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- ! klogical Repal 85(7.25): ;‘*’ <

September 1989

THE ECOLOGY OF THE

SEAGRASS MEADOWS

OF THE WEST COAST

OF FLORIDA:

A

Community

Profile

a

Minerals Management Service

and

Fish and Wildlife Service

U.S. Department of the Interior
Biological Report 85(7.25)

September 1989

THE ECOLOGY OF THE SEAGRASS MEADOWS OF THE WEST

COAST OF FLORIDA: A COMMUNITY PROFILE

Joseph C. Zieman

Rita T. Zieman

Department of Environmental Sciences

University of Virginia

Charlottesville, VA 22903

Project Officer

Edward Pendleton

U.S. Fish and Wildlife Service

National Wetlands Research Center

1010 Gause Boulevard

Slidell, LA 70458

Conducted in Cooperation With

Minerals Management Service

Gulf of Mexico

U.S. Department of the Interior

Fish and Wildlife Service

Research and Development

Washington, D C 20240
DISCLAIMER

The opinions and recommendations expressed in this report are those of the authors

and do not necessarily reflect the views of the U.S. Fish and Wildlife Service, nor

does the mention of trade names constitute endorsement or recommendations for use by

the Federal Government.

Library of Congress Cataloging-in-Publication Data

Zieman, Joseph C.

The ecology of the seagrass meadows of the west coast of Florida.

(Biological report ; 85 (7.25)

“National Wetlands Research Center.”

“Conducted in cooperation with Minerals Management Service, Gulf of Mexico.”

“September 1989.”

Bibliography: p.

1. Marine ecology--Florida. 2. Marine ecology--Mexico, Gulf of. 3.

Seagrasses--Florida--Ecology. 4. Seagrasses--Mexico, Gulf of--Ecology. I.

Zieman, Rita T. II. Pendleton, Edward C. III. National Wetlands Research Center

(U.S.) IV. United States. Minerals Management Service. V. Title. VI. Series:

Biological report (Washington, D.C.) ; 857.25.

QH105.F6Z49 1989 574.5’2636’0916364 89-600197

Suggested citation:

Zieman, J.C., and R.T. Zieman. 1989. The ecology of the seagrass meadows of the west

coast of Florida: a community profile. U.S. Fish Wildl. Serv. Biol. Rep.

85(7.25). 155 pp.
PREFACE

Seagrass beds have come to be known as

extremely productive and valuable coastal

wetland resources. They are critical

nursery areas for a number of fish,

shrimp, and crab species, and support the

adults of these and other species that

forage around seagrass beds, preying on

the rich and varied fauna that occur in

these habitats. Seagrass beds support

several endangered and threatened

species, including sea turtles and

manatees along the west coast of Florida,

the geographic area covered in this

profile.

For these reasons and others, seagrass

beds or meadows have been the topic of

several of the reports in this community

profile series. This report, covering

the seagrass community of the Florida

Gulf of Mexico coastline from south of

Tampa Bay to Pensacola, is the fifth

community profile to deal with submerged

aquatic vegetation beds; others in the

series have synthesized ecologic data on

seagrasses of south Florida, eelgrass

beds in the Pacific Northwest and along

the Atlantic coast, and kelp forests of

the central California coastline.

These reports in total represent a

major effort toward summarizing and

synthesizing what is known of the

ecologic structure, functioning, and

values of these marine and estuarine

communities. This profile in particular

builds on the author's earlier profile on

the seagrass meadows of south Florida.

As will become apparent to the reader,

while enough is known to describe the

gulf coast seagrass community, there has

been little study of the finer points of

the structure and function of seagrass

beds in this region. To shed light on

the ecology of Thalassia, Syringodium,

and Halodule meadows on Florida's aulf .,

coast, one is forced to extrapolate a

good deal from information from studies

conducted on the south and southeast

Florida coasts and elsewhere. However,

in so doing the author has been able to

update his own earlier communitv profile.

Thus, The Ecology of the Seagra;s'Meadows - -

of the West Coast of Florida is not only - -

a synthexof &IC, but also serves

as- a state-of-the-art review of

subtropical seagrass ecology and a

this series, the profile finally highlights how much is still left to learn

about these valuable natural habitats.

iii
CONVERSION FACTORS

Multiply

millimeters (mm)

centimeters (cm)

meters (m)

meters (m)

kilometers (km)

kilometers (km)

BY To Obtain

0.03937 inches

0.3937 inches

3.281 feet

0.5468 fathoms

0.6214 statute miles

0.5396 nautical miles

square meters (m’) 10.76

square kilometers (km’) 0.3861

hectares (ha) 2.471

liters (I)

cubic meters (m3)

cubic meters (m3)

0.2642 gallons

35.31 cubic feet

0.0008110 acre-feet

milligrams (mg)

grams (9)

kilograms (kg)

metric tons (1)

metric tons (1)

0.00003527 ounces

0.03527 ounces

2.205 pounds

2205.0 pounds

1.102 short tons

kilocalories (kcal)

Celsius degrees (‘C)

3.968 British thermal units

1.8(%) + 32 Fahrenheit degrees

inches 25.40

inches 2.54

feet (ft) 0.3048

fathoms 1.829

statute miles (mi) 1.609

nautical miles (nmi) i ,852

square feet (ft2)

square miles (mi2)

acres

gallons (gal)

cubic feet (ft3)

acre-feet

ounces (02)

ounces (02)

pounds (lb)

pounds (lb)

short tons (ton)

British thermal units (Etu) 0.2520

Metric to U.S. Customary

U.S. Customary to Metric

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

kilocalories

Fahrenheit degrees (“F) 0.5556 (“F - 32) Celsius degrees

square feet

square mrles

acres

millimeters

centimeters

meters

meters

kilometers

kilometers

iv
CONTENTS

PREFACE ...........................................................................

CONVERSION FACTORS ................................................................

FIGURES ...........................................................................

TABLES ............................................................................

ACKNOWLEDGMENTS ...................................................................

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

:*:

Seagrass Ecosystems .....................................................

1:3

The Seagrasses of the West Coast of Florida .............................

Physical Environment ....................................................

:::

Geologic Environment ....................................................

Succession and Ecosystem Development ....................................

CHAPTER 2 AUTECOLOGY OF FLORIDA GULF COAST SEAGRASSES ...........................

2.1 Plant Morphology and Growth .............................................

z

Reproduction ............................................................

214

Plant Constituents ......................................................

Physiological Ecology ...................................................

2.4.1 Environmental Tolerances and Responses ...........................

2.4.2 Photosynthetic Carbon Fixation ...................................

2.4.3 Isotopic Fractionation ...........................................

2.5 Nutrient Uptake and Supply ..............................................

CHAPTER 3 DISTRIBUTION, BIOMASS, AND PRODUCTIVITY ...............................

3.1 Distribution ... ........................................................

3.1.1 Seagrass Distribution in Tampa Bay ...............................

3.1.2 Seagrass Distribution in the Big Bend Area .......................

3.2 Biomass .................................................................

3.2.1 Seagrass Biomass in Tampa Bay ....................................

3.2.2 Seagrass Biomass in the Big Bend Area ............................

3.3 Productivity ............................................................

3.3.1 Seagrass Productivity in Tampa Bay ...............................

3.3.2 Seagrass Productivity in the Big Bend Area .......................

CHAPTER 4. COMPONENTS OF THE SEAGRASS COMMUNITY ..................................

4.1 Algal Associates ........................................................

4.1.1 Phytoplankton ....................................................

4.1.2 Benthic Algae ....................................................

4.1.3 Epiphytic Algae ..................................................

4.2 Invertebrates ...........................................................

4.3 Fishes ..................................................................

V

Page

iii

iv

vii

viii

ix

1

11

:2'

14

;:

23

23

24

27

27

27

29

34

::

37

:;

40

t;

t:

46

48
Page

4.4 Reptiles ................................................................

4.5 Birds ...................................................................

4.6 Mammals .................................................................

CHAPTER 5. STRUCTURAL AND FUNCTIONAL RELATIONSHIPS IN SEAGRASS SYSTEMS...........

5.1

5.2

5.3

CHAPTER 6

6.1

6.2

6.3

6.4

6.5

The Relationship of Structure, Shelter, and Predation ...................

5.1.1 Fauna1 Abundance and Structure ...................................

5.1.2 Structure and Predation ..........................................

5.1.3 Fauna1 Sampling: The Problems of Gear and Technique ..............

General Trophic Structure ...............................................

5.2.1 Seagrass Grazers .................................................

5.2.2 Epiphyte Seagrass Complex ........................................

5.2.3 Detrital Feeding .................................................

5.2.4 Carnivory........................................................

5.2.5 Trophies and Ontogenetic Development

of Grassbed Fishes ...............................................

Decomposition and Detrital Processing ...................................

INTERFACES WITH OTHER SYSTEMS .........................................

Salt Marsh and Mangrove .................................................

Gulf Reefs ..............................................................

Continental Shelf .......................................................

Export of Seagrass ......................................................

Nursery Grounds .........................................................

6.5.1 Blue Crabs .......................................................

6.5.2 Shrimp ...........................................................

6.5.3 Fish...............................~ .............................

6.5.4 Detached Macrophytes as Nursery Habitat ..........................

CHAPTER 7. HUMAN IMPACTS AND APPLIED ECOLOGY .....................................

7.1 Dredging, Filling, and Other Physical Damage ............................

7.1.1 Acute Stress .....................................................

7.1.2 Other Physical Damage ............................................

7.1.3 Chronic Effects ..................................................

7.2 Eutrophication and Sewage ...............................................

7.3 Oil .....................................................................

7.4 Temperature and Salinity ................................................

7.5 Paper Mill Effluents ....................................................

7.6 Disturbance, Recolonization, and Restoration ............................

7.6.1

7.6.2

7.6.3

7.7 Final

REFERENCES.....

APPENDIX: FISH

Disturbance ......................................................

Recolonization ...................................................

Restoration ......................................................

Thoughts ..........................................................

SpECIEj.;;kVEVs.IN.SbUjH'ANb'WESiikN'iib~~~~::::::::::::::::::::::

53

53

54

58

58

58

60

66

67

68

70

70

71

72

72

77

77

79

81

83

84

84

85

86

86

88

88

88

90

91

91

91

93

95

95

95

96

99

101

103

131

vi
Number

FIGURES

Page

17

18

19

20

21

22

23

24

Z

27

28

Location Map of Florida ...................................................... 1

The seagrasses of the west Florida coast ..................................... 4

Temperatures at four locations in coastal Florida ........................... 5

Coastal geology of the Florida west coast .................................... 8

General morphology of a Thalassia plant ...................................... 12

Flowers of Thalassia and Syringodium (Durako) ................................ 13

Temperature responses of Thalassia and Syringodium

on the west Florida coast .................................................... 19

Carbon isotopic variation at two locations in Florida ........................ 24

Seagrass coverage in Tampa Bay, 1879 and 1982 ................................ 28

Seagrass meadow types in Tampa Bay ........................................... 29

Seagrass distribution and density in Big Bend area ........................... 30

Seagrass species distribution in the Big Bend area ........................... 31

Depth distribution of seagrass biomass in Apalachee Bay ...................... 32

Seasonal cycle of Thalassia at two stations in Apalachee Bay ................. 37

Location of recently fixed carbon photosynthate in Thalassia ................. 38

Seasonal changes in productivity of seagrasses and red

algae in Apalachee Bay ....................................................... 39

Distribution and diversity of benthic marine plants in the

Gulf of Mexico ............................................................... 42

Representative temperate (Carolinean) invertebrate communities ............... 47

Representative tropical (West Indian) invertebrate communities ............... 48

Comparison of fauna1 abundance between seagrass beds and

adjacent habitats ............................................................ 58

Salt-marsh zonation in Florida ............................................... 79

Life histories of spotted sea trout and snook on the west

Florida coast ................................................................ 80

Fauna1 zonation of west Florida shelf ........................................ 82

Eastern Gulf of Mexico current patterns during summer ........................ 83

Blue crab spawning migrations and larval transport ........................... 85

Channel through grassbed with open-water dredge disposal area

in Tampa Bay ................................................................. 89

Dredged and filled areas in Boca Ciega Bay ................................... 90

Crystal River power plant .................................................... 93

vii
TABLES

Number

1

2

3

4

z

7

8

9

1':

12

13

14

15

16

17

18

19

Page

Precipitation statistics for gulf coast stations .............................

Sediment characteristics of the west coast of Florida ........................

Constituents of seagrasses

!

...................................................

Seasonal changes in protein and carbohydrates in seagrasses in Tampa Bay

15

..... 18

Representative values of seagrass biomass

Biomass partitioning in seagrasses

.................................... 35

...........................................

Seagrass biomass in Tampa Bay area

36

........................................... 36

Representative values of seagrass productivity ...............................

Macroalgae of seagrass communities of west Florida

37

Algal epiphytes of the seagrasses of Florida

........................... 43

..............................

Fishes of Apalachee Bay...................................................:::

Seagrass-associated fish families

:;

..............................

Seagrass and wetlands associated birds of the Florida west coast:::::::::::::

Comparative abundance of organisms in seagrass and sand habitats

z:

.............

Influence of seagrass community structure on fauna1 abundance

59

................

Wetlands acreage on the west Florida coast

61

.......................... 77

Historic human impact on Florida seagrass meadows...................:::::::: 1 97

Seagrass damage and restoration assessment

Success of seagrass restoration techniques

................................... 99

................................... 100

. . . VIII
ACKNOWLEDGMENTS

The production of this manuscript turned

into a much larger project than was

envisioned when we began. During that time,

many people contributed greatly towards the

production of the final product. The

authors are especially grateful to Richard

L . Iverson who contributed both written

material and numerous published and

unpublished figures for Chapters 2 and 3.

We wish to give special thanks to our

project officer, Edward C. Pendleton, who

has been unusually conscientious throughout

all aspects of the project, starting with

the outline and continuing to the final

production. We especially thank him for his

patience in the face of numerous

unanticipated delays.

Critical comments and reviews were made

by Ron Phillips, Robin Lewis, Mike Durako,

Laura Gabanski, Cheryl Vaughn, Charles Hill,

Robert Rogers, David Moran, Ed Pendleton,

and Lorna Sicarello. Robin Lewis and Mike

Durako also thoughtfully provided several

illustrative photographs.

Sue Lauritzen did the layout and Daisy

Singleton and Joyce Rodberg keyboarded the

final draft.

ix

CHAPTER 1. INTRODUCTION

1 .l SEAGRASS ECOSYSTEMS

Seagrass meadows are recognized today as

one of the most important communities in

shallow coastal waters. Rapidly growing

seagrass leaves serve as the basis of a

productive grazing and detrital food web,

while the canopy structure formed by these

leaves offers shelter and protection from

predation for innumerable small organisms,

many of which are the juveniles of

important commercial species. The coastal

waters of Florida are especially rich in

seagrass resources. The two largest

seagrass meadows in Florida have received

little human disturbance thus far. The

largest, in Florida Bay, is approximately

5,500 km2, and is protected from

large-scale human impact because it is

mostly within the boundaries of Everglades

National Park. The second largest bed is

just off the northwest coast of Florida,

between Tarpon Springs and St. Marks, and

is approximately 3,000 km2 (Iverson and

Bittaker 1986). Other seagrass meadows,

especially those within urbanized

estuaries, have not fared as well. Lewis

et al. (1985a) found that in 1982, Tampa

Bay contained 5,750 ha of seagrass cover.

From old maps and aerial photographs they

estimated the historical coverage to be

nearly 31,000 ha, thus showing a reduction

to less than 20% of the historical

coverage.

The coastline of western Florida is a

major ecocline for the tropical seagrass

species. Although the distance is not

great, about 650 km from Florida Bay to

Apalachicola Bay, it represents a shift

from a region in the south where tropical

seagrasses reach their highest

development, to areas that are the

northern limits of distribution for

several of the species, notably Thalassia

and Syringodium. While this report

addresses the west and northwest coast of

Florida, the area of central interest for

this community profile is the region from

Tampa Bay to Apalachicola Bay (Figure 1).

This region contains the large offshore

beds of the Big Bend area, as well as

several representative estuarine systems.

It is largely defined by the available

data base for the Florida west coast.

Compared with seagrass meadows in

southern Florida, communities of western

Florida and the northeastern Gulf of

Mexico have received little attention from

the research community; therefore, this

community profile will refer to data from

south Florida and the Caribbean when

Apalachicolo

BQY

GULF OF

MEXICO

Figure 1. Location map of Florida.

1
comparable studies from western Florida do

not exist. Interestingly, the west coast

area was the location of the seminal

seagrass studies of Florida, in

particular, and the Southeast, in general.

This work culminated in the monograph on

the seagrasses of Florida by Ronald C.

Phillips published in 1960. Within the

past 10 years, research on these systems

has accelerated in the bays and estuaries

of north Florida and in central Florida;

however, less work has been done on the

large offshore bed between these two

regions. This extensive seagrass meadow

is unique among Florida's seagrass

resources since it is truly offshore, and

does not lie behind any form of protective

barrier.

Seagrass ecosystems are among the

richest, most productive, and most

important of all coastal systems. They

are also paradoxical in nature--

simultaneously simple and complex. They

are simple in that there are few species

of seagrasses, unique marine angiosperms

that live and carry out their life cycle

in seawater. Vast and extensive undersea

meadows stretching for hundreds of

kilometers may be composed of only one to

perhaps four species. The ecosystems,

however, are complex ,because there are

hundreds to thousands of species of

associated flora and fauna that inhabit

the seagrass meadows and utilize the food,

substrate, and shelter provided by the

plants.

The pioneering work of Petersen (1918)

in the Baltic region provided the first

documentation of the value of seagrass

beds to shallow coastal ecosystems. These

studies demonstrated how the primary

production from these plants was channeled

through the detrital food web and

supported the rich commercial fisheries of

the region. Despite the thoroughness and

quality of Petersen's work, only in the

past two decades have the richness and

value of seagrass ecosystems begun to be

realized (Wood et al. 1969; McRoy and

McMillan 1977; Zieman and Wetzel 1980).

The first conceptualization of the

functions of seagrasses was provided by

Wood et al. (1969). The generalizations

have now been shown to be applicable to a

wide variety of systems and situations.

The following is an updated version

(Zieman 1982) of the earlier conceptual

framework.

1.

2.

3 .

4 .

5 .

High Production and Growth

The ability of seagrasses to exert a

major influence on the marine seascape

is due in large part to their

extremely rapid growth and high net

productivity. The leaves grow at

rates of typically 5 mm per day, but

growth rates of over 10 mm per day are

not uncommon under favorable

circumstances.

Food and Feeding Pathways

The photosynthetically fixed energy

from the seagrasses may follow two

general pathways: direct grazing of

organisms on the living plant material

or utilization of detritus from

decaying seagrass material, primarily

leaves. The export of seagrass

material, both living and detrital, to

a location some distance from the

seagrass bed allows for further

distribution of energy away from its

original source.

Shelter

Seagrass beds serve as a nursery

ground, that is, a place of both food

and shelter, for the juveniles of a

variety of finfish and shellfish of

commercial and sportfishing

importance.

Habitat Stabilization

Seagrasses stabilize the sediments

in two ways: the leaves slow and

retard current flow to reduce water

velocity near the sediment-water

interface, which promotes

sedimentation of particles as well as

inhibiting resuspension of both

organic and inorganic material.

Secondly, roots and rhizomes form a

complex, interlocking matrix with

which to bind the sediment and retard

erosion.

Nutrient Effects

The production of detritus

promotion of sedimentation

leaves of seagrasses provide

and the

by the

organic

matter for the sediments and maintain

an active environment for nutrient

recycling. Epiphytic algae on the

leaves of seagrasses have been shown

2
to fix nitrogen, thus adding to the

nutrient pool of the region. In

addition, seagrasses have been shown

to take up nutrients from the

sediments, transporting them through

the plant and releasing the nutrients

into the water column through the

leaves, thus acting as a nutrient

pump.

In addition to providing

shelter, the seagrass leaves

food resource in coastal

habitat and

are a major

ecosystems,

functioning through three major pathways:

direct herbivory, detrital food webs, and

export to adjacent ecosystems. Direct

herbivory on green seagrass leaves is

confined to a small number of species and

is most prevalent in tropical and

subtropical regions, especially in the

vicinity of coral reefs. Since the time

of Petersen (1918), the detrital food web

has been considered the main trophic

pathway in seagrass meadows, and current

studies continue to support this concept,

although direct herbivory can be locally

important in some areas (Zieman et al.

1984a; Thayer et al. 1984). In addition

to the internal utilization of seagrasses

as a food source, many beds, especially

those dominated by Syringodium, export

large quantities of organic material to

other distant ecosystems.

In the subtropical waters of south

Florida, seagrass meadows often bridge

large areas between the mangrove and coral

reef communities, while also serving as a

primary nursery and feeding ground

themselves (Zieman 1982). On the west

coast of Florida, they function in a

similar manner, as nurseries and feeding

grounds, but also serve as an interface

between the coastal salt marsh communities

and offshore habitats of the eastern Gulf

of Mexico.

1.2 THESEAGRASSESOFTHEWESTCOASTOF

FLORIDA

Seagrasses compose the relatively small

group of monocots which have evolved the

ability to carry out their life cycle

completely submerged in the marine

environment. Worldwide, they include 2

families divided into 12 genera and

approximately 45 species. The

Potamogetonaceae include 9 genera and 34

species and are represented on the west

coast of Florida by Syringodium filiforme

Kutz, whose common name is manatee grass,

and Halodule wrightii Ascherson, shoal

grass; the Hydrocharitaceae contains 3

genera with 11 species (Phillips 1978), of

which Thalassia testudinum Konig, (turtle

grass), and two species of Halophila, H.

engelmanni Acherson and H. decipiens

Ostenfeld, are found in the waters of the

west coast of Florida. Ruppia maritima

Linneaus (widgeon or ditch grass)

euryhaline angiosperm found abundantly in

fresh waters and in the marine environment

grows primarily in lower salinity areas.

The small number of species occurring in

these waters, and their distinctive gross

morphologies (Figure 2) preclude the need

for a dichotomous key, although systematic

works such as den Hartog (1970) and

Tomlinson (1980) are available for

comparison of seagrasses in other areas.

Phillips (1960a) still provides the best

treatment of local species.

The three dominant species of the open

coastal waters are Thalassia testudinum,

Syringodium filiforme, and Halodule

wrightii.

Thalassia is the largest and most robust

of the west Florida seaarasses. and the

densest growth in the vast" grassded of the

Big Bend area is dominated by a mixture of

this species and Syringodium (Iverson and

Bittaker 1986). While this species is not

abundant in the lower salinity waters of

Tampa Bay (Lewis et al. 1985a), it is the

dominant seagrass in the adjacent waters

of Boca Ciega Bay (Taylor and Saloman

1968; Bauersfeld et al. 1969), and in the

Tarpon Springs area (Phillips 1960a).

Among the local seagrasses, Syringodium

is distinctive in having cylindrical

leaves which are quite brittle and

buoyant, and thus are readily broken off

and exported from the immediate area by

winds and currents. This species is more

widely distributed in Tampa Bay than is

Thalassia (Phillips 1960a; Lewis et al.

-and while it is codominant in the

Big Bend grassbed, its biomass is

generally lower than that of Thalassia in

the mixed stands of that area, although

3
Halodule wrightii

Syringodium filiforme

Thalassla testudlnum

Halophila engelmanni Halophila decipiens Ruppia maritima

Figure 2. The seagrasses of the west Florida coast.

there are localized areas where it is

abundant.

Halodule, which has narrow leaves and a

shmot system,

pioneer species in

is recognized as the

the successional

development of grassbeds in the gulf and

Caribbean. It is more tolerant of low

salinity than both Thalassia and

Fy

and thus occurs in areas of

ampa Bay where those seagrasses cannot

survive

1985a).

(Phillips 1960a; Lewis et al.

As its common name, shoal grass,

indicates, it is often found in shallow

waters where it is subjected to repeated

4

exposure to the atmosphere. In the Big

Bend grassbed, this plant often forms both

the shallowest shoreward fringe of and the

deepest, outermost stands of seagrass, and

exhibits different morphologies in the two

zones (Phillips 1960b; McMillan 1978;

R.L. Iverson, unpubl. data).

1.3 PHYSICAL ENVIRONMENT

The west coast of Florida has a mild

maritime climate varying from temperate in

the north to semitropical * the

southernmost regions. For much':f the
year the southern portion of Florida is

dominated by the southeasterly trade

winds, while the airflow in the northern

and central portion is from the west,

under the influence of the westerlies and

accompanying cyclones (counterclockwise

circulation about a center of low

pressure) in the winter, and the western

margin of the Bermuda-Azores anticyclone

(clockwise circulation about a center of

high pressure) in summer.

The resulting differences in temperature

patterns are evident in Figure 3, which

shows the average monthly water

temperatures at several locations from

Pensacola to Key West (McNulty et al.

1972). The Cedar Key station is in the

center of the region under consideration

here. Both the average and maximum summer

temperatures vary little among the

stations, with highs around 33 OC. Most

obvious are the lower winter temperatures

and greater seasonal range at the northern

stations. Key West has a monthly low

average of 22 OC and a range of 14-26 OC

during January, while Cedar Key has a

January average temperature of 13.5 'C

with a range of 4-22 OC.

Earle (1969) found a similar pattern

with inshore gulf temperatures of 13-15 OC

in the north and 22.6-22.9 OC in the

Florida Keys. However, north of Cedar

Key, extreme winter lows of O-5 OC have

been recorded. The average winter

temperatures in the northern gulf in

winter are similar to the summer high

temperatures in New England, and Earle

(1969) noted that many winter species in

the northern gulf are the same as the

summer species in New England waters.

Precipitation generally increases

northward and westward along the Florida

coast from a low of 100 cm annually at Key

West to 163 cm at Pensacola (Table 1).

However, in the region from Tampa to

Apalachicola the precipitation is

relatively uniform with a minimum annually

of 118 cm at Cedar Key to a maximum of 140

cm at Apalachicola with about half of the

annual amount falling between June and

September. The average annual and monthly

Key West St. Petersburg Cedar Key Pensacola

JFMAMJJASOND JFMAMJJASOND JFMAMJJASOND JFMAMJJASOND

Figure 3. Temperatures atfourlocations in coastal Florida (from McNulty eta11972).

5
Table 1. Precipitation statistics for coastal stations on the eastern Gulf of Mexico

(from Jordan 1973).

Precipitation, Precipitation, Precipitation,

Mean Annual June-Sept. Dec.-March

(inches) G) G)

Mobile 65.5 41.4 34.9

Pensacola 63.4 43.3 30.0

Apalachicola 56.2 52.5 25.8

Tallahassee 56.9 47.5 28.5

Cedar Key 46.6 55.9 23.8

Tampa 51.6 60.2 20.6

Fort Meyers 53.3 63.6 14.3

Everglades 54.7 62.5 12.4

Key West 40.0 48.0 17.4

rates show the general patterns, but the

extreme months and years are highly

variable and can have severe effects on

the local biota. For Cedar Key, annual

rainfall has varied between 68-208 cm,

while monthly values at Apalachicola have

varied from a low of 0.03 cm to a high of

57 cm.

In the shallow waters of the estuaries

and the inshore gulf, water temperature

and salinity are locally affected by both

seasonal and isolated storms. The most

severe storms are tropical hurricanes with

their high winds, heavy rainfall, and

often devastating storm surges.

Hurricanes occur most frequently in the

late summer months when the oceanic

surface temperatures are at their highest,

but can occur in any month. The

probability of encountering hurricane

force winds in any one year varies greatly

along the Florida coast, being 1 in 8 at

Key West and Pensacola, 1 in 17 at

Apalachicola and St. Marks, and 1 in 25 at

Tampa-St. Petersburg (Bradley 1972). In

addition to the immediate local effects of

these storms, water quality is affected

following their passage by greatly

increased runoff from rivers and streams,

accompanied by increased turbidity and

biochemical oxygen demand.

In most locations, seagrass beds are

relatively protected from the surges of

large storms. However, in the Big Bend of

Florida these beds are subject to the full

force of storm waves. In 1985, two

hurricanes, "Kate" and "Elena" passed

directly through the area causing

localized disruption and bottom scouring.

Qualitative observations of stations

sampled before and after the hurricanes

suqqested complete recovery of the denser

inshore beds' of Thalassia, Syringodium,

and Halodule and the sparse offshore

Halophila beds in the vicinity of Tarpon

Sorinas Shelf Associates

1986):

(Continental

In the vicinity of Cedar Key,

where Hurricane "Elena" stalled for about

48 hours, seagrasses appeared to be

recovering, but at a slower rate than the

other site.

Tidal ranges are low to moderate along

most of the Florida west coast. From

Florida Bay northward to St. Joseph Bay

the tides are predominately semi-diurnal

(McNulty et al. 1972), shifting to diurnal

west of this point. Throughout the entire

area, the mean diurnal range is 0.5-1.1 m.

Daily ranges at Tampa Bay are 0.6-0.8 m.

Just north of Tampa Bay, the range

increases to 1.1 m until Apalachee Bay

where it begins to decrease slightly and

reaches 0.4-0.7 m at Apalachicola Bay.

Offshore circulation is dominated by two

large counter-rotating gyres. The

northern one is influenced by coastal

estuarine waters, while the southern one

is influenced by waters from Florida Bay.

In addition, there are periodic incursions

of the loop current with waters from the

6
tropical Caribbean and the Yucutan Channel

(Chew 1955; Austin 1970).

1.4 GEOLOGIC ENVIRONMENT

The present Florida peninsula is the

emergent portion of the Floridan Plateau,

consisting of layers of limestone and

unconsolidated sediments over a base of

sandstone and volcanic rocks (Puri and

Vernon 1959; NcNulty et al. 1972). The

limestone and ancient sediments are at

least 1,000 m in thickness over the entire

region. The rivers that. enter the gulf

east of Apalachicola Bay drain the coastal

plain, carrying small amounts of sediments

that are primarily carbonates and

anhydrites (McNulty et al. 1972). From

Apalachicola Bay westward, the rivers

drain areas of the Piedmont plateau and

the Appalachian highlands, and carry

primarily elastic sediments. Table 2

gives the characteristics of sediments for

several locations on the west Florida

coast.

The coastline of west Florida has been

divided and classified (Figure 4)

according to several different criteria

and schemes, including coastal beach and

interface characteristics (Price 1954;

Tanner 1960; McNulty et al. 1972), fauna1

community affinities (Lyons and Collard

1974), and underlying substrates and

outcrops (Brooks 1973). The coastal

divisions resulting from these differing

schemes are very highly correlated, and

the divisions used in this paper are a

combination of the above schemes.

The coastline west of Lighthouse Point,

near Apalachicola Bay, is the northern

gulf barrier coastline, with attached sand

Table 2. Sediment characteristics of the west Florida coast (from Folger 1972).

Carbonate

Location Organic content content Texture

Florida Bay

Whitewater

Bay

Gullivan Bay

(very open)

Port Charlotte

Harbor

Tampa Bay

Apalachicola

Bay

St. Joseph

Bay

Pensacola Bay

Average = 2.1% west

1% on shelf

l%-4% in lagoon

O.l%-1.0%

maximum = 3.1%

0.5%-2.0%

0.5%-4.5%

__

up to 90%

(Quartz 3.5% east,

up to 30%)

Up to 65%

(quartz 5%-10%)

lo%-40% typically

Locally to 60%-80%

Quartz 4%-8% near

islands

maximum = 24%

-_

0.5%-40%

lO%-40%

lo%-80%

1.3%-5%

Median size east = 0.025mm

west = 0.028mm

W = 70% silt, 30% sand

Non CaCOs = fine to very

fine sand

Very fine to fine sand

Variable, typically

sand sized

Variable, very coarse

sand to clay

Variable, very coarse

sand and gravel to clay

Coarse sand to silt

7
rend beaches and

-low duns, o” Gulf;

,;do, marshes and

c

Figure4. Coastalgeologyof the Florida west coast (from McNultyet al. 1972).

elastic

barrier

found to

beaches alternating with barrier islands. that they carry little suspended

A similar attached beach-barrier island material to form beaches or

interface exists from Anclote Key islands (Ross 1973) such as those

southward along the western edge of the the south or to the west.

central and lower Florida peninsula.

Along both the northern gulf and the Of equal or greater importance

central and lower peninsula, the barrier the region between St. Marks ant

_ .

is that

II Tarpon

beaches and spits enclose the major

estuaries and lagoons. However, the Big

Bend, the upper coastline of the

peninsula, is unique for the region in

that it is an extensive area with no

offshore barrier, where rivers, creeks,

and marshes grade directly into the

eastern Gulf of Mexico. A number of

physical, geological, and hydrological

features interact to produce this effect.

The rivers of the Big Bend are notable in

Springs is one of the few examples

world-wide of a zero-energy coastline

(Murali 1982). This is defined as a coast

where "the average breaker heights are

3-4 cm or less, and there is no significant littoral transport of sand" (Murali

1982). The major factors that contribute

to this phenomenon include the wide,

gently sloping shelf; the divergence of

approaching wave trains into the large,

expanding coastal concavity; the location

8
of the coast in a generally upwind direction; a small supply of new sediment; and

the wave dampening effects of old submerged beaches and the submerged seagrass

meadows (Murali 1982). Although the

presence of submerged seagrass meadows

interfacing directly with salt marshes

has been considered to be a contributing

factor to the zero-energy coast, it is

more likely that their presence in this

area is in fact the result of existing low

energy conditions, as seagrass beds are

rare on open oceanic, unprotected coasts.

Once established, the seagrass beds could

enhance the effects of those primary

factors responsible for reduced energy

conditions.

1.5 SUCCESSIONANDECOSYSTEM DEVELOPMENT

Throughout their range, few plants

participate in the successional sequence

leading to seagrasses because there are so

few marine plants that can colonize soft

sediments. In general, this sequence

consists only of the seagrasses and the

rhizophytic green algae. Seagrasses are

vital to the coastal ecosystem because

they are the only plants capable of

providing the basis for a mature,

productive ecosystem in these regions.

Few other systems are so dominated and

controlled by a single species as a climax

Thalassia or Zostera meadow.

Odum (1974) classified Thalassia beds as

"natural tropical ecosystems with high

diversity." Compared to other natural

systems, tropical seagrass beds are

regions of very high diversity, but this

can be misleading. These comparisons were

made at a time when high diversity was

equated with high biological stability.

The prevailing concept was that the

multitude of different organisms, with

their widely differing requirements and

interactions, functioned as a highly

intricate web structure that lessened the

importance of each link to the maintenance

of the total system. There was much

natural redundance built into such

systems. The problem is that at climax

there is one species for which there is no

redundancy - the seagrass. If the

seagrass disappears, the entire associated

community disappears along with it; there

is no other organism that can sustain and

support the system.

The initial colonizers are typically

rhizophytic macroalgae, of which various

species of Halimeda and Penicillus are the

most common, although species of Caulerpa,

Udotea, Rhipocephalus, and Avrainvilla

occur also. These algae have some

sediment binding capability, but their

ability to stabilize the sediments is

minimal and their major function in the

early successional stage seems to be the

contribution of sedimentary particles as

they die and decompose.

Halodule wrightii, the local pioneer

species of seagrasses, colonizes readily

either from seed or rapid vegetative

branching. The carpet laid by Halodule

further stabilizes the sediment surface;

the numerous leaves forming a better

buffer to protect the integrity of the

sediment surface than the algal

communities. In some sequences

Syringodium will appear next, intermixed

with Halodule at one edge of its

distribution and Thalassia at the other.

However, it is the least constant member

of this sequence and is frequently absent.

In areas with consistent disturbance and

sediments low . content

Syringodium may ber:me %Fniist abundant

species. It is commonly found lining

natural channels with hiqh velocity waters

and higher turbidity than Thalaisia can

tolerate.

As successional development proceeds,

Thalassia will begin to colonize the

region. Its strong straplike leaves and

massive rhizome and root system

efficiently trap and retain particles,

increasing the organic matter of the

sediment. The sediment height rises until

the rate of deposition and erosion of

sediment particles is in balance. This is

a function of the intensity of wave

action, current velocity, and leaf

density.

In shallow-water successional sequences

leading to Thalassia, the early stages are

often characterized by low sediment

organic matter and open nutrient supply;

that is, the community relies on nutrients

brought in from adjacent areas by water

movement as opposed to in situ - -

9
regeneration. With the progression from

rhizophytic algae to Thalassia, there is a

progressive increase in the below ground

biomass of the community as well as the

portion exposed in the water column. With

the progressive increase in leaf area of

the plants, the sediment trapping and

particle retention increases. This

material adds organic matter to further

fuel the sedimentary microbial cycles.

In summary, as species succession occurs

in these shallow marine systems, important

structural changes occur. The most

obvious change with community development

is the increase in leaf area, which

provides an increase in surface area for

the colonization of epiphytic algae and

fauna, with the surface area of the climax

community being many times that of either

the pioneer seagrass, Halodule, or the

initial algal colonizers. In addition to

providing a substrate, the increasing leaf

area also increases the leaf baffling and

sediment trapping effects. Thus, as the

canopy component increases, so does the

material in the sediment. Thalassia, the

climax species, has the highest leaf area,

the highest total biomass, and by far the

greatest amount of material in the

sediments of any of the successional

stages.

10
CHAPTER 2. AUTECOLOGY OF FLORIDA GULF COAST SEAGRASSES

2.1 PLANT MORPHOLOGY AND GROWTH

Seagrasses worldwide show a remakable

similarity in their structure and growth

(den Hartog 1970; Zieman and Wetzel 1980).

For the seagrasses of the northwest coast

of Florida, we shall focus primarily on

the growth and morphology of Thalassia,

considering this as representative of the

local species.

Detailed descriptions of the anatomy and

morphology of Thalassia were presented by

Tomlinson and -966) and Tomlinson

(1969a, 1969b, 1972). Flat, straplike

leaves with rounded tips emerge from erect

short shoots which branch laterally from

horizontal rhizomes at regular intervals.

In this species rhizomes occur from 1 to

25 cm below the sediment surface, but are

typically found in the depth range of

3-10 cm. (The rhizomes of Halodule and

&

Halo hila are near the surfamften

 While the rhizomes of

Syringodium are generally found at an

intermediate depth, in strong currents,

they may be exposed, even extending up

into the water column.) Roots of

Thalassia emerge from the rhizomes and the

short shoots. Much smaller in cross

section than rhizomes, the roots vary in

length according to sediment composition

and depth.

On a Thalassia short shoot, new leaves

grow on alternating sides of a central

meristem that is enclosed by old leaf

sheaths. New growth on leaves is produced

by the basal meristem, thus the base of a

leaf is the freshest, youngest portion.

Short shoots of this species typically

have two to five leaves at a time.

