FWS/OBS-82/25 September 1982 Reprinted September 1985 THE ECOLOGY OF THE SEAGRASSES OF SOUTH FLORIDA: A Community Profile
Bureau of Land Management Fish and Wildlife Service U.S. Department of the Interior FWS/OBS-82/25 September 1982 Reprinted September 1985
THE ECOLOGY OF THE SEAGRASSES OF SOUTH FLORinA: A ITV PROFILE
by
Joseph C. Zier1an Department of Environmental Sciences University of Virginia Charlottesville, VA 22903
Project Officer Ken Adams National Coastal Ecosystems Team U.S. Fish and Wildlife Service 1010 Gause Boulevard Slidell, LA 70458
Prepared for National Coastal Ecosystems lean Office of Biological Services U.S. Department of the Interior Washington, nc 20240 DISCLAIMER
The findings in this report are not to be construed as an official U.S. Fish and Wildlife Service position unless so designated by other authorized documents.
Library of Contress Card Number 82-600617.
This report should be cited as: Zieman, J.C. 1982. The ecology of the seagrasses of south Florida: a community profile. U.S. Fish and Wildlife Services, Office of Biological Services, Washington, D.C. FWS/OBS-82/25. 158 pp. i. PREFACE
This profile of the seagrass corimun treat~ent of a specific facet of seagrass i ty of south Florida is one in a series of ecology. The format, style, and level of community profiles that treat coastal and presentation make this synthesis report marine habitats important to humans. Sea adaptab 1e to a variety of needs such as grass meadows are highly productive habi the preparation of environmental assess tats which provide 1iving space and pro ment reports, supplementary reading in tection from predation for large popula marine science courses, and the education tions of invertebrates and fishes, many of of participants in the democratic process which have commercial value. Seaqrass of natural resource management. also provides an important henefit by stabilizing sediment. Any questions or comments about, or requests for pub1 ications should be di The information in the report can rected to: give a basic understanding of the seagrass community and its role in the regional Information Transfer Specialist ecosystem of south Florida. The primary National Coastal Ecosystems Team geographic area covered lies along the U.S. Fish and Wildlife Service coast between Biscayne Bay on the east NASA/Slidell Computer Complex and Tampa Bay on the west. References 1010 Gause Boulevard are provided for those seeking indepth Slidell, Louisiana 70458
iii CONTENTS
PREFACE, , ••• ; ; i FIGURES •••• vi TABLES ••••• ...... "' , • , , • Vi i ACKNOWLEDGMENTS • • • • •• viii CHAPTER 1. INTRODUCTION 1 1.1 Seagrass Ecosystems . . . . . 1 1.2 Climatic Environment 4 1.3 Geologic Environment . . . . 6 1.4 Regional Seagrass Distribution ...... 7 1. 5 Seagrasses of South Florida . 7 CHAPTER 2. AUTECOLOGY OF SEAGRASSES . . . . 11 2.1 Growth ...... 11 2.2 Reproductive Strategies ...... 11 2.3 Temperature...... 12 2.4 Salinity ...... 14 2.5 Sedir:ients ...... 14 2.6 Current Velocity 17 2. 7 Oxygen ...... 17 2.8 Solar Radiation. . . . 17 2.9 Zonation ...... 18 2,10 Exposure ...... 19 CHAPTER 3. PRODUCTION ECOLOGY . . . . 20 3.1 Biomass ...... 20 3.2 Productivity ...... 22 3.3 Productivity Measurement ...... 22 3.4 Nutrient Supply...... 25 3.5 Seagrass Physiology ...... 26 3.6 Plant Constituents . . . . 29 CHAPTER 4. THE SEAGRASS SYSTEM...... 33 4.1 Functions of Seagrass Ecosystems . . . . . 33 4.2 Succession and Ecosystem Development 34 4.3 Species Succession ...... 34 4.4 The Central Position of the Seagrasses to the Seagrass Ecosystem ...... 38 4.5 Structural and Process Succession in Seagrass ...... 39 iv CONTENTS (continued)
CHAPTER 5. THE SEAGRASS COMMUNITY - COMPONENTS, STRUCTURE, AND FUNCTION 41 5.1 Associated Algae •• 42 Benthic Algae •• 42 Epiphytic Algae 44 5.2 Invertebrates •••. 45 Composition ••. 45 Structure and Function. 46 5.3 Fishes •••••.•••• 49 Composition ...... 49 Structure and Function • 51 5.4 Reptiles 53 5.5 Birds .••..... 54 5.6 Mammals •••••.• 56 CHAPTER 6. TROPHIC RELATIONSHIPS IN SEAGRASS SYSTEMS .• 57 6.1 General Trophic Structure. 57 6.2 Direct Herbivory •••••••• 59 6.3 Detrital Processing •••• 69 Physical Breakdown •••••••••••• 70 Microbial Colonization and Activities 71 Microflora in Oetritivore Nutrition ••• 72 Chemical Changes During Decomposition ••• 73 Chemical Changes as Indicators of Food Value 73 Release of Dissolved Organic Matter ••• 74 Role of the Detrital Food Web 74 CHAPTER 7. INTERFACES WITH OTHER SYSTEMS 75 7.1 Mangrove •.•••• 75 7.2 Coral Reef .••• 75 7.3 Continental Shelf •• 78 7.4 Export of Seagrass •••• 78 7.5 Nursery Grounds • 80 Shrimp • • • . • 80 Spiny Lobster •• 81 Fish ••.•••• 82 CHAPTER 8. HUMAN IMPACTS AND APPLIED ECOLOGY 84 8.1 Dredging and Filling •••••• ...... 84 8.2 Eutrophication and Sewage •••• ...... 86 8.3 Oi 1 • • • • • • • • • • • • • • • 87 8.4 Temperature and Salinity ••••••• ...... 88 8.5 Disturbance and Recolonization • 91 8.6 The Lesson of the Wastfng Diseas~ • 93 8.7 Present, Past, and Future • 93 REFERENCES ••••••••••••••• 96 APPENDIX ••••••.•••••••• A-1 Key to Fish Surveys in South Florida ••••••••.•••.• A-1 List of Fishes and their Diets from Collections in South Florida • A-2
