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i

J _‘.; . ,I b : I .. - ! 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 synthesizing what is known of the extremely productive and valuable coastal ecologic structure, functioning, and wetland resources. They are critical values of these marine and estuarine nursery areas for a number of fish, communities. This profile in particular shrimp, and crab species, and support the builds on the author's earlier profile on adults of these and other species that the seagrass meadows of south Florida. forage around seagrass beds, preying on As will become apparent to the reader, the rich and varied fauna that occur in while enough is known to describe the these habitats. Seagrass beds support gulf coast seagrass community, there has several endangered and threatened been little study of the finer points of species, including sea turtles and the structure and function of seagrass manatees along the west coast of Florida, beds in this region. To shed light on the geographic area covered in this the ecology of Thalassia, Syringodium, profile. and Halodule meadows on Florida's aulf., coast, one is forced to extrapolate a For these reasons and others, seagrass good deal from information from studies beds or meadows have been the topic of conducted on the south and southeast several of the reports in this community Florida coasts and elsewhere. However, profile series. This report, covering in so doing the author has been able to the seagrass community of the Florida update his own earlier communitv profile. Gulf of Mexico coastline from south of Thus, The Ecology --of the Seagra;s'Meadows Tampa Bay to Pensacola, is the fifth --of the West Coast of Florida is not only community profile to deal with submerged a synthexof &IC, but also serves aquatic vegetation beds; others in the as- a state-of-the-art review of series have synthesized ecologic data on subtropical seagrass ecology and a seagrasses of south Florida, eelgrass beds in the Pacific Northwest and along the Atlantic coast, and kelp forests of the central California coastline. this series, the profile finally high- lights how much is still left to learn These reports in total represent a about these valuable natural habitats. major effort toward summarizing and

iii CONVERSION FACTORS

Metric to U.S. Customary

Multiply BY To Obtain millimeters (mm) 0.03937 inches centimeters (cm) 0.3937 inches meters (m) 3.281 feet meters (m) 0.5468 fathoms kilometers (km) 0.6214 statute miles kilometers (km) 0.5396 nautical miles square meters (m’) 10.76 square feet square kilometers (km’) 0.3861 square mrles hectares (ha) 2.471 acres liters (I) 0.2642 gallons cubic meters (m3) 35.31 cubic feet cubic meters (m3) 0.0008110 acre-feet milligrams (mg) 0.00003527 ounces grams (9) 0.03527 ounces kilograms (kg) 2.205 pounds metric tons (1) 2205.0 pounds metric tons (1) 1.102 short tons kilocalories (kcal) 3.968 British thermal units Celsius degrees (‘C) 1.8(%) + 32 Fahrenheit degrees U.S. Customary to Metric inches 25.40 millimeters inches 2.54 centimeters feet (ft) 0.3048 meters fathoms 1.829 meters statute miles (mi) 1.609 kilometers nautical miles (nmi) i ,852 kilometers square feet (ft2) 0.0929 square meters square miles (mi2) 2.590 square kilometers acres 0.4047 hectares gallons (gal) 3.785 liters cubic feet (ft3) 0.02831 cubic meters acre-feet 1233.0 cubic meters ounces (02) 28350.0 milligrams ounces (02) 28.35 grams pounds (lb) 0.4536 kilograms pounds (lb) 0.00045 metric tons short tons (ton) 0.9072 metric tons

British thermal units (Etu) 0.2520 kilocalories Fahrenheit degrees (“F) 0.5556 (“F - 32) Celsius degrees

iv CONTENTS

Page

PREFACE ...... iii CONVERSION FACTORS ...... iv FIGURES ...... vii TABLES ...... viii ACKNOWLEDGMENTS ...... ix

CHAPTER 1. INTRODUCTION ...... 1

Seagrass Ecosystems ...... :*: The Seagrasses of the West Coast of Florida ...... 1:3 Physical Environment ...... Geologic Environment ...... ::: Succession and Ecosystem Development ......

CHAPTER 2 AUTECOLOGY OF FLORIDA GULF COAST SEAGRASSES ...... 11

2.1 Plant Morphology and Growth ...... Reproduction ...... :2' z Plant Constituents ...... 14 214 Physiological Ecology ...... 2.4.1 Environmental Tolerances and Responses ...... ;: 2.4.2 Photosynthetic Carbon Fixation ...... 23 2.4.3 Isotopic Fractionation ...... 23 2.5 Nutrient Uptake and Supply ...... 24

CHAPTER 3 DISTRIBUTION, BIOMASS, AND PRODUCTIVITY ...... 27

3.1 Distribution ...... 27 3.1.1 Seagrass Distribution in Tampa Bay ...... 27 3.1.2 Seagrass Distribution in the Big Bend Area ...... 29 3.2 Biomass ...... 34 3.2.1 Seagrass Biomass in Tampa Bay ...... 3.2.2 Seagrass Biomass in the Big Bend Area ...... :: 3.3 Productivity ...... 37 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 ...... 40

4.1 Algal Associates ...... 4.1.1 Phytoplankton ...... t; 4.1.2 Benthic Algae ...... 4.1.3 Epiphytic Algae ...... t: 4.2 Invertebrates ...... 46 4.3 Fishes ...... 48

V Page

4.4 Reptiles ...... 53 4.5 Birds ...... 53 4.6 Mammals ...... 54

CHAPTER 5. STRUCTURAL AND FUNCTIONAL RELATIONSHIPS IN SEAGRASS SYSTEMS...... 58

5.1 The Relationship of Structure, Shelter, and Predation ...... 58 5.1.1 Fauna1 Abundance and Structure ...... 58 5.1.2 Structure and Predation ...... 60 5.1.3 Fauna1 Sampling: The Problems of Gear and Technique ...... 66 5.2 General Trophic Structure ...... 67 5.2.1 Seagrass Grazers ...... 68 5.2.2 Epiphyte Seagrass Complex ...... 70 5.2.3 Detrital Feeding ...... 70 5.2.4 Carnivory ...... 71 5.2.5 Trophies and Ontogenetic Development of Grassbed Fishes ...... 72 5.3 Decomposition and Detrital Processing ...... 72

CHAPTER 6 INTERFACES WITH OTHER SYSTEMS ...... 77

6.1 Salt Marsh and Mangrove ...... 77 6.2 Gulf Reefs ...... 79 6.3 Continental Shelf ...... 81 6.4 Export of Seagrass ...... 83 6.5 Nursery Grounds ...... 84 6.5.1 Blue Crabs ...... 84 6.5.2 Shrimp ...... 85 6.5.3 Fish...... ~ ...... 86 6.5.4 Detached Macrophytes as Nursery Habitat ...... 86

CHAPTER 7. HUMAN IMPACTS AND APPLIED ECOLOGY ...... 88

7.1 Dredging, Filling, and Other Physical Damage ...... 88 7.1.1 Acute Stress ...... 88 7.1.2 Other Physical Damage ...... 90 7.1.3 Chronic Effects ...... 91 7.2 Eutrophication and Sewage ...... 91 7.3 Oil ...... 91 7.4 Temperature and Salinity ...... 93 7.5 Paper Mill Effluents ...... 95 7.6 Disturbance, Recolonization, and Restoration ...... 95 7.6.1 Disturbance ...... 95 7.6.2 Recolonization ...... 96 7.6.3 Restoration ...... 99 7.7 Final Thoughts ...... 101

REFERENCES..... SpECIEj.;;kVEVs.IN.SbUjH'ANb'WESiikN'iib~~~~:::::::::::::::::::::: 103 APPENDIX: FISH 131

vi FIGURES

Number Page

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 17 Distribution and diversity of benthic marine plants in the Gulf of Mexico ...... 42 18 Representative temperate (Carolinean) invertebrate communities ...... 47 19 Representative tropical (West Indian) invertebrate communities ...... 48 20 Comparison of fauna1 abundance between seagrass beds and adjacent habitats ...... 58 21 Salt-marsh zonation in Florida ...... 79 22 Life histories of spotted sea trout and snook on the west Florida coast ...... 80 23 Fauna1 zonation of west Florida shelf ...... 82 24 Eastern Gulf of Mexico current patterns during summer ...... 83 Blue crab spawning migrations and larval transport ...... 85 Z Channel through grassbed with open-water dredge disposal area in Tampa Bay ...... 89 27 Dredged and filled areas in Boca Ciega Bay ...... 90 28 Crystal River power plant ...... 93

vii TABLES

Number Page

1 Precipitation statistics for gulf coast stations ...... 2 Sediment characteristics of the west coast of Florida ...... ! 3 Constituents of seagrasses ...... 15 4 Seasonal changes in protein and carbohydrates in seagrasses in Tampa Bay ..... 18 Representative values of seagrass biomass ...... 35 z Biomass partitioning in seagrasses ...... 36 7 Seagrass biomass in Tampa Bay area ...... 36 8 Representative values of seagrass productivity ...... 37 9 Macroalgae of seagrass communities of west Florida ...... 43 Algal epiphytes of the seagrasses of Florida ...... 1': Fishes of Apalachee Bay...... ::: :; 12 Seagrass-associated fish families ...... 13 Seagrass and wetlands associated birds of the Florida west coast::::::::::::: z: 14 Comparative abundance of organisms in seagrass and sand habitats ...... 59 15 Influence of seagrass community structure on fauna1 abundance ...... 61 16 Wetlands acreage on the west Florida coast ...... 77 17 Historic human impact on Florida seagrass meadows...... :::::::: 1 97 18 Seagrass damage and restoration assessment ...... 99 19 Success of seagrass restoration techniques ...... 100

. . . VIII ACKNOWLEDGMENTS

The production of this manuscript turned production. We especially thank him for his into a much larger project than was patience in the face of numerous envisioned when we began. During that time, unanticipated delays. many people contributed greatly towards the production of the final product. The Critical comments and reviews were made authors are especially grateful to Richard by Ron Phillips, Robin Lewis, Mike Durako, L. Iverson who contributed both written Laura Gabanski, Cheryl Vaughn, Charles Hill, material and numerous published and Robert Rogers, David Moran, Ed Pendleton, unpublished figures for Chapters 2 and 3. and Lorna Sicarello. Robin Lewis and Mike Durako also thoughtfully provided several We wish to give special thanks to our illustrative photographs. project officer, Edward C. Pendleton, who has been unusually conscientious throughout Sue Lauritzen did the layout and Daisy all aspects of the project, starting with Singleton and Joyce Rodberg keyboarded the the outline and continuing to the final final draft.

ix

CHAPTER 1. INTRODUCTION

1 .l SEAGRASS ECOSYSTEMS addresses the west and northwest coast of Florida, the area of central interest for Seagrass meadows are recognized today as this community profile is the region from one of the most important communities in Tampa Bay to Apalachicola Bay (Figure 1). shallow coastal waters. Rapidly growing This region contains the large offshore seagrass leaves serve as the basis of a beds of the Big Bend area, as well as productive grazing and detrital food web, several representative estuarine systems. while the canopy structure formed by these It is largely defined by the available leaves offers shelter and protection from data base for the Florida west coast. predation for innumerable small organisms, many of which are the juveniles of Compared with seagrass meadows in important commercial species. The coastal southern Florida, communities of western waters of Florida are especially rich in Florida and the northeastern Gulf of seagrass resources. The two largest Mexico have received little attention from seagrass meadows in Florida have received the research community; therefore, this little human disturbance thus far. The community profile will refer to data from largest, in Florida Bay, is approximately south Florida and the Caribbean when 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. Apalachicolo From old maps and aerial photographs they BQY estimated the historical coverage to be nearly 31,000 ha, thus showing a reduction to less than 20% of the historical coverage. GULF OF The coastline of western Florida is a MEXICO 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 Figure 1. Location map of Florida.

1 comparable studies from western Florida do (Zieman 1982) of the earlier conceptual not exist. Interestingly, the west coast framework. area was the location of the seminal seagrass studies of Florida, in 1. High Production and Growth particular, and the Southeast, in general. The ability of seagrasses to exert a This work culminated in the monograph on major influence on the marine seascape the seagrasses of Florida by Ronald C. is due in large part to their Phillips published in 1960. Within the extremely rapid growth and high net past 10 years, research on these systems productivity. The leaves grow at has accelerated in the bays and estuaries rates of typically 5 mm per day, but of north Florida and in central Florida; growth rates of over 10 mm per day are however, less work has been done on the not uncommon under favorable large offshore bed between these two circumstances. regions. This extensive seagrass meadow is unique among Florida's seagrass 2. Food and Feeding Pathways resources since it is truly offshore, and The photosynthetically fixed energy does not lie behind any form of protective from the seagrasses may follow two barrier. general pathways: direct grazing of organisms on the living plant material Seagrass ecosystems are among the or utilization of detritus from richest, most productive, and most decaying seagrass material, primarily important of all coastal systems. They leaves. The export of seagrass are also paradoxical in nature-- material, both living and detrital, to simultaneously simple and complex. They a location some distance from the are simple in that there are few species seagrass bed allows for further of seagrasses, unique marine angiosperms distribution of energy away from its that live and carry out their life cycle original source. in seawater. Vast and extensive undersea meadows stretching for hundreds of 3. Shelter kilometers may be composed of only one to Seagrass beds serve as a nursery perhaps four species. The ecosystems, ground, that is, a place of both food however, are complex ,because there are and shelter, for the juveniles of a hundreds to thousands of species of variety of finfish and shellfish of associated flora and fauna that inhabit commercial and sportfishing the seagrass meadows and utilize the food, importance. substrate, and shelter provided by the plants. 4. Habitat Stabilization Seagrasses stabilize the sediments The pioneering work of Petersen (1918) in two ways: the leaves slow and in the Baltic region provided the first retard current flow to reduce water documentation of the value of seagrass velocity near the sediment-water beds to shallow coastal ecosystems. These interface, which promotes studies demonstrated how the primary sedimentation of particles as well as production from these plants was channeled inhibiting resuspension of both through the detrital food web and organic and inorganic material. supported the rich commercial fisheries of Secondly, roots and rhizomes form a the region. Despite the thoroughness and complex, interlocking matrix with quality of Petersen's work, only in the which to bind the sediment and retard past two decades have the richness and erosion. value of seagrass ecosystems begun to be realized (Wood et al. 1969; McRoy and 5. Nutrient Effects McMillan 1977; Zieman and Wetzel 1980). The production of detritus and the The first conceptualization of the promotion of sedimentation by the functions of seagrasses was provided by leaves of seagrasses provide organic Wood et al. (1969). The generalizations matter for the sediments and maintain have now been shown to be applicable to a an active environment for nutrient wide variety of systems and situations. recycling. Epiphytic algae on the The following is an updated version leaves of seagrasses have been shown

2 to fix nitrogen, thus adding to the approximately 45 species. The nutrient pool of the region. In Potamogetonaceae include 9 genera and 34 addition, seagrasses have been shown species and are represented on the west to take up nutrients from the coast of Florida by Syringodium filiforme sediments, transporting them through Kutz, whose common name is manatee grass, the plant and releasing the nutrients and Halodule wrightii Ascherson, shoal into the water column through the grass; the Hydrocharitaceae contains 3 leaves, thus acting as a nutrient genera with 11 species (Phillips 1978), of pump. which Thalassia testudinum Konig, (turtle grass), and two species of Halophila, H. In addition to providing habitat and engelmanni Acherson and H. decipiens shelter, the seagrass leaves are a major Ostenfeld, are found in the waters of the food resource in coastal ecosystems, west coast of Florida. Ruppia maritima functioning through three major pathways: Linneaus (widgeon or ditch grass) direct herbivory, detrital food webs, and euryhaline angiosperm found abundantly in export to adjacent ecosystems. Direct fresh waters and in the marine environment herbivory on green seagrass leaves is grows primarily in lower salinity areas. confined to a small number of species and is most prevalent in tropical and The small number of species occurring in subtropical regions, especially in the these waters, and their distinctive gross vicinity of coral reefs. Since the time morphologies (Figure 2) preclude the need of Petersen (1918), the detrital food web for a dichotomous key, although systematic has been considered the main trophic works such as den Hartog (1970) and pathway in seagrass meadows, and current Tomlinson (1980) are available for studies continue to support this concept, comparison of seagrasses in other areas. although direct herbivory can be locally Phillips (1960a) still provides the best important in some areas (Zieman et al. treatment of local species. 1984a; Thayer et al. 1984). In addition to the internal utilization of seagrasses The three dominant species of the open as a food source, many beds, especially coastal waters are Thalassia testudinum, those dominated by Syringodium, export Syringodium filiforme, and Halodule large quantities of organic material to wrightii. other distant ecosystems. Thalassia is the largest and most robust In the subtropical waters of south of the west Florida seaarasses. and the Florida, seagrass meadows often bridge densest growth in the vast" grassded of the large areas between the mangrove and coral Big Bend area is dominated by a mixture of reef communities, while also serving as a this species and Syringodium (Iverson and primary nursery and feeding ground Bittaker 1986). While this species is not themselves (Zieman 1982). On the west abundant in the lower salinity waters of coast of Florida, they function in a Tampa Bay (Lewis et al. 1985a), it is the similar manner, as nurseries and feeding dominant seagrass in the adjacent waters grounds, but also serve as an interface of Boca Ciega Bay (Taylor and Saloman between the coastal salt marsh communities 1968; Bauersfeld et al. 1969), and in the and offshore habitats of the eastern Gulf Tarpon Springs area (Phillips 1960a). of Mexico. Among the local seagrasses, Syringodium is distinctive in having cylindrical leaves which are quite brittle and 1.2 THESEAGRASSESOFTHEWESTCOASTOF buoyant, and thus are readily broken off FLORIDA and exported from the immediate area by winds and currents. This species is more Seagrasses compose the relatively small widely distributed in Tampa Bay than is group of monocots which have evolved the Thalassia (Phillips 1960a; Lewis et al. ability to carry out their life cycle -and while it is codominant in the completely submerged in the marine Big Bend grassbed, its biomass is environment. Worldwide, they include 2 generally lower than that of Thalassia in families divided into 12 genera and 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 exposure to the atmosphere. In the Big abundant. Bend grassbed, this plant often forms both the shallowest shoreward fringe of and the Halodule, which has narrow leaves and a deepest, outermost stands of seagrass, and shmot system, is recognized as the exhibits different morphologies in the two pioneer species in the successional zones (Phillips 1960b; McMillan 1978; development of grassbeds in the gulf and R.L. Iverson, unpubl. data). Caribbean. It is more tolerant of low salinity than both Thalassia and and thus occurs in areas of 1.3 PHYSICAL ENVIRONMENT Fyampa Bay where those seagrasses cannot survive (Phillips 1960a; Lewis et al. The west coast of Florida has a mild 1985a). As its common name, shoal grass, maritime climate varying from temperate in indicates, it is often found in shallow the north to semitropical * waters where it is subjected to repeated the southernmost regions. For much':f the

4 year the southern portion of Florida is January average temperature of 13.5 'C dominated by the southeasterly trade with a range of 4-22 OC. winds, while the airflow in the northern and central portion is from the west, Earle (1969) found a similar pattern under the influence of the westerlies and with inshore gulf temperatures of 13-15 OC accompanying cyclones (counterclockwise in the north and 22.6-22.9 OC in the circulation about a center of low Florida Keys. However, north of Cedar pressure) in the winter, and the western Key, extreme winter lows of O-5 OC have margin of the Bermuda-Azores anticyclone been recorded. The average winter (clockwise circulation about a center of temperatures in the northern gulf in high pressure) in summer. winter are similar to the summer high temperatures in New England, and Earle The resulting differences in temperature (1969) noted that many winter species in patterns are evident in Figure 3, which the northern gulf are the same as the shows the average monthly water summer species in New England waters. temperatures at several locations from Pensacola to Key West (McNulty et al. Precipitation generally increases 1972). The Cedar Key station is in the northward and westward along the Florida center of the region under consideration coast from a low of 100 cm annually at Key here. Both the average and maximum summer West to 163 cm at Pensacola (Table 1). temperatures vary little among the However, in the region from Tampa to stations, with highs around 33 OC. Most Apalachicola the precipitation is obvious are the lower winter temperatures relatively uniform with a minimum annually and greater seasonal range at the northern of 118 cm at Cedar Key to a maximum of 140 stations. Key West has a monthly low cm at Apalachicola with about half of the average of 22 OC and a range of 14-26 OC annual amount falling between June and during January, while Cedar Key has a 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 force of storm waves. In 1985, two extreme months and years are highly hurricanes, "Kate" and "Elena" passed variable and can have severe effects on directly through the area causing the local biota. For Cedar Key, annual localized disruption and bottom scouring. rainfall has varied between 68-208 cm, Qualitative observations of stations while monthly values at Apalachicola have sampled before and after the hurricanes varied from a low of 0.03 cm to a high of suqqested complete recovery of the denser 57 cm. inshore beds' of Thalassia, Syringodium, and Halodule and the sparse offshore In the shallow waters of the estuaries Halophila beds in the vicinity of Tarpon and the inshore gulf, water temperature Sorinas (Continental Shelf Associates and salinity are locally affected by both 1986): In the vicinity of Cedar Key, seasonal and isolated storms. The most where Hurricane "Elena" stalled for about severe storms are tropical hurricanes with 48 hours, seagrasses appeared to be their high winds, heavy rainfall, and recovering, but at a slower rate than the often devastating storm surges. other site. Hurricanes occur most frequently in the late summer months when the oceanic Tidal ranges are low to moderate along surface temperatures are at their highest, most of the Florida west coast. From but can occur in any month. The Florida Bay northward to St. Joseph Bay probability of encountering hurricane the tides are predominately semi-diurnal force winds in any one year varies greatly (McNulty et al. 1972), shifting to diurnal along the Florida coast, being 1 in 8 at west of this point. Throughout the entire Key West and Pensacola, 1 in 17 at area, the mean diurnal range is 0.5-1.1 m. Apalachicola and St. Marks, and 1 in 25 at Daily ranges at Tampa Bay are 0.6-0.8 m. Tampa-St. Petersburg (Bradley 1972). In Just north of Tampa Bay, the range addition to the immediate local effects of increases to 1.1 m until Apalachee Bay these storms, water quality is affected where it begins to decrease slightly and following their passage by greatly reaches 0.4-0.7 m at Apalachicola Bay. increased runoff from rivers and streams, accompanied by increased turbidity and Offshore circulation is dominated by two biochemical oxygen demand. large counter-rotating gyres. The northern one is influenced by coastal In most locations, seagrass beds are estuarine waters, while the southern one relatively protected from the surges of is influenced by waters from Florida Bay. large storms. However, in the Big Bend of In addition, there are periodic incursions Florida these beds are subject to the full of the loop current with waters from the

6 tropical Caribbean and the Yucutan Channel primarily elastic sediments. Table 2 (Chew 1955; Austin 1970). gives the characteristics of sediments for several locations on the west Florida coast. 1.4 GEOLOGIC ENVIRONMENT The coastline of west Florida has been The present Florida peninsula is the divided and classified (Figure 4) emergent portion of the Floridan Plateau, according to several different criteria consisting of layers of limestone and and schemes, including coastal beach and unconsolidated sediments over a base of interface characteristics (Price 1954; sandstone and volcanic rocks (Puri and Tanner 1960; McNulty et al. 1972), fauna1 Vernon 1959; NcNulty et al. 1972). The community affinities (Lyons and Collard limestone and ancient sediments are at 1974), and underlying substrates and least 1,000 m in thickness over the entire outcrops (Brooks 1973). The coastal region. The rivers that. enter the gulf divisions resulting from these differing east of Apalachicola Bay drain the coastal schemes are very highly correlated, and plain, carrying small amounts of sediments the divisions used in this paper are a that are primarily carbonates and combination of the above schemes. anhydrites (McNulty et al. 1972). From Apalachicola Bay westward, the rivers The coastline west of Lighthouse Point, drain areas of the Piedmont plateau and near Apalachicola Bay, is the northern the Appalachian highlands, and carry 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 Average = 2.1% west up to 90% Median size east = 0.025mm (Quartz 3.5% east, west = 0.028mm up to 30%) W = 70% silt, 30% sand

Whitewater Up to 65% Bay (quartz 5%-10%)

Gullivan Bay 1% on shelf lo%-40% typically Non CaCOs = fine to very (very open) l%-4% in lagoon Locally to 60%-80% fine sand Quartz 4%-8% near islands maximum = 24%

Port Charlotte O.l%-1.0% Very fine to fine sand Harbor maximum = 3.1% -_

Tampa Bay 0.5%-40% Variable, typically sand sized

Apalachicola 0.5%-2.0% lO%-40% Variable, very coarse Bay sand to clay

St. Joseph 0.5%-4.5% lo%-80% Variable, very coarse Bay sand and gravel to clay

Pensacola Bay __ 1.3%-5% 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).

beaches alternating with barrier islands. that they carry little suspended elastic A similar attached beach-barrier island material to form beaches or barrier interface exists from Anclote Key islands (Ross 1973) such as those found to 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 is that central and lower peninsula, the barrier the_ . region between St. Marks ant II Tarpon beaches and spits enclose the major Springs is one of the few examples estuaries and lagoons. However, the Big world-wide of a zero-energy coastline Bend, the upper coastline of the (Murali 1982). This is defined as a coast peninsula, is unique for the region in where "the average breaker heights are that it is an extensive area with no 3-4 cm or less, and there is no signi- offshore barrier, where rivers, creeks, ficant littoral transport of sand" (Murali and marshes grade directly into the 1982). The major factors that contribute eastern Gulf of Mexico. A number of to this phenomenon include the wide, physical, geological, and hydrological gently sloping shelf; the divergence of features interact to produce this effect. approaching wave trains into the large, The rivers of the Big Bend are notable in expanding coastal concavity; the location

8 of the coast in a generally upwind direc- is no other organism that can sustain and tion; a small supply of new sediment; and support the system. the wave dampening effects of old sub- merged beaches and the submerged seagrass The initial colonizers are typically meadows (Murali 1982). Although the rhizophytic macroalgae, of which various presence of submerged seagrass meadows species of Halimeda and Penicillus are the interfacing directly with salt marshes most common, although species of Caulerpa, has been considered to be a contributing Udotea, Rhipocephalus, and Avrainvilla factor to the zero-energy coast, it is occur also. These algae have some more likely that their presence in this sediment binding capability, but their area is in fact the result of existing low ability to stabilize the sediments is energy conditions, as seagrass beds are minimal and their major function in the rare on open oceanic, unprotected coasts. early successional stage seems to be the Once established, the seagrass beds could contribution of sedimentary particles as enhance the effects of those primary they die and decompose. factors responsible for reduced energy conditions. Halodule wrightii, the local pioneer species of seagrasses, colonizes readily either from seed or rapid vegetative branching. The carpet laid by Halodule 1.5 SUCCESSIONANDECOSYSTEM DEVELOPMENT further stabilizes the sediment surface; the numerous leaves forming a better Throughout their range, few plants buffer to protect the integrity of the participate in the successional sequence sediment surface than the algal leading to seagrasses because there are so communities. In some sequences few marine plants that can colonize soft Syringodium will appear next, intermixed sediments. In general, this sequence with Halodule at one edge of its consists only of the seagrasses and the distribution and Thalassia at the other. rhizophytic green algae. Seagrasses are However, it is the least constant member vital to the coastal ecosystem because of this sequence and is frequently absent. they are the only plants capable of In areas with consistent disturbance and providing the basis for a mature, sediments low . content productive ecosystem in these regions. Syringodium may ber:me %Fniist abundant Few other systems are so dominated and species. It is commonly found lining controlled by a single species as a climax natural channels with hiqh velocity waters Thalassia or Zostera meadow. and higher turbidity than Thalaisia can tolerate. Odum (1974) classified Thalassia beds as "natural tropical ecosystems with high As successional development proceeds, diversity." Compared to other natural Thalassia will begin to colonize the systems, tropical seagrass beds are region. Its strong straplike leaves and regions of very high diversity, but this massive rhizome and root system can be misleading. These comparisons were efficiently trap and retain particles, made at a time when high diversity was increasing the organic matter of the equated with high biological stability. sediment. The sediment height rises until The prevailing concept was that the the rate of deposition and erosion of multitude of different organisms, with sediment particles is in balance. This is their widely differing requirements and a function of the intensity of wave interactions, functioned as a highly action, current velocity, and leaf intricate web structure that lessened the density. importance of each link to the maintenance of the total system. There was much In shallow-water successional sequences natural redundance built into such leading to Thalassia, the early stages are systems. The problem is that at climax often characterized by low sediment there is one species for which there is no organic matter and open nutrient supply; redundancy - the seagrass. If the that is, the community relies on nutrients seagrass disappears, the entire associated brought in from adjacent areas by water community disappears along with it; there movement as opposed to in--situ

9 regeneration. With the progression from provides an increase in surface area for rhizophytic algae to Thalassia, there is a the colonization of epiphytic algae and progressive increase in the below ground fauna, with the surface area of the climax biomass of the community as well as the community being many times that of either portion exposed in the water column. With the pioneer seagrass, Halodule, or the the progressive increase in leaf area of initial algal colonizers. In addition to the plants, the sediment trapping and providing a substrate, the increasing leaf particle retention increases. This area also increases the leaf baffling and material adds organic matter to further sediment trapping effects. Thus, as the fuel the sedimentary microbial cycles. canopy component increases, so does the material in the sediment. Thalassia, the In summary, as species succession occurs climax species, has the highest leaf area, in these shallow marine systems, important the highest total biomass, and by far the structural changes occur. The most greatest amount of material in the obvious change with community development sediments of any of the successional is the increase in leaf area, which stages.

10 CHAPTER 2. AUTECOLOGY OF FLORIDA GULF COAST SEAGRASSES

2.1 PLANT MORPHOLOGY AND GROWTH in areas of relatively low productivity in Biscayne Bay, Florida, averaged 3.3 leaves Seagrasses worldwide show a remakable per short shoot, while in the more similarity in their structure and growth productive meadows of the Florida Keys, (den Hartog 1970; Zieman and Wetzel 1980). plants averaged 3.7 leaves per short shoot For the seagrasses of the northwest coast (Zieman 1975a). The width of leaves of Florida, we shall focus primarily on increased with age of the short shoot, the growth and morphology of Thalassia, reaching maximum width five to seven considering this as representative of the shoots back from the growing rhizome tip local species. (Figure 5). Leaf width can also reflect morphogeographic variation: in Florida, Detailed descriptions of the anatomy and Durako and Moffler (1981) identified the morphology of Thalassia were presented by effects of a latitudinal stress gradient Tomlinson and -966) and Tomlinson in leaves of Thalassia seedlings, with the (1969a, 1969b, 1972). Flat, straplike greatest widths occurring in the Keys and leaves with rounded tips emerge from erect the narrowest leaves found in northern short shoots which branch laterally from Florida. In another study, leaf widths horizontal rhizomes at regular intervals. did not reflect a latitudinal or stress In this species rhizomes occur from 1 to gradient, but showed sexual differences: 25 cm below the sediment surface, but are female short shoots tended to have typically found in the depth range of narrower leaves than male shoots (Durako 3-10 cm. (The rhizomes of Halodule and and Moffler 1985a). Transplant Halo hila are near the surfamften exoeriments found that narrow-leaved & While the rhizomes of plants of Thalassia, Syringodium, and Syringodium are generally found at an Halodule from the north coast of the Gulf intermediate depth, in strong currents, of Mexico continued to produce narrow they may be exposed, even extending up leaves, and broader-leaved plants from the into the water column.) Roots of southern gulf and Caribbean likewise Thalassia emerge from the rhizomes and the continued to produce wider leaves, even short shoots. Much smaller in cross when moved to different habitats (McMillan section than rhizomes, the roots vary in 1978). length according to sediment composition and depth. Thalassia leaves in Biscayne Bay grew an average of 2.5 mm/day in length, but On a Thalassia short shoot, new leaves growth rates as high as 1 cm/day were grow on alternating sides of a central measured over periods of 15-20 days meristem that is enclosed by old leaf (Zieman 1975a). Leaf growth rate in sheaths. New growth on leaves is produced Thalassia usually decreases exponentially by the basal meristem, thus the base of a with leaf age (Patriquin 1973; Zieman leaf is the freshest, youngest portion. 1975a). In contrast, leaf elongation in Short shoots of this species typically Syringodium proceeded at a relatively have two to five leaves at a time. steady rate throughout the growth phase (Fry 1983). The first few leaves produced Studies of seagrass growth and on a new Thalassia short shoot are reduced morphology have revealed patterns of in size and are tapered; the regular temporal and spat ial variation. Grassbeds straplike leaves are produced at a rate of

11 AVERAGE LEAF WIDTH (MM)

85 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 variation was evident, with shorter leaves days. The rate of leaf production in occurring in the middle of the grassbed Biscayne Bay was dependent on temperature, where the water was shallower. with low growth occurring in the cooler winter months (Zieman 1975a). Less seasonal variation was found in the 2.2 REPRODUCTION tropical Caribbean waters of Barbados and Jamaica by Patriquin (1973) and Greenway Vegetative reproduction in seagrasses (1974) respectively. Durako and Moffler accounts for their capacity to produce (1981) found a gradient of root and leaf high biomass and area1 cover; however, growth in Thalassia seedlings, from high sexual reproduction is important in rates in the Florida Keys to low growth providing the genetic plasticity for rates in north Florida waters. successful adaptation and competition in the species. Studies of flower production In Tampa Bay, Durako and Moffler (1985c) in the seagrasses considered here have found pronounced seasonal patterns in focused primarily on Thalassia. This maximum leaf lengths of Thalassia. There plant is sexually dimorphic, producing was a slight decrease in the middle of separate male and female flowers. Grey summer, coincident with high temperatures and Moffler (1978) found that short shoots and floral production, but maximum lengths occurring on a common rhizome segment were much less in the cold winter months, produced flowers of the same sex, reflecting both leaf die-off and depressed suggesting that Thalassia is also growth rates due to exposure to low dioecious, that is, has separate male and temperatures. A pattern of spatial female plants.