Studies of

morphology have

temporal and spat

seagrass growth and

revealed patterns of

ial variation. Grassbeds

11

in areas of relatively low productivity in

Biscayne Bay, Florida, averaged 3.3 leaves

per short shoot, while in the more

productive meadows of the Florida Keys,

plants averaged 3.7 leaves per short shoot

(Zieman 1975a). The width of leaves

increased with age of the short shoot,

reaching maximum width five to seven

shoots back from the growing rhizome tip

(Figure 5). Leaf width can also reflect

morphogeographic variation: in Florida,

Durako and Moffler (1981) identified the

effects of a latitudinal stress gradient

in leaves of Thalassia seedlings, with the

greatest widths occurring in the Keys and

the narrowest leaves found in northern

Florida. In another study, leaf widths

did not reflect a latitudinal or stress

gradient, but showed sexual differences:

female short shoots tended to have

narrower leaves than male shoots (Durako

and Moffler 1985a). Transplant

exoeriments found that narrow-leaved

plants of Thalassia, Syringodium, and

Halodule from the north coast of the Gulf

of Mexico continued to produce narrow

leaves, and broader-leaved plants from the

southern gulf and Caribbean likewise

continued to produce wider leaves, even

when moved to different habitats (McMillan

1978).

Thalassia leaves in Biscayne Bay grew an

average of 2.5 mm/day in length, but

growth rates as high as 1 cm/day were

measured over periods of 15-20 days

(Zieman 1975a). Leaf growth rate in

Thalassia usually decreases exponentially

with leaf age (Patriquin 1973; Zieman

1975a). In contrast, leaf elongation in

Syringodium proceeded at a relatively

steady rate throughout the growth phase

(Fry 1983). The first few leaves produced

on a new Thalassia short shoot are reduced

in size and are tapered; the regular

straplike leaves are produced at a rate of
AVERAGE LEAF WIDTH (MM)

8 5 8 7 7.5 7 4

LEAF

BRANCH OR

SHORT SHOOT-.

DISTANCE BETWEEN BRANCHES (CM)

Figure 5. General morphology of a Thalassia plant.

one-new-leaf-per-short-shoot every 14-16

days. The rate of leaf production in

Biscayne Bay was dependent on temperature,

with low growth occurring in the cooler

winter months (Zieman 1975a). Less

seasonal variation was found in the

tropical Caribbean waters of Barbados and

Jamaica by Patriquin (1973) and Greenway

(1974) respectively. Durako and Moffler

(1981) found a gradient of root and leaf

growth in Thalassia seedlings, from high

rates in the Florida Keys to low growth

rates in north Florida waters.

In Tampa Bay, Durako and Moffler (1985c)

found pronounced seasonal patterns in

maximum leaf lengths of Thalassia. There

was a slight decrease in the middle of

summer, coincident with high temperatures

and floral production, but maximum lengths

were much less in the cold winter months,

reflecting both leaf die-off and depressed

growth rates due to exposure to low

temperatures. A pattern of spatial

variation was evident, with shorter leaves

occurring in the middle of the grassbed

where the water was shallower.

2.2 REPRODUCTION

Vegetative reproduction in seagrasses

accounts for their capacity to produce

high biomass and area1 cover; however,

sexual reproduction is important in

providing the genetic plasticity for

successful adaptation and competition in

the species. Studies of flower production

in the seagrasses considered here have

focused primarily on Thalassia. This

plant is sexually dimorphic, producing

separate male and female flowers. Grey

and Moffler (1978) found that short shoots

occurring on a common rhizome segment

produced flowers of the same sex,

suggesting that Thalassia is also

dioecious, that is, has separate male and

female plants.

12
Flower production in Florida populations

of Thalassia occurs from April to August

or September, peaking in June (Orpurt and

Boral 1964; Grey and Moffler 1978) (Figure

6). While Phillips (1960a) found no

flowering north of Tarpon Springs, more

recent studies have revealed flowering in

the grassbeds of the Florida panhandle

(Marmelstein et al. 1968; Phillips et al.

1981). The percent of short shoots in a

grassbed bearing reproductive structures

varies greatly: less than I_% of plants

from north Florida beds reproduced

sexually, while reproductive densities in

plants from south and central Florida

ranged from l% to 15% (Phillips 1960a;

Orpurt and Boral 1964; Zieman 1975). More

recently Moffler et al. (1981) found

reproductive densities of 44% in Tampa

Bay. A later study in Tampa Bay recorded

reproductive densities of 11.4%, 20.7%,

and 10.0% for 1981, 1982, and 1983,

respectively, and found that increased

numbers of male flowers accounted for the

higher reproductive density of 1982

(Durako and Moffler 1985b). Spatial

density distributions showed higher

numbers of female plants occurred on the

fringes of the bed where short shoots are

generally younger, while more male plants

were found in the center on presumably

older short shoots. This pattern could

reflect an age-related sexual expression

in the plants, although environmental

factors and clonal differences also can

influence leaf width (Durako and Moffler

1985b). (Thalassia seed production in

Tampa Bay was apparently low compared with

south Florida and probably could not

provide an adequate supply for restoration

projects (Lewis and Phillips 1981).

Phillips (1960a) found flowering Ruppia

abundant in Tampa Bay; however, he did not

observe seedling germination. Flower and

fruit production in Ruppia of this area

peak in May and disappear in June (Lewis

et al. 1985a). Phillips (1960a) did not

find reproductive Halodule, Syringodium,

or Halophila in Tampa Bay; however,

several reproductive specimens of Halodule

were later found in nearby waters (Lewis

et al. 1985a). Although reproductive

plants are rare in Syringodium, female

plants have been collected in the bay

(Lewis et al. 1985a). Zimmerman and

Figure 6. Flowers of Thalassia (left) and Syringodium (right) (photo by M. J. Durako.)

13
Livingston (1976b) found a number of

flowering Syringodium plants in their

Apalachee Bay samples in May, 1972. These

authors also found numerous flowering

plants of Ruppia in May and June.

In 1 aboratory studies, cultures of

Thalassia, Syringodium, Halodule, and

Halophila engelmannii flowered under

continuous light, suggesting that

flowering was independent of day length.

The temperature range for flowering in

these plants was 22-26 OC (McMillan 1982).

Lewis et al. (1985a) also found that

flower production in Thalassia was

probably controlled by factors other than

photoperiod.

2.3 PLANT CONSTITUENTS

Because of their high productivity and

wide distribution, seagrasses are

recognized as a potentially important food

source in shallow coastal marine systems.

The fact that this abundant food source is

subjected to relatively low levels of

direct grazing on the living plant

material has prompted studies of the

chemical constituents and relative food

value of seagrasses. Various authors have

performed such constituent analyses for

the seagrasses considered here

(Burkholder et al. 1959; Bauersfeld et al.

1969; Walsh and Grow 1972; Lowe and

Lawrence 1976; Bjorndal 1980; Dawes and

Lawrence 1980; Vicente et al. 1980; Dawes

and Lawrence 1983). A summary of these

results is given in Table 3. Dawes and

Lawrence (1980) noted that the differences

in sample preparation and chemical

analyses employed make direct comparison

of the data difficult, and subsequently

proposed a procedure to standardize

analyses so that future data will be

comparable, making it possible to

determine the effect of seasonal and other

environmental changes on the chemical

content of the plants.

The relative amount of protein in the

plant tissues has been used as a measure

of the potential food value of tropical

seagrasses. Comparative studies have

shown that turtle grass leaves are roughly

equal in percent protein to phytoplankton

and Bermuda grass (Burkholder et al. 1959)

and 2 to 3 times higher than 10 species of

tropical forage grass (Vicente et al.

1980).

Walsh and Grow (1972) found that

Thalassia protein content compared

favorably with reported values for grain

crops: corn contained from 9.8% to 16%

protein, sorghum 8.6% to 16.5%, and wheat

8.3% to 12%. Various studies of the

protein content of Thalassia leaves have

yielded results ranging from a low of 3%

of dry weight for unwashed epiphytized

leaves (Dawes et al. 1979) to a maximum of

29.7% for leaves rinsed with .distilled

water (Walsh and Grow 1972). The low

value for unwashed leaves reflects the

inclusion of sea water salts, and possibly

sediment particles which settle on leaves,

into the total dry weight. Values more

typically range between 10% and 15% of dry

weight.

Dawes and Lawrence (1983) and Durako and

Moffler (1985c) have reported spatial and

temporal variations of protein content.

In Tampa Bay values for Thalassia and

S rin odium varied from 8% to 22% and from

*, respectively, with maximum

values occurrinq in the summer (Table 4).

Thalassia leaves collected in July 1979

from Tamna Bav. Kev West. and Glovers

Reef, Belize,-' showed a significant

increase in protein content from Tampa to

Belize, even though the sites were similar

in depth, salinity, and temperature (Dawes

and Lawrence 1983). If such a latitudinal

trend holds, Thalassia from the Big Bend

area, for which constituent analyses have

not been performed, could have even lower

protein content, and thus lower food

value. Such a decrease in nutritional

value might be reflected in the results of

Kitting et al. (1984), who found that

several seagrass "detritivores" in the

northern gulf actually derived most of

their nutrition from epiphytes.

The new growth of the basal portions of

leaves of Thalassia are higher in protein

and lower in Inorganic content (Cawes and

Lawrence 1980). The green turtle has been

shown to exploit this fact in its pattern

of grazing: a patch of seagrass is

initially cropped, with the upper older

portions of the leaves left to float away,

and such patches are subsequently

maintained for a period of time by

repeated grazing (Bjorndal 1980). Thus,

14
Table 3. Constituent analysis of seagrasses (from Zieman 1982).

Season/ % as CarboSpecies Component date Referenced Ash

Energy

Nitrogen Protein Fat hydrates (kcal/g) Reference

Thalassia Leaves February %DW 24.8 2.1 (13.1) 0.5 35.6 1.99 Burkholder

et al. 1959

Annual %AFDW 1.6-4.8 25.7

mean %DW 24.5 (10.3-29.7)

January

April

July

October

Mean

%DW 29

37

33

44

x

8 0.9

9 4.0

22 1.0

23.6 4.66 Walsh and

Grow 1972

?

45

50

44

2.4 Dawes and

3.0 Lawrence

3.1 1980

41 2.6

E 2.8

13

13

22 0

2.0

%DW

(unwashed)

%DW

(washed)

47.3 11.0 0.7

13.0 0.5

38

24.8 35.6

%DW 24.7 9.1 2.3 63.9

Bauersfeld

et al. 1969

JulyAugustLowe and

Lawrence

1976

January

August

%DW 16.7 Bjorndal

1980

17 Vicente

et al.

1978

(Continued)
Table 3. (Continued).

Species Component

Season/ % as Carbo- Energy

date Referenced Ash Protein Fat hydrates (kcal/g) Reference

Thalassia Rhizomes

Roots

Photosynthesis

inactive part

of short shoot

Rhizomes

Syringodium Leaves

Leaves

Short shoots

photosynthesis

inactive

parts

Annual

mean

January

April

July

October

Mean

January

April

July

October

Mean

JulyAugust

January

April

July

October

Mean

January

April

July

October

Mean

%DW

%AFDW

%DW

23.8

50.5

24.1

5.8-12.2

11.0

19.6

15.0

72.1

%DW 39

51

48

56

7E

9 1.0

7 0.5

16 0.7

8 0.8

lo 0.8

51 2.7

42 2.2

35 2.5

35 2.0

a 2.4

%DW 26

24

33

36

m

9 0.5 65 3.2

8 1.6 66 3.4

16 0.2 51 3.0

7 1 1

i-0

A

0.9

56 2.8

m 3.1

%DW 27.0 3.10 3.4 66.3

%DW 30

28

33

32

x

9 1.7 59

8 6.2 58

13 4.0 50

13

ii

1.8

3.4

53

!Z

%DW 28 10 1.3 61

27 11 3.6 58

31 14 0.9 54

41 11 1.1 47

Z? Tz 1.7 !Z

4.88 Walsh and Grow 1972

Bauersfeld et al.

1969

Dawes and Lawrence

1980

Lowe and Lawrence

1976

3.1 Dawes and Lawrence

2.4 1980

3.2

3.1

3.0

3.2

3.3

3.1

2.6

3.1

(Continued)
Table 3. (Concluded).

Species Component

Season/ % as Carbodate Referenced Ash Protein

Energy

Fat hydrates (kcal/g) Reference

January %DW 16 9

April 18 5

July 17 12

October 19 6

Mean 18 8

1.0 74 3.6

4.7 72 3.7

0.1 71 3.6

0.5

1.6

75 3.5

73 3.6

Syringodium Rhizomes

January %DW 32

April 25

July 25

October 26

Mean T

January

April

July

October

Mean

%DW 25

29

36

34

Ti

January

April

July

October

Mean

%DW 14

17 8

i-G 8

19 1.0 48

18 3.2 54

19 1.2 55

Halodule Leaves 3.1 Dawes and Lawrence

3.5 1980

3.3

3.3

3.3

14

T;s

1.4

1.7

59

55

Short shoots

photosynthesis

inactive part

5

9

8

9

8

1.1

3.5

0.8

A

1 2

1.7

69

59

55

56

60

3.2

3.0

2.9

2.9

3.0

Rhizomes 0.7

1.6

0.1

;

1 1

0.9

76

74

70

74

T-4

3.7

3.7

3.4

3.6

3.6
Table 4. Seasonal content of protein and soluble carbohydrates (% dry weight) in Tampa Bay (after

Dawes 1987).

Species Component January April July October

Thalassia testudinum

Leaves Protein 8

Carbohydrate 6

9

9

22

9

13

7

Protein 9 8 16 7

Carbohydrate 12 21 24 36

Rhizomes

Syringodium filiforme

Leaves 13

20

Protein 9 8 13

Carbohydrate 22 16 18

Protein 9 5 12 16

Carbohydrate 36 38 50 46

Rhizomes

Halodule wrightii

Leaves Protein 19 18

Carbohydrate 14 19

19

15

14

13

Protein 9 7 8 8

Carbohydrate 43 40 43 54

Rhizomes

higher levels of soluble carbohydrates in

Thalassia rhizomes compared to the leaves.

In Tampa Bay, seasonal variation in

soluble carbohydrate content occurred in

the rhizomes of both Thalassia and

Syringodium, reflecting production and

storage of starch during summer and fall

(Dawes and Lawrence 1980). Mean values

for the lipid content of Thalassia leaves

varied from 1.2% to 4.2%, and were

comparable to the "fat" content of

tropical terrestrial grasses.

the turtles create a more energetically

and nutritionally rich food source, and,

indeed, Zieman et al. (1984) found that

the nitrogen content of leaves within

turtle patches was similar to the content

of the basal portions of ungrazed leaves

and higher than the upper portions of

those leaves.

The values reported for ash content of

Thalassia leaves range from 45% dry weight

for unwashed samples to a low of about 25%

for samples rinsed in fresh water.

Samples washed in ambient seawater

contained 29%-44% ash (Dawes and Lawrence

1980). Thalassia rhizomes from the west

coast of Florida had ash content

significantly lower than did the leaves,

with mean values ranging from 2l% to 26%

dry weight (Dawes and Lawrence 1983).

Cell wall carbohydrates (cellulose,

hemicellulose, and lignin) accounted for

45%-60% of the dry weight of turtle grass

leaves (Bjorndal 1980; Vicente et al.

1980). Dawes and Lawrence (1983) found

2.4 PHYSIOLOGICAL ECOLOGY

2.4.1 Environmental Tolerances

and Responses

a. Temperature. The range of thermal

tolerance in tropical organisms is

often about half that of their

temperate counterparts. Although

the upper temperature limits are

similar, the tropical organisms have

18
reduced cold tolerance. McMillan

(1979) found a gradient of chill

tolerance in Florida seagrasses,

with those from northern Florida

most tolerant of low temperatures

and those of the Florida Keys least

tolerant. After growing in culture

for 22 months, Thalassia seedlings

maintained their original pattern of

chill tolerance: those from

Apalachee Bay, Florida, showed less

damage than seedlings from the

Florida Keys and St. Croix.

In the thermally impacted waters

of Anclote Estuary north of Tampa

Bay, Barber and Behrens (1985) found

that maximal growth in Syringodium

occurred between 23 and 29 OC, and

between 23 and 31 OC in Thalassia

(Figure 7). In the cooler months,

thermally impacted stations had

higher productivities than did

non-impacted areas, but in the

summer months, Syringodium

productivity was depressed at the

warmer stations when the upper

thermal tolerance limit of this

seagrass was exceeded. In Apalachee

Bay, Zimmerman and Livingston

(1976b) found that Syringodium

tolerated lower temperatures than

Thalassia, which suffered leaf kill

when temperatures fell below 15 OC.

Some defoliation of Thalassia also

occurred when summer temperatures

rose to 30 OC.

Thalassia

IO 15 20 25 30

TEMPERATURE (“C)

Figure 7. Temperature responses of Thalassia

Behrens 1985).

In Texas waters, vigorous growth

of Ruppia in the spring correlated

with cool temperatures rather than

lowered salinities (Pulich 1985).

Phillips (1960a) reported a

temperature range of 7-35 OC for

Ruppia in Tampa Bay; growth and

reproduction was highest with spring

temperatures, and decreased when

high summer temperatures were

reached. In Texas, a similar pattern

of temperature response was evident

for Ruppia in a mixed stand with

Halodule; in contrast, Halodule

biomass at that site peaked in the

warmer summer months and declined in

the fall. Phillips (1960a) reported

that Halodule in Tampa Bay suffered

winter leaf kill, even at sites

which were always submerged.

However, Halodule suffered little

leaf kill in Apalachee Bay, where

the minimum winter temperature was 9

OC. This temperature was a new

minimum reDorted for HaloDhila

en elmanni (Zimmerman and Livingston i!kijT

b. Salinity. Although the seagrasses

considered here are able to tolerate

fluctuations in salinity, the

optimum concentration for growth

varies among the species.

Experiments with transplanted

seagrasses showed that, of the

species considered here, Halodule

had the broadest salinity tolerance,

4.0

3.0

2.0

1.0

Syrinqodium

0

1 1 1 I

10 15 20 25 30 35

TEMPERATURE (“C)

and Syringodium on the west Florida coast (after Barber and

19
/ -

Thalassia and Syringodium

(==E;c$;;ea)t;eere intermediate, and

most stenohaline.

Ruppia sho;;im a wide tolerancz:

ranging freshwater

hypersaline conditions (McMillan

1974). Evaluating the upper limits

of salinity tolerance, McMillan and

Mosely (1967) found that Halodule

(=Diplanthera) tolerated the highest

salinities, surviving up to 80 ppt,

followed, in order, by Thalassia,

Ruppia, and Syringodium, with

Halophila's relative tolerance

aoparentlv somewhere between

Halodule -and Syringodium McMillan

salinities was Ruppia, followed by

Halodule, Thalassla, Syringodium

(=Cymodocea), and Halophila. While

both Ruppia and Halodule exhibit

broad ranges of salinity tolerance,

the former is the only seagrass

species, of this region capable of

surviving in freshwater. According

to McMahan (1968), Halodule does not

survive in salinities less than 3.5

ppt and has an optimum salinity of

44 ppt.

Thalassia and Syringodium do not

grow in areas of low salinity in the

eastern Gulf of Mexico (Phillips

1960a), and were not reported in

areas with salinities less than

about 17 ppt in the northern

seagrass bed (Zimmerman and

Livingston 1976). Turtle grass can

survive short periods of exposure to

extremes ranging from a low of 3.5

ppt (Sculthorpe 1967) to a maximum

of 60 ppt (McMillan and Mosely

1967); however, significant leaf

loss frequently follows exposure to

salinity extremes. The optimum

salinity reported for this seagrass

ranges 24-35 ppt (Phillips 1960;

McMillan and Mosely 1967; Zieman

1975a). In turtle grass, maximum

photosynthetic activity occurred in

fullstrength seawater, and decreased

linearly with decreasing salinity

(Hammer 1968b). The effect of

freshwater runoff following a

hurricane was considered more

damaging to seagrasses than the

effects of high winds and tidal

surge (Thomas et al. 1961).

According to Humm (I973),

Halophila does not tolerate reduced

salinities; however, Zimmerman and

Livingston (1976b) found a bed of y.

engelmanni off the mouth of the

Econfina River, an area of

relatively low salinity.

addition, Earle (1972) report::

Halophila occurring at depths

ranging from intertidal to 13 m, and

Strawn (1961) found this species

mixed with Halodule and Ruppia on an

old oyster bar. Thus, it appears

that tialophila may in fact be quite

euryhaline.

Ruppia traditionally has been

considered a brackish-water species

(Verhoeven 1975) and, indeed, among

the seagrasses it alone can be

maintained in tap water (McMillan

1974). Phillips (1960a) reported

that it occurred most frequently in

salinities below 25 ppt, which

correspond with the findings of

Zimmerman and Livingston (1976b).

In the Big Bend seagrass bed, Ruppia

was observed growing near river

mouths (R.L. Iverson, Forida State

University, Tallahassee; pers.

comm.) However, Dawes (1974) found

it growing in areas of relatively

high but stable salinity in the

lower portions of Tampa Bay.

transplants

Ruppia

survived in salinities

up to 74 ppt (McMillan and Mosely

1967); this species also grew in

Texas waters at a site where

salinities averaged 25-32 ppt and at

hypersaline

for several

another site where

conditions persisted

months (Pulich 1985).

has been observed

hypersaline waters in

(J. Fourqurean, Un

also Ruppia

growing in

Florida Bay

iversity of

Virginia, Charlottesville; pers.

comm.). Thus Ruppia also appears to

be quite euryhaline.

The oxygen contained in the

column of seagrass beds

generally provides a supply adequate

to meet the respiratory demands of

the plants themselves and associated

organisms. In Thalassia beds,

20
photosynthetic oxygen production can

be so high that bubbles escape from

the leaf margins in the late

afternoon. The seagrasses are less

susceptible to low oxygen

concentrations than the animals of

the grassbeds; nevertheless, leaf

mortality and increased microbial

activity coincided with lowered

oxygen levels in Japanese Zostera

beds (Kikuchi 1980). Low 0s levels

do slow their rate of respiration,

and when internal O2 concentrations

are lowered, the plant's rate of

resgiration is controlled by

diffusion of oxygen from the water

column. During the night, the

respiratory demand of the seagrasses

and associated plant and animal

communities can lower concentrations

of the surrounding waters (Durako et

al. 1982). In Puerto Rico (Odum et

al. 1960) and in Florida and Texas

(Odum and Wilson 1962) nighttime

oxygen concentrations were typically

4-7 mg 0s L-l, and a low of 2-3 mg

02 L-l recorded on a calm night in

August during an extreme low tide.

d. Light. The fact that well-developed

seaarass beds do not occur at depths

greater than 10 m has been

considered indirect evidence that

photosynthesis i n seagrasses

requires high light intensity, and

that light penetration limits the

depth to which seagrasses can grow

(Humm 1956; Buesa 1975; Wiginton and

McMillan 1979). Gessner and Hammer

(1961) suggested that increased

hydrostatic pressure, as well as

decreased light, may limit

photosynthesis suggesting that light

is probably not the sole factor

restricting photosynthesis at depth;

however, there were no significant

pressure effects on photosynthetic

rates of Thalassia and Syringodium

for plants collected from various

depths near Buck Island, St. Croix,

and subjected to 1 and 3 atmospheres

of pressure (R.L. Iverson,

Department of Oceanography, Florida

State University; unpubl. data). It

therefore unlikely that the

i:essures that exist over the depth

gradients where these seagrasses are

found can explain the significant

decrease in Thalassia biomass at

the limit of its depth distribution.

However, the maximum depth at which

seagrasses occur does indeed

correlate with the available light

regime. Buesa (1975) reported the

following depth maxima for the

seaarasses off the northwest coast

of _ Cuba:

Syringodium,

decipiens 24

englemann;, 14.

Thalassia

16.5 m;

.3 m; and

4 m.

14 m;

Halophila

Halophila

Of the visible light spectrum, the

longer red wavelengths are absorbed

in the first few meters in both

clear and turbid waters. The clear

tropical waters of the Caribbean Sea

are enriched in blue light, while in

turbid shallow waters, such as parts

of Florida Bay and coastal waters of

Texas, enrichment of green

wavelength occurs. In a study of

the effects of specific wavelengths

of light on seagrass photosynthesis,

Buesa (1975) found that Thalassia

responded best to red light-)

and S rin odium grew best with blue

wave-0 nm). Wiginton and

McMillan (1979) reported increasing

chlorophyll a to chlorophyll b

ratios for seagrasses obtained from

increasing depths near Buck Island,

St. Croix, but concluded that light

quantity rather than light quality

was the primary environmental

determinant of seagrass depth

distribution along the Buck Island

gradient. Thalassia growing in

outer Florida Bay has considerably

more non-photosynthetic tissue than

compensation light-energy level

(below which annual net increase of

total plant biomass cannot occur)

for Thalassia growing in tropical

habitats is less than the

compensation light energy level for

Syringodium and for Halodule as a

conseauence of the

demands

respiratory

created by the 'greatei

orooortion of nonohotosvnthetic

tissue mass of Thalassia <n those

habitats.

Humm (1973) observed that Ruppia

occurred in areas of low light and

21
high turbidity. Phillips (1960a)

also noted the growth of this

species in areas of poor light

penetration.

in addition to!%$!$%ng~~

light of deeper waters also grows in

areas of high turbidity (Zimmerman

and Livingston 1976b).

e. Current. Seagrass biomass and

production are greatly influenced by

current velocity (Conover 1968).

The maximum standing crops for both

Thalassia and Zostera were found

where current velocities averaged

0.5 m set-l. Rapid currents are

thought to disrupt diffusion

gradients and increase the

availability of CO2 and nutrients to

the plants (Conover 1968). In south

Florida, the densest stands of

Thalassia and Syringodium are found

in the tidal channels separating

mangrove islands. Off the coast of

Nicaragua, samples from mangrove

tidal channels had a leaf standing

crop of 262 g dry weight m-2 and

total biomass of 4,570 g m-2. By

comparison, values for samples from

a quiescent lagoon were 185 and

1,033 g m-2 respectively (McRoy,

Zieman, and Ogden, unpubl. data).

Strong currents can affect the

structure of seagrass beds. In some

areas of high current, lunate

features called blowouts occur

(Patriquin 1975). These

crescent-shaped erosional features

migrate through the bed in the

direction of the current.

Recolonization takes place at the

trailing edge of the blowout, and

here the successional sequence of

seagrass colonization can be

observed.

f. Sediment. Seagrasses are found in a

variety of substrates, ranging in

texture from fine muds to coarse

sands. Because they are rooted

plants, they do have minimum

sediment-depth requirements, which

differ among the species.

Halodule's shallow surficial root

system allows it to colonize thin

sediments in areas of minimal

hydraulic stability (Fonseca et al.

1981). Thalassia is more robust,

reauirina up to 50 cm of sediment

for lush-growth, although it occurs

shallower

G72).

sediments (Zieman

In the Bahamas, Thalassia

did not occur in sediments less than

7 cm deep (Scoffin 1970). Phillips

(1962) reported that seagrasses in

Tampa Bay grew only in muddy sand

substrates, and patches of pure sand

were unvegetated.

Reduced sediments seem always to

be associated with well-developed

Thalassia beds and most likely

reflect the greater importance of

sediment-nutrient content and

microbial nutrient recycling in

meadows of this species, rather than

a specific requirement for reducing

conditions. Halodule is generally

thought to grow in more aerobic

substrates; however, Pulfch (1985),

working in Texas waters, postulated

that Ruppia normally occurs in

low-nutrient sediments while

Halodule prefers organic-rich

sediments where sulfate reduction is

substantial. Phillips (1960a)

reported that Syringodium

distribution was apparently

independent of sediment type and

this species is found in both

oxidized and reduced sediments

(Patriquin and Knowles 1972).

Ruppia is generally found in finer

substrates than the above species

(Phillips 1960a), while Halophila

grows in a wide range of substrates

from muddy sands to limestone, and

even on mangrove roots (Earle 1972).

In the Big Bend area of the west

coast of Florida, Iverson and

Bittaker (1986) also recorded

Thalassia growing in coarser

sediments than the other species of

that northern grassbed. Syringodium

and Halodule biomass were greater in

fine sediments (Iverson and Bittaker

1986). Similarly, Buesa (1975)

found that Thalassia off the

northwest coast of Cuba grew in

coarser sediments than Syringodium

or Halophila.

g. Exposure. Thalassia and Syringodium

are subtidal plants and do not

22
tolerate exposure to the air. While

Thalassia does grow on flats that

are infrequently exposed, unless

such exposure is brief, desiccation

will cause leaf kill. Halodule can

withstand repeated exposure at low

tide, and is most abundant between

neap-low and spring-low tide marks

higher

iG6Oa).

salinities (Phillips

In low-salinity intertidal

areas, Ruppia and Halodule often

occur in mixed stands (Phillips

1962; Earle 1972). Dawes (1987)

noted that Ruppia forms extensive

meadows on flats where it can be

exposed to intense sun and appears

to tolerate a degree of desiccation.

2.4.2 Photosynthetic Carbon Fixation

Three separate biochemical pathways by

which plants can fix inorganic carbon

photosynthetically have been identified.

The majority of terrestrial plants

utilize the Cs pathway, in which CO2 is

initially incorporated into a threecarbon product. In the C, pathway, found

primarily in plants from tropical and

arid areas, a four-carbon product results

from the first step of CO;! incorporation. The third pathway, CAM (crassulacean acid metabolism), by which plants

take up CO:! at night and store it as

malic acid until daytime when it is then

used in photosynthesis, occurs in waterstressed plants such as desert succulents. A major factor in the differences

of photosynthetic physiology between Cs

and C4 is the greater efficiency of

refixation of photorespired CO2 found in

the C, plants (Hough 1974; Moffler et al.

1981). High rates of refixation have

been detected, however, in some Cs plants

with specialized leaf anatomy and gas

lacunae (Sondergaard and Wetzel 1980) and

may be implicated in seagrass carbon

metabolism (Beer and Wetzel 1982). Seagrass leaves possess large internal

lacunar spaces which facilitate gas

transport (Zieman and Wetzel 1980). The

presence of these lacunae and the absence

of stomata provide the plants with a

relatively closed pool of carbon dioxide,

thus promoting recycling of CO*.

Seagrasses share with C4 plants such

physiological adaptations as high thermal

and light optima for photosynthesis and

high productivity rates. Although

Thalassia was originally thought to be a

C, plant, Beer and Wetzel (1982), using

radiolabel led HCOm3, concluded that both

this seagrass and Halodule were

intermediaries between Cs and C4 in their

carbon metabolism. Syringodium and

Zostera exhibited the most typically Cs

pattern of the seagrasses studied.

2.4.3 Isotopic Fractionation

A significant result of the differences

in carbon metabolic pathways is that

imprints are left in the form of

characteristic ratios of the stable

isotopes of carbon in the plant tissues

produced. In biochemical reactions,

plants do not utilize 12C and 13C in the

exact ratios found in the environment,

but discriminate between the two,

favoring the lighter isotope. Plants

using the C3 pathway are relatively

depleted in 13C, while C4 plants have

higher ratios of l3C to l2C. The

relative content of 1% to 12C is

compared to the isotopic ratio of a

standard and expressed as a "del" value

(6) as follows:

13C/l2C

(513c, sample lx103

13c/12c standard

The range of 613C values for Cs plants

is -24 to -34 ppt, while C4 plants vary

from -6 to -9 ppt (Smith and Epstein

1971). Seagrass values, particularly

those of Thalassia and Syringodium, are

similar to those of the C4 plants.

McMillan et al. (1980) reported that 45

of 47 species examined fell within the

range of -3 to -19 ppt, with only two

species of Halophila having lower values.

Samples of Thalassia from the Gulf of

Mexico and the Caribbean range from -8.3

to -12.5 ppt, with a mean of -10.4 ppt.

Halophila had similar isotopic

composition, with means of -10.2 ppt for

gulf and -12.6 ppt for Caribbean samples.

Syringodium, by comparison, had

relatively fewer negative numbers, with a

mean of -5 ppt and a range of -3 to -9.5

PPt. This species has a greater

proportion of lacunar spaces, and the

lacunae are more completely partitioned

than those of the other seagrasses

considered. This greater lacunar

23
isolation presumably enhances the

recycling of C02, which occurs in C,

plants! and thus the similarity in

isotopic composition is not unexpected.

Tropical seagrasses in general have

values less neaative than those of

temperate specie;. A study of Zostera

showed little seasonal variation in

isotopic composition (Thayer et al.

1978). The isotopic composition can

vary, however, with habitat (Smith et al.

1976; Zieman et al. 1984c). McMillan and

Smith (1982) found that seagrasses grown

in laboratory cultures had more negative

values, that is, were more depleted in

the heavier 13C than samples from the

natural environment. They concluded that

such results could reflect differences in

carbon sources and in recycling of

internal carbon.

Since plants have characteristic

isotopic compositions, and the animals

that consume them retain to within t2 ppt

the same ratio (DeNiro and Epstein 1978;

Fry et al 1978), these isotope

"signatures" provide a useful tracer for

food chain studies (Figure 8). In the

marine environment, seagrasses have

isotopic ratios distinct from other

marine plants. Thus carbon derived from

seagrasses (-3 to -15 ppt) is

distingished from that of marine

macroalgae (-12 to -20 ppt), particulate

organic carbon and phytoplankton (-18 to

-25 ppt) and mangroves (-24 to -27 ppt)

(Fry and Parker 1979). In Texas,

sediment organic matter within a seagrass

bed was more depleted in 13C compared to

sediment organic matter from adjacent

bays without seagrasses (Fry et al.

1977), and the same pattern was reflected

in the animals (Fry 1981). The 6 13C of

the polychaete worm Diapatra cuprea

varied from an average of -13 ppt in

seagrass-dominated areas to -18 ppt where

phytoplankton were the dominant primary

producers (Fry and Parker 1979). Similar

trends were observed for fish and shrimp.

The utility of

method of food

restricted at the

cost of analytical

limitations of data

this carbon isotope

chain analysis is

present by the high

equipment and by the

interpretation. When _^

a consumer organism has a 6 l"C value

which falls within a range specific for a

particular plant source, the relationship

is readily apparent; however, if the

animal has a de1 value falling between

two identifiable pl,ant groups, it is

unclear whether this represents a food

source which itself has a value

intermediate between the two known groups

or whether the organism is consuming a

mixed diet.

2.5 NUTRIENTUPTAKEANDSUPPLY

Seagrasses are highly productive plants

that can grow in low-nutrient

environments; thus, the manner in which

plant nutrient demands are met is of

particular interest. Since seagrasses

occupy both the water column and the

CARBON ISOTOPE ANALYSIS OF PRODUCERS AND CONSUMERS

6 13c

ROOKERY BAY ---- T H PA PP ELMM

PINE CHANNEL ---- S PPTHL A MM

! 11 ll! lrrl!llrl!llrl!llll!

-5 -10 -15 -20 -25 -30

Legend: T = Thalassia P = Pink Shrimp E = Epiphytes M = Mangroves L = Litter A = Macroalgae

H = Halodule S = Syringodium

Figure 8. Carbon isotopic variation at two locations in Florida (after Zieman et al. 1984c).

24
sediments, controversy existed in the

past over whether nutrients were taken in

throuah the leaves or the roots. The

tempeiate seagrass Zostera is capable of

takina in nutrients both from the water

columi and through the roots (McRoy and

Barsdate 1970); however, uptake through

the root system was shown to be faster

and more efficient (Penhale and Thayer

1980). McRoy and Barsdate (1970) found

that Zostera could translocate ammonium

and phosphate from the sediments to the

leaves and excrete these nutrients into

surrounding waters. Such nutrient

pumping may be important only in

sediments with high nutrient

concentrations (Penhale and Thayer 1980).

Studies of nutrient supply to

seagrasses have concentrated on nitrogen

and phosphorus because these, along with

carbon, are the primary constituents of

plant material. In Zostera beds in

Chesapeake Bay, the addition of

commercial fertilizer containing both

nitrogen and phosphorus stimulated leaf

growth (Orth 1977a). Harlin and

Thorne-Miller (1981) observed similar

growth enhancement when inorganic

ammonium and phosphate were added to

waters overlying Zostera beds in a Rhode

Island bay. The relative importance of

these major nutrients in limiting plant

growth has not been determined and

probably depends on local nutrient

supplies and processes.

Three sources of nitrogen are available

to the plants: microbially recycled

nitrogen from organic matter in the

sediment, dissolved ammonium and nitrate

in the water column, and ammonium from

the microbial fixation of dissolved NZ.

Sources of organic matter for

decomposition in the sediment include

animal excretions and dead roots and

rhizomes, Sediment bacteria convert the

organic nitrogen to ammonia in the anoxic

zone, which begins only a few millimeters

below the surface. Ammonia that is not

quickly bound either by biological uptake

or chemical adsorption by sediment

particles can diffuse upward to the

aerobic zone, where it can then diffuse

into overlying waters or be converted to

nitrate by nitrifying bacteria. Nitrate

concentrations are low in the sediments;

nitrate is either rapidly assimilated or

converted to N2 by denitrifying bacteria.

Patriquin (1972) and Capone and Taylor

(1980) identified the recycled organic

material as the primary source of

nitrogen for leaf growth; however,

nitrogen fixed by sediment microbes

could supply 20% to 50% of the plants'

requirements (Capone and Taylor 1980).

In contrast, Capone et al. (1979) found

that fixation by phyllosphere microbes

contributed primarily to epiphyte growth.

The relative importance of the different

nitrogen pools to the plants is indicated

by such factors as sediment

characteristics and water column

concentrations.

Inorganic phosphorus, unlike nitrogen,

has no gaseous phase and does not change

valence state in normal environmental

reactions. Thus the source of phosphorus

to the seagrasses is dissolved inorganic

orthophosphate (PO,), derived either from

the breakdown of organic matter or from

the weathering of minerals, some of which

are biologically precipitated. While

water-column concentrations in tropical

waters are normally low, phosphate may be

quite abundant in the sediments. High

levels of HCl-extractable phosphate were

found in the carbonate sediments of

seagrass beds of Barbados, but pore-water

concentrations and concentrations in

overlying waters were low (Patriquin

1972). Because the high sediment

concentrations probably reflected

undissolved phosphate not available for

uptake by the plants, Patriquin concluded

that the nutrient-poor overlying waters

were the primary source of phosphate to

the seagrasses. Sediment type influences

the dissolution of phosphate, and,

therefore, its availability to the

plants. Silicious sediments readily

exchange phosphate with overlying waters

(Nixon et al. 1980), but carbonate

sediments tend to absorb phosphate,

removing it from solution. Rosenfeld

(1979) reported that pore-water phosphate

concentrations of Florida Bay sediments

were two orders of magnitude lower than

concentrations in Long Island Sound pore

waters and attributed the difference to

calcium carbonate adsorption of

phosphate.

Terrestrial runoff also can be an

important factor affecting the

25
concentration of dissolved nutrients. In limiting plant growth can be expected to

Apalachicola Bay, nutrient concentration vary accordingly. At this time, the

peaks coincided with periods of maximum degree to which phosphorous and nitrogen

river discharge (Myers and Iverson 1981). are limiting the growth of Florida's

The bays and estuaries of the northwest seagrasses is still unknown, and is a

coast of Florida vary widely in sediment timely and important topic for further

composition and terrestrial input; thus, research.

the supply of phosphate and its role in

26
CHAPTER 3. DISTRIBUTION, BIOMASS, AND PRODUCTIVITY

3.1 DISTRIBUTION

Distribution of seagrasses along the

west coast of Florida is unique in that

the plants not only occur in protected

estuarine grassbeds typically found along

the Gulf of Mexico coast (represented in

this area by the grassbeds in embayments

such as Rookery Bay, Charlotte Harbor,

Tampa Bay, and St. Joseph Bay), but also

form an extensive offshore bed located

along the coastal reach between the St.