V FIGURES
Nu111ber Page 1 Panoramic view of a south Florida turtle grass bed 2 2 Map of south Florida ••••.••.••••• 3 3 Average monthly tell'peratures in Florida • • • • • • 6 4 Seagrasses of south Florida •••.•••.••••••• 9 5 Diagram of a typical Thalassia shoot ••••••• 12 6 Response of Thalassia production to temperature •••.• . . . 13 7 Response of a Thalassia bed to increasing sediment depth 16 8 Depth distribution of four seagrasses • • . • • •• 19 9 Blowout disturbance and recovery zones •.••••••• 35 10 Idea 1 i zed sequence through a seagrass blowout • • • . • . • • • • • • 35 11 Representative calcareous green algae from seagrass bess ••• 35 12 Origin of sedimentary particles in south Florida marine waters ••• 36 13 Ecosystem development patterns in south Florida marine waters • 37 14 Calcareous algae (Udotea sp.) from the fringes of a seagrass bed ...... •.•..••••.. 43 15 Thalassia blades showing tips encrusted with calcareous epiphytic algae ••••••••••••••••••••• 45 16 Large invertebrates from seagrass beds • • • • • • ••• 47 17 Snail grazing on the tip of an encrusted Thalassia leaf. 48 18 Relative abundance of fishes and invertebrates over seagrass beds and adjacent habitats • • • • • • • • 49 19 Small grouper (Serranidae) foraging in seagrass bed. 52 20 Seagrass bed following grazing by green sea turtle 53 21 Shallow seagrasses adjacent to red mangrove roots • 54 22 Principal energetic pathways in seagrass beds ••••.. 57 23 Comparative decay rates. • • • • • • • . • • • • • ••• 71 24 Grunt school over coral reef during daytime • • • • •.• 76 25 Seagrass export from south Fl or i da to the eastern Gulf of Mexico ••••••••••••.•••• 79 26 Housing development in south Florida •••••• 85 27 Scallop on the surface of a shallow Halodule bed 95
vi TABLES
Number Page 1 Temperature, salinity, and rainfall at Key West 5 2 Seagrasses of south Florida •••••••••• 8 3 Representative seagrass biomass •••.•••• 21 4 Comparison of biomass distribution for three species of seagrasses ••••••••••••••••••••• 23 5 Representative seagrass productivities •••• 24 6 C values for gulf and Caribbean seagrasses ••••••••• 28 7 Constituents of seagrasses ••••.••••• 30 8 A gradient of parameters of seagrass succession 40 9 Birds that use seagrass flats in south Florida ••••••••• 55 10 Direct consumers of seagrass • • • • • • ••• 60
vii ACKNm1LEDGMENTS
In producing a work such as this pro Two of the sections were written by file, it is impossible to catalog fully my students, Michael Robblee and t~ark and accurately the individuals that have Robertson. To them and other students, provided either factual information or present and past, I must give thanks for intellectual stimulus. Here much of the keeping life and work fresh (if occasion credit goes to the mutual stimulation pro ally exasperating). The numerous drafts vided by my colleagues in the Seagrass of this manuscript were typed by Deborah Ecosystem Study of the International Coble, who also provided much of the edit Decade of Ocean Exploration. Special ing, Marilyn Mclane, and Louise Cruden. recognition must be given to the magus of Original drafting was done by Rita Zieman, seagrass idiom during those frantic and who al so aided in the production of Chap memorable years, Peter Mc Roy. ter 8, and Betsy Blizard. I cannot thank enough Ken Adams, the project officer, for At one stage or another in its gesta his patience and help in the production of tion, the manuscript was reviewed and com this work, which went on longer than any ments provided by Gordon Thayer, Richard of us imagined. Iverson, James Tilmant, Iver Brook, and Polly Penhale. Other information, advice, Thanks are also expressed to Gay or v1elcomed criticism was provided by John Farris, Elizabeth Krebs, Sue Lauritzen, OC'den, Ronald Phillips, Patrick Parker, and Randy Smith of the U.S. Fish and r,obin Lewis, Mark Fonseca, Jud Kenworthy, Wildlife Service for editorial and typ Brian Fry, Stephen Macko, James Kushlan, ing assistance. Photographs and figures William Odum, and Aaron Mills. were by the author unless otherwise noted.