12 Flower production in Florida populations fringes of the bed where short shoots are of Thalassia occurs from April to August generally younger, while more male plants or September, peaking in June (Orpurt and were found in the center on presumably Boral 1964; Grey and Moffler 1978) (Figure older short shoots. This pattern could 6). While Phillips (1960a) found no reflect an age-related sexual expression flowering north of Tarpon Springs, more in the plants, although environmental recent studies have revealed flowering in factors and clonal differences also can the grassbeds of the Florida panhandle influence leaf width (Durako and Moffler (Marmelstein et al. 1968; Phillips et al. 1985b). (Thalassia seed production in 1981). The percent of short shoots in a Tampa Bay was apparently low compared with grassbed bearing reproductive structures south Florida and probably could not varies greatly: less than I_% of plants provide an adequate supply for restoration from north Florida beds reproduced projects (Lewis and Phillips 1981). sexually, while reproductive densities in plants from south and central Florida Phillips (1960a) found flowering Ruppia ranged from l% to 15% (Phillips 1960a; abundant in Tampa Bay; however, he did not Orpurt and Boral 1964; Zieman 1975). More observe seedling germination. Flower and recently Moffler et al. (1981) found fruit production in Ruppia of this area reproductive densities of 44% in Tampa peak in May and disappear in June (Lewis Bay. A later study in Tampa Bay recorded et al. 1985a). Phillips (1960a) did not reproductive densities of 11.4%, 20.7%, find reproductive Halodule, Syringodium, and 10.0% for 1981, 1982, and 1983, or Halophila in Tampa Bay; however, respectively, and found that increased several reproductive specimens of Halodule numbers of male flowers accounted for the were later found in nearby waters (Lewis higher reproductive density of 1982 et al. 1985a). Although reproductive (Durako and Moffler 1985b). Spatial plants are rare in Syringodium, female density distributions showed higher plants have been collected in the bay numbers of female plants occurred on the (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 tropical forage grass (Vicente et al. flowering Syringodium plants in their 1980). Apalachee Bay samples in May, 1972. These authors also found numerous flowering Walsh and Grow (1972) found that plants of Ruppia in May and June. Thalassia protein content compared favorably with reported values for grain In 1 aboratory studies, cultures of crops: corn contained from 9.8% to 16% Thalassia, Syringodium, Halodule, and protein, sorghum 8.6% to 16.5%, and wheat Halophila engelmannii flowered under 8.3% to 12%. Various studies of the continuous light, suggesting that protein content of Thalassia leaves have flowering was independent of day length. yielded results ranging from a low of 3% The temperature range for flowering in of dry weight for unwashed epiphytized these plants was 22-26 OC (McMillan 1982). leaves (Dawes et al. 1979) to a maximum of Lewis et al. (1985a) also found that 29.7% for leaves rinsed with .distilled flower production in Thalassia was water (Walsh and Grow 1972). The low probably controlled by factors other than value for unwashed leaves reflects the photoperiod. inclusion of sea water salts, and possibly sediment particles which settle on leaves, into the total dry weight. Values more 2.3 PLANT CONSTITUENTS typically range between 10% and 15% of dry weight. Because of their high productivity and wide distribution, seagrasses are Dawes and Lawrence (1983) and Durako and recognized as a potentially important food Moffler (1985c) have reported spatial and source in shallow coastal marine systems. temporal variations of protein content. The fact that this abundant food source is In Tampa Bay values for Thalassia and subjected to relatively low levels of S rin odium varied from 8% to 22% and from direct grazing on the living plant *, respectively, with maximum material has prompted studies of the values occurrinq in the summer (Table 4). chemical constituents and relative food Thalassia leaves collected in July 1979 value of seagrasses. Various authors have from Tamna Bav. Kev West. and Glovers performed such constituent analyses for Reef, Belize,-' showed a significant the seagrasses considered here increase in protein content from Tampa to (Burkholder et al. 1959; Bauersfeld et al. Belize, even though the sites were similar 1969; Walsh and Grow 1972; Lowe and in depth, salinity, and temperature (Dawes Lawrence 1976; Bjorndal 1980; Dawes and and Lawrence 1983). If such a latitudinal Lawrence 1980; Vicente et al. 1980; Dawes trend holds, Thalassia from the Big Bend and Lawrence 1983). A summary of these area, for which constituent analyses have results is given in Table 3. Dawes and not been performed, could have even lower Lawrence (1980) noted that the differences protein content, and thus lower food in sample preparation and chemical value. Such a decrease in nutritional analyses employed make direct comparison value might be reflected in the results of of the data difficult, and subsequently Kitting et al. (1984), who found that proposed a procedure to standardize several seagrass "detritivores" in the analyses so that future data will be northern gulf actually derived most of comparable, making it possible to their nutrition from epiphytes. determine the effect of seasonal and other environmental changes on the chemical The new growth of the basal portions of content of the plants. leaves of Thalassia are higher in protein and lower in Inorganic content (Cawes and The relative amount of protein in the Lawrence 1980). The green turtle has been plant tissues has been used as a measure shown to exploit this fact in its pattern of the potential food value of tropical of grazing: a patch of seagrass is seagrasses. Comparative studies have initially cropped, with the upper older shown that turtle grass leaves are roughly portions of the leaves left to float away, equal in percent protein to phytoplankton and such patches are subsequently and Bermuda grass (Burkholder et al. 1959) maintained for a period of time by and 2 to 3 times higher than 10 species of repeated grazing (Bjorndal 1980). Thus,

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

Season/ % as Carbo- Energy Species Component date Referenced Ash 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 23.6 4.66 Walsh and mean %DW 24.5 (10.3-29.7) Grow 1972

January %DW 29 8 0.9 45 2.4 Dawes and April 37 9 4.0 50 3.0 Lawrence July 33 22 1.0 44 3.1 1980 October 44 13 220 41 2.6 Mean x 13 2.0 E 2.8

? %DW 47.3 11.0 0.7 38 Bauersfeld (unwashed) et al. 1969 %DW 24.8 13.0 0.5 35.6 (washed)

July- %DW 24.7 9.1 2.3 63.9 Lowe and August Lawrence 1976

January %DW 16.7 Bjorndal August 1980

17 Vicente et al. 1978

(Continued) Table 3. (Continued).

Season/ % as Carbo- Energy Species Component date Referenced Ash Protein Fat hydrates (kcal/g) Reference

Thalassia Rhizomes Annual %DW 23.8 5.8-12.2 4.88 Walsh and Grow 1972 mean %AFDW 11.0 72.1 Roots %DW 50.5 19.6 Bauersfeld et al. 24.1 15.0 1969

Photosynthesis January %DW 39 9 1.0 51 2.7 Dawes and Lawrence inactive part April 51 7 0.5 42 2.2 1980 of short shoot July 48 16 0.7 35 2.5 October 56 8 0.8 35 2.0 Mean 7E lo 0.8 a 2.4

Rhizomes January %DW 26 9 0.5 65 3.2 April 24 8 1.6 66 3.4 July 33 16 0.2 51 3.0 October 36 7 A11 56 2.8 Mean m i-0 0.9 m 3.1

Syringodium Leaves July- %DW 27.0 3.10 3.4 66.3 Lowe and Lawrence August 1976

Leaves January %DW 30 9 1.7 59 3.1 Dawes and Lawrence April 28 8 6.2 58 2.4 1980 July 33 13 4.0 50 3.2 October 32 13 1.8 53 3.1 Mean x ii 3.4 !Z 3.0

Short shoots January %DW 28 10 1.3 61 3.2 photosynthesis April 27 11 3.6 58 3.3 inactive July 31 14 0.9 54 3.1 parts October 41 11 1.1 47 2.6 Mean Z? Tz 1.7 !Z 3.1

(Continued) Table 3. (Concluded).

Season/ % as Carbo- Energy Species Component date Referenced Ash Protein Fat hydrates (kcal/g) Reference

Syringodium Rhizomes January %DW 16 9 1.0 74 3.6 April 18 5 4.7 72 3.7 July 17 12 0.1 71 3.6 October 19 6 0.5 75 3.5 Mean 18 8 1.6 73 3.6

Halodule Leaves January %DW 32 19 1.0 48 3.1 Dawes and Lawrence April 25 18 3.2 54 3.5 1980 July 25 19 1.2 55 3.3 October 26 14 1.4 59 3.3 Mean T T;s 1.7 55 3.3

Short shoots January %DW 25 5 1.1 69 3.2 photosynthesis April 29 9 3.5 59 3.0 inactive part July 36 8 0.8 55 2.9 October 34 9 A12 56 2.9 Mean Ti 8 1.7 60 3.0

Rhizomes January %DW 14 0.7 76 3.7 April 1.6 74 3.7 July 0.1 70 3.4 October 17 8 ;11 74 3.6 Mean i-G 8 0.9 T-4 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 9 22 13 Carbohydrate 6 9 9 7

Rhizomes Protein 9 8 16 7 Carbohydrate 12 21 24 36

Syringodium filiforme

Leaves Protein 9 8 13 13 Carbohydrate 22 16 18 20

Rhizomes Protein 9 5 12 16 Carbohydrate 36 38 50 46

Halodule wrightii

Leaves Protein 19 18 19 14 Carbohydrate 14 19 15 13

Rhizomes Protein 9 7 8 8 Carbohydrate 43 40 43 54

the turtles create a more energetically higher levels of soluble carbohydrates in and nutritionally rich food source, and, Thalassia rhizomes compared to the leaves. indeed, Zieman et al. (1984) found that In Tampa Bay, seasonal variation in the nitrogen content of leaves within soluble carbohydrate content occurred in turtle patches was similar to the content the rhizomes of both Thalassia and of the basal portions of ungrazed leaves Syringodium, reflecting production and and higher than the upper portions of storage of starch during summer and fall those leaves. (Dawes and Lawrence 1980). Mean values for the lipid content of Thalassia leaves The values reported for ash content of varied from 1.2% to 4.2%, and were Thalassia leaves range from 45% dry weight comparable to the "fat" content of for unwashed samples to a low of about 25% tropical terrestrial grasses. for samples rinsed in fresh water. Samples washed in ambient seawater contained 29%-44% ash (Dawes and Lawrence 2.4 PHYSIOLOGICAL ECOLOGY 1980). Thalassia rhizomes from the west coast of Florida had ash content 2.4.1 Environmental Tolerances significantly lower than did the leaves, and Responses with mean values ranging from 2l% to 26% dry weight (Dawes and Lawrence 1983). a. Temperature. The range of thermal Cell wall carbohydrates (cellulose, tolerance in tropical organisms is hemicellulose, and lignin) accounted for often about half that of their 45%-60% of the dry weight of turtle grass temperate counterparts. Although leaves (Bjorndal 1980; Vicente et al. the upper temperature limits are 1980). Dawes and Lawrence (1983) found similar, the tropical organisms have

18 reduced cold tolerance. McMillan In Texas waters, vigorous growth (1979) found a gradient of chill of Ruppia in the spring correlated tolerance in Florida seagrasses, with cool temperatures rather than with those from northern Florida lowered salinities (Pulich 1985). most tolerant of low temperatures Phillips (1960a) reported a and those of the Florida Keys least temperature range of 7-35 OC for tolerant. After growing in culture Ruppia in Tampa Bay; growth and for 22 months, Thalassia seedlings reproduction was highest with spring maintained their original pattern of temperatures, and decreased when chill tolerance: those from high summer temperatures were Apalachee Bay, Florida, showed less reached. In Texas, a similar pattern damage than seedlings from the of temperature response was evident Florida Keys and St. Croix. for Ruppia in a mixed stand with Halodule; in contrast, Halodule In the thermally impacted waters biomass at that site peaked in the of Anclote Estuary north of Tampa warmer summer months and declined in Bay, Barber and Behrens (1985) found the fall. Phillips (1960a) reported that maximal growth in Syringodium that Halodule in Tampa Bay suffered occurred between 23 and 29 OC, and winter leaf kill, even at sites between 23 and 31 OC in Thalassia which were always submerged. (Figure 7). In the cooler months, However, Halodule suffered little thermally impacted stations had leaf kill in Apalachee Bay, where higher productivities than did the minimum winter temperature was 9 non-impacted areas, but in the OC. This temperature was a new summer months, Syringodium minimum reDorted for HaloDhila productivity was depressed at the en elmanni (Zimmerman and Livingston warmer stations when the upper i!kijT thermal tolerance limit of this seagrass was exceeded. In Apalachee b. Salinity. Although the seagrasses Bay, Zimmerman and Livingston considered here are able to tolerate (1976b) found that Syringodium fluctuations in salinity, the tolerated lower temperatures than optimum concentration for growth Thalassia, which suffered leaf kill varies among the species. when temperatures fell below 15 OC. Experiments with transplanted Some defoliation of Thalassia also seagrasses showed that, of the occurred when summer temperatures species considered here, Halodule rose to 30 OC. had the broadest salinity tolerance,

Thalassia Syrinqodium 4.0 0

3.0

2.0

1.0

1 1 1 I IO 15 20 25 30 10 15 20 25 30 35 TEMPERATURE (“C) TEMPERATURE (“C)

Figure 7. Temperature responses of Thalassia and Syringodium on the west Florida coast (after Barber and Behrens 1985).

19 / -

Thalassia and Syringodium effects of high winds and tidal (==E;c$;;ea)t;eere intermediate, and surge (Thomas et al. 1961). most stenohaline. Ruppia sho;;im a wide tolerancz: According to Humm (I973), ranging freshwater Halophila does not tolerate reduced hypersaline conditions (McMillan salinities; however, Zimmerman and 1974). Evaluating the upper limits Livingston (1976b) found a bed of y. of salinity tolerance, McMillan and engelmanni off the mouth of the Mosely (1967) found that Halodule Econfina River, an area of (=Diplanthera) tolerated the highest relatively low salinity. salinities, surviving up to 80 ppt, addition, Earle (1972) report:: followed, in order, by Thalassia, Halophila occurring at depths Ruppia, and Syringodium, with ranging from intertidal to 13 m, and Halophila's relative tolerance Strawn (1961) found this species aoparentlv somewhere between mixed with Halodule and Ruppia on an Halodule -and Syringodium McMillan old oyster bar. Thus, it appears that tialophila may in fact be quite euryhaline. salinities was Ruppia, followed by Halodule, Thalassla, Syringodium Ruppia traditionally has been (=Cymodocea), and Halophila. While considered a brackish-water species both Ruppia and Halodule exhibit (Verhoeven 1975) and, indeed, among broad ranges of salinity tolerance, the seagrasses it alone can be the former is the only seagrass maintained in tap water (McMillan species, of this region capable of 1974). Phillips (1960a) reported surviving in freshwater. According that it occurred most frequently in to McMahan (1968), Halodule does not salinities below 25 ppt, which survive in salinities less than 3.5 correspond with the findings of ppt and has an optimum salinity of Zimmerman and Livingston (1976b). 44 ppt. In the Big Bend seagrass bed, Ruppia was observed growing near river mouths (R.L. Iverson, Forida State Thalassia and Syringodium do not University, Tallahassee; pers. grow in areas of low salinity in the comm.) However, Dawes (1974) found eastern Gulf of Mexico (Phillips it growing in areas of relatively 1960a), and were not reported in high but stable salinity in the areas with salinities less than lower portions of Tampa Bay. Ruppia about 17 ppt in the northern transplants survived in salinities seagrass bed (Zimmerman and up to 74 ppt (McMillan and Mosely Livingston 1976). Turtle grass can 1967); this species also grew in survive short periods of exposure to Texas waters at a site where extremes ranging from a low of 3.5 salinities averaged 25-32 ppt and at ppt (Sculthorpe 1967) to a maximum another site where hypersaline of 60 ppt (McMillan and Mosely conditions persisted for several 1967); however, significant leaf months (Pulich 1985). alsoRuppia loss frequently follows exposure to has been observed growing in salinity extremes. The optimum hypersaline waters in Florida Bay salinity reported for this seagrass (J. Fourqurean, Un iversity of ranges 24-35 ppt (Phillips 1960; Virginia, Charlottesville; pers. McMillan and Mosely 1967; Zieman comm.). Thus Ruppia also appears to 1975a). In turtle grass, maximum be quite euryhaline. photosynthetic activity occurred in fullstrength seawater, and decreased The oxygen contained in the linearly with decreasing salinity column of seagrass beds (Hammer 1968b). The effect of generally provides a supply adequate freshwater runoff following a to meet the respiratory demands of hurricane was considered more the plants themselves and associated damaging to seagrasses than the organisms. In Thalassia beds,

20 photosynthetic oxygen production can decrease in Thalassia biomass at be so high that bubbles escape from the limit of its depth distribution. the leaf margins in the late However, the maximum depth at which afternoon. The seagrasses are less seagrasses occur does indeed susceptible to low oxygen correlate with the available light concentrations than the animals of regime. Buesa (1975) reported the the grassbeds; nevertheless, leaf following depth maxima for the mortality and increased microbial seaarasses off the northwest coast activity coincided with lowered of _ Cuba: Thalassia 14 m; oxygen levels in Japanese Zostera Syringodium, 16.5 m; Halophila beds (Kikuchi 1980). Low 0s levels decipiens 24 .3 m; and Halophila do slow their rate of respiration, englemann;, 14. 4 m. and when internal O2 concentrations are lowered, the plant's rate of Of the visible light spectrum, the resgiration is controlled by longer red wavelengths are absorbed diffusion of oxygen from the water in the first few meters in both column. During the night, the clear and turbid waters. The clear respiratory demand of the seagrasses tropical waters of the Caribbean Sea and associated plant and animal are enriched in blue light, while in communities can lower concentrations turbid shallow waters, such as parts of the surrounding waters (Durako et of Florida Bay and coastal waters of al. 1982). In Puerto Rico (Odum et Texas, enrichment of green al. 1960) and in Florida and Texas wavelength occurs. In a study of (Odum and Wilson 1962) nighttime the effects of specific wavelengths oxygen concentrations were typically of light on seagrass photosynthesis, 4-7 mg 0s L-l, and a low of 2-3 mg Buesa (1975) found that Thalassia 02 L-l recorded on a calm night in responded best to red light-) August during an extreme low tide. and S rin odium grew best with blue wave-0 nm). Wiginton and d. TheLight. fact that well-developed McMillan (1979) reported increasing seaarass beds do not occur at depths chlorophyll a to chlorophyll b greater than 10 m has been ratios for seagrasses obtained from considered indirect evidence that increasing depths near Buck Island, photosynthesis in seagrasses St. Croix, but concluded that light requires high light intensity, and quantity rather than light quality that light penetration limits the was the primary environmental depth to which seagrasses can grow determinant of seagrass depth (Humm 1956; Buesa 1975; Wiginton and distribution along the Buck Island McMillan 1979). Gessner and Hammer gradient. Thalassia growing in (1961) suggested that increased outer Florida Bay has considerably hydrostatic pressure, as well as more non-photosynthetic tissue than decreased light, may limit photosynthesis suggesting that light is probably not the sole factor compensation light-energy level restricting photosynthesis at depth; (below which annual net increase of however, there were no significant total plant biomass cannot occur) pressure effects on photosynthetic for Thalassia growing in tropical rates of Thalassia and Syringodium habitats is less than the for plants collected from various compensation light energy level for depths near Buck Island, St. Croix, Syringodium and for Halodule as a and subjected to 1 and 3 atmospheres conseauence of the respiratory of pressure (R.L. Iverson, demands created by the 'greatei Department of Oceanography, Florida orooortion of nonohotosvnthetic State University; unpubl. data). It tissue mass of Thalassia

21 high turbidity. Phillips (1960a) 1981). Thalassia is more robust, also noted the growth of this reauirina up to 50 cm of sediment species in areas of poor light for lush-growth, although it occurs penetration. shallower sediments (Zieman in addition to!%$!$%ng~~ G72). In the Bahamas, Thalassia light of deeper waters also grows in did not occur in sediments less than areas of high turbidity (Zimmerman 7 cm deep (Scoffin 1970). Phillips and Livingston 1976b). (1962) reported that seagrasses in Tampa Bay grew only in muddy sand e. Current. Seagrass biomass and substrates, and patches of pure sand production are greatly influenced by were unvegetated. current velocity (Conover 1968). The maximum standing crops for both Reduced sediments seem always to Thalassia and Zostera were found be associated with well-developed where current velocities averaged Thalassia beds and most likely 0.5 m set-l. Rapid currents are reflect the greater importance of thought to disrupt diffusion sediment-nutrient content and gradients and increase the microbial nutrient recycling in availability of CO2 and nutrients to meadows of this species, rather than the plants (Conover 1968). In south a specific requirement for reducing Florida, the densest stands of conditions. Halodule is generally Thalassia and Syringodium are found thought to grow in more aerobic in the tidal channels separating substrates; however, Pulfch (1985), mangrove islands. Off the coast of working in Texas waters, postulated Nicaragua, samples from mangrove that Ruppia normally occurs in tidal channels had a leaf standing low-nutrient sediments while crop of 262 g dry weight m-2 and Halodule prefers organic-rich total biomass of 4,570 g m-2. By sediments where sulfate reduction is comparison, values for samples from substantial. Phillips (1960a) a quiescent lagoon were 185 and reported that Syringodium 1,033 g m-2 respectively (McRoy, distribution was apparently Zieman, and Ogden, unpubl. data). independent of sediment type and this species is found in both Strong currents can affect the oxidized and reduced sediments structure of seagrass beds. In some (Patriquin and Knowles 1972). areas of high current, lunate Ruppia is generally found in finer features called blowouts occur substrates than the above species (Patriquin 1975). These (Phillips 1960a), while Halophila crescent-shaped erosional features grows in a wide range of substrates migrate through the bed in the from muddy sands to limestone, and direction of the current. even on mangrove roots (Earle 1972). Recolonization takes place at the trailing edge of the blowout, and In the Big Bend area of the west here the successional sequence of coast of Florida, Iverson and seagrass colonization can be Bittaker (1986) also recorded observed. Thalassia growing in coarser sediments than the other species of f. Sediment. Seagrasses are found in a that northern grassbed. Syringodium variety of substrates, ranging in and Halodule biomass were greater in texture from fine muds to coarse fine sediments (Iverson and Bittaker sands. Because they are rooted 1986). Similarly, Buesa (1975) plants, they do have minimum found that Thalassia off the sediment-depth requirements, which northwest coast of Cuba grew in differ among the species. coarser sediments than Syringodium Halodule's shallow surficial root or Halophila. system allows it to colonize thin sediments in areas of minimal g. Exposure. Thalassia and Syringodium hydraulic stability (Fonseca et al. are subtidal plants and do not

22 tolerate exposure to the air. While high productivity rates. Although Thalassia does grow on flats that Thalassia was originally thought to be a are infrequently exposed, unless C, plant, Beer and Wetzel (1982), using such exposure is brief, desiccation radiolabel led HCOm3, concluded that both will cause leaf kill. Halodule can this seagrass and Halodule were withstand repeated exposure at low intermediaries between Cs and C4 in their tide, and is most abundant between carbon metabolism. Syringodium and neap-low and spring-low tide marks Zostera exhibited the most typically Cs higher salinities (Phillips pattern of the seagrasses studied. iG6Oa). In low-salinity intertidal areas, Ruppia and Halodule often 2.4.3 Isotopic Fractionation occur in mixed stands (Phillips 1962; Earle 1972). Dawes (1987) A significant result of the differences noted that Ruppia forms extensive in carbon metabolic pathways is that meadows on flats where it can be imprints are left in the form of exposed to intense sun and appears characteristic ratios of the stable to tolerate a degree of desiccation. isotopes of carbon in the plant tissues produced. In biochemical reactions, 2.4.2 Photosynthetic Carbon Fixation plants do not utilize 12C and 13C in the exact ratios found in the environment, Three separate biochemical pathways by but discriminate between the two, which plants can fix inorganic carbon favoring the lighter isotope. Plants photosynthetically have been identified. using the C3 pathway are relatively The majority of terrestrial plants depleted in 13C, while C4 plants have utilize the Cs pathway, in which CO2 is higher ratios of l3C to l2C. The initially incorporated into a three- relative content of 1% to 12C is carbon product. In the C, pathway, found compared to the isotopic ratio of a primarily in plants from tropical and standard and expressed as a "del" value arid areas, a four-carbon product results (6) as follows: from the first step of CO;! incorpora- tion. The third pathway, CAM (crassula- 13C/l2C cean acid metabolism), by which plants (513c, sample lx103 take up CO:! at night and store it as 13c/12c standard malic acid until daytime when it is then used in photosynthesis, occurs in water- The range of 613C values for Cs plants stressed plants such as desert succu- is -24 to -34 ppt, while C4 plants vary lents. A major factor in the differences from -6 to -9 ppt (Smith and Epstein of photosynthetic physiology between Cs 1971). Seagrass values, particularly and C4 is the greater efficiency of those of Thalassia and Syringodium, are refixation of photorespired CO2 found in similar to those of the C4 plants. the C, plants (Hough 1974; Moffler et al. McMillan et al. (1980) reported that 45 1981). High rates of refixation have of 47 species examined fell within the been detected, however, in some Cs plants range of -3 to -19 ppt, with only two with specialized leaf anatomy and gas species of Halophila having lower values. lacunae (Sondergaard and Wetzel 1980) and Samples of Thalassia from the Gulf of may be implicated in seagrass carbon Mexico and the Caribbean range from -8.3 metabolism (Beer and Wetzel 1982). Sea- to -12.5 ppt, with a mean of -10.4 ppt. grass leaves possess large internal Halophila had similar isotopic lacunar spaces which facilitate gas composition, with means of -10.2 ppt for transport (Zieman and Wetzel 1980). The gulf and -12.6 ppt for Caribbean samples. presence of these lacunae and the absence Syringodium, by comparison, had of stomata provide the plants with a relatively fewer negative numbers, with a relatively closed pool of carbon dioxide, mean of -5 ppt and a range of -3 to -9.5 thus promoting recycling of CO*. PPt. This species has a greater proportion of lacunar spaces, and the Seagrasses share with C4 plants such lacunae are more completely partitioned physiological adaptations as high thermal than those of the other seagrasses and light optima for photosynthesis and considered. This greater lacunar

23 isolation presumably enhances the bed was more depleted in 13C compared to recycling of C02, which occurs in C, sediment organic matter from adjacent plants! and thus the similarity in bays without seagrasses (Fry et al. isotopic composition is not unexpected. 1977), and the same pattern was reflected Tropical seagrasses in general have in the animals (Fry 1981). The 6 13C of values less neaative than those of the polychaete worm Diapatra cuprea temperate specie;. A study of Zostera varied from an average of -13 ppt in showed little seasonal variation in seagrass-dominated areas to -18 ppt where isotopic composition (Thayer et al. phytoplankton were the dominant primary 1978). The isotopic composition can producers (Fry and Parker 1979). Similar vary, however, with habitat (Smith et al. trends were observed for fish and shrimp. 1976; Zieman et al. 1984c). McMillan and Smith (1982) found that seagrasses grown The utility of this carbon isotope in laboratory cultures had more negative method of food chain analysis is values, that is, were more depleted in restricted at the present by the high the heavier 13C than samples from the cost of analytical equipment and by the natural environment. They concluded that limitations of data interpretation._^ When such results could reflect differences in a consumer organism has a 6 l"C value carbon sources and in recycling of which falls within a range specific for a internal carbon. particular plant source, the relationship is readily apparent; however, if the Since plants have characteristic animal has a de1 value falling between isotopic compositions, and the animals two identifiable pl,ant groups, it is that consume them retain to within t2 ppt unclear whether this represents a food the same ratio (DeNiro and Epstein 1978; source which itself has a value Fry et al 1978), these isotope intermediate between the two known groups "signatures" provide a useful tracer for or whether the organism is consuming a food chain studies (Figure 8). In the mixed diet. marine environment, seagrasses have isotopic ratios distinct from other marine plants. Thus carbon derived from 2.5 NUTRIENTUPTAKEANDSUPPLY seagrasses (-3 to -15 ppt) is distingished from that of marine Seagrasses are highly productive plants macroalgae (-12 to -20 ppt), particulate that can grow in low-nutrient organic carbon and phytoplankton (-18 to environments; thus, the manner in which -25 ppt) and mangroves (-24 to -27 ppt) plant nutrient demands are met is of (Fry and Parker 1979). In Texas, particular interest. Since seagrasses sediment organic matter within a seagrass 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!ll rl!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 converted to N2 by denitrifying bacteria. past over whether nutrients were taken in Patriquin (1972) and Capone and Taylor throuah the leaves or the roots. The (1980) identified the recycled organic tempeiate seagrass Zostera is capable of material as the primary source of takina in nutrients both from the water nitrogen for leaf growth; however, columi and through the roots (McRoy and nitrogen fixed by sediment microbes Barsdate 1970); however, uptake through could supply 20% to 50% of the plants' the root system was shown to be faster requirements (Capone and Taylor 1980). and more efficient (Penhale and Thayer In contrast, Capone et al. (1979) found 1980). McRoy and Barsdate (1970) found that fixation by phyllosphere microbes that Zostera could translocate ammonium contributed primarily to epiphyte growth. and phosphate from the sediments to the The relative importance of the different leaves and excrete these nutrients into nitrogen pools to the plants is indicated surrounding waters. Such nutrient by such factors as sediment pumping may be important only in characteristics and water column sediments with high nutrient concentrations. concentrations (Penhale and Thayer 1980). Inorganic phosphorus, unlike nitrogen, Studies of nutrient supply to has no gaseous phase and does not change seagrasses have concentrated on nitrogen valence state in normal environmental and phosphorus because these, along with reactions. Thus the source of phosphorus carbon, are the primary constituents of to the seagrasses is dissolved inorganic plant material. In Zostera beds in orthophosphate (PO,), derived either from Chesapeake Bay, the addition of the breakdown of organic matter or from commercial fertilizer containing both the weathering of minerals, some of which nitrogen and phosphorus stimulated leaf are biologically precipitated. While growth (Orth 1977a). Harlin and water-column concentrations in tropical Thorne-Miller (1981) observed similar waters are normally low, phosphate may be growth enhancement when inorganic quite abundant in the sediments. High ammonium and phosphate were added to levels of HCl-extractable phosphate were waters overlying Zostera beds in a Rhode found in the carbonate sediments of Island bay. The relative importance of seagrass beds of Barbados, but pore-water these major nutrients in limiting plant concentrations and concentrations in growth has not been determined and overlying waters were low (Patriquin probably depends on local nutrient 1972). Because the high sediment supplies and processes. concentrations probably reflected undissolved phosphate not available for Three sources of nitrogen are available uptake by the plants, Patriquin concluded to the plants: microbially recycled that the nutrient-poor overlying waters nitrogen from organic matter in the were the primary source of phosphate to sediment, dissolved ammonium and nitrate the seagrasses. Sediment type influences in the water column, and ammonium from the dissolution of phosphate, and, the microbial fixation of dissolved NZ. therefore, its availability to the Sources of organic matter for plants. Silicious sediments readily decomposition in the sediment include exchange phosphate with overlying waters animal excretions and dead roots and (Nixon et al. 1980), but carbonate rhizomes, Sediment bacteria convert the sediments tend to absorb phosphate, organic nitrogen to ammonia in the anoxic removing it from solution. Rosenfeld zone, which begins only a few millimeters (1979) reported that pore-water phosphate below the surface. Ammonia that is not concentrations of Florida Bay sediments quickly bound either by biological uptake were two orders of magnitude lower than or chemical adsorption by sediment concentrations in Long Island Sound pore particles can diffuse upward to the waters and attributed the difference to aerobic zone, where it can then diffuse calcium carbonate adsorption of into overlying waters or be converted to phosphate. nitrate by nitrifying bacteria. Nitrate concentrations are low in the sediments; Terrestrial runoff also can be an nitrate is either rapidly assimilated or 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 have been studied most extensively (Thorne 1954; Phillips 1962; Taylor and Saloman Distribution of seagrasses along the 1968; Lewis and Phillips 1980; Lewis et west coast of Florida is unique in that al. 1985a). While this estuary has the plants not only occur in protected received intense human impact and cannot estuarine grassbeds typically found along be considered necessarily typical or the Gulf of Mexico coast (represented in representative of west Florida bays, the this area by the grassbeds in embayments abundance of information on Tampa Bay such as Rookery Bay, Charlotte Harbor, seagrasses provides a useful base for Tampa Bay, and St. Joseph Bay), but also comparison with other areas. form an extensive offshore bed located along the coastal reach between the St. Thorne (1954) identified five seagrasses Marks River and Tampa Bay, known as the occurring in the bay: Thalassia, Syringo- Big Bend area. dium, Halodule, Ruppia maritima and Halo- philaengelmannii. In his survey of sea- Seagrass distribution in the eastern grasses of Tampa Bay, Phillips (1962) Gulf of Mexico has been investigated at reported the presence of all species but several different levels of spatial Halophila; however, this seagrass was resolution. Humm (1956) reported later observed in the bay by Lewis and seagrasses observed at specific sites Phillips (1981) and Moffler and Durako along the northern coast of the Gulf of (reported in Lewis et al. 1985a). Mexico. Phillips (1960a) described the Phillips (1962) noted that the southern general location of seagrasses around the part of the bay was dominated by Diplan- Gulf of Mexico based on literature reports athera (Halodule) and in the northern and on field surveys. Bauersfeld et al. part Ruppia was more abundant, presumably (1969) and Earle (1972) estimated area1 due to a salinity gradient. Thalassia is seagrass distribution in the eastern Gulf relatively sparse in Tampa Bay, possibly of Mexico using indirect methods. McNulty because of low salinities (Phillips 1962), et al. (1972) reported seagrass but is the dominant species in the adja- distribution within embayments and cent waters of Boca Ciega Bay (Pomeroy estuaries in the eastern Gulf of Mexico 1960; Phillips 1962; Taylor and Saloman based on field observations and on 1968). Lewis et al. (1985a) estimated analysis of aerial photography. While the that the current distribution of sea- seagrass distribution within embayments grasses in the bay, covering 5,750 ha adjacent to the northeastern Gulf of (14,203 acres) represents a reduction of Mexico has been reasonably well described, 81% of historical coverage prior to human the spatial extent and biomass of impact (Figure 9). seagrasses of the Big Bend area have been only recently investigated (Continental a. Seagrass associations. There are Shelf Associates 1985; Iverson and five types of seaqrass meadows found Bittaker 1986). in Tampa Bay (Figure 10). Mid-bay shoal perennial beds contain Tha- 3.1.1 Seagrass Distribution in Tampa Bay lassia, Syringodium, and Halodule, but rarelv RuoDia. due to either the Among the estuarine grassbeds of the fast currents or increased salini- west coast of Florida, those of Tampa Bay ties 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 zomes are more readily fragmented beds contain all five species found and dispersed to unvegetated areas. in the bay. In these beds, Ruppia is found in the shallowest water b. Sediment effects. According to close to shore, followed by almost Thorne (1954) seagrass distribution pure stands of Halodule, Thalassia, in the Gulf of Mexico was limited to and Syringodium, respectively, as soft marl, mud, or sand substrates. depth increases. These meadows Phillips (1962) found that all sea- generally have an unvegetated sand grasses in Tampa Bay grew in muddy bar separating the seagrasses from sand: while sandy substrates the main body of the bay. Stressed- remained unvegetated. The sediments fringe perennial beds are similar to of the bay contain varying amounts their healthy counterparts except of carbonates, which may be impor- coverage is reduced, and migration tant in determining the availability of a destabilized sand bar of essential nutrients. eventually leads to the dis- appearance of the bed. These beds C. Depth distribution. Phillips (1962) occur in areas of the bay where reported that seagrass growth was phytoplankton are abundant, possibly limited to depths of less than one competing with the benthic fathom (2 m) in the turbid waters of macrophytes. Finally, colonizing Tampa Bay. Syringodium dominates perennial grassbeds are found in below the spring low-tide mark, and in bands in the euphotic zone of man- deeper water frequently occurs in made fill areas. The dominant soe- mixed stands with Thalassia (Humm ties here are Halodule and Syringo- 1956; Phillips 1960a; Phillips 1962). dium, presumably because their rhi- Shallow areas are dominated by Ruppia