Marks River and Tampa Bay, known as the

Big Bend area.

have been studied most extensively (Thorne

1954; Phillips 1962; Taylor and Saloman

1968; Lewis and Phillips 1980; Lewis et

al. 1985a). While this estuary has

received intense human impact and cannot

be considered necessarily typical or

representative of west Florida bays, the

abundance of information on Tampa Bay

seagrasses provides a useful base for

comparison with other areas.

Seagrass distribution in the eastern

Gulf of Mexico has been investigated at

several different levels of spatial

resolution. Humm (1956) reported

seagrasses observed at specific sites

along the northern coast of the Gulf of

Mexico. Phillips (1960a) described the

general location of seagrasses around the

Gulf of Mexico based on literature reports

and on field surveys. Bauersfeld et al.

(1969) and Earle (1972) estimated area1

seagrass distribution in the eastern Gulf

of Mexico using indirect methods. McNulty

et al. (1972) reported seagrass

distribution within embayments and

estuaries in the eastern Gulf of Mexico

based on field observations and on

analysis of aerial photography. While the

seagrass distribution within embayments

adjacent to the northeastern Gulf of

Mexico has been reasonably well described,

the spatial extent and biomass of

seagrasses of the Big Bend area have been

only recently investigated (Continental

Shelf Associates 1985; Iverson and

Bittaker 1986).

Thorne (1954) identified five seagrasses

occurring in the bay: Thalassia, Syringodium, Halodule, Ruppia maritima and Halophila engelmannii. In his survey of seagrasses of Tampa Bay, Phillips (1962)

reported the presence of all species but

Halophila; however, this seagrass was

later observed in the bay by Lewis and

Phillips (1981) and Moffler and Durako

(reported in Lewis et al. 1985a).

Phillips (1962) noted that the southern

part of the bay was dominated by Diplanathera (Halodule) and in the northern

part Ruppia was more abundant, presumably

due to a salinity gradient. Thalassia is

relatively sparse in Tampa Bay, possibly

because of low salinities (Phillips 1962),

but is the dominant species in the adjacent waters of Boca Ciega Bay (Pomeroy

1960; Phillips 1962; Taylor and Saloman

1968). Lewis et al. (1985a) estimated

that the current distribution of seagrasses in the bay, covering 5,750 ha

(14,203 acres) represents a reduction of

81% of historical coverage prior to human

impact (Figure 9).

3.1.1 Seagrass Distribution in Tampa Bay

a. Seagrass associations. There are

five types of seaqrass meadows found

in Tampa Bay (Figure 10). Mid-bay

shoal perennial beds contain Thalassia, Syringodium, and Halodule,

but rarelv RuoDia. due to either the

Among the estuarine grassbeds of the

west coast of Florida, those of Tampa Bay

fast currents or increased salinities found on the shoals where these

27
10 mi

15 km

Figure 9. Seagrass coverage in Tampa Bay in 1879 and 1982 (after Lewis et al. 1985).

beds grow. Healthy fringe perennial

beds contain all five species found

in the bay. In these beds, Ruppia

is found in the shallowest water

close to shore, followed by almost

pure stands of Halodule, Thalassia,

and Syringodium, respectively, as

depth increases. These meadows

generally have an unvegetated sand

bar separating the seagrasses from

the main body of the bay. Stressedfringe perennial beds are similar to

their healthy counterparts except

coverage is reduced, and migration

of a destabilized sand bar

eventually leads to the disappearance of the bed. These beds

occur in areas of the bay where

phytoplankton are abundant, possibly

competing with the benthic

macrophytes. Finally, colonizing

perennial grassbeds are found in

bands in the euphotic zone of manmade fill areas. The dominant soeties here are Halodule and Syringodium, presumably because their rhizomes are more readily fragmented

and dispersed to unvegetated areas.

b. Sediment effects. According to

Thorne (1954) seagrass distribution

in the Gulf of Mexico was limited to

soft marl, mud, or sand substrates.

Phillips (1962) found that all seagrasses in Tampa Bay grew in muddy

sand: while sandy substrates

remained unvegetated. The sediments

of the bay contain varying amounts

of carbonates, which may be important in determining the availability

of essential nutrients.

C. Depth distribution. Phillips (1962)

reported that seagrass growth was

limited to depths of less than one

fathom (2 m) in the turbid waters of

Tampa Bay. Syringodium dominates

below the spring low-tide mark, and in

deeper water frequently occurs in

mixed stands with Thalassia (Humm

1956; Phillips 1960a; Phillips 1962).

Shallow areas are dominated by Ruppia

28
MBS(P)

HF(P)

S F (PI

Figure 10. Seagrass meadow types in Tampa Bay.

MBS(P) = mid-bay shoal perennial; HF(P) = healthy

fringe perennial; SF(P) q stressed fringe perennial; E

q ephemeral; C(P) = colonizing perennial (after Lewis

et al. 1985).

and Halodule (Phillips 1962). Three

mOrDhOl oaicallv distinct forms of

Halbdule-in the bay were identified

according to depth distribution

Dwarfed plants occurred in areas

exposed at neap and spring low tides,

while subtidal plants were more robust

(Phillips 1960d). Salinity rather

than tidal exposure was thought to

control the distribution of Ruppia in

the bay (Phillips 1962).

3.1.2 Seagrass Distribution in

the Big Bend Area

The Big Bend seagrass bed overlies

drowned karst topography which extends

from the town of St. Marks south to Tarpon

Springs. The sediments of this low energy

region are composed of clay and silicious

sand over limestone. Results of recent

investigations suggest that seagrasses are

the dominant benthic feature of the

nearshore environment from St. Marks to

Tampa (Iverson and Bittaker 1986;

Continental Shelf Associates 1985)

Analysis of a photographic composite

obtained from aerial photography

(Continental Shelf Associates 1985)

revealed some broad-scale patterns in

seagrass distribution with beds of

greatest density in shallow water well

removed from river mouths. Beds of lesser

density extended as far as 112 km offshore

(Figure 11).

Samples for characterization of seagrass

distribution in eastern Gulf of Mexico

coastal waters were taken by Iverson and

Bittaker (1986) from St. Marks to Tampa

during the month of October for several

years. Visual observations of the

presence or absence of different seagrass

species were made at each of about 300

stations in the Big Bend area of north

Florida (Figure 12). Samples for

estimation of seasonal seagrass biomass

changes were collected within a 10 m

radius of a metal marker stake located in

1 m water depth at stations near the

Florida State University Marine Laboratory

at Turkey Point, and in St. Joseph Bay.

The line marking the outer limit of the

seagrass beds in Figure 12 indicates the

maximum depth to which seagrass coverage

of about 80% or more of the bottom

extended within each major area.

Vegetation covered about 3,000 km*, with

seagrasses occurring as a band varying

from 11 to 35 km wide between St. Marks

and Tarpon Springs, Florida.

All six species of seagrasses presented

in Chapter 1 were found in the Big Bend

grassbeds. Halodule occasionally formed

both the innermost and the outermost

monospecific stands in this area.

Shallow-water Halodule growing on shoals

often exposed at low tide, generally had

short, narrow leaves, and deep-water

Halodule was tall with wider leaves

(Iverson and Bittaker 1986).

Shallow-water and deep-water forms of

Halodule appear to be morphologically

different clones (Phillips 1960b; McMillan

1978). Shallow areas not exposed on low

tides contained mixtures of Thalassia,

Syringodium, and Halodule. Densest

portions of the seagrass bed were

dominated by Thalassia and Syringodium in

29
‘7.

-CRY5

Bl

:TAL

Y

Figure 11. Seagrass distribution and density in the Big Bend area (adapted from Continental Shelf

Associates 1985).

30
OUTER LIMIT OF

SEAGRASS BEDS

29” N

EM0 w+

GULF OF

50 kilometers

SrSteinhatchee

;PRINGS

casassa

PHOTO TRANSEC’I-

.%?=Y

I * 1

SEAGRASS PRESENT

0 Thalassia testudinum

Q

Syrlngodium filiforme

(3 Halodule wriahtii

Q Halophila enqelmanni

Q Halophtla decipiens

Q Ruppia maritima

9m. MLW -c-y“

a

Figure 12.

1986).

Seagrass species distribution in the Big Bend area (after lverson and Bittaker

31
various mixtures. Halophila engelmanni

was common in this orassbed. and was often

mixed with Thalassia and Syringodium.

Halophila engelmanni was also abundant

outside the major seagrass bed to depths

of at least 20 m where it occurred in

monotypic stands (Continental Shelf Associates. 1985). Halophila decipiens

occasionallv occurred in small monotvoic

stands or mixed with sparse Halodule'or

Caulerpa populations in northern offshore

areas deeper than 5 m, as well as in some

of the shallowest areas (Continental Shelf

Associates 1985). Ruppia was primarily

restricted to low salinity areas such as

the mouths of the Econfina and Suwannee

Rivers.

a. Depth distribution control. Iverson

and Bittaker (1986) showed that the

major seagrass species were distributed throughout the seagrass beds

in mixed associations (Figure 12),

in contrast to south Florida, where

large monospecific beds are far more

common. Thalassia and Syringodium

comprised most of the biomass which

extended to about 5 m water depth.

Halodule wrightii and Halophila

engelmanni contributed very little

to total seagrass leaf biomass.

A transect taken across a grassbed

near the Florida State University

Marine Laboratory showed that Thalassia was present in greatest leaf

biomass at depths between 0.5 and

2 m, while Syringodium reached

greatest leaf biomass at 2.5 m

(Figure 13). Halodule occurred at

both ends of the transect (Iverson

and Bittaker 1986). The general

pattern in fine-scale depth distribution of seagrass species appears

to be similar among the various

American tropical seagrass beds for

which observations have been

reported. Strawn (1961) described

the cross-bed, seagrass distribution

near Cedar Key in the northeast Gulf

of Mexico. Halodule occurred in

monotypic stands on shoals exposed

to the atmosphere at low tide and

was distributed throughout the seagrass bed. Thalassia grew only in

subtidal areas and did not extend to

the deepest limits of the bed which

contained Syringodium. This depth

Thalassia B -

qi Halodule

Svrinaodium

I234

DEPTH (m)

5oor T

DEPTH (m)

Figure 13. Depth distribution of seagrass biomass

in Apalachee Bay (after lverson and Bittaker 1986).

distribution pattern was evident in

several diverse areas: in the grass

bed samples in northern Apalachee

Bay (Iverson and Bittaker 1986), in

the northwest Cuban seagrass bed

(Buesa 1974), in a Nicaraguan seagrass bed (Phillips et al. 1982),

and in a seagrass bed near Buck

Island, St. Croix (Wiginton and

McMillan 1979).

32
For many kilometers along the

outer limit of the Big Bend seagrass

bed between Tarpon Springs and

Crystal River, an observer on the

waters' surface notices a distinct

transition from the dark green outer

edge of the seagrass bed and the

light sediment bottom seaward of the

bed edge. The outer edge of the

grassbed is deeper north of Tarpon

Springs, in the Big Bend bed, compared with the part between St.

Marks and the Crystal River. This

variation is a consequence of

increased water clarity in the

southern part of the Big Bend seagrass bed, as indicated by the

extinction coefficients for light

energy in the water column measured

in those areas. In addition, subjective observations made over a

period of years suggest that the

relative differences in water

clarity from the two areas are consistent (R.L. Iverson, unpubl.

data). The nearshore waters of the

Big Bend area receive river runoff

colored

(Bittaker $75) o$?~~c

compounds

in addition

to particulates, contr\butes to the

increased turbidity and higher

extinction coefficients observed in

that area (Zimmerman and Livingston

1979).

Based on the depth-distribution

data obtained in several different

investigations, the light-energy

compensation level for the annual

growth of American tropical seagrass

communities dominated by Thalassia

appears to be about 10% of seasurface photosynthetically active

light energy. The depths to which

10% of sea-surface light energy

penetrated, calculated from measured

extinction coefficients, were 7 m

for the part of the seagrass bed

between Tarpon Springs and Crystal

River, and 4.5 m for the portion

north of Crystal River. These

depths,approximate the seaward limit

of the major seaqrass beds comoosed

of Thalassia, -Syringodium, ’ and

Halodule in those respective areas

of the eastern Gulf of Mexico.

Although Thalassia and Syringodium

were distributed to greater depths

in Cuban coastal waters (Buesa 1974)

and in St. Croix waters (Wiginton

and McMillan 1979) compared with the

Big Bend area and Florida Bay, most

of the leaf biomass in the northwest

Cuban and the Buck Island, St.

Croix, seagrass beds was located

shallower than the depth to which

10% of surface light energy penetrated. The maximum possible area

in which Thalassia can form welldeveloped beds appears to be constrained by the slope of the sea

floor and the bottom depth of the

isolume corresponding to 10% of

surface light energy (Iverson and

Bittaker 1986).

b. Salinity and temperature effects.

The nearshore species composition of

seagrass assemblages in the northern

bed is influenced by freshwater discharges entering the northeastern

Gulf of Mexico from several rivers

along the coast. Thalassia testudinum and Syringodium filiforme do

not grow in areas of low salinitv

water in the northeastern Gulf o?

Mexico (Phillips 1960a) and were not

reported in areas with salinities

less than about 17 ppt in the

northern seagrass bed (Zimmerman and

Livingston 1976a).

The seagrasses of the Big Bend

area experience a large temperature

range (8-33 "C) (Goulet and Haynes

1978). Seagrasses from this bed

were more tolerant of very cold temperatures than were seagrasses from

Florida bay (McMillan 1979; McMillan

and Phillips 1979); however, each

winter, leaves of Big Bend seagrasses die back to within several

centimeters of the sediment-water

interface (Zimmerman and Livingston

1976b), a phenomenon also observed

in seagrass beds in Texas waters

during cold winters (Phillips 1980).

C . Sediment effects. Thalassia grew in

coarser sediments than did the other

seagrasses of the Big Bend area

(Iverson and Bittaker 1986). Buesa

(1975) reported that Thalassia in

northwest Cuban grassbeds also grew

in coarser sediments than did other

seagrasses.

33
Sediment deposition on leaf surfaces significantly interferes with

the growth of both Thalassia testudinum and Halodule wrightii

(Phillips 1980). Water turbidity

was inversely related to distance

from the Econfina River mouth

(Bittaker 1975; Zimmerman and

Livingston 1979), suggesting that

turbidity effects on seagrass growth

occur primarily nearshore as proposed by Humm (1956). Moore (1963a)

reDOrted that hiah-water turbiditv

precluded the griwth of Thalassia

testudinum in Louisiana coastal

waters within the Mississippi River

plume.

3.2 BIOMASS

Seagrass biomass can vary greatly

depending not only on the species but on

such environmental variables as available

light, sediment depth, nutrient availability, and circulation. The biomass of

Halophila is always low, but Thalassia

biomass can reach values greater than 7 kg

m-2 (Burkholder et al. 1959). Ranges of

biomass values for Thalassia, Syringodium, and Halodule are presented in Table

5. The results of many of these studies

have been summarized by various authors

(McRoy and McMillan 1977; Zieman and

Wetzel 1980; Zieman 1982; Thayer et al.

1984b; Lewis et al. 1985a). Since the

studies involve a wide range of experimental conditions, including differences

in habitat, sampling times and seasons,

and sample replication, attempts to compare or generalize based on the cumulative

data are of questionable value.

The majority of seagrass biomass,

particularly in the larger species, is

below the sediment surface. Ordinarily,

15%-20% of Thalassia's biomass is in the

leaves (although reported values range

from 10% to 45%) with the rest made up by

roots, rhizomes, short shoots, and

sheathing leaves (Zieman 1975, 1982).

Sediment type can affect the relative

amount of biomass above and below the

surface: the ratio of leaf to root and

rhizome biomass in Thalassia increased

from 1:3 in fine mud to 1:5 in mud and 1:7

in coarse sand (Burkholder et al. 1959).

It is unclear whether this reflects

enhanced leaf production in nutrientricher fine sediments or the need for

greater root development for increased

nutrient absorption in the aenerallv

poorer coarse sediments. Thalassia has

the most robust root and rhizome svstem of

the seagrasses of Florida. Halodule and

Syringodium have shallower, less welldeveloped roots and rhizomes, and tend to

have a greater portion of their total

biomass, 50% to 60%, in leaves (Zieman

1982). However, Pulich (1985) reported

that Halodule from Redfish Bay, Texas had

66% of total biomass below the sedjment

surface, compared to 3l.% for Ruppia.

Reported values for the relative portions

of' above- and below-ground biomass in

Florida west coast species are shown in

Table 6.

3.2.1 Seagrass Biomass in Tampa Bay

Both above- and below-ground biomass of

the seagrasses of the bay were determined

by Lewis and Phillips (1980). Ruppia had

the lowest biomass, both for standing crop

(portion of plant above sediment surface)

and root and rhizome (below sediment surface). Thalassia had the highest belowground biomass, but its leaf standing crop

was similar to that of Syringodium.

In nearby Boca Ciega Bay, Thalassia leaf

standing crop exhibited seasonal variation, reflecting temperature extremes.

Dry weights peaked in spring and early

summer, declined during mid-summer temperature maxima, and dropped to the lowest

values during winter months (Phillips

1960a). Durako and Moffler (1985c)

observed a similar seasonal pattern in

maximum leaf lengths of Thalassia in Tampa

Bay. Seagrass biomass for the Tampa Bay

area, as reported by Lewis et al. (1985a),

is given in Table 7.

3.2.2 Seagrass Biomass in

the Big Bend Area

Thalassia and Syringodium comprised 84%

of total leaf biomass in the Big Bend

area; Thalassia alone accounted for 58% of

leaf biomass compared to 64% for grassbeds in Florida Bay (Iverson and Bittaker

1986). Thalassia leaf biomass reached a

seasonal maximum during August and then

declined rapidly at stations located near

the Florida State University Marine

34
Table 5. Representative values of seagrass biomass (g dry weight m-*1.

Species Biomass Location Source

maritima Ruppia

Halodule wrightii

60-160

10-400

22-208

10-300

Syringodium filiforme

15-1100

30-70

Thalassia testudinum

30-500

60-718 Puerto Rico

60-250 Texas

20-1800 Florida (east

coast)

57-6,400 Florida (west

coast)

Texas

Texas

North Carolina

South Florida

South Florida

Texas

Cuba

Pulich 1985

McMahan 1968;

McRoy 1974;

Pulich 1985

Kenworthy 1981

Zieman unpubl.

Zieman unpubl.

McMahan 1968

Buesa 1972,1974;

Buesa and

Oleachea 1970

Burkholder et al.

1959; Margalef

and River0 1958

Odum 1963;

MCRoy 1974

Odum 1963; Jones

1968 ;

Zieman 1975b

Bauersfeld et al.

1969; Phillips

1960a; Taylor et

al. 1973a

Laboratory and in St. Joseph Bay (Figure with significant blade densities, the

14). The seasonal effect is related to density decreased by over 50% at 7 of 11

cycles of light intensity and water tem- stations in the winter months. Most

perature (Iverson and Bittaker 1986). The stations that showed no difference or a

ratios of seasonal maximum to seasonal slight increase had only sparse seagrass

minimum values at these sites were between cover.

6:l and 8:1, showing the difficulty of

comparing sites on the basis of biomass The seagrass beds of St. Joseph Bay are

data, particularly in higher latitudes primarily composed of Thalassia testudinum

where seasonal patterns are more pro- growing in monospecific stands. McNulty

nounced. Continental Shelf Associates et al.

(1985) found that for offshore stations

(1972) estimated 2,560 ha of

seagrass coverage within St. Joseph Bay.

35
Species

Table 6. Biomass partitioning In seagrasses.

Biomass % of

Component (g dry wt m-*> Total Reference

Ruppia

maritima

Above ground

Below ground

Above ground

Below ground

Halodule

wrightii

Above ground

Below ground

Above ground

Below ground

Syringodium Above ground

filiforme Below ground

Thalassia

testudinum

Above ground

Below ground

110

50

48

48

150

290

5-54 11-33

10-200 67-89

28-102 16-47

31-521 53-84

58-267 11-15

321-2,346 85-90

69

31

50

50

34

66

Pulich 1985a

Lewis and

Phillips 1980

Pulich 1985

Zieman 1982

Zieman 1982

Zieman 1982

aPeak seasonal biomass values.

Table 7. Seagrass biomass of the Tampa Bay area (g dry wt mm*) (from Lewis et al. 1985a).

Species

Biomass

Location Above ground Below ground Reference

Ruppia maritima Tampa Bay

Halodule wrightii Tampa Bay

Syringodium filiforme Tampa Bay 50-170

Thalassia testudinum Boca Ciega

Bay

Bird Key

Cat's Point

Boca Ciega

Bay

32.4

325

98

636

320-1,198

601-819

25-180

Tarpon Springs

Tampa Bay

1.48 18-48

38-50 60-140

160-400 Lewis and

Phillips 1980

48.6

Bauersfeld et

al. 1969

Taylor and

Saloman 1969

Dawes et al.

1979

600-900 Lewis and

Phillis 1980

Lewis and

Phillips 1980

Lewis and

Phillips 1980

Pomeroy 1960

Phillips 1960a

Phillips 1960a
AMJJASOND

MONTH

Figure 14. Seasonal cycle of Thalassia at two

stations in Apalachee Bay(after lverson and Bittaker

1986).

Another estimate of St. Joseph Bay

seagrass coverage obtained during 1978 was

2,300-2,400 ha of coverage, suggesting

that seagrass beds are a stable feature of

the benthos of St. Joseph Bay and are not

markedly affected in spatial coverage by

seasonal cycles in leaf biomass density

(Savastano et al. 1984). Iverson and

Bittaker (1986) found that short-shoot

densities did not change significantly

throughout the year, and suggested that,

during the fall of the year, the use of

shoot densities

comparisons would

this area.

for interbed biomass

be more appropriate for

3.3 PRODUCTIVITY

The high rates of primary productivity

of seagrasses is well recognized. Studies

of biomass literature have reported a wide

spectrum of productivity measurements

(Table 8). Past studies have focused on

Table 8. Seagrass productivity measurements.

Species

Productivity

(g C m-2 day-l) Site Reference

Halodule

wrightii 0.5- 2.0 North Carolina

1.1 Florida (east

coast)

Syringodium

filiforme 0.8- 3.0

0.6- 9.0

Thalassia

testudinum 0.6- 7.2 Cuba

2.5- 4.5 Puerto Rico

1.9- 3.0 Jamaica

0.5- 3.0 Barbados

Florida

Texas

0.9-16.0 Florida (east

coast

Dillon 1971

Virnstein 198Za

Zieman unpubl.

Odum and Hoskin

1958; McRoy 1974

Buesa 1972,1974

Odum et al. 1960

Greenway 1974

Patriquin 1972b;

1973

Odum 1957,1963;

Jones 1968; Zieman

1975a

aCalculated as 38% of reported dry weight.

37
Thalassia, but more recently Halodule and

Syringodium have been studied.

A major problem encountered in attempts

to synthesize the results of various productivity studies is that the three major

methods of measurement--leaf marking, O2

evolution, and l*C uptake --each yield

somewhat different results. In the

literature, the highest values are

obtained using the O2 method, the lowest

values result from leaf marking, while 14C

measurements provide intermediate values

(Zieman and Wetzel 1980; Kemp et al.

1986). In a carefully developed study,

Bittaker and Iverson (1976) found that 14C

and leaf marking gave essentially identical results when the 14C results were

corrected for inorganic losses, incubation

chamber light absorption, and differences

in light energy resulting from differences

in experimental design. In a study of

Thalassia in Bimini, Capone et al. (1979)

found, however, that productivity measured

by the 14C method was double the rates

obtained from the leaf marking technique

(Zieman 1974; Fry 1983) which underestimates net productivity since it does not

measure below-ground productivity,

excreted carbon, or herbivory. The 14C

method allows the investigator to determine the partitioning of photosynthate

within the plant. Figure 15 shows the

location of 14C in Thalassia after a

4-hour incubation period. The leaves

contained 49% of the radiocarbon although

they made up only 13% of the total biomass.

Despite the methodological differences,

studies of the productivity of seagrasses

have shown that these are highly productive systems, especially when growing

under optimal or near-optimal conditions.

3.3.1 Seagrass Productivity in Tampa Bay

Surprisingly little data exist on the

productivity of the seagrasses of this

area. In nearby Boca Ciega Bay, Pomeroy

(1960) estimated that Thalassia and

Syringodium occurring at depths less than

2 m, fixed 500 g C.m-2. yr-I. He concluded that, at these depths, seagrasses,

microflora, and phytoplankton were equally

important primary producers, whereas

sheath

rhizome

roots

% Total 14C uptake % Total weight

.:.

n

49.0

23.3 34.1

26.6 50.3

I ,I 3.3

13.3

Figure 15. Location of recently fixed carbon photosynthate in Thalassia after4 hour incubation. The right hand

column shows the typical weight distribution in the plants (after Bittaker and lverson 1976).

38
phytoplankton production dominated in

deeper waters. Johansson et al. (1985)

estimated that phytoplankton productivity

in Tampa Bay was higher in deep waters

(340 g C.m-2. yr-l) than in shallow waters

(50 g C.m-2. yr-l), and concluded that, in

contrast to the results of McNulty (1970),

phytoplankton production was ten times

higher than benthic production in the bay.

Studies of Thalassia leaf growth in

Tampa Bay show that leaf lengths can

increase at a rate of 5 cm per month

during the period of maximum growth in the

spring. Maximum leaf length occurs in

early summer, before high temperatures

cause a mid-summer die-back (Lewis et al.

1985a).

3.3.2 Seagrass Productivity in

the Big Bend Area

A seasonal cycle was evident in

macrophyte carbon-production data obtained

over a period of several years at a

station in the northern part of the Big

Bend area (Figure 16). Thalassia

testudinum contributed most of the carbon

production per unit area (up to

2.2 g C.m-2.d-1 in July), except for a

brief midsummer period when red drift

macroalgae were the largest source of

photosynthetic carbon fixation. Data from

which these composite carbon production

figures were made were taken from Bittaker

(1975), who showed that the annual carbon

production cycle was related to annual

variations in solar radiation and water

temperature.

Near the Anclote River, seagrass

productivity estimated from leaf growth

measurements was reported as 2-15 mg

C.m-2.h-1 for Thalassia, 2-37 mg C.m-2.h-1

and 0.9-1.4 mg C m-L h-l for Syringodium

and Halodule, respectively (Ford 1974 et

al .; Ford and Humm 1975).

I -

THALASSIA

(a)

OTHER SEAGRASSES

I

d!tbkiI

RED MACROALGAE

(cl

I=

IlI

‘JFMAMJJASON

MONTH

Figure 16. Seasonal changes in productivity of

seagrasses and red algae in Apalachee Bay

(unpublished data from Ft. L. Iverson).

39
CHAPTER 4. COMPONENTS OF THE SEAGRASS COMMUNITY

The distribution and density of seagrass

species are dependent on the physical,

chemical, and geological environment,

while the associated community is the

product of this seagrass composition as

well as the abiotic variables. Along the

west coast of Florida, from Florida Bay to

Apalachicola Bay, there are large

variations in all of the major

physico-chemical parameters. This

environmental gradient is reflected in the

changes of species associations and

community structure within the seagrass

system.

Although it is obvious that large

changes in abiotic variables and plant

composition and density can produce major

changes in the community structure, even

subtle variations apparently can produce

major community differences. At five

sample sites in a single south Florida

estuary with Thalassia blade densities of

over 3,000 m-2 the total number of

macrofaunal taxa'varied from 38 to 80, and

the average density of individuals varied

over two orders of magnitude, from 292 to

10,644 individuals m-2 (Brook 1978).

Organisms found in seagrass communities

can be classified in a number of ways,

depending on the objectives of the

classification. The biota present in a

seagrass ecosystem can be classified in a

scheme that recognizes the central role of

the seagrass canopy in the organization of

the system, and classifies the organisms

according to their position relative to

the canopy. The principal groups are:

(1) epiphytic organisms, (2) epibenthic

organisms, (3) infaunal organisms, (4) the

planktonic organisms, and (5) the nektonic

organisms.

and Zieman (1982) as any sessile organism

growing on a plant (not just a plant

living on a plant). Epibenthic organisms

are those that live on the surface of the

sediment, and include, in the broadest

sense, motile organisms such as large

gastropods and sea urchins, as well as

sessile forms, such as sponges and sea

anemones or macroalgae. Infaunal

organisms are those that live buried in

the sediments, such as sedentary

polychaetes and bivalves, and relatively

mobile infauna, such as irregular urchins.

Organisms that are buried part-time, for

shelter, such as penaeid shrimp or blue

crabs, or while waiting for prey, like

flounders, are considered epibenthic and

not infauna. Planktonic organisms are the

minute plants and animals, such as

diatoms, dinoflagellates, and many

copepods that drift in the water column.

They may show local movement, and

especially may migrate vertically, but are

largely at the mercy of water currents for

their lateral movement. By comparison,

nektonic organisms are highly mobile

organisms living in or above the plant

canopy, such as fishes and squids.

Another classification scheme, first

proposed by Kikuchi (1980), and slightly

modified by Zieman (1982), is based on the

mode of utilization of the seagrass beds

by the associated fauna. This

classification is based on whether

organisms are: (1) permanent residents,

(2) seasonal residents, (3) temporal

migrants, (4) transients, or (5) casual

visitors.

4.1 ALGAL ASSOCIATES

Epiphytic organisms are defined

according to the usage of Harlin (1980)

The major sources of primary production

for coastal and estuarine areas are: (1)

macrophytes (seagrasses, macroalgae, salt

40
marsh plants, and mangroves), (2) benthic

microalgae (benthic and epiphytic diatoms,

dinoflagellates, filamentous green and

bluegreen algae), and (3) phytoplankton.

In estuarine and coastal regions the

relative balance of standing crop and

productivity between the major groups of

primary producers is a function of many

environmental variables, but the major

determinants are water column nutrients,

turbidity, and substrate. In areas of

high water-column nutrients, phytoplankton

and microalgal growth will dominate,

because these small or single-cell algae

rapidly respond to the increased nutrient

supply. Because benthic plants take up

nutrients from the sediments via their

roots, these plants are less able to

exploit increased nutrient levels in the

water column. The turbidity created by

increased algal growth, along with

suspended sediments, will cause

attenuation of the light reaching the

bottom of the water column and thus

decrease the light available to benthic

plants for photosynthesis. Thus,

increased nutrient levels_favor suspended

and epiphytic plants (both of which derive

their nutrients from the water column) at

the expense of the benthic attached forms.

Turbidity favors phytoplankton primarily

since they are capable of moving upward in

the water column to intercept the light

necessary for photosynthesis. Sediment

type is also important in determining

benthic communities. - Soft sediments favor

seagrasses and certain rhizophytic green

algae, while rocky substrates favor the

development of macroalgal communities.

While portions of the coastal region of

west Florida are still miraculously

pristine, much of the area is heavily

urbanized or otherwise disturbed. Still,

as late as 1968, Taylor and Saloman

estimated that in Boca Ciega Bay total

production, dominated by macrophytes, was

six times the annual phytoplankton

production.

4.1.1 Phytoplankton

In the coastal and estuarine waters of

west Florida, Steidinger (1973) identified

four phytoplankton assemblages:

estuarine, estuarine-coastal, coastal-open

Gulf of Mexico and open gulf. Within

these areas, diatoms generally dominate

the estuarine and inshore regions, while

dinoflagellates are more diverse and

abundant in the open gulf and in

gulf-influenced areas. The predominant

organisms are ubiquitous, cosmopolitan

species that are coastal residents, but

occasional secondary abundance peaks are

attributed to sporadic visitor species.

Standing crop and productivity are higher

in areas of terrestrial runoff or river

mouths, and are lowest offshore in the

open gulf, except in areas where

divergence or upwelling make more

nutrients available (Steidinger 1972,

1973).

The phytoplankton of Tampa Bay are

typically dominated by nannoplankton (less

than 20 pm), except for periodic blooms of

blue-green algae (Schizothrix)

dinoflagellates (Gonyaulax, Gymnodiniik

nelsonii and others). The dominant

species in the bay is the diatom Skeletonema costatum. The red-tide organism

Ptychodiscus brevis (= Gymnodinium breve),

a toxic coastal species. has invaded the

bay 12 times between 1946 and 1982, dominating once for over three months

(Steidinger and Gardiner 1985).

Johansson et al. (1985) estimated that

phytoplankton in Tampa Bay accounted for

9l% of the submerged vegetative production. In deep areas of the bay

phytoplankton production was estimated at

340 8 C.m-2.yr-1; a maximum value of 620 g

C.m- .yr-l was calculated from 14C data

(Johansson et al. 1985). In Boca Ciega

Bay, Pomeroy (1960) estimated that phytoplankton, benthic microflora, and

Thalassia production were of equal importance in depths less than 2 m, which

included 75% of the bay. Phytoplankton

production dominated in deeper areas.

4.1.2 Benthic Algae

The coastal regions and estuaries of

west Florida have a diverse benthic algal

flora, occupying several different

habitats. Although once regarded as

depauperate (Taylor 1954), the flora of

the eastern gulf have been shown to be

quite diverse in numerous subsequent

studies (summarized in Earle 1972; Dawes

1974). In addition to cosmopolitan gulf

and Caribbean species, the region also has

a pronounced seasonal peak of species with

41
a discontinuous Atlantic-northern gulf Mexico: west Florida waters exhibit less

distribution (Earle 1972). Figure 17 variation in algal flora than the waters

shows the relative richness and diversity of south Florida and northern Cuba but are

of the algal flora of the region when more diverse in its algal composition than

compared to other areas of the Gulf of the northern Gulf of Mexico. Table 9

Taxonomlc Group Number of Specfes In Different Areas

Chlorophyta

Chrysophyta

Cryptophyta

Cyanophyta

Phaeophyta

Rhodophyta

Tracheophyta

Xanthophyta

A B C D E F Total

85 42 45 43 97 151

1

6 16 21 21 30 2:

41 33 23 24 52 58

120 121 86 42 171 270

6 5 4 6 6 6

1 1

174

1

31

82

349

Figure 17. Distribution and diversity of benthic marine plants in the Gulf of Mexico. Total is the actual

number of species counted in areas A-F (after Earle 1972).

42
Table 9. Macroalgae of seagrass communities of the west Florida coast.

Location

Total

Species Cyanophyceae Chlorophyceae Phaeophyceae Rhodophyceae

Anclote Anchoragea 124 18 39 17 50

Apalachee Bayb 34 13 4 17

Seven SitesC 30 11 2 17

Crystal Riverd 106 19 24 63

Southwest Coaste 148 50 28 70

Table modified from Dawes (1987), with additional material. (a) Hamm and Humm

(1976); (b) Zimmerman and Livingston (1976b); (c) Dawes (1985) Dominant species

only; (d) Steidinger and van Breedveld (1971); (e) Dawes et al. (1967). Many

stations in this survey were offshore of developed seagrass beds.

lists the total number of macroalgal taxa

from several sites in Florida and shows

the distribution by division at each area.

Because of the combination of protected

estuaries on the central and southern

portions of the Florida west coast and the

gently sloping shelf and moderate wave

climate to the north of Tampa Bay, the

west coast offers an enormous area for the

colonization of either algae or

seagrasses. The primary substrates

available for algae in the region include:

(1) rocky outcrops and hard bottom (2)

soft sediments (3) seagrass leaves and

mangrove roots and (4) the water column.

Much of the shallow region north of Tampa

Bay consists of rocky outcrops suitable

for algal attachment. Throughout the

area, oyster reefs, mangrove prop roots,

and scattered rocks or shells offer

additional algal substrate, in addition

to: human-made structures like pilings,

bridge supports, and canal walls.

The only marine and estuarine algae able

to consistently utilize sediments as

substrate are the mat-forming algae and

members of the order Caulerpales of the

division Chlorophyta, which possess

creeping rhizoids that provide an anchor

in sediments (Humm 1973; Dawes 1981).

Among the most important genera are

Halimeda, Penicillus, Caulerpa, and

Udotea, which are primary producers of

organic carbon. Halimeda and Penicillus

also deposit rigid skeletons of calcium

carbonate that become a major component of

the sediments upon the death of the plant.

These algae do not have ability to

stabilize the sediments as effectively as

the seagrasses, although they do buffer

currents to some degree, and by their

extremely rapid growth can accomodate

changes in shifting sediments.

Historically, the main utility of their

rhizoidal holdfasts was considered to be

serving as an anchor for the plant in the

substrate, but Williams (1981) has shown

that they can take in nutrients through

their rhizoids and translocate these

throughout the plant in a manner similar

to higher plants.

In many tropical and subtropical seas,

the calcareous green algae are the major

source of sediments. The different genera

produce characteristic particles, with

Halimeda tending to form sand-grain-sized

plates, while Penicillus produces

fine-grained aragonitic mud. At current

growth rates, Penicillus alone could

account for all of the fine mud behind the

Florida reef tract and one third of the

fine mud in northeastern Florida Bay

(Stockman et al. 1967). In addition, the

combination of Rhipocephalus, Udotea, and

43
Acetabularia generates at least as much

mud as Penicillus in the same locations.

In the Bight of Abaco, Bahamas, Neumann

and Land (19751 calculated that the arowth

of Peniciilus,'Rhipocephalus, and Haiimeda

has produced 1.5 to 3 times the amount of

mud and Halimeda sand now in the basin and

that in a typical Bahamian Bank lagoon,

calcareous green algae alone produce more

sediment than can be accomodated. Bach

(1979) measured the rates of organic and

inorganic production of calcareous green

algae in Card Sound, south of Miami.

Organic production was low in this lagoon,

ranging from 8.6 to 38.4 g ash-free dry

weight.m-2.yr-1, and 4.2 to 16.8 g

CaC03.m-2.yr-1 for all the species

combined.

In areas of western Florida with hard

substrate, numerous species of attached

algae are found. Amona the most common

brown algae (Phaeophyta) are Dictyota

dichotoma, Sargassum filipendula, S.

pteropleuron, and Padina vickersiae

(Zimmerman and Livingston 1976a; Dawes

1987). The diversity of the red algae

(Rhodophyta) is much greater throughout

the area. Some of the more common

attached forms include Digenia simplex,

Chondria littoralis, and several species

of Gracilaria (Dawes 1987). The red algae

are the dominant forms in the drift algae

of western Florida waters, large mats or

algae that have become detached from their

anchorages. Rather than floatinq at the

surface-like Sargassum, they tend to roll

alona on the bottom in clumas or lona

cylindrical windrows, moved along by tidal

currents or wind action. The dominant

drift alga is Laurencia, but members of

other genera, including Acanthophora,

Hypnea, Spyridea, and Gracilaria, are

common and may be locally abundant (Dawes

1987).

Although information on the distribution, standing stock, and seasonality of

macroalgae on the west coast of Florida is

beginning to accumulate, studies on productivity on these plants are still sparse.

In a study of seven seagrass communities

on the west coast of Florida, macroalgae,

both attached and drifting, comprised from

2% to 39% of the total plant standing

stock (above ground biomass) (Dawes et al.