viii CHAPTER 1
INTRODUCTION
1.1 SEAGRASS ECOSYSTEMS Studies in the south Florida region over the past 20 years have demonstrated Seagrasses are unique for the marine the importance of the complex coastal environment as they are the only land estuarine and lagoon habitats to the pro plant that has totally returned to the ductivity of the abundant fisheries and sea. Salt marsh vegetation and mangroves wildlife of the region. Ear1 ier studies are partially submerged in salt water, but describing the link between estuarine sys the seagrasses live fully submerged, tems and life cycles of important species carrying out their entire life cycle com focused on the mangrove regions of the pletely and obligately in sea water (Fig Everglades (W.E. Odum et al. 1982), al ure 1). though the seagrass beds of Florida Bay and the Florida Keys have been i den ti fied Seagrass meadows are highly produc as habitats for commercially valuable spe tive, faunally rich, and ecologically cies, as well as for organisms that are important habitats within south Florida I s important trophic intermediaries. Many estuaries and coastal lagoons (Figure 2) species are dependent on the bays,. 1 a as well as throughout the world. The com goons, and tidal creeks for shelter and plex structure of the meadow represents food during a critical phase in their life living space and protection from predation cycle. for large populations of invertebrates and fishes. The combination of plentiful shel Many organisms that are primarily ter and food results in seagrass meadows' characterized by their presence and abun being perhaps the richest nursery and dance over coral reefs, such as the enor feeding grounds in south Florida's coastal mous and colorful schools of snappers and waters. As such, many commercially and grunts, are residents of the reef only by ecologically significant species within day for the she1 ter its comp1 ex structure mangrove, coral reef, and continental provides, foraging in adjacent grass beds shelf communities are linked with seagrass at night. These seagrass meadows, often beds. located adjacent to the back reef areas of barrier reefs or surrounding patch reefs, Al though the importance of seagrass provide a rich feeding ground for diurnal beds to shallow coastal ecosystems was reef residents; many of these organisms demonstrated over 60 years ago by the may feed throughout their life cycle in pioneering work of Petersen (1918) in the the grass bed. The juveniles of many Baltic Sea, it is only in the past 1~ to Pomadasyid species are resident in the 15 years that seagrasses have bec?me w1de gr-ass beds. As they grow,. however •.their ly recognized as one of the richest. of increasing size will no longer allow them ecosystems. rivaling cultivated tropical to seek shelter in the grass and they move agriculture in productivity (~lest1 ake on to the more complex structure of the 1963; Wood et al. 1969; McRoy and McMillan reef for better protection (Ogden and 1977; Zieman and Wetzel 1980). Zieman 1977).
1 Figure 1. Panoramic view of a south Florida turtle grass bed. 2 0
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<) 0 ro
..,(;I "' 1,' .. ;... 0 a \; 1,1.. in .., Si ' a,,
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. C,.1
0 (lJ r<) l.. ::, (f\ j ,,..,Cl• I.,, Mangroves and coral reefs are rarely, When assessing the role of seagrass if ever, in close proximity because of es, sediment stabilization is also of key their divergent physio-chemical require importance. Although the seagrasses them ments, but seagrasses freely intermingle selves are only one, or at most three spe with both communities. Seagrasses al so cies, in a system that comprises hundreds fonn extensive submarine meadows that fre or thousands of associated plant and ani quently bridge the distances between reefs mal species, their presence is critical and mangroves. Seagrass beds of the larger because much, if not all, of the community rnangrove-1 ined bays of the Everglades and exists as a result of the seagrasses. In Ten Thousand Island region, while being a their absence most of the regions that srnal 1 proportion of the total bottom cov they inhabit would be a seascape of un erage of these bays, are the primary zones stable shifting sand and mud. Production where important juvenile organisms, such and sediment stabilization would then be as shrimp, are found. due to a few species of rhizophytic green algae. There are two major internal pathways along which the energy from seagrasses is made available to the community in which 1. 2 CLIMATIC ENVIRONMENT they exist: direct herbivory and detrital food webs. In many areas a significant South Florida has a mild, semitropi amount of material is exported to adjacent cal maritime climate featuring a small communities. daily range of temperatures. The average precipitation, air temperature, surface Direct grazing of seagrasses is con water temperature, and surface water sa- fined to a small number of species, al 1 inity, for Key West are given in Table 1. though in certain areas, these species may Water temperature and salinity vary sea be quite abundant. Primary herbivores of sonally and are affected by individual seagrasses in south Florida are sea tur storms and seasonal events. Winds affect tles, parrotfish, surgeonfish, sea ur ing the area are primarily mild southeast chins, and possibly pinfish. In south to easterly winds bringing moist tropical Florida the amount of direct grazing air. Occasional major storms, usually varies greatly, as many of these herbi hurricanes, affect the region on an aver vores are at or near the northern limit of age of every 7 years, producing high winds their distribution. The greatest quandry and great quantities of rain that lower concerns the amount of seagrass consumed the salinity of shallow waters. During by the sea turtles. Today turtles are the winter, cold fronts often push through scarce and consume a quantitatively insig the area causing rapid drops in tempera nificant amount of seagrass. However, in ture and high winds that typically last 4 pre:,.;,Columbian times the population was to 5 days (Warzeski 1977, in Multer 1977). vast, being 100 to 1,000 times - if not In general, summer high temperatures are greater - than the existing population. no higher than elsewhere in the State, but winter low temperatures are more moderate Some grazers, such as the queen (Figure 3}. conch, appear to graze the leaves, but primarily scrape the epiphytic algae on Water temperatures are least affected the leaf surface. Parrotfish preferen on the outer reef tract where surface wa tially graze the epiphytized tips of sea ters are consistently mixed with those grass leaves, consuming the old portion of from the Florida Current. By contrast the the leaf plus the encrusting epiphytes. inner regions of Florida Bay are shallow and circulation is restricted. Thus water The de-ttitus .. food.weh has classically t@ll'pe.ratures "here-change-rapidly with sud been considered the main path by which the den air temperature variations and rain. energy of seagrasses makes its way through Water temperatures in Pine Channel dropped the food web. Although recent studies :f.. com 20° to 12°c (68° to 54°F) in 1 day have pointed to increased importance of following the passage of a major winter grazing in some areas (Ogden and Zieman storm {Zieman, personal observation). 1977). this generalization continues to be These storms cause rapid increases in sus supported. pended sediments because of wind-induced 4 Table 1. Temperature, salinity, and r11infa1l at Key West (froin Zeitschke, in Multer 1977). Precipitation and air temperature data are fror, 1?51 to 1960, water temperatures and salinity are fron 1955 to 1962.