28 nearshore environment from St. Marks to Tampa (Iverson and Bittaker 1986; MBS(P) Continental Shelf Associates 1985) Analysis of a photographic composite obtained from aerial photography (Continental Shelf Associates 1985) revealed some broad-scale patterns in HF(P) 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 S F (PI (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 Figure 10. Seagrass meadow types in Tampa Bay. 1 m water depth at stations near the MBS(P) = mid-bay shoal perennial; HF(P) = healthy Florida State University Marine Laboratory fringe perennial; SF(P) q stressed fringe perennial; E at Turkey Point, and in St. Joseph Bay. q ephemeral; C(P) = colonizing perennial (after Lewis et al. 1985). 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. and Halodule (Phillips 1962). Three Vegetation covered about 3,000 km*, with mOrDhOl oaicallv distinct forms of seagrasses occurring as a band varying Halbdule-in the bay were identified from 11 to 35 km wide between St. Marks according to depth distribution and Tarpon Springs, Florida. Dwarfed plants occurred in areas exposed at neap and spring low tides, All six species of seagrasses presented while subtidal plants were more robust in Chapter 1 were found in the Big Bend (Phillips 1960d). Salinity rather grassbeds. Halodule occasionally formed than tidal exposure was thought to both the innermost and the outermost control the distribution of Ruppia in monospecific stands in this area. the bay (Phillips 1962). Shallow-water Halodule growing on shoals often exposed at low tide, generally had 3.1.2 Seagrass Distribution in short, narrow leaves, and deep-water the Big Bend Area Halodule was tall with wider leaves (Iverson and Bittaker 1986). The Big Bend seagrass bed overlies Shallow-water and deep-water forms of drowned karst topography which extends Halodule appear to be morphologically from the town of St. Marks south to Tarpon different clones (Phillips 1960b; McMillan Springs. The sediments of this low energy 1978). Shallow areas not exposed on low region are composed of clay and silicious tides contained mixtures of Thalassia, sand over limestone. Results of recent Syringodium, and Halodule. Densest investigations suggest that seagrasses are portions of the seagrass bed were the dominant benthic feature of the dominated by Thalassia and Syringodium in

29 ‘7. -CRY5 :TAL Bl Y

Figure 11. Seagrass distribution and density in the Big Bend area (adapted from Continental Shelf Associates 1985).

30 SrSteinhatchee OUTER LIMIT OF SEAGRASS BEDS

casassa

29” N EM0 w+ a GULF OF

PHOTO TRANSEC’I - .%?=Y 50 kilometers I * 1 SEAGRASS PRESENT 0 Thalassia testudinum ;PRINGS

Q Syrlngodium filiforme

(3 Halodule wriahtii Q Halophila enqelmanni

Halophtla decipiens Q 9m. MLW -c-y“ Q Ruppia maritima

Figure 12. Seagrass species distribution in the Big Bend area (after lverson and Bittaker 1986).

31 various mixtures. Halophila engelmanni Thalassia was common in this orassbed. and was often qi Halodule mixed with Thalassia and Syringodium. Svrinaodium Halophila engelmanni was also abundant outside the major seagrass bed to depths B - of at least 20 m where it occurred in monotypic stands (Continental Shelf Asso- ciates. 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. I234

a. Depth distribution control. Iverson DEPTH (m) and Bittaker (1986) showed that the major seagrass species were distri- buted throughout the seagrass beds 5oor T 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 Tha- lassia 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 DEPTH (m) and Bittaker 1986). The general pattern in fine-scale depth distri- Figure 13. Depth distribution of seagrass biomass bution of seagrass species appears in Apalachee Bay (after lverson and Bittaker 1986). to be similar among the various American tropical seagrass beds for which observations have been reported. Strawn (1961) described the cross-bed, seagrass distribution distribution pattern was evident in near Cedar Key in the northeast Gulf several diverse areas: in the grass of Mexico. Halodule occurred in bed samples in northern Apalachee monotypic stands on shoals exposed Bay (Iverson and Bittaker 1986), in to the atmosphere at low tide and the northwest Cuban seagrass bed was distributed throughout the sea- (Buesa 1974), in a Nicaraguan sea- grass bed. Thalassia grew only in grass bed (Phillips et al. 1982), subtidal areas and did not extend to and in a seagrass bed near Buck the deepest limits of the bed which Island, St. Croix (Wiginton and contained Syringodium. This depth McMillan 1979).

32 For many kilometers along the in Cuban coastal waters (Buesa 1974) outer limit of the Big Bend seagrass and in St. Croix waters (Wiginton bed between Tarpon Springs and and McMillan 1979) compared with the Crystal River, an observer on the Big Bend area and Florida Bay, most waters' surface notices a distinct of the leaf biomass in the northwest transition from the dark green outer Cuban and the Buck Island, St. edge of the seagrass bed and the Croix, seagrass beds was located light sediment bottom seaward of the shallower than the depth to which bed edge. The outer edge of the 10% of surface light energy pene- grassbed is deeper north of Tarpon trated. The maximum possible area Springs, in the Big Bend bed, com- in which Thalassia can form well- pared with the part between St. developed beds appears to be con- Marks and the Crystal River. This strained by the slope of the sea variation is a consequence of floor and the bottom depth of the increased water clarity in the isolume corresponding to 10% of southern part of the Big Bend sea- surface light energy (Iverson and grass bed, as indicated by the Bittaker 1986). extinction coefficients for light energy in the water column measured b. Salinity and temperature effects. in those areas. In addition, sub- The nearshore species composition of jective observations made over a seagrass assemblages in the northern period of years suggest that the bed is influenced by freshwater dis- relative differences in water charges entering the northeastern clarity from the two areas are con- Gulf of Mexico from several rivers sistent (R.L. Iverson, unpubl. along the coast. Thalassia testu- data). The nearshore waters of the dinum and Syringodium filiforme do Big Bend area receive river runoff not grow in areas of low salinitv colored compounds water in the northeastern Gulf o? (Bittaker $75) o$?~~c in addition Mexico (Phillips 1960a) and were not to particulates, contr\butes to the reported in areas with salinities increased turbidity and higher less than about 17 ppt in the extinction coefficients observed in northern seagrass bed (Zimmerman and that area (Zimmerman and Livingston Livingston 1976a). 1979). The seagrasses of the Big Bend Based on the depth-distribution area experience a large temperature data obtained in several different range (8-33 "C) (Goulet and Haynes investigations, the light-energy 1978). Seagrasses from this bed compensation level for the annual were more tolerant of very cold tem- growth of American tropical seagrass peratures than were seagrasses from communities dominated by Thalassia Florida bay (McMillan 1979; McMillan appears to be about 10% of sea- and Phillips 1979); however, each surface photosynthetically active winter, leaves of Big Bend sea- light energy. The depths to which grasses die back to within several 10% of sea-surface light energy centimeters of the sediment-water penetrated, calculated from measured interface (Zimmerman and Livingston extinction coefficients, were 7 m 1976b), a phenomenon also observed for the part of the seagrass bed in seagrass beds in Texas waters between Tarpon Springs and Crystal during cold winters (Phillips 1980). River, and 4.5 m for the portion north of Crystal River. These C. Sediment effects. Thalassia grew in depths,approximate the seaward limit coarser sediments than did the other of the major seaqrass beds comoosed seagrasses of the Big Bend area of Thalassia, -Syringodium, ’ and (Iverson and Bittaker 1986). Buesa Halodule in those respective areas (1975) reported that Thalassia in of the eastern Gulf of Mexico. northwest Cuban grassbeds also grew Although Thalassia and Syringodium in coarser sediments than did other were distributed to greater depths seagrasses.

33 Sediment deposition on leaf sur- enhanced leaf production in nutrient- faces significantly interferes with richer fine sediments or the need for the growth of both Thalassia testu- greater root development for increased dinum and Halodule wrightii nutrient absorption in the aenerallv (Phillips 1980). Water turbidity poorer coarse sediments. Thalassia has was inversely related to distance the most robust root and rhizome svstem of from the Econfina River mouth the seagrasses of Florida. Halodule and (Bittaker 1975; Zimmerman and Syringodium have shallower, less well- Livingston 1979), suggesting that developed roots and rhizomes, and tend to turbidity effects on seagrass growth have a greater portion of their total occur primarily nearshore as pro- biomass, 50% to 60%, in leaves (Zieman posed by Humm (1956). Moore (1963a) 1982). However, Pulich (1985) reported reDOrted that hiah-water turbiditv that Halodule from Redfish Bay, Texas had precluded the griwth of Thalassia 66% of total biomass below the sedjment testudinum in Louisiana coastal surface, compared to 3l.% for Ruppia. waters within the Mississippi River Reported values for the relative portions plume. of' above- and below-ground biomass in Florida west coast species are shown in Table 6. 3.2 BIOMASS 3.2.1 Seagrass Biomass in Tampa Bay Seagrass biomass can vary greatly depending not only on the species but on Both above- and below-ground biomass of such environmental variables as available the seagrasses of the bay were determined light, sediment depth, nutrient avail- by Lewis and Phillips (1980). Ruppia had ability, and circulation. The biomass of the lowest biomass, both for standing crop Halophila is always low, but Thalassia (portion of plant above sediment surface) biomass can reach values greater than 7 kg and root and rhizome (below sediment sur- m-2 (Burkholder et al. 1959). Ranges of face). Thalassia had the highest below- biomass values for Thalassia, Syringo- ground biomass, but its leaf standing crop dium, and Halodule are presented in Table was similar to that of Syringodium. 5. The results of many of these studies have been summarized by various authors In nearby Boca Ciega Bay, Thalassia leaf (McRoy and McMillan 1977; Zieman and standing crop exhibited seasonal varia- Wetzel 1980; Zieman 1982; Thayer et al. tion, reflecting temperature extremes. 1984b; Lewis et al. 1985a). Since the Dry weights peaked in spring and early studies involve a wide range of experi- summer, declined during mid-summer tem- mental conditions, including differences perature maxima, and dropped to the lowest in habitat, sampling times and seasons, values during winter months (Phillips and sample replication, attempts to com- 1960a). Durako and Moffler (1985c) pare or generalize based on the cumulative observed a similar seasonal pattern in data are of questionable value. maximum leaf lengths of Thalassia in Tampa Bay. Seagrass biomass for the Tampa Bay The majority of seagrass biomass, area, as reported by Lewis et al. (1985a), particularly in the larger species, is is given in Table 7. below the sediment surface. Ordinarily, 15%-20% of Thalassia's biomass is in the 3.2.2 Seagrass Biomass in leaves (although reported values range the Big Bend Area from 10% to 45%) with the rest made up by roots, rhizomes, short shoots, and Thalassia and Syringodium comprised 84% sheathing leaves (Zieman 1975, 1982). of total leaf biomass in the Big Bend Sediment type can affect the relative area; Thalassia alone accounted for 58% of amount of biomass above and below the leaf biomass compared to 64% for grass- surface: the ratio of leaf to root and beds in Florida Bay (Iverson and Bittaker rhizome biomass in Thalassia increased 1986). Thalassia leaf biomass reached a from 1:3 in fine mud to 1:5 in mud and 1:7 seasonal maximum during August and then in coarse sand (Burkholder et al. 1959). declined rapidly at stations located near It is unclear whether this reflects the Florida State University Marine

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

Species Biomass Location Source

maritimaRuppia 60-160 Texas Pulich 1985 Halodule wrightii 10-400 Texas McMahan 1968; McRoy 1974; Pulich 1985

22-208 North Carolina Kenworthy 1981

10-300 South Florida Zieman unpubl.

Syringodium filiforme 15-1100 South Florida Zieman unpubl.

30-70 Texas McMahan 1968

Thalassia testudinum 30-500 Cuba Buesa 1972,1974; Buesa and Oleachea 1970

60-718 Puerto Rico Burkholder et al. 1959; Margalef and River0 1958

60-250 Texas Odum 1963; MCRoy 1974

20-1800 Florida (east Odum 1963; Jones coast) 1968 ; Zieman 1975b

57-6,400 Florida (west Bauersfeld et al. coast) 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. (1972) estimated 2,560 ha of (1985) found that for offshore stations seagrass coverage within St. Joseph Bay.

35 Table 6. Biomass partitioning In seagrasses.

Biomass % of Species Component (g dry wt m-*> Total Reference

Ruppia Above ground 110 69 maritima Below ground 50 31 Pulich 1985a Above ground 48 50 Below ground 48 50 Lewis and Phillips 1980 Halodule Above ground 150 34 wrightii Below ground 290 66 Pulich 1985

Above ground 5-54 11-33 Below ground 10-200 67-89 Zieman 1982

Syringodium Above ground 28-102 16-47 filiforme Below ground 31-521 53-84 Zieman 1982

Thalassia Above ground 58-267 11-15 testudinum Below ground 321-2,346 85-90 Zieman 1982

aPeak seasonal biomass values.

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

Biomass Species Location Above ground Below ground Reference

Ruppia maritima Tampa Bay 1.48 18-48 Lewis and Phillips 1980

Halodule wrightii Tampa Bay 38-50 60-140 Lewis and Phillips 1980

Syringodium filiforme Tampa Bay 50-170 160-400 Lewis and Phillips 1980 Thalassia testudinum Boca Ciega Bay 32.4 48.6 Pomeroy 1960 Bird Key 325 Phillips 1960a Cat's Point 98 Phillips 1960a Boca Ciega Bay 636 Bauersfeld et al. 1969 320-1,198 Taylor and Saloman 1969 Tarpon Springs 601-819 Dawes et al. 1979 Tampa Bay 25-180 600-900 Lewis and Phillis 1980 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 for interbed biomass comparisons would be more appropriate for this area.

3.3 PRODUCTIVITY AMJJASOND The high rates of primary productivity MONTH of seagrasses is well recognized. Studies Figure 14. Seasonal cycle of Thalassia at two of biomass literature have reported a wide stations in Apalachee Bay(after lverson and Bittaker spectrum of productivity measurements 1986). (Table 8). Past studies have focused on

Table 8. Seagrass productivity measurements.

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

Halodule wrightii 0.5- 2.0 North Carolina Dillon 1971

1.1 Florida (east Virnstein 198Za coast)

Syringodium filiforme 0.8- 3.0 Florida Zieman unpubl. 0.6- 9.0 Texas Odum and Hoskin 1958; McRoy 1974

Thalassia testudinum 0.6- 7.2 Cuba Buesa 1972,1974 2.5- 4.5 Puerto Rico Odum et al. 1960 1.9- 3.0 Jamaica Greenway 1974 0.5- 3.0 Barbados Patriquin 1972b; 1973 0.9-16.0 Florida (east Odum 1957,1963; coast Jones 1968; Zieman 1975a

aCalculated as 38% of reported dry weight.

37 Thalassia, but more recently Halodule and measure below-ground productivity, Syringodium have been studied. excreted carbon, or herbivory. The 14C method allows the investigator to deter- A major problem encountered in attempts mine the partitioning of photosynthate to synthesize the results of various pro- within the plant. Figure 15 shows the ductivity studies is that the three major location of 14C in Thalassia after a methods of measurement--leaf marking, O2 4-hour incubation period. The leaves evolution, and l*C uptake --each yield contained 49% of the radiocarbon although somewhat different results. In the they made up only 13% of the total bio- literature, the highest values are mass. obtained using the O2 method, the lowest values result from leaf marking, while 14C Despite the methodological differences, measurements provide intermediate values studies of the productivity of seagrasses (Zieman and Wetzel 1980; Kemp et al. have shown that these are highly produc- 1986). In a carefully developed study, tive systems, especially when growing Bittaker and Iverson (1976) found that 14C under optimal or near-optimal conditions. and leaf marking gave essentially identi- cal results when the 14C results were 3.3.1 Seagrass Productivity in Tampa Bay corrected for inorganic losses, incubation chamber light absorption, and differences Surprisingly little data exist on the in light energy resulting from differences productivity of the seagrasses of this in experimental design. In a study of area. In nearby Boca Ciega Bay, Pomeroy Thalassia in Bimini, Capone et al. (1979) (1960) estimated that Thalassia and found, however, that productivity measured Syringodium occurring at depths less than by the 14C method was double the rates 2 m, fixed 500 g C.m-2. yr-I. He con- obtained from the leaf marking technique cluded that, at these depths, seagrasses, (Zieman 1974; Fry 1983) which underesti- microflora, and phytoplankton were equally mates net productivity since it does not important primary producers, whereas

% Total 14C uptake % Total weight

.:. n 49.0 13.3

sheath 23.3 34.1

rhizome 26.6 50.3

roots I ,I 3.3

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) THALASSIA estimated that phytoplankton productivity I - (a) 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. OTHER SEAGRASSES 1985a). I 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 I=d!tbkiI Bend area (Figure 16). Thalassia RED MACROALGAE 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 I- (cl 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 l- temperature.

Near the Anclote River, seagrass I productivity estimated from leaf growth measurements was reported as 2-15 mg ‘JFMAMJJASON 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 MONTH and Halodule, respectively (Ford 1974 et Figure 16. Seasonal changes in productivity of al .; Ford and Humm 1975). 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 and Zieman (1982) as any sessile organism species are dependent on the physical, growing on a plant (not just a plant chemical, and geological environment, living on a plant). Epibenthic organisms while the associated community is the are those that live on the surface of the product of this seagrass composition as sediment, and include, in the broadest well as the abiotic variables. Along the sense, motile organisms such as large west coast of Florida, from Florida Bay to gastropods and sea urchins, as well as Apalachicola Bay, there are large sessile forms, such as sponges and sea variations in all of the major anemones or macroalgae. Infaunal physico-chemical parameters. This organisms are those that live buried in environmental gradient is reflected in the the sediments, such as sedentary changes of species associations and polychaetes and bivalves, and relatively community structure within the seagrass mobile infauna, such as irregular urchins. system. Organisms that are buried part-time, for shelter, such as penaeid shrimp or blue Although it is obvious that large crabs, or while waiting for prey, like changes in abiotic variables and plant flounders, are considered epibenthic and composition and density can produce major not infauna. Planktonic organisms are the changes in the community structure, even minute plants and animals, such as subtle variations apparently can produce diatoms, dinoflagellates, and many major community differences. At five copepods that drift in the water column. sample sites in a single south Florida They may show local movement, and estuary with Thalassia blade densities of especially may migrate vertically, but are over 3,000 m-2 the total number of largely at the mercy of water currents for macrofaunal taxa'varied from 38 to 80, and their lateral movement. By comparison, the average density of individuals varied nektonic organisms are highly mobile over two orders of magnitude, from 292 to organisms living in or above the plant 10,644 individuals m-2 (Brook 1978). canopy, such as fishes and squids.

Organisms found in seagrass communities Another classification scheme, first can be classified in a number of ways, proposed by Kikuchi (1980), and slightly depending on the objectives of the modified by Zieman (1982), is based on the classification. The biota present in a mode of utilization of the seagrass beds seagrass ecosystem can be classified in a by the associated fauna. This scheme that recognizes the central role of classification is based on whether the seagrass canopy in the organization of organisms are: (1) permanent residents, the system, and classifies the organisms (2) seasonal residents, (3) temporal according to their position relative to migrants, (4) transients, or (5) casual the canopy. The principal groups are: visitors. (1) epiphytic organisms, (2) epibenthic organisms, (3) infaunal organisms, (4) the planktonic organisms, and (5) the nektonic 4.1 ALGAL ASSOCIATES organisms. The major sources of primary production Epiphytic organisms are defined for coastal and estuarine areas are: (1) according to the usage of Harlin (1980) macrophytes (seagrasses, macroalgae, salt

40 marsh plants, and mangroves), (2) benthic the estuarine and inshore regions, while microalgae (benthic and epiphytic diatoms, dinoflagellates are more diverse and dinoflagellates, filamentous green and abundant in the open gulf and in bluegreen algae), and (3) phytoplankton. gulf-influenced areas. The predominant In estuarine and coastal regions the organisms are ubiquitous, cosmopolitan relative balance of standing crop and species that are coastal residents, but productivity between the major groups of occasional secondary abundance peaks are primary producers is a function of many attributed to sporadic visitor species. environmental variables, but the major Standing crop and productivity are higher determinants are water column nutrients, in areas of terrestrial runoff or river turbidity, and substrate. In areas of mouths, and are lowest offshore in the high water-column nutrients, phytoplankton open gulf, except in areas where and microalgal growth will dominate, divergence or upwelling make more because these small or single-cell algae nutrients available (Steidinger 1972, rapidly respond to the increased nutrient 1973). supply. Because benthic plants take up nutrients from the sediments via their The phytoplankton of Tampa Bay are roots, these plants are less able to typically dominated by nannoplankton (less exploit increased nutrient levels in the than 20 pm), except for periodic blooms of water column. The turbidity created by blue-green algae (Schizothrix) increased algal growth, along with dinoflagellates (Gonyaulax, Gymnodiniik suspended sediments, will cause nelsonii and others). The dominant attenuation of the light reaching the species in the bay is the diatom Skeleto- bottom of the water column and thus nema costatum. The red-tide organism decrease the light available to benthic Ptychodiscus brevis (= Gymnodinium breve), plants for photosynthesis. Thus, a toxic coastal species. has invaded the increased nutrient levels_favor suspended bay 12 times between 1946 and 1982, domi- and epiphytic plants (both of which derive nating once for over three months their nutrients from the water column) at (Steidinger and Gardiner 1985). the expense of the benthic attached forms. Turbidity favors phytoplankton primarily Johansson et al. (1985) estimated that since they are capable of moving upward in phytoplankton in Tampa Bay accounted for the water column to intercept the light 9l% of the submerged vegetative produc- necessary for photosynthesis. Sediment tion. In deep areas of the bay type is also important in determining phytoplankton production was estimated at benthic communities. - Soft sediments favor 340 8 C.m-2.yr-1; a maximum value of 620 g seagrasses and certain rhizophytic green C.m- .yr-l was calculated from 14C data algae, while rocky substrates favor the (Johansson et al. 1985). In Boca Ciega development of macroalgal communities. Bay, Pomeroy (1960) estimated that phyto- plankton, benthic microflora, and While portions of the coastal region of Thalassia production were of equal impor- west Florida are still miraculously tance in depths less than 2 m, which pristine, much of the area is heavily included 75% of the bay. Phytoplankton urbanized or otherwise disturbed. Still, production dominated in deeper areas. as late as 1968, Taylor and Saloman estimated that in Boca Ciega Bay total 4.1.2 Benthic Algae production, dominated by macrophytes, was six times the annual phytoplankton The coastal regions and estuaries of production. west Florida have a diverse benthic algal flora, occupying several different 4.1.1 Phytoplankton habitats. Although once regarded as depauperate (Taylor 1954), the flora of In the coastal and estuarine waters of the eastern gulf have been shown to be west Florida, Steidinger (1973) identified quite diverse in numerous subsequent four phytoplankton assemblages: studies (summarized in Earle 1972; Dawes estuarine, estuarine-coastal, coastal-open 1974). In addition to cosmopolitan gulf Gulf of Mexico and open gulf. Within and Caribbean species, the region also has these areas, diatoms generally dominate 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

A B C D E F Total

Chlorophyta 85 42 45 43 97 151 174 Chrysophyta 1 1 Cryptophyta Cyanophyta 6 16 21 21 30 2: 31 Phaeophyta 41 33 23 24 52 58 82 Rhodophyta 120 121 86 42 171 270 349 Tracheophyta 6 5 4 6 6 6 Xanthophyta 1 1

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.

Total Location 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 Udotea, which are primary producers of from several sites in Florida and shows organic carbon. Halimeda and Penicillus the distribution by division at each area. also deposit rigid skeletons of calcium carbonate that become a major component of Because of the combination of protected the sediments upon the death of the plant. estuaries on the central and southern portions of the Florida west coast and the These algae do not have ability to gently sloping shelf and moderate wave stabilize the sediments as effectively as climate to the north of Tampa Bay, the the seagrasses, although they do buffer west coast offers an enormous area for the currents to some degree, and by their colonization of either algae or extremely rapid growth can accomodate seagrasses. The primary substrates changes in shifting sediments. available for algae in the region include: Historically, the main utility of their (1) rocky outcrops and hard bottom (2) rhizoidal holdfasts was considered to be soft sediments (3) seagrass leaves and serving as an anchor for the plant in the mangrove roots and (4) the water column. substrate, but Williams (1981) has shown Much of the shallow region north of Tampa that they can take in nutrients through Bay consists of rocky outcrops suitable their rhizoids and translocate these for algal attachment. Throughout the throughout the plant in a manner similar area, oyster reefs, mangrove prop roots, to higher plants. and scattered rocks or shells offer additional algal substrate, in addition In many tropical and subtropical seas, to: human-made structures like pilings, the calcareous green algae are the major bridge supports, and canal walls. source of sediments. The different genera produce characteristic particles, with The only marine and estuarine algae able Halimeda tending to form sand-grain-sized to consistently utilize sediments as plates, while Penicillus produces substrate are the mat-forming algae and fine-grained aragonitic mud. At current members of the order Caulerpales of the growth rates, Penicillus alone could division Chlorophyta, which possess account for all of the fine mud behind the creeping rhizoids that provide an anchor Florida reef tract and one third of the in sediments (Humm 1973; Dawes 1981). fine mud in northeastern Florida Bay Among the most important genera are (Stockman et al. 1967). In addition, the Halimeda, Penicillus, Caulerpa, and combination of Rhipocephalus, Udotea, and

43 Acetabularia generates at least as much estimated the production of Laurencia in mud as Penicillus in the same locations. Card Sound to average about 8.1 g dry weight.m-2.year-1, which was less than 1% In the Bight of Abaco, Bahamas, Neumann of the production of Thalassia in the and Land (19751 calculated that the arowth area, algal production is undoubtedly much of Peniciilus,'Rhipocephalus, and Haiimeda higher in areas where the macroalgae form has produced 1.5 to 3 times the amount of a substantial portion of the total mud and Halimeda sand now in the basin and biomass. that in a typical Bahamian Bank lagoon, calcareous green algae alone produce more The least studied components of the sediment than can be accomodated. Bach algal flora continue to be the benthic (1979) measured the rates of organic and microalgae. In studies of benthic inorganic production of calcareous green production performed throughout the algae in Card Sound, south of Miami. Caribbean, Bunt et al. (1972) found the Organic production was low in this lagoon, production in Caribbean sediments to ranging from 8.6 to 38.4 g ash-free dry average 8.1 mg C.m-2.h-1 (range 2.5-13.8) weight.m-2.yr-1, and 4.2 to 16.8 g using 14C uptake. By comparison, in the CaC03.m-2.yr-1 for all the species Florida Keys sediment microbes fixed 0.3 combined. to 7.4 mg C.m-2.h-1. These values were found to be equivalent to the production In areas of western Florida with hard in the water column. Lewis et al. (1985a) substrate, numerous species of attached have suggested that within areas of excess algae are found. Amona the most common nutrients and eutrophication, phytoplank- brown algae (Phaeophyta) are Dictyota ton and benthic microalgae increase in dichotoma, Sargassum filipendula, S. abundance at the expense of seagrasses. pteropleuron, and Padina vickersiae (Zimmerman and Livingston 1976a; Dawes 4.1.3 Epiphytic Algae 1987). The diversity of the red algae (Rhodophyta) is much greater throughout For many species of algae requiring a the area. Some of the more common fixed substrate for colonization and attached forms include Digenia simplex, growth (both microalgae and those reaching Chondria littoralis, and several species relatively large size), the seagrasses of Gracilaria (Dawes 1987). The red algae provide that substrate in a habitat that are the dominant forms in the drift algae otherwise consists of inhospitable soft of western Florida waters, large mats or sediments. Although unifying patterns are algae that have become detached from their beginning to emerge, the study of anchorages. Rather than floatinq at the epiphytes has suffered from what Harlin surface-like Sargassum, they tend to roll (1980) has described as the "bits and alona on the bottom in clumas or lona pieces" approach, with most studies cylindrical windrows, moved along by tidal consisting of either extended species currents or wind action. The dominant lists or suggestive but largely drift alga is Laurencia, but members of observational approaches (Dawes 1987). other genera, including Acanthophora, Literature is currently emerging that Hypnea, Spyridea, and Gracilaria, are focuses on the important role that common and may be locally abundant (Dawes seagrass epiphytes play as a trophic base 1987). in certain seagrass systems.

