trachymedusae Liriope tetraphylla










Meroplankton fall into two groups,
invertebrate and fish meroplankton
(ichthyoplankton). Meroplankton data for
Tampa Bay have been summarized by Weiss
and Phillips (1985). Hopkins (1977), in
sampling for holoplankton, found 19% of
total zooplankton numbers and 8% of the
total biomass (3.2 g dry wt/m3) were
meroplankton. Table 16 lists his general
data for meroplankton abundance. No
detailed taxonomic descriptions were
attempted for these collections.

Invertebrate meroplankton have been
sampled primarily to locate and quantify
larvae of invertebrates important in
commercial fisheries. Thus, most early
studies concentrated on examining samples
for pink shrimp (Penaeus duorarum) and
stone crab (Menippe mercenaria) larvae.
Eldred et al. (1961, 1965) examined the
distribution of larval and postlarval
penaeid shrimp in the bay area. They
reported spawning by the adult shrimp
16-64 km offshore in the Gulf of Mexico
between April and June; postlarvae moved
inshore and into the bay in July, where
they sought seagrass meadows as nursery
habitat (Joyce and Eldred 1966). While
maturing in the bay, the shrimp may be
taken in small commercial roller-frame
trawls and sold as bait shrimp, both alive
and dead. After the shrimp mature, they



Table 16. Meroplankton species collected by Hopkins
(1977).


Size


Group I >1,000/m3



Group II 100-1,000/m3


Group III <100/m3


Bivalve larvae
Barnacle larvae
Polychaete larvae
Gastropod larvae
Echinoderm larvae
Bryozoan larvae
Decapod larvae
Polyclad larvae
Phoronid larvae
Brachipod larvae
Enteropneust larvae
Ascidian larvae
Cephalochordate larvae


Fish eggs <500/m3


migrate from the bay to spawn offshore.
During this period, the seafood industry
harvests the adults. This life cycle is
shown in Figure 70. In addition to pink
shrimp, the larvae of penaeid shrimp of
the genera Sicyonia and Trachypenaeus have
been collected in the bay.

Stone crabs are believed to spawn
within the bay, and very young larvae are
abundant during spring and summer in
zooplankton samples (Weiss et al. 1979).
Nursery areas in the bay include seagrass
beds, oyster bars, live bottoms, and
artificial reefs and riprap shorelines.
Although blue crabs (Callinectes sagidus)
are important in local commercial
fisheries, no work on their life history
has been done in the bay.

Blanchet et al. (1977) and Phillips
and Blanchet (1980) examined meroplankton
at stations in Hillsborough and Middle
Tampa Bays and found 105 invertebrate
species, of which 86 were decapod
crustaceans. Table 17 lists the most
abundant of the species found, in
decreasing order. The pinnotherid crab,
Pinnixia savana, was the most abundant,
averaging 35% of the total invertebrate
larvae collected. Xanthid crabs were
second in abundance.

It is important to note that the
dominant meroplankton species in the bay
(Table 16) are not penaeid shrimp or other
decapods but are bivalve, polychaete, and
gastropod larvae. Thus, the latter
species, and not the ones most studied,
may be more important in terms of biomass
and energy transfer to other consumers.
This hypothesis is suggested by the fact
that polychaetes and mollusks are the
dominant infauna in the bay.

Ichthyoplankton include the eggs and
larvae of fish. Routine sampling for
ichthyoplankton can provide data to
determine the life history of a particular
species. For example, if both eggs and
larvae of a given species are found in
sufficient numbers in the bay, the bay
serves as both a spawning ground and
nursery area for the species. Finding
only larvae and postlarvae may indicate
that spawning occurs offshore in the Gulf
of Mexico, with larvae migrating into the
bay to utilize it as a nursery area.


Group









-y


Adult female spawning in open sea


Adult migrating to sea


Larva
(nauplius-magnified)


nursery grounds


Larva (protozoea-magnified)

r/ 'Larva
Postlarva entering bay (mysis-magnified)
S -- (magnified) (

Figure 70. Life cycle of the pink shrimp (Penaeus duorarum), Illustrating the use of Inshore
estuarine habitat as nursery areas (Joyce and Eldred 1966).


Table 17. Dominant meroplankton species collected
by Blanchet et al. (1977) and Phillips and Blanchet
(1980).


Family Species


Decapods Pinnixia sayana
Eurypanopeus depressus
Hexapanopeus ancustifrons
Upoqebia affinis
Menippe mercenaria
Rhithropanopeus harrisii
Panopeus herbstii
Neopanope texana


Penaeids Penaeus duorarum
Sicyonia sp.
Trachypenaeus sp.


Weiss and Phillips (1985) listed the
dominant ichthyoplankton from three
surveys (Table 18). In all three surveys
the groups dominant as eggs were anchovy
(Engraulidae) and drum (Sciaenidae). In
addition to these two families of fish,
gobies (Gobiidae), sardines (Harengula),
sheepshead (Archosargus) and pigfish
(Orthopristis) were common as both eggs
and larvae.

The seasonal occurrence of the two
dominant ichthyoplankton groups is
illustrated in Figure 71. The greatest
densities of eggs occurred in spring and
the greatest diversity of larvae in the
summer months. The bimodal peaks of
larval densities are theorized by Weiss
and Phillips (1985) to represent a
protracted spawning season. Winter
collections were dominated by blenny
(Blennidae) and gobies (Gobiidae),
although numbers usually were low.