Mean t•~ean Surface water terno. (°C Surface water sa1initt % r-~onth precipitation (~m) air temp. ( °C) ranoe 1>Jean ran9e (mean}
January 44.0 20.8 13.8-25.0 (10,6) 22.0-37.9 (3S.9) February 54.8 21. 7 16.0-27.5 {22.2) 33.1-38.0 (36.0) tiarch 36.9 23.2 18.2-22.1 (23.5) 33.2-3!3.2 (36.4) April 40.7 25.3 21. 5-29. 7 (25.2) 33.5-38.8 (36.7) u, May 85.6 27.0 23.7-30.8 (27. 7) 33.3-38.6 (37.0)
June 93.5 2D. 3 25.9-31.9 (29.4) 32.1-38.8 (36.6) July 91.C 29.1 27.0-32.5 ( 30. 1) 31. 5-38. B ( 36. 6)
'JO 4 August 101.C (....,;. ' 27.0-33.0 (30.3) 31. 5-3t:. l (36.6) September 165.8 28.5 27.0-32.5 {29.4) 33.7-37.6 (36.0) October 115.9 26.5 22.0-30.B (27.3) 29.0-38.1 (35.8) November 99.8 24.1 18.7-28.1 (24.2) 32.5-38.8 (36.3) December 4C.6 21.5 16.5-26.4 (22.1) 32.7-38.4 (3G.2) Key West St P11ter11burg Cedar Key Penaocolo JFMAMJJASONO JFMAMJJASONO 4 FIIIAIIIJJASOND J fll!AMJJASOND
- 90
- 80 : : 25 : :
. . ► (.) . ~ Q : : • 70 i ~ 20 -- - --+-1--l...... L-.l_.~-~-----'-~ ~ Q ~ z E ... .. •0. E l ! {!. 15 ; : ·:··~•J.-i-••"------+--1-- 60 ~
l ; : 10 ------1--+-I-''------+--+-! +-+-+-----J..-.1. - 50 ! ! ! : i 5 . - 40
Figure 3. Average monthly temperatures in Florida, 1965 (McNul ty et al. 1972). turbulence and occasionally reduced sa1in• 1.3 GEOLOGIC ENVIRONMENT ities, a11 of which stress the local shal low water communities. It is thought that The south Florida mainland is low the rapid influx of this type of water lying limestone rock known as Miami lime from Florida Bay through the relatively s tone. For descriptive purposes the region open pas sages of the centra 1 Keys, when can be broken into four sections: the pushed by strong northwesterly winter south peninsular mainland (including the winds, is the major factor in the reduced Everglades), the sedimentary barrier abundance of coral reefs in the central islands, the Florida Keys and reef tract, Keys (Marsza1ek et al. 1977). and Florida Bay. Tides are typically about 0.75 m (2.5 The sedimentary barrier islands of ft) at the Miami harbor mouth. This range north Biscayne Bay, Miami Beach, Virginia is reduced to 0.5 m (1.6 ft) in the embay- Key, and Key Biscayne are unique for the ments such as South Biscayne Bay and to area because they are composed 1argely of 0.3 m (1 ft) in restricted embayments like quartz sand. The islands are the southern Card Sound (Van de Kreeke 1976). The mean terminus of the 1 ongshore transport of range decreases to the south and is 0.4 m sand that moves down the east coast and (1.3 ft) at Key West Harbor. Tidal heights ultimately out to sea south of Key Bis and velocities are extremely complex in cayne. All other sediments of the region south Florida as the Atlantic tides are are primarily biogenic carbonate. semidiurnal, the gulf tides tend to be di- 11rnal. and much of this region isbetween The Florida Keys are a narrow chain these two regimes. Neither tidal regime of tslands extending from tiny Soldier is particularly strong, however, and winds ... Key, just south of Key Biscayne, in first frequently overcome the predicted tides. a southerly and then westerly arc 260 km
These factors 1 coupled with the baffling (163 mi) to Key West and ultimately to the effects of mudbanks, channels, and keys, Marquesas and the Ory Tortugas some 110 km create an exceedingly complex tidal circu- (69 mi) further west. The upper keys, 1 at ion. from Big Pine northward, are composed of 6 ancient coral kmMn as Key Largo 1 ine this <1rea (8ittaker and Iverson, in stone, whereas the lower keys from Biq press}. In an inventory of the estuaries Pinc \~est are CO!'lpOsed of oolitic facies of the gulf coast of Florida, ~~cNul ty of the Miami linestone. (A note to boaters et al. (1972) estimated that over 45% of and researchers in these shallow waters: the total area in the reoion of Florida the 1 i1:1es tone of th1: 1ower keys is much Bay west of the Keys and '1 and ward to the harder than in the upper keys, and occa freshwater line to Cape Sab 1 e was sub sional brushes with the bottor1, which merged vegetation. By comparison, r:ian- wou 1d be 1:ii nor in the upper keys, wil 1 9rove vegetation comprised less than 7% of inan9le or destroy outboard propellers and the ania. lower drive units.) The ai'1ount of seagrass coverage drops The Florida reef tract is a shallow off rapidly to the north of this area on harrier-type reef and lagoon extending both coasts. On the Atlantic coast. the east and south of the Florida Keys. It shifting sand beaches signal a chan~e to a averages 6 to 7 km (4 to 4.4 mi) in width high-energy coast that is unprotected from with an irregular surface and depths vary waves and has a relatively unstable sub ing from O to 17 11 (56 ft}. The outer strate, coupled with the littoral drift of reef tract is not continuous, hut consists sand from the north. Throuohout this area of various reefs, often with wide gaps be seagrasses are usually founJ only in small tween ther1. The development is greatest pockets in protected inlets and la9oons. in the upper keys. The patch reefs are On the Gulf of ~exico coast north of Cape irregular knolls rising froi:1 the limestone Sable, seagrasses are virtually eliminated platform in the area between the outer hy drainage from the Everglades with its reef and the keys. Behind the outer reef, increased turbidity and reduced salinity. the back reef zone or lagoonal area is a Seagrasses are then found only in rela mosaic of patchreefs, 1 inestone bedrock, tively small beds within