Although information on the distribu- Humm (1964) compiled an annotated list tion, standing stock, and seasonality of of 113 species of algae found epiphytic on macroalgae on the west coast of Florida is Thalassia in south Florida. Of these only beginning to accumulate, studies on pro- a few were specific to seagrasses; most ductivity on these plants are still sparse. were also found on other plants or solid In a study of seven seagrass communities substrate. Later Ballantine and Humm on the west coast of Florida, macroalgae, (1975) reported 66 species of benthic both attached and drifting, comprised from algae which were found to be epiphytic on 2% to 39% of the total plant standing the seagrasses of the west coast of stock (above ground biomass) (Dawes et al. Florida. Table ID, shows the relative 1985; Dawes 1987). While Josselyn (1975) distributions of algal epiphytes of sea-

44 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 in Florida. the production of some antibiotic compound Dawes (1987) further notes that fila- by the leaf. On tropical seagrasses the mentous forms predominate as epiphytes, heaviest coatings of epiphytes occur only constituting 73% of the epiphytes from the after the leaf has been colonized by the Indian River and 58% of the epiphytes from coraline red algae, Fosliella Anclote Estuary. Harlin (1980) compiled, Melobesia. The coral skeleton of the:: from 27 published works, a species list of algae may form a protective barrier as the microalgae, macroalgae, and animals well as a suitable roughened and adherent that have been recorded as epiphytic on surface. seagrasses. The algal lists are quite comprehensive, but none of the reports list the epiphytic invertebrates from Expressed in terms of population inter- Northwest Florida. actions, the relationship between epiphyte and seagrass host is basically that of an Harlin (1975) listed the factors ectoparasite. The relationship is bene- influencing distribution and abundance of ficial to the epiphyte ectoparasite, but epiphytes as: detrimental to the seagrass host. While the epiphytes enjoy the benefit of being 1. Physical substrate, raised higher in the photic zone, the 2. Access to photic zone, shading effect of the epiphytes has been 3. A free ride through moving waters, shown to be detrimental to the seagrass 4. Nutrient exchange with host, and hosts (Orth and van Montfrans 1984), 5. Organic carbon source. decreasing photosynthesis in Zostera by 31% (Sand-Jensen 1977). In Australia, Providing a relatively stable (if Bulthis and Woelkling (1983) found that somewhat swaying) substrate seems to be shading from accumulated epiphytes reduced the most fundamental role played by the by half the lifespan over which a leaf of seagrasses. The majority of the epiphytic Heterozostera tasmanica showed positive species are sessile and need a surface for net photosynthesis. In areas of high attachment. The turnover of the epiphytic epiphyte growth, the action of epiphyte community is relatively rapid, since the grazers is extremely important in main- lifetime of a single leaf is quite taining seagrass productivity, as well as limited. A typical Thalassia leaf has a the longevity of the host seagrasses, lifetime of 30 to 60 days. After a leaf without which the system would be non- emerges, there is a period of time before existent (Orth and van Montfrans 1984). epiphytic organisms appear. This may be Epiphyte coverage is limited not only by due to the relatively smooth surface or the activity of grazers, but, to a certain

45 extent, by the growth habit of the sea- 4.2 INVERTEBRATES grass plant, since individual leaves senesce and decay at such a rate that they The invertebrate fauna of seagrass beds provide a relatively temporary substrate. can at times be exceedingly rich and difficult to characterize, except in very In nutrient-poor waters, the epiphytes broad terms, unless one is dealing with a can benefit from the nutrients available defined area or is willing to produce an to the seagrasses in the sediments; exhaustive, comprehensive species list several studies have shown that there can since hundreds of species can potentially be a transfer of nutrients from seagrasses be represented within a small area. This to epiphytes. The upper surfaces of the same fauna can be highly variable, with leaves are subjected to much greater water dramatic changes occurring in the fauna1 motion than the lower parts. One effect composition and density within relatively of the increased water movement is to small changes of time or distance (Brook reduce nutrient gradients produced by 1978). biological uptake, thus increasing availability of these nutrients to From south to north along the western photosynthetic organisms. In addition, a coast of Florida, there is a change in the much greater volume of water containing invertebrate fauna of the seagrass beds particulate and dissolved nutrients is and associated habitats, beginning as a delivered to suspension feeding animals. Caribbean-West Indian fauna at the south Harlin (1975) described the uptake of PO4 and emerging as a predominately temperate orthophosphates translocated up the leaves fauna in the northern gulf. Collard and of Zostera and Phyllospadix. Epiphytic D'Asaro (1973) noted that the southerly blue-green algae have the capacity to fix fauna with West Indian affinities changes molecular nitrogen, but require phosphorus to one with Carolinian affinities in the especially in tropical waters. However, north. They tentatively divide the faunas Goering and Parker (1972) showed that at the vicinity of Cedar Key but state soluble nitrate fixed by epiphytes could, that the change is gradual and that there in return, be utilized by seagrasses. are no clear-cut fauna1 province boundaries in the eastern Gulf of Mexico. The standing crop and productivity of seagrass epiphytes and their resultant The characteristic species of seagrass contribution to the trophic base of the beds and associated communities from the system are highly variable. In some west coast of Florida have been described areas, such as immediately behind a coral by Collard and D'Asaro (1973) and these reef, there are few epiphytes and little associations are listed for the northern contribution, but in other areas, (Carolinian) fauna (Figure 18) and for the especially those with high external more southerly (West Indian) fauna (Figure nutrient enrichment, the amount of 19). Some of the cosmopolitan fauna that production is quite high. Jones (1968) are found in both regions are the sea estimated that in northern Biscayne Bay, urchin Lytechinus variegatus; the bivalves epiphytes contributed from 25% to 33% of Argopecten irradians, Modiolus modiolus, the community metabolism. Penhale (1977) and Cardita floridana; and the gastropods found that epiphytes contributed 18% of fasciataTegula and Bittium varium. In productivity of Zostera meadows in North the classification of Collard and D'Asaro, Carolina. The trophic structure of these the West Indian fauna coincide with the leaf communities can be quite complex and invertebrate fauna described in detail for important in many areas, such as the the seagrass communities of south Florida shallow, turbid seagrass beds of the by Zieman (1982). Indian River in Florida (Fry 1984) and parts of Redfish and Corpus Christi Bays In Apalachee Bay, Hooks et al. (1976) in Texas (Kitting et al. 1984), and will found that 6 of the 10 most abundant be discussed later. Much of the epiphytic "trawlable" species (=epibenthic and large material, both plant and animal, epiphytic fauna) in the area were ultimately becomes part of the litter and seagrass-associated fauna. Some of the detritus as the leaf senesces and most common organisms found in the bay detaches. were the caridean shrimps, especially

46 BAY AND SOUND COMMUNITIES FORESHORE TROUGH BAR OFFSHORE GRASS i MLtiST Bureatella leachi (cj

. .: : ‘Macoma constricta (vc) .:

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

Figure 18. Representative temperate (Carolinean) invertebrate communities (after Collard and D’Asaro 1973).

Palaemonetes pugio, Palaemonetes square meter (Stoner 1980b). The relative intermedius, Periclimenes longicaudatus, abundances of epifaunal species were Palaemon floridanus, Tozeuma carolinense, directly related to macrophyte density; and HiAlsoppolyte pleuracantha. abundant however, densities of burrowing were the scallop irradians; the polychaetes varied inversely with hermit crab bonairensi>;Pagurus the macrophyte density. In this study echinoderms Lytechinus variegatus and amphipods made up 47% of the macrofauna Echinaster serpentarius; and the majid and reached densities of 1,578 m-* (Stoner crabs Libinia dubia, Metoporhaphis 1980b). Normally, small crustaceans such calcerata. and Podochela riisei. Workina as amphipods and isopods will be in the same area, Dugan and Livingston numerically in great abundance; however, (1982) found similar species associations. the larger penaeid and caridean shrimp often represent a larger biomass within In Tampa Bay, Santos and Simon (1974) the bed. Data from Brook (1977) for found that the Thalassia zone supported a Card Sound Thalassia grass bed shows the laraest number of infaunal polvchaetes that amphipods and caridean shrimp of any of the sampled habitats of the bay, represent respectively 5.8% and 23.3% of although only three of the nine most estimated biomass of principal taxa abundant species showed their highest collected and 12.4% and 50.3% of densities in this zone. In grassbeds crustacean biomass. offshore from the mouth of the Econfina River in Apalachee Bay, polychaetes made The data of Collard and D'Asaro suggest up 35% of macrofaunal numbers, reaching that there is a greater proportion of maximum densities of 2,947 polychaetes per emergent organisms (those living at or

47 BAY AND SOUND COMMUNITIES FORESHORE TROUGH BAR OFFSHORE 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) MYST Mithrax spinosissimus (c) Holothuria floridana (c) Jardisomi guanhumi Ophioderma brevispinum (vc) Ocypo$e albicans _Tegula fasciata (c) ; ‘I;- pugilator (vc) Turbo castanous (c) f ._~_~~~~__~~“~~Chhh~~ Modulus modulus (c)~A*-hhhhhhhh/i ._~______,l_lrl IlllALlA.IY \.-, Cerithium muscarum (c) i Ophiolephis elegans (vc) C. Boridanum (C) i Limulus poly,,hpi,,c (,.\ -.::_;; ::?td i Nmnmnne rc=x~nn Irl Bittium varium (vc) i

: ,,... :;...... : ::.‘..~::;. ‘, -:,.. . ..*. ,,.. . . ‘.‘.i . . ...,’ ,pkna caTnea cc) :- 'c , .;, ::,;:..‘; .,. .: :Lutota senegan .’ .:< : . . . . ,.: .:..: .. ... *.; .., ...,’ . .., ‘.! .‘_‘..,‘. \ ..’ .;c. .;...:_ hetero chaelis (vc 2. : .: :.,:.: . . . :.: :: .., ::.:, . . . . I : ...... , . . ,,,’ ;,., . ..:.,:.,‘p::.:‘,,,. Codakia orbiculata (c) :,‘..’ ’ .. ” 'Alpheus i;:::,,: ,.,,‘,,, 1. _..:.. :.:..,::. ,‘,.,.,.,.: :.: “,:‘,..,.,. ‘..‘., . . . .,’ . ..’ i,:: :,. :, . :’ .:’ :’ :, ,: ,..., ‘.. ‘..‘...’ “.:;.‘,,.‘,‘...... ‘.‘.....,‘...... “... . .,.. . ‘.,...’ .‘. . .. ‘,‘,‘;‘. : ‘..,‘.. Chione cmce,lata cvC. ::I ‘: . . . :::: 1. 1. Tdllina alternalta (vc) ._‘_ ,,:::. ..; :.. ‘,‘. ‘. ‘.. . . . ; .\ ,_::.:‘..?.,.. : :::::::,. .,. . ,.<: ;.;,:,._ ,..’ ,,.,,, . .,:. . ,..,:,._. .,: :.., ‘:_.. : 1 .;: :::I I:i‘Anomalocardia cuneimeris (vi) ‘li ., :. Cistenides gouldii (c) I:,:::: :i+ .:_.: . ..r. .::,: ‘,I. . .., .:.;.:., :,.‘. . ..” _.,.. ‘.. ,.::.. . .: :, : ,.:::.,, I;,: ,.:: .:.:::..:: 1. ‘, ,:.:. .:. .,,.: 1.1. i. ., .:“Tellina promera (vc) .: ,:‘,.,‘-;m~.: .:.:,::::I! .“:.‘. _’ .

above the sediment surface) than infaunal permanent residents. These also can feed organisms (those living in the sediment) on the abundant invertebrate fauna of the in the seagrass beds of the southern part seagrass meadows, on the microalgae, on of the west Florida coast, changing to a the living seagrasses themselves, or on lesser proportion of dominant emergent seagrass detritus. In addition, because forms in the north. In addition, they of the abundance of smaller fishes and suggest that there are more abundant large invertebrate predators, such as blue fauna, both emergent and infaunal, in the crabs and penaeid shrimps, larger fishes surrounding sand and muddy areas in the in pursuit of prey organisms transit the areas of the Carolinian fauna1 provinces meadows, using them as feeding grounds. than in the West Indian provinces. Numerous surveys have documented the fish faunas of a variety of areas along the west coast of Florida. These have most 4.3 FISHES recently been reviewed and synthesized by Comp (1985). Seagrass meadows are often populated by diverse and abundant fish faunas. The Fishes that are permanent residents in seagrasses and their attendant epiphytic the seagrass beds are typically small, and benthic fauna and flora provide less mobile, more cryptic species that shelter and food to the fishes in several spend their entire lives there. These ways. The grass canopy provides shelter species are normally of little or no for juvenile fishes and for small direct commercial value but are often

48 characteristic organisms of the seagrass Comp (1985) found two main spawning habitat and may be highly important as times in Tampa Bay. The larger one occurs forage for larger fishes, including those in the spring and early summer, which of commercial and sportfishing importance. enables the juvenile fishes to take The families and species comprising this advantage of the high summer primary category for seagrass meadows on the production. The second, smaller spawning Florida west coast are nearly identical to occurs in the late summer and early fall those in south Florida (Zieman 1982). months (Comp 1985). Members of families Syngnathidae, Gobiidae, and Clinidae are characteristic The most abundant fishes in the seagrass of this group. Pipefishes and seahorses, beds of Apalachee Bay are listed in Table including Syngnathus scovelli S. 11. The most abundant is the pinfish, floridae, Micrognathus cr;niger, rhomboides,Lagodon which numerically can Hippocampus zosterae and H. erectus, often exceed all other fishes combined in abound in the western Florlrda seagrass abundance (Ryan and Livingston 1980). The meadows. The gobies and clinids show pinfish was also observed to be one of the strong affinities with the south Florida most common fishes in Tampa Bay (Springer species, and are represented commonly by and Woodburn 1960; Comp 1985) and the Gobiosoma robustum, Microgobius gulosus, seagrass beds off Crystal River (Mountain and Paraclinus fasciatus. Also 1972). McNulty et al. (1974) found the characteristic of the more cryptic pinfish to be the most common fish in a grassbed fauna are the predators that-iurk composite list from five estuarine areas within the beds or at their edge waiting from St. Marks to Chokoloskee. The for mobile prey. Representative of these most common, the sciaenids, were are the toadfish, Opsanus beta, the Leiostomus xanthurus, the spot, and batfish Ogcocephalus radiatus, and the Bairdiella chrysoura, the silver perch. lizardfish, Synodus foetens (Mountain In general, the fishes abundant in the 1972; Springer and Woodburn 1960). The seagrass beds of the Florida west coast most common stinqray in the northeast are similar to those of south Florida, inshore gulf is Dasyatis sabina (Mountain especially the fauna found in the seagrass 1972). beds of Florida Bay (Zieman 1982). Table 12 gives a comparison of the relative 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 Table 11. Most abundant fish of Apalachee Bay (after obtain repeatable quantitative samples Livingston 1984a). using an encircling net and rotenone. "natural experiment," Capitalizing on a Species Common name Springer and Woodburn (1960) observed large numbers of the ophicthid eel, Ophichthus gomesi, following a severe red rhomboidesLagodon Pinfish tide. Mountain (1972) noted that off Leiostomus xanthurus spot Crystal River the most common eel in trawl Bairdiella chrysura Silver perch samples was the blackedge moray, Monacanthus ciliatus Fringed filefish Gymnothorax nigromarginatus, a common Diplodus holbrooki Spottail pinfish nocturnal forager in seagrass beds. Sygnathus floridae Disky pipefish Orthopristis chrysop tera Pigfish Seasonal resident fishes in the Eucinostomous gula Silver jenny grassbeds are those which spend their Centropomus melana Gulf black sea juvenile or sub-adult stages or their bass spawning season there. These are abundant Monacanthus hispidus Planehead fishes that are usually highly visible and filefish are characteristic of grassbed fauna. Eucinostomus argentius Spotfin mojarra They include the Sciaenidae, Sparidae, Paraclinus fasciatus Banded blenny Pomadasyidae, Lutjanidae, and Gerreidae. Sygnathus scovelli Gulf pipefish Some of these species are also found in Anchoa mitchelli Bay anchovy residence throughout the year.

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 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

Syngnathidae 1 + 4 2 4 + 7 15 Gobiidae 2 14 + 8 4 14 + 15 10 Monacanthidae 3 -_ __ 3 39 8 __ 9 4 Sparidae 4 1 + 1 5 5 + 13 Labridae 5 __ -_ -______- :; 14 Gerreidae 6 6 + 7 9 3 + 2 3 Scorpaenidae 7 30 -_ __ 21 8 Sciaenidae 8 2 + 2 1 1 + 37 17 Tetraodontidae 9 13 + 15 16 11 _- 19 5 Blenniidae 10 9 __ 12 14 19 -_ __ 31 Clupeidae 11 8 + 25 7 -_ _- 11 18 Ambassidae 12 _- ______-_ Apogonidae 13 __ _- 30 __ -_ _- 22 Engraulidae 14 5 + 19 6 22 + 1 26 Bothidae 15 __ + 16 24 14 + 10 16 Mugilidae 16 __ + 30 8 + 25 __ Teraponidae 17 ______- -_ Cyprinodontidae 18 __ + 25 3 -_ + 5 Muliidae 19 __ __ _- 37 11 Haemulidae 20 3 + 6 24 2 + 4 6 __ 10 Clinidae 21 __ __ _- 12 31 Centracanthidae 22 _- _- __ __ _- -_ Searidae 23 _- __ 13 __ 6 2 __ __ 5 Serranidae 24 __ 7 _- 37 7 __ _- Diodontidae 25 11 24 9 -_ 26 12 Gasterosteidae 26 _- _- -_ _- -_ -_ __ Lutjanidae 27 22 16 6 _- 8 1

(Continued) m .. .-- __. - _- _^ _

Table 12. (Continued).

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. Florida Panama Latitude 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 11 + __ 19 + 14 Batrachoididae 33 __ __ 9 24 10 + 24 Cottidae 34 ______+ __ __ I? Atherinidae 35 7 11 + 3 40 Sillaginidae 36 ______Arripidae 37 ______Aulorhynchidae 38 __ -_ __ -_ __ Carangidae 39 4 __ 22 10 12 30 22 Platycephalidae 40 ______Solcidae 41 15 __ 20 10 17 41 24 Plotosidae 42 ______Anguillidae 43 -_ -_ _- -_ _- ______Gobiesocidae 44 ______24 __ 22 __ Hemiramphidae 45 10 + __ 24 __ -_ 33 Callionymidae 46 ______41 Lethrinidae 47 ______Pomacentridae 48 -______41 36 Siganidae 49 ______-_ Gadidae 50 14 24 36 __ Scorpididae 51 ______Cynoglossidae 52 20 24 31 36 Pleuronectidae 53 -______Acanthuridae _- -_ __ __ 54 -_ 20 20 Muraenidae ______55 12 __ __ 34

(Continued) Table 12. (Concluded).

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. Florida Panama Latitude 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 Hoese Springer Weinstein Adams (1962) (1975) Woodburn and Heck and and and Heck (1973) (1960) (1979) Jones McErlean (1979) (1963) (1962) Fish Family Rank

Chaetodontidae 56 -- __ __ -______9 Aulostomidae 57 -- __ -_ -- -_ __ __ 31

No. fish species 21 31 57 93 49 19 106 106 No. fish families 15 20 36 47 25 13 48 45 Other seagrass Ruppia Ruppia Syringodium Halodule ? Halodule Halodule Syringodium genera present Syringodium VI N Depth range (m) 1 1 2 ? ? 1 2 12 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 4.4 REPTILES meadows in the region. The only reptiles that are commonly associated with seagrass meadows are the In addition to the fishes readily caught sea turtles, of which there are several in in trawl surveys, there are numerous the eastern Gulf of Mexico. The only seasonal residents and a few permanent herbivorous sea turtle is the green sea residents, that are highly mobile and are turtle, Chelonia mydas. Throughout its quite abundant, but are not easily sampled range, the primary food of the green with this gear. Such fishes include the turtles is sea grasses and the preferred Atlantic spadefish, Chaetodipterus faber; food is Thalassia (hence its common name, the sheepshead, Archosargus turtle grass). Although not a seagrass probatocephalus; the red drum, Sciaenops feeder, the Atlantic ridley, Lepidochelys ocellatus; and the mullets Mugil cephalus, kempi, is often caught in commercial nets M. trichodon. and M. curema (Sorinaer and set for green turtles in seagrass areas on Roodburn 196b; Mo&ain72): M&y of the upper Florida west coast (Carr and the fishes in this category are those with Caldwell 1956). significant commercial or sportfisheries importance (Thayer et al. 1978a). In pre-Columbian times, green turtles were abundant throughout the Gulf and Caribbean, but from very early on were hunted extensively for their succulent Notable by their absence in northwest meat and calipee (fat), the ingredient Florida grassbeds are the large numbers of that gives turtle soup its unique and juvenile snappers and grunts that use the delicious flavor. Concern over the seagrass meadows of south Florida as reduced populations of green turtles dates nurseries, move to the offshore reefs as back to the previous century (Munroe adults, and commonly return to the 1896). Although limited nesting occurs on seagrass beds at night to feed (Starck and the small beaches of south Florida, the Schroder 1970). The white grunt Haemulon region has almost certainly been primarily plumieri seems to be the only lutjanid a feeding rather than nesting site. Carr found through out the region and the gray and Caldwell (1956) noted that the green snapper, Lutjanus griseus has the widest turtle populations of Florida were distribution of the serranids (Springer composed almost entirely of nonbreeding and Woodburn 1960; Mountain 1972; Ryan and juveniles. The former turtle fishery on Livingston 1980). The spotted sea trout, the Florida west coast was a seasonal one Cynoscion nebulosus, is a major gamefish that began in April and extended until the during much of the year over seagrass first cold front of the fall. Most beds, often found following large schools scientists believed that the turtles left of foraging mullet. 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 The large roaming predators, or throughout the winter (Carr and Caldwell 'occasional migrants" a 1956). Although turtling was carried out classification scheme of Kikuck: (196EFe to some degree throughout the west coast are not normally present, visiting thi of Florida from the Florida Keys to Cape grass beds to forage only infrequently and San Blas, the greatest activity was in the (if You are sportsfisherman) grass beds near the mouths of the unpredictably. On the" Florida west coast Withlacoochee and Crystal Rivers, an area two of the most sought afte; of superior turtle habitat (Carr and representatives of this qroup are the Caldwell 1956). tarpon, Megalops atlanticus, and the king mackerel, Scomberomorus cavalla. Such transient predatory species represent only 4.5 BIRDS a small proportion of the biomass present but may be quite important in determining Shallow seagrass meadows offer feeding fish community structure. and resting areas for many species of

53 birds, but in most cases the exact found wherever the water is sufficiently relationship between the birds and deep for them to swim and clear enough for seagrass meadows is unknown. The them to spot their prey. embayments of the west coast of Florida are one of the most important areas for The groups of birds described above use many bird species, which either winter in two of the dominant feeding modes of the these sheltered bays or use the areas as marine avifauna. A third group hunts by resting and feeding sites during flying some distance above the water until migration. The ecology of wading birds prey is spotted and then plummeting from and their feeding behavior have been the air to seize it. Ospreys, Pandion reviewed by Kushlan (1976, 1978). Odum et haliaetus, and bald eagles, Haliaeetus al. (1982) reviewed the avifauna of the leucocephalus, feed in a similar manner by mangrove regions of southern Florida, seizing prey on the surface of the water while Woolfenden and Schreiber (1973) gave with their claws, while the brown pelican, an extensive review of the birds of marine Pelicanus occidentalis, plunges from some and brackish-water habitats of the western distance in the air to catch fishes in its coast of Florida. pouch. For these birds, the seagrass meadows provide an abundant source of food Table 13 lists 81 species of birds that by concentrating their quarry more than utilize saline habitats in the eastern much of the surrounding habitat. Larger Gulf of Mexico. This information, based birds such as these require great on Christmas bird-count data, shows at quantities of food for themselves and least one broad generalization of habitat their young, and are dependent on the usage. Nearly all of the 81 species local environment not only for protected listed occur throughout the coastal waters nesting sites, but for a healthy of western Florida, but there is a forage-fish population. Woolfenden and variation in the relative abundance, which Shreiber (1973) stated that a juvenile may be related to habitat usage. In south brown pelican requires approximately 120 Florida, with its high concentration of lb of fish to fledge successfully. shallow seagrass flats, the most abundant birds are the wading birds that feed in shallow water or on seagrass or mudflats, 4.6 MAMMALS especially the Ardeidae (herons and egrets) and the Scolopacidae (sandpipers). On the west coast of Florida, Caldwell In contrast, throughout the peninsular and and Caldwell (1973) reported that 27 panhandle bays, the most abundant groups species of marine mammals have been were the Anatidae, containing geese and observed or reported stranded on beaches. ducks; the Gaviidae, including the common Ode11 (1979) reported the same number in loon; and the Rallidae, including the south Florida. Many of the sightings are American coot. Unlike the wading birds, rare or of dubious value; only two marine these birds tend to rest on the open water mammals are commonly found in the shallow of the bays, commonly in rafts of dozens coastal waters of west Florida: the to hundreds or even thousands of manatee, Trichechus manatus; and the individuals. Many of these species feed bottlenose dolphin, Tursiops truncatus. A in the bays, diving to capture fishes or third species, the spotted dolphin, invertebrates or to forage for grasses, Stenella plagiodon, is common offshore, plant tubers, or rhizomes. The most and on occasion will venture in close common waterfowl is the lesser scaup, enough to be observed from shore. Ay;;y;,affinia, which is most abundant in Numerous sightings of a pinniped, the saltwater habitats, often California sea lion, Zalophus occurring in flocks of over 10,000 californianus, were reported (Gunter individuals. Its primary food is benthic 1968). however. Caldwell and Caldwell invertebrates, along with some fish and (1973) question'that the feral sea lions plant material (Woolfenden and Schreiber have established a breeding population. (1973). Another common swimming bird is the double-crested cormorant, The bottlenose dolphin is, by a Phalacrocorax auritus, which pursues fish considerable margin, the most common in the water column. Cormorants may be 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).

Pan- Penin- Coot Common name Scientific name handle sula Bay Keys Totala

Common Loon --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 tt

Double-crested Cormorant Phalacrocorax auritus 40 63 98 121 71

Magnificent Frigatebird magnificensFregata 0 1 t 6 1

Great White Heron -_Ardea occidentalis 0 t 19 12 5 Great Blue Heron Ardea t-lerodias 5 8 26 6 10 Green Heron Butori;-ies virescens t 1 13 2 3 Little Blue Heron Florid; _I -caerulea 5 14 54 14 19 Reddish Egret Dichronianlassa rufescens 0 2 3 1 Common Egret Casmerc,dius albus 13 1; 129 9 32 Snowy Egret Leucopt zthula 2 14 132 7 29 Louisiana Heron Hydran; lssa tricolor 4 7 40 14 13 Black-crowned Night Heron Nycticorax nycticorax 1 1 7 t 2 Yellow-crowned Night HeronNyctanassa violacea t 4 3 3 3

Wood Stork Mycteria americana t 5 65 1 13

White Ibis Eudocimus albus 3 34 267 11 62 Roseate Spoonbill Ajaia ajaja 0 t 19 8 4

Canada Goose Branta canadensis 114 t 0 0 25 Mallard Anas platyrhynchos 26 1 0 6 Black Duck Anas rubripes 4 i 0 1 Mottled Duck Anas fulvigula 0 5 7 2 Gadwall Anas strepera 9 1 i 3 Pintail Anas acuta 28 8 17; t 38 Green-winged Teal Anas carolinensis 4 3 81 1 15 American Widgeon Mareca americana 49 7 45 1 21 Shoveler clypeataSpatula 3 1 44 8 Redhead Aythya americana 88 t t 0" 19 Canvasback valisineriaAythya 2 t 0 1 Lesser Scaup affinisAythya 203 185 17:. 163 Common Goldeneye Bucephala clangula 9 t 0 : 2 Bufflehead Bucephala albeola 26 t t 0 5 Ruddy Duck Oxyura jamaicensis 3 t 43 0 8 Red-breasted Merganser Mergus serrator 26 27 30 33 28

(Continued)

55 Table 13. (Continued).

Pan- Penin- Coot Common name Scientific name handle sula Bay Keys Totala Bald Eagle Haliaeetus leucocephalus t 1 2 11

Osprey Pandion haliaetus t 1 7 5 2 Clapper Rail 1 t 111 Sora American Coot 15: 32 t 24: t 3 8;

American Oystercatcher Haematopus palliatus t

Semipalmated Plover semipalmatus 7 10 19 8 Piping Plover melodus 1 Snowy Plover alexandrinus 1 Wilson Plover wilsonia 4 Black-bellied Plover squatarola 13

Ruddy Turnstone Arenaria interpres 2 8 6 24 Willet Catoptrophorus semipalmatus 11 11 45 6 1: Greater Yellowlegs Totanus melanoleucus 1 1 8 5 3 Lesser Yellowlegs Totanus flavipes 26 1 4 13 White-rumped Sandpiper Erolia fusiocollis : 0 0 0 Least Sandpiper Erolia minutilla 2 6 115 35 2: Dunlin Erolia alpina 59 49 211 37 76 Short-billed Dowitcher 5 11 54 134 33 Semipalmated Sandpiper 12 18 153 54 43 Western Sandpiper 1 6 62 21 59 Marbled Godwit 1 1 7 t 2 Sanderling 10 26 1 12 17

American Avocet Recurvirostra americana t t 8 tl Black-necked Stilt Himantopus mexicanus 0 t t t t

Parasitic Jaeger Stercorarius parasiticus t 0 t t t

Herring Gull Larus argentatus 39 35 3 15 28 Ring-billed Gull Larus delawarensis 76 316 38 74 183 Laughing Gull Larus atricilla 15 104 92 132 86 Bonaparte Gull Larus Philadelphia 19 1 t 15 Gull-billed Tern Gelochelidon nilotica t 1 1 t Forster Tern Sterna forsteri 10 8 5 ; 8 Roseate Tern Sterna dougallii 0 t 1t Sooty Tern Sterna fuscasa 0 0 0" t 0 Least Tern Sterna albifrons t t 0 0 Royal Tern Thalasseus maximus 3 29 12 56 2: Sandwich Tern Thalasseus sandvicensis t 5 14 3 Caspian Tern Hydroprongne caspia 1 7 2 2 BlackBrown TernNoddy AnousChlidonias 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 counted in all areas combined.

although accurate censuses of their in the coastal grassbeds and winter abundance and distribution are rare. In shelter in the spring-fed rivers of the the Everglades Park region of south region, notably the Crystal and Homosassa Florida, Ode11 (1976) found that 36% of Rivers, which during the winter are warmer the animals seen were in open Gulf of than the coastal waters (Powell and Mexico waters, 33% were in Whitewater Bay, Rathbun 1984). Recently heated effluents 20% were in inland waters and 11% were of large power plants, especially nuclear seen in Florida Bay. The relatively low plants with their lower thermal efficiency numbers in Florida Bay were presumed to be and greatly increased heat output, have due to extremely shallow waters which provided additional refuges. would inhibit the movement of this large mammal. In a later survey, Irvine et al. Normally, manatees forage singly, or (1982) found 700 individuals in 146 herds with a mother and calf pair, in the in the Gulf of Mexico, 491 individuals in shallow estuarine grassbeds during the 185 herds in bays, and 192 individuals in warmer months. The major summer feeding 100 herds in marsh and river habitats of grounds are the estuaries and offshore western peninsular Florida. Bottlenose grass beds of the Crystal, Homosassa, dolphin are opportunistic feeders, Suwanee, Withlacoochee, and Chasshowitzka subsisting primarily on fish, squid, and rivers (Powell and Rathbun 1984). Hartman benthic invertebrates (Caldwell and (1969) reported that they spend a quarter Caldwell 1973). Their diets are not well of each day feeding, and will consume at known, but they are frequently observed least 10% of their body weight a day in pursuing schools of mullet. vegetation, a significant amount of seagrass considering adults weigh up to The Caribbean manatee or sea cow, 500 kg. Trichechus manatus, is primarily tropical in distribution, but its range formerly A survey of western peninsular Florida extended across the Gulf of Mexico. On the counted a total of 554 manatees, with the west coast of Florida, it is found in the highest percentage sighted in the shallow, shallow coastal seagrass meadows or in the brackish waters of Collier and Monroe coastal rivers. Although its numbers have counties in extreme south and southwest greatly declined (in recent years) causing Florida (Irvine et al. 1982). In an it to be placed on the Federal Endangered earlier study of the Everglades and the Species List, recent large increases in south Florida region, Ode11 (1976) found a populations along the southern Big Bend total of 302 herds with 772 individuals; coast of Florida have been reported 46% were sighted within Whitewater Bay, (Powell and Rathbun 1984). This coastline 20% in the Gulf of Mexico, 23% in inland provides abundant summer feeding grounds waters, and only I% in Florida Bay.

57 CHAPTER 5. STRUCTURAL AND FUNCTIONAL RELATIONSHIPS IN SEAGRASS SYSTEMS

The importance of seagrasses to the studies quantified these differences in productivity of shallow coastal waters is fauna1 abundance (Roessler et al. 1974; well-recognized: they provide shelter and Yokel 1975a, 1975b; Thorhaug and Roessler serve as nursery and feeding grounds for 1977; Weinstein et al. 1977). The concise diverse assemblages of organisms. The study of Yokel (1975b) reports the variety observed in community structure in findings of this phase of studies. seagrass beds has stimulated efforts to Results from trawls showed that in the identify the functional relationships Rookery Bay Sanctuary, 3.5 times as many within the beds, and thus provide a fishes were captured in seaqrass as in framework for understanding the bare sand and shell substrates (Figure interactions and pathways common to these ZO), and the standing crop of crustaceans systems. (estimated from trawls) was 3.9 times larger in mixed seagrass and algal flats than on nearby unvegetated bottoms. 5.1 THE RELATIONSHIP OF STRUCTURE, SHELTER, AND PREDATION The amount of literature demonstrating the increased abundance of organisms in Seagrasses, with leaf canopies extending seagrass communities . becoming into the water column and rhizome systems extensive. Table 14, from"Virnstein et penetrating the sediment, present a a1.(1983) summarizes much of the pertinent structurally complex habitat where calm literature. Numerous studies ranging in water, a stable substrate, and an area from Florida to Japan to Belize show abundance of detrital and microalgal food that in nearly all cases, the ratio of 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 m F\sh the predators. ( Invertebrates

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 HEAVY THIN SAND/ MUD/ SEAGRASS SEAGRASS SHELL SAND/ ( Halodule a 1 Holodule 1 SHELL Early ecological surveys of Florida Thalassiq) coastal waters included observations of increased densities of fishes and Figure 20. Comparison of fauna1 abundance between invertebrates within seagrass beds seagrass beds and adjacent habitats (after Yokel compared to adjacent habitats. Later 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).