1985; Dawes 1987). While Josselyn (1975)

estimated the production of Laurencia in

Card Sound to average about 8.1 g dry

weight.m-2.year-1, which was less than 1%

of the production of Thalassia in the

area, algal production is undoubtedly much

higher in areas where the macroalgae form

a substantial portion of the total

biomass.

The least studied components of the

algal flora continue to be the benthic

microalgae. In studies of benthic

production performed throughout the

Caribbean, Bunt et al. (1972) found the

production in Caribbean sediments to

average 8.1 mg C.m-2.h-1 (range 2.5-13.8)

using 14C uptake. By comparison, in the

Florida Keys sediment microbes fixed 0.3

to 7.4 mg C.m-2.h-1. These values were

found to be equivalent to the production

in the water column. Lewis et al. (1985a)

have suggested that within areas of excess

nutrients and eutrophication, phytoplankton and benthic microalgae increase in

abundance at the expense of seagrasses.

4.1.3 Epiphytic Algae

For many species of algae requiring a

fixed substrate for colonization and

growth (both microalgae and those reaching

relatively large size), the seagrasses

provide that substrate in a habitat that

otherwise consists of inhospitable soft

sediments. Although unifying patterns are

beginning to emerge, the study of

epiphytes has suffered from what Harlin

(1980) has described as the "bits and

pieces" approach, with most studies

consisting of either extended species

lists or suggestive but largely

observational approaches (Dawes 1987).

Literature is currently emerging that

focuses on the important role that

seagrass epiphytes play as a trophic base

in certain seagrass systems.

Humm (1964) compiled an annotated list

of 113 species of algae found epiphytic on

Thalassia in south Florida. Of these only

a few were specific to seagrasses; most

were also found on other plants or solid

substrate. Later Ballantine and Humm

(1975) reported 66 species of benthic

algae which were found to be epiphytic on

the seagrasses of the west coast of

Florida. Table ID, shows the relative

distributions of algal epiphytes of sea44
Table 10. Algal epiphytes of the seagrasses of Florida (after Dawes 1987).

Site Total Cyanophyceae Chlorophyceae Phaeophyceae Rhodophyceae

Anclote Anchoragea 66 14 13 8 31

(west coast)

Indian Riverb 41 4 10 10 17

(east coast)

All FloridaC 113 10 15 19 69

aSeasonal collections (Ballantine and Humm 1975).

bSeasonal collections (Hall and Eiseman 1981).

'Non-seasonal (Humm 1964).

grasses at several locations

Dawes (1987) further notes

in Florida.

that filamentous forms predominate as epiphytes,

constituting 73% of the epiphytes from the

Indian River and 58% of the epiphytes from

Anclote Estuary. Harlin (1980) compiled,

from 27 published works, a species list of

the microalgae, macroalgae, and animals

that have been recorded as epiphytic on

seagrasses. The algal lists are quite

comprehensive, but none of the reports

list the epiphytic invertebrates from

Northwest Florida.

Harlin (1975) listed the factors

influencing distribution and abundance of

epiphytes as:

1. Physical substrate,

2 . Access to photic zone,

3 . A free ride through moving waters,

4. Nutrient exchange with host, and

5 . Organic carbon source.

Providing a relatively stable (if

somewhat swaying) substrate seems to be

the most fundamental role played by the

seagrasses. The majority of the epiphytic

species are sessile and need a surface for

attachment. The turnover of the epiphytic

community is relatively rapid, since the

lifetime of a single leaf is quite

limited. A typical Thalassia leaf has a

lifetime of 30 to 60 days. After a leaf

emerges, there is a period of time before

epiphytic organisms appear. This may be

due to the relatively smooth surface or

the production of some antibiotic compound

by the leaf. On tropical seagrasses the

heaviest coatings of epiphytes occur only

after the leaf has been colonized by the

coraline red algae, Fosliella

Melobesia. The coral skeleton of the::

algae may form a protective barrier as

well as a suitable roughened and adherent

surface.

Expressed in terms of population interactions, the relationship between epiphyte

and seagrass host is basically that of an

ectoparasite. The relationship is beneficial to the epiphyte ectoparasite, but

detrimental to the seagrass host. While

the epiphytes enjoy the benefit of being

raised higher in the photic zone, the

shading effect of the epiphytes has been

shown to be detrimental to the seagrass

hosts (Orth and van Montfrans 1984),

decreasing photosynthesis in Zostera by

31% (Sand-Jensen 1977). In Australia,

Bulthis and Woelkling (1983) found that

shading from accumulated epiphytes reduced

by half the lifespan over which a leaf of

Heterozostera tasmanica showed positive

net photosynthesis. In areas of high

epiphyte growth, the action of epiphyte

grazers is extremely important in maintaining seagrass productivity, as well as

the longevity of the host seagrasses,

without which the system would be nonexistent (Orth and van Montfrans 1984).

Epiphyte coverage is limited not only by

the activity of grazers, but, to a certain

45
extent, by the growth habit of the seagrass plant, since individual leaves

senesce and decay at such a rate that they

provide a relatively temporary substrate.

In nutrient-poor waters, the epiphytes

can benefit from the nutrients available

to the seagrasses in the sediments;

several studies have shown that there can

be a transfer of nutrients from seagrasses

to epiphytes. The upper surfaces of the

leaves are subjected to much greater water

motion than the lower parts. One effect

of the increased water movement is to

reduce nutrient gradients produced by

biological uptake, thus increasing

availability of these nutrients to

photosynthetic organisms. In addition, a

much greater volume of water containing

particulate and dissolved nutrients is

delivered to suspension feeding animals.

Harlin (1975) described the uptake of PO4

orthophosphates translocated up the leaves

of Zostera and Phyllospadix. Epiphytic

blue-green algae have the capacity to fix

molecular nitrogen, but require phosphorus

especially in tropical waters. However,

Goering and Parker (1972) showed that

soluble nitrate fixed by epiphytes could,

in return, be utilized by seagrasses.

The standing crop and productivity of

seagrass epiphytes and their resultant

contribution to the trophic base of the

system are highly variable. In some

areas, such as immediately behind a coral

reef, there are few epiphytes and little

contribution, but in other areas,

especially those with high external

nutrient enrichment, the amount of

production is quite high. Jones (1968)

estimated that in northern Biscayne Bay,

epiphytes contributed from 25% to 33% of

the community metabolism. Penhale (1977)

found that epiphytes contributed 18% of

productivity of Zostera meadows in North

Carolina. The trophic structure of these

leaf communities can be quite complex and

important in many areas, such as the

shallow, turbid seagrass beds of the

Indian River in Florida (Fry 1984) and

parts of Redfish and Corpus Christi Bays

in Texas (Kitting et al. 1984), and will

be discussed later. Much of the epiphytic

material, both plant and animal,

ultimately becomes part of the litter and

detritus as the leaf senesces and

detaches.

4.2 INVERTEBRATES

The invertebrate fauna of seagrass beds

can at times be exceedingly rich and

difficult to characterize, except in very

broad terms, unless one is dealing with a

defined area or is willing to produce an

exhaustive, comprehensive species list

since hundreds of species can potentially

be represented within a small area. This

same fauna can be highly variable, with

dramatic changes occurring in the fauna1

composition and density within relatively

small changes of time or distance (Brook

1978).

From south to north along the western

coast of Florida, there is a change in the

invertebrate fauna of the seagrass beds

and associated habitats, beginning as a

Caribbean-West Indian fauna at the south

and emerging as a predominately temperate

fauna in the northern gulf. Collard and

D'Asaro (1973) noted that the southerly

fauna with West Indian affinities changes

to one with Carolinian affinities in the

north. They tentatively divide the faunas

at the vicinity of Cedar Key but state

that the change is gradual and that there

are no clear-cut fauna1 province

boundaries in the eastern Gulf of Mexico.

The characteristic species of seagrass

beds and associated communities from the

west coast of Florida have been described

by Collard and D'Asaro (1973) and these

associations are listed for the northern

(Carolinian) fauna (Figure 18) and for the

more southerly (West Indian) fauna (Figure

19). Some of the cosmopolitan fauna that

are found in both regions are the sea

urchin Lytechinus variegatus; the bivalves

Argopecten irradians, Modiolus modiolus,

and Cardita floridana; and the gastropods

fasciata Tegula and Bittium varium. In

the classification of Collard and D'Asaro,

the West Indian fauna coincide with the

invertebrate fauna described in detail for

the seagrass communities of south Florida

by Zieman (1982).

In Apalachee Bay, Hooks et al. (1976)

found that 6 of the 10 most abundant

"trawlable" species (=epibenthic and large

epiphytic fauna) in the area were

seagrass-associated fauna. Some of the

most common organisms found in the bay

were the caridean shrimps, especially

46
BAY AND SOUND COMMUNITIES

FORESHORE

MLtiST

TROUGH

GRASS i

Bureatella leachi (cj

BAR OFFSHORE

. .: : ‘Macoma constricta (vc) .:

” :. ” .. ‘: :‘::Diplodonta punctata (c)

Figure 18. Representative temperate (Carolinean) invertebrate communities (after Collard and D’Asaro

1973).

Palaemonetes pugio, Palaemonetes

intermedius, Periclimenes longicaudatus,

Palaemon floridanus, Tozeuma carolinense,

and HiAlso abundant ppolyte pleuracantha.

were the scallop irradians; the

hermit crab bonairensi>; Pagurus the

echinoderms Lytechinus variegatus and

Echinaster serpentarius; and the majid

crabs Libinia dubia, Metoporhaphis

calcerata. and Podochela riisei. Workina

in the same area, Dugan and Livingston

(1982) found similar species associations.

In Tampa Bay, Santos and Simon (1974)

found that the Thalassia zone supported

the laraest number of infaunal polvchaetes

of any of the sampled habitats of the bay,

although only three of the nine most

abundant species showed their highest

densities in this zone. In grassbeds

offshore from the mouth of the Econfina

River in Apalachee Bay, polychaetes made

up 35% of macrofaunal numbers, reaching

maximum densities of 2,947 polychaetes per

square meter (Stoner 1980b). The relative

abundances of epifaunal species were

directly related to macrophyte density;

however, densities of burrowing

polychaetes varied inversely with

macrophyte density. In this study

amphipods made up 47% of the macrofauna

and reached densities of 1,578 m-* (Stoner

1980b). Normally, small crustaceans such

as amphipods and isopods will be

numerically in great abundance; however,

the larger penaeid and caridean shrimp

often represent a larger biomass within

the bed. Data from Brook (1977) for

a Card Sound Thalassia grass bed shows

that amphipods and caridean shrimp

represent respectively 5.8% and 23.3% of

estimated biomass of principal taxa

collected and 12.4% and 50.3% of

crustacean biomass.

The data of Collard and D'Asaro suggest

that there is a greater proportion of

emergent organisms (those living at or

47
FORESHORE

MYST

Jardisomi guanhumi

Ocypo$e albicans

BAY AND SOUND COMMUNITIES

TROUGH BAR

Haminoea antillarum [vc)

H. elegans (c)

Argopecten irradians ic)

Cardita floridana (vc)!

Thor floridanus (c) i

Tozeuma carolinensisi(c)

Pagurus annulipes (VC)

Fasciolaria tulipa (c)

Echinaster sentus (c) /

Lytechinus variegatus’ (vc)

Mithrax spinosissimus (c)

Holothuria floridana (c)

Ophioderma brevispinum (vc)

Tegula fasciata (c) ; _

OFFSHORE

: ,,... :;.... ..: ::.‘..~::;. ‘, -:,..

.’ .:< :

. ..*.

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2. : .: :.,:.: . . . :.: :: .., ::.:, . . . . I : . . . . . .

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‘..‘...’ “.:;.‘,,.‘,‘.. . . . . ‘.‘.....,‘.... “,:‘,..,.,. ‘..‘., . . . .,’ . ..’ i,:: :,. :, Codakia orbiculata (c) :,‘..’ . :’ .:’ :’:, ,: ,..., ‘..

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,_::.: : . .,. .

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. . .‘.‘I. ‘., ,.

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._~_~~~~__~~“~~Chhh~~ Modulus modulus (c)~A*-hhhhhhhh/ i

,l_lrl IlllALlA.IY \.-, Cerithium muscarum (c)

._~__ _________

-.::_;; ::?td

i Ophiolephis elegans (vc) C. Boridanum (C)

i Nmnmnne rc=x~nn Irl

i Limulus poly,,hpi,,c (,.\

Bittium varium (vc) i

Figure 19. Representative tropical (West Indian) invertebrate communities (after Collard and D’Asaro 1973).

above the sediment surface) than infaunal

organisms (those living in the sediment)

in the seagrass beds of the southern part

of the west Florida coast, changing to a

lesser proportion of dominant emergent

forms in the north. In addition, they

suggest that there are more abundant

fauna, both emergent and infaunal, in the

surrounding sand and muddy areas in the

areas of the Carolinian fauna1 provinces

than in the West Indian provinces.

4.3 FISHES

Seagrass meadows are often populated by

diverse and abundant fish faunas. The

seagrasses and their attendant epiphytic

and benthic fauna and flora provide

shelter and food to the fishes in several

ways. The grass canopy provides shelter

for juvenile fishes and for small

permanent residents. These also can feed

on the abundant invertebrate fauna of the

seagrass meadows, on the microalgae, on

the living seagrasses themselves, or on

seagrass detritus. In addition, because

of the abundance of smaller fishes and

large invertebrate predators, such as blue

crabs and penaeid shrimps, larger fishes

in pursuit of prey organisms transit the

meadows, using them as feeding grounds.

Numerous surveys have documented the fish

faunas of a variety of areas along the

west coast of Florida. These have most

recently been reviewed and synthesized by

Comp (1985).

Fishes that are permanent residents in

the seagrass beds are typically small,

less mobile, more cryptic species that

spend their entire lives there. These

species are normally of little or no

direct commercial value but are often

48
characteristic organisms of the seagrass

habitat and may be highly important as

forage for larger fishes, including those

of commercial and sportfishing importance.

The families and species comprising this

category for seagrass meadows on the

Florida west coast are nearly identical to

those in south Florida (Zieman 1982).

Members of families Syngnathidae,

Gobiidae, and Clinidae are characteristic

of this group. Pipefishes and seahorses,

including Syngnathus scovelli S.

floridae, Micrognathus cr;niger,

Hippocampus zosterae and H. erectus,

abound in the western Florlrda seagrass

meadows. The gobies and clinids show

strong affinities with the south Florida

species, and are represented commonly by

Gobiosoma robustum, Microgobius gulosus,

and Paraclinus fasciatus. Also

characteristic of the more cryptic

grassbed fauna are the predators that-iurk

within the beds or at their edge waiting

for mobile prey. Representative of these

are the toadfish, Opsanus beta, the

batfish Ogcocephalus radiatus, and the

lizardfish, Synodus foetens (Mountain

1972; Springer and Woodburn 1960). The

most common stinqray in the northeast

inshore gulf is Dasyatis sabina (Mountain

1972).

A group of resident fishes that are

rarely caught with conventional methods

are the eels. In St. Croix seagrass beds,

Robblee and Zieman (1984) were able to

obtain repeatable quantitative samples

using an encircling net and rotenone.

Capitalizing on a "natural experiment,"

Springer and Woodburn (1960) observed

large numbers of the ophicthid eel,

Ophichthus gomesi, following a severe red

tide. Mountain (1972) noted that off

Crystal River the most common eel in trawl

samples was the blackedge moray,

Gymnothorax nigromarginatus, a common

nocturnal forager in seagrass beds.

Seasonal resident fishes in the

grassbeds are those which spend their

juvenile or sub-adult stages or their

spawning season there. These are abundant

fishes that are usually highly visible and

are characteristic of grassbed fauna.

They include the Sciaenidae, Sparidae,

Pomadasyidae, Lutjanidae, and Gerreidae.

Some of these species are also found in

residence throughout the year.

Comp (1985) found two main spawning

times in Tampa Bay. The larger one occurs

in the spring and early summer, which

enables the juvenile fishes to take

advantage of the high summer primary

production. The second, smaller spawning

occurs in the late summer and early fall

months (Comp 1985).

The most abundant fishes in the seagrass

beds of Apalachee Bay are listed in Table

11. The most abundant is the pinfish,

rhomboides, Lagodon which numerically can

often exceed all other fishes combined in

abundance (Ryan and Livingston 1980). The

pinfish was also observed to be one of the

most common fishes in Tampa Bay (Springer

and Woodburn 1960; Comp 1985) and the

seagrass beds off Crystal River (Mountain

1972). McNulty et al. (1974) found the

pinfish to be the most common fish in a

composite list from five estuarine areas

from St. Marks to Chokoloskee. The

most common, the sciaenids, were

Leiostomus xanthurus, the spot, and

Bairdiella chrysoura, the silver perch.

In general, the fishes abundant in the

seagrass beds of the Florida west coast

are similar to those of south Florida,

especially the fauna found in the seagrass

beds of Florida Bay (Zieman 1982). Table

12 gives a comparison of the relative

Table 11. Most abundant fish of Apalachee Bay (after

Livingston 1984a).

Species Common name

rhomboides Lagodon

Leiostomus xanthurus

Bairdiella chrysura

Monacanthus ciliatus

Diplodus holbrooki

Sygnathus floridae

Orthopristis chrysop

Eucinostomous gula

Centropomus melana

tera

Pinfish

spot

Silver perch

Fringed filefish

Spottail pinfish

Disky pipefish

Pigfish

Silver jenny

Gulf black sea

bass

Monacanthus hispidus Planehead

filefish

Eucinostomus argentius Spotfin mojarra

Paraclinus fasciatus Banded blenny

Sygnathus scovelli Gulf pipefish

Anchoa mitchelli Bay anchovy

49
Table 12. Relative abundance of fish families in seagrass meadows (Pollard 1984.

State number 7 8 9 10 11 12 13 14

Region Gulf of Mexico - Florida area Caribbean

Locality N.W. Florida Texas N.W. Florida C.W. Florida S.W. Florida Texas S.E. Florid Panama

Latitude 29'N 28'N 30°N 28'N 26'N 28'N 26ON 9ON

Main seagrass genus

Reference

Halodule Thalassia

Carr and Hellier Livingston Springer and Weinstein Hoese Springer Weinstein

Adams (1962) (1975) Woodburn and Heck and and and Heck

(1973) (1960) (1979) Jones McErlean (1979)

(1963) (1962)

Fish Family Rank

Syngnathidae 1

Gobiidae 2

Monacanthidae 3

Sparidae 4

Labridae 5

Gerreidae 6

Scorpaenidae 7

Sciaenidae 8

Tetraodontidae 9

Blenniidae 10

Clupeidae 11

Ambassidae 12

Apogonidae 13

Engraulidae 14

Bothidae 15

Mugilidae 16

Teraponidae 17

Cyprinodontidae 18

Muliidae 19

Haemulidae 20

Clinidae 21

Centracanthidae 22

Searidae 23

Serranidae 24

Diodontidae 25

Gasterosteidae 26

Lutjanidae 27

+

14 +

-_ __

1 +

__ -_

6 +

2 +

13 +

9

__

8 +

__ _-

5 +

__ +

__ +

__ +

3 +

__ __

__ __

__ _-

-_ __

4 2

8 4

3 39

1 5

-_ __

7 9

30 -_

2 1

15 16

12 14

25 7

_- __

30 __

19 6

16 24

30 8

__ __

25 3

__ __

6 24

10 __

_- _-

_- __

5 __

11 24

_- _-

22 16

(Continued)

4

14

8

5

__

3

1

11

19

-_

__

22

14

__

-_

2

__

13

7

9

-_

6

+

+

__

+

_-

+

__

+

_-

-_

_-

__

-_

+

+

+

_-

+

_-

+

_-

__

__

_-

-_

_-

_-

7

15

9

:;

2

21

37

19

__

11

_-

1

10

25

5

37

4

12

_-

6

37

26

8

15

10

4

13

14

3

8

17

5

31

18

-_

22

26

16

__

-_

11

6

31

-_

2

7

12

-_

1
m ..

.-- __. - _- _^ _

Table 12. (Continued).

State number 7 8 9 10 11 12 13

Region

14

Gulf of Mexico - Florida area

Locality

Caribbean

Latitude

N.W. Florida Texas N.W. Florida C.W. Florida S.W. Florida Texas S.E. Florida Panama

29'N 28'N 30°N 28ON 26ON 28'N 26'N 9='N

Main seagrass genus Halodule Thalassia

Reference Carr and Hellier Livingston Springer and Weinstein Hoese Springer Weinstein -

Adams (1962) (1975) Woodburn and Heck and and and Heck

(1973) (1960) (1979) Jones McErlean (1979)

(1963) (1962)

Fish Family Rank

Odacidae 28

Kyphosadae 29

Eleotridae 30

Congiopodidae 31

Belonidae 32

Batrachoididae 33

Cottidae 34

I? Atherinidae 35

Sillaginidae 36

Arripidae 37

Aulorhynchidae 38

Carangidae 39

Platycephalidae 40

Solcidae 41

Plotosidae 42

Anguillidae 43

Gobiesocidae 44

Hemiramphidae 45

Callionymidae 46

Lethrinidae 47

Pomacentridae 48

Siganidae 49

Gadidae 50

Scorpididae 51

Cynoglossidae 52

Pleuronectidae 53

Acanthuridae 54

Muraenidae 55

__ __

-_ __

__ __

-_ -_

__

__

__

+

+

__

+

__ __ __

__

14

24

__

3

__

11 + __ 19

9 24 10 __ __

__ __

7 + 40 __ 11 __

__ __

__ __

__ -_

__

__ -_ __

12 30 22

__

41

__

__

22

33

41

__

41

__

36

4 __ 22 10

__ __

17

__

15 __ 24

__

20 10

__

__

__ __

-_ -_

__ __

_- -_ _- __

__ __ 24

__ 24

__

__

__

10 + -_

__

__

__

__ __

__ __

__ -_

__ __

__ -_

__ __

__ __

-_ __

_- -_

__ __

__ __

__ __

__ __

36

14 24 __

__

31

__

20

__

20 24 36

__

20

34

__ __

__ __

__ 12

__

-_

__

(Continued)
Table 12. (Concluded).

State number 7 8 9 10 11

Region

12 13 14

Gulf of Mexico - Florida area

Locality

Caribbean

Latitude

N.W. Florida Texas N.W. Florida C.W. Florida S.W. Florida Texas S.E. Florida Panama

29'N 28'N 30°N 28'N 26ON 28'N 26ON 9'N

Main seagrass genus Halodule Thalassia

Reference Carr and Hellier Livingston Springer and Weinstein

Adams (1962) (1975)

Hoese Springer Weinstein

Woodburn and Heck and and

(1973)

and Heck

(1960) (1979) Jones McErlean (1979)

(1963) (1962)

Fish Family Rank

Chaetodontidae 56 -- __ __ -_ __ __ __

Aulostomidae

9

57 -- __ -_ -- -_ __ __ 31

No. fish species

No. fish families

Other seagrass

genera present

21 31 57 93 49 19 106 106

15 20 36 47 25 13 48 45

Ruppia Ruppia Syringodium Halodule ? Halodule Halodule

Syringodium

Syringodium

VI

N

Depth range (m) 1 1 2 ? ? 1 2 1 2

Main ~011. method Seine net Drop Otter trawl Various Otter trawl Drop net Seine net Otter

net trawl

"+"indicates presence.

"--"indicates none found.
abundance of fish families in seagrass

meadows in the region.

In addition to the fishes readily caught

in trawl surveys, there are numerous

seasonal residents and a few permanent

residents, that are highly mobile and are

quite abundant, but are not easily sampled

with this gear. Such fishes include the

Atlantic spadefish, Chaetodipterus faber;

the sheepshead, Archosargus

probatocephalus; the red drum, Sciaenops

ocellatus; and the mullets Mugil cephalus,

M. trichodon. and M. curema (Sorinaer and

Roodburn 196b; Mo&ain72): M&y of

the fishes in this category are those with

significant commercial or sportfisheries

importance (Thayer et al. 1978a).

Notable by their absence in northwest

Florida grassbeds are the large numbers of

juvenile snappers and grunts that use the

seagrass meadows of south Florida as

nurseries, move to the offshore reefs as

adults, and commonly return to the

seagrass beds at night to feed (Starck and

Schroder 1970). The white grunt Haemulon

plumieri seems to be the only lutjanid

found through out the region and the gray

snapper, Lutjanus griseus has the widest

distribution of the serranids (Springer

and Woodburn 1960; Mountain 1972; Ryan and

Livingston 1980). The spotted sea trout,

Cynoscion nebulosus, is a major gamefish

during much of the year over seagrass

beds, often found following large schools

of foraging mullet.

The large roaming predators, or

'occasional migrants" a

classification scheme of Kikuck: (196EFe

are not normally present, visiting thi

grass beds to forage only infrequently and

(if You are sportsfisherman)

unpredictably. On the" Florida west coast

two of the most sought afte;

representatives of this qroup are the

tarpon, Megalops atlanticus, and the king

mackerel, Scomberomorus cavalla. Such

transient predatory species represent only

a small proportion of the biomass present

but may be quite important in determining

fish community structure.

4.4 REPTILES

The only reptiles that are commonly

associated with seagrass meadows are the

sea turtles, of which there are several in

the eastern Gulf of Mexico. The only

herbivorous sea turtle is the green sea

turtle, Chelonia mydas. Throughout its

range, the primary food of the green

turtles is sea grasses and the preferred

food is Thalassia (hence its common name,

turtle grass). Although not a seagrass

feeder, the Atlantic ridley, Lepidochelys

kempi, is often caught in commercial nets

set for green turtles in seagrass areas on

the upper Florida west coast (Carr and

Caldwell 1956).

In pre-Columbian times, green turtles

were abundant throughout the Gulf and

Caribbean, but from very early on were

hunted extensively for their succulent

meat and calipee (fat), the ingredient

that gives turtle soup its unique and

delicious flavor. Concern over the

reduced populations of green turtles dates

back to the previous century (Munroe

1896). Although limited nesting occurs on

the small beaches of south Florida, the

region has almost certainly been primarily

a feeding rather than nesting site. Carr

and Caldwell (1956) noted that the green

turtle populations of Florida were

composed almost entirely of nonbreeding

juveniles. The former turtle fishery on

the Florida west coast was a seasonal one

that began in April and extended until the

first cold front of the fall. Most

scientists believed that the turtles left

the area in mass migrations in the fall,

but some local fisherman insisted that the

turtles would "bury up" in the mud bottoms

and in holes on mud flats and remain there

throughout the winter (Carr and Caldwell

1956). Although turtling was carried out

to some degree throughout the west coast

of Florida from the Florida Keys to Cape

San Blas, the greatest activity was in the

grass beds near the mouths of the

Withlacoochee and Crystal Rivers, an area

of superior turtle habitat (Carr and

Caldwell 1956).

4.5 BIRDS

Shallow seagrass meadows offer feeding

and resting areas for many species of

53
birds, but in most cases the exact

relationship between the birds and

seagrass meadows is unknown. The

embayments of the west coast of Florida

are one of the most important areas for

many bird species, which either winter in

these sheltered bays or use the areas as

resting and feeding sites during

migration. The ecology of wading birds

and their feeding behavior have been

reviewed by Kushlan (1976, 1978). Odum et

al. (1982) reviewed the avifauna of the

mangrove regions of southern Florida,

while Woolfenden and Schreiber (1973) gave

an extensive review of the birds of marine

and brackish-water habitats of the western

coast of Florida.

Table 13 lists 81 species of birds that

utilize saline habitats in the eastern

Gulf of Mexico. This information, based

on Christmas bird-count data, shows at

least one broad generalization of habitat

usage. Nearly all of the 81 species

listed occur throughout the coastal waters

of western Florida, but there is a

variation in the relative abundance, which

may be related to habitat usage. In south

Florida, with its high concentration of

shallow seagrass flats, the most abundant

birds are the wading birds that feed in

shallow water or on seagrass or mudflats,

especially the Ardeidae (herons and

egrets) and the Scolopacidae (sandpipers).

In contrast, throughout the peninsular and

panhandle bays, the most abundant groups

were the Anatidae, containing geese and

ducks; the Gaviidae, including the common

loon; and the Rallidae, including the

American coot. Unlike the wading birds,

these birds tend to rest on the open water

of the bays, commonly in rafts of dozens

to hundreds or even thousands of

individuals. Many of these species feed

in the bays, diving to capture fishes or

invertebrates or to forage for grasses,

plant tubers, or rhizomes. The most

common waterfowl is the lesser scaup,

Ay;;y;,affinia, which is most abundant in

saltwater habitats, often

occurring in flocks of over 10,000

individuals. Its primary food is benthic

invertebrates, along with some fish and

plant material (Woolfenden and Schreiber

(1973). Another common swimming bird is

the double-crested cormorant,

Phalacrocorax auritus, which pursues fish

in the water column. Cormorants may be

found wherever the water is sufficiently

deep for them to swim and clear enough for

them to spot their prey.

The groups of birds described above use

two of the dominant feeding modes of the

marine avifauna. A third group hunts by

flying some distance above the water until

prey is spotted and then plummeting from

the air to seize it. Ospreys, Pandion

haliaetus, and bald eagles, Haliaeetus

leucocephalus, feed in a similar manner by

seizing prey on the surface of the water

with their claws, while the brown pelican,

Pelicanus occidentalis, plunges from some

distance in the air to catch fishes in its

pouch. For these birds, the seagrass

meadows provide an abundant source of food

by concentrating their quarry more than

much of the surrounding habitat. Larger

birds such as these require great

quantities of food for themselves and

their young, and are dependent on the

local environment not only for protected

nesting sites, but for a healthy

forage-fish population. Woolfenden and

Shreiber (1973) stated that a juvenile

brown pelican requires approximately 120

lb of fish to fledge successfully.

4.6 MAMMALS

On the west coast of Florida, Caldwell

and Caldwell (1973) reported that 27

species of marine mammals have been

observed or reported stranded on beaches.

Ode11 (1979) reported the same number in

south Florida. Many of the sightings are

rare or of dubious value; only two marine

mammals are commonly found in the shallow

coastal waters of west Florida: the

manatee, Trichechus manatus; and the

bottlenose dolphin, Tursiops truncatus. A

third species, the spotted dolphin,

Stenella plagiodon, is common offshore,

and on occasion will venture in close

enough to be observed from shore.

Numerous sightings of a pinniped, the

California sea lion, Zalophus

californianus, were reported (Gunter

1968). however. Caldwell and Caldwell

(1973) question'that the feral sea lions

have established a breeding population.

The bottlenose dolphin is, by a

considerable margin, the most common

marine mammal in coastal Florida waters,

54
Table 13. Number of individuals per 10 party hours based on Christmas Bird Count Data, 1957-71, from 17

selected localities grouped in four regions, and for all counts combined (t = trace, less than 0.5 individuals; lines

separate the families) (from Woolfenden and Schreiber 1973).

Common name

Common Loon

Pan- Penin- Coot

Scientific name handle sula Bay Keys Totala

- -

Gavia immer 12 1 t t 3

Horned Grebe Podiceps auritus 17 1 3 2 5

Wilson Petrel Oceanites oceanicus 0 0 0 0 0

White Pelican Pelecanus erythrorhynchos t 3 142 2 25

Brown Pelican Pelecanus occidentalis t 52 37 54 39

Gannet Morus bassanus t 0 0 t t

Double-crested Cormorant Phalacrocorax auritus 40 63 98 121 71

Magnificent Frigatebird magnificens Fregata 0 1 t 6 1

Great White Heron

Great Blue Heron

Green Heron

Little Blue Heron

Reddish Egret

Common Egret

Snowy Egret

Louisiana Heron

-_

Ardea occidentalis

Ardea t-lerodias

Butori;ies - virescens

Florid;I_ -caerulea

Dichronian

Casmerc,dius albus

Leucopt zthula

Hydran;lssa tricolor

lassa rufescens

Black-crowned Night Heron Nycticorax nycticorax

Yellow-crowned Night HeronNyctanassa violacea

0

5

t

5

0

13

2

4

1

t

t

8

1

14

1;

14

7

1

4

19

26 6

13 2

54 14

2 3

129 9

132 7

40 14

7 t

3 3

12 5

10

3

19

1

32

29

13

2

3

Wood Stork Mycteria americana t 5 65 1 13

White Ibis

Roseate Spoonbill

Eudocimus albus

Ajaia ajaja

3 34 267 11 62

0 t 19 8 4

Canada Goose Branta canadensis 114

Mallard Anas platyrhynchos 26

Black Duck Anas rubripes 4

Mottled Duck Anas fulvigula 0

Gadwall Anas strepera 9

Pintail Anas acuta 28

Green-winged Teal Anas carolinensis 4

American Widgeon Mareca americana 49

Shoveler clypeata Spatula 3

Redhead Aythya americana 88

Canvasback valisineria Aythya 2

Lesser Scaup affinis Aythya 203

Common Goldeneye Bucephala clangula 9

Bufflehead Bucephala albeola 26

Ruddy Duck Oxyura jamaicensis 3

Red-breasted Merganser Mergus serrator 26

t

1

5

1

8

3

7

1

t

t

185

t

t

t

27

0

i

7

17;

81

45

44

t

17:.

0

t

43

30

0

0

0

i

t

1

1

0"

0

:

0

0

33

25

6

1

2

3

38

15

21

8

19

1

163

2

5

8

28

(Continued)

55
Table 13. (Continued).

Common name Scientific name

Pan- Penin- Coot

handle sula Bay Keys Totala

Bald Eagle Haliaeetus leucocephalus t 1 2 1 1

Osprey Pandion haliaetus t 1 7 5 2

Clapper Rail

Sora

American Coot

1 t 111

15: 32 t 24: t 3 8;

American Oystercatcher Haematopus palliatus t

Semipalmated Plover

Piping Plover

Snowy Plover

Wilson Plover

Black-bellied Plover

Ruddy Turnstone

Willet

Greater Yellowlegs

Lesser Yellowlegs

White-rumped Sandpiper

Least Sandpiper

Dunlin

Short-billed Dowitcher

Semipalmated Sandpiper

Western Sandpiper

Marbled Godwit

Sanderling

semipalmatus

melodus

alexandrinus

wilsonia

squatarola

Arenaria interpres 2

Catoptrophorus semipalmatus 11

Totanus melanoleucus 1

Totanus flavipes

Erolia fusiocollis :

Erolia minutilla 2

Erolia alpina 59

8 6 24

11 45 6 1:

1 8 5 3

26 1 4 13

0 0 0

6 115 35 2:

49 211 37 76

11 54 134 33

18 153 54 43

6 62 21 59

1 7 t 2

26 1 12 17

5

12

1

1

10

7 10 19 8

1

1

4

13

American Avocet Recurvirostra americana t t

Black-necked Stilt

8 tl

Himantopus mexicanus 0 t t t t

Parasitic Jaeger Stercorarius parasiticus t 0 t t t

Herring Gull Larus argentatus 39 35

Ring-billed Gull

3 15 28

Larus delawarensis 76 316 38 74 183

Laughing Gull Larus atricilla 15 104 92 132 86

Bonaparte Gull Larus Philadelphia 19 1

Gull-billed Tern

t 15

Gelochelidon nilotica t 1 1

Forster Tern

t

Sterna forsteri 10 8 5

Roseate Tern

; 8

Sterna dougallii 0 t 1t

Sooty Tern Sterna fuscasa 0 0

Least Tern

0" t 0

Sterna albifrons t t 0 0

Royal Tern Thalasseus maximus 3 29

Sandwich Tern

12 56 2:

Thalasseus sandvicensis t 5 14 3

Caspian Tern

Black Tern

Hydroprongne caspia 1 7 2 2

Brown Noddy Anous Chlidonias niger 0" 0 0 0 0

stolidus 0 0 0 0 0

(Continued)

56
Table 13. (Concluded).

Pan- Penin- Coot

Common name Scientific name handle sula Bay Keys Totala

Black Skimmer Rynchops nigra 3 41 161 28 50

Mangrove Cuckoo Coccyzus minor 0 t t t t

Seaside Sparrow Ammospiza maritima 2 t t 0 t

aTotal represents the average of all birds

although accurate censuses of their

abundance and distribution are rare. In

the Everglades Park region of south

Florida, Ode11 (1976) found that 36% of

the animals seen were in open Gulf of

Mexico waters, 33% were in Whitewater Bay,

20% were in inland waters and 11% were

seen in Florida Bay. The relatively low

numbers in Florida Bay were presumed to be

due to extremely shallow waters which

would inhibit the movement of this large

mammal. In a later survey, Irvine et al.

(1982) found 700 individuals in 146 herds

in the Gulf of Mexico, 491 individuals in

185 herds in bays, and 192 individuals in

100 herds in marsh and river habitats of

western peninsular Florida. Bottlenose

dolphin are opportunistic feeders,

subsisting primarily on fish, squid, and

benthic invertebrates (Caldwell and

Caldwell 1973). Their diets are not well

known, but they are frequently observed

pursuing schools of mullet.

The Caribbean manatee or sea cow,

Trichechus manatus, is primarily tropical

in distribution, but its range formerly

extended across the Gulf of Mexico. On the

west coast of Florida, it is found in the

shallow coastal seagrass meadows or in the

coastal rivers. Although its numbers have

greatly declined (in recent years) causing

it to be placed on the Federal Endangered

Species List, recent large increases in

populations along the southern Big Bend

coast of Florida have been reported

(Powell and Rathbun 1984). This coastline

provides abundant summer feeding grounds

counted in all areas combined.

in the coastal grassbeds and winter

shelter in the spring-fed rivers of the

region, notably the Crystal and Homosassa

Rivers, which during the winter are warmer

than the coastal waters (Powell and

Rathbun 1984). Recently heated effluents

of large power plants, especially nuclear

plants with their lower thermal efficiency

and greatly increased heat output, have

provided additional refuges.

Normally, manatees forage singly, or

with a mother and calf pair, in the

shallow estuarine grassbeds during the

warmer months. The major summer feeding

grounds are the estuaries and offshore

grass beds of the Crystal, Homosassa,

Suwanee, Withlacoochee, and Chasshowitzka

rivers (Powell and Rathbun 1984). Hartman

(1969) reported that they spend a quarter

of each day feeding, and will consume at

least 10% of their body weight a day in

vegetation, a significant amount of

seagrass considering adults weigh up to

500 kg.

A survey of western peninsular Florida

counted a total of 554 manatees, with the

highest percentage sighted in the shallow,

brackish waters of Collier and Monroe

counties in extreme south and southwest

Florida (Irvine et al. 1982). In an

earlier study of the Everglades and the

south Florida region, Ode11 (1976) found a

total of 302 herds with 772 individuals;

46% were sighted within Whitewater Bay,

20% in the Gulf of Mexico, 23% in inland

waters, and only I% in Florida Bay.

57
CHAPTER 5. STRUCTURAL AND FUNCTIONAL RELATIONSHIPS IN SEAGRASS SYSTEMS

The importance of seagrasses to the

productivity of shallow coastal waters is

well-recognized: they provide shelter and

serve as nursery and feeding grounds for

diverse assemblages of organisms. The

variety observed in community structure in

seagrass beds has stimulated efforts to

identify the functional

within the beds,

relationships

and thus provide a

framework for understanding the

interactions and pathways common to these

systems.