bays and estuar and grass-covered sedimented areas. ies until north of Tarpon Sprincs, where an extensive (3,000 km 2 or 1,158.mi ) bed Florida Ray is a triangular region exists on the extremely broad shelf of the lying west of the upper keys and south of northern gulf. Several bays on the gulf the Everglades. This large (226,000 ha or coast, including Tampa Bay and Boca Ciega 558,220 acres), extremely shallow basin f\ay, formerly possessed extensive seagrass reaches a rnaxirr1un depth of only 2 to 3 m resources, but dredge and fill operations (7 to 10 ft), but averages less than 1 1:1 and other human perturbations have greatly (3.3 ft) over a great area. Surface sedi reduced the extent of these beds. ments of fine carbonate mud occ,ff in wind ing, anastonosing nud hanks, seagrass This profile is primarily directed at filled "lakes" or basins, and mangrove the seagrass ecosystef11 of southern Flor islands. ida. It is necessary, however, to draw on the pertinent work that has been done in other seagrass systeMs. 1.4 REGIONAL SEACRASS DISTRIBUTION Florida possesses one of the largest 1.5 SEAGRASSES OF SOUTH FLORIDA seagrass resources on earth. Of the 2 10,000 km>' (3,860 mi ) of seagrasses in Plants needed five properties to suc the Gulf of Mexico, over 8,500 k,,,:: (3,280 cessfully colonize the sea, according to mi 2 ) are in Florida waters, primarily in Arber (1920) and den Harto9 (1970): two major areas (Bi ttaker and Iverson, in press). The southern seagrass bed,. which (1) The ability to live in a saline is bounded by Cape Sable, north Biscayne nediur1. Bay, and the Dry Tortugas, and includes the warm, shallow waters of Florida Ray (2) The ability to function while and the Florida coral reef tract, extends fully sub1:1erged. over 5,500 km 2 (2,120 mi 2 ). Although cov erage is broken in numerous places, ov:r (3) A wel1-deve1 oped anchoring sys 80% of the sea bottom contains seagrass 10 teri. 7 (4) The ability to complete their systenatic treatments such as den Hartog reproductive cycle while fully (1970) and Tomlinson (1980) should be con submerged. sulted, however, when comparing the sea grasses of other areas. The best descrip (5) The ability to compete with tions of the local species are still to be other organisms in the marine found in Phillips (1960). environment. Turtle grass (Thalassia testudinum) Only a small, closely related group of is the laroest and most robust of the monocotyledonous angiosperms have evolved south Florida seagrasses. Leaves are rib all of these characteristics. bon-like, typically 4 to 12 mm wide with rounded tips and are 10 to 35cm in length. Worldwide there are approximately 45 There are commonly two to five 1eaves per species of seagrasses that are divided short shoot. Rhizomes are typically 3 to between 2 families and 12 genera. The 5 mm wide and may be found as deep as Potamogetonaceae contains 9 genera with 34 25 cm (10 inches) in the sediment. Thalas species, while the family Hydrocharitaceae sia forms extensive meadows throughout has 3 genera and 11 species (Phillips most of its range. 1978). In south Florida there are four genera and six species of seagrasses Manatee grass {Syringodium filiforme) (Table 2). The two genera in the family is the most unique of the local seagrass Potamogetonaceae have been reclassified es, as the leaves are found in cross sec comparatively recently and many of the tion. There are commonly t\'10 to four widely quoted papers on the south Florida leaves per shoot, and these are 1.0 to 1.5 seagrasses show Cymodocea for Syringodium mm in diameter. Length is highly vari and Oiplanthera for Halodule. Recent dis able, but can exceed 50 cm (20 inches) in cussion in the 1 iterature speculates on some areas. The rhizome is less robust the possibility of several species of than that of Thalassia and more surfici Halodule in south Florida (den Hartog ally roote Table 2. Seagrasses of south Florida. Family and species Common name Hydrocha ri taceae Thalassia testudinun Konig Turtle grass Halophila decioiens Ostenfeld Halo..e_hil a engelmann!_ Ascherson · HaTophil i! _jp_!i_nsoni i Ei senan Potanogetonacea .~1.1:::!J2R~dium filiforme Kutz Manatee grass llaJ..Q_~y__l_f:}. wrighti i Ascherson Shoal grass ------·---•-·-•·--- 8 1!! '; II/ ~ I/ ii ~I:,,, 11 \i II 'I, :f t, ,,, I '\ ) l '\ I \ I ,/ I '/ Holophilo engelmanni Holophilo decipiens Holodule wrightii . } Syringodium filiforme Thalossia tesrudinum Figure 4. Seagrasses of south Florida, 9 in disturbed areas, and in areas where .!:!_ • .,iQ_l}_n_~oni i, was described (Ei sernan and Thalassia or Syringo9iu~ are excluded McMillan 1980) and could be easily confus because of the prevailing conditions. ed with .!:!_. de~ioiens. The most obvious Shoal grass grows commonly in water either differences are that .!:!_. _j_Q_tl_nsoni i lacks too sha 11 ow or too deep for these sea hairs entirely on the leaf surface and the grasses. Leaves are flat, typically 1 to veins anerge from the midrib at 45° angles 3 mm wide and 10 to 20 cm long, and arise instead of 60°. The initial description from erect shoots. The tips of the leaves recorded .!:!_. johf!.~oni i from Indian River to are not rounded, but have two or three Biscayne Bay, but its range could ulti points, an important recoonition charac mately be much wider. ter. Halodule is the most ~tolerant of all the seagrasses to variations in tempera The major problem in positive identi ture and salinity (Phillips 1960; McMillan fication of seaorasses is between Halodule and Moseley 1967). In low salinity areas, and Ruppia maritima, corir:1only knOl;in-as care must be taken to avoid confusing it widgeongrass.