Sieve Abundance Fauna1 Coll. mesh Grass Sand G:S Area Seagrass group gear (mm) (G) (S) ratio Source

Indian River, FL Thalassia/Halodu le M co 0.5 17,479 5,844 3.0 PS II P co 0.5 6,248 3,403 1.8 PS II Cr co 0.5 3,152 485 6.5 PS II De co 0.5 215 15 14.3 PS 11 F Dr 3.2 6.1 0.7 8.8 G (unpubl.) Halodule M co 1.0 7,460 2,530 2.9 (1978) Chesapeake Bay, VA Zostera M co 0.5 39,000 7,850 5.0 ; (1978) Zostera M co i.5" 48,900 13,313 8,462 1,160 42.2 1.6 0 ss (1974) (1977) Tampa Bay, FL Halodule P co Thalassia P co 0:5 33,485 4.0 ss (1974) Biscayne Bay, FL Halodule co 1.0 1.6 OW (1967) Thalassia z co 1.0 "iz (7i4) 1.0 OW (1967) Carrie Bow, BELIZE Thalassia Mo+P co 1.0 6,476 8,000 0.8 YY ii;;;; % Seto Sea, JAPAN Zostera M Sl -_ (2,755) II Cr Sl __ (2,054) (824) :*; K (1974) Chesapeake Bay, VA Zostera De Tr __ (17,292) '(:z:; 18:7 HO (1980) Zostera F Tr __ (1,090) (164) 6.7 OH (1980) Long Is. Sound, NY Zostera F Se __ (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 associated animal complex. Experimental from sand is greatly in favor of the evidence suggests that grass bed seagrass organisms, with ratios of up to invertebrates actively select vegetated 42:l. However, a cautionary note must be habitat rather than bare sand, indicating added: The ratios are highest in the that habitat preference is an important temperate zone stations and in turbid force contributing to observed fauna1 subtropical areas such as Indian River. densities in grass beds. Selection often The three lowest ratios are from Biscayne appears to be based on the form or Bay, Florida, and Belize, which represent structural characteristics of the not only the most tropical stations, but seagrass. also those with the clearest water. It is quite possible, as in other facets of While the relative abundance of seagrass ecology, that there are distinct invertebrates in seagrass is usually high differences in functional relationship when compared to surrounding habitats, the between temperate and tropical systems. actual numbers are highly variable. Large However, studies from the west coast of changes in abundance and even the species Florida, which is a transitional area, encountered are frequently seen over small suggest that here the grassbeds are denser changes in space (Brook 1978) and time and richer in invertebrate abundance than (Greening and Livingston 1982). When the adjacent habitats (Santos and Simgn comparing strictly infaunal organisms, a 1974; Hooks et al. 1976; Stoner 1980 ; different pattern may appear. Stoner Stoner et al. 1983). (1983) found that the relative abundances of infaunal organisms in sand decreased in Stoner (1980b) found that the density of the order, Halodule, Syringodium, macrofaunal organisms and the number of Thalassia, as well as from low to higher species taken was directly related to the biomass of the seagrasses. density of macrophyte biomass. Here the fauna1 dominance was different between the The least-defined patterns of vegetated and unvegetated stations. The distribution and abundance are available analysis of sediments showed that the for seagrass-associated meiofaunal particulate size distribution did not organisms. Bell et al. (1984) reviewed differ and that differences in animal seagrass meiofaunal studies and concluded densities could more directly be that while little comparative literature attributable to macrophyte biomass and not exists that can be directly intercompared, sediment characteristics. due to both a paucity of studies and the large differences in sampling techniques In another study, in the Indian River, and sample processing, their studies Virnstein et al. (1983) surveyed the concluded that nematodes and copepods were macrofaunal invertebrates of seagrass beds the most abundant taxa found in the and nearby bare sand sediments and found sediments; that nematode densities were that the seagrass beds supported three higher in the sediments than on seagrass times the density of invertebrates and 38% blades; and that copepod densities on more species compared with the adjacent blades were equal or greater than nematode sandy sediments. The abundance of densities in the sediments in winter and epitaunal organisms was 13 times greater spring. in the seagrass beds compared with the sand flats. In the seagrass beds 54% of 5.1.2 Structure and Predation the individuals were epifaunal compared to 12% in the sand flats. Virnstein et al. With the correlation between the plants (1983) also found that the epifaunal and animal abundance established, organisms were much more trophically questions followed addressing the nature important, and consequently more heavily of plant-animal interactions and how these preyed upon, than the infauna. relationships shape community structure. Of particular interest is the role of Table 15 summarizes numerous studies on plants in mediating predator-prey the relationship between the structural interactions. There is abundant indirect complexity of seagrass beds and the evidence that the grass carpet offers distribution and abundance of the 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).

Animal species Feature - Taxa Function of seagrass or community patterns Reference

Zostera marina roots macroinvertebrates, infauna roots and rhizomes protect more species and individuals in vege- Orth 1977a,b and rhiromes only, >0.5 mm infauna from predators tated than in bare sand areas

Z. noltii roots macroinvertebrates, epifauna roots and rhizomes provide diverse and dense assemblage of fauna Reise 1978 andrhizomes and infauna. >0.25 mm spatial refuge from preda- associated with vegetation. Greater tors abundance of epifauna and infauna in dense eelgrass compared to low density eelgrass

Halodule wrightii macroinvertebrates, both in- leaves serve as protection response pattern (increase or decrease) Young and Young leaves fauna and epifauna, >l.O against predation depends on individual macrobenthic 1977 mm species

Z. marina leaves amphipods as prey; pinfish, predation rate decreases with susceptibility to predators depends on Nelson 1979a, Lagodon rhomboides, and increasing blade density amphipod life style, i.e., infauna 1979b, 1980 shrimp, Palaemonetes vul- but not in linear function or epifauna, tube builders, or garis, as predators epifaunal free-living forms

Thalassia testudinum ampipods as prey; pinfish, degree of species specific se- amphipod consumption diverged from Stoner 1979 leaves Lagodon rhomboides, as lectivity function of macro- that predicted by heavy macrophyte predator phyte biomass cover; epifaunal forms preferred by 2 fish predator more than infaunal forms

I. testudinum, H. amphipods as prey; pinfish, blade surface area best esti- selection for high seagrass density, Stoner 1980a wrightii, Syringo- Lagodon rhomboides, as mate of habitat complexity i.e., large surface area, based on ~~dium filiforme leaves predator vulnerability of amphipod to predation by Lagodon rhomboides

_T. testudinum, S. fili- macroinvertebrates, infauna biomass of benthic vegetation abundance of epifaunal amphipods and Stoner 1980b forme-leaves - and epifauna, >0.5 mm independent of sediment polychaetes directly related to granulometry, exerts strong macrophyte biomass. Infaunal influence on abundance, amphipods inversely related to dominance, diversity and biomass trophic organization of mac- robenthic infauna and epi- fauna

_T. testudinum, S. fili- amphipods blade density and plant majority of amphipod species associ- Stoner 198Oc forme leaves - species composition me- ated with seagrasses diate predation

Artificial leaves and shrimp, Palaemonetes vulgar- protection from predation shrimp less vulnerable to predation in Coen et al. 1981 rhizomes is and Palaemon floridan- vegetated vs nonvegetated habitats. ~,asprey,pinfish,Q- Competitive displacement of p. c- -don rhomboides, as garis by p. floridanus made p. fi- predator e more susceptible to predation

(Continued) Table 15. (Continued).

Animal species Feature Taxa Function of seagrass or community patterns Reference

Artificial leaves and shrimp, Palaemonetes pugio, shoot density affects foraging significant survival of prey only at Heck and Thoman rhizomes as prey, killifish, Fundulus success of predator high vegetation densities 1981 heteroclitus as predator

Brenchley 1982 _Z. marina roots and macroinvertebrate burrowers root-mats prevent hard bod- size distributions skewed toward small l-hizomeS including polychaetes, echi- ied taxa from burrowing sizes in seagrass bed noderms, bivalves, and more than soft bodied taxa crustaceans

Artificial leaves and b arenaria as prey, Calli- plant structure prevents dig- increased bivalve survival in presence Blundon and Kennedy rhizomes ne=idus as predator ging activities of predator of sparse and dense artificial 1982 vegetation

Z. marina shoots macroinvertebrates, both in- shoot density regulates struc- increasing diversity of fauna1 assem- Homriak et al. 1982 fauna and epifauna, >0.5 mm ture of developing community blage with increasing shoot density

Z. marina, artificial two prey species, juvenile Cal- leaves reduce predatory effi- shallow-dwelling M. lateralis elimi- Orth and van Mont- _ _( leaves and rhizomes linectes sapidus and Muli- ciency of adult Callinectes nated at all densltles of seagrass frans 1982 -lateralis as prey; adult sapidus leaves. Juvenile C. sapidus pro- C. sapidus as predator tected at three dTfferent densities of leaves g H. wrightii roots and two bivalve species, Chione roots and rhizomes function both clam species less vulnerable to Peterson 1982 rhizomes cancellata and Mercenaria as refuge from predation whelk predation but shallower dwell- mercenaria and bind sediments thus ing form more susceptible than deep- increasing sediment com- er dwelling form paction

2. marina whole plant two bivalve species, Prototha- plant serves as protection bivalve densitities higher compared to Peterson and -~ca staminea and -Macoma against siphon nipping by clean sand; reduced siphon nipping Quammen 1982 nasuta fish. Fish shift feeding to in vegetation results in greater net more obvious --M. nasuta growth of p. staminea I. testudinum, S. vFili- amphipods as prey, Lagodon leaves reduce foraging effi- number of amphipods consumed de- Stoner 1982 -_forme. H. wright), rhomboides as predator ciency of predator creases with increasing seagrass leaves biomass, differences occur among macrophyte species. Predator efficiency function of size

_T. testudinum shoots macroinvertebrates, both in- standing crop does not affect similar densities in bare sand and Young and Young fauna and epifauna, >l.O mm species densities vegetation 1982

_T. testudinum whole macrofauna, infauna and eip- increased habitat complexity greater numbers of species and greater Lewis and Stoner plant fauna, >0.5 mm fauna1 densities in close proximity 1983 to seagrass shoots

y. wrightii leaves juvenile red drum, Sciaenops protection from predators, more red drum along ecotone of sea- Holt et al. 1983 ocellatus patchiness more important grass and bare sand than for more than plant length and homogeneously vegetated sites above ground biomass

(Continued) Table 15. (Concluded).

Animal species Feature Taxa Function of seagrass or community patterns Reference

_T. testudinum, H. amphipods and tanaidaceans seagrass growth form and relative abundance of crustaceans Stoner 1983 wrightii, S. filiforme, biomass mediate distribu- function of seagrass species and leaves, roots and tion and foraging behavior biomass. Significance of sea- rhizomes of important predators grass biomass in structuring crustacean assemblages held within, but not across, seagrass species

1. marina and H. infauna and epifauna >1.2 seagrass growth mediates ef- average density of epibentt,os 52x Summerson and wrightii leaves, roots mm fects of large epibentic and of infauna 3x the level Peterson 1984 and rhizomes consumers observed on the sand flat. Epibenthic predators reside in grass bed by day and forage on sand flat at night

1. marina whole plant Mercenaria mercenaria seagrass baffles current, re- growth rates of M. mercencaria Peterson et al. 8 sults in higher particulate paradoxically iiigher in seagrass 1984 food concentrations beds than bare sand, but may be consequence of more particulate food living in it, with the dense seagrass The shifts in amphipod abundance blades and rhizomes providing cover for appeared to be related also to the invertebrates and small fishes, while also relative abundance of predators. In interfering with the feeding efficiency of Halodule beds where amphipod abundance was their potential predators. Heck and low, the number of predatory fish was 2 to Wetstone (1977) hypothesized that the 2.5 times the abundance in beds of the significant plant biomass, invertebrate other seagrasses. In particular, Stoner abundance relationships observed in (1983) found that pinfish made up 67% of Panamanian grass beds largely resulted the fish population, and was the major from predation pressure which is mediated amphipod consumer. by the structural complexity of the grass carpet. Stoner (1980b) observed that Numerous attempts have been made to numbers of macrobenthic animals increased assess the role of predation on epifauna noticeably in the fall with emigration of in structuring invertebrate populations fishes from grass beds in Apalachee Bay. utilizing exclosure-caging experi-mental Stoner (1979) also demonstrated that the manipulations. Excluding fish predators amphipods consumed most frequently by has generally resulted in increases in pinfish were epifaunal. Given the species richness and density (Young et al. behavioral characteristics of amphipods 1976; Orth 1977b; Young and Young 1977), and the feeding preference of pinfish, it although the results can often be follows (Nelson found) that infaunal confounding (Virnstein et al. 1983). amphipods were 1.3 times more abundant Where increases did not occur, it was than epifaunal tube-dwelling amphipods and assumed that decapod predators had 4 times more abundant than free-living increased sufficiently in numbers within epifaunal amphipods with the seasonal the cages, presumably due to a release influx of pinfish, reiterating the role from predation by fishes, that they in predators play in controlling both turn were capable of significantly abundances and species composition within reducing fauna1 numbers within the grass the grass carpet (Nelson 1979a; Stoner carpet (Young and Young 1977). 1979). Virnstein et al. (1983) attempted to determine the importance of small decapod crustaceans as predators, while also In laboratory experiments, Stoner (1980) admitting that they were simultaneously found that common epifaunal amphipods were demonstrating the problems and capable of detecting small differences in difficulties of caging experiments. In the density of seagrass and actively both the seagrass and sand communities, selected areas of high blade density. nested cages were erected with an outer When equal blade biomass of the three cage 2 m square with 12 mm mesh, and an common seagrasses--Thalassia testudinum, inner cage 1.4 m square with 3 mm mesh. Syringodium filiforme and Halodule Both extended above the surface of the wrightii--were offered in preference water. It was anticipated that, with the tests, Halodule was chosen. When equal protection afforded by the fine mesh, the surface areas were offered, no preferences smaller organisms in the inner cage would were observed, suggesting that surface increase in abundance. In fact, the area was the grass habitat characteristic opposite occurred with the numbers of chosen. In later field studies, Stoner small crustaceans and polychaetes (1983) found that amphipods and decreasing in the inner cages; large tanaidaceans were most abundant in beds of crustaceans and fishes decreased in Thalassia or Syringodium, intermediate in numbers somewhat, but also increased in Halodule, and least abundant in bare sand, size. The conclusion was that the larger with a superficial correlation related to crustaceans such as Penaeus duorarum, plant standing crop. However, Thalassia Palaeomonetes intermedius, and Alpheus and Halodule supported nearly equal heteroclitus, and fishes such as numbers when compared on a unit-biomass or Bairdiella chrysura and Gobiosoma robustum unit-surface area basis. Syringodium was entered the cages as juveniles and grazed consistently higher than the other two heavily on the captive prey as they grew species on a unit-surface area basis. (Virnstein et al. 1983). In turn these

64 intermediate sized organizms were released fishes should increase with increasing from predation pressure from larger structural complexity until the feeding carnivores. Leber (1985) alleviated such efficiency of the fishes is reduced due to problems associated with caging interference with the grass blades or experiments by documenting predator conditions within the grass canopy become species, using a smaller mesh size to unfavorable, at which point fish densitigs exclude them, and employing short-term should decline. Nelson (1979 > experiments. He concluded that demonstrated that the predatory efficiency differential predation could account for of the uinfish on amohipods decreased with the strong correlation of amphipods with increasing Zostera marina blade densities. macrophyte abundance, whereas microhabitat Coen (1979) that with increasina selection was the primary factor cover of -red algae (Digenia simplex: determining the strong relationship Laurencia Gracilaria between the abundance of the caridean othersb)dththe'TifJ;-$ for$r;;a~micie~~~ shrimp Latreutes and plant biomass. The on and author noted that the refuge value of the Palaemonetes vulgaris was reduced. Using seagrass canopy depends on the artificial seaarass. Heck and Thoman relationship of prey size to canopy (1981) observed ieduced feeding efficiency architecture, with smaller organisms in the killifish, Fundulus heteroditus, on afforded more protection from predation. the grass shrimp, Palaemonetes pugio, with The relative importance of predation increasing grass density. avoidance versus microhabitat selection in determining community structure among Attempts are being made to sift and seagrass prey organisms should vary due to synthesize the information contained in physical and behavioral differences among the large, and often bewildering, data these populations (Leber 1985). base now accumulating on the relation between the plant and fauna1 components of The above paragraph serves to illustrate the seagrass community. In a review of the complex interactions between predator the relationships of the plant structure and prey populations. Surprisingly little on the predator-prey relationships in is still known about the interaction of seagrass communities, Orth et al. (1984) fishes with the structural complexity of developed the following "framework" for the grass canopy. Because of the the assessment of fauna1 abundance. restricted size of fishes typically inhabiting seagrass beds, Ogden and Zieman 1. In general, epifauna are more sus- (1977) suggested that large predators such ceptible to predation by epibenthic as barracudas, jacks, and mackerels may be predators than infauna. Among the responsible for restricting permanent epifauna, tube dwellers and highly residents to those small enough to hide mobile species will be less suscep- within the grass carpet. For fishes tible than free-living and less larger than about 20 cm SL the grass bed mobile species. For infaunal can be thought of as a two dimensional species, tube dwellers and burrowers environment; these fishes are too large to living at or below the rhizome layer find shelter within the grass carpet. will be better protected than those Mid-sized fishes (20-40 cm SL) are thought living above it. The depth at which to be excluded from the majority of the a prey species attains a refuge in grass beds by the larger predators the sediments will be shallower in a occasionally present; their activities are vegetated habitat than ’ limited to brief forays from the shelter unvegetated habitat, provid:: t$ of reefs or mangrove roots. Although species can burrow into or beneath these fishes are restricted to areas of the rhizome layer. shelter by day, they may move into the beds at night when predation is less 2. The density of shoots, the patch- intense (Ogden and Zieman 1977; Ogden iness of the grassbed, plant bio- 1980). mass, individual leaf area, leaf morphology and the thickness, struc- Heck and Orth (1980a) have hypothesized ture and proximity of the rhizome that both abundance and diversity of layer to the sediment surface are

65 the key characteristics of the plant species that utilize the seagrass that potentially can mitigate the habitat, coupled with the influence effects of predation. However, a of the plant itself and its varia- linear relationship between some of tions in shoot density, biomass, and these characteristics and predator leaf area, all function to determine success does not appear to exist. the structure of fauna1 communities. Instead, a threshold level of these plant characteristics seems neces- 5.1.3 Fauna1 Sampling: The Problems sary for significant protection from of Gear and Technique predation to occur. Because of the variety of leaf sizes and shapes A major difficulty with studying this present in the diverse seagrass abundant fauna is the proper quantitative species and the different character- sampling of the organisms of interest. No istics of the prey and predator one set of gear or techniques samples all species, this threshold level is segments of the community evenly, and some variable. methods are highly selective, which must be taken into account when comparing 3. Heterogeneous grass beds (bare sand different studies that use even slightly areas interspersed within the bed) different sampling gear or sampling should provide more favorable for- schemes. For instance, the pink shrimp, aging areas for motile fishes or Penaeus duorarum, is normally buried in invertebrates, since motile fish or the sediments by day and active at night. invertebrates can forage over the Sampling schemes that utilized daytime unvegetated areas while at the same trawling would greatly underestimate the time remaining in close proximity to abundance of this and other organisms with their protective vegetated habitat. similar habits. Particularly important to juveniles, seagrass beds may serve as a refuge When devices are used which yield from which animals may forage in a relatively small quantitative samples, manner similar to a coral reef amphipods, isopods, gastropods, and (Summerson and Peterson 1984). In polychaetes are typically found to be most addition, it is felt that, in the abundant, (Nagle 1968; Carter et al. 1973; manner of optimal foraging strategy, Marsh 1973; Kikuchi 1974; Brook 1975, prey organisms will "balance preda- 1977, 1978; Lewis and Stoner 1981). Brook tion risk with resource availability (1975, 1977) used a water-powered suction in order to maximize energy gain and dredge in a Card Sound Thalassia bed and growth" (Orth et al. 1984). found that amphipods represented 62.2% of all crustaceans captured. In Apalachee 4. The predator-prey relationships Bay, Lewis and Stoner (1981) compared the discussed above can be affected by sampling results obtained by different- other equally important, yet poorly sized corers (5.5 to 10.5 cm diameter) and investigated, biological and physi- sieve sizes (0.5 and 1.0 mm) in a northern cal processes that occur in these Florida seagrass meadow. They found that multispecies assemblages, such as most organisms collected were within the adult-larval interactions (Woodin upper 5 cm of sediment, although all sizes 1976), adult-adult competitive of corers captured similar numbers of interactions (Peterson 1979; Coen et species and showed very similar species al. 1981), macrofauna-meiofaunal accumulation curves. However, the small relationships (S.J. Bell, pers. corers yielded significantly greater comm. in Orth et al. 1984), and numbers of organisms, and many of the migration patterns due to reproduc- species that were undersampled with the tion and/or feeding, or response to larger corers were those that were closely strong physical gradients such as associated with the seagrass cover. This day-night temperature differences study also investigated the relative (Adams 1976a; Robertson and Howard capture efficiency of 2 sieve sizes, and 1978; Stoner 1980a). The behav- found that the 1.0 mm mesh retained only ioral, physiological, and morpho- 5l%-57% of the individuals captured on the logical differences among all the 0.5 mm mesh. The differences were due to

66 undersampling species with a small amphipods and caridean shrimp often are terminal size as well as juveniles of the captured in large numbers by trawls, whose larger species. mesh size is nearly always larger than amphipods. The trawls are usually not While the previously described studies directly capturing the animals, however, addressed the efficiency 0: but instead are efficiently capturing the different-sized core samplers, the sessile drift algae which the organisms relative efficiency of corers compared are utilizing for shelter. with suction samplers was examined by Stoner et al. (1983) for vegetated and While it is important to recognize that unvegetated sites in Pensacola Bay. They some data will reflect sampling-gear found that with similar mesh sizes for selectivity, it should not obscure the sieving of the cores and for the filter fact that definite patterns of species bag of the suction sampler (0.5 mm) both abundance exist in seagrass meadows when samplers collected similar numbers of compared to adjacent habitats. species. The corers, however, yielded 33% more individuals from a Haloduie bed, and 73% more individuals from a bare sand 5.2 GENERALTROPHICSTRUCTURE habitat than the suction sampler when compared on an equal-area basis. Seagrasses and associated epiphytes provide food for trophically higher The other major type of sampling device organisms by means of three distinct used in sampling fauna in and around routes: (1) direct herbivory, (2) detrital seagrass beds is some form of trawl, food webs within grass beds, and (3) whether a fixed-frame or beam trawl, or a exported material that is consumed in device such as an otter trawl, which other systems, either as macroplant requires a certain velocity through the material identifiable with the naked eye, water column to maintain the trawl in the or as detritus. Despite the fact that expanded condition in which it is able to seagrasses have a relatively high protein fish. In collections in seagrass beds content (see Section 2.3), they are where these sampling devices have been directly grazed by relatively few animals. used, decapods (including penaeid and caridean shrimp and true crabs) and The most vexing questions surrounding gastropods generally dominate numerically seagrass food webs continue to relate to in invertebrate collections (Tabb and the relative roles of detrital and Manning 1961; Tabb et al. 1962; Roessler microalgae-epiphyte grazing pathways, and and Tabb 1974; Yokel 1975a, 1975b; Hooks the functional processes and et al. 1976; Thorhaug and Roessler 1977). intermediaries by which the detrital food pathway supplies nutrition to consumers. Trawl sampling for organisms, especially Most studies continue to show that the fishes, in the clear waters of many primary pathway of energy and nutrient seagrass beds can yield highly variable transfer is through the detrital food web, results that greatly underestimate the and in many systems it may be the only mobile fish fauna within a grassbed. When significant food web. During the past few visibility underwater is 10 to 20 meters, years, new information has been gathered it requires no great effort for highly on the relative role of the other modes of mobile organisms to evade the trawls that utilization, in particular, the role of are deployed behind small boats. Drop active epiphyte grazers, a pathway that nets have been used effectively in shallow has previously been recognized but little water environments, but can be difficult studied. The picture emerging is that all to construct and are not useful in deeper of the pathways exist, but find different waters. For clear waters and deeper degrees of expression, depending on local seagrass beds, a diver-deployed encircling conditions and the consumers present. net has proved highly effective and While the detrital food web appears to be replicable (Robblee and Zieman 1984). the primary pathway of trophic energy transfer, any of the others may be Somewhat paradoxically, small and quantitatively the most important at intermediate-sized organisms, such as specific sites.

67 5.2.1 Seagrass Grazers grass. By comparison, the ragged edge produced by urchin grazing is not obvious, Throughout south Florida and in the and usually resembles a leaf that has been grassbeds of the Caribbean, often large physically torn, until one learns to look numbers of direct consumers ingest living carefully for the stepwise nibble marks. seagrass leaves in significant quantities. The grazing effects of green turtles and These include several species of sea manatees are not obvious until one learns urchins, the queen conch, numerous fishes, what to look for, and are increasingly the green turtle, the Caribbean manatee, difficult because of the rarity of the and assorted invertebrates, especially animals and the decreased likelihood of crustaceans and gastropods (McRoy and observing them feeding. Helfferich 1980; Ogden 1980; and Zieman 1982). In south Florida, grazing on The green sea turtle, Chelonia mydas, is seagrasses is highest in those grassbeds a diurnal grazer of seagrass meadows. The of the Florida Keys and outer margin of grazing behavior of the green turtles is Florida Bay which are in relatively close similar to some of the large, reef proximity to coral reefs. Major seagrass parrotfish in the sense that they graze consumers in that area are parrotfish the seagrass meadows and seek shelter at (Scaridae) (Randall 1965; Ogden and Zieman night, frequently in deep holes or near 1977): surgeonfishes (Randall 1967; fringing reefs, surfacing at intervals to Clav1 JO 1974), porgies and halfbeaks breathe. The turtles then swim some (Randall 1967). With increasing distance unknown distance to the seagrass beds to from the reef tract or patch reef, the feed. What is unique is that they return intensity of grazing by large parrotfish consistently to the same spot and regraze and acanthurids decreases. The dominant the previously grazed patches, maintaining grazers become the small grassbed-dwelling blade lengths of only a few centimeters parrotfish, typified by the bucktooth (Bjorndal 1980). The persistence of these parrotfish Sparisoma radians and sea characteristic patches of neatly cropped urchins, the most abundant of which is leaves provides indirect evidence of usually Lytechinus variegatus, although turtle grazing. Thayer et al. (1982) have Eucidaris * tribuloides Tripneustes calculated that an intermediate sized venticosus and juvenile Djadema antillarum Chelonia (64 kg) consumes daily about are also found g, seagrass beds (Moore et 280 g dry weight of Thalassia blades. al. 1963a, 1963 ; McPherson 1964, 1968; Turtle consumption of seagrass has been Randall et al. 1964; Kier and Grant 1965; estimated to be 2.2% of body weight per Moore and McPherson 1965; Ogden et al. day (Thayer et al. 1980), 1.65% (Bjorndal 1973; Prim 1973; Greenway 1976; and 1980), and 0.6% (Fenchel et al. 1979). others). Turtles do not consume the entire blade Assessments of the quantitative impor- on their first graze of an area, but bite tance of direct seagrass consumption have only the lower portion and allow the appeared only recently, and for relatively epiphytized upper portion to float away few areas. The tacit assumption is that (Bjorndal 1980; Zieman et al. 1984a). few organisms consume seagrasses directly, Many researchers assumed that the epiphyte and that herbivory has substantially complex at the tip of seagrass leaves was decreased with the decline of the popula- of higher food value than the plain tions of green sea turtles and manatees. seagrass leaf, but other studies have Like many assumptions of tropical and shown that the basal portion of the green semi-tropical ecosystems, this resulted leaves is higher in nitrogen concentration from too much reliance on analogy from than the epiphytized tips (Mortimsr 1976; temperate-zone seagrass systems, and a Bjorndal 1980; Zieman et al. 1984 ). The paucity of direct observation. When the nitrogen content of Thalassia leaves widespread use of scuba enabled prolonged decrease with age as well as with underwater observation, the grazing epiphytization. The basal portion of effects of some groups of direct consumers Thalassia leaves from St. Croix contained were instantly recognizable, namely the 1.6% to 2.0% N on a dry weight basis, paper-punch, half-moon shaped holes pro- while the older brown tips of these leaves duced by parrotfish grazing on turtle contained 0.6% to 1.1% N, and the

68 epiphytized tips ranged from 0.5% to Sparisoma radians, 48.1% was consumed by 1.7% N (Zieman et al. 1984a). Thus, the the urchin, Lytechinus variegatus, 42.1% current evidence indicates that the green was deposited on the bottom and available seagrass leaves contain more nitrogen than to detritivores, with the remaining 9.5% either the senescent leaves or the being exported from the system (Greenway leaf-epiphyte complex. By successively 1976). recropping leaves from a plot, the turtle maintains a diet that is consistently The values from St. Croix are similar to higher in nitrogen and lower in fiber other studies in the Caribbean and south content than whole leaves (Bjorndal, Florida (Zieman, unpubl. data), although 1980). The maximum length of grazing time the Jamaica study may overemphasize the on one distinct patch is not known, but quantity of seagrass material entering the Ogden (West Indies Lab, St. Croix, USVI, grazing food chain since urchins are not pers. comm.) has observed patches that normally found at densities of 20 urchins have been repeatedly grazed for up to nine per square meter as were found in Kingston months. Harbor (Ogden 1980). While the overall quantitative importance of urchin grazing Manatees can weigh over 1000 kg and have on the seagrasses of the west coast of been reported to consume up to 20% of Florida has not been determined, several their body weight per day in aquatic reports indicate that, at times it can be plants. When feeding on aquatic plants, locally significant. A population manatees have been reported to feed "explosion" of Lytechinus variegatus off indiscriminately on available plants the coast of Dixie County, Florida, (Hartman 1969). While in marine seagrass resulted in densities of 636 m-2 in meadows, manatees dig into the sediment aggregates of urchins, which denuded using their stiff facial bristles, then approximately 20% of a seagrass bed (Camp uproot the plants and shake them free of et al. 1973). In Apalachee Bay, Zimmerman adhered sediment. A similar mode of and Livingston (1976a) reported that this feeding has been observed in manatees urchin was observed to graze Thalassia feeding in Thalassia beds by this author. leaves down to substrate level, and Feeding patches average from 30 by 50 cm postulated that this was, at least in up to about 50 by 50 cm and usually form a part, responsible for low macrophyte conspicuous trail in seagrass beds. The biomass at certain stations. Urchins were excess sediments from the hole created by also present at stations with low seagrass plant removal are mounded on the side of biomass near Florida State Marine the holes as if the manatee had pushed Laboratory (R.L. Iverson, pers. comm.). much of it to the side before attempting Grazing by the few remaining sea turtles to uproot the plants. and manatees is very localized and reduced. While the shallow seagrass In the Caribbean and south Florida, the meadows of south Florida are used by few amount of material grazed directly is ducks, geese, and related waterfowl, the relatively high. It has been estimated shallow bays and estuaries of the upper (Odgen 1980) that direct grazing on western coast of Florida offer abundant seagrasses is higher in the Caribbean than waterfowl for viewing of hunting, as this in any other marine area. In St. Croix it area is used extensively as either a has been estimated that an amount resting stop or for wintering. Direct equivalent to 5%-10% of daily production grazing by these birds of the Ruppia of Thalassia is directly consumed, commonly found in low-salinity and inshore primarily by Sparisoma radians and areas of upper western Florida is a secondarily by the urchins Diadema feature of this area not seen further antillarum and Tripneustes ventricosus and south. onlv about 1% was exported. while 60% to 100% of the productio'n of Syringodium was An important by-product of heavy grazing exoorted (Zieman et al. 1979). Thus about on living seagrasses is an increase in the 70% of the daily production'of seagrasses turnover rate of the standing crop of was available to the detrital system. In leaves and the increased production of Kingston Harbor, Jamaica, 0.3% of the detrital particles from the fragmentation production of Thalassia was consumed by of living seagrass blades following

69 feeding and passage through the gut these amphipods (48%, 43%, and 75% (Thayer et al. 1984a; Zieman et al. respectively) than other food sources 1984a). In addition, the manner of tested, including macrophytic drift algae, feeding by green turtles, urchins, and live seagrass and seagrass detritus. parrotfish results in the release of often large quantities of torn or fragmented Kitting (1984) has used a unique living seagrass and its subsequent monitoring system to show that grazing of deposition as litter locally or after small invertebrates is highest while the export from the bed (Greenway 1976; Zieman invertebrates are on the upper grass et al. 1979). blades at night and not while at the base of the leaves among the detritus. It is 5.2.2 Epiphyte-Seagrass Complex suggested that these grazers select the rapidly growing ephemeral algae when Many of the literally hundreds of available, but that detritus may be species of small organisms in grass beds important when the algae are not available utilize algal epiphytes and detritus as or overgrazed. Kitting et al. (1984) their food sources. Gastropods, later showed that in Texas estuaries, de1 polychaetes, as well as amphipods, 13C ratios suggested a higher assimilation isopods, crabs, and other crustaceans of epiphyte carbon than seagrass carbon. ingest a mixture of epiphytic and benthic Fry (1984) obtained similar results in a algae as well as detritus (Odum and Heald study in the Indian River in Florida, but 1972). As research continues, it is noted that the dominant seagrass there was becoming apparent that this represents one Syringodium which floats- readily and of the major energy transfer pathways to drifts from the bed with little higher organisms. As one progresses from contribution to the local detritus. In the clear, low-nutrient waters of the the Texas estuaries and the Indian River, Caribbean and the Florida keys, to the the turbidity is very high, and epiphytic more turbid and higher nutrient waters on growth is very high compared with that in the west coast of Florida, there is an the south Florida estuaries. Epiphytes apparent increased dependence on the are thus a higher potential food source epiphytic grazing pathway (Fry 1984; than in clearer waters where the epiphytic Kitting et al. 1984). growths are relatively lower. In highly eutrophic and turbid estuaries, epiphytic In addition to those organisms which grazers can be essential to the health of feed mainly on the epiphytes of old the seagrasses. Orth and van Montfrans seagrass leaves, many species that ingest (1984) have shown that in estuaries with primarily seagrass, such as the excessive nutrient loads, the elimination parrotfish; will preferentially graze the of epiphytic grazers can cause the death epiphytized portion of the seagrass blade. of seagrasses when epiphytes proliferate As a result, seagrass epiphytes may be and block incoming light on the surface of quite important in the flow of energy leaves, restricting seagrass within the grass carpet. Many of the photosynthesis. small, mobile epifaunal species so abundant in the grass bed and important as 5.2.3 Oetrital Feeding food for fishes, feed at least in part on epiphytes. Tozeuma carolinense, a common Detritus food webs are consistently caridean shrimp, feeds on epiphytic algae considered to be the major pathway through attached to seagrass blades; undoubtedly which energy flows in seagrass ecosystems. epifauna are consumed coincidentally In areas where it is present, Thalassia (Ewald 1969). Three of the four common generally forms the predominant fraction south Florida seagrass-dwelling amphipods of the decaying material, with Syringodium utilize seagrass epiphytes, seagrass and Halodule nearly always forming a minor detritus and drift algae as food sources, portion of the detritus. Seagrass litter in this order of importance (Zimmerman et decomposes by being broken down over a al. 1979). Eoinhvtic alaae were eaten at period of months by bacteria, fungi and a high rate by' Cymadusa"compta, Gammarus other organisms. In Biscayne Bay, Fenchel mucronatus, and Melltanitida. The algae (1970) found that Thalassia was the were also assimilated more efficiently by principal detrital component present

70 (87.1%); other portions included: 2.1% mollusks and polychaetes have been other seagrasses, 4.6% algae, 0.4% animal recorded as consuming detritus (Bloom et remains, 3.3% mangrove leaves, and 2.5% al. 1972; Santos and Simon 1974; Young and terrestrial material. The microbial Young 1977). community living in the detritus consisted mainly of bacteria, small zooflagellates, diatoms, unicellular algae and ciliates. These types of organisms form the major 5.2.4 Carnivory source of nutrition for detrital feeders. Typically the infauna in seagrass beds Detrital consumers ingest entire is not as heavily preyed upon as the particles, but also strip bacteria and epifauna (Kikuchi 1974, 1980). The other organisms from the detritus. Very protection from predation afforded the frequently detrital feeders are infauna of grass beds by dense leaf coprophagous, with the recently released canopies and by the fibrous rhizome mats fecal pellet being subsequently reingested of the more robust species of seagrass following a time during which like Thalassia, is great enough that few recolonization and regrowth of the fishes specialize on infauna when feeding microbes occurs (Fenchel 1970). (Orth 1977). In the Indian River, Young and Young (1977) found that epifaunal Mullet and other fishes are abundant and crustaceans such as Cymadusa compta, important feeders on detrital particles Melita elongata, and Erichsonella and benthic microalgae throughout the filiformis, which were apparently heavily entire gulf region (Odum 1970). Carr and preyed upon by fish predators, increased Adams (1973) found that detritus in abundance during exclusion experiments, consumption was of major importance in at while the infaunal species were not least one feeding stage of 15 out of 21 affected. Stoner (1983) noted low species of juvenile marine fishes, abundances and smaller sizes of epifaunal including sparids, hemiramphids, blennies, amphipods at Halodule sites, relative to gobies, atherinids, clupeids and a Thalassia and Syringodium sites. By tetraodontid. comparison, bottom dwelling and infaunal amphipods showed nearly uniform As Stoner (1979) and Livingston (1982a) distribution in both aabundance and size of noted, it can be difficult to impossible the organisms among all the seagrasses. to define when an organism is a true detritivore, because many detritivorous Stoner (1983) believed that the increase organisms are highly omnivorous organisms, in abundance of certain infaunal tanaids consuming many other available substrates, and amphipods in Halodule beds was due to in addition to organic detritus. Most the "thick, tough underground mat of roots penaeid and caridean shrimp are considered and rhizomes produced by Halodule," and to be omnivores, but they are highly that "this underground complex may provide dependent on detritus as juveniles, a more effective refuge from invertebrate becoming more omnivorous, even predators than the larqe diameter rhizomes carnivorous, as adults. Penaeus OdCorarum and sparse roots o‘i Syringodium and the pink shrimp, in addition to organi: Thalassia." While the assumptions detritus, consumes sand, polychaetes, described here may be valid, the nematodes, caridean shrimp, mysids, explanation does not seem consistent with copepods, isopods, amphipods, ostracods, other observations. Halodule beds mollusks and foraminiferans (Eldred 1958; characteristically have fine-grained Eldred et al. 1961). Several of the large sediments which fishes like sea trout and conspicuous invertebrates such as the (Cynoscion) readily forage, while gastropod, Strombus gigas, and the Thalassia beds are much more stabilized asteroid, Oreaster reticulatus, while and resistant to penetration, making primarily consuming other substrates, will foraging by infaunal feeders much more ingest seagrass litter and detritus as a difficult (Zieman, 1982). Much work yet part of their food (Randall 1964; remains in determining the controls on Scheibling 1980). In the seagrass meadows abundance of infaunal organisms in of the upper Florida coast numerous seagrass beds and surrounding areas.