5.1 THE RELATIONSHIP OF STRUCTURE,

SHELTER, AND PREDATION

Seagrasses, with leaf canopies extending

into the water column and rhizome systems

penetrating the sediment, present a

structurally complex habitat where calm

water, a stable substrate, and an

abundance of detrital and microalgal food

support dense populations of motile and

sessile organisms. The increased

abundance of infaunal and epifaunal

organisms which find shelter and

protection from predation within the

grassbeds promotes, in turn, the value of

seagrass habitats as feeding grounds for

the predators.

While the fauna1 richness of seagrass

beds was recognized in early studies, more

recent works have begun to identify

specifically the interactions among

component plant and animal species and to

define their functional relationships.

5.1.1 Fauna1 Abundance and Structure

Early ecological surveys of Florida

coastal waters included observations of

increased densities of fishes and

invertebrates within seagrass beds

compared to adjacent habitats. Later

studies quantified these differences in

fauna1 abundance (Roessler et al. 1974;

Yokel 1975a, 1975b; Thorhaug and Roessler

1977; Weinstein et al. 1977). The concise

study of Yokel (1975b) reports the

findings of this phase of studies.

Results from trawls showed that in the

Rookery Bay Sanctuary, 3.5 times as many

fishes were captured in seaqrass as in

bare sand and shell substrates (Figure

ZO), and the standing crop of crustaceans

(estimated from trawls) was 3.9 times

larger in mixed seagrass and algal flats

than on nearby unvegetated bottoms.

The amount of literature demonstrating

the increased abundance of organisms in

seagrass communities . becoming

extensive. Table 14, from"Virnstein et

a1.(1983) summarizes much of the pertinent

literature. Numerous studies ranging in

area from Florida to Japan to Belize show

that in nearly all cases, the ratio of

m F\sh

( Invertebrates

HEAVY THIN SAND/ MUD/

SEAGRASS SEAGRASS SHELL SAND/

( Halodule a 1 Holodule 1 SHELL

Thalassiq)

Figure 20. Comparison of fauna1 abundance between

seagrass beds and adjacent habitats (after Yokel

1975a).

58
Table 14. Comparison of seagrass: sand fauna1 density ratio (G:S) with other studies. Abundances are per m2 except those listed in parentheses

(from Virnstein et al. 1983).

Area Seagrass

Sieve Abundance

Fauna1 Coll. mesh Grass Sand G:S

group gear (mm) (G) (S) ratio Source

Indian River, FL

Chesapeake Bay, VA

Tampa Bay, FL

Biscayne Bay, FL

%

Carrie Bow, BELIZE

Seto Sea, JAPAN

Chesapeake Bay, VA

Long Is. Sound, NY

Thalassia/Halodu II

II

II

11

Halodule

Zostera

Zostera

Halodule

Thalassia

Halodule

Thalassia

Thalassia

Zostera II

Zostera

Zostera

Zostera

l e M

P

Cr

De

F

M

M

M

P

P

z

Mo+P

M

Cr

De

F

F

co

co

co

co

Dr

co

co

co

co

co

co

co

co

Sl

Sl

Tr

Tr

Se

0.5 17,479 5,844 3.0 PS

0.5 6,248 3,403 1.8 PS

0.5 3,152 485 6.5 PS

0.5 215 15 14.3 PS

3.2 6.1 0.7 8.8 G (unpubl.)

1.0 7,460 2,530 2.9 (1978)

0.5 39,000 7,850 5.0 ; (1978)

i.5"

0:5

48,900 13,313 8,462 1,160 42.2 1.6 0 ss (1974) (1977)

33,485

(7i4)

4.0 ss (1974)

1.0

"iz

1.6 OW (1967)

1.0 1.0 OW (1967)

1.0 6,476 8,000 0.8

-_ (2,755)

YY ii;;;;

_ _ (2,054) (824) :*; K (1974)

__ (17,292) '(:z:; 18:7 HO (1980)

_ _ (1,090) (164) 6.7 OH (1980)

__ (337,677) (139,264) 2.4 BO (1971)

M = macrobenthos, P = polychaetes, Cr = crustaceans, De = decapods, F = fishes, MO = mollusks. Collection gear: Co

= corer, Dr = dropnet, Sl = sledge, Tr = trawl, Se = seine. References: PS = present study, G = Gilmore

(unpubl.), V = Virnstein (1978), 0 = Orth (1977), SS = Santos and Simon (1974), OW = O'Gower and Wacassey (1967),

YY = Young and Young (1982), K = Kikuchi (1974), HO = Heck and Orth (1980), OH = Orth and Heck (1980), BO = Briggs

and O'Connor (1971).
organisms from seagrasses to organisms

from sand is greatly in favor of the

seagrass organisms, with ratios of up to

42:l. However, a cautionary note must be

added: The ratios are highest in the

temperate zone stations and in turbid

subtropical areas such as Indian River.

The three lowest ratios are from Biscayne

Bay, Florida, and Belize, which represent

not only the most tropical stations, but

also those with the clearest water. It is

quite possible, as in other facets of

seagrass ecology, that there are distinct

differences in functional relationship

between temperate and tropical systems.

However, studies from the west coast of

Florida, which is a transitional area,

suggest that here the grassbeds are denser

and richer in invertebrate abundance than

the adjacent habitats (Santos and Simgn

1974; Hooks et al. 1976; Stoner 1980 ;

Stoner et al. 1983).

Stoner (1980b) found that the density of

macrofaunal organisms and the number of

species taken was directly related to the

density of macrophyte biomass. Here the

fauna1 dominance was different between the

vegetated and unvegetated stations. The

analysis of sediments showed that the

particulate size distribution did not

differ and that differences in animal

densities could more directly be

attributable to macrophyte biomass and not

sediment characteristics.

In another study, in the Indian River,

Virnstein et al. (1983) surveyed the

macrofaunal invertebrates of seagrass beds

and nearby bare sand sediments and found

that the seagrass beds supported three

times the density of invertebrates and 38%

more species compared with the adjacent

sandy sediments. The abundance of

epitaunal organisms was 13 times greater

in the seagrass beds compared with the

sand flats. In the seagrass beds 54% of

the individuals were epifaunal compared to

12% in the sand flats. Virnstein et al.

(1983) also found that the epifaunal

organisms were much more trophically

important, and consequently more heavily

preyed upon, than the infauna.

Table 15 summarizes numerous studies on

the relationship between the structural

complexity of seagrass beds and the

distribution and abundance of the

associated animal complex. Experimental

evidence suggests that grass bed

invertebrates actively select vegetated

habitat rather than bare sand, indicating

that habitat preference is an important

force contributing to observed fauna1

densities in grass beds. Selection often

appears to be based on the form or

structural characteristics of the

seagrass.

While the relative abundance of

invertebrates in seagrass is usually high

when compared to surrounding habitats, the

actual numbers are highly variable. Large

changes in abundance and even the species

encountered are frequently seen over small

changes in space (Brook 1978) and time

(Greening and Livingston 1982). When

comparing strictly infaunal organisms, a

different pattern may appear. Stoner

(1983) found that the relative abundances

of infaunal organisms in sand decreased in

the order, Halodule, Syringodium,

Thalassia, as well as from low to higher

biomass of the seagrasses.

The least-defined patterns of

distribution and abundance are available

for seagrass-associated meiofaunal

organisms. Bell et al. (1984) reviewed

seagrass meiofaunal studies and concluded

that while little comparative literature

exists that can be directly intercompared,

due to both a paucity of studies and the

large differences in sampling techniques

and sample processing, their studies

concluded that nematodes and copepods were

the most abundant taxa found in the

sediments; that nematode densities were

higher in the sediments than on seagrass

blades; and that copepod densities on

blades were equal or greater than nematode

densities in the sediments in winter and

spring.

5.1.2 Structure and Predation

With the correlation between the plants

and animal abundance established,

questions followed addressing the nature

of plant-animal interactions and how these

relationships shape community structure.

Of particular interest is the role of

plants in mediating predator-prey

interactions. There is abundant indirect

evidence that the grass carpet offers

protection from predation for the animals

60
Table 15. Summary of studies describing the influence of seagrass plant architecture on the associated animal distribution and abundance (from

Orth et al. 1984).

Feature

-

Taxa Function of seagrass

Animal species

or community patterns Reference

Zostera marina roots

and rhiromes

Z. noltii roots

andrhizomes

Halodule wrightii

leaves

Z. marina leaves

Thalassia testudinum

leaves

2

I. testudinum, H.

wrightii, Syringo-

~~

dium filiforme leaves

T. testudinum, S. fili- _

forme-leaves -

T. testudinum, S. fili- _

forme leaves -

Artificial leaves and

rhizomes

macroinvertebrates, infauna

only, >0.5 mm

macroinvertebrates, epifauna

and infauna. >0.25 mm

macroinvertebrates, both infauna and epifauna, >l.O

mm

amphipods as prey; pinfish,

Lagodon rhomboides, and

shrimp, Palaemonetes vulgaris, as predators

ampipods as prey; pinfish,

Lagodon rhomboides, as

predator

amphipods as prey; pinfish,

Lagodon rhomboides, as

predator

macroinvertebrates, infauna

and epifauna, >0.5 mm

amphipods

shrimp, Palaemonetes vulgaris and Palaemon floridan-

~,asprey,pinfish,Q-

-

don rhomboides, as

predator

roots and rhizomes protect more species and individuals in vege- Orth 1977a,b

infauna from predators tated than in bare sand areas

roots and rhizomes provide

spatial refuge from predators

diverse and dense assemblage of fauna Reise 1978

associated with vegetation. Greater

abundance of epifauna and infauna

in dense eelgrass compared to low

density eelgrass

leaves serve as protection

against predation

predation rate decreases with

increasing blade density

but not in linear function

degree of species specific selectivity function of macrophyte biomass

blade surface area best estimate of habitat complexity

biomass of benthic vegetation

independent of sediment

granulometry, exerts strong

influence on abundance,

dominance, diversity and

trophic organization of macrobenthic infauna and epifauna

blade density and plant

species composition mediate predation

protection from predation

response pattern (increase or decrease) Young and Young

depends on individual macrobenthic 1977

species

susceptibility to predators depends on

amphipod life style, i.e., infauna

or epifauna, tube builders, or

epifaunal free-living forms

amphipod consumption diverged from

that predicted by heavy macrophyte

cover; epifaunal forms preferred by

fish predator more than infaunal

forms

selection for high seagrass density,

i.e., large surface area, based on

vulnerability of amphipod to

predation by Lagodon rhomboides

abundance of epifaunal amphipods and

polychaetes directly related to

macrophyte biomass. Infaunal

amphipods inversely related to

biomass

majority of amphipod species associated with seagrasses

shrimp less vulnerable to predation in

vegetated vs nonvegetated habitats.

Competitive displacement of p. cgaris by p. floridanus made p. fie more susceptible to predation

Nelson 1979a,

1979b, 1980

Stoner 1979

Stoner 1980a

Stoner 1980b

Stoner 198Oc

Coen et al. 1981

(Continued)
Table 15. (Continued).

Feature Taxa Function of seagrass

Animal species

or community patterns Reference

Artificial leaves and

rhizomes

Z. marina roots and _

l-hizomeS

Artificial leaves and b arenaria as prey, Callirhizomes ne=idus as predator

Z. marina shoots macroinvertebrates, both infauna and epifauna, >0.5 mm

Z. marina, artificial _

leaves and rhizomes

g H. wrightii roots and

rhizomes

2. marina whole plant

I. testudinum, S. Filiforme. H. wright),

v

-_

leaves

T. testudinum shoots _

T. testudinum whole _

plant

y. wrightii leaves

shrimp, Palaemonetes pugio,

as prey, killifish, Fundulus

heteroclitus as predator

macroinvertebrate burrowers

including polychaetes, echinoderms, bivalves, and

crustaceans

shoot density affects foraging

success of predator

root-mats prevent hard bodied taxa from burrowing

more than soft bodied taxa

plant structure prevents digging activities of predator

shoot density regulates structure of developing community

two prey species, juvenile Callinectes sapidus and Mulileaves reduce predatory effi-

-lateralis as prey; adult

ciency of adult Callinectes

C. sapidus as predator

sapidus

two bivalve species, Chione

cancellata and Mercenaria

mercenaria

two bivalve species, Prototha-

-~

ca staminea and -Macoma

nasuta

amphipods as prey, Lagodon

rhomboides as predator

macroinvertebrates, both infauna and epifauna, >l.O mm

macrofauna, infauna and eipfauna, >0.5 mm

juvenile red drum, Sciaenops

ocellatus

roots and rhizomes function

as refuge from predation

and bind sediments thus

increasing sediment compaction

plant serves as protection

against siphon nipping by

fish. Fish shift feeding to

more obvious M. nasuta

- -

leaves reduce foraging efficiency of predator

standing crop does not affect

species densities

increased habitat complexity

protection from predators,

patchiness more important

than plant length and

above ground biomass

significant survival of prey only at

high vegetation densities

size distributions skewed toward small

sizes in seagrass bed

increased bivalve survival in presence

of sparse and dense artificial

vegetation

increasing diversity of fauna1 assemblage with increasing shoot density

shallow-dwelling M. lateralis _(eliminated at all densltles of seagrass

leaves. Juvenile C. sapidus protected at three dTfferent densities

of leaves

both clam species less vulnerable to

whelk predation but shallower dwelling form more susceptible than deeper dwelling form

bivalve densitities higher compared to

clean sand; reduced siphon nipping

in vegetation results in greater net

growth of p. staminea

number of amphipods consumed decreases with increasing seagrass

biomass, differences occur among

macrophyte species. Predator

efficiency function of size

similar densities in bare sand and

vegetation

greater numbers of species and greater

fauna1 densities in close proximity

to seagrass shoots

more red drum along ecotone of seagrass and bare sand than for more

homogeneously vegetated sites

Heck and Thoman

1981

Brenchley 1982

Blundon and Kennedy

1982

Homriak et al. 1982

Orth and van Montfrans 1982

Peterson 1982

Peterson and

Quammen 1982

Stoner 1982

Young and Young

1982

Lewis and Stoner

1983

Holt et al. 1983

(Continued)
Table 15. (Concluded).

8

Feature Taxa Function of seagrass

Animal species

or community patterns Reference

T. testudinum, H. _

wrightii, S. filiforme,

amphipods and tanaidaceans seagrass growth form and

biomass mediate distribuleaves, roots and tion and foraging behavior

rhizomes of important predators

1. marina and H.

wrightii leaves, roots

and rhizomes

infauna and epifauna >1.2

mm

seagrass growth mediates effects of large epibentic

consumers

1. marina whole plant Mercenaria mercenaria seagrass baffles current, results in higher particulate

food concentrations

relative abundance of crustaceans

function of seagrass species and

biomass. Significance of seagrass biomass in structuring

crustacean assemblages held

within, but not across, seagrass

species

Stoner 1983

average density of epibentt,os 52x

and of infauna 3x the level

observed on the sand flat.

Epibenthic predators reside in

grass bed by day and forage on

sand flat at night

Summerson and

Peterson 1984

growth rates of M. mercencaria

paradoxically iiigher in seagrass

beds than bare sand, but may be

consequence of more particulate

food

Peterson et al.

1984
living in it, with the dense seagrass

blades and rhizomes providing cover for

invertebrates and small fishes, while also

interfering with the feeding efficiency of

their potential predators. Heck and

Wetstone (1977) hypothesized that the

significant plant biomass, invertebrate

abundance relationships observed in

Panamanian grass beds largely resulted

from predation pressure which is mediated

by the structural complexity of the grass

carpet. Stoner (1980b) observed that

numbers of macrobenthic animals increased

noticeably in the fall with emigration of

fishes from grass beds in Apalachee Bay.

Stoner (1979) also demonstrated that the

amphipods consumed most frequently by

pinfish were epifaunal. Given the

behavioral characteristics of amphipods

and the feeding preference of pinfish, it

follows (Nelson found) that infaunal

amphipods were 1.3 times more abundant

than epifaunal tube-dwelling amphipods and

4 times more abundant than free-living

epifaunal amphipods with the seasonal

influx of pinfish, reiterating the role

predators play in controlling both

abundances and species composition within

the grass carpet (Nelson 1979a; Stoner

1979).

In laboratory experiments, Stoner (1980)

found that common epifaunal amphipods were

capable of detecting small differences in

the density of seagrass and actively

selected areas of high blade density.

When equal blade biomass of the three

common seagrasses--Thalassia testudinum,

Syringodium filiforme and Halodule

wrightii--were offered in preference

tests, Halodule was chosen. When equal

surface areas were offered, no preferences

were observed, suggesting that surface

area was the grass habitat characteristic

chosen. In later field studies, Stoner

(1983) found that amphipods and

tanaidaceans were most abundant in beds of

Thalassia or Syringodium, intermediate in

Halodule, and least abundant in bare sand,

with a superficial correlation related to

plant standing crop. However, Thalassia

and Halodule supported nearly equal

numbers when compared on a unit-biomass or

unit-surface area basis. Syringodium was

consistently higher than the other two

species on a unit-surface area basis.

The shifts in amphipod abundance

appeared to be related also to the

relative abundance of predators. In

Halodule beds where amphipod abundance was

low, the number of predatory fish was 2 to

2.5 times the abundance in beds of the

other seagrasses. In particular, Stoner

(1983) found that pinfish made up 67% of

the fish population, and was the major

amphipod consumer.

Numerous attempts have been made to

assess the role of predation on epifauna

in structuring invertebrate populations

utilizing exclosure-caging experi-mental

manipulations. Excluding fish predators

has generally resulted in increases in

species richness and density (Young et al.

1976; Orth 1977b; Young and Young 1977),

although the results can often be

confounding (Virnstein et al. 1983).

Where increases did not occur, it was

assumed that decapod predators had

increased sufficiently in numbers within

the cages, presumably due to a release

from predation by fishes, that they in

turn were capable of significantly

reducing fauna1 numbers within the grass

carpet (Young and Young 1977).

Virnstein et al. (1983) attempted to

determine the importance of small decapod

crustaceans as predators, while also

admitting that they were simultaneously

demonstrating the problems and

difficulties of caging experiments. In

both the seagrass and sand communities,

nested cages were erected with an outer

cage 2 m square with 12 mm mesh, and an

inner cage 1.4 m square with 3 mm mesh.

Both extended above the surface of the

water. It was anticipated that, with the

protection afforded by the fine mesh, the

smaller organisms in the inner cage would

increase in abundance. In fact, the

opposite occurred with the numbers of

small crustaceans and polychaetes

decreasing in the inner cages; large

crustaceans and fishes decreased in

numbers somewhat, but also increased in

size. The conclusion was that the larger

crustaceans such as Penaeus duorarum,

Palaeomonetes intermedius,

heteroclitus,

and Alpheus

and fishes such as

Bairdiella chrysura and Gobiosoma robustum

entered the cages as juveniles and grazed

heavily on the captive prey as they grew

(Virnstein et al. 1983). In turn these

64
intermediate sized organizms were released

from predation pressure from larger

carnivores. Leber (1985) alleviated such

problems associated with caging

experiments by documenting predator

species, using a smaller mesh size to

exclude them, and employing short-term

experiments. He concluded that

differential predation could account for

the strong correlation of amphipods with

macrophyte abundance, whereas microhabitat

selection was the primary factor

determining the strong relationship

between the abundance of the caridean

shrimp Latreutes and plant biomass. The

author noted that the refuge value of the

seagrass canopy depends on the

relationship of prey size to canopy

architecture, with smaller organisms

afforded more protection from predation.

The relative importance of predation

avoidance versus microhabitat selection in

determining community structure among

seagrass prey organisms should vary due to

physical and behavioral differences among

these populations (Leber 1985).

The above paragraph serves to illustrate

the complex interactions between predator

and prey populations. Surprisingly little

is still known about the interaction of

fishes with the structural complexity of

the grass canopy. Because of the

restricted size of fishes typically

inhabiting seagrass beds, Ogden and Zieman

(1977) suggested that large predators such

as barracudas, jacks, and mackerels may be

responsible for restricting permanent

residents to those small enough to hide

within the grass carpet. For fishes

larger than about 20 cm SL the grass bed

can be thought of as a two dimensional

environment; these fishes are too large to

find shelter within the grass carpet.

Mid-sized fishes (20-40 cm SL) are thought

to be excluded from the majority of the

grass beds by the larger predators

occasionally present; their activities are

limited to brief forays from the shelter

of reefs or mangrove roots. Although

these fishes are restricted to areas of

shelter by day, they may move into the

beds at night when predation is less

intense (Ogden and Zieman 1977; Ogden

1980).

Heck and Orth (1980a) have hypothesized

that both abundance and diversity of

fishes should increase with increasing

structural complexity until the feeding

efficiency of the fishes is reduced due to

interference with the grass blades or

conditions within the grass canopy become

unfavorable, at which point fish densitigs

should decline. Nelson (1979 >

demonstrated that the predatory efficiency

of the uinfish on amohipods decreased with

increasing Zostera marina blade densities.

Coen (1979) that with increasina

cover of -red algae (Digenia simplex:

Laurencia Gracilaria

othersb)dththe'TifJ;-$ for$r;;a~micie~~~

on and

Palaemonetes vulgaris was reduced. Using

artificial seaarass. Heck and Thoman

(1981) observed ieduced feeding efficiency

in the killifish, Fundulus heteroditus, on

the grass shrimp, Palaemonetes pugio, with

increasing grass density.

Attempts are being made to sift and

synthesize the information contained in

the large, and often bewildering, data

base now accumulating on the relation

between the plant and fauna1 components of

the seagrass community. In a review of

the relationships of the plant structure

on the predator-prey relationships in

seagrass communities, Orth et al. (1984)

developed the following "framework" for

the assessment of fauna1 abundance.

1. In general, epifauna are more susceptible to predation by epibenthic

predators than infauna. Among the

epifauna, tube dwellers and highly

mobile species will be less susceptible than free-living and less

mobile species. For infaunal

species, tube dwellers and burrowers

living at or below the rhizome layer

will be better protected than those

living above it. The depth at which

a prey species attains a refuge in

the sediments will be shallower in a

vegetated habitat than ’

unvegetated habitat, provid:: t$

species can burrow into or beneath

the rhizome layer.

2. The density of shoots, the patchiness of the grassbed, plant biomass, individual leaf area, leaf

morphology and the thickness, structure and proximity of the rhizome

layer to the sediment surface are

65
the key characteristics of the plant

that potentially can mitigate the

effects of predation. However, a

linear relationship between some of

these characteristics and predator

success does not appear to exist.

Instead, a threshold level of these

plant characteristics seems necessary for significant protection from

predation to occur. Because of the

variety of leaf sizes and shapes

present in the diverse seagrass

species and the different characteristics of the prey and predator

species, this threshold level is

variable.

3. Heterogeneous grass beds (bare sand

areas interspersed within the bed)

should provide more favorable foraging areas for motile fishes or

invertebrates, since motile fish or

invertebrates can forage over the

unvegetated areas while at the same

time remaining in close proximity to

their protective vegetated habitat.

Particularly important to juveniles,

seagrass beds may serve as a refuge

from which animals may forage in a

manner similar to a coral reef

(Summerson and Peterson 1984). In

addition, it is felt that, in the

manner of optimal foraging strategy,

prey organisms will "balance predation risk with resource availability

in order to maximize energy gain and

growth" (Orth et al. 1984).

4. The predator-prey relationships

discussed above can be affected by

other equally important, yet poorly

investigated, biological and physical processes that occur in these

multispecies assemblages, such as

adult-larval interactions (Woodin

1976), adult-adult competitive

interactions (Peterson 1979; Coen et

al. 1981), macrofauna-meiofaunal

relationships (S.J. Bell, pers.

comm. in Orth et al. 1984), and

migration patterns due to reproduction and/or feeding, or response to

strong physical gradients such as

day-night temperature differences

(Adams 1976a; Robertson and Howard

1978; Stoner 1980a). The behavioral, physiological, and morphological differences among all the

species that utilize the seagrass

habitat, coupled with the influence

of the plant itself and its variations in shoot density, biomass, and

leaf area, all function to determine

the structure of fauna1 communities.

5.1.3 Fauna1 Sampling: The Problems

of Gear and Technique

A major difficulty with studying this

abundant fauna is the proper quantitative

sampling of the organisms of interest. No

one set of gear or techniques samples all

segments of the community evenly, and some

methods are highly selective, which must

be taken into account when comparing

different studies that use even slightly

different sampling gear or sampling

schemes. For instance, the pink shrimp,

Penaeus duorarum, is normally buried in

the sediments by day and active at night.

Sampling schemes that utilized daytime

trawling would greatly underestimate the

abundance of this and other organisms with

similar habits.

When devices are used which yield

relatively small quantitative samples,

amphipods, isopods, gastropods, and

polychaetes are typically found to be most

abundant, (Nagle 1968; Carter et al. 1973;

Marsh 1973; Kikuchi 1974; Brook 1975,

1977, 1978; Lewis and Stoner 1981). Brook

(1975, 1977) used a water-powered suction

dredge in a Card Sound Thalassia bed and

found that amphipods represented 62.2% of

all crustaceans captured. In Apalachee

Bay, Lewis and Stoner (1981) compared the

sampling results obtained by differentsized corers (5.5 to 10.5 cm diameter) and

sieve sizes (0.5 and 1.0 mm) in a northern

Florida seagrass meadow. They found that

most organisms collected were within the

upper 5 cm of sediment, although all sizes

of corers captured similar numbers of

species and showed very similar species

accumulation curves. However, the small

corers yielded significantly greater

numbers of organisms, and many of the

species that were undersampled with the

larger corers were those that were closely

associated with the seagrass cover. This

study also investigated the relative

capture efficiency of 2 sieve sizes, and

found that the 1.0 mm mesh retained only

5l%-57% of the individuals captured on the

0.5 mm mesh. The differences were due to

66
undersampling species with a small

terminal size as well as juveniles of the

larger species.

While the previously described studies

addressed the efficiency 0:

different-sized core samplers, the

relative efficiency of corers compared

with suction samplers was examined by

Stoner et al. (1983) for vegetated and

unvegetated sites in Pensacola Bay. They

found that with similar mesh sizes for

sieving of the cores and for the filter

bag of the suction sampler (0.5 mm) both

samplers collected similar numbers of

species. The corers, however, yielded 33%

more individuals from a Haloduie bed, and

73% more individuals from a bare sand

habitat than the suction sampler when

compared on an equal-area basis.

The other major type of sampling device

used in sampling fauna in and around

seagrass beds is some form of trawl,

whether a fixed-frame or beam trawl, or a

device such as an otter trawl, which

requires a certain velocity through the

water column to maintain the trawl in the

expanded condition in which it is able to

fish. In collections in seagrass beds

where these sampling devices have been

used, decapods (including penaeid and

caridean shrimp and true crabs) and

gastropods generally dominate numerically

in invertebrate collections (Tabb and

Manning 1961; Tabb et al. 1962; Roessler

and Tabb 1974; Yokel 1975a, 1975b; Hooks

et al. 1976; Thorhaug and Roessler 1977).

Trawl sampling for organisms, especially

fishes, in the clear waters of many

seagrass beds can yield highly variable

results that greatly underestimate the

mobile fish fauna within a grassbed. When

visibility underwater is 10 to 20 meters,

it requires no great effort for highly

mobile organisms to evade the trawls that

are deployed behind small boats. Drop

nets have been used effectively in shallow

water environments, but can be difficult

to construct and are not useful in deeper

waters. For clear waters and deeper

seagrass beds, a diver-deployed encircling

net has proved highly effective and

replicable (Robblee and Zieman 1984).

Somewhat paradoxically, small and

intermediate-sized organisms, such as

amphipods and caridean shrimp often are

captured in large numbers by trawls, whose

mesh size is nearly always larger than

amphipods. The trawls are usually not

directly capturing the animals, however,

but instead are efficiently capturing the

sessile drift algae which the organisms

are utilizing for shelter.

While it is important to recognize that

some data will reflect sampling-gear

selectivity, it should not obscure the

fact that definite patterns of species

abundance exist in seagrass meadows when

compared to adjacent habitats.

5.2 GENERALTROPHICSTRUCTURE

Seagrasses and associated epiphytes

provide food for trophically higher

organisms by means of three distinct

routes: (1) direct herbivory, (2) detrital

food webs within grass beds, and (3)

exported material that is consumed in

other systems, either as macroplant

material identifiable with the naked eye,

or as detritus. Despite the fact that

seagrasses have a relatively high protein

content (see Section 2.3), they are

directly grazed by relatively few animals.

The most vexing questions surrounding

seagrass food webs continue to relate to

the relative roles of detrital and

microalgae-epiphyte grazing pathways, and

the functional processes and

intermediaries by which the detrital food

pathway supplies nutrition to consumers.

Most studies continue to show that the

primary pathway of energy and nutrient

transfer is through the detrital food web,

and in many systems it may be the only

significant food web. During the past few

years, new information has been gathered

on the relative role of the other modes of

utilization, in particular, the role of

active epiphyte grazers, a pathway that

has previously been recognized but little

studied. The picture emerging is that all

of the pathways exist, but find different

degrees of expression, depending on local

conditions and the consumers present.

While the detrital food web appears to be

the primary pathway of trophic energy

transfer, any of the others may be

quantitatively the most important at

specific sites.

67
5.2.1 Seagrass Grazers

Throughout south Florida and in the

grassbeds of the Caribbean, often large

numbers of direct consumers ingest living

seagrass leaves in significant quantities.

These include several species of sea

urchins, the queen conch, numerous fishes,

the green turtle, the Caribbean manatee,

and assorted invertebrates, especially

crustaceans and gastropods (McRoy and

Helfferich 1980; Ogden 1980; and Zieman

1982). In south Florida, grazing on

seagrasses is highest in those grassbeds

of the Florida Keys and outer margin of

Florida Bay which are in relatively close

proximity to coral reefs. Major seagrass

consumers in that area are parrotfish

(Scaridae) (Randall 1965; Ogden and Zieman

1977): surgeonfishes (Randall 1967;

Clav1 JO 1974), porgies and halfbeaks

(Randall 1967). With increasing distance

from the reef tract or patch reef, the

intensity of grazing by large parrotfish

and acanthurids decreases. The dominant

grazers become the small grassbed-dwelling

parrotfish, typified by the bucktooth

parrotfish Sparisoma radians and sea

urchins, the most abundant of which is

usually Lytechinus variegatus, although

Eucidaris * tribuloides Tripneustes

venticosus and juvenile Djadema antillarum

are also found

al.

g, seagrass beds (Moore et

1963a, 1963 ; McPherson 1964, 1968;

Randall et al. 1964; Kier and Grant 1965;

Moore and McPherson 1965; Ogden et al.

1973; Prim 1973; Greenway 1976; and

others).

Assessments of the quantitative importance of direct seagrass consumption have

appeared only recently, and for relatively

few areas. The tacit assumption is that

few organisms consume seagrasses directly,

and that herbivory has substantially

decreased with the decline of the populations of green sea turtles and manatees.

Like many assumptions of tropical and

semi-tropical ecosystems, this resulted

from too much reliance on analogy from

temperate-zone seagrass systems, and a

paucity of direct observation. When the

widespread use of scuba enabled prolonged

underwater observation, the grazing

effects of some groups of direct consumers

were instantly recognizable, namely the

paper-punch, half-moon shaped holes produced by parrotfish grazing on turtle

grass. By comparison, the ragged edge

produced by urchin grazing is not obvious,

and usually resembles a leaf that has been

physically torn, until one learns to look

carefully for the stepwise nibble marks.

The grazing effects of green turtles and

manatees are not obvious until one learns

what to look for, and are increasingly

difficult because of the rarity of the

animals and the decreased likelihood of

observing them feeding.

The green sea turtle, Chelonia mydas, is

a diurnal grazer of seagrass meadows. The

grazing behavior of the green turtles is

similar to some of the large, reef

parrotfish in the sense that they graze

the seagrass meadows and seek shelter at

night, frequently in deep holes or near

fringing reefs, surfacing at intervals to

breathe. The turtles then swim some

unknown distance to the seagrass beds to

feed. What is unique is that they return

consistently to the same spot and regraze

the previously grazed patches, maintaining

blade lengths of only a few centimeters

(Bjorndal 1980). The persistence of these

characteristic patches of neatly cropped

leaves provides indirect evidence of

turtle grazing. Thayer et al. (1982) have

calculated that an intermediate sized

Chelonia (64 kg) consumes daily about

280 g dry weight of Thalassia blades.

Turtle consumption of seagrass has been

estimated to be 2.2% of body weight per

day (Thayer et al. 1980), 1.65% (Bjorndal

1980), and 0.6% (Fenchel et al. 1979).

Turtles do not consume the entire blade

on their first graze of an area, but bite

only the lower portion and allow the

epiphytized upper portion to float away

(Bjorndal 1980; Zieman et al. 1984a).

Many researchers assumed that the epiphyte

complex at the tip of seagrass leaves was

of higher food value than the plain

seagrass leaf, but other studies have

shown that the basal portion of the green

leaves is higher in nitrogen concentration

than the epiphytized tips (Mortimsr 1976;

Bjorndal 1980; Zieman et al. 1984 ). The

nitrogen content of Thalassia leaves

decrease with age as well as with

epiphytization. The basal portion of

Thalassia leaves from St. Croix contained

1.6% to 2.0% N on a dry weight basis,

while the older brown tips of these leaves

contained 0.6% to 1.1% N, and the

68
epiphytized tips ranged from 0.5% to

1.7% N (Zieman et al. 1984a). Thus, the

current evidence indicates that the green

seagrass leaves contain more nitrogen than

either the senescent leaves or the

leaf-epiphyte complex. By successively

recropping leaves from a plot, the turtle

maintains a diet that is consistently

higher in nitrogen and lower in fiber

content than whole leaves (Bjorndal,

1980). The maximum length of grazing time

on one distinct patch is not known, but

Ogden (West Indies Lab, St. Croix, USVI,

pers. comm.) has observed patches that

have been repeatedly grazed for up to nine

months.

Manatees can weigh over 1000 kg and have

been reported to consume up to 20% of

their body weight per day in aquatic

plants. When feeding on aquatic plants,

manatees have been reported to feed

indiscriminately on available plants

(Hartman 1969). While in marine seagrass

meadows, manatees dig into the sediment

using their stiff facial bristles, then

uproot the plants and shake them free of

adhered sediment. A similar mode of

feeding has been observed in manatees

feeding in Thalassia beds by this author.

Feeding patches average from 30 by 50 cm

up to about 50 by 50 cm and usually form a

conspicuous trail in seagrass beds. The

excess sediments from the hole created by

plant removal are mounded on the side of

the holes as if the manatee had pushed

much of it to the side before attempting

to uproot the plants.

In the Caribbean and south Florida, the

amount of material grazed directly is

relatively high. It has been estimated

(Odgen 1980) that direct grazing on

seagrasses is higher in the Caribbean than

in any other marine area. In St. Croix it

has been estimated that an amount

equivalent to 5%-10% of daily production

of Thalassia is directly consumed,

primarily by Sparisoma radians and

secondarily by the urchins Diadema

antillarum and Tripneustes ventricosus and

onlv about 1% was exported. while 60% to

100% of the productio'n of Syringodium was

exoorted (Zieman et al. 1979). Thus about

70% of the daily production'of seagrasses

was available to the detrital system. In

Kingston Harbor, Jamaica, 0.3% of the

production of Thalassia was consumed by

Sparisoma radians, 48.1% was consumed by

the urchin, Lytechinus variegatus, 42.1%

was deposited on the bottom and available

to detritivores, with the remaining 9.5%

being exported from the system (Greenway

1976).

The values from St. Croix are similar to

other studies in the Caribbean and south

Florida (Zieman, unpubl. data), although

the Jamaica study may overemphasize the

quantity of seagrass material entering the

grazing food chain since urchins are not

normally found at densities of 20 urchins

per square meter as were found in Kingston

Harbor (Ogden 1980). While the overall

quantitative importance of urchin grazing

on the seagrasses of the west coast of

Florida has not been determined, several

reports indicate that, at times it can be

locally significant. A population

"explosion" of Lytechinus variegatus off

the coast of Dixie County, Florida,

resulted in densities of 636 m-2 in

aggregates of urchins, which denuded

approximately 20% of a seagrass bed (Camp

et al. 1973). In Apalachee Bay, Zimmerman

and Livingston (1976a) reported that this

urchin was observed to graze Thalassia

leaves down to substrate level, and

postulated that this was, at least in

part, responsible for low macrophyte

biomass at certain stations. Urchins were

also present at stations with low seagrass

biomass near Florida State Marine

Laboratory (R.L. Iverson, pers. comm.).

Grazing by the few remaining sea turtles

and manatees is very localized and

reduced. While the shallow seagrass

meadows of south Florida are used by few

ducks, geese, and related waterfowl, the

shallow bays and estuaries of the upper

western coast of Florida offer abundant

waterfowl for viewing of hunting, as this

area is used extensively as either a

resting stop or for wintering. Direct

grazing by these birds of the Ruppia

commonly found in low-salinity and inshore

areas of upper western Florida is a

feature of this area not seen further

south.

An important by-product of heavy grazing

on living seagrasses is an increase in the

turnover rate of the standing crop of

leaves and the increased production of

detrital particles from the fragmentation

of living seagrass blades following

69
feeding and passage through the gut

(Thayer et al. 1984a; Zieman et al.

1984a). In addition, the manner of

feeding by green turtles, urchins, and

parrotfish results in the release of often

large quantities of torn or fragmented

living seagrass and its subsequent

deposition as litter locally or after

export from the bed (Greenway 1976; Zieman

et al. 1979).

5.2.2 Epiphyte-Seagrass Complex

Many of the literally hundreds of

species of small organisms in grass beds

utilize algal epiphytes and detritus as

their food sources. Gastropods,

polychaetes, as well as amphipods,

isopods, crabs, and other crustaceans

ingest a mixture of epiphytic and benthic

algae as well as detritus (Odum and Heald

1972). As research continues, it is

becoming apparent that this represents one

of the major energy transfer pathways to

higher organisms. As one progresses from

the clear, low-nutrient waters of the

Caribbean and the Florida keys, to the

more turbid and higher nutrient waters on

the west coast of Florida, there is an

apparent increased dependence on the

epiphytic grazing pathway (Fry 1984;

Kitting et al. 1984).

In addition to those organisms which

feed mainly on the epiphytes of old

seagrass leaves, many species that ingest

primarily seagrass, such as the

parrotfish; will preferentially graze the

epiphytized portion of the seagrass blade.

As a result, seagrass epiphytes may be

quite important in the flow of energy

within the grass carpet. Many of the

small, mobile epifaunal species so

abundant in the grass bed and important as

food for fishes, feed at least in part on

epiphytes. Tozeuma carolinense, a common

caridean shrimp, feeds on epiphytic algae

attached to seagrass blades; undoubtedly

epifauna are consumed coincidentally

(Ewald 1969). Three of the four common

south Florida seagrass-dwelling amphipods

utilize seagrass epiphytes, seagrass

detritus and drift algae as food sources,

in this order of importance (Zimmerman et

al. 1979). Eoinhvtic alaae were eaten at

a high rate by' Cymadusa"compta, Gammarus

mucronatus, and Melltanitida. The algae

were also assimilated more efficiently by

70

these amphipods (48%, 43%, and 75%

respectively) than other food sources

tested, including macrophytic drift algae,

live seagrass and seagrass detritus.