~though typically found with ,BURRia_. alongside Halodule, primarily in areas of reduced salinity, ~a._ is not a true Three species of Halophila, all small seagrass, but rather a freshwater pl ant and delicate, are sparsely distributed in that h,3s a pronounced salinity tolerance. south Florida. Halo_,e__hila engelmanni is It is an extremely important food for the most recognizable with a whorl of four waterfowl and is 1videly distributed. to eight oblong leaves 10 to 30 mm lono Where it occurs, it functions similarly to borne on the end of a stem 2 to 4 cm long: the seagrasses. In contrast with Halo This species has been recorded from as dule, the leaves are expanded at the base deep as 90 m (295 ft) near the Dry Tortu and arise alternately fr0ff1 the sheath, and gas. ~J:;.i__~ de~ipie11_~ has paired the leaf tips are tapered to a long point. oblong-elT1r1bc leaves 10 to 25 mm lono It should he noted, however, that leaf and 3 to 6 mr.1 wide arising directly fro,n tips are comcionly missing fro1'1 older the node of the rhizome. A new species, leaves of both species. 10 CHAPTER 2 AUTECOLOGY OF SEAGRASSES 2.1 GROv!TH in the denser grass beds east of the Fl or ida Keys. Short shoots in areas exposed A remarkable sic1il arity of vegetative to heavy waves or currents tend to have appearance, gro~Jth, and morphology exists fewer leaves. among the seagrasses (den Hartog 1970; Zieman and Wetzel 1980). Of the local The growth of individual leaves of species, ti.1rtle grass is the nost abun turtle grass in Biscayne Ray averages 2.5 dant; its growth and norphol ogy provide mM/day, increasing with leaf width and a typical scheme for seagrasses of the robustness. Rates of up to 1 cm/day were area. observed for a 15- to 20-day period (Zie man 1975b). Leaf growth decreased exponen Tor1linson and Vargo (1966) and Tom tially with age of the leaf (Patriouin linson (1969a, 196%, 1972) described in 1973; Zieman 1975b). detail the morphology and anatomy of tu r tl e grass. The round-tipped, strap-like Leaf width increases with short shoot leaves emanate from vertical short shoots age and thus \.'Jith distance fron the rhi 1-1hich branch laterally from the horizontal zome ,neristen, reaching the community max rhizomes at regular intervals. Turtle iriur1 5 to 7 short shoots hack frori the grass rhizomes are buried in 1 to 25 w growing tip (Figure 5). The short shoot (0.4 to 10 inches) of sedi,~ent, although has an average 1 ife of 2 years (Patriquin they usually occur 3 to 10 en (1 to 4 1975) and may reach a 1 ength of 10 er: inches) below the sediment. In contrast, (Tor1linson and Vargo 1966). A n~w short rh i zories of s hoa 1 grass and Ha 1 oph il a are shoot first pt1ts out a few small, td!J~red near the surface and often exposed, while 1 eaves about 2 Cfl1 wide before producing manatee grass rhizomes are most typically the reoular leaves. New leaves are produc found at an intermediate depth. Turtle ed throughout the year at an avera9e rate grass roots originate at the rhizoc1es or of one new leaf per short shoot every 14 less frequently at the short shoots. They to 16 days, and times as short as 10 days are much smaller in cross section than the have been reported. In south F1 orida the rhizomes, and their length varies with rate of leaf production depended on temp sediment type, organic matter, and depth erature, with a rate decrease in the cool to bedrock. er winter months (Zieman 1975b). The rate of leaf production varies less throughout On a turtle grass short shoot, new the year in the tropical waters of Bart-a leaves gro1v on alternatjng sides frori a dos and Ja!"laica. according to Patriquin central neristem which is enclosed by old (1973) and Greenway (1974), respectively. leaf sheaths. Short shoots typically carry two to five 1 eaves at a time; in south Florida, Zieman (1975b) found an 2.2 REPRODUCTIVE STRATEGIES average of 3.3 leaves per shoot in the less productive inshore areas of Biscayne Seagrasses reproduce vegetatively and Bay, and 3. 7 leaves per shoot at stations sexually, but the inforriation on sexual 11 AVERAGE LEAF WIDTH 8.5 8 7 7.5 7 4 LEAF---- RHIZOME MERISTEM BRANCH OR SHORT SHOOT--! 6 8 9 RHIZOME~ DISTANCE BETWEEN BRANCHES (CM) Figure 5. Oiagram of a typical Thalassia shoot. Note increasing blade length and width on the older, vertical short shoots. reproduction of the south Florida sea is only partially correct. Tropical grasses is sketchy at best. The greatest oceanic water in the Caribbean is typi amount of information exists for turtle cally 26° to 30°C (79° to 86°F), and feels grass, because of the extensive beds and cooler than one would at first suspect. because the fruit and seeds are relatively In the past, lack of familiarity with large and easily identified for seagrass tropical organisms led many otherwise cap es. In south Florida buds develop in Jan able scientists to view the tropics and uary (Moffler et al. 1981}; flowers, from subtropics as simply warmer versions of mid-April until August or September (Or the temperate zone. Compared with their purt and Boral 1964; Grey and Moffler temperate counterparts, tropical organisms 1978). In a study of plant parameters in do not have greatly enhanced thermal tol permanently marked quadrats, Zieman noted erances; the upper thermal limit