71 Some organisms are quite flexible in feed primarily on copepods, amphipods, and their response to prey abundance. The plant debris and detritus. The earliest blue crab, Callinectes sapidus, has been stages of the pinfish and spot occur in observed to shift its feeding from Zostera late winter when they selectively feed on infauna to epibiota. Because of the planktonic copepods. With development, protectiveness of the rhizome layer to the all become more omnivorous; the spot and infauna, and the accessibility of the the mojarras become primarily benthic epifauna, the impact of blue crab feeders. The second major grouping of predation may be greatest on epibenthic Livingston (1982a) is primarily composed fauna (Orth 1977b). of benthic omnivores and carnivores. Included in this group are the Many of the important top carnivores intermediate stages of the pinfish, the present on the grass flats of south spotted pinfish Diplodus holbrooki, and Florida also inhabit the seagrass meadows the monacanthids. While the monacanthids throughout the western coast of Florida. show similar feeding habits, the two These include the widely distributed lemon pinfish species showed little dietary shark (Negaprion brevirostris) and the overlap despite being both temporally and bonnethead shark (Sphyrna tiburo), the spatially sympatric (Livingston 1982a). tarpon (Megalops atlanticus), the With further development, the pinfish lizardfish (Synodon foetens), the coronet becomes primarily an herbivore. The third fish (Fistularia tobami the barracuda group contained the pigfish, Orthopristis (Sphyraena barracuda), carangids, the grey chrysoptera, the silver perch, Bairdiella snapper (Lutjanus griesus), and the chrysura, and the pipe fish Sygnathus spotted seatrout (Cynoscion nebulosus). floridae, which may be generalist feeders While some of these carnivores are juveniles,as but specialize on resident, such as the lizardfish and the crustaceans such as shrimp, crabs, and gray snapper, others, like the tarpon, amphipods as adults. While some species undergo extensive seasonal migrations. showed the progressive trophic changes with development, others such as the bay 5.2.5 Trophies and Ontogenetic anchovy, Anchoa mitchilli, and the banded Development of Grassbed Fishes blenny, Panus fasciatus, showed more persistent feeding patterns throughout Carr and Adams (1973), Stoner (1979), their development. and Livingston (1980b) have all demonstrated ontogenetic changes in the feeding habits of fishes inhabiting 5.3 DECOMPOSITIONANDDETRITAL PROCESSING seagrass meadows on the west coast of Florida. Much of the work has emphasized Detrital food-web theory in marine and the life history changes in the feeding aquatic ecosystems is based on the concept habits of the pinfish, which is one of that for the majority of animals that the most abundant fish throughout the area derive all or part of their nutrition from and is extremely important as a forage macrophytes, the greatest proportion of fish. Although the pinfish undergoes fresh plant material is not readily usable progressive trophic changes with as a food source. For these organisms, development, detritus and seagrasses are a macrophyte organic matter becomes a food component of its diet at all stages source of nutritional value only after (Stoner 1979; Livingston 1980b). As an undergoing decomposition to particulate adult, usually 75% to 90% of its diet organic detritus, which is defined as dead consists of seagrasses or detritus and organic matter along with its associated plant debris. Livingston (1982a) microorganisms (Heald 1969). investigated the trophic organization of 14 fish species over an eight year period This section will describe only briefly in the shallow grass beds of Apalachee the detrital food-web concept and will Bay. He divided the fishes into three then discuss recent work that is pertinent major trophic groups. The first group was to the understanding of detrital food webs primarily planktivorous forms and included in seagrass ecosystems. Numerous general the early life stages of anchovies, spot, review papers exist on the subject of mojarras, and pinfish. These juveniles detrital processing and detrital food-web

72 theory relating to seagrass systems; among simple physical agitation, or of grazing them are Fenchel and Jorgensen (1977), Lee by active detritivores, such as amphipods (1980), Tenore and Rice (1980), and and isopods. Reduction of particle size Nedwell (1983). Review papers directed increases the surface area available for more specifically to seagrasses include microbial colonization, thus increasing Fenchel (1977), Klug (1980), Robertson the decomposition rate. The fine detrital (1982), and Thayer et al. (1984b). Recent particles, whether utilized locally as and significant work is reported in the suspended or deposited organic matter or Proceedings of the Symposium on Detritus transported by the water to distant areas, Dynamics in Aquatic Ecosystems (Roman and provide food for trophically important Tenore 1984). Much of this section has fauna of seagrass beds and adjacent been liberally (and literally) extracted benthic communities, such as polychaete from two previous works (Zieman 1982, worms, amphipods, isopods, ophiuroids, 1987). certain gastropods, and mullet.

As plant litter begins to decay, it The food value of detritus has commonly generally passes through three been considered a function of the nitrogen recognizable phases (Godshalk and Wetzel content of the material (Odum and de la 1978). The first phase is a rapid weight Cruz 1967). However, considering nitrogen loss due to leaching and autolysis of content alone can overestimate the plant compounds. This phase is generally nutritional value of the material since up very rapid and the materials released are to 30% of the nitrogen can exist in readily utilized by a variety of tightly bound non-protein fractions organisms. In the second phase, decay is (Harrison and Mann 1975b; Suberkropp et slower and weight reduction is due to a al. 1976; Odum et al. 1979). As combination of fragmentation and the decomposition progresses, the non-protein simultaneous degradation of the substrate nitrogen fraction can increase by microbial activity. At the end of this proportionally to total nitrogen yielding phase, the remaining substrate is highly a food source of lower value as the result refractory and of greatly lowered food of several processes: complexing of value. (Although the material may have a proteins . the lignin fraction relatively high caloric value, the (Suberkropp 'e?t al. 1976); production of calories are in the form of structural chitin, a major cell wall compound of compounds which most organisms cannot fungi (Odum et al. 1979); and degrade enzymatically.) The third phase decomposition of bacterial exudates (Lee of decay involves the relatively slow et al. 1980). However, protein (Thayer et decomposition and fragmentation of this al. 1977) and amino acid (Zieman et al. highly resistant residual material. 1984c) have been shown to increase in some macrophytes during decomposition Depending on the source material and presumably leading to an enriched food environmental conditions, this degradation source. Inhibitory compounds found in process may take from several weeks to macrophyte leaves have also been found to years. Increasing resistance to decrease in older and decomposing degradation is roughly in the order: macrophyte leaves and litter (Harrison and algae, seagrasses, salt marsh plants, and Chan 1980), which may increase their mangroves. The rate of degradation is palatability to consumers. increased by physical breakdown and fragmentation, alternate wetting and Bacteria, fungi, and other drying (Zieman 1975a), the action of microorganisms have the enzymatic capacity grazers (Fenchel 1970; Morrison and White that many animals lack to degrade the 1980), and increased nutrients in the increasingly refractory macrophyte organic medium (Fenchel and Harrison 1976). matter! converting a portion of it to microbial protoplasm and mineralizing a During decomposition and detritus large fraction. Whereas nitrogen is formation, the size of the particulate typically 2% to 45% dry weight of matter is decreased, making it available seagrasses, microflora contain 5% to 10% as food for a wider variety of animals. nitrogen. The microflora may use nitrogen This size reduction may be the result of from the macrophyte substrate, but they

73 also have the capacity to incorporate compounds with high efficiencies, ranging inorganic nitrogen from the surrounding from 50% to nearly lOO%, often with low medium (either the sediments or the water corresponding assimilation of detrital column) into their cells during the plant compounds (Yingst 1976; Lopez et al. decomposition process, thus enriching the 1977; Cammen 1980). Deposit feeding detritus with proteins and other soluble mollusks were found to remove nitrogen nitrogen compounds. In addition, carbon from sediment particles by removal of the compounds of the microflora are much less microorganisms but did not measurably resistant to digestion than the fibrous reduce the total organic carbon content of components of macrophyte litter. Thus, as the sediments which was presumably decomposition occurs there will be a dominated by detrital plant carbon (Newell gradual mineralization of the highly 1965). When the nitrogen-poor, resistant fraction of the seagrass organic carbon-rich feces were incubated in matter and corresponding synthesis of seawater, their nitrogen content increased microbial biomass that contains a much due to the growth of attached higher proportion of soluble compounds. microorganisms. A new cycle of ingestion by the animals would again reduce the In addition to the refractory material nitrogen content as the fresh crop of of detritus, the dissolved organic carbon microorganisms was digested. By selective and nitrogen, released by seagrasses (DOC grazing, amphipods and other crustaceans and DON) during both growth and ingested the microbial component on leaf decomposition, provide nutrition for litter without ingesting the substrate microbes. The DOC-DON fraction released (Morrison and White 1980). However, the during growth and early decomposition grazing action of detritivores can also stages is readily utilized, containing have a positive feedback and enhance the much of the soluble carbohydrate and production of microbial populations on the protein of the plants. It is quickly detrital particles. Microbial respiration assimilated by microorganisms, but is rates associated with macrophyte detritus generally available to consumers as food were stimulated bv the feedina activities in significant quantities only after the of animals, possibly as a- result of conversion to microbial biomass. During physical fragmentation of the detri photosynthesis, living Thalassia leaves (Fenchel 1970; Foulds and Mann 1978) or bu; were found to release 2% to 10% of the removal of inhibitory decomposit on recently-fixed material (Wetzel and products (Lee 1980). Penhale 1979). Fresh-dried Thalassia and Syringodium leaves released 13% and 20% While the importance of the microb al respectively of their organic carbon components of detritus to detritivores is content during leaching under sterile firmly established, other studies have conditions (Robertson et al. 1982). This indicated that consumers may be capable of dissolved fraction was rapidly assimilated assimilating the plant substrate (Foulds by microbial organisms, and in 14 days the and Mann 1978). In some instances, the DOC released by Thalassia and Syringodium high abundance of particulate material leaves supported 10 times more microbial compensates for its low assimilation biomass per unit of carbon than did the efficiency (Hargrave 1976). Cammen (1980) particulate fraction (Robertson et al. found that only 26% of the carbon 1982). requirements of a population of deposit feeding polychaetes would be met by A major tenet of detrital food-web ingested microbial biomass, although the theory has been that microorganisms are a microbial biomass could supply 90% of the necessary trophic intermediary between the population's nitrogen requirements. Thus macrophyte litter and detritivorous while microbial biomass is assimilated at animals. Much evidence suggests that high efficiencies of 50% to 100% (Yingst these consumers derive the largest portion 1976; Lopez et al. 1977) and can supply of their nutritional requirements from the proteins and essential growth factors, the microbial component of detritus (Fenchel large quantities of plant material that 1970; Hargrave 1970; Tenore 1977; see also are ingested also may be assimilated at a review in Levinton et al. 1984). low efficiencies (less than 5%) to supply Detritivores assimilate microfloral carbon requirements.

74 In its broadest form, the detrital food for seagrasses (Rice 1982; Zieman et al. web still seems the most applicable to the 1984b). widest array of seagrass systems. In many areas, undoubtedly detrital and epiphytic When decomposed under similar food sources are used jointly, based on conditions, the stable isotope ratios of the relative availability and food value carbon did not change for either of the material. seagrasses or mangroves. The stable isotope ratio of nitrogen did not change The wide variety of information now during seagrass decomposition, but changed available permits us to re-examine the markedly for mangrove (Zieman et al. role of seagrasses as food sources and the 1984c). The mangrove litter also showed manner in which that food is utilized by much greater uptake rates of ammonium per consumers. Fundamental to this gram of plant litter (R.T. Zieman, unpubl. re-examination is the recognition that the data). From this and other parameters it initial composition of macrophyte litter was concluded that the seagrass varies widely, and that this variation decomposition primarily used the internal affects the food value of the initial nitrogen pool while the mangroves required material, the decomposition rate of the extensive exogenous nitrogen input by the material, and the functioning of the microbes. microbial community (Tenore 1977, 1983; Rice 1982). The variation in composition In another study, Roger Zimmerman (NMFS, is not only a function of species or type Galveston, TX.; pers. comm.) found that of plant, i.e. Thalassia vs Spartina, but amphipods from seagrass and mangrove also a function of the source of the habitats survived on seagrass detritus and material, with Thalassia showing a wide soon acquired the seagrass carbon isotope variation in nutritional content as a signature. When fed on mangrove detritus, function of the latitude in which it grew. the amphipods from the seagrass habitat This variation can affect strongly the could not obtain sufficient nutrients and apparent trophic role of the seagrasses in died. Those naturally occurring in the individual seagrass beds. mangrove habitat survived, but never fully acquired the mangrove isotope signature. Although seagrasses are marine The conclusion of this study and that of macrophytes, they are different in many Zieman et al. (1984) is that detrital ways from their counterparts, salt-marsh consumers can obtain more nutritional plants and mangroves, with which they are value from the seagrass substrate than frequently compared. Seagrass leaves, for from the mangrove substrate, and that many instance, are initially much higher in organisms cannot be sustained solely by nitrogen content than either salt-marsh the microbial flora of refractory plants or mangrove leaves, when each substrates such as mangrove detritus. enters the system under normal conditions Findlay and Tenore (1983) and Tenore et (Rice 1982), and contain up to 4% total al. (1984) found similar patterns between nitrogen (Zieman et al. 1984c) and up to the macroalga Gracilaria containing 25% protein (Vicente et al. 1980; Dawes relatively available nutritive components and Lawrence 1983). While the senescent and the marsh grass Spartina, a refractory leaf tips are low in nitrogen, the bases substrate similar to mangroves. of recently detached leaves usually retain a significant proportion of living green In addition to compositional differences material. between seagrasses and other macrophytes that can lead to different mechanisms of During decomposition, mangrove and decomposition, the plants themselves vary salt-marsh material increases in nitrogen widely among locales. Dawes and Lawrence content (Odum and de la Cruz 1967; Heald (1983) showed a shift in the protein 1969; Rice 1982), while seagrasses remain content of Thalassia leaves from 13% in relatively constant (Rice 1982), or Tampa Bay, to 16% at Key West, to 25% in decrease somewhat (Zieman et al. 1984c). Belize. Thus, within a single species the Similarly, the protein and amino acid mode of decomposition and the quality of content of mangroves rise during the resulting detritus, which affects both decomposition but show less or no change initial and ultimate food value of the

75 material, may be quite different depending addition. Seagrasses occupy a range from on regional origin. the middle of the spectrum to one overlapping with algae, depending on region and environmental conditions. In Synthesis. From the diverse studies the tropics, they are a high-protein described above, a pattern emerges of the source that encourages microbial relative utility of the detrital substrate utilization of the nutrients contained in to consumers based on (1) the initial the seagrass substrate. In more temperate chemical composition of the material, (2) locations, they may be a lower quality the time of decay, and (3) the external protein source and require more extensive environmental conditions. Mangroves and microbial processing to become a useful salt-marsh plants are recalcitrant food. In regions of high nutrient substrates with low nitrogen content, and loadings, the seagrasses may develop an require extensive microbial growth and extensive epiphytic growth that may be processing growth to become nutritionally more productive and a less refractory food useful. For many organisms, macroalgae source than the seagrasses themselves, but and epiphytes are useful substrates this level of epiphytism is not seen in directly or with little microbial clear, nutrient-poor waters.

76 CHAPTER 6. INTERFACES WITH OTHER SYSTEMS

6.1 SALT MARSH AND MANGROVE northward from the vicinity of Charlotte Harbor on the lower west coast, the amount In addition to the seagrass meadows, the of mangrove coverage declines with west coast of Florida has extensive marsh increasing latitude until near Suwannee and mangrove resources. West Florida Sound, north of Tampa, where mangroves are claims 9% of the 6 million acres of marsh completely replaced by coastal marshes. bordering the Gulf of Mexico (Linda11 and Salt-marsh development is particularly Saloman 1977, Thayer and Ustach 1981>, but extensive from Apalachicola Bay eastward. over 85% of the mangroves bordering the Here, in the Big Bend region, the marshes gulf (Thayer and Ustach 1981). In some extend from landward directly into the areas, these habitats form only small, Gulf of Mexico without any form of narrow fringes around the estuary, while protective barrier. In addition to in other areas they extend many kilometers marshes of smooth cordgrass, Spartina inland. alterniflora, the Big Bend area has extensive marshes of black needlerush, Like the seagrasses of Florida Bay, a Juncus roemerianus. While the typical vast quantity of the Florida marsh and Florida salt marsh shows Spartina mangroves are contained within Everglades occupying the low marsh, and Juncus the National Park (Table 16). Moving 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).

Submerged Emergent vegetation Study area vegetation Tidal marsh Mangrove

Acres Acres Acres

Florida bay ...... 256,609 12,148 36,897 Lake Ingraham ...... _ 1,024 0 891 Whitewater Bay ...... 155 68,757 75,976 Cape Sable to Lostmans River ...... 789 108,644 49,349 Lostmans River to Mormon Key ...... 768 23,840 36,000 Mormon Key to Caxambas Pass ...... 4,319 52,181 92,385 Caxambas Pass to Gordon River ...... 501 7,445 13,387

(Continued)

77 Table 16. (Concluded).

Submerged Emergent vegetation Study area vegetation Tidal marsh Mangrove

Acres Acres Acres

Doctors Pass to Ester0 Pass ...... 11 2,959 9,720 Caloosahatchee River ..... 726 1,698 2,973 Pine Island Sound ...... 26,966 7,476 18,657 Charlotte Harbor ...... 23,383 9,087 23,474 Lemon Bay ...... 2,145 331 971 Sarasota Bay System ...... 7,610 235 3,616 Tampa Bay .I..:...... 7,890 843 8,949 Hillsborough Bay ...... 383 203 1,077 Old Tampa Bay ...... 6,809 533 5,024 Boca Ciega Bay ...... 5,800 149 2,464 St. Joseph Sound ...... 8,723 608 1,259 Baileys Bluff to Saddle Key ...... 4,084 16,683 1,301 Saddle Key to S. Mangrove Pt ...... 62,730 32,587 7,915 Waccassa Bay ...... 24,223 30,752 448 Suwannee Sound ...... 5,556 17,643 427 Suwannee Sound to Deadman Bay ...... 2,420 14,763 0 Deadman Bay ...... 1,834 2,549 0 Deadman Bay to St. Marks River ...... 8,110 14,325 0 Apalachee Bay ...... 23,521 55,669 0 St. George Sound ...... 8,641 3,605 0 Apalachicola Bay ...... 737 17,696 0 St. Joseph Bay ...... 6,325 853 0 St. Andrew Sound ...... 373 576 0 East Bay (St. Andrew) .... 1,146 4,597 0 St. Andrew Bay ...... 2,540 875 0 West Bay ...... 1,542 3,349 0 North Bay ...... 1,030 1,664 0 Choctawatche Bay ...... 3,092 2,816 0 Santa Rosa Sound ...... 4,683 309 0 East Bay (Pensacola) ..... 310 3,307 0 Escambia Bay ...... 43 5,152 0 Pensacola Bay ...... 1,547 213 0 Perdido Bay ...... 1,333 1,408 0

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

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 been found to recruit initially in actually form the land-sea interface seagrass habitat but with growth move into without an intermediate Spartina zone the mangrove habitat for the next several (Carlton 1977; Stout 1984). years (Heald and Odum 1970). Since both areas serve as nursery grounds for The importance of wetlands habitat to uncounted small organisms, both also the estuary has been established in a provide feeding grounds for larger variety of locations (Odum and Heald 1972, predators. Some of the game fish that are 1975; Thayer et al. 1978a; Thayer and found both in mangroves and seagrass beds Ustach 1981; Odum et al. 1982), but the include the tarpon, Megalops atlanticus, fauna1 interactions between these habitats the snook, Centropomus undecimalis, the and adjacent seagrass beds are poorly ladyfish, Elops saurus, the crevalle jack, understood. Thayer and Ustach (1981) Caranx hippos, the gafftopsail catfish, concluded that "although extensive Bagre marinus, and the jewfish, information exists on tidal marsh and Epinephelus itajara, (Heald and Odum mangrove plant species structure and 1970). While similar interrelationships distribution in the gulf and on commercial undoubtedly exist between certain fauna of species such as shrimp, quantitative the seagrass beds and salt marshes, these studies on the distribution and abundance are not documented. figure 22, from Lewis of submergent plants and on wetland fauna et al. (1985b), shows the life history of and fishes are scarce." two of the most important fishes on the west Florida coast. For a detailed review In particular, it is not known how the of the mangrove ecosystems of Florida, and faunas of the various areas interact, nor their necessity to fishery organisms, see what role the respective habitats play in Odum et al. (1982) and Lewis et al. the life histories of the organisms. (1985b), while Stout (1984) reviews the Fishes and invertebrates congregate within irregularly flooded marshes of the the mangrove prop roots for protection and northeastern Gulf of Mexico. shelter similar to the manner in which the seagrass canopy can provide nursery shelter. Gray snapper, Lutjanus griseus, 6.2 GULF REEFS sheepshead, Archosargus probatocephalus, spotted seatrout, Cynoscion nebulasus, and One of the major influences on the the red drum. Sciaenoes ocellatus. have structuring of seagrass communities along

79 .,.;,. .,.;;,. 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 Carolinian affinities in the north (Smith with the south Florida grass beds, is the 1976; Lyons 1979). This change is lack of shallow coral reefs in close primarily related to the decreasing winter proximity to the seagrasses. While not as temperatures with the northward intensely studied, the Big Bend area has progression. numerous and extensive limestone outcrops which should function in an analogous Moving from the shoreline to the edge of manner. In the coral reef areas the most the shelf, several zones of fauna1 prominent reef-grass bed interaction similarity are recognizable, controlled involves nocturnally active coral reef largely by changes in the physical fishes of several families feeding over characteristics of the water column and grass beds at night. Randall (1963) noted the substrate. This zonation is based on that grunts and snappers were so abundant the classification developed by Lyons and on some isolated patch reefs in the Collard (1974) and Lyons (1979). The Florida Keys that it was obvious that the nearshore zone extends from the beachline reefs could not possibly provide food or out to 10 m (Figure 23). This area is even shelter for all of them. The major either carpeted with seagrasses or has a groups that shelter on the reef by day and sediment of quartz sand in which the forage into the seagrass beds nocturnally seagrasses are not found. Salinities vary are members of the Pomadasyidae, from 31 to 34 ppt and temperatures vary Lutjanidae, and Holocentridae (Longley and widely over the year due to the Hildebrand 1941; Starck and Davis 1966). shallowness of the water. Lyons (1979) Typically, both juveniles and adults form characterized the fauna as being a "rich, large heterotypic resting schools over warm-temperate fauna with obvious prominent coral heads or find shelter in relationship to the estuary." caves and crevices of the reef. At dusk these fishes migrate (Ogden and Ehrlich The next zone seaward, the shallow shelf 1977; MacFarland et al. 1979) into zone, extends to approximately 30- 40 m in adjacent seagrass beds and sand flats depth, and while salinities are slightly where they feed on available invertebrates higher and more constant, in the range of (Randall 1967, 1968), returning to the 35-36 ppt, the temperatures in the green reef at dawn. These fishes epitomize what coastal water are still seasonally Kikuchi and Peres (1977) have defined as variable. Where they exist, the sediments "temporal visitors" to the grass bed, are calcareous, and the area also has utilizing it as a feeding ground (Hobson numerous scattered outcrops of the 1973). limestone bedrock, which provide substrate and shelter for many organisms, especially shallow water tropical species (Lyons 6.3 CONTINENTALSHELF 1979). Near the outer edge of this zone, the clear blue offshore waters are found The ecology of all shallow water with nearly constant salinities and communities on the west coast of Florida temperatures that vary only 3 to 4 degrees is strongly influenced by the enormous seasonally. This is the middle shelf continental shelf in the region, zone, extending down to about 140 m, encompassing more than 78,000 km2. The although it has been previously divided extremely low gradient in this region is into inner and outer subzones at 60-70 m responsible for seagrasses being found at (Lyons and Collard 1974). The sediments what would normally be great distances in this area are calcareous and the offshore. Throughout the region there are limestone outcrops often extensive. The gradual fauna1 changes that occur both on fauna is primarily tropically derived a north-south gradient along the shore, (Lyons 1979). and along a depth gradient offshore. Near the junction of the shallow and Along the latitudinal gradient, the middle shelf zones southeast of Cape San fauna of the shallow water communities Blas lies a rich, rocky reef area known as changes from a predominantly tropical West the Florida Middle Ground, a 1500 km2 area Indian fauna in the south to a more with a mixture of irregular limestone warm-temperate continental fauna with escarpments and knolls that rise as much

81 MISSISSIPPI-ALABAMA SHELF \ \\,\

WESTFLORIDA SHEL~F

0.10m IO-30m

IO-60m

Mddle she If !I 60 140 m

E Deep sh,lf 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 Inshore circulation is dominated by two substrate (Smith et al. 1975). The highly large gyres (Figure 24), with elements of tropical fauna of the area is Florida estuarine waters in the north, characterized by corals of the genera Florida Bay waters in the south, and Porites and Oculina, and the hydrocoral tropical waters from the Loop Current, Millipora, along with other brought in from the Yucutan Channel (Chew scleractineans, alcxonarians, 1955; Austin 1970), which has the actiniarians, and zoantharians (Smith et potential for transporting large numbers al. 1975). In addition, benthic algae of tropical larvae into the region (Smith (Cheney and Dyer 1974), invertebrate 1976). There is also evidence for (Austin 1970; Smith et al 1975), and fish seasonal upwelling along the outer edge of (Smith et al. 1975) communities have been the Middle Ground (Austin 1970), which found to be highly tropical in Smith (1976) attributes as the reason for composition. the large numbers of planktivorous fishes in the region. The distribution of tropical reef organisms along the northwestern Florida Throughout south Florida and in other shelf is a function of the highly areas, more and more studies are showing irregular, shallow shelf-bottom topography the interactions between the faunas of the and the influence of warm water masses. reefs and the seagrass meadows, as well

82 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 fragments off the coast of North Carolina in 3,160 m of water, although the nearest source of Thalassia was 1,000 km south. Roper and Brundage (1972) found blades of 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 Figure 24. Eastern Gulf of Mexico current patterns Caribbean as deep as 6,740 m. Much of the during summer (after Chew 1955 and Austin 1970). material showed bite marks of shallow water parrotfish as well as indications of recent consumption.

Grazing by herbivores, mortality caused as with mangroves and coastal marshes by low tides on shallow banks, and (Ogden and Gladfelter 1983). Such studies wave-induced severing of leaves that are for the seagrass meadows and the offshore becoming senescent are the primary sources reef and shelf fauna of the west Florida of drift material. Sporadic large coast are lacking, but the potential for releases of material occur during major these fauna1 interactions is high (Darnell storms, in which both living leaves and and Soniat 1979). rhizomes are uprooted (Thomas et al. 1961).