Kitting (1984) has used a unique

monitoring system to show that grazing of

small invertebrates is highest while the

invertebrates are on the upper grass

blades at night and not while at the base

of the leaves among the detritus. It is

suggested that these grazers select the

rapidly growing ephemeral algae when

available, but that detritus may be

important when the algae are not available

or overgrazed. Kitting et al. (1984)

later showed that in Texas estuaries, de1

13C ratios suggested a higher assimilation

of epiphyte carbon than seagrass carbon.

Fry (1984) obtained similar results in a

study in the Indian River in Florida, but

noted that the dominant seagrass there was

Syringodium which floats- readily and

drifts from the bed with little

contribution to the local detritus. In

the Texas estuaries and the Indian River,

the turbidity is very high, and epiphytic

growth is very high compared with that in

the south Florida estuaries. Epiphytes

are thus a higher potential food source

than in clearer waters where the epiphytic

growths are relatively lower. In highly

eutrophic and turbid estuaries, epiphytic

grazers can be essential to the health of

the seagrasses. Orth and van Montfrans

(1984) have shown that in estuaries with

excessive nutrient loads, the elimination

of epiphytic grazers can cause the death

of seagrasses when epiphytes proliferate

and block incoming light on the surface of

leaves, restricting seagrass

photosynthesis.

5.2.3 Oetrital Feeding

Detritus food webs are consistently

considered to be the major pathway through

which energy flows in seagrass ecosystems.

In areas where it is present, Thalassia

generally forms the predominant fraction

of the decaying material, with Syringodium

and Halodule nearly always forming a minor

portion of the detritus. Seagrass litter

decomposes by being broken down over a

period of months by bacteria, fungi and

other organisms. In Biscayne Bay, Fenchel

(1970) found that Thalassia was the

principal detrital component present
(87.1%); other portions included: 2.1%

other seagrasses, 4.6% algae, 0.4% animal

remains, 3.3% mangrove leaves, and 2.5%

terrestrial material. The microbial

community living in the detritus consisted

mainly of bacteria, small zooflagellates,

diatoms, unicellular algae and ciliates.

These types of organisms form the major

source of nutrition for detrital feeders.

Detrital consumers ingest entire

particles, but also strip bacteria and

other organisms from the detritus. Very

frequently detrital feeders are

coprophagous, with the recently released

fecal pellet being subsequently reingested

following a time during which

recolonization and regrowth of the

microbes occurs (Fenchel 1970).

Mullet and other fishes are abundant and

important feeders on detrital particles

and benthic microalgae throughout the

entire gulf region (Odum 1970). Carr and

Adams (1973) found that detritus

consumption was of major importance in at

least one feeding stage of 15 out of 21

species of juvenile marine fishes,

including sparids, hemiramphids, blennies,

gobies, atherinids, clupeids and a

tetraodontid.

As Stoner (1979) and Livingston (1982a)

noted, it can be difficult to impossible

to define when an organism is a true

detritivore, because many detritivorous

organisms are highly omnivorous organisms,

consuming many other available substrates,

in addition to organic detritus. Most

penaeid and caridean shrimp are considered

to be omnivores, but they are highly

dependent on detritus as juveniles,

becoming more omnivorous, even

carnivorous, as adults. Penaeus OdCorarum

the pink shrimp, in addition to organi:

detritus, consumes sand, polychaetes,

nematodes, caridean shrimp, mysids,

copepods, isopods, amphipods, ostracods,

mollusks and foraminiferans (Eldred 1958;

Eldred et al. 1961). Several of the large

and conspicuous invertebrates such as the

gastropod, Strombus gigas, and the

asteroid, Oreaster reticulatus, while

primarily consuming other substrates, will

ingest seagrass litter and detritus as a

part of their food (Randall 1964;

Scheibling 1980). In the seagrass meadows

of the upper Florida coast numerous

mollusks and polychaetes have been

recorded as consuming detritus (Bloom et

al. 1972; Santos and Simon 1974; Young and

Young 1977).

5.2.4 Carnivory

Typically the infauna in seagrass beds

is not as heavily preyed upon as the

epifauna (Kikuchi 1974, 1980). The

protection from predation afforded the

infauna of grass beds by dense leaf

canopies and by the fibrous rhizome mats

of the more robust species of seagrass

like Thalassia, is great enough that few

fishes specialize on infauna when feeding

(Orth 1977). In the Indian River, Young

and Young (1977) found that epifaunal

crustaceans such as Cymadusa compta,

Melita elongata, and Erichsonella

filiformis, which were apparently heavily

preyed upon by fish predators, increased

in abundance during exclusion experiments,

while the infaunal species were not

affected. Stoner (1983) noted low

abundances and smaller sizes of epifaunal

amphipods at Halodule sites, relative to

Thalassia and Syringodium sites. By

comparison, bottom dwelling and infaunal

amphipods showed nearly uniform

distribution in both aabundance and size of

the organisms among all the seagrasses.

Stoner (1983) believed that the increase

in abundance of certain infaunal tanaids

and amphipods in Halodule beds was due to

the "thick, tough underground mat of roots

and rhizomes produced by Halodule," and

that "this underground complex may provide

a more effective refuge from invertebrate

predators than the larqe diameter rhizomes

and sparse roots o‘i Syringodium and

Thalassia." While the assumptions

described here may be valid, the

explanation does not seem consistent with

other observations. Halodule beds

characteristically have fine-grained

sediments which fishes like sea trout

(Cynoscion) readily forage, while

Thalassia beds are much more stabilized

and resistant to penetration, making

foraging by infaunal feeders much more

difficult (Zieman, 1982). Much work yet

remains in determining the controls on

abundance of infaunal organisms in

seagrass beds and surrounding areas.

71
Some organisms are quite flexible in

their response to prey abundance. The

blue crab, Callinectes sapidus, has been

observed to shift its feeding from Zostera

infauna to epibiota. Because of the

protectiveness of the rhizome layer to the

infauna, and the accessibility of the

epifauna, the impact of blue crab

predation may be greatest on epibenthic

fauna (Orth 1977b).

Many of the important top carnivores

present on the grass flats of south

Florida also inhabit the seagrass meadows

throughout the western coast of Florida.

These include the widely distributed lemon

shark (Negaprion brevirostris) and the

bonnethead shark (Sphyrna tiburo), the

tarpon (Megalops atlanticus), the

lizardfish (Synodon foetens), the coronet

fish (Fistularia tobami the barracuda

(Sphyraena barracuda), carangids, the grey

snapper (Lutjanus griesus), and the

spotted seatrout (Cynoscion nebulosus).

While some of these carnivores are

resident, such as the lizardfish and the

gray snapper, others, like the tarpon,

undergo extensive seasonal migrations.

5.2.5 Trophies and Ontogenetic

Development of Grassbed Fishes

Carr and Adams (1973), Stoner (1979),

and Livingston (1980b) have all

demonstrated ontogenetic changes in the

feeding habits of fishes inhabiting

seagrass meadows on the west coast of

Florida. Much of the work has emphasized

the life history changes in the feeding

habits of the pinfish, which is one of

the most abundant fish throughout the area

and is extremely important as a forage

fish. Although the pinfish undergoes

progressive trophic changes with

development, detritus and seagrasses are a

component of its diet at all stages

(Stoner 1979; Livingston 1980b). As an

adult, usually 75% to 90% of its diet

consists of seagrasses or detritus and

plant debris. Livingston (1982a)

investigated the trophic organization of

14 fish species over an eight year period

in the shallow grass beds of Apalachee

Bay. He divided the fishes into three

major trophic groups. The first group was

primarily planktivorous forms and included

the early life stages of anchovies, spot,

mojarras, and pinfish. These juveniles

72

feed primarily on copepods, amphipods, and

plant debris and detritus. The earliest

stages of the pinfish and spot occur in

late winter when they selectively feed on

planktonic copepods. With development,

all become more omnivorous; the spot and

the mojarras become primarily benthic

feeders. The second major grouping of

Livingston (1982a) is primarily composed

of benthic omnivores and carnivores.

Included in this group are the

intermediate stages of the pinfish, the

spotted pinfish Diplodus holbrooki, and

the monacanthids. While the monacanthids

show similar feeding habits, the two

pinfish species showed little dietary

overlap despite being both temporally and

spatially sympatric (Livingston 1982a).

With further development, the pinfish

becomes primarily an herbivore. The third

group contained the pigfish, Orthopristis

chrysoptera, the silver perch, Bairdiella

chrysura, and the pipe fish Sygnathus

floridae, which may be generalist feeders

juveniles, as but specialize on

crustaceans such as shrimp, crabs, and

amphipods as adults. While some species

showed the progressive trophic changes

with development, others such as the bay

anchovy, Anchoa mitchilli, and the banded

blenny, Panus fasciatus, showed more

persistent feeding patterns throughout

their development.

5.3 DECOMPOSITIONANDDETRITAL PROCESSING

Detrital food-web theory in marine and

aquatic ecosystems is based on the concept

that for the majority of animals that

derive all or part of their nutrition from

macrophytes, the greatest proportion of

fresh plant material is not readily usable

as a food source. For these organisms,

macrophyte organic matter becomes a food

source of nutritional value only after

undergoing decomposition to particulate

organic detritus, which is defined as dead

organic matter along with its associated

microorganisms (Heald 1969).

This section will describe only briefly

the detrital food-web concept and will

then discuss recent work that is pertinent

to the understanding of detrital food webs

in seagrass ecosystems. Numerous general

review papers exist on the subject of

detrital processing and detrital food-web
theory relating to seagrass systems; among

them are Fenchel and Jorgensen (1977), Lee

(1980), Tenore and Rice (1980), and

Nedwell (1983). Review papers directed

more specifically to seagrasses include

Fenchel (1977), Klug (1980), Robertson

(1982), and Thayer et al. (1984b). Recent

and significant work is reported in the

Proceedings of the Symposium on Detritus

Dynamics in Aquatic Ecosystems (Roman and

Tenore 1984). Much of this section has

been liberally (and literally) extracted

from two previous works (Zieman 1982,

1987).

As plant litter begins to decay, it

generally passes through three

recognizable phases (Godshalk and Wetzel

1978). The first phase is a rapid weight

loss due to leaching and autolysis of

plant compounds. This phase is generally

very rapid and the materials released are

readily utilized by a variety of

organisms. In the second phase, decay is

slower and weight reduction is due to a

combination of fragmentation and the

simultaneous degradation of the substrate

by microbial activity. At the end of this

phase, the remaining substrate is highly

refractory and of greatly lowered food

value. (Although the material may have a

relatively high caloric value, the

calories are in the form of structural

compounds which most organisms cannot

degrade enzymatically.) The third phase

of decay involves the relatively slow

decomposition and fragmentation of this

highly resistant residual material.

Depending on the source material and

environmental conditions, this degradation

process may take from several weeks to

years. Increasing resistance to

degradation is roughly in the order:

algae, seagrasses, salt marsh plants, and

mangroves. The rate of degradation is

increased by physical breakdown and

fragmentation, alternate wetting and

drying (Zieman 1975a), the action of

grazers (Fenchel 1970; Morrison and White

1980), and increased nutrients in the

medium (Fenchel and Harrison 1976).

During decomposition and detritus

formation, the size of the particulate

matter is decreased, making it available

as food for a wider variety of animals.

This size reduction may be the result of

simple physical agitation, or of grazing

by active detritivores, such as amphipods

and isopods. Reduction of particle size

increases the surface area available for

microbial colonization, thus increasing

the decomposition rate. The fine detrital

particles, whether utilized locally as

suspended or deposited organic matter or

transported by the water to distant areas,

provide food for trophically important

fauna of seagrass beds and adjacent

benthic communities, such as polychaete

worms, amphipods, isopods, ophiuroids,

certain gastropods, and mullet.

The food value of detritus has commonly

been considered a function of the nitrogen

content of the material (Odum and de la

Cruz 1967). However, considering nitrogen

content alone can overestimate the

nutritional value of the material since up

to 30% of the nitrogen can exist in

tightly bound non-protein fractions

(Harrison and Mann 1975b; Suberkropp et

al. 1976; Odum et al. 1979). As

decomposition progresses, the non-protein

nitrogen fraction can increase

proportionally to total nitrogen yielding

a food source of lower value as the result

of several processes: complexing of

proteins . the

(Suberkropp 'e?t al.

lignin fraction

1976); production of

chitin, a major cell wall compound of

fungi (Odum et al. 1979); and

decomposition of bacterial exudates (Lee

et al. 1980). However, protein (Thayer et

al. 1977) and amino acid (Zieman et al.

1984c) have been shown to increase in some

macrophytes during decomposition

presumably leading to an enriched food

source. Inhibitory compounds found in

macrophyte leaves have also been found to

decrease in older and decomposing

macrophyte leaves and litter (Harrison and

Chan 1980), which may increase their

palatability to consumers.

Bacteria, fungi, and other

microorganisms have the enzymatic capacity

that many animals lack to degrade the

increasingly refractory macrophyte organic

matter! converting a portion of it to

microbial protoplasm and mineralizing a

large fraction. Whereas nitrogen is

typically 2% to 45% dry weight of

seagrasses, microflora contain 5% to 10%

nitrogen. The microflora may use nitrogen

from the macrophyte substrate, but they

73
also have the capacity to incorporate

inorganic nitrogen from the surrounding

medium (either the sediments or the water

column) into their cells during the

decomposition process, thus enriching the

detritus with proteins and other soluble

nitrogen compounds. In addition, carbon

compounds of the microflora are much less

resistant to digestion than the fibrous

components of macrophyte litter. Thus, as

decomposition occurs there will be a

gradual mineralization of the highly

resistant fraction of the seagrass organic

matter and corresponding synthesis of

microbial biomass that contains a much

higher proportion of soluble compounds.

In addition to the refractory material

of detritus, the dissolved organic carbon

and nitrogen, released by seagrasses (DOC

and DON) during both growth and

decomposition, provide nutrition for

microbes. The DOC-DON fraction released

during growth and early decomposition

stages is readily utilized, containing

much of the soluble carbohydrate and

protein of the plants. It is quickly

assimilated by microorganisms, but is

generally available to consumers as food

in significant quantities only after the

conversion to microbial biomass. During

photosynthesis, living Thalassia leaves

were found to release 2% to 10% of

recently-fixed material (Wetzel and

Penhale 1979). Fresh-dried Thalassia and

Syringodium leaves released 13% and 20%

respectively of their organic carbon

content during leaching under sterile

conditions (Robertson et al. 1982). This

dissolved fraction was rapidly assimilated

by microbial organisms, and in 14 days the

DOC released by Thalassia and Syringodium

leaves supported 10 times more microbial

biomass per unit of carbon than did the

particulate fraction (Robertson et al.

1982).

A major tenet of detrital food-web

theory has been that microorganisms are a

necessary trophic intermediary between the

macrophyte litter and detritivorous

animals. Much evidence suggests that

these consumers derive the largest portion

of their nutritional requirements from the

microbial component of detritus (Fenchel

1970; Hargrave 1970; Tenore 1977; see also

a review in Levinton et al. 1984).

Detritivores assimilate microfloral

compounds with high efficiencies, ranging

from 50% to nearly lOO%, often with low

corresponding assimilation of detrital

plant compounds (Yingst 1976; Lopez et al.

1977; Cammen 1980). Deposit feeding

mollusks were found to remove nitrogen

from sediment particles by removal of the

microorganisms but did not measurably

reduce the total organic carbon content of

the sediments which was presumably

dominated by detrital plant carbon (Newell

1965). When the nitrogen-poor,

carbon-rich feces were incubated in

seawater, their nitrogen content increased

due to the growth of attached

microorganisms. A new cycle of ingestion

by the animals would again reduce the

nitrogen content as the fresh crop of

microorganisms was digested. By selective

grazing, amphipods and other crustaceans

ingested the microbial component on leaf

litter without ingesting the substrate

(Morrison and White 1980). However, the

grazing action of detritivores can also

have a positive feedback and enhance the

production of microbial populations on the

detrital particles. Microbial respiration

rates associated with macrophyte detritus

were stimulated bv the feedina activities

of animals, possibly as a- result

physical fragmentation of the detri

(Fenchel 1970; Foulds and Mann 1978) or

the removal of inhibitory decomposit

products (Lee 1980).

While the importance of the microb

components of detritus to detritivores

of

bu;

on

al

is

firmly established, other studies have

indicated that consumers may be capable of

assimilating the plant substrate (Foulds

and Mann 1978). In some instances, the

high abundance of particulate material

compensates for its low assimilation

efficiency (Hargrave 1976). Cammen (1980)

found that only 26% of the carbon

requirements of a population of deposit

feeding polychaetes would be met by

ingested microbial biomass, although the

microbial biomass could supply 90% of the

population's nitrogen requirements. Thus

while microbial biomass is assimilated at

high efficiencies of 50% to 100% (Yingst

1976; Lopez et al. 1977) and can supply

proteins and essential growth factors, the

large quantities of plant material that

are ingested also may be assimilated at

low efficiencies (less than 5%) to supply

carbon requirements.

74
In its broadest form, the detrital food

web still seems the most applicable to the

widest array of seagrass systems. In many

areas, undoubtedly detrital and epiphytic

food sources are used jointly, based on

the relative availability and food value

of the material.

The wide variety of information now

available permits us to re-examine the

role of seagrasses as food sources and the

manner in which that food is utilized by

consumers. Fundamental to this

re-examination is the recognition that the

initial composition of macrophyte litter

varies widely, and that this variation

affects the food value of the initial

material, the decomposition rate of the

material, and the functioning of the

microbial community (Tenore 1977, 1983;

Rice 1982). The variation in composition

is not only a function of species or type

of plant, i.e. Thalassia vs Spartina, but

also a function of the source of the

material, with Thalassia showing a wide

variation in nutritional content as a

function of the latitude in which it grew.

This variation can affect strongly the

apparent trophic role of the seagrasses in

individual seagrass beds.

Although seagrasses are marine

macrophytes, they are different in many

ways from their counterparts, salt-marsh

plants and mangroves, with which they are

frequently compared. Seagrass leaves, for

instance, are initially much higher in

nitrogen content than either salt-marsh

plants or mangrove leaves, when each

enters the system under normal conditions

(Rice 1982), and contain up to 4% total

nitrogen (Zieman et al. 1984c) and up to

25% protein (Vicente et al. 1980; Dawes

and Lawrence 1983). While the senescent

leaf tips are low in nitrogen, the bases

of recently detached leaves usually retain

a significant proportion of living green

material.

During decomposition, mangrove and

salt-marsh material increases in nitrogen

content (Odum and de la Cruz 1967; Heald

1969; Rice 1982), while seagrasses remain

relatively constant (Rice 1982), or

decrease somewhat (Zieman et al. 1984c).

Similarly, the protein and amino acid

content of mangroves rise during

decomposition but show less or no change

for seagrasses (Rice 1982; Zieman et al.

1984b).

When decomposed under similar

conditions, the stable isotope ratios of

carbon did not change for either

seagrasses or mangroves. The stable

isotope ratio of nitrogen did not change

during seagrass decomposition, but changed

markedly for mangrove (Zieman et al.

1984c). The mangrove litter also showed

much greater uptake rates of ammonium per

gram of plant litter (R.T. Zieman, unpubl.

data). From this and other parameters it

was concluded that the seagrass

decomposition primarily used the internal

nitrogen pool while the mangroves required

extensive exogenous nitrogen input by the

microbes.

In another study, Roger Zimmerman (NMFS,

Galveston, TX.; pers. comm.) found that

amphipods from seagrass and mangrove

habitats survived on seagrass detritus and

soon acquired the seagrass carbon isotope

signature. When fed on mangrove detritus,

the amphipods from the seagrass habitat

could not obtain sufficient nutrients and

died. Those naturally occurring in the

mangrove habitat survived, but never fully

acquired the mangrove isotope signature.

The conclusion of this study and that of

Zieman et al. (1984) is that detrital

consumers can obtain more nutritional

value from the seagrass substrate than

from the mangrove substrate, and that many

organisms cannot be sustained solely by

the microbial flora of refractory

substrates such as mangrove detritus.

Findlay and Tenore (1983) and Tenore et

al. (1984) found similar patterns between

the macroalga Gracilaria containing

relatively available nutritive components

and the marsh grass Spartina, a refractory

substrate similar to mangroves.

In addition to compositional differences

between seagrasses and other macrophytes

that can lead to different mechanisms of

decomposition, the plants themselves vary

widely among locales. Dawes and Lawrence

(1983) showed a shift in the protein

content of Thalassia leaves from 13% in

Tampa Bay, to 16% at Key West, to 25% in

Belize. Thus, within a single species the

mode of decomposition and the quality of

the resulting detritus, which affects both

initial and ultimate food value of the

75
material, may be quite different depending

on regional origin.

Synthesis. From the diverse studies

described above, a pattern emerges of the

relative utility of the detrital substrate

to consumers based on (1) the initial

chemical composition of the material, (2)

the time of decay, and (3) the external

environmental conditions. Mangroves and

salt-marsh plants are recalcitrant

substrates with low nitrogen content, and

require extensive microbial growth and

processing growth to become nutritionally

useful. For many organisms, macroalgae

and epiphytes are useful substrates

directly or with little microbial

addition. Seagrasses occupy a range from

the middle of the spectrum to one

overlapping with algae, depending on

region and environmental conditions. In

the tropics, they are a high-protein

source that encourages microbial

utilization of the nutrients contained in

the seagrass substrate. In more temperate

locations, they may be a lower quality

protein source and require more extensive

microbial processing to become a useful

food. In regions of high nutrient

loadings, the seagrasses may develop an

extensive epiphytic growth that may be

more productive and a less refractory food

source than the seagrasses themselves, but

this level of epiphytism is not seen in

clear, nutrient-poor waters.

76
CHAPTER 6. INTERFACES WITH OTHER SYSTEMS

6.1 SALT MARSH AND MANGROVE

In addition to the seagrass meadows, the

west coast of Florida has extensive marsh

and mangrove resources. West Florida

claims 9% of the 6 million acres of marsh

bordering the Gulf of Mexico (Linda11 and

Saloman 1977, Thayer and Ustach 1981>, but

over 85% of the mangroves bordering the

gulf (Thayer and Ustach 1981). In some

areas, these habitats form only small,

narrow fringes around the estuary, while

in other areas they extend many kilometers

inland.

Like the seagrasses of Florida Bay, a

vast quantity of the Florida marsh and

mangroves are contained within Everglades

National Park (Table 16). Moving

northward from the vicinity of Charlotte

Harbor on the lower west coast, the amount

of mangrove coverage declines with

increasing latitude until near Suwannee

Sound, north of Tampa, where mangroves are

completely replaced by coastal marshes.

Salt-marsh development is particularly

extensive from Apalachicola Bay eastward.

Here, in the Big Bend region, the marshes

extend from landward directly into the

Gulf of Mexico without any form of

protective barrier. I n addition to

marshes of smooth cordgrass, Spartina

alterniflora, the Big Bend area has

extensive marshes of black needlerush,

Juncus roemerianus.

Florida

While the typical

salt marsh shows Spartina

occupying the low marsh, and Juncus the

region landward (Figure 21), throughout

Table 16. The areas and major species of submerged vegetation, tidal

marsh, and mangrove swamps of estuarine study areas, west coast of

Florida (from McNulty et al. 1972).

Study area

Submerged Emergent vegetation

vegetation Tidal marsh Mangrove

Acres Acres Acres

Florida bay . . . . . . . . . . . . . . 256,609

Lake Ingraham . . . . . . . . . .._ 1,024

Whitewater Bay . . . . . . . . . . . 155

Cape Sable to

12,148 36,897

0 891

68,757 75,976

Lostmans River . . . . . . . . .

Lostmans River to

Mormon Key . . . . . . . . . . . . .

Mormon Key to

789

768

108,644 49,349

23,840 36,000

Caxambas Pass . . . . . . . . . . 4,319

Caxambas Pass to

52,181 92,385

Gordon River . . . . . . . . . . . 501 7,445 13,387

(Continued)

77
Table 16. (Concluded).

Study area

Submerged Emergent vegetation

vegetation Tidal marsh Mangrove

Doctors Pass to

Ester0 Pass ............

Caloosahatchee River .....

Pine Island Sound ........

Charlotte Harbor .........

Lemon Bay ................

Sarasota Bay System ......

Tampa Bay .I..:..

Hillsborough Bay

Old Tampa Bay . . .

Boca Ciega Bay . .

St. Joseph Sound

Baileys Bluff to

Saddle Key . . . .

Saddle Key to

S. Mangrove Pt

Waccassa Bay . . . .

Suwannee Sound . .

.........

.........

.........

.........

.........

.........

.........

.........

.........

Suwannee Sound to

Deadman Bay ............

Deadman Bay ..............

Deadman Bay to

St. Marks River ........

Apalachee Bay ............

St. George Sound .........

Apalachicola Bay .........

St. Joseph Bay ...........

St. Andrew Sound .........

East Bay (St. Andrew) ....

St. Andrew Bay ...........

West Bay .................

North Bay ................

Choctawatche Bay .........

Santa Rosa Sound .........

East Bay (Pensacola) .....

Escambia Bay .............

Pensacola Bay ............

Perdido Bay ..............

Total . . . . . . . .._........ 523,431 528,328 392,860

Acres Acres Acres

11 2,959 9,720

726 1,698 2,973

26,966 7,476 18,657

23,383 9,087 23,474

2,145 331 971

7,610 235 3,616

7,890 843 8,949

383 203 1,077

6,809 533 5,024

5,800 149 2,464

8,723 608 1,259

4,084 16,683 1,301

62,730 32,587 7,915

24,223 30,752 448

5,556 17,643 427

2,420 14,763 0

1,834 2,549 0

8,110 14,325 0

23,521 55,669 0

8,641 3,605 0

737 17,696 0

6,325 853 0

373 576 0

1,146 4,597 0

2,540 875 0

1,542 3,349 0

1,030 1,664 0

3,092 2,816 0

4,683 309 0

310 3,307 0

43 5,152 0

1,547 213 0

1,333 1,408 0

78
_-----

MHW (Mean high water)

Figure 21. Zonation in Florida salt marsh dominated by Spartina alterniflora and Juncos roemerianUS (from

Darovec et al. 1975).

much of the Big Bend area, Juncus will

actually form the land-sea interface

without an intermediate Spartina zone

(Carlton 1977; Stout 1984).

The importance of wetlands habitat to

the estuary has been established in a

variety of locations (Odum and Heald 1972,

1975; Thayer et al. 1978a; Thayer and

Ustach 1981; Odum et al. 1982), but the

fauna1 interactions between these habitats

and adjacent seagrass beds are poorly

understood. Thayer and Ustach (1981)

concluded that "although extensive

information exists on tidal marsh and

mangrove plant species structure and

distribution in the gulf and on commercial

species such as shrimp, quantitative

studies on the distribution and abundance

of submergent plants and on wetland fauna

and fishes are scarce."

In particular, it is not known how the

faunas of the various areas interact, nor

what role the respective habitats play in

the life histories of the organisms.

Fishes and invertebrates congregate within

the mangrove prop roots for protection and

shelter similar to the manner in which the

seagrass canopy can provide nursery

shelter. Gray snapper, Lutjanus griseus,

sheepshead, Archosargus probatocephalus,

spotted seatrout, Cynoscion nebulasus, and

the red drum. Sciaenoes ocellatus. have

been found to recruit initially in

seagrass habitat but with growth move into

the mangrove habitat for the next several

years (Heald and Odum 1970). Since both

areas serve as nursery grounds for

uncounted small organisms, both also

provide feeding grounds for larger

predators. Some of the game fish that are

found both in mangroves and seagrass beds

include the tarpon, Megalops atlanticus,

the snook, Centropomus undecimalis, the

ladyfish, Elops saurus, the crevalle jack,

Caranx hippos, the gafftopsail catfish,

Bagre marinus, and the jewfish,

Epinephelus itajara, (Heald and Odum

1970). While similar interrelationships

undoubtedly exist between certain fauna of

the seagrass beds and salt marshes, these

are not documented. figure 22, from Lewis

et al. (1985b), shows the life history of

two of the most important fishes on the

west Florida coast. For a detailed review

of the mangrove ecosystems of Florida, and

their necessity to fishery organisms, see

Odum et al. (1982) and Lewis et al.

(1985b), while Stout (1984) reviews the

irregularly flooded marshes of the

northeastern Gulf of Mexico.

6.2 GULF REEFS

One of the

structuring of

79

major influences on the

seagrass communities along
.,.;,. .,.;;,. SPOTTED SEA TROUT

Mangroves ,._.. :.:<:.:.:.:.: ‘.‘,‘,‘.‘.‘.‘.‘.‘.

* ,.......... ‘.‘,‘.‘,‘. :.:.:.:.:

* ^ ^.:;:;:,‘,‘,:,:.~,‘:

1 ^ .~:.I..

AA..

,. A . 1

Figure 22. Life histories of spotted sea trout and snook on the west Florida COaSt

(after Lewis et al. 1985b).

80
the gulf coast of Florida, when compared

with the south Florida grass beds, is the

lack of shallow coral reefs in close

proximity to the seagrasses. While not as

intensely studied, the Big Bend area has

numerous and extensive limestone outcrops

which should function in an analogous

manner. In the coral reef areas the most

prominent reef-grass bed interaction

involves nocturnally active coral reef

fishes of several families feeding over

grass beds at night. Randall (1963) noted

that grunts and snappers were so abundant

on some isolated patch reefs in the

Florida Keys that it was obvious that the

reefs could not possibly provide food or

even shelter for all of them. The major

groups that shelter on the reef by day and

forage into the seagrass beds nocturnally

are members of the Pomadasyidae,

Lutjanidae, and Holocentridae (Longley and

Hildebrand 1941; Starck and Davis 1966).

Typically, both juveniles and adults form

large heterotypic resting schools over

prominent coral heads or find shelter in

caves and crevices of the reef. At dusk

these fishes migrate (Ogden and Ehrlich

1977; MacFarland et al. 1979) into

adjacent seagrass beds and sand flats

where they feed on available invertebrates

(Randall 1967, 1968), returning to the

reef at dawn. These fishes epitomize what

Kikuchi and Peres (1977) have defined as

"temporal visitors" to the grass bed,

utilizing it as a feeding ground (Hobson

1973).

6.3 CONTINENTALSHELF

The ecology of all shallow water

communities on the west coast of Florida

is strongly influenced by the enormous

continental shelf in the region,

encompassing more than 78,000 km2. The

extremely low gradient in this region is

responsible for seagrasses being found at

what would normally be great distances

offshore. Throughout the region there are

gradual fauna1 changes that occur both on

a north-south gradient along the shore,

and along a depth gradient offshore.

Along the latitudinal gradient, the

fauna of the shallow water communities

changes from a predominantly tropical West

Indian fauna in the south to a more

warm-temperate continental fauna with

Carolinian affinities in the north (Smith

1976; Lyons 1979). This change is

primarily related to the decreasing winter

temperatures with the northward

progression.

Moving from the shoreline to the edge of

the shelf, several zones of fauna1

similarity are recognizable, controlled

largely by changes in the physical

characteristics of the water column and

the substrate. This zonation is based on

the classification developed by Lyons and

Collard (1974) and Lyons (1979). The

nearshore zone extends from the beachline

out to 10 m (Figure 23). This area is

either carpeted with seagrasses or has a

sediment of quartz sand in which the

seagrasses are not found. Salinities vary

from 31 to 34 ppt and temperatures vary

widely over the year due to the

shallowness of the water. Lyons (1979)

characterized the fauna as being a "rich,

warm-temperate fauna with obvious

relationship to the estuary."

The next zone seaward, the shallow shelf

zone, extends to approximately 30- 40 m in

depth, and while salinities are slightly

higher and more constant, in the range of

35-36 ppt, the temperatures in the green

coastal water are still seasonally

variable. Where they exist, the sediments

are calcareous, and the area also has

numerous scattered outcrops of the

limestone bedrock, which provide substrate

and shelter for many organisms, especially

shallow water tropical species (Lyons

1979). Near the outer edge of this zone,

the clear blue offshore waters are found

with nearly constant salinities and

temperatures that vary only 3 to 4 degrees

seasonally. This is the middle shelf

zone, extending down to about 140 m,

although it has been previously divided

into inner and outer subzones at 60-70 m

(Lyons and Collard 1974). The sediments

in this area are calcareous and the

limestone outcrops often extensive. The

fauna is primarily tropically derived

(Lyons 1979).

Near the junction of the shallow and

middle shelf zones southeast of Cape San

Blas lies a rich, rocky reef area known as

the Florida Middle Ground, a 1500 km2 area

with a mixture of irregular limestone

escarpments and knolls that rise as much

81
MISSISSIPPI-ALABAMA SHELF \\\,\

WESTFLORIDA SHEL~F

0.10m

IO-30m

IO-60m

Mddle she If !I

E Deep sh,lf

60 140 m

140.200m

r--J Slope 200 -2ooo+m

Figure 23. Fauna1 zonation of the west Florida shelf (after Lyons and Collard 1974).

as 10 to 15 m from the shell and sand

substrate (Smith et al. 1975). The highly

tropical fauna of the area is

characterized by corals of the genera

Porites and Oculina, and the hydrocoral

Millipora, along with other

scleractineans, alcxonarians,

actiniarians, and zoantharians (Smith et

al. 1975). In addition, benthic algae

(Cheney and Dyer 1974), invertebrate

(Austin 1970; Smith et al 1975), and fish

(Smith et al. 1975) communities have been

found to be highly tropical in

composition.

The distribution of tropical reef

organisms along the northwestern Florida

shelf is a function of the highly

irregular, shallow shelf-bottom topography

and the influence of warm water masses.

Inshore circulation is dominated by two

large gyres (Figure 24), with elements of

Florida estuarine waters in the north,

Florida Bay waters in the south, and

tropical waters from the Loop Current,

brought in from the Yucutan Channel (Chew

1955; Austin 1970), which has the

potential for transporting large numbers

of tropical larvae into the region (Smith

1976). There is also evidence for

seasonal upwelling along the outer edge of

the Middle Ground (Austin 1970), which

Smith (1976) attributes as the reason for

the large numbers of planktivorous fishes

in the region.

Throughout south Florida and in other

areas, more and more studies are showing

the interactions between the faunas of the

reefs and the seagrass meadows, as well

82
Figure 24. Eastern Gulf of Mexico current patterns

during summer (after Chew 1955 and Austin 1970).

as with mangroves and coastal marshes

(Ogden and Gladfelter 1983). Such studies

for the seagrass meadows and the offshore

reef and shelf fauna of the west Florida

coast are lacking, but the potential for

these fauna1 interactions is high (Darnell

and Soniat 1979).

6.4 EXPORT OF SEAGRASS

One potentially important interaction of

the west-coast seagrass beds and the

offshore communities is the transport of

detached seagrass leaves and particulate

material from the highly productive

inshore beds to the offshore areas. The

material exported from the seagrass

meadows can serve as both a carbon and

nitrogen source for benthic, midwater, and

surface feeding organisms at considerable

distances from the original source of its

formation (Zieman et al. 1979; Wolff

1980). In south Florida, the prevailing

winds move detached blades westward from

the shallow grass flats. This material is

carried in considerable density over the

productive Tortugas shrimping grounds and

has been observed nearly 400 km west of

the source beds (Zieman, unpubl. data).

Incze and Roman (1983) found that

particulate organic carbon, largely of

benthic macrophyte origin, accumulated in

Biscayne Bay during the calm summer months

and was then discharged following

resuspension by the cold fronts and

accompanying turbulence at the onset of

the winter season.

Other studies have shown that seagrasses

can be transported great distances from

their sources. Menzies et al. (1967)

collected Thalassia leaves and

off the coast of North Carolina

of water, although the nearest

Thalassia was 1,000 km south.

Brundage (1972) found blades of

fragments

in 3,160 m

source of

Roper and

Thalassia

and Syringodium in nearly all of 5,000

bottom ohotoaraohs taken in the Virain

Islands 'basin-at' depths averaging 3,500-m.

Wolff (1976) collected seagrasses,

primarily Thalassia, from trenches in the

Caribbean as deep as 6,740 m. Much of the

material showed bite marks of shallow

water parrotfish as well as indications of

recent consumption.

Grazing by herbivores, mortality caused

by low tides on shallow banks, and

wave-induced severing of leaves that are

becoming senescent are the primary sources

of drift material. Sporadic large

releases of material occur during major

storms, in which both living leaves and

rhizomes are uprooted (Thomas et al.

1961).

For all species of seagrasses, blades

that are fresh and healthy when detached

will float better than senescent leaves.

Because of the difference in size and

shape of Thalassia and Syringodium blades,

grazing or nibbling by most herbivores

will completely sever a Syringodium blade

and allow it to float off, while the same

bite will not sever a Thalassia blade

(Zieman et al. 1979). In addition.

Syringodium blades float better than those

of Thalassia. so that a much hiaher

proportion of' the Syringodium producgion

is transported from the source bed. In

St. Croix, 60%-100% of the daily

production of Syringodium was detached and

exported, whereas only 1% of Thalassia was

exported, primarily as bedload (Zieman et

al. 1979). In the Indian River, Fry

(1984) found that 47% of the Syringodium

production was transoorted from the

system, which, in part,' could account for

83
the absence of seagrass isotopic signature

in the consumers there. No studies as yet

exist on the export or transport of

seagrass material from the meadows of the

west Florida coast; however, because of

the demonstrated importance in other

Florida seagrass beds, it is likely that

there is a large amount of material

transported from this region. Its

destination and fate, however, remain to

be quantified.

6.5 NURSERY GROUNDS

One of the most important roles of

seagrass beds in the coastal ecosystem is

that of a nursery ground in which

postlarval stages of fishes and

invertebrates concentrate and develop. In

addition, important species, such as the

spotted seatrout, Cynoscion nebulosus,

spawn in, or just adjacent to, seagrass

beds (Tabb 1966a,b; Lassuy 1983).

Seagrass habitats offer high productivity,

surface areas, and blade densities, as

well as a rich and varied fauna and flora.

Seagrass provides abundant nursery habitat

and, based on abundance and size data,

many important species prefer it over

available alternatives in the estuaries

and coastal lagoons (Yokel 1975a). In

Apalachicola Bay, Livingston (1984) noted

that numerous invertebrates and fishes

used the seagrass beds as nurseries. Most

of the penaeid shrimp and fishes found in

the beds were seasonally abundant during

early stages of their reproductive cycles

(Livingston 1984b).

Numerous species of fishes and

invertebrates have been found to use

Florida grass beds as nursery grounds. In

Tampa Bay, 23 species of finfish, crab,

and shrimp, of major importance in Gulf of

Mexico fisheries, were found as immature

forms (Sykes and Finucane 1966).

Livingston (1984) found Apalachicola Bay

to be an important nursery for numerous

invertebrates and fishes, and listed the

abundance, natural history, and

seasonality of 26 of the most important

species (Table 17 in Livingston 1984b). A

third of the species collected at

Matecumbe Key seagrass beds by Springer

and McErlean (1962), including all grunts,

snappers, filefishes, and parrot fishes,

occurred only as young, indicating the

8

nursery value of the seagrass-dominated

shoreline habitat sampled.