V I










Table 18. Dominant fish egg and larval taxa as percentage of all eggs or larvae collected from three
ichthyoplankton surveys in Tampa Bay (Weiss and Phillips 1985).


Lower Hillsborough Lower Hillsborough Upper Old
Bay (1976) Bay (1979) Tampa Bay (1978)



Engraulidaea 73.1 Engraulidae 51.1 Engraulidae 82.2
Sciaenidaeb 26.1 Sciaenidae 48.7 Sciaenidae 15.4
Carangidaec 0.4 Soleidae' 0.1 Soleidae 1.1


Larvae
Anchoa spp. 87.4 A. mitchilli 74.4 Anchoa sp. 83.6
Sciaenidae 3.9 H. jaguana 16.3 GobiidaeT 13.3
Gobiidae 2.7 Sciaenidae 3.1 Sciaenidae 1.1
Pomadasyidaee 2.1 Blennidae 1.5 Atherinidgeg 1.1
Carangidae 1.1 Prionotus sp. 0.9 Blennidae" 0.3


aAnchovies.
bDrums.
cJacks.
dSoles.


eGrunts.
fGobies.
gSilversides.
hBlennies.


3.12 BENTHOS

The benthic community consists of
animals that live in the sediment as
infauna by burrowing or forming permanent
or semi-permanent tubes extending just
above the sediment surface; animals that
live on the sediment surface either as
mobile epifauna or sedentary epifauna; and
animals that form specialized communities
such as oyster reefs or live-bottom
communities.

Taylor (1973) and Simon (1974)
summarized the benthic studies conducted
in Tampa Bay. Early work (Hutton et al.
1956; Bullock and Boss 1963; Dragovich and
Kelly 1964) listed species from random
collections and identified 82 species of
invertebrates from the bay. The National
Marine Fisheries Service conducted more
intensive sampling starting in 1963 along
a series of transects containing more than
400 stations. From this work and a number
of more recent intensive quantitative
infaunal studies related to red-tide


effects and pollution studies (Bloom et
al. 1970; Dauer and Simon 1976; Dauer and
Conner 1980; Santos and Simon 1980a,
1980b; Dauer 1984) a fairly detailed
understanding of the species composition
and seasonal variations in density of the
macroinfauna (retained on a 0.5-mm sieve)
has developed. Work has just begun on the
meiofauna (small organisms from 0.5 mm to
0.063mm in size (Bell and Coen 1982); and
the larger mobile and sedentary epifauna
still need more study, as do the fauna
associated with seagrasses, mangroves, and
marshes.

Benthic studies have resulted in the
following general conclusions regarding
this group of invertebrates in Tampa Bay:

1. The estuary supports "an extremely
abundant and diverse assemblage of
bottom organisms, except in
Hillsborough Bay, dredged regions of
Boca Ciega Bay, and a system of
inland canals developed in upper
Tampa Bay" (Taylor 1973). Taylor











ANCHOA SPP. LARVAE


MONTH


SCIAENIDAE EGGS


J FMAMJJASOND
MONTH


t0
C-
w
Ill
I-

D
Ul



Ul0
zi
uo
00



w

-J
GC
_1


SCIAENIDAE LARVAE


MONTH


Figure 71. Mean densities of Anchoa spp. (anchovy) and Sclaenldae (drum) eggs and larvae
reported In three studies of Tampa Bay Ichthyoplankton (from Weiss and Phillips 1985).


ANCHOA SPP. EGGS












listed 207 species of polychaetes,
231 species of mollusks, and 29
species of echinoderms found in the
bay. Simon and Mahadevan (1985)
stated that approximately 1,200
infaunal and epifaunal benthic
species (excluding the meiofauna)
occur in the bay.

2. Seasonal fluctuations in the
abundance and diversity of these
organisms are pronounced. Seasonal
variability in benthic populations is
high and densities can range from 0
to 200,000/mi (Figure 72),
particularly in areas of
pollution-related stress.

3. Seagrass beds have declined with a
concomitant decrease in faunal
diversity. As discussed earlier,
seagrass meadows in Tampa Bay have


BOTTOM WATER TEMPERATURE


30
27
24
21
18
15
o 12
9
6
3
0
10


35
30
.- 25
0. 20
15
10
5
0


BOTTOM SALINITY


not been sampled extensively for
invertebrates, but existing data
indicate they typically support a
greater number and diversity of
benthic invertebrates than do
unvegetated areas (Figure 60) (Santos
and Simon 1974). The 81% decline in
seagrass meadow coverage in the bay
would thus be expected to have
greatly reduced the populations of
invertebrates.

4. Opportunistic and "pollution
indicator" species are abundant,
particularly in Hillsborough Bay
where pollution problems have been
well documented for many years. Both
Santos and Simon (1980a) and Dauer
(1984) noted that parts of the bay
periodically undergo catastrophic
disturbance due to anoxia (no
oxygen). This condition was first


.'K Ps


1975 1976


1977 1978


Figure 72. Trends in environmental parameters and benthic invertebrates, Hillsborough Bay 1975-78 (from Santos
and Simon 1980b).


1975 1976 1977 1978




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