6.4 EXPORT OF SEAGRASS For all species of seagrasses, blades that are fresh and healthy when detached One potentially important interaction of will float better than senescent leaves. the west-coast seagrass beds and the Because of the difference in size and offshore communities is the transport of shape of Thalassia and Syringodium blades, detached seagrass leaves and particulate grazing or nibbling by most herbivores material from the highly productive will completely sever a Syringodium blade inshore beds to the offshore areas. The and allow it to float off, while the same material exported from the seagrass bite will not sever a Thalassia blade meadows can serve as both a carbon and (Zieman et al. 1979). In addition. nitrogen source for benthic, midwater, and Syringodium blades float better than those surface feeding organisms at considerable of Thalassia. so that a much hiaher distances from the original source of its proportion of' the Syringodium producgion formation (Zieman et al. 1979; Wolff is transported from the source bed. In 1980). In south Florida, the prevailing St. Croix, 60%-100% of the daily winds move detached blades westward from production of Syringodium was detached and the shallow grass flats. This material is exported, whereas only 1% of Thalassia was carried in considerable density over the exported, primarily as bedload (Zieman et productive Tortugas shrimping grounds and al. 1979). In the Indian River, Fry has been observed nearly 400 km west of (1984) found that 47% of the Syringodium the source beds (Zieman, unpubl. data). production was transoorted from the Incze and Roman (1983) found that system, which, in part,' could account for

83 the absence of seagrass isotopic signature nursery value of the seagrass-dominated in the consumers there. No studies as yet shoreline habitat sampled. exist on the export or transport of seagrass material from the meadows of the 6.5.1 Blue Crabs west Florida coast; however, because of the demonstrated importance in other The blue crab, Callinectes sapidus, is Florida seagrass beds, it is likely that an abundant and important resource along there is a large amount of material the gulf coast for both sport and transported from this region. Its commercial fisheries, ranking as the third destination and fate, however, remain to largest food fishery in the Gulf of Mexico be quantified. (Perry 1975; Oesterling and Evink 1977). Blue crabs are caught throughout Florida, but are in lowest abundance in the Florida 6.5 NURSERY GROUNDS Keys and reach their highest abundance in the area between Tampa and Apalachicola One of the most important roles of Bay (Steele 1979). Like nearly all of the seagrass beds in the coastal ecosystem is fishery resources of the gulf coast, blue that of a nursery ground in which crabs are estuarine dependent throughout postlarval stages of fishes and much of their life. invertebrates concentrate and develop. In addition, important species, such as the Following spawning, the young crab spotted seatrout, Cynoscion nebulosus, larvae drift with the currents and spawn in, or just adjacent to, seagrass metamorphose into a megalops stage. The beds (Tabb 1966a,b; Lassuy 1983). young crabs enter the estuary either as Seagrass habitats offer high productivity, megalopi or as early juveniles, using a surface areas, and blade densities, as form of tidal migration, burying in the well as a rich and varied fauna and flora. sediments on the ebb tide and rising into Seagrass provides abundant nursery habitat the water column to be transported into and, based on abundance and size data, the estuary on the flood tide (Williams many important species prefer it over 1971; Sulkin 1974), a mechanism first available alternatives in the estuaries proposed for pink shrimp larval and coastal lagoons (Yokel 1975a). In migrations. In the estuary they grow and Apalachicola Bay, Livingston (1984) noted mature, using the seagrass meadows as that numerous invertebrates and fishes nurseries during their juvenile stages. used the seagrass beds as nurseries. Most Mature crabs are found throughout the of the penaeid shrimp and fishes found in estuary, with many continuing to forage in the beds were seasonally abundant during the seagrass beds. When mature, the early stages of their reproductive cycles females will move into lower salinity (Livingston 1984b). waters and protected areas such as tidal creeks, molt a final time, and breed while Numerous species of fishes and still soft (Oesterling and Evink 1977). invertebrates have been found to use The females cannot molt once fertilized. Florida grass beds as nursery grounds. In After hardening and as their egg masses Tampa Bay, 23 species of finfish, crab, develop, the females begin to migrate and shrimp, of major importance in Gulf of offshore to higher salinity waters. The Mexico fisheries, were found as immature adult males generally remain within the forms (Sykes and Finucane 1966). estuary and continue to grow. Livingston (1984) found Apalachicola Bay to be an important nursery for numerous The typical patterns described for blue invertebrates and fishes, and listed the crab spawning indicate that the females abundance, natural history, and move offshore and spawn in the general seasonality of 26 of the most important vicinity of their source estuary. species (Table 17 in Livingston 1984b). A However, tagging studies in Florida have third of the species collected at shown that females migrate extensive Matecumbe Key seagrass beds by Springer distances, up to 500 km, to spawn in the and McErlean (1962), including all grunts, Apalachicola Bay region (Oesterling and snappers, filefishes, and parrot fishes, Evink 1977). Following spawning, the occurred only as young, indicating the planktonic larvae become entrained in eddy

84 currents related to the Loop Current and shrimp fishery is the largest in dollar the two inshore gyres, and are distributed value (Taylor et al. 1973b). The two along the coast of Florida (Figure 25). major shrimping grounds are the Tortugas The losses with this type of reproduction grounds to the north and west of the Dry are apparent; it has been estimated that Tortugas, and the Sanibel grounds, only one millionth of the spawn reach stretching from just north of Naples to maturity (Van Engel 1958). The migration south of Tampa (Saloman et al. 1968). The of the female crabs coincides with the nurseries for this fishery are in the flooding of the Apalachicola and adjacent seagrass beds, mangroves, and marshes of river systems, which is thought to coastal Florida (Tabb et al. 1962, increase the amount of suspended Costello and Allen 1966). The shrimp particulate detritus and aid in providing spawn on the fishing grounds in deeper food for the larvae and juvenile crabs water throughout much of the year, and the (Oesterling and Evink 1977; Livingston larvae are carried back into the coastal 1984b). Oesterling and Evink (1977) and wetlands (Tabb et al. 1962; Munro et al. Livingston (1984b) correctly pointed out 1968). Roessler and Rehrer (1971) found that current plans by the Army Corps of post-larval pink shrimp entering the Engineers to place additional dams in the estuaries of Everglades National Park in Apalachicola drainage basin ostensibly all months of the year. for flood control and navigation, could be disastrous to this vital fishery. Throughout Florida, the most copious Likewise, the diversion of fresh water penaeid is the pink shrimp, Penaeus flow for additional development could have duorarum. South of Tampa, individuals of similar deleterious effects. the brown shrimp, Penaeus aztecus, and the Caribbean white shrimp, Penaeus 6.5.2 Shrimp brasieliensis, are found intermixed with the pink shrimp, but are usually not Penaeid shrimp are an important fishery abundant (Saloman et al. 1968). North of resource in Florida, especially in the Tampa: the pink shrimp is the most gulf coast region. While the menhaden plentiful, being the seventh to ninth most fishery is the largest in the Gulf of abundant invertebrate in Apalachee Bay, Mexico in terms of pounds landed, the 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 Figure 25. Blue crab spawning migrations and larval sand flats and forage in the grass bed at transport (after Oesterling and Evink 1977). night. As they near maturity, they

a5 migrate to the deeper waters offshore, much less numerous sparids that frequent usually at the onset of the first major grassbeds in this region. cold front passage of the season (Hildebrand 1955, Williams 1965). Recent Several sciaenid species may be found in studies using stable isotope tracers have the grassbeds of west Florida, but the shown populations from two contiguous most common are the spotted seatrout, the bodies of water, Rookery Bay and Johnson spot, and the silver perch. The spotted Bay, to have distinct isotopic signatures seatrout is one of the few larger which take weeks to months to acquire. carnivorous fishes present in south This indicates that the populations Florida waters to spawn within the estuary are staying within their embayment, and (Tabb 1961, 1966). Its eggs sink to the are not moving freely throughout the bottom and hatching takes place in bottom habitat of the region (Zieman et al. vegetation or debris (Tabb 1966). The 1984c). silver perch is the most abundant sciaenid (often second to the pinfish) in northern 6.5.3 Fish Florida and Whitewater Bays, being taken throughout the year (Tabb and Manning Like those in south Florida (Zieman 1961). 1982), the seagrass beds of the west Florida coast are important nursery The pigfish is the most common pomo- grounds tor numerous species of commercial dasyid, inhabiting areas with grassy or and sportfish, and for small forage muddy bottoms and turbid water in west species that serve as food for larger Florida estuaries. The white grunt is carnivores. While the composition of the less abundant, but is common throughout grassbeds of the Florida Keys and portions the area, occurring most commonly over of Florida Bay are distinct because of the Thalassia beds in clear water as juveniles influence of reef-related juveniles, the (Tabb and Manning 1961; Roessler 1965; fauna from northwestern Florida Bay is Bader and Roessler 1971; Weinstein and highly similar to all the inshore regions Heck 1979). of the west coast to Apalachicola Bay, both in terms of the important families The two snappers (Lutjanidae) that are and the numerically most abundant species. most common throughout the region are the The major families containing predators two most often associated with grassbeds, that are associated with seagrass beds at the gray snapper and the Lane snapper. some stage in their life cycle are the Both occur throughout the range, and are Sparidae, Sciaenidae, Pomadasyidae, especially common in south Florida. Sygnathidae, Balistidae, and Serranidae Juvenile gray snappers have been (Joseph and Yerger 1956; Springer and considered the most common snapper in Woodburn 1960; Tabb and Manning 1961; Wang northern Florida and Whitewater Bays, and Raney 1971; Mountain 1972; Yokel including freshwater regions (Tabb and 1975a; Livingston 1984a). Manning 1961), while juvenile Lane snappers have been abundant in Thalassia In virtually every survey of fish fauna habitat in northern Florida Bay when of the west coast of Florida, the pinfish salinities were above 30 ppt (Tabb et al. was the most abundant fish collected, and 1962) in northern Florida Bay, and were nearly all abundant the most common snapper taken in grass i:roughout the year.c?~e~ook~~~ Bay (Yokel habitat of the Ten Thousand Island region 1975a) and in Fakahatchee Bay (Yokel of the southwestern Florida coast (Yokel 1975b) on the southwest Florida coast, 1975a,b; Weinstein et al. 1977; Weinstein juvenile pinfish showed a strong and Heck 1979). preference for vegetated areas. The sheepshead, another sparid, initially 6.5.4 Detached Macrophytes as emigrates to grass beds but quickly moves Nursery Habitat into mangrove habitats (Heald and Odum 1970) or rocks and pilings (Hildebrand and In the previous chapter, it was noted Cable 1938). The spottail pinfish, that even using such a coarse sampling Diplodus holbrooki, and‘the gras; porgy; device as a large mesh otter trawl will Calamus arctifrons, are other common but yield many small organisms, such as

86 amphipods and isopods (see Chapter 5), as juveniles appeared to correspond with the well as numerous juveniles which use greatest accumulations of the drift algae. detached macrophytes as shelter. Although seagrasses may be associated with these While seagrass beds may be important materiais, it is primarily composed of habitat for pre-adult and immature adult 1 drge balls or amorphous masses of spiny lobsters, Panulirus argus, in south drifting algae (Cowper 1978). While many Florida, drift algae have been found to be algae can go into the makeup of the drift a critical habitat for the newly settled algae, the most common ones in western and juvenile lobsters (Marx and Herrnkind sotithern Florida are species of the 1985). The earliest stages of lobsters rhodophyte genus Laurencia. were found solitarily occupying clumps of Laurencia, using it for shelter and abundant food. After reaching approximately 17 mm in carapace length, Currently, there are few studies of this the juvenile lobsters leave their solitary highly important but ephemeral habitat. existence in the drift algae and begin to In western Australia, Lenanton et al. accumulate in dens, becoming more (1982) showed that the concentrations of gregarious with the transition (Marx and several important fish were highest in the Herrnkind 1985). Although other studies zone of the drift algae near the shore. are lacking at this time, drift algae is The main food of these fishes were an associated habitat of potentially great amphipods that were profuse in the drift importance as a nursery and needs much algae. In addition, the arrival of the more study.

87 CHAPTER 7. HUMAN IMPACTS AND APPLIED ECOLOGY

The west coast of Florida possesses vast termed acute stress as opposed to chronic regions of highly productive coastal sea- stress. Acute stress is stress resulting grass, mangrove, and marsh habitats that from direct damage that physically kills continue to be relatively undisturbed by or removes the plants. The most common human impact. This same region also has example of this type is the extensive areas like Tampa Bay that could serve as losses that have been caused by direct case studies on how to rape and plunder a habitat removal by dredging and filling. formerly productive natural system with By comparison, chronic stress gradually utterly no concern for the future. While kills the plants over a period of time, some forms of human impact, such as oil creating conditions in which either spills, have less impact on seagrass respiration exceeds production or in which meadows than on the emergent interface the plants lose their ability to compete communities (mangroves and salt marshes), with other species for light, nutrients, other stresses, especially dredging, and space. Two of the major causes of filling, and eutrophication are highly this type of stress are eutrophication, destructive to the seagrasses. Heavy with its excessive algal growth, and the population influx and the resulting suspended sediments and nutrients from developmental pressures have severely dredging and filling operations. Both of impacted some areas, but others, such as these causes of pollution operate in a the Big Bend area, have been less similar manner on the seagrasses; that is, threatened due to their relatively low they increase turbidity and decrease the population density, inacessibility! and light incident on the seagrass leaf, recent conservation efforts. In addition, reducing its net production and while all of Florida's coastal waters now competitive fitness. have increased protection, Rookery Bay, Apalachicola Bay, and much of Charlotte Most of the recorded seagrass losses Harbor and Pine Island Sound have now been have been attributed to acute stress made estuarine sanctuaries and marine effects. However, this may simply be due preserves. to the easier accountability when a brief, obvious stress, such as a canal dredging, Many publications now document the destroys a grass bed. The great losses ecological importance of these habitats that are now being documented for many of and the extent of human impact, both Florida's estuaries have been caused by potential and realized, upon them (Zieman the insidious, continual decline of water 1975b, 1982; Thayer et al. 1975, 1984a; quality in these estuaries. Phillips 1978; Ferguson et al. 1980; Livingston 1984a; Zieman et al. 1984c). 7.1 DREDGING, FILLING, AND OTHER previous reviews (Zieman 1975b, PHYSICAL DAMAGE 19:;) human impacts were categorized based' on the activity causing the 7.1.1 Acute Stress damage. This study adopts a somewhat more functionally based approach. Seagrasses The most common and obvious destructive can be killed off by human impacts, or in influence on seagrass beds in Florida has some cases natural disturbances, either historically been the dredging and filling directly or indirectly, by what will be of estuaries and adjacent wetlands.

88 Florida ranks third among the gulf coast Saloman (1968) found only 20% of those States, after Texas and Louisiana, in same species in the canals. Most of those amount of submerged land that has been were fish which are highly mobile and thus filled by dredge spoil with 9,520 ha not restricted to the canals durinq (Linda11 and Saloman 1977). In Texas and extreme conditions. Species numbers were Louisiana, most of the spoil created came higher in undisturbed areas, but 30% more from dredged navigation channels, while in fish were found in the canals. The most Florida, it accounts for less than 5% of abundant (the bay anchovy, the Cuban the State total (Figure 26). Not anchovy, and the scaled sardine), are surprisingly, the majority of filling of planktivorous, and may have benefitted submerged areas in Florida has been to from the higher nutrient levels in the create land for residential and industrial canals and the shelter provided. development. Recolonization was negligible at the bottom of the canals and it was concluded Studies conducted in Tampa Bay and Boca that the sediments there were unsuitable Ciega Bay were among the first to for most of the bay's benthic inverte- demonstrate the long-term impact of brates. Light transmission values were dredging activities, and remain some of highest in the open bay away from land- the most definitive. Between 1950 and fills, lowest near the filled areas, and 1968, an estimated 1,400 ha of the bay increased somewhat in the quiescent waters were filled during projects involving the of the canals. Due to the depth of the construction of causeways and the creation canals, however, light at the bottom was of new waterfront homesites (Figure 27). insufficient for seagrass growth. Taylor In undisturbed areas of the bay, luxuriant and Saloman (1968), using conservative and seagrasses grew in stable sediments incomplete data, estimated that fill averaging 94% sand and shell. At the operations in the bay resulted in a n bottom of dredged canals the unvegetated annual loss of $1.4 million for fisheries sediments averaged 92% silt and clay and recreation. (Taylor and Saloman 1968). While several studies of Boca Ciega Bay collectively At the time these canals were built, described nearly 700 species of plants and developers dredged them as deep as I animals occurring there, Taylor and 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 Figure 26. Channel through grassbed with possible. Thorhaug et al. (1973) found open-water dredge disposal area in Tampa Bay (photo that construction of a canal in Card Sound by R. R. Lewis). temporarily covered turtle grass in an

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

area of 2-3 ha with up to 10 cm of sections into the Niles Channel bridge. sediment, killing the leaves, but not the Instead of using the deep water access on rhizome system. Regr owth occurred when the Atlantic side, the contractor used a the dredging. operatLions ceased and large tugboat to prop-dredge a new passage currents carried the sediment away. through a shallow Thalassia flat. The resulting swath was several hundreds of meters in length, about 10 m in width, and 7.1.2 Other Physical Damage up to 2 m in depth. This, in effect, created a new tidal pass, and with the Any physical damage to the sediments and high water velocities during tidal flow rhizome structure of seagrass beds can through it, it is doubtful that the cut have long-term effects, no matter how will ever return to normal. Fortunately, insignificant the damage may seem the federal courts determined that such visually. Small cuts, no more than 10 cm wanton distruction constituted illegal wide and a similar depth in the sediments, dredging and filling (Zieman, unpubl. from the propellers of the innumerable data). outboard boats crossing Florida seagrass beds, can take from 3 to 5 years to In estuaries near Tampa and Tarpon recover in a Thalassia bed (Zieman 1976). Springs, Godcharles (1971) found no recovery of ei,ther Thalassia Damage by larger boats can be vastly Syringodium in areas where commercii\; more severe and long lasting. During the hydraulic clam dredges had severed construction of the new bridges in the rhizomes or uprooted the plants, although Florida Keys, a contractor attempted to at one station recolonization of Halodule cut transit time barging new bridge was observed.

90 7.1.3 Chronic Effects previously, and the choking growths of epiphytes are also less obvious. Thus, In addition to the direct effect of the natural communities are diminished and burial, secondary effects from turbidity, their valuable functions as habitat and which restricts nearby productivity, shelter are either decreased or lost chokes filter feeders by excessive entirely. suspended matter, and depletes oxygen by rapid utilization of suspended organic Seagrass beds subjected to both matter, can have serious consequences. eutrophication and suspended sediments in The dredged sediments are unconsolidated Christiansted Harbor, St. Croix, declined and readily resuspended. Thus, a spoil and were replaced by the green alga, bank can serve as a source of excess Enteromorpha, reducing the area1 extent of suspended matter for a protracted time the seagrasses by 66% over a 17-year after deposition. period (Dong et al. 1972). In Hillsborough Bay, phytoplankton In 1968, lush growths of Thalassia had productivity increased due to nutrient been recorded at depths UD to 10 m in enrichment from domestic sewage and Lindberg Bay, in St. Thomas,'U.S.V.I., but phosphate mining discharges (Taylor et al. by 1971 this species was restricted, by 1973b). Phytoplankton blooms contributed turbidity caused by dredging, to sparse to the problem of turbidity, which was patches usually occurring in water 2.5 m increased to such a level that seagrasses deep or less (Van Eepoel and Grigg 1970). persisted only in small, sparse patches. Similar declines were observed by Grigg et The only important macrophyte found in the al. (1971) in Brewers Bay, St. Thomas. bay was the red alga, Gracillaria. Soft sediments in combination with low oxygen Odum (1963) found light penetration was levels limited diversity and abundance of reduced in seagrass flats adjacent to the benthic invertebrates (Taylor et al. dredging site of an intracoastal waterway 1973b). in Redfish Bay, Texas. Subsequent decreases in productivity of Thalassia In northern Biscayne Bay, McNulty (1970) were attributed to the stress caused by found few seagrasses in waters that were suspended silts. Growth increased the polluted by sewage discharge in 1956. following year and Odum attributed this to Within 1 km of the outfall only small nutrients released from the dredge patches of Halodule and Halophila were material. While dredging altered the 38 m found. Following the construction of an long channel and a 0.5 km zone of spoil offshore outfall, postabatement studies in island and adjacent beds, in this instance 1960 found that the seagrasses had no permanent damage occurred to the continued to decline, probably due to the seagrasses outside this area beyond this persistent resuspension of sediment from a region. causeway and other nearby construction projects. The fine sediments of this area are highly prone to resuspension when 7.2 EUTROPHICATIONANDSEWAGE lacking the stabilizing influence of the seagrass canopy. The greatest losses of seagrass habitat are caused by the effects of physical damage from dredging and the chronic 7.3 OIL stresses placed on the plants by suspended sediments and eutrophic algal growth, Increased demand for local petroleum manifested in the form of increased supplies has intensified exploration for turbidity and resultant light reduction. offshore sources in shallow continental In many ways it is the most insidious form shelf, such as is found off the west of pollution, for it usually appears as a Florida coast. The potential for damage slow and gradual worsening of local water to local marine communities, as well as quality. With gradually increasing those at some distance, is present at all turbidity and decreasing water clarity, it stages of oil production, including is less noticeable that seagrasses are no exploration, production, and transporta- longer distributed as deep as they were tion, although not all of the risks are

91 equal. The National Academy of Sciences Although much more laboratory work is (NAS 1975) has found that the greatest needed, the few studies existing that have risks are associated with shipping acci- studied the effects of petroleum products dents, followed by those spills associated on seagrass community components have with loading and unloading oil. Getter et shown them to be toxic to the organisms. al. (1980) noted that of 16 oil spills in Seagrasses exposed to low levels of water the Gulf of Mexico and Caribbean 75% were suspensions of kerosene and toluene showed transit accidents. By comparison, NAS significantly reduced rates of carbon (1975) estimates that about 1.3% of the uptake (McRoy and Williams 1977). annual input of oil to the oceans is the result of drilling and production losses. Refined products have consistently been On the west coast of Florida, the remain- found to be more toxic to marine organisms ing seagrasses of busy ports like Tampa, than crude oils. Larval stages of grass as well as the beds of South Florida, shrimp were slightly more resistant to the would seem to be the most vulnerable to oil than the adults, while all forms of damage from oil spills. The large beds of the oils were more toxic to the larval and the Big Bend region are deeper and well juvenile stages of white and brown shrimp removed from major shipping lanes. The than to adults. Changes in temperature known effects of oil spills, cleanup pro- and salinity, which are routine in cedures, and restoration on seagrass estuaries, enhanced the toxic effects of communities and associated organisms were the petroleum hydrocarbons (Anderson et reviewed by Zieman et al. (1984b). al. 1974). The best indicator of oil toxicity is probably the aromatic Petroleum products can damage seagrass hydrocarbon content of the oil (Anderson ecosystems in a variety of ways. These et al. 1974; Tatem et al. 1978). have been summarized by Blumer (1971), Cintron et al. (1981), and Zieman et al. Numerous studies have indicated that (1984b) and include: intertidal communities are the most vulnerable of all marine communities; 1. Direct mortality of organisms due to thus, seagrass ecosystems are usually less smothering, fouling, and asphyxia- vulnerable due to their generally subtidal tion; poisoning by direct contact nature. There would seem to be a with oil (especially fresh oil); and decreasing likelihood of damage with absorption of toxic fractions from increasing depth, so that grassbeds the water column. several meters or more in depth are possibly better protected from oil spills 2. Indirect mortality due to the death than intertidal beds. of food sources or the destruction or removal of habitat. The impact on marine and estuarine communities, including seagrass 3. Mortality of sensitive juvenile communities, of several large-scale oil forms, especially those using the spills has been investigated but these are grassbed as a nursery ground. after-the-fact damage assessments. The results were highly variable, ranging from 4. Incorporation of sublethal amounts heavy destruction to little damage, a of petroleum fractions into body factor of the size of the spill and tissues, potentially lowering numerous other variables in environmental tolerance to other stresses. conditions. The case studies reviewed in Zieman et al. (1984b) are among the 5. Reduction or destruction of the food best-documented examples of oil spills or market value of fisheries due to affecting seagrass beds. In general, the tainting of flavor by absorption seagrasses suffered relatively little of hydrocarbons, even though the damage because of the subtidal nature of amounts are sublethal. the systems; the primary impact was on the associated fauna1 communities. Those beds 6. Incorporation of potentially car- that were exposed to oil at low tide did cinogenic or mutagenic substances not suffer greatly, due in part to their into the food chain. 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. Figure 28. Crystal River power plant (photo by R. R. The time of exposure to either extreme Lewis). high or low temperatures is critical in assessing the effect of thermal stress. Many organisms can tolerate large- amplitude temperature changes on a short-term basis, but are intolerant of chronic exposure to smaller changes. Effluent from the Bartow power plant near Seagrasses have buried rhizome systems the mouth of Old Tampa Bay, which reached that include the meristematic regions for a level of 7.2 'C above ambient leaf, root, and rhizome growth, and the temperature, killed 81 ha of seagrasses relatively poor thermal conductivity of (Blake et al. 1976). Where temperatures the sediments serves as an effective were 2 OC above ambient or less, all of buffer against short-term temperature the local seagrass species survived, but damage. Therefore, the seagrasses are at 3OC above ambient, only sparse more resistant to brief high temperature Halodule survived. Several parameters of increases than the commonly occurring Halodule were measured in the effluent algae. Continued heating, however, can plume and at a control station on the raise the sediment temperature to levels intake side of the plant. At the intake lethal to the plants (Zieman 1975). The station, the biomass varied from 5 to 10 animal components of the seagrass systems times greater than on the effluent side, show the same ranges of thermal tolerances while the length of the leaves and as the plants. Sessile forms are more emergent short shoots on the intake side affected, being unable to escape either were over twice the length of leaves from short-term acute effects or long-term the effluent side. During summers, chronic stresses. blue-green algal mats covered a large portion of the area where the temperature The primary sources of human-induced was greater than 3 "C above ambient (Blake thermal stress in estuaries are the et al. 1976), a condition similar to that cooling systems of electrical power plants found at Turkey Point in south Biscayne (Figure 28). In addition, some industrial Bay (Zieman and Wood 1975). plants produce waste heat, and, in some cases! heated wastewater that also In addition to the seagrasses, changes contains a variety of waste chemical were found in the associated animal products. communities in the effluent of the Bartow power plant. On the intake side of the Damage to communities subjected to these plant, 104 species of invertebrates were influences has been reported at various identified, primarily polychaetes, study sites in Florida (Zieman and Wood mollusks, crustaceans, and echinoderms, 1975; Thorhaug et al. 1978, Zieman 1982). while on the effluent side only 60 species

93 were found (Blake et al. 1976). Numbers station except for a brief period at the of individual polychaetes were greater on end of the summer, which was not the effluent transects, crustacean statistically significant. Syringodium numbers were greater along the intake productivity at the thermally-effected transects, and mollusk numbers were station exceeded that of the control similar in both areas (Blake et al. 1976). station in early May, but fell Virnstein (1977) found a decrease in precipitously at the end of the month. density and diversity of benthic infauna Barber and Behrens (1985) concluded that the where temperatures of the heated effluents in this central li-37 OC wzLzarsecorded. Florida region had a positive effect on seagrass productivity, until it reached On the west coast of Florida, effluents the upper optimal growth temperature for from the Crystal River power plant each species was reached. Above this impacted shallow-water seagrass and upper thermal limit, productivity macroalgal communities, but because of the declined. changing nature of the studies over the years, and particularly due to the highly The response patterns to thermal qualitative methods used in the early effluents seen in these west Florida surveys, full assessment of the impact estuaries are similar to those previously from thermal effluents is not possible. reported in south Florida. As the Numerous studies have shown a reduction in temperatures in south Biscayne Bay were the number of macroalgal species and their raised by the effluent of the Turkey Point abundance in the vicinity of the effluent power plant, the productivity, biomass, (Steidinger and Van Breedveld 1971; Van and area1 distribution of seagrasses Tine 1981). In the most recent study, decreased along the path of the effluent stations outside the area of the thermal plume of the power plant (Zieman and Wood effects to the south showed greater 1975). Increases in ambient temperature seagrass species diversity, biomass, and of 4 OC or more killed nearly all fauna productivity than those associated with and flora present (Roessler and Zieman the thermal effluent (Stone and Webster 1969). A rise of 3 OC above ambient 1985). Sample stations north of the caused both species numbers and diversity thermally-affected area showed patterns of algae to decrease. The optimal similar to those near the effluent, but temperature range for maximal species conditions at these stations proved to be diversity and numbers of individuals for inconsistent with the southern control animals was between 26 and 30 OC; stations. They were in an area of reduced temperatures between 30 and 34 OC excluded salinities caused by the Withlacoochee 50% of the invertebrates and fishes, and River and the western section of the Cross temperatures between 35 and 37 OC excluded Florida Barge Canal. Turbidity was high 75% (Roessler 1971; Zieman and Wood 1975). in this region due to the resuspension of sediments from the abandoned barge canal Throughout their range, Thalassia and its spoil islands, thereby limiting communities seem to show similar thermal its usefulness as a comparison area. response patterns. Thorhaug et al. (1978) collated and compared the response of Barber and Behrens (1985) studied the these communities in the Caribbean tropics effects of the effluent of an oil-fired (Guyanilla Bay, Puerto Rico), subtropics power plant near Anclote Key, about 50 km (Biscayne Bay and Card Sound, Florida), north of Tampa Bay, on the seasonal and subtropical warm-temperate border productivity of Thalassia and Syringodium. (Tampa Bay). The summer mean temperatures Throughout the fall and winter months, in all of the estuaries averaged about 30 both species showed greater productivity OC. Temperature elevations of 5 OC in the effluent than at the control destroyed and denuded the Thalassia station. As temperatures rose in the meadows; elevations of 4 OC showed severe spring, the productivity increased damage to all components of the comparably at all stations, ver.y rapidly communities. With a 3 OC temperature in March and April: Thalassia elevation, damage was severe in the higher productivity at the thermally stressed latitudes and less in the more tropical station was less than at the control environments. Data was insufficient to

94 allow intercomparisons of lesser 7.5 PAPERMILLEFFLUENTS temperature elevations, but it was clearly indicated that temperature elevations of Throughout the gulf coast region, with greater than 3 OC above ambient in the its enormous timber resources, there are warmer months produced severe and numerous paper mills discharging huge sustained damage (Thorhaug et al. 1978). quantities of waste materials into rivers, which almost immediately wash this While all of the local seagrass species material into the nearby estuaries. are euryhaline to varying degrees, Through numerous publications, Livingston Thalassia and Syringodium show a decrease (1975, 1984a, 1987) has chronicled the in photosynthetic rate as salinity drops changes in the seagrass communities due to below full-strenqth seawater, while kraft mill effluents, and the subsequent Halodule is less affected (McMillan and recovery process following a pollution Moselev 1967). The seasonalitv of abatement program. Zimmerman and seagrasses in Florida is largely explained Livingston (1976a) found that a pulp mill by temperature and salinity effects on the Fenholloway River dumped from (Zieman 1974; Barber and Behrens 1985). 200,000 to 220,000 m3 of kraft mill The greatest decline in plant populations effluents into Apalachee Bay over the 20 was found when combinations of high year period from 1954 to 1974, at which temperature and low salinity occurred time a pollution abatement program was simultaneously. The reduction of seagrass enacted. The effluents altered water biomass and productivity at one set of quality and caused increased turbidity and stations near the Crystal River power reduced light penetration, which, in turn, plant which were intended to serve as reduced species diversity of macroalgae controls, was attributed to reduced and reduced productivity in the bay salinities emanating from the Cross compared with a similar region off the Florida Barge Canal and the Withlacoochee unpolluted Econfina River (Heck 1976; River (Stone and Webster 1985). Hooks et al. 1976; Livingston 1984b). The changes in water quality and plant While h$igher salinities may yield communities caused significant changes in somewhat lusher and more productive the fishes and macroinvertebrates. seagrass beds compared to those found in Numbers of individuals and species numbers mesohaline waters, the intermediate were reduced in areas of severe impact. salinities seem to be most important for In areas of moderate but chronic impact, the nursery function of the seagrass the annual species numbers were equivalent meadows. Tabb et al. (1962) stated: to control stations, but this proved to be "Most of the effects of man-made changes the result of the recruitment of a few on plant and animal populations in Florida individuals of rare species (Livingston estuaries (and in many particulars in 1975). Livingston (1987) also noted that estuaries in adjacent regions of the Gulf although recovery was occurring, the of Mexico and south Atlantic) are a result seagrasses, especially Thalassia, were of alterations in salinity and turbidity . slow to respond following the removal of . . . High salinities (30-40 ppt) favor the stress. the survival of certain species like sea trout, redfish, and other marine fishes, and therefore improve angling for these 7.6 DISTURBANCE, RECOLONIZATION, AND species. On the other hand these higher RESTORATION salinities reduce survival of the young stages of such important species as 7.6.1 Disturbance commercial penaeid shrimp, menhaden, oysters, and others. It seems clear that While the large offshore seagrass the balance favors the low to moderate meadows in the Big Bend region of Florida salinity situation over the high salinity. have remained relatively intact and Therefore, control in southern estuaries undisturbed, the beds that are found should be in the direction of maintaining within the enclosed estuaries on the west the supply of sufficient quantities of coast of Florida have suffered fresh water which would result in tremendously. The greatest losses have estuarine salinities of 18 to 30 ppt."‘ occurred in Tampa Bay, where there are

95 only 5,750 ha of seagrasses remaining from species, it can rapidly cover a damaged estimated historical coverage of area. ii 970 ha a reduction of 81% (Figure 9 f&n Lewi; et al. 1985a). Because of the Compared to the other seagrasses, high turbidity caused in part by the Thalassia is much slower to recolonize a now-unvegetated bottom, seagrass disturbed area. At least 10 months are distribution is presently limited to less required for Thalassia to begin new short than 2 m in depth in nearly all cases. shoot development (Fuss and Kelly 1969), The problems and destruction encountered and the initiation of new growth seems to in Tampa Bay are not unique, but are be sensitive to environmental conditions. mirrored in nearly all estuaries with After 13 months, Kelly et al. (1971) found heavy urbanization and industrialization that 40% of transplanted plants in a (Taylor and Saloman 1968; Simon 1974; control area had initiated new rhizome Lewis et al. 1985a; Livingston 1987). growth, while only 15% to 18% of the plants transplanted to disturbed sediments Other estuaries on the west Florida had initiated new growth. coast have shown similar losses (Table 17). In the vicinity of Bayport, It has been well documented that small seagrasses have declined by 13% (Haddad disturbances in seagrass beds require 1986). St. Joseph Bay, in an area of low surprisingly long recovery times. The population density, has not shown most common form of disturbance to significant changes in seagrass density in seagrass beds in the shallow banks and 15 years (Savastano et al. 1984), and bays of south Florida results from cuts by Apalachicola Bay has shown minimal boat propellers. Although it would seem degradation (Livingston 1987). The that these relatively small-scale coverage of submerged vegetation in disturbances would heal rapidly, it Choctawhatchee Bay has declined by 30% typically takes two to five years to since 1949 (Haddad 1986), but the causes recolonize a Thalassia bed (Zieman 1976). are unknown (Burch 1983; Livingston 1987). The scarred areas rapidly fill in with Within the Pensacola Bay system, sediment from the surrounding beds, but occasional beds of Thalassia and Halodule the sediment is slightly coarser and has a are found in Santa Rosa Sound, but there lower pH and Eh, and probably other was a complete loss of seagrass in physico-chemical differences that the Escambia Bay, East Bay, and Pensacola Bay plants can detect (the rhizome apex will between 1949 and 1979 (Olinger et al. frequently grow up to one of these areas 1975; Livingston 1987). Big Lagoon, west and then literally turn back into the of Pensacola, has increased coverage by parent bed and away from the filled-in 55%, one of the few areas in the state to cut; Zieman 1976). do so (Haddad 1986). In Charlotte Harbor, on the southwest coast, seagrass beds have Seagrass ecosystems show differential declined nearly 30% to 9,300 ha remaining recovery rates from disturbances based on (Harris et al. 1983; Haddad and Hoffman a variety of factors including species 1986). involved, the type and magnitude of the disturbance, and especially whether or not 7.6.2 Recolonization the sediments were disturbed. Along the west Florida coast, if the disturbance is The natural recolonization of seagrasses great enough, a number of rhizophytic is a highly variable process, the rate of algae act as precursors to the seagrasses. which can be affected by local One of the primary determinants of the environmental parameters, as well as the duration of recovery time is the extent of species of the seagrass. Halodule is the damage to the sediments. If the sediments normal pioneer species in the region and and seagrass rhizomes are not severely can colonize an area rapidly if disturbed, the probability of recovery is sedimentary conditions are favorable and greatly increased. Table 18, (1984b), if there is a source of seed or other attempts to synthesize and categorize the propagule material. With its surficial levels of damage to seagrass ecosystems, rhizome system and smaller investment in system effects, and the likely outcome of belowground biomass than the climax 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 Southeast Florida Historic declines in number and coverage Goodwin and Goodwin 1976; Florida Atlantic Ocean of seagrass meadows. Declines in Vero Department of Natural Resources, Beach area, Fort Pierce Inlet (25%), and unpubl. data Sebastian Inlet (38%) from 1951 through 1984.