6.5.1 Blue Crabs

The blue crab, Callinectes sapidus, is

an abundant and important resource along

the gulf coast for both sport and

commercial fisheries, ranking as the third

largest food fishery in the Gulf of Mexico

(Perry 1975; Oesterling and Evink 1977).

Blue crabs are caught throughout Florida,

but are in lowest abundance in the Florida

Keys and reach their highest abundance in

the area between Tampa and Apalachicola

Bay (Steele 1979). Like nearly all of the

fishery resources of the gulf coast, blue

crabs are estuarine dependent throughout

much of their life.

Following spawning, the young crab

larvae drift with the currents and

metamorphose into a megalops stage. The

young crabs enter the estuary either as

megalopi or as early juveniles, using a

form of tidal migration, burying in the

sediments on the ebb tide and rising into

the water column to be transported into

the estuary on the flood tide (Williams

1971; Sulkin 1974), a mechanism first

proposed for pink shrimp larval

migrations. In the estuary they grow and

mature, using the seagrass meadows as

nurseries during their juvenile stages.

Mature crabs are found throughout the

estuary, with many continuing to forage in

the seagrass beds. When mature, the

females will move into lower salinity

waters and protected areas such as tidal

creeks, molt a final time, and breed while

still soft (Oesterling and Evink 1977).

The females cannot molt once fertilized.

After hardening and as their egg masses

develop, the females begin to migrate

offshore to higher salinity waters. The

adult males generally remain within the

estuary and continue to grow.

The typical patterns described for blue

crab spawning indicate that the females

move offshore and spawn in the general

vicinity of their source estuary.

However, tagging studies in Florida have

shown that females migrate extensive

distances, up to 500 km, to spawn in the

Apalachicola Bay region (Oesterling and

Evink 1977). Following spawning, the

planktonic larvae become entrained in eddy

4
currents related to the Loop Current and

the two inshore gyres, and are distributed

along the coast of Florida (Figure 25).

The losses with this type of reproduction

are apparent; it has been estimated that

only one millionth of the spawn reach

maturity (Van Engel 1958). The migration

of the female crabs coincides with the

flooding of the Apalachicola and adjacent

river systems, which is thought to

increase the amount of suspended

particulate detritus and aid in providing

food for the larvae and juvenile crabs

(Oesterling and Evink 1977; Livingston

1984b). Oesterling and Evink (1977) and

Livingston (1984b) correctly pointed out

that current plans by the Army Corps of

Engineers to place additional dams in the

Apalachicola drainage basin ostensibly

for flood control and navigation, could be

disastrous to this vital fishery.

Likewise, the diversion of fresh water

flow for additional development could have

similar deleterious effects.

6.5.2 Shrimp

Penaeid shrimp are an important fishery

resource in Florida, especially in the

gulf coast region. While the menhaden

fishery is the largest in the Gulf of

Mexico in terms of pounds landed, the

Figure 25. Blue crab spawning migrations and larval

transport (after Oesterling and Evink 1977).

shrimp fishery is the largest in dollar

value (Taylor et al. 1973b). The two

major shrimping grounds are the Tortugas

grounds to the north and west of the Dry

Tortugas, and the Sanibel grounds,

stretching from just north of Naples to

south of Tampa (Saloman et al. 1968). The

nurseries for this fishery are in the

seagrass beds, mangroves, and marshes of

coastal Florida (Tabb et al. 1962,

Costello and Allen 1966). The shrimp

spawn on the fishing grounds in deeper

water throughout much of the year, and the

larvae are carried back into the coastal

wetlands (Tabb et al. 1962; Munro et al.

1968). Roessler and Rehrer (1971) found

post-larval pink shrimp entering the

estuaries of Everglades National Park in

all months of the year.

Throughout Florida, the most copious

penaeid is the pink shrimp, Penaeus

duorarum. South of Tampa, individuals of

the brown shrimp, Penaeus aztecus, and the

Caribbean white shrimp, Penaeus

brasieliensis, are found intermixed with

the pink shrimp, but are usually not

abundant (Saloman et al. 1968). North of

Tampa: the pink shrimp is the most

plentiful, being the seventh to ninth most

abundant invertebrate in Apalachee Bay,

while individuals of the white shrimp,

Penaeus setiferus, occupy the same habitat

but are not numerous in this area (Hooks

et al. 1976; Dugan and Livingston 1982).

Moving westward from Florida, the pink

shrimp catch decreases and the brown and

white shrimp catches increase greatly.

Studies throughout south-west Florida

estuaries in Rookery Bay, Marco Island,

and Fakahatchee Bay have shown that the

shrimp were most abundant at stations with

seagrass-covered bottoms, and within these

stations, where benthic vegetation was

dense (Yokel 1975a, 1975b). Post-larval

shrimp with carapace lengths less than 3

mm were taken only at stations where

Halodule and Thalassia were present in

Rookery Bay Sanctuary, while stations

without grass always had larger mean

sizes. The smallest shrimp are

continuously within the seagrass bed. As

they increase in size and become too large

to burrow between the seagrass short

shoots, they tunnel by day in adjacent

sand flats and forage in the grass bed at

night. As they near maturity, they

a5
migrate to the deeper waters offshore,

usually at the onset of the first major

cold front passage of the season

(Hildebrand 1955, Williams 1965). Recent

studies using stable isotope tracers have

shown populations from two contiguous

bodies of water, Rookery Bay and Johnson

Bay, to have distinct isotopic signatures

which take weeks to months to acquire.

This indicates that the populations

are staying within their embayment, and

are not moving freely throughout the

habitat of the region (Zieman et al.

1984c).

6.5.3 Fish

Like those in south Florida (Zieman

1982), the seagrass beds of the west

Florida coast are important nursery

grounds tor numerous species of commercial

and sportfish, and for small forage

species that serve as food for larger

carnivores. While the composition of the

grassbeds of the Florida Keys and portions

of Florida Bay are distinct because of the

influence of reef-related juveniles, the

fauna from northwestern Florida Bay is

highly similar to all the inshore regions

of the west coast to Apalachicola Bay,

both in terms of the important families

and the numerically most abundant species.

The major families containing predators

that are associated with seagrass beds at

some stage in their life cycle are the

Sparidae, Sciaenidae, Pomadasyidae,

Sygnathidae, Balistidae, and Serranidae

(Joseph and Yerger 1956; Springer and

Woodburn 1960; Tabb and Manning 1961; Wang

and Raney 1971; Mountain 1972; Yokel

1975a; Livingston 1984a).

In virtually every survey of fish fauna

of the west coast of Florida, the pinfish

was the most abundant fish collected, and

nearly all abundant

i:roughout the year.c?~e~ook~~~ Bay (Yokel

1975a) and in Fakahatchee Bay (Yokel

1975b) on the southwest Florida coast,

juvenile pinfish showed a strong

preference for vegetated areas. The

sheepshead, another sparid, initially

emigrates to grass beds but quickly moves

into mangrove habitats (Heald and Odum

1970) or rocks and pilings (Hildebrand and

Cable 1938). The spottail pinfish,

Diplodus holbrooki, and‘the gras; porgy;

Calamus arctifrons, are other common but

much less numerous sparids that frequent

grassbeds in this region.

Several sciaenid species may be found in

the grassbeds of west Florida, but the

most common are the spotted seatrout, the

spot, and the silver perch. The spotted

seatrout is one of the few larger

carnivorous fishes present in south

Florida waters to spawn within the estuary

(Tabb 1961, 1966). Its eggs sink to the

bottom and hatching takes place in bottom

vegetation or debris (Tabb 1966). The

silver perch is the most abundant sciaenid

(often second to the pinfish) in northern

Florida and Whitewater Bays, being taken

throughout the year (Tabb and Manning

1961).

The pigfish is the most common pomodasyid, inhabiting areas with grassy or

muddy bottoms and turbid water in west

Florida estuaries. The white grunt is

less abundant, but is common throughout

the area, occurring most commonly over

Thalassia beds in clear water as juveniles

(Tabb and Manning 1961; Roessler 1965;

Bader and Roessler 1971; Weinstein and

Heck 1979).

The two snappers (Lutjanidae) that are

most common throughout the region are the

two most often associated with grassbeds,

the gray snapper and the Lane snapper.

Both occur throughout the range, and are

especially common in south Florida.

Juvenile gray snappers have been

considered the most common snapper in

northern Florida and Whitewater Bays,

including freshwater regions (Tabb and

Manning 1961), while juvenile Lane

snappers have been abundant in Thalassia

habitat in northern Florida Bay when

salinities were above 30 ppt (Tabb et al.

1962) in northern Florida Bay, and were

the most common snapper taken in grass

habitat of the Ten Thousand Island region

of the southwestern Florida coast (Yokel

1975a,b; Weinstein et al. 1977; Weinstein

and Heck 1979).

6.5.4 Detached Macrophytes as

Nursery Habitat

In the previous chapter, it was noted

that even using such a coarse sampling

device as a large mesh otter trawl will

yield many small organisms, such as

86
amphipods and isopods (see Chapter 5), as

well as numerous juveniles which use

detached macrophytes as shelter. Although

seagrasses may be associated with these

materiais, it is primarily composed of

1 drge balls or amorphous masses of

drifting algae (Cowper 1978). While many

algae can go into the makeup of the drift

algae, the most common ones in western and

sotithern Florida are species of the

rhodophyte genus Laurencia.

Currently, there are few studies of this

highly important but ephemeral habitat.

In western Australia, Lenanton et al.

(1982) showed that the concentrations of

several important fish were highest in the

zone of the drift algae near the shore.

The main food of these fishes were

amphipods that were profuse in the drift

algae. In addition, the arrival of the

juveniles appeared to correspond with the

greatest accumulations of the drift algae.

While seagrass beds may be important

habitat for pre-adult and immature adult

spiny lobsters, Panulirus argus, in south

Florida, drift algae have been found to be

a critical habitat for the newly settled

juvenile lobsters (Marx and Herrnkind

1985). The earliest stages of lobsters

were found solitarily occupying clumps of

Laurencia, using it for shelter and

abundant food. After reaching

approximately 17 mm in carapace length,

the juvenile lobsters leave their solitary

existence in the drift algae and begin to

accumulate in dens, becoming more

gregarious with the transition (Marx and

Herrnkind 1985). Although other studies

are lacking at this time, drift algae is

an associated habitat of potentially great

importance as a nursery and needs much

more study.

87
CHAPTER 7. HUMAN IMPACTS AND APPLIED ECOLOGY

The west coast of Florida possesses vast

regions of highly productive coastal seagrass, mangrove, and marsh habitats that

continue to be relatively undisturbed by

human impact. This same region also has

areas like Tampa Bay that could serve as

case studies on how to rape and plunder a

formerly productive natural system with

utterly no concern for the future. While

some forms of human impact, such as oil

spills, have less impact on seagrass

meadows than on the emergent interface

communities (mangroves and salt marshes),

other stresses, especially dredging,

filling, and eutrophication are highly

destructive to the seagrasses. Heavy

population influx and the resulting

developmental pressures have severely

impacted some areas, but others, such as

the Big Bend area, have been less

threatened due to their relatively low

population density, inacessibility! and

recent conservation efforts. In addition,

while all of Florida's coastal waters now

have increased protection, Rookery Bay,

Apalachicola Bay, and much of Charlotte

Harbor and Pine Island Sound have now been

made estuarine sanctuaries and marine

preserves.

termed acute stress as opposed to chronic

stress. Acute stress is stress resulting

from direct damage that physically kills

or removes the plants. The most common

example of this type is the extensive

losses that have been caused by direct

habitat removal by dredging and filling.

By comparison, chronic stress gradually

kills the plants over a period of time,

creating conditions in which either

respiration exceeds production or in which

the plants lose their ability to compete

with other species for light, nutrients,

and space. Two of the major causes of

this type of stress are eutrophication,

with its excessive algal growth, and the

suspended sediments and nutrients from

dredging and filling operations. Both of

these causes of pollution operate in a

similar manner on the seagrasses; that is,

they increase turbidity and decrease the

light incident on the seagrass leaf,

reducing its net production and

competitive fitness.

Many publications now document the

ecological importance of these habitats

and the extent of human impact, both

potential and realized, upon them (Zieman

1975b, 1982; Thayer et al. 1975, 1984a;

Phillips 1978; Ferguson et al. 1980;

Livingston 1984a; Zieman et al. 1984c).

Most of the recorded seagrass losses

have been attributed to acute stress

effects. However, this may simply be due

to the easier accountability when a brief,

obvious stress, such as a canal dredging,

destroys a grass bed. The great losses

that are now being documented for many of

Florida's estuaries have been caused by

the insidious, continual decline of water

quality in these estuaries.

19:;)

previous reviews (Zieman 1975b,

human

based' on

impacts were categorized

the activity causing the

damage. This study adopts a somewhat more

functionally based approach. Seagrasses

can be killed off by human impacts, or in

some cases natural disturbances, either

directly or indirectly, by what will be

7.1 DREDGING, FILLING, AND OTHER

PHYSICAL DAMAGE

7.1.1 Acute Stress

The most common and obvious destructive

influence on seagrass beds in Florida has

historically been the dredging and filling

of estuaries and adjacent wetlands.

88
I

Florida ranks third among the gulf coast

States, after Texas and Louisiana, in

amount of submerged land that has been

filled by dredge spoil with 9,520 ha

(Linda11 and Saloman 1977). In Texas and

Louisiana, most of the spoil created came

from dredged navigation channels, while in

Florida, it accounts for less than 5% of

the State total (Figure 26). Not

surprisingly, the majority of filling of

submerged areas in Florida has been to

create land for residential and industrial

development.

Studies conducted in Tampa Bay and Boca

Ciega Bay were among the first to

demonstrate the long-term impact of

dredging activities, and remain some of

the most definitive. Between 1950 and

1968, an estimated 1,400 ha of the bay

were filled during projects involving the

construction of causeways and the creation

of new waterfront homesites (Figure 27).

In undisturbed areas of the bay, luxuriant

seagrasses grew in stable sediments

averaging 94% sand and shell. At the

bottom of dredged canals the unvegetated

sediments averaged 92% silt and clay

(Taylor and Saloman 1968). While several

studies of Boca Ciega Bay collectively

described nearly 700 species of plants and

animals occurring there, Taylor and

Figure 26. Channel through grassbed with

open-water dredge disposal area in Tampa Bay (photo

by R. R. Lewis).

Saloman (1968) found only 20% of those

same species in the canals. Most of those

were fish which are highly mobile and thus

not restricted to the canals durinq

extreme conditions. Species numbers were

higher in undisturbed areas, but 30% more

fish were found in the canals. The most

abundant (the bay anchovy, the Cuban

anchovy, and the scaled sardine), are

planktivorous, and may have benefitted

from the higher nutrient levels in the

canals and the shelter provided.

Recolonization was negligible at the

bottom of the canals and it was concluded

that the sediments there were unsuitable

for most of the bay's benthic invertebrates. Light transmission values were

highest in the open bay away from landfills, lowest near the filled areas, and

increased somewhat in the quiescent waters

of the canals. Due to the depth of the

canals, however, light at the bottom was

insufficient for seagrass growth. Taylor

and Saloman (1968), using conservative and

incomplete data, estimated that fill

operations in the bay resulted in a n

annual loss of $1.4 million for fisheries

and recreation.

At the time these canals were built,

developers dredged them as deep as

possible to produce cheap fill material

locally, frequently to depths of 5-8 m in

areas where the original water depth was

only 1 m or less. Combined with the

easily suspended sediments, this

relatively great depth and the shading

effects of the vertical canal walls

prevented the regrowth of productive

seagrasses. The depth and the shallow

sill near the opening caused them to

become stagnant, organic traps with highly

reducing sediments that were easily

disturbed. When storm action resuspends

these sediments, the water column can

quickly become anoxic, causing localized

mortality. Many of these problems dere

alleviated in recent years when permitting

of deep canals was curtailed.

Burial of seagrasses can be as

destructive as dredging; however, if

seagrasses are only lightly covered and

the rhizome system is not damaged,

regrowth through the sediment is sometimes

possible. Thorhaug et al. (1973) found

that construction of a canal in Card Sound

temporarily covered turtle grass in an

89
area of 2-3 ha with up to 10 cm of

sediment, killing the leaves, but not the

rhizome system. Regr owth occurred when

the dredging operatLions ceased and

.

currents carried the sediment away.

7.1.2 Other Physical Damage

Any physical damage to the sediments and

rhizome structure of seagrass beds can

have long-term effects, no matter how

insignificant the damage may seem

visually. Small cuts, no more than 10 cm

wide and a similar depth in the sediments,

from the propellers of the innumerable

outboard boats crossing Florida seagrass

beds, can take from 3 to 5 years to

recover in a Thalassia bed (Zieman 1976).

Damage by larger boats can be vastly

more severe and long lasting. During the

construction of the new bridges in the

Florida Keys, a contractor attempted to

cut transit time barging new bridge

Figure 27. Dredged and filled areas in Boca Ciega Bay (photo by M. J. Durako).

sections into the Niles Channel bridge.

Instead of using the deep water access on

the Atlantic side, the contractor used a

large tugboat to prop-dredge a new passage

through a shallow Thalassia flat. The

resulting swath was several hundreds of

meters in length, about 10 m in width, and

up to 2 m in depth. This, in effect,

created a new tidal pass, and with the

high water velocities during tidal flow

through it, it is doubtful that the cut

will ever return to normal. Fortunately,

the federal courts determined that such

wanton distruction constituted illegal

dredging and filling (Zieman, unpubl.

data).

In estuaries near Tampa and Tarpon

Springs, Godcharles (1971) found no

recovery of ei,ther Thalassia

Syringodium in areas where commercii\;

hydraulic clam dredges had severed

rhizomes or uprooted the plants, although

at one station recolonization of Halodule

was observed.

90
7.1.3 Chronic Effects

In addition to the direct effect of

burial, secondary effects from turbidity,

which restricts nearby productivity,

chokes filter feeders by excessive

suspended matter, and depletes oxygen by

rapid utilization of suspended organic

matter, can have serious consequences.

The dredged sediments are unconsolidated

and readily resuspended. Thus, a spoil

bank can serve as a source of excess

suspended matter for a protracted time

after deposition.

In 1968, lush growths of Thalassia had

been recorded at depths UD to 10 m in

Lindberg Bay, in St. Thomas,'U.S.V.I., but

by 1971 this species was restricted, by

turbidity caused by dredging, to sparse

patches usually occurring in water 2.5 m

deep or less (Van Eepoel and Grigg 1970).

Similar declines were observed by Grigg et

al. (1971) in Brewers Bay, St. Thomas.

Odum (1963) found light penetration was

reduced in seagrass flats adjacent to the

dredging site of an intracoastal waterway

in Redfish Bay, Texas. Subsequent

decreases in productivity of Thalassia

were attributed to the stress caused by

suspended silts. Growth increased the

following year and Odum attributed this to

nutrients released from the dredge

material. While dredging altered the 38 m

long channel and a 0.5 km zone of spoil

island and adjacent beds, in this instance

no permanent damage occurred to the

seagrasses outside this area beyond this

region.

7.2 EUTROPHICATIONANDSEWAGE

The greatest losses of seagrass habitat

are caused by the effects of physical

damage from dredging and the chronic

stresses placed on the plants by suspended

sediments and eutrophic algal growth,

manifested in the form of increased

turbidity and resultant light reduction.

In many ways it is the most insidious form

of pollution, for it usually appears as a

slow and gradual worsening of local water

quality. With gradually increasing

turbidity and decreasing water clarity, it

is less noticeable that seagrasses are no

longer distributed as deep as they were

91

previously, and the choking growths of

epiphytes are also less obvious. Thus,

the natural communities are diminished and

their valuable functions as habitat and

shelter are either decreased or lost

entirely.

Seagrass beds subjected to both

eutrophication and suspended sediments in

Christiansted Harbor, St. Croix, declined

and were replaced by the green alga,

Enteromorpha, reducing the area1 extent of

the seagrasses by 66% over a 17-year

period (Dong et al. 1972). In

Hillsborough Bay, phytoplankton

productivity increased due to nutrient

enrichment from domestic sewage and

phosphate mining discharges (Taylor et al.

1973b). Phytoplankton blooms contributed

to the problem of turbidity, which was

increased to such a level that seagrasses

persisted only in small, sparse patches.

The only important macrophyte found in the

bay was the red alga, Gracillaria. Soft

sediments in combination with low oxygen

levels limited diversity and abundance of

benthic invertebrates (Taylor et al.

1973b).

In northern Biscayne Bay, McNulty (1970)

found few seagrasses in waters that were

polluted by sewage discharge in 1956.

Within 1 km of the outfall only small

patches of Halodule and Halophila were

found. Following the construction of an

offshore outfall, postabatement studies in

1960 found that the seagrasses had

continued to decline, probably due to the

persistent resuspension of sediment from a

causeway and other nearby construction

projects. The fine sediments of this area

are highly prone to resuspension when

lacking the stabilizing influence of the

seagrass canopy.

7.3 OIL

Increased demand for local petroleum

supplies has intensified exploration for

offshore sources in shallow continental

shelf, such as is found off the west

Florida coast. The potential for damage

to local marine communities, as well as

those at some distance, is present at all

stages of oil production, including

exploration, production, and transportation, although not all of the risks are
equal. The National Academy of Sciences

(NAS 1975) has found that the greatest

risks are associated with shipping accidents, followed by those spills associated

with loading and unloading oil. Getter et

al. (1980) noted that of 16 oil spills in

the Gulf of Mexico and Caribbean 75% were

transit accidents. By comparison, NAS

(1975) estimates that about 1.3% of the

annual input of oil to the oceans is the

result of drilling and production losses.

On the west coast of Florida, the remaining seagrasses of busy ports like Tampa,

as well as the beds of South Florida,

would seem to be the most vulnerable to

damage from oil spills. The large beds of

the Big Bend region are deeper and well

removed from major shipping lanes. The

known effects of oil spills, cleanup procedures, and restoration on seagrass

communities and associated organisms were

reviewed by Zieman et al. (1984b).

Petroleum products can damage seagrass

ecosystems in a variety of ways. These

have been summarized by Blumer (1971),

Cintron et al. (1981), and Zieman et al.

(1984b) and include:

1. Direct mortality of organisms due to

smothering, fouling, and asphyxiation; poisoning by direct contact

with oil (especially fresh oil); and

absorption of toxic fractions from

the water column.

2. Indirect mortality due to the death

of food sources or the destruction

or removal of habitat.

3. Mortality of sensitive juvenile

forms, especially those using the

grassbed as a nursery ground.

4. Incorporation of sublethal amounts

of petroleum fractions into body

tissues, potentially lowering

tolerance to other stresses.

5. Reduction or destruction of the food

or market value of fisheries due to

the tainting of flavor by absorption

of hydrocarbons, even though the

amounts are sublethal.

6. Incorporation of potentially carcinogenic or mutagenic substances

into the food chain.

Although much more laboratory work is

needed, the few studies existing that have

studied the effects of petroleum products

on seagrass community components have

shown them to be toxic to the organisms.

Seagrasses exposed to low levels of water

suspensions of kerosene and toluene showed

significantly reduced rates of carbon

uptake (McRoy and Williams 1977).

Refined products have consistently been

found to be more toxic to marine organisms

than crude oils. Larval stages of grass

shrimp were slightly more resistant to the

oil than the adults, while all forms of

the oils were more toxic to the larval and

juvenile stages of white and brown shrimp

than to adults. Changes in temperature

and salinity, which are routine in

estuaries, enhanced the toxic effects of

the petroleum hydrocarbons (Anderson et

al. 1974). The best indicator of oil

toxicity is probably the aromatic

hydrocarbon content of the oil (Anderson

et al. 1974; Tatem et al. 1978).

Numerous studies have indicated that

intertidal communities are the most

vulnerable of all marine communities;

thus, seagrass ecosystems are usually less

vulnerable due to their generally subtidal

nature. There would seem to be a

decreasing likelihood of damage with

increasing depth, so that grassbeds

several meters or more in depth are

possibly better protected from oil spills

than intertidal beds.

The impact on marine and estuarine

communities, including seagrass

communities, of several large-scale oil

spills has been investigated but these are

after-the-fact damage assessments. The

results were highly variable, ranging from

heavy destruction to little damage, a

factor of the size of the spill and

numerous other variables in environmental

conditions. The case studies reviewed in

Zieman et al. (1984b) are among the

best-documented examples of oil spills

affecting seagrass beds. In general,

seagrasses suffered relatively little

damage because of the subtidal nature of

the systems; the primary impact was on the

associated fauna1 communities. Those beds

that were exposed to oil at low tide did

not suffer greatly, due in part to their

buried rhizome system.

92

t
7.4 TEMPERATUREANDSALINITY

Because of the latitudinal variation

along the coast of west Florida, thermal

pollution will have different effects

along this gradient. At the southern end,

the seasonal programming is tropical and

many organisms are growing near their

thermal maxima in the summer under normal

conditions (Mayer 1914, 1918). At the

northern end of the gradient, the

seagrasses are at the northern limits in

their distribution and are more likely to

be restrained by winter minima. However,

even in this region, summer temperatures

are high and areas with shallow water and

restricted circulation can become

extremely hot in the summer.

The time of exposure to either extreme

high or low temperatures is critical in

assessing the effect of thermal stress.

Many organisms can tolerate largeamplitude temperature changes on a

short-term basis, but are intolerant of

chronic exposure to smaller changes.

Seagrasses have buried rhizome systems

that include the meristematic regions for

leaf, root, and rhizome growth, and the

relatively poor thermal conductivity of

the sediments serves as an effective

buffer against short-term temperature

damage. Therefore, the seagrasses are

more resistant to brief high temperature

increases than the commonly occurring

algae. Continued heating, however, can

raise the sediment temperature to levels

lethal to the plants (Zieman 1975). The

animal components of the seagrass systems

show the same ranges of thermal tolerances

as the plants. Sessile forms are more

affected, being unable to escape either

short-term acute effects or long-term

chronic stresses.

The primary sources of human-induced

thermal stress in estuaries are the

cooling systems of electrical power plants

(Figure 28). In addition, some industrial

plants produce waste heat, and, in some

cases! heated wastewater that also

contains a variety of waste chemical

products.

Damage to communities subjected to these

influences has been reported at various

study sites in Florida (Zieman and Wood

1975; Thorhaug et al. 1978, Zieman 1982).

Figure 28. Crystal River power plant (photo by R. R.

Lewis).

Effluent from the Bartow power plant near

the mouth of Old Tampa Bay, which reached

a level of 7.2 'C above ambient

temperature, killed 81 ha of seagrasses

(Blake et al. 1976). Where temperatures

were 2 OC above ambient or less, all of

the local seagrass species survived, but

at 3OC above ambient, only sparse

Halodule survived. Several parameters of

Halodule were measured in the effluent

plume and at a control station on the

intake side of the plant. At the intake

station, the biomass varied from 5 to 10

times greater than on the effluent side,

while the length of the leaves and

emergent short shoots on the intake side

were over twice the length of leaves from

the effluent side. During summers,

blue-green algal mats covered a large

portion of the area where the temperature

was greater than 3 "C above ambient (Blake

et al. 1976), a condition similar to that

found at Turkey Point in south Biscayne

Bay (Zieman and Wood 1975).

In addition to the seagrasses, changes

were found in the associated animal

communities in the effluent of the Bartow

power plant. On the intake side of the

plant, 104 species of invertebrates were

identified, primarily polychaetes,

mollusks, crustaceans, and echinoderms,

while on the effluent side only 60 species

93
were found (Blake et al. 1976). Numbers

of individual polychaetes were greater on

the effluent transects, crustacean

numbers were greater along the intake

transects, and mollusk numbers were

similar in both areas (Blake et al. 1976).

Virnstein (1977) found a decrease in

density and diversity of benthic infauna

the

li-37

where

OC wzLzarsecorded.

temperatures of

On the west coast of Florida, effluents

from the Crystal River power plant

impacted shallow-water seagrass and

macroalgal communities, but because of the

changing nature of the studies over the

years, and particularly due to the highly

qualitative methods used in the early

surveys, full assessment of the impact

from thermal effluents is not possible.

Numerous studies have shown a reduction in

the number of macroalgal species and their

abundance in the vicinity of the effluent

(Steidinger and Van Breedveld 1971; Van

Tine 1981). In the most recent study,

stations outside the area of the thermal

effects to the south showed greater

seagrass species diversity, biomass, and

productivity than those associated with

the thermal effluent (Stone and Webster

1985). Sample stations north of the

thermally-affected area showed patterns

similar to those near the effluent, but

conditions at these stations proved to be

inconsistent with the southern control

stations. They were in an area of reduced

salinities caused by the Withlacoochee

River and the western section of the Cross

Florida Barge Canal. Turbidity was high

in this region due to the resuspension of

sediments from the abandoned barge canal

and its spoil islands, thereby limiting

its usefulness as a comparison area.

Barber and Behrens (1985) studied the

effects of the effluent of an oil-fired

power plant near Anclote Key, about 50 km

north of Tampa Bay, on the seasonal

productivity of Thalassia and Syringodium.

Throughout the fall and winter months,

both species showed greater productivity

in the effluent than at the control

station. As temperatures rose in the

spring, the productivity increased

comparably at all stations, ver.y rapidly

in March and April: Thalassia

productivity at the thermally stressed

station was less than at the control

station except for a brief period at the

end of the summer, which was not

statistically significant. Syringodium

productivity at the thermally-effected

station exceeded that of the control

station in early May, but fell

precipitously at the end of the month.

Barber and Behrens (1985) concluded that

the heated effluents in this central

Florida region had a positive effect on

seagrass productivity, until it reached

the upper optimal growth temperature for

each species was reached. Above this

upper thermal limit, productivity

declined.

The response patterns to thermal

effluents seen in these west Florida

estuaries are similar to those previously

reported in south Florida. As the

temperatures in south Biscayne Bay were

raised by the effluent of the Turkey Point

power plant, the productivity, biomass,

and area1 distribution of seagrasses

decreased along the path of the effluent

plume of the power plant (Zieman and Wood

1975). Increases in ambient temperature

of 4 OC or more killed nearly all fauna

and flora present (Roessler and Zieman

1969). A rise of 3 OC above ambient

caused both species numbers and diversity

of algae to decrease. The optimal

temperature range for maximal species

diversity and numbers of individuals for

animals was between 26 and 30 OC;

temperatures between 30 and 34 OC excluded

50% of the invertebrates and fishes, and

temperatures between 35 and 37 OC excluded

75% (Roessler 1971; Zieman and Wood 1975).

Throughout their range, Thalassia

communities seem to show similar thermal

response patterns. Thorhaug et al. (1978)

collated and compared the response of

these communities in the Caribbean tropics

(Guyanilla Bay, Puerto Rico), subtropics

(Biscayne Bay and Card Sound, Florida),

and subtropical warm-temperate border

(Tampa Bay). The summer mean temperatures

in all of the estuaries averaged about 30

OC. Temperature elevations of 5 OC

destroyed and denuded the Thalassia

meadows; elevations of 4 OC showed severe

damage to all components of the

communities. With a 3 OC temperature

elevation, damage was severe in the higher

latitudes and less in the more tropical

environments. Data was insufficient to

94
allow intercomparisons of lesser

temperature elevations, but it was clearly

indicated that temperature elevations of

greater than 3 OC above ambient in the

warmer months produced severe and

sustained damage (Thorhaug et al. 1978).

While all of the local seagrass species

are euryhaline to varying degrees,

Thalassia and Syringodium show a decrease

in photosynthetic rate as salinity drops

below full-strenqth seawater, while

Halodule is less affected (McMillan and

Moselev 1967). The seasonalitv of

seagrasses in Florida is largely explained

by temperature and salinity effects

(Zieman 1974; Barber and Behrens 1985).

The greatest decline in plant populations

was found when combinations of high

temperature and low salinity occurred

simultaneously. The reduction of seagrass

biomass and productivity at one set of

stations near the Crystal River power

plant which were intended to serve as

controls, was attributed to reduced

salinities emanating from the Cross

Florida Barge Canal and the Withlacoochee

River (Stone and Webster 1985).

While h$igher salinities may yield

somewhat lusher and more productive

seagrass beds compared to those found in

mesohaline waters, the intermediate

salinities seem to be most important for

the nursery function of the seagrass

meadows. Tabb et al. (1962) stated:

"Most of the effects of man-made changes

on plant and animal populations in Florida

estuaries (and in many particulars in

estuaries in adjacent regions of the Gulf

of Mexico and south Atlantic) are a result

of alterations in salinity and turbidity .

. . . High salinities (30-40 ppt) favor

the survival of certain species like sea

trout, redfish, and other marine fishes,

and therefore improve angling for these

species. On the other hand these higher

salinities reduce survival of the young

stages of such important species as

commercial penaeid shrimp, menhaden,

oysters, and others. It seems clear that

the balance favors the low to moderate

salinity situation over the high salinity.

Therefore, control in southern estuaries

should be in the direction of maintaining

the supply of sufficient quantities of

fresh water which would result in

estuarine salinities of 18 to 30 ppt."‘

7.5 PAPERMILLEFFLUENTS

Throughout the gulf coast region, with

its enormous timber resources, there are

numerous paper mills discharging huge

quantities of waste materials into rivers,

which almost immediately wash this

material into the nearby estuaries.

Through numerous publications, Livingston

(1975, 1984a, 1987) has chronicled the

changes in the seagrass communities due to

kraft mill effluents, and the subsequent

recovery process following a pollution

abatement program. Zimmerman and

Livingston (1976a) found that a pulp mill

on the Fenholloway River dumped from

200,000 to 220,000 m3 of kraft mill

effluents into Apalachee Bay over the 20

year period from 1954 to 1974, at which

time a pollution abatement program was

enacted. The effluents altered water

quality and caused increased turbidity and

reduced light penetration, which, in turn,

reduced species diversity of macroalgae

and reduced productivity in the bay

compared with a similar region off the

unpolluted Econfina River (Heck 1976;

Hooks et al. 1976; Livingston 1984b). The

changes in water quality and plant

communities caused significant changes in

the fishes and macroinvertebrates.

Numbers of individuals and species numbers

were reduced in areas of severe impact.

In areas of moderate but chronic impact,

the annual species numbers were equivalent

to control stations, but this proved to be

the result of the recruitment of a few

individuals of rare species (Livingston

1975). Livingston (1987) also noted that

although recovery was occurring, the

seagrasses, especially Thalassia, were

slow to respond following the removal of

the stress.

7.6 DISTURBANCE, RECOLONIZATION, AND

RESTORATION

7.6.1 Disturbance

While the large offshore seagrass

meadows in the Big Bend region of Florida

have remained relatively intact and

undisturbed, the beds that are found

within the enclosed estuaries on the west

coast of Florida have suffered

tremendously. The greatest losses have

occurred in Tampa Bay, where there are

95
only 5,750 ha of seagrasses remaining from

estimated

ii 970 ha

historical coverage of

a reduction of 81% (Figure 9

f&n Lewi; et al. 1985a). Because of the

high turbidity caused in part by the

now-unvegetated bottom, seagrass

distribution is presently limited to less

than 2 m in depth in nearly all cases.

The problems and destruction encountered

in Tampa Bay are not unique, but are

mirrored in nearly all estuaries with

heavy urbanization and industrialization

(Taylor and Saloman 1968; Simon 1974;

Lewis et al. 1985a; Livingston 1987).

Other estuaries on the west Florida

coast have shown similar losses (Table

17). In the vicinity of Bayport,

seagrasses have declined by 13% (Haddad

1986). St. Joseph Bay, in an area of low

population density, has not shown

significant changes in seagrass density in

15 years (Savastano et al. 1984), and

Apalachicola Bay has shown minimal

degradation (Livingston 1987). The

coverage of submerged vegetation in

Choctawhatchee Bay has declined by 30%

since 1949 (Haddad 1986), but the causes

are unknown (Burch 1983; Livingston 1987).

Within the Pensacola Bay system,

occasional beds of Thalassia and Halodule

are found in Santa Rosa Sound, but there

was a complete loss of seagrass in

Escambia Bay, East Bay, and Pensacola Bay

between 1949 and 1979 (Olinger et al.

1975; Livingston 1987). Big Lagoon, west

of Pensacola, has increased coverage by

55%, one of the few areas in the state to

do so (Haddad 1986). In Charlotte Harbor,

on the southwest coast, seagrass beds have

declined nearly 30% to 9,300 ha remaining

(Harris et al. 1983; Haddad and Hoffman

1986).

7.6.2 Recolonization

The natural recolonization of seagrasses

is a highly variable process, the rate of

which can be affected by local

environmental parameters, as well as the

species of the seagrass. Halodule is the

normal pioneer species in the region and

can colonize an area rapidly if

sedimentary conditions are favorable and

if there is a source of seed or other

propagule material. With its surficial

rhizome system and smaller investment in

belowground biomass than the climax

species, it can rapidly cover a damaged

area.

Compared to the other seagrasses,

Thalassia is much slower to recolonize a

disturbed area. At least 10 months are

required for Thalassia to begin new short

shoot development (Fuss and Kelly 1969),

and the initiation of new growth seems to

be sensitive to environmental conditions.

After 13 months, Kelly et al. (1971) found

that 40% of transplanted plants in a

control area had initiated new rhizome

growth, while only 15% to 18% of the

plants transplanted to disturbed sediments

had initiated new growth.

It has been well documented that small

disturbances in seagrass beds require

surprisingly long recovery times. The

most common form of disturbance to

seagrass beds in the shallow banks and

bays of south Florida results from cuts by

boat propellers. Although it would seem

that these relatively small-scale

disturbances would heal rapidly, it

typically takes two to five years to

recolonize a Thalassia bed (Zieman 1976).

The scarred areas rapidly fill in with

sediment from the surrounding beds, but

the sediment is slightly coarser and has a

lower pH and Eh, and probably other

physico-chemical differences that the

plants can detect (the rhizome apex will

frequently grow up to one of these areas

and then literally turn back into the

parent bed and away from the filled-in

cut; Zieman 1976).

Seagrass ecosystems show differential

recovery rates from disturbances based on

a variety of factors including species

involved, the type and magnitude of the

disturbance, and especially whether or not

the sediments were disturbed. Along the

west Florida coast, if the disturbance is

great enough, a number of rhizophytic

algae act as precursors to the seagrasses.

One of the primary determinants of the

duration of recovery time is the extent of

damage to the sediments. If the sediments

and seagrass rhizomes are not severely

disturbed, the probability of recovery is

greatly increased. Table 18, (1984b),

attempts to synthesize and categorize the

levels of damage to seagrass ecosystems,

system effects, and the likely outcome of

the disturbances. Although originally

96
Table 17. List of data concerning historic anthropogenous impacts on seagrass meadows in Florida (from Livingston 1987).

Study area Location Status of seagrass meadows Information source

Indian River

Biscayne Bay

Florida Keys

co4Florida Bay

Tampa Bay

system

Charlotte

Harbor

Southeast Florida

Atlantic Ocean

Southeast Florida

Atlantic Ocean

South Florida Few data found. Little effect of Key

Atlantic Ocean West desalination plant.

South Florida Postulated altered species relationships

due to increased salinity caused by

redirection of freshwater runoff.

Southwest Florida

Gulf of Mexico

Southwest Florida

Gulf of Mexico

Historic declines in number and coverage

of seagrass meadows. Declines in Vero

Beach area, Fort Pierce Inlet (25%), and

Sebastian Inlet (38%) from 1951 through

1984.