of tropi that at Biscayne Bay stations flowers ap cal organisms is generally no greater than peared during the third week in May and that of organisms from warm temperate re fruits appeared from 2 to 4 weeks 1ater. gions (Zieman 1975a). In tropical waters, The fruits persisted until the third week the range of temperature tolerance is low, of July, when they detached and floated often only half that of organisms from away. equivalent temperate waters (Moore 1963a). This is reflected in the seasonal range of the surrounding waters. At 40° north lat 2.3 TEMPERATURE itude, the seasonal temperature range of oceanic surface water is approximately One of the first mental images to 10°c {50°F), while at 20° north, the range be conjured up when considering the trop is only 3°C, reaching a low of only l°C ics is that of warm, clear, calm water, ( 33. 8°F} at about 5 ° north. However, be abounding with fish and corals. This image cause of the extensive winter cooling and 12 summer heating of shallow coastal water, In a study of the ecology of tidal Moore (1963a) found that the ratio of mean flats in Puerto Rico, Glynn (1968) observ temperature range (30° to 50° N) to mean ed that the 1eaves of turtle grass were tropical range (20° N to 20° S) to be killed by temperatures of 35° to 40°C (95° 2.5:1 for oceanic waters, but increased to to 104°F), but that the rhizomes of the 4.2:1 for shallow coastal waters. plants were apparently unaffected. On shallow banks and grass plots, tempera Because of thermal tolerance reduc tures rise rapidly during low spring tion in the tropics, the biological result tides; high temperatures, coupled with is a loss of cold tolerance; that is, the desiccation, kill vast quantities of range of thermal tolerance of tropical leaves that are later sloughed off. The organisms is about half that of temperate process occurs sporadically throughout the counterparts, whereas the upper tolerance year and seems to pose no long-term prob limit is similar (Zieman and Wood 1975). lem for the plants. Wood and Zieman (1969) warn, however, that prolonged heating of Turtle grass thrives best in tempera substrate could destroy the root and rhi tures of 20° to 30°C ( 68° to 86 °F) in zome system. In this case, recovery could south Florida (Phillips 1960). Zieman take several years even if the stress were (1975a, 1975b} found that the optimum removed. temperature for net photosynthesis of turtle grass in Biscayne Bay was 28° to The most severe mortalities of organ 30°C (82° to 86°F} and that growth rates isms in the waters of south Florida are declined sharply on either side of this usually caused by severe cold rather than range (Figure 6). Turtle grass can toler heat, as extreme cold water temperatures ate short term emersion in high tempera are more irregular and much wider spaced tures (33° to 35°C or 91° to 95°F), but phenomena than extreme high temperatures. growth rapidly falls off if these tempera McMillan (1979) tested the chill tolerance tures are sustained (Zieman 1975a, 1975b). of populations of turtle grass, manatee 10 8 .. • • • • .. ' * . ·.. . . :·· . ""...... • ·: .,.:· :· •• * 2 . il ¾; ·- • "' . ., •::••· - ."' : ...... • •.,Ii':·····...... :·• 11 . ... • • • ,Ii •• • ,., ...... · ...... ,.• 20 25 30 35 TEMPERATURE °C Figure 6. Response of Thalassia production to temperature in south Florida. 13 grass, and shoal grass in various loca embayments with restricted circulation, tions from Texas to St. Croix and Jamaica. such as southwest Biscayne Bay, r.,any Populations from south Florida were inter al gal species are reduced during sumr.ier mediate in tolerance between plants from high temperatures and some of the r1ore Texas and the northern Florida coast sensitive types such as Caulerra, Cladop and those from St. Croix and Jamaica in hora and laurencia may be kil ed (Zienan the Caribbean. In south Florida, the 1975a). most chill-tolerant plants were fror,i the shallow bays, while the populations that were least tolerant of cold temperatures 2.4 SALINITY were from cora 1 reef areas, where less fluctuation and greater buffering would be While all of the common south Florida expected. During winter, the cold north seagrasses can tolerate considerable sa- ern winds quickly cool off the shallow 1 inity fluctuations, all have an optimum (0.3 to 1 m or 1 to 3.3 ft) waters of range near, or just below, the concentra Florida Bay. The deeper waters, however, tion of oceanic water. The doMinant sea in the area he 1ow the Keys and the reef grass, turtle grass, can survive in salin line (up to 15 rn or 50 ft) not only have a ities from 3.5 ppt (Sculthorpe 1967} to 60 much greater mass to be coo 1ed, hut are ppt {McMillan and Moseley 1967), but can also flushed daily with warmer Gulf Stream tolerate these extremes for only short water which further tends to buffer the periods. Even then, severe leaf loss is environmental fluctuations. common; turtle grass lost leaves when salinity was reduced below 20 ppt (den The anount of direct evidence for the Harto~ 1970). The optirnu111 salinity for temperature ranges of shoal grass and man turtle grass ranges from 24 ppt to 35 ppt atee grass is far less than for turtle (Phillips 1960; McMillan and Moseley 1%7; grass. Phillips (1960) suggested that Zieman 1975b). Turtle grass showed maxinum shoal grass genera11y prefers temperatures photosynthetic activity in ful 1-strength of 20 to 30°C (68° to 86°F), but that it seawater and a linear