Biscayne Bay Southeast Florida Undetermined deterioration in northern McNulty 1961; Rosessler and Atlantic Ocean Biscayne Bay. Some damage to Thalassia- Zieman 1969; Thorhaug et al. Halodule beds near power plant (heated 1973; Zieman 1970, 1982 effluents) in south Biscayne Bay. Card Sound unaffected by power plant discharge.

Florida Keys South Florida Few data found. Little effect of Key Chesher 1971 Atlantic Ocean West desalination plant. co Florida Bay South Florida Postulated altered species relationships Zieman 1982 4 due to increased salinity caused by redirection of freshwater runoff.

Tampa Bay Southwest Florida Almost 40% reduction in Boca Ciega Simon 1974; Taylor 1971; system Gulf of Mexico Bay due to dredging, filling, and Taylor and Saloman 1968; associated activity from 1950 through Lewis and Phillips 1980 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).

Charlotte Southwest Florida Decline of 29% of seagrass beds Florida Department of Natural Harbor Gulf of Mexico from 1943 through 1984. Resources, unpubl. data

(Continued) Table 17. (Concluded).

Study area Location Status of seagrass meadows Information source

Pensacola Bay Northwest Florida Complete loss of seagrass beds in Livingston et al. 1972; Olinger et System Gulf of Mexico Escambia Bay, East Bay and Pensacola al. 1975; Livingston 1979 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.

Choctawhatchee Northwest Florida Historical deterioration of seagrass Burch 1983 Bay Gulf of Mexico beds from 1949-1983. Causes unknown.

St. Andrews Bay Northwest Florida No data found. Presumed impact due to Gulf of Mexico urbanization, industrialization.

St. Joseph Bay Northwest Florida Extensive coverage unchanged from 1972 McNulty et al. 1972; Savastano Gulf of Mexico through 1983. Relatively unpopulated et al. 1984 area.

Apalachicola North Florida Generally healthy assemblages of sea- Livingston 198Oc, 1983 Bay System Gulf of Mexico grasses. 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.

Apalachee Bay North Florida Impacts due to disposal of pulp mill Heck 1976; Hooks et al. 1976; Gulf of Mexico wastes (Fenholloway Estuary) from 1954 Livingston 1975, 1982a, 1984a; to the present. Slow recovery noted in Zimmerman and Livingston 1976a,b outer portions of impact area (associated with pollution abatement program). Area now threatened by proposed inshore navigation channel and possible offshore oil drilling operations.

______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 Possible fauna1 Natural Weeks-year No damage damage recovery

2 Leaf damage Fauna1 damage may Natural 6 months- No and removal be extensive recovery year likely

3 Severe damage Fauna1 damage is Natural 5 years- Yes to rhizomes likely extensive recovery decades slow or unlikely

4 Severe system System completely Return to ? No damage altered same state not possible

developed for the recommendation of of seagrass transplants was greatly strategy following an oil spill, the enhanced by utilizing a ball of sediment, results and recommendations are not as in the techniques for terrestrial specific to any particular type of stress transplantation of garden plants. He also and are of general utility. Following a noted that transplantation should be done disturbance to the seagrass system, the when the plants are in a semidormant state primary management strategy and objectives (as in winter) to give the plants time to should be directed towards minimizing the stabilize, another logical outgrowth of impact. While all efforts should be terrestrial technique. Where possible, directed towards keeping damage at level the objective of restoration in general, one or two where recovery may proceed not just of seagrasses, should be to naturally, it is most important to keep restore the lost community or some level-three damage from becoming level intermediate successional stage. In some four, where recovery or restoration to a cases, restoration of the original functioning seagrass system is not community may not be feasible or possible. At this level of cost-effective, and it may be necessary to transformation, sediment erosion is restore to an earlier successional stage allowed to proceed to the point where and allow natural successional progression there is insufficient sediment remaining to take place. for seagrass colonization. Transplantation of seagrasses has been 7.6.3 Restoration attempted since the time of the wasting disease, but there has been a dramatic According to the concept of ecological increase in its use during the past decade succession, there are two basic ways to (See Phillips 1980; Fonseca et al. 1981, restore a mature community: (1) establish 1987; Zieman et al. 1984b for recent the pioneer species and allow succession reviews). Darovec et al. (1975) discuss a to take its course, and (2) create the variety of techniques for restoring environmental conditions necessary for the coastal regions, including seagrasses, in survival and growth of the climax species. Florida. This publication is useful Van Breedveld (1975) noted that survival because it consolidates a diverse

99 literature, but the seagrass techniques the highest degree of short-term sediment are rudimentary and somewhat dated, and stabilization of any of the methods. On the other reviews mentioned should be the negative side, the plug technique is consulted. Until recently, most logistically more difficult due to the transplant studies reported primarily on need to collect the plug intact, move transplant technique and survival success, large amounts of sediment, and create and did not address environmental sites of disturbance at the donor variables such as sediment type, nutrient location. conditions, light, turbidity, current velocity, and wave climate, all of which Methods using bare shoots have shown affect the success or failure of the mixed results, being very successful with experiment (Fonseca et al. 1981, 1987). pioneer species such as Halodule wrightii and Zostera marina, but not really The myriad techniques that have been successful with Thalassia, which is a tried for transplanting seagrass have climax species. Shoot methods require yielded highly variable results. Those anchoring' to approach the sediment techniques that have shown the most stability of the plug technique (Fonseca consistent success are plugs, seeds, and et al. 1984). The logistics are somewhat shoots--both anchored and unanchored simpler than the plug method since there (Phillips 1980). Because of the variety is no mass of sediment to be transported. of methods and the different levels of description of these methods in the literature, direct comparison among Transplantations utilizing seeds and seemingly similar methods varies from seedlings have been attempted for several difficult, at best, to impossible. Table species, but have been successful only 19 summarizes the relative successes with Thalassia. If an abundant source of recorded in the seagrass transplant seeds can be readily located, this literature. technique can be very attractive, because of simple transportation and planting From this diverse literature, a few logistics. Recently, Lewis and Phillips generalizations stand out. The most (1981) have reported on sites of high seed obvious is that the plug technique is the availability in the Florida Keys in late only one that has worked with all species summer. On the negative side, seeds are upon which it has been tested. This is only seasonally available and newly- not ecologically surprising, as the plug planted seeds or seedlings do not offer minimizes trauma to the roots and rhizomes any sediment stabilization capacity. by taking part of its environment along to However, interplanting of Thalassia the new site. The plug technique provides seedlings in beds of recently established

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

Shoot Shoot Species 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" or failure of a particular project. Several approach, was tested by Durako and Moffler recent projects have elegantly tested the (1984), and may prove to be a useful mixed- viability of different methodologies in a planting technique. proper scientific manner, but none of these can tell whv a particular method succeeded In 1982, Zieman wrote that "transplants of or failed. tropical seagrasses may ultimately be a useful restorative technique to reclaim One of the major problems in offsite damaged areas, but at this time the results restoration as it is currently practiced, are not consistent or dependable, and the is the selection of a suitable and costs seem prohibitive for any effort other potentially viable site for restoration, if than experimental revegetation it is not to be the recently disturbed site. especial?; when the relative survival of the Many times the sites chosen are plants is considered." In the intervening inappropriate and there are sound ecological time, a number of additional projects have reasons why seagrasses are not growing there been completed, but the situation has not now, even if there was seagrass coverage at changed significantly. Fonseca et al. some point in past history (Lewis et al. (1987) stated that "for the most part, 1985a; Fonseca et al. 1987). If it can be seagrass transplanting as a management tool established that an area meets the is not working. Isolated cases of success environmental conditions to support or partial success can be found, but these seagrasses, but has probably not recovered are overshadowed by many costly failures. due to lack of natural propagules, then This lack of success is largely due to the restoration may be indicated. general disregard for and the lack of Unfortunately, probably the major problem scientific information on environmental inhibiting seagrass success today is the requirements of the transplant species.” deteriorating water quality associated with Further, they feel that "the pressure to industrialization and development. If poor make management decisions has grown water quality increases turbidity and disproportionatelytothe increase regarding decreases incident light at the sediment seagrass habitat management. With much level past a certain point, then all the emphasis having been put on methodology of transplanting in the world will not work. transplanting and much less on collection of In any restored area, the plants must have environmental data, we have been at a loss sufficient light to yield a significantly to explain successes and failures in a high positive net photosyntheses to survive quantitative fashion." and grow. If turbidity is too high, or eutrophication is sufficient to cause a In the State of Florida, seagrass rapid growth of epiphytic algae or transplantation and restoration is often phytoplankton, then the effort and money treated as if it were a proven-and-fixed will be wasted. technology, capable of producing a product upon specification, when, in fact, it is really a series of loosely coupled 7.7 FINAL THOUGHTS experiments. The concept of seagrass transplanting for "mitigation" of The gathering and assimilation of data for environmental damages is becoming an this community profile has been highly accepted practice in Florida under the enlightening. Dozens of studies have shown assumption that if an environmental the importance of submerged vegetation to disturbance or destruction is "necessary" major commercial and forage organisms or "in the public interest," then this (Linda11 and Saloman 1977; Thayer et al. perturbation can be "mitigated" by a 1978a; Peters et al. 1979; Thayer and Ustach parallel restoration. As a step toward 1981). In the gulf States the recreational accepting seagrass transplanting as a viable saltwater fish catch exceeded $168 million mitigation method, numerous Federal, State, in 1973, representing about 30% of the total and local agencies have funded projects U.S. recreational fishery (Linda11 and aimed at seagrass restoration. However, Saloman 1977). Of the organisms caught, 59% only recently have any studies been funded were dependent on wetlands at some state of to conduct a scientific investigation on the their life cycles. In the Gulf of Mexico, environmental variables causing the success this estimate was even higher with over 70%

101 of gulf recreational fisheries of the region the seagrasses of Chesapeake Bay as some of being estuarine dependent. The ecological the most devastated and degraded in the dependence of important commercial fisheries entire country (Lewis et al. 1985a; on the estuarine wetlands is even greater. Livingston 1987). The importance of these The Gulf of Mexico is the leading region of losses to both the ecology and the economy the United States in terms of both landings of Florida are far out of proportion to the (36% of the total U.S. catch) and value (27% total hectares lost versus those remaining, of total U.S. fishery value), and 90% of the due to the critical nature of the estuarine total Gulf of Mexico and south Atlantic seagrass beds as nurseries. While measures fishery catch is estuarine dependent must be taken to ensure the continued (Linda11 and Saloman 1977). productivity of the offshore beds, it is most critical that the water quality The west Florida coast contains vast degradation that has caused the extensive seagrass resources, in the form of offshore losses in the estuarine grass beds be beds of the Big Bend region, that have been arrested and reversed. Once the beds are largely untouched by human activities. totally destroyed, they are likely to remain However, the seagrass resources within the lost forever, along with the myriad west Florida estuaries must rank alongside organisms that they feed and shelter.

102

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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 Roessler 1965 2 South Biscayne Bay Bader and Roessler 1971 3 Card Sound Brook 1975 4 Matecutie Key Springer and McErlean 1962 5 Porpoise Lake Hudson et al. 1970 6 Whitewater Bay Tabb and Manning 1961 Fakahatchee Bay Carter et al. 1973 : Marco Island Weinstein et al. 1971 9 Rookery Bay Yokel 1975a 10 Charlotte Harbor Wang and Raney 1971 11 Offshore Tampa Pbe and Martin 1965 12a Tampa Bay Mouth to Offshore Springer and Woodburn 1960 Reefs (Stns. 1 - 3) 12b Tampa Bay Grassbed Stations Springer and Woodburn 1960 (Stns. 4 - 6) 13 Crystal Bay Area Mountain 1972 14 Cedar Key Reid 1954 15 Alligator Harbor Joseph and Yerger 1956; Yerger 1961 16 Apalachicola Bay Livingston 1984

Key to abundance

= rare = present = abundant = common

Note: 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 P lemon shark

Rhizoprionodon terraenovae P Atlantic sharpnose shark

Carcharhinus acronatus P P blacknose shark

Carcharhinus isodon P finetoothed shark

Carcharhinus leucas P P P bull shark

Carcharhinus limbatus PP P blacktip shark

Carcharhinus plumbeus P sandbar shark

Sphyrnidae/hammerhead sharks

tiburoSphyrna P P PP P bonnethead

diplana*Sphyrna P

Sphyrna mokarran P great hammerhead

Pristidae/sawfishes

Pristis pectinata P P smalltooth sawfish

Rhinobatidae/guitarfishes

Rhinobatus lentiginosus r Atlantic guitarfish

(Continued)

132 Appendix (Continued).

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

Torpedinidae/electric rays

Narcine brasiliensis r r r lesser electric ray

Rajidae/skates

Raja texana r roundel skate

Raja eglanteria clearnose skate P

Dasyatidae/stingrays

Urolophus jamaicensis r r yellow stingray

micruraGymnura r r PPPP PP smooth butterfly ray

Dasyatis americana" P southern stingray

Dasyatis sabina r r P P P Atlantic stingray

Dasyatis sayi P P blunt nosed stingray

Myliobatidae/eagle rays

Aetobates narinari P spotted eagle ray

Rhinoptera bonasus a P P cownose ray

Mobulidae/mantas

Manta birostis P P Atlantic manta

Lepisosteidae/gars

Lepisosteus osseus P P P longnosed gar

Lepisosteus platyrhinchus Florida gar

(Continued)

133 Appendix(Continued).

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

Elopidae/tarpons

Elops saurus P ladyfish

Megalops atlanticus P P P tarpon

Albulidae/bonefishes

Albula vulpes P bonefish

Anguillidae/freshwater eels

Anguilla rostrata P American eel

Muraenidae/morays

Gymnothorax nigromarginatus r P blackedge moray

Gymnothorax saxicola P ocellated moray

Ophichthidae/snake eels

Myrophis punctatus r r r r P a P P speckled worm eel

Ophichthus gomesi r r P P P P shrimp eel

Echiophis intertinctus rr P P spotted spoon-nose eel

Echiophis mordax r snapper eel

Bascanichthys bascanium P P sooty eel

Bascanichthys scuticanis whip eel

Clupeidae/herrings

Harengula jaguana r r r r c aa P P P P scaled sardine

(Continued)

134 Appendix (Continued).

Abundance by survey number Species 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. r

Brevoortia smithi yellowfin menhaden

Brevoortia patronus pap PP gulf menhaden

Etrumeus sadina" P

Dorosoma petenense P P threadfin shad

Opisthonema oglinum r r r a P p P Atlantic thread herring

Sardinella auria r r P a P Spanish sardine

Engraulidae/anchovies

Anchoa cubana r P P Cubananchovy

Anchoa lamprotaenia a P bigeye anchovy

Anchoa mitchilli r rpcr rc a a P P P P bay anchovy

Anchoviella perfasciata r flat anchovy

Anchoa hepsetus r r r c PP P P P striped anchovy

Synodontidae/lizardfishes

foetensSynodus rrrrpcrrrr pp p P P P inshore lizardfish

Synodus intermedius P sand diver

(Continued)

135 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

Ictaluridae/bullhead catfishes

Ictalurus catus P white catfish

Ictalurus nebulosus P brown bullhead

Ari idae/sea catfishes

marinusBagre P P gafftopsail catfish

Arius felis P r r r r P P P P P hardheadcatfish

Batrachoididae/toadfishes

Opsanus beta carrpcccr P P P P P P gulf toadfish

Opsanus pardus P P leopard toadfish

Porichthys plectrodon r r P P Atlantic midshipman

Gobiesocidae/clingfishes

Acyrtops beryllinus r r emerald clingfish

Gobiesox strumosus r P r P P P P skilletfish

Antennariidae/frogfishes

Histrio histrio r r sargassumfish

Antennarius ocellatus P ocellated frogfish

Ogcocephalidae/batfishes

Ogcocephalus cubifrons" r

Ogcocephalus nasutus r P P shortnose batfish

(Continued)

136 Appendix (Continued).

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

Ogcocephalidae/batfishes (Continued)

Ogcocephalus radiatus P polka-dot batfish

Ogcocephalus sp. P P

Halieutichthys aculeatus P pancake batfish

Gadidae/codfishes

Urophycis floridana r southern hake

Ophidiidae/cusk-eels

Lepophidium jeannae mottled tusk-eel

Ophidion grayi blotched tusk-eel

Ophidion welshi P P crested tusk-eel

Ophidion holbrooki r r P bank tusk-eel

Ophidion beani P longnose tusk-eel

Ophidion marginatum P striped tusk-eel

Bythitidae/viviparous brotulas

cayorumOgilbia r r P P key brotula

Gunterichthys longipenis gold brotula

Carapidae/pearlfishes

bermudensisCarapus r pearlfish

(Continued)

137 Appendix (Continued).

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

Exocoetidae/fly i ng fishes and halfbeaks

Hemiramphus brasiliensis r ballyhoo

Chriodorus atherinoides P hardhead halfbeak

Hyporhamphus unfasciatus p r r PPP P halfbeak

Belonidae/needlefishes

Strongylura notata r r p r PPP P redfin needlefish

Strongylura timucu r r a P timucu

Strongylura marina P P Atlantic neemh

crocodilusTylosurus r houndfish

Tylosorus raphidoma" P

Cyprinodontidae/killifishes

Flordichthys carpio c a r P P goldspotted killifish

Adinia xenica r r P diamondkillifish

Lucania parva a r r p r r r P P P P P rainwater killifish

Fundulus heteroclitus r mummichog

Fundulus grandis PP P gulf kill Ifish

Fundulus similis r P P longnose killifish

Fundulus confluentus P marsh kil'lifish

(Continued) Appendix (Continued).

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

Cyprinodontidae/killifishes (continued)

Cyprinodon variegatus P r P P sheepshead minnow

Rivulus marmoratus r rivulus

Poeciliidae/livebearers

Poecilia latipinna P r P P sailfin molly

Gambusia affinis r P mosquitoflsh

Heterandria formosa r least killifish

Atherinidae/silversides

Hypoatherina harringtonensis C r P reef silverside

Atherinomorus stipes a a hardhead silverside

Menidia beryllina r c a a P P P tidewater silverside

Membras martinica rough silverside

Membras vagrans" r r

Membras sp. a P

Holocentridae/squirrelfishes

Holocentrus ascensionis a squirrelfish

Syngnathidae/pipefishes and seahorses

Cosmocampus albirostris r r r whltenose pipefish

Cosmocampus brachycephalus r crested pipefish

(Continued)

139 Appendix(Continued).

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

Syngnathidae/pipefishes and seahorses (continued)

Hippocampus hudsonius* r P P P P

Hippocampus zosterae rcrrprrrr P dwarf seahorse

Hippocampus erectus r r r r r r lined seahorse

Hippocampus reidi r longsnout seahorse

Hippocampus regulus* P

Hippocampus sp. P

Syngnathus sp. P Syngnathus dunckeri r pugnose pipefish

Syngnathus floridae crrrpr r r P P P dusky pipefish

Syngnathus louisianae r r r r r r r r P P P chain pipefish

Syngnathus elucens shortfin pipefish

Syngnathus springeri bull pipefish

Syngnathus scovelli rrcrpcaccc P P P gulf pipefish

Micrognathus crinigerus a r P r P P fringed pipefish

Centropomidae/snooks

Centropomus undecimalis P P snook

Serranidae/sea basses

Centropristis striata r r P P P P black sea bass

(Continued)

140 Appendix(Continued).

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

Serranidae/sea basses

Centropristis ocyurus P bank sea bass

Mycteroperca bonaci r P black grouper

Mycteroperca microlepis r r p rrr a P P. gag

Mycteroptera falcata"

Serraniculus pumilio r P P P pygmy sea bass

Serranus subliqarius r P a r belted sandfish

Diplectrum bivittatum dwarf sand perch

Diplectrum formosum rrrrr p P P P P sand perch

Epinephalus morio P a P red grouper

Epinephalus itajara P P P jewfish

Epinephalus adscensionis r rock hind

Grammistidae/soapfishes

Rypticus saponaceus P greater soapfish

Apogonidae/cardinalfishes

Phaeoptyx conklini r freckled cardinalfish

Apogon aurolineatus P bridle cardinalfish

Astrapogon alutus r r P R P bronze cardinalfish

(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 PPP PP bluefish

Rachycentridae/cobias

Rachycentron canadum P P P cobia

Echeneidae/remoras

Echeneis naucrates r P P P P P sharksucker

Carangidae/jacks and pompanos

Caranx hippos r P r P P P P crevalle jack

Caranx latus r P horse-eyejack

Caranx ruber P -jack

Caranx bartholomaei yellow jack

Caranx crysos r P blue runner

Hemicaranx amblyrhynchus bluntnose jack

Trachinotus falcatus r permit

Trachinotus carolinus Florida pompano

Trachinotus sp. P

Trachurus lathami a rough scad

(Continued)

142 Appendix (Continued).

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

Carangidae/jacks and pompanos (continued)

Seriola zonata a a banded rudderfish

Chloroscombrus chrysurus PPP PP Atlantic bumper

Oligoplites saurus P r r PPP PP leatherjacket

Selene vomer r r r P P P P lookdown

Vomer setapinnis P P Atlantic moonfish

Lutjanidae/snappers

Lutjanus analis r r mutton snapper

Lutjanus apodus r a P schoolmaster

Lutjanus griseus r rcprrrr P P P P P P gray snapper

Lutjanus jocu r dog snapper

Lutjanus synagris r pcracr p P P lane snapper

Lutjanus campechanus P red snapper

Rhomboplites aurorubens P vermilion snapper

chrysurusOcyurus r r yellowtail snapper

Lobotidae/tripletails

Lobotes surinamensis r P P P tripletails

(Continued)

143 Appendix (Continued).

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

Gerreidae/mojarras

Eucinostomus argenteus r c c r p r r r r c p a P P P P spotfin mojarra

Eucinostomus gula r r a a p a a a a a P P P P P P silver jenny

Eucinostomus lefroyi r mottled mojarra

Gerres cinereus yellowfTiii$Z%a

Diapterus plumieri P striped mojarra

Haemulidae/grunts

Haemulon flavolineatum r r French grunt

Haemulon parrai r r r c sailors choice

Haemulon sciurus r c r p r P P bluestriped grunt

Haemulon aurolineatum r r r a r P tomtate

Haemulon plumieri a r a a r P a P P P white grunt

Haemulon carbonarium r Caesar grunt

Anisotremus virginicus r r porkfish

Orthopristis chrysoptera r pcaaar pa P P P P pigfish

Sparidae/porgies

Archosargus probatocephalus r p r r r pap PP sheepshead

Archosargus rhomboidalis r P P sea bream (Continued)

144 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 r Pr rp P P grass porgy

Calamus calamus r saucereye porgy

Diplodus holbrooki P P P P P spottail pinfish

Sciaenidae/drums

Menticirrhus saxatilis r C P P P northern kingfish

Menticirrhus littoralis a P gulf kingfish

Sciaenops ocellatus P r r PPP PP red drum

Bairdiella chrysoura r r C aaCC PP a pp P silver perch

Cynoscion nebulosus prcrrr pr p P P P P spotted seatrout

acuminatusEquetus r P a high-hat

Fquetus lanceolatus P Jackknife fish

Bairdiella batabana blue croaker

Odontoscion dentex r P reef croaker

Leiostomus xanthurus ca pa a P P P P spot

Cynoscion arenarius r r rp PP p P P sand seatrout

Micropogonias undulatus r p P P P Atlantic croaker (Continued)

145 Appendix (Continued).

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

Sciaenidae/drums (continued)

Pogonias cromis a P black drum

Stellifer lanceolatus P P star drum

Larimus fasciatus P P banded drum

Menticirrhus americanus r rc PP P P P P southern kingfish

Mullidae/goatfishes

Pseudupenueus maculatus r spotted goatfish

Ephippidae/spadefishes

Chaetodipterus faber r P r r r PP P P P P P Atlantic spadefish

Chaetodontidae/butterflyfishes

Chaetodon ocellatus P spotfin butterflyfish

Pomacanthidae/angelfishes

Holacanthus bermudensis P blue angelfish

Pomacanthus arcuatus r gray angelfish

Pomacentridae/damselfishes

Pomacentrus leucostictus r beaugregory

Pomacentrus variablis cocoa damselfish

Abudefduf saxatilis sergeant major

Chromis enchrysurus yellowtail reeffish

(Continued)

146 Appendix (Continued).

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

Labridae/wrasses

Doratonatus megalepis r r dwarf wrasse

Halichoeres bivittatus r p a r P slippery dlck

Halichoeres caudalis r painted wrasse

Halichoeres radiatus P puddingwife

Hemipteronotus martinicensis r rosy razorfish

Hemipteronotus novacula r pearly razorfish

Lachnolaimus maximus C P P P P hogfish

Scaridae/parrotfishes

Nicholsina usta r r r emerald parrotfish

Scarus coelestinus r midnight parrotfish

Scarus croicensis r striped parrotfish

Scarus guacamaia r rainbow parrotfish

Sparisoma chrysopterum r redtail parrotfish

Sparisoma radians r bucktooth parrotfish

Sparisoma rubripinne a r C redfin parrotfish

Sparisoma viride r stoplight parrotfish

Cryptotomus auropunctatus"

(Continued)

147 Appendix (Continued).

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

Mugilidae/mullets

cephalusMugil r P a a a P P striped mullet

Mugil curema r r P C P P P white mullet

trichodonMugil r P P fantail mullet

Mugil sp.

Sphyraenidae/barracudas

Sphyraena barracuda r r r p r a P great barracuda

Sphyraena borealis P P northern sennet

Sphyraena sp. P

Polynemidae/threadfins

Polydactylus octonemeus r r P P Atlantic threadfin

Opistognathidae/jawfishes

Opistognathus maxillosus r mottled jawfish

Opistognathus macrognathus banded jawfish

Dactyloscopidae/sand stargazers

Dactyloscopus tridigitatus r r sand stargazer

Uranoscopidae/stargazers

Astroscopus y-graecum PP P P P southern stargazer

Clinidae/clinids

Bramerella sp.*

(Continued)

148 Appendix (Continued).

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

Clinidae/clinids (Continued)

Malacoctenus macropus r rosy blenny

Malacoctenus culebrae* P

Emblemaria atlantica r banner blenny

Paraclinus fasciatus r r c P P banded blenny

Paraclinus nigripinnis r P blackfin blenny

Paraclinus marmoratus r r r r p marbled blenny

Chaenopsis ocellata P bluethroat pikeblenny

Blenniidae/combtooth blennies

Chasmodes saburrae r r r r r r P P P P Florida blenny

Parablennius marmoreus P P a seaweed blenny

Lupinoblennius nicholsi P highfin blenny

Blennius sp. P

Hypleurochilus geminatus P crested blenny

Hypsoblennius hentzi P P P P P feather blenny

Hypsoblennius ionthas P freckled blenny

Callionymidae/dragonets

Callionymus pauciradiatus r r r r p spotted dragonet

Callionymus calliurus"

(Continued)

149 Appendix (Continued).

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

Gobiidae/gobies

Barbulifer ceuthoecus r bearded goby

Microgobius microlepis r P banner goby

Microgobius gulosus per r P P P P clown goby

Microgobius thalassinus r green goby

Microgobius carri a _.. Seminole goby

Bathygobius curacao C notchtongue goby

Bathygobius soporator r P frillfin goby

Coryphopterus sp.

Gobionellus hastatus P P sharptail goby

Gobionellus bolesoma r P P darter goby

Gobionellus smaragdus r emerald goby

Gobionellus shufeldti r freshwater goby

Gobionellus stigmaturus r spottail goby

Gobiosoma robustum a r r pccrrr a P P code goby

Gobiosoma longipala r twoscale goby

Gobiosoma macrodon r r P P tiger goby

Gobiosoma longurn" r

(Continued)

150 Appendix (Continued).

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

Gobiidae/gobies (continued)

Gobiosoma bosci r P P naked goby

Ioglossus calliurus P blue goby

Lophogobius cyprinoides r crested goby

Coryphopterus glaucofraenum r bridled goby

Acanthuridae/surgeonfishes

Acanthurus bahianus r ocean surgeon

Acanthurus coeruleus P blue tang

Acanthurus chirurgus doctorfish

Trichiuridae/cutlass fishes

Trichiurus lepturus P P P Atlantic cutlassfish

Scombridae/mackerels

Scomberomorus maculatus a P P P P Spanish mackerel

Scomberomorus cavalla a P P king mackerel

Euthyhnus alletteratus P little tunny

Thunnus atlanticus r blackfin tuna

Istiophoridae/billfishes

Istiophorus platypterus P sailfish

(Continued)

151 Appendix (Continued).

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

Stromateidae/butterfishes

Peprilus burti P gulf butterfish

Peprilus paru* P P

Peprilus alepidotus P P harvestfish

Peprilus triacanthus P butterfish

Nomeus gronovii r man-of-war fish

Scorpaenidae/scorpionfishes

Scorpaena brasiliensis r r r prr P barbfish

Scorpaena grandicornis r r r piumed scorpionfish

Scorpaena plumeiri r spotted scorpionfish

Triglidae/searobins

Bellator militaris horned searobin

Prionotus pectoralis*

Prionotus salmonicolor r P

blackwing searobin

Prionotus scitulus r r r r r r r P P P P P leopard searobin

Prionotus tribulus r r r c rr P P P P P bighead searobin

Prionotus roseus P bluespotted searobin

(Continued)

152 Appendix(Continued).

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

Bothidae/lefteye flounder

Bothus ocellatus r r r P eyed flounder

Ancylopsetta quadrocellata r P r P P P ocellated flounder

Cyclopsetta fimbriatta P spotfin flounder

Citharichthys macrops r r P P P spotted whiff

Citharichthys spilopterus r r r r P P bay whiff

Paralichthys albigutta r r r r r r PP P P P P gulf flounder

Paralichthys lethostigma P P southern flounder

papillosumSyacium P P dusky flounder

Etropus crossotus r P P P P P fringed flounder

Etropus rimosus P P gray flounder

Soleidae/soles

Thunnus atlanticus blackfin tuna

Istiophoridae/billfishes

Istiophorus platypterus sailfish

Stromateidae/butterfishes

Peprilus burti P gulf butterfish

Peprilus paru* P P

Peprilus alepidotus P P harvestfish (Continued) Appendix (Continued).

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

Stromateidae/butterfishes (continued)

Peprilus triacanthus P butterfish

Nomeus gronovii r man-of-war fish

Trinectes inscriptus r r scrawled sole

Trinectes maculatus r r r PP PP hogchoker

Achirus lineatus rrrpcc r r PP PP lined sole

Cynoglossidae/tonguefishes

Symphurus plagiusa r r r c c r P PP PP blackcheek tonguefish

Symphurus diomedianus P spottedfin tonguefish

Bal i stidae/triggerfishes and filefishes

Balistes capriscus r P gray triggerfish

Monocanthus ciliatus c r r c r r a a P P P fringed filefish

Monocanthus hispidus c r r c r rrrr PP P P P planehead filefish

Alutera zchoepfi r P P orange filefish

Ostraciidae/boxfishes

Lactophrys quadricornis r c r r P r r P P scrawled cowfish

Lactophrys trigonus r r C r P trunkfish

Lactophrys triqueter r r smooth trunkfish

(Continued)

154 Appendix (Continued).

Abundance by survey number Species 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* P

Sphoeroides harperi* P

Sphoeroides testudineus r checkered puffer

Lagcocephalus laevigatus P smooth puffer

Diodontidae/porquepinefishes

Chilomycterus schoepfi rcrrprrcrr pp p p P P striped burrfish

Chilomycterus antennatus r bridled burrfish

Diodon holocanthus r r P r balloonfish

155 so272 -101 REPORT DOCUMENTATION 11. REPORT NO. PAGE 1 Biological Report 85(7.25) 1'. .____--. .._ _..______.______~__ 4. TotIe and Subtetls 1 September 1989 The Ecology of the Seagrass Meadows of the West 6. Coast of Florida: A Community Profile i

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