Undetermined deterioration in northern

Biscayne Bay. Some damage to ThalassiaHalodule beds near power plant (heated

effluents) in south Biscayne Bay. Card

Sound unaffected by power plant

discharge.

Almost 40% reduction in Boca Ciega

Bay due to dredging, filling, and

associated activity from 1950 through

1968. Multiple sources (urbanization,

storm water runoff, sewage discharge,

industrialization, toxic substances).

Reduction of seagrass meadows in Tampa

Bay, Old Tampa Bay, and Hillsborough

Bay from 15,161 to 3,091 acres (1876-

1980).

Decline of 29% of seagrass beds

from 1943 through 1984.

Goodwin and Goodwin 1976; Florida

Department of Natural Resources,

unpubl. data

McNulty 1961; Rosessler and

Zieman 1969; Thorhaug et al.

1973; Zieman 1970, 1982

Chesher 1971

Zieman 1982

Simon 1974; Taylor 1971;

Taylor and Saloman 1968;

Lewis and Phillips 1980

Florida Department of Natural

Resources, unpubl. data

(Continued)
Table 17. (Concluded).

Study area Location Status of seagrass meadows Information source

Pensacola Bay Northwest Florida

System Gulf of Mexico

Choctawhatchee Northwest Florida Historical deterioration of seagrass

Bay Gulf of Mexico beds from 1949-1983. Causes unknown.

St. Andrews Bay Northwest Florida

Gulf of Mexico

No data found. Presumed impact due to

urbanization, industrialization.

Extensive coverage unchanged from 1972

through 1983. Relatively unpopulated

area.

St. Joseph Bay Northwest Florida

Gulf of Mexico

Apalachicola North Florida

Bay System Gulf of Mexico

Apalachee Bay North Florida

Gulf of Mexico

Complete loss of seagrass beds in

Escambia Bay, East Bay and Pensacola

Bay from 1949-1979. Some fresh-brackish

water species extant in delta areas.

Some Thalassia-Halodule beds still alive

in Santa Rosa Sound. Losses due to

urbanization, industrial waste discharge

dredging and filling, cultural

eutrophication.

Generally healthy assemblages of seagrasses. Local impact due to dredged

opening in associated barrier island.

Introduced species spreading in delta

areas with as yet undetermined impact.

Area under increased pressure from

urbanization.

Impacts due to disposal of pulp mill

wastes (Fenholloway Estuary) from 1954

to the present. Slow recovery noted in

outer portions of impact area

(associated with pollution abatement

program). Area now threatened by

proposed inshore navigation channel and

possible offshore oil drilling

operations.

Livingston et al. 1972; Olinger et

al. 1975; Livingston 1979

Burch 1983

McNulty et al. 1972; Savastano

et al. 1984

Livingston 198Oc, 1983

Heck 1976; Hooks et al. 1976;

Livingston 1975, 1982a, 1984a;

Zimmerman and Livingston 1976a,b

______I.- ..-
Table 18. Seagrass damage and restoration assessment (from Zieman et al. 1984b).

Associated

Damage Plant community System Recovery Restoration

level effects effects fate time indicated

1 No visible

damage

2 Leaf damage

and removal

3 Severe damage

to rhizomes

4 Severe system

damage

Possible fauna1

damage

Fauna1 damage may

be extensive

Fauna1 damage is

likely extensive

System completely

altered

Natural Weeks-year No

recovery

Natural 6 months- No

recovery year

likely

Natural 5 years- Yes

recovery decades

slow or

unlikely

Return to ? No

same state

not possible

developed for the recommendation of

strategy following an oil spill, the

results and recommendations are not

specific to any particular type of stress

and are of general utility. Following a

disturbance to the seagrass system, the

primary management strategy and objectives

should be directed towards minimizing the

impact. While all efforts should be

directed towards keeping damage at level

one or two where recovery may proceed

naturally, it is most important to keep

level-three damage from becoming level

four, where recovery or restoration to a

functioning seagrass system is not

possible. At this level of

transformation, sediment erosion is

allowed to proceed to the point where

there is insufficient sediment remaining

for seagrass colonization.

7.6.3 Restoration

According to the concept of ecological

succession, there are two basic ways to

restore a mature community: (1) establish

the pioneer species and allow succession

to take its course, and (2) create the

environmental conditions necessary for the

survival and growth of the climax species.

Van Breedveld (1975) noted that survival

of seagrass transplants was greatly

enhanced by utilizing a ball of sediment,

as in the techniques for terrestrial

transplantation of garden plants. He also

noted that transplantation should be done

when the plants are in a semidormant state

(as in winter) to give the plants time to

stabilize, another logical outgrowth of

terrestrial technique. Where possible,

the objective of restoration in general,

not just of seagrasses, should be to

restore the lost community or some

intermediate successional stage. In some

cases, restoration of the original

community may not be feasible or

cost-effective, and it may be necessary to

restore to an earlier successional stage

and allow natural successional progression

to take place.

Transplantation of seagrasses has been

attempted since the time of the wasting

disease, but there has been a dramatic

increase in its use during the past decade

(See Phillips 1980; Fonseca et al. 1981,

1987; Zieman et al. 1984b for recent

reviews). Darovec et al. (1975) discuss a

variety of techniques for restoring

coastal regions, including seagrasses, in

Florida. This publication is useful

because it consolidates a diverse

99
literature, but the seagrass techniques

are rudimentary and somewhat dated, and

the other reviews mentioned should be

consulted. Until recently, most

transplant studies reported primarily on

transplant technique and survival success,

and did not address environmental

variables such as sediment type, nutrient

conditions, light, turbidity, current

velocity, and wave climate, all of which

affect the success or failure of the

experiment (Fonseca et al. 1981, 1987).

The myriad techniques that have been

tried for transplanting seagrass have

yielded highly variable results. Those

techniques that have shown the most

consistent success are plugs, seeds, and

shoots--both anchored and unanchored

(Phillips 1980). Because of the variety

of methods and the different levels of

description of these methods in the

literature, direct comparison among

seemingly similar methods varies from

difficult, at best, to impossible. Table

19 summarizes the relative successes

recorded in the seagrass transplant

literature.

From this diverse literature, a few

generalizations stand out. The most

obvious is that the plug technique is the

only one that has worked with all species

upon which it has been tested. This is

not ecologically surprising, as the plug

minimizes trauma to the roots and rhizomes

by taking part of its environment along to

the new site. The plug technique provides

the highest degree of short-term sediment

stabilization of any of the methods. On

the negative side, the plug technique is

logistically more difficult due to the

need to collect the plug intact, move

large amounts of sediment, and create

sites of disturbance at the donor

location.

Methods using bare shoots have shown

mixed results, being very successful with

pioneer species such as Halodule wrightii

and Zostera marina, but not really

successful with Thalassia, which is a

climax species.

anchoring' to

Shoot methods require

approach the sediment

stability of the plug technique (Fonseca

et al. 1984). The logistics are somewhat

simpler than the plug method since there

is no mass of sediment to be transported.

Transplantations utilizing seeds and

seedlings have been attempted for several

species, but have been successful only

with Thalassia. If an abundant source of

seeds can be readily located, this

technique can be very attractive, because

of simple transportation and planting

logistics. Recently, Lewis and Phillips

(1981) have reported on sites of high seed

availability in the Florida Keys in late

summer. On the negative side, seeds are

only seasonally available and newlyplanted seeds or seedlings do not offer

any sediment stabilization capacity.

However, interplanting of Thalassia

seedlings in beds of recently established

Table 19. Success of seagrass restoration techniques (from Zieman et al. 1984b).

Species

Shoot Shoot

Plug (anchored) (unanchored) Seed

Zostera marina --~

Halodule wrightii

Syringodium filiforme

Thalassia testudinum

+/+ +/+ +/+ +/-

+/+ +/+ +/- __

+/+ +/+ +/- ?

+/+ +/- +/- +/+

Key: attempted/success, -- = not attempted, + = yes, - = no, ? = not sure

100
Halodule termed a "compressed successional"

approach, was tested by Durako and Moffler

(1984), and may prove to be a useful mixedplanting technique.

In 1982, Zieman wrote that "transplants of

tropical seagrasses may ultimately be a

useful restorative technique to reclaim

damaged areas, but at this time the results

are not consistent or dependable, and the

costs seem prohibitive for any effort other

than experimental revegetation

especial?; when the relative survival of the

plants is considered." In the intervening

time, a number of additional projects have

been completed, but the situation has not

changed significantly. Fonseca et al.

(1987) stated that "for the most part,

seagrass transplanting as a management tool

is not working. Isolated cases of success

or partial success can be found, but these

are overshadowed by many costly failures.

This lack of success is largely due to the

general disregard for and the lack of

scientific information on environmental

requirements of the transplant species.”

Further, they feel that "the pressure to

make management decisions has grown

disproportionatelytothe increase regarding

seagrass habitat management. With much

emphasis having been put on methodology of

transplanting and much less on collection of

environmental data, we have been at a loss

to explain successes and failures in a

quantitative fashion."

In the State of Florida, seagrass

transplantation and restoration is often

treated as if it were a proven-and-fixed

technology, capable of producing a product

upon specification, when, in fact, it is

really a series of loosely coupled

experiments. The concept of seagrass

transplanting for "mitigation" of

environmental damages is becoming an

accepted practice in Florida under the

assumption that if an environmental

disturbance or destruction is "necessary"

or "in the public interest," then this

perturbation can be "mitigated" by a

parallel restoration. As a step toward

accepting seagrass transplanting as a viable

mitigation method, numerous Federal, State,

and local agencies have funded projects

aimed at seagrass restoration. However,

only recently have any studies been funded

to conduct a scientific investigation on the

environmental variables causing the success

or failure of a particular project. Several

recent projects have elegantly tested the

viability of different methodologies in a

proper scientific manner, but none of these

can tell whv a particular method succeeded

or failed.

One of the major problems in offsite

restoration as it is currently practiced,

is the selection of a suitable and

potentially viable site for restoration, if

it is not to be the recently disturbed site.

Many times the sites chosen are

inappropriate and there are sound ecological

reasons why seagrasses are not growing there

now, even if there was seagrass coverage at

some point in past history (Lewis et al.

1985a; Fonseca et al. 1987). If it can be

established that an area meets the

environmental conditions to support

seagrasses, but has probably not recovered

due to lack of natural propagules, then

restoration may be indicated.

Unfortunately, probably the major problem

inhibiting seagrass success today is the

deteriorating water quality associated with

industrialization and development. If poor

water quality increases turbidity and

decreases incident light at the sediment

level past a certain point, then all the

transplanting in the world will not work.

In any restored area, the plants must have

sufficient light to yield a significantly

high positive net photosyntheses to survive

and grow. If turbidity is too high, or

eutrophication is sufficient to cause a

rapid growth of epiphytic algae or

phytoplankton, then the effort and money

will be wasted.

7.7 FINAL THOUGHTS

The gathering and assimilation of data for

this community profile has been highly

enlightening. Dozens of studies have shown

the importance of submerged vegetation to

major commercial and forage organisms

(Linda11 and Saloman 1977; Thayer et al.

1978a; Peters et al. 1979; Thayer and Ustach

1981). In the gulf States the recreational

saltwater fish catch exceeded $168 million

in 1973, representing about 30% of the total

U.S. recreational fishery (Linda11 and

Saloman 1977). Of the organisms caught, 59%

were dependent on wetlands at some state of

their life cycles. In the Gulf of Mexico,

this estimate was even higher with over 70%

101
of gulf recreational fisheries of the region

being estuarine dependent. The ecological

dependence of important commercial fisheries

on the estuarine wetlands is even greater.

The Gulf of Mexico is the leading region of

the United States in terms of both landings

(36% of the total U.S. catch) and value (27%

of total U.S. fishery value), and 90% of the

total Gulf of Mexico and south Atlantic

fishery catch is estuarine dependent

(Linda11 and Saloman 1977).

The west Florida coast contains vast

seagrass resources, in the form of offshore

beds of the Big Bend region, that have been

largely untouched by human activities.

However, the seagrass resources within the

west Florida estuaries must rank alongside

the seagrasses of Chesapeake Bay as some of

the most devastated and degraded in the

entire country (Lewis et al. 1985a;

Livingston 1987). The importance of these

losses to both the ecology and the economy

of Florida are far out of proportion to the

total hectares lost versus those remaining,

due to the critical nature of the estuarine

seagrass beds as nurseries. While measures

must be taken to ensure the continued

productivity of the offshore beds, it is

most critical that the water quality

degradation that has caused the extensive

losses in the estuarine grass beds be

arrested and reversed. Once the beds are

totally destroyed, they are likely to remain

lost forever, along with the myriad

organisms that they feed and shelter.

102

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Production ecology of seagrass

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Wiginton, J.R., and C. McMillan. 1979.

Chlorophyll composition under controlled

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129

APPENDIX

FISH SPECIES SURVEYS IN SOUTH AND WESTERN FLORIDA

Use these keys to interpret the table that follows.

Key to survey numbers

Survey No. Location Reference

1 North Biscayne Bay

2 South Biscayne Bay

3 Card Sound

4 Matecutie Key

5 Porpoise Lake

6 Whitewater Bay

:

Fakahatchee Bay

Marco Island

9 Rookery Bay

10 Charlotte Harbor

11 Offshore Tampa

12a Tampa Bay Mouth to Offshore

Reefs (Stns. 1 - 3)

12b Tampa Bay Grassbed Stations

(Stns. 4 - 6)

13 Crystal Bay Area

1 4 Cedar Key

15 Alligator Harbor

16 Apalachicola Bay

Key to abundance

Roessler 1965

Bader and Roessler 1971

Brook 1975

Springer and McErlean 1962

Hudson et al. 1970

Tabb and Manning 1961

Carter et al. 1973

Weinstein et al. 1971

Yokel 1975a

Wang and Raney 1971

Pbe and Martin 1965

Springer and Woodburn 1960

Springer and Woodburn 1960

Mountain 1972

Reid 1954

Joseph and Yerger 1956;

Yerger 1961

Livingston 1984

Note:

= rare

= present

= abundant

= common

Species names are according to Robbins et al. 1980, except where an

asterisk (*) indicates that they are given as originally published.

131
Appendix (Continued).

Abundance by survey number

Species 1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Orectolobidae/carpet sharks

Ginglymostoma cirratum r r P P P

nurse shark

Carcharhinidae/requiem sharks

Negaprion brevirostris

lemon shark

Rhizoprionodon terraenovae

Atlantic sharpnose shark

Carcharhinus acronatus

blacknose shark

Carcharhinus isodon

finetoothed shark

Carcharhinus leucas

bull shark

Carcharhinus limbatus

blacktip shark

Carcharhinus plumbeus

sandbar shark

Sphyrnidae/hammerhead sharks

tiburo Sphyrna

bonnethead

diplana* Sphyrna

Sphyrna mokarran

great hammerhead

Pristidae/sawfishes

Pristis pectinata

smalltooth sawfish

Rhinobatidae/guitarfishes

Rhinobatus lentiginosus

Atlantic guitarfish

P

r

P

P

(Continued)

132

P

P P

P

P P P

PP P

P

P PP P

P

P

P
Appendix (Continued).

Species

Abundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Torpedinidae/electric rays

Narcine brasiliensis

lesser electric ray

Rajidae/skates

Raja texana

roundel skate

Raja eglanteria

clearnose skate

r

r

Dasyatidae/stingrays

Urolophus jamaicensis r r

yellow stingray

micrura Gymnura

smooth butterfly ray

Dasyatis americana"

southern stingray

Dasyatis sabina

Atlantic stingray

Dasyatis sayi

blunt nosed stingray

Myliobatidae/eagle rays

Aetobates narinari

spotted eagle ray

Rhinoptera bonasus

cownose ray

Mobulidae/mantas

Manta birostis

Atlantic manta

Lepisosteidae/gars

Lepisosteus osseus

longnosed gar

Lepisosteus platyrhinchus

Florida gar

r r

P

r r PPPP PP

P

r r P P P

P P

P

a P P

P P

P P P

(Continued)

133
Appendix(Continued).

Species

Abundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Elopidae/tarpons

Elops saurus

ladyfish

Megalops atlanticus

tarpon

Albulidae/bonefishes

Albula vulpes

bonefish

Anguillidae/freshwater eels

Anguilla rostrata

American eel

Muraenidae/morays

Gymnothorax nigromarginatus r

blackedge moray

Gymnothorax saxicola

ocellated moray

Ophichthidae/snake eels

Myrophis punctatus

speckled worm eel

Ophichthus

shrimp eel

gomesi

Echiophis intertinctus

spotted spoon-nose eel

Echiophis mordax

snapper eel

Bascanichthys bascanium

sooty eel

Bascanichthys scuticanis

whip eel

Clupeidae/herrings

Harengula jaguana

scaled sardine

P

P

P

r r r r

r r

r r r r c

P P

P

P

P

P a

P P

rr P

r

P P

P P

P P

P

aa P P P P

(Continued)

134
Appendix (Continued).

Species

Abundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Clupeidae/herrings (continued)

Harengula humeralis r

redear sardine

Jenkinsia sp.

Brevoortia smithi

yellowfin menhaden

Brevoortia patronus

gulf menhaden

Etrumeus sadina"

Dorosoma petenense

threadfin shad

Opisthonema oglinum

Atlantic thread herring

Sardinella auria

Spanish sardine

Engraulidae/anchovies

Anchoa cubana

Cubananchovy

Anchoa lamprotaenia

bigeye anchovy

Anchoa mitchilli

bay anchovy

Anchoviella perfasciata

flat anchovy

Anchoa hepsetus

striped anchovy

Synodontidae/lizardfishes

foetens Synodus

inshore lizardfish

Synodus intermedius

sand diver

r

r r

r

r

r

pap PP

P

P P

a P p P

P a P

r P P

a P

r rpcr rc a a P P P P

r

r r r c PP P P P

rrrrpcrrrr pp p P P P

P

(Continued)

135
P

Appendix (Continued).

Species

Abundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Ictaluridae/bullhead catfishes

Ictalurus catus

white catfish

Ictalurus nebulosus

brown bullhead

Ari idae/sea catfishes

P

P

marinus Bagre

gafftopsail catfish

Arius felis

hardheadcatfish

Batrachoididae/toadfishes

Opsanus beta

gulf toadfish

Opsanus pardus

leopard toadfish

Porichthys plectrodon

Atlantic midshipman

Gobiesocidae/clingfishes

Acyrtops beryllinus

emerald clingfish

P r r r

carrpcccr

r

Gobiesox strumosus

skilletfish

Antennariidae/frogfishes

Histrio histrio

sargassumfish

Antennarius ocellatus

ocellated frogfish

Ogcocephalidae/batfishes

Ogcocephalus cubifrons"

Ogcocephalus nasutus r

shortnose batfish

r

r

r P r

P P

r P P P P P

P P P P P P

P P

r P P

P P P P

r r

P

r

P P

(Continued)

136
Appendix (Continued).

Species

Abundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Ogcocephalidae/batfishes (Continued)

Ogcocephalus radiatus

polka-dot batfish

P

Ogcocephalus sp. P P

Halieutichthys aculeatus

pancake batfish

Gadidae/codfishes

Urophycis floridana

southern hake

Ophidiidae/cusk-eels

Lepophidium jeannae

mottled tusk-eel

Ophidion grayi

blotched tusk-eel

Ophidion welshi

crested tusk-eel

Ophidion holbrooki

bank tusk-eel

Ophidion beani

longnose tusk-eel

Ophidion marginatum

striped tusk-eel

Bythitidae/viviparous brotulas

cayorum Ogilbia

key brotula

Gunterichthys longipenis

gold brotula

Carapidae/pearlfishes

bermudensis Carapus

pearlfish

r

r

r r

P

P

r

P

r P

P

P

P P

(Continued)

137
Appendix (Continued).

Species

Abundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Exocoetidae/fly

halfbeaks

Hemiramphus

ballyhoo

i ng fishes and

brasiliensis

Chriodorus atherinoides

hardhead halfbeak

Hyporhamphus unfasciatus

halfbeak

Belonidae/needlefishes

Strongylura notata

redfin needlefish

Strongylura timucu

timucu

Strongylura marina

Atlantic neemh

crocodilus Tylosurus

houndfish

Tylosorus raphidoma"

Cyprinodontidae/killifishes

Flordichthys carpio

goldspotted killifish

Adinia xenica

diamondkillifish

Lucania parva

rainwater killifish

Fundulus heteroclitus

mummichog

Fundulus

gulf kill

grandis

Ifish

Fundulus similis

longnose killifish

Fundulus confluentus

marsh kil'lifish

r

P

p r

r r p r

r r

r

c a r

r

a r r p r

r

r

r r

PPP P

PPP P

a P

P P

P

P P

r P

P P P P P

PP P

r P P

P

(Continued)
Appendix (Continued).

Species

Abundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Cyprinodontidae/killifishes (continued)

P Cyprinodon variegatus r P P

sheepshead minnow

Rivulus marmoratus

rivulus

r

Poeciliidae/livebearers

Poecilia latipinna P r P P

sailfin molly

Gambusia affinis

mosquitoflsh

r P

Heterandria formosa r

least killifish

Atherinidae/silversides

C r P

a a

Hypoatherina harringtonensis

reef silverside

Atherinomorus stipes

hardhead silverside

Menidia beryllina r c a a P P P

tidewater silverside

Membras martinica

rough silverside

Membras vagrans"

Membras sp.

Holocentridae/squirrelfishes

r r

a P

Holocentrus ascensionis

squirrelfish

Syngnathidae/pipefishes and

seahorses

a

Cosmocampus albirostris r r

whltenose pipefish

r

Cosmocampus brachycephalus

crested pipefish

r

(Continued)

139
Appendix(Continued).

Species

Abundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Syngnathidae/pipefishes and

seahorses (continued)

Hippocampus hudsonius*

Hippocampus zosterae

dwarf seahorse

Hippocampus erectus

lined seahorse

Hippocampus reidi

longsnout seahorse

Hippocampus regulus*

Hippocampus sp.

Syngnathus sp.

Syngnathus dunckeri

pugnose pipefish

Syngnathus floridae

dusky pipefish

Syngnathus louisianae

chain pipefish

Syngnathus elucens

shortfin pipefish

Syngnathus springeri

bull pipefish

Syngnathus scovelli

gulf pipefish

Micrognathus crinigerus

fringed pipefish

Centropomidae/snooks

Centropomus undecimalis

snook

Serranidae/sea basses

Centropristis striata

black sea bass

r

rcrrprrrr

r r r r r r

r

r

crrrpr r r

r r r r r r r r

rrcrpcaccc

a r P r

P P P P

P

P

P

P

P P P

P P P

P P P

P P

P P

r r P P P P

(Continued)

140
Appendix(Continued).

Species

Abundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Serranidae/sea basses

Centropristis ocyurus

bank sea bass

Mycteroperca bonaci r

black grouper

Mycteroperca microlepis r r

gag

Mycteroptera falcata"

Serraniculus pumilio

pygmy sea bass

Serranus subliqarius

belted sandfish

Diplectrum bivittatum

dwarf sand perch

Diplectrum formosum

sand perch

Epinephalus morio

red grouper

Epinephalus itajara P

jewfish

Epinephalus adscensionis

rock hind

Grammistidae/soapfishes

Rypticus saponaceus

greater soapfish

Apogonidae/cardinalfishes

Phaeoptyx conklini

freckled cardinalfish

Apogon aurolineatus

bridle cardinalfish

Astrapogon alutus r r

bronze cardinalfish

P

p rrr a

r P P

r P a

P

P

P P.

P

r

rrrrr p P P P P

P a P

P

r

P

r

P

P R P

(Continued)

141
Appendix (Continued).

Abundance by survey number

Species 1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Apogonidae/cardinalfishes (continued)

Astrapogon stellatus r

conchfish

Pomatomidae/bluefishes

Pomatomus saltatrix

bluefish

Rachycentridae/cobias

Rachycentron canadum

cobia

Echeneidae/remoras

Echeneis naucrates

sharksucker

Carangidae/jacks and pompanos

Caranx hippos

crevalle jack

Caranx latus

horse-eyejack

Caranx ruber

-jack

Caranx bartholomaei

yellow jack

Caranx crysos

blue runner

Hemicaranx amblyrhynchus

bluntnose jack

Trachinotus falcatus

permit

Trachinotus carolinus

Florida pompano

Trachinotus sp.

Trachurus lathami

rough scad

r

r

r

r P

P

(Continued)

142

r

PPP PP

P P P

P P P P P

P P P P

P

r P

P

a
Appendix (Continued).

Species

Abundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Carangidae/jacks and

pompanos (continued)

Seriola zonata

banded rudderfish

Chloroscombrus chrysurus

Atlantic bumper

Oligoplites saurus

leatherjacket

Selene vomer

lookdown

Vomer setapinnis

Atlantic moonfish

Lutjanidae/snappers

Lutjanus analis

mutton snapper

Lutjanus apodus

schoolmaster

Lutjanus griseus

gray snapper

Lutjanus jocu

dog snapper

Lutjanus synagris

lane snapper

Lutjanus campechanus

red snapper

Rhomboplites aurorubens

vermilion snapper

chrysurus Ocyurus

yellowtail snapper

Lobotidae/tripletails

Lobotes surinamensis

tripletails

P r

r

r r

r a P

r rcprrrr

r

r

r r

r

a a

PPP PP

r PPP PP

r r P P P P

P P

P P P P P P

pcracr p P

P

P

P P

P

P

(Continued)

143
Appendix (Continued).

Species

Abundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Gerreidae/mojarras

Eucinostomus argenteus

spotfin mojarra

Eucinostomus gula

silver jenny

Eucinostomus lefroyi

mottled mojarra

Gerres cinereus

yellowfTiii$Z%a

Diapterus plumieri

striped mojarra

Haemulidae/grunts

Haemulon flavolineatum

French grunt

Haemulon parrai

sailors choice

Haemulon sciurus

bluestriped grunt

Haemulon aurolineatum

tomtate

Haemulon plumieri

white grunt

Haemulon carbonarium

Caesar grunt

Anisotremus virginicus

porkfish

Orthopristis chrysoptera

pigfish

Sparidae/porgies

Archosargus probatocephalus

sheepshead

Archosargus rhomboidalis

sea bream

r c c r p r r r r c p a P P P P

r r a a p a a a a a P P P P P P

r

r r

r r r c

r c r p r

r r

a r a

r

r

r

a r

P

P P

a r P

P a P P P

r

r pcaaar pa P P P P

r p r r

r

(Continued)

144

r pap P P

P P
Appendix (Continued).

Abundance by survey number

Species 1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Sparidae/porgies (continued)

rhomboides ,'QcJ&I;: c c r c paaaaa pa a P a P P

Calamus arctifrons

grass porgy

Calamus calamus

saucereye porgy

Diplodus holbrooki

spottail pinfish

Sciaenidae/drums

Menticirrhus saxatilis

northern kingfish

Menticirrhus littoralis

gulf kingfish

Sciaenops ocellatus

red drum

Bairdiella chrysoura

silver perch

Cynoscion nebulosus

spotted seatrout

acuminatus Equetus

high-hat

Fquetus lanceolatus

Jackknife fish

Bairdiella batabana

blue croaker

Odontoscion dentex

reef croaker

Leiostomus xanthurus

spot

Cynoscion arenarius

sand seatrout

Micropogonias undulatus

Atlantic croaker

r

r r

r

r

r

r

P r r PPP PP

C aaCC PP a pp P

prcrrr pr p P P P P

P a

Pr rp P P

C P

a

P P P P P

P P

P

P

P

ca pa a P P P P

r r rp PP p P P

r p P P P

(Continued)

145
Appendix (Continued).

Species

Abundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Sciaenidae/drums (continued)

Pogonias cromis

black drum

a

Stellifer lanceolatus

star drum

Larimus fasciatus

banded drum

Menticirrhus americanus r rc P P

southern kingfish

Mullidae/goatfishes

Pseudupenueus maculatus r

spotted goatfish

Ephippidae/spadefishes

Chaetodipterus faber

Atlantic spadefish

Chaetodontidae/butterflyfishes

Chaetodon ocellatus

spotfin butterflyfish

Pomacanthidae/angelfishes

Holacanthus bermudensis

blue angelfish

Pomacanthus arcuatus

gray angelfish

Pomacentridae/damselfishes

Pomacentrus leucostictus

beaugregory

Pomacentrus variablis

cocoa damselfish

Abudefduf saxatilis

sergeant major

Chromis enchrysurus

yellowtail reeffish

P

P P

P P

P P P P

r P r r r PP P P P P P

P

P

r

r

(Continued)

146
Appendix (Continued).

Species

Abundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Labridae/wrasses

Doratonatus megalepis r

dwarf wrasse

Halichoeres bivittatus

slippery dlck

Halichoeres caudalis

painted wrasse

Halichoeres radiatus

puddingwife

Hemipteronotus martinicensis

rosy razorfish

Hemipteronotus novacula

pearly razorfish

Lachnolaimus maximus

hogfish

Scaridae/parrotfishes

Nicholsina usta

emerald parrotfish

Scarus coelestinus

midnight parrotfish

Scarus croicensis

striped parrotfish

Scarus guacamaia

rainbow parrotfish

Sparisoma chrysopterum

redtail parrotfish

Sparisoma radians

bucktooth parrotfish

Sparisoma rubripinne

redfin parrotfish

Sparisoma viride

stoplight parrotfish

Cryptotomus auropunctatus"

r

C

r

r p

r

r r

r

r

r

r

r

a r C

r

r

a r

r

P

P

P

P P P

(Continued)

147
Appendix (Continued).

Species

Mugilidae/mullets

Abundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

cephalus Mugil

striped mullet

Mugil curema

white mullet

r P

a a a P P

r r P C P P P

trichodon Mugil r P P

fantail mullet

Mugil sp.

Sphyraenidae/barracudas

Sphyraena barracuda

great barracuda

Sphyraena borealis

northern sennet

Sphyraena sp.

Polynemidae/threadfins

Polydactylus octonemeus

Atlantic threadfin

Opistognathidae/jawfishes

Opistognathus maxillosus r

mottled jawfish

Opistognathus macrognathus

banded jawfish

r r r p r

Dactyloscopidae/sand stargazers

Dactyloscopus tridigitatus r r

sand stargazer

Uranoscopidae/stargazers

Astroscopus y-graecum

southern stargazer

Clinidae/clinids

Bramerella sp.*

(Continued)

148

a P

P

r r

P

P

P P

PP P P P
Appendix (Continued).

Species

Abundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Clinidae/clinids

Malacoctenus

rosy blenny

Malacoctenus

(Continued)

macropus r

culebrae*

Emblemaria atlantica

banner blenny

Paraclinus fasciatus

banded blenny

Paraclinus nigripinnis

blackfin blenny

Paraclinus marmoratus

marbled blenny

Chaenopsis ocellata

bluethroat pikeblenny

Blenniidae/combtooth blennies

Chasmodes saburrae

Florida blenny

Parablennius marmoreus

seaweed blenny

Lupinoblennius

highfin blenny

Blennius sp.

Hypleurochilus

crested blenny

nicholsi

geminatus

Hypsoblennius hentzi

feather blenny

Hypsoblennius ionthas

freckled blenny

r r c

r

r r r r p

P

r r r r r r

P

Callionymidae/dragonets

Callionymus pauciradiatus r r r r p

spotted dragonet

Callionymus calliurus"

r

P P

P

P

P P P P

P a

P

P

P

P P P P P

P

(Continued)

149
Appendix (Continued).

1 2 3 4

Abundance by survey number

Species 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Gobiidae/gobies

Barbulifer ceuthoecus

bearded goby

r

P

per r

r

Microgobius

banner goby

Microgobius

clown goby

Microgobius

green goby

microlepis r

gulosus

thalassinus

Microgobius

Seminole goby

carri

_..

P P P P

a

Bathygobius curacao

notchtongue goby

C

Bathygobius soporator

frillfin goby

r P

Coryphopterus sp.

Gobionellus hastatus

sharptail goby

P P

P P Gobionellus bolesoma r

darter goby

Gobionellus smaragdus

emerald goby

r

Gobionellus shufeldti

freshwater goby

r

Gobionellus stigmaturus

spottail goby

r

a r r pccrrr

r

Gobiosoma robustum

code goby

a P P

Gobiosoma longipala

twoscale goby

Gobiosoma macrodon

tiger goby

r r P P

Gobiosoma longurn" r

(Continued)

150
Appendix (Continued).

Species

Abundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Gobiidae/gobies (continued)

Gobiosoma bosci

naked goby

Ioglossus calliurus

blue goby

Lophogobius cyprinoides r

crested goby

Coryphopterus glaucofraenum r

bridled goby

Acanthuridae/surgeonfishes

Acanthurus bahianus

ocean surgeon

Acanthurus coeruleus

blue tang

Acanthurus chirurgus

doctorfish

Trichiuridae/cutlass fishes

Trichiurus lepturus

Atlantic cutlassfish

Scombridae/mackerels

Scomberomorus maculatus

Spanish mackerel

Scomberomorus cavalla

king mackerel

Euthyhnus alletteratus

little tunny

Thunnus atlanticus

blackfin tuna

Istiophoridae/billfishes

Istiophorus platypterus

sailfish

r

P

r

P

P P P

a P P

a P

P

r

P

P P

P P

P

(Continued)

151
Appendix (Continued).

Species

Abundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Stromateidae/butterfishes

Peprilus burti

gulf butterfish

Peprilus paru*

Peprilus alepidotus

harvestfish

Peprilus triacanthus

butterfish

Nomeus gronovii

man-of-war fish

Scorpaenidae/scorpionfishes

Scorpaena brasiliensis

barbfish

Scorpaena grandicornis

piumed scorpionfish

Scorpaena plumeiri

spotted scorpionfish

Triglidae/searobins

Bellator militaris

horned searobin

Prionotus pectoralis*

Prionotus salmonicolor

blackwing searobin

Prionotus scitulus

leopard searobin

Prionotus tribulus

bighead searobin

Prionotus roseus

bluespotted searobin

r

r r r

r r r

r

r P

r r r r r r r P

r r r c rr P

P

P

P P

P P

P

prr P

P P P P

P P P P

(Continued)

152
Appendix(Continued).

Species

Abundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Bothidae/lefteye flounder

Bothus ocellatus

eyed flounder

Ancylopsetta quadrocellata

ocellated flounder

Cyclopsetta fimbriatta

spotfin flounder

Citharichthys macrops

spotted whiff

Citharichthys spilopterus

bay whiff

Paralichthys albigutta

gulf flounder

Paralichthys lethostigma

southern flounder

papillosum Syacium

dusky flounder

Etropus crossotus

fringed flounder

Etropus rimosus

gray flounder

Soleidae/soles

Thunnus atlanticus

blackfin tuna

Istiophoridae/billfishes

Istiophorus platypterus

sailfish

Stromateidae/butterfishes

Peprilus burti

gulf butterfish

Peprilus paru*

Peprilus alepidotus

harvestfish

r r r

r

r r

r r

r r

P P

r P P P P P

P P

P

P r P P P

P

P P P

r r P P

r r r r PP P P P P

P P

P

P P

P P

(Continued)
Appendix (Continued).

Species

Abundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Stromateidae/butterfishes (continued)

Peprilus triacanthus

butterfish

P

r

r r

Nomeus gronovii

man-of-war fish

Trinectes inscriptus

scrawled sole

r r r

rrrpcc

PP PP

PP PP

Trinectes maculatus

hogchoker

Achirus lineatus r r

lined sole

Cynoglossidae/tonguefishes

r r r c c r P

P

Symphurus plagiusa PP PP

blackcheek tonguefish

Symphurus diomedianus

spottedfin tonguefish

stidae/triggerfishes and

filefishes

Balistes capriscus

gray triggerfish

Bal i

r P

c r r c r r a a P P P

c r r c r rrrr PP P P P

r P P

Monocanthus ciliatus

fringed filefish

Monocanthus hispidus

planehead filefish

Alutera zchoepfi

orange filefish

Ostraciidae/boxfishes

Lactophrys quadricornis r c

scrawled cowfish

r r P r r P

r

P

Lactophrys trigonus r r

trunkfish

C P

Lactophrys triqueter r

smooth trunkfish

r

(Continued)

154
Appendix (Continued).

Species

Abundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Tetraodontidae/puffers

Sphoeroides nephelus r r p r c r r PP P P P

southern puffer

Sphoeroides spengleri r r r r r r P

bandtail puffer

Sphoeroides marmoratus*

Sphoeroides harperi*

P

P

r

P

Sphoeroides testudineus

checkered puffer

Lagcocephalus laevigatus

smooth puffer

Diodontidae/porquepinefishes

Chilomycterus schoepfi rcrrprrcrr pp p p

striped burrfish

Chilomycterus antennatus r

bridled burrfish

Diodon holocanthus r r P r

balloonfish

P P

155
so272 -101

REPORT DOCUMENTATION 11. REPORT NO.

PAGE 1 Biological Report 85(7.25) 1'.

.____--. .._ _..______._______ __~__

4. TotIe and Subtetls

The Ecology of the Seagrass Meadows of the West 1 September 1989

Coast of Florida: A Community Profile i

6.

7. Author(r)

Joseph C. Zieman and Rita T. Zieman

3r.s~

_ _____-

lo. ProlKt/Tatk/Work “n,t No.

Department of Environmental Sciences 11. COntrXtK) or Grant(G) No.

University of Virginia

Charlottesville, VA 22903

12. Soonrorm6 Orsamratton Name and Addrers

__ .___~~

13. Type of Repart 6 Penod Covers,

U.S. Department of the Interior

Fish and Wildlife Service

National Wetlands Research Center ----

Washington, DC 20240

_______ ___ .~

16. Abstract (Limit: 200 wards,

This report summarizes information on the ecology of seagrass meadows on the west coast

of Florida, from south of Tampa Bay to Pensacola. This area contains more than 3,500 ha

of seagrass beds, dominated by three species, Thalassia testudinum (turtle grass),

Syringodium filiforme (manatee grass), and HaTodule wrightii (shoal grass). Beds occur

both on the shallow,

_____

zero-energy Continental Shelf and in inshore bays and estuaries.

Species ecology, distribution, biomass, and productivity of these dominant seagrass

species are discussed.

Seagrass beds support a very diverse and abundant algal flora and fauna, and these

organisms and seagrass detritus form the base of a productive food chain. Seagrass beds

are important nursery areas providing both cover and food, for a number of commercial and

sports fishery species.

Along the west Florida coast, estuarine grass beds are noticeably more stressed and

impacted by human activities than the more pristine nearshore beds. Urban development

and dredging and filling are the major threates to seagrass beds in this region.

___

17. Document Analysn a. Descnptors

Ecology Syringodium

Aquatic beds Halodule

Thalassia Halophila

b. Identihsn/Own~Endcd Terms

Seagrass Ecosystem

Florida gulf coast Nursery utilization

c. COSATI Field/Group

16. AvaIlability Statement 19. Secunty Class (Thns Report)

Unlimited distribution : 20. Sccurfty Class Vh!s Page)

(See ANSI-239.16) OPTIONAL FORM 2?2 (4-7

(Formcrl. NTIS-35)

Dcp*rtment at commerce