decrease in activity is somewhat more eurythermal than turtle with decreasing sa 1 in i ty ( Hammer 196Gb). grass. This fits its ecological role as a At 50% strength seawater, the photosynthe pioneer or colonizing species. S~oal grass tic rate was only one-third of that in is commonly found in shallower water than full-strength seawater. Following the either turtle grass or manatee grass, passage of a hurricane in south Florida in where thermal variation would tend to be 1960, Thomas et al. (1961) considered the greater. Mc~illan {1979) found that shoal damage to the turtle grass by freshwater grass had a greater chill tolerance than runoff to have been more severe than the turtle grass, while manatee grass showed physical effects of the high winds and less resistance to chilling. water surge. Seagrasses are partial 1y buffered The tolerance of local seagrass spe fra1 temperature extrenes in the overlying cies to salinity variation is similar to water because of the sedfr1ents covering their temperature tolerances. Shoal 9rass the roots and rhizomes. Sediments are is the ~ost broadly euryhaline, turtle poorer conductors of heat than seawater grass is intermediate, and manatee grass and they absorb heat more slowly. In a and Halophila have the narrowest tolerance study by Redfield (1965), changes in the ranges, with Halophila being even ~ore temperature of the water colurnn decrease stenohal ine than manatee grass (Md'il 1 an exponentially with depth in sediMents. 1979). Macroalgae associated with grass bc 15 4 Sediment Elevation 2 (cm) 0 30 Leaf Density 20 (leaves/ 100cm2 ) 10 20 0 Leaf Length 10 (cm) 0 0 Sediment Depth 10 (cm) 20 30 0 .5 1.0 I. 5 2.0 2.5 Distance Across Bed ( m} (} Figure 7. Response of a Thalassia bed to increasing sediment depth. Note increasing blade length and density with increasing depth of sediment. The increase in elevation in the center of the bed is due to the trapping action of the denser blades. Particles of carbonate are locally overcome the carbonate buffer capacity of produced in seagrass beds and removed from seawater and drive the pH up to 9.4. the surrounding water. Older leaves are usually colonized by encrusting coralline The rnicrobially mediated chemical algae such as Melobesia or Fosliella. It processes in marine sediments provide a has been estimated that these encrusting major source of nutrients for seagrass a 1 gae produce from 40 to 180 g/m 2/yr of growth (Capone and Taylor 1980). Bacte calcium carbonate sediment in Jamaica rial processes convert organic nitrogen {Land 1970) and upwards to 2,800 g/m 2/yr compounds to ammonia (Capone and Taylor in Barbados (Patriquin 1972a). 1980; Smith et al. 1981b), primarily in the anoxic sediment which usually exists The high production of seagrasses can only a few millimeters beneath the sedi- aJfect the production oLinorganic partic- ment surface. The ammonia that is not ulates also. Cloud (1962} estimated that rapidly utilized will diffuse upward to 75% of aragonitic mud in a region of the the aerobic zone where it can either Barbados was due to direct precipitation escape to the water column or be converted of carbonate when the seagrasses had to nitrate by nitrifying bacteria in the removed CO2 from the water during periods presence of oxygen. Endobacteria were of extremely high primary productivity. found in the roots of the seagrass Zostera Zieman (1975b) also noted the ability marina {Smith et al. 1981a), and were of seagrasses under calm conditions to associated with nitrogen fixation (Smith 16 et al. 1981b). The amount of nitrate is 2. 7 OXYGEN usually lov1 or absent in sediments as it is either rapidly metabolized or converted Most seaarass meadows have sufficient to dinitrogen (N.;) via denitrifying bac- oxygen in the-water column for survival of teria. · the associated plants and animals. Often the shallow beds can be heard to hiss from Sulfur bacteria are primarily respon the escaping 0 2 bubbles in the late after sible for r1aintaining conditions necessary noon. Dense beds in shallow water with for the remineral ization of nutrients in restricted circulation can show extrenely the sedil:1ent. By reducing su1 fate to sul reduced 0,1 levels or even anoxia late at fide, these bacteria maintain the environ nioht on '"a slack tide. This can be a mental conditions (Eh and pH) at a level 9reater problei11 if there is a heavy load where the nitrogen mineralization proceeds of suspended oraanic sediment that would at a rate greater than its utilization by. al so consume oxygen. Generally the 1vind the microbial conmunity. This produces requ irect to <1encra te the turbu1 ence neces the available nutrient fractions. sary to susp.end large quantities of sedi- 11ent offsets this effect t:-y aerating the water. 2.6 CURRENT VELOCITY Lo~~ 0 2 levels can also slow plant Litt1 e work has been done to deter respiration; internal concentrations of O? rni ne the response of seagrass comr1un i ti es decrease rapidly and CO? increases. Respi: to different current velocities ( Fonseca ration then is limited by the ability of et al. in press a, b). Seagrass production oxygen to diffuse from the water. Plants, and bio111ass are strongly influenced by however, are 1 ess affected by 1 ow oxygen current velocity (Conover 1968). Roth levels than animals. Although Kikuchi turtle grass and Zostera showed 1:1aximur1 ( 1?80) recorded a marked decrease in oxy standins crops where current velocities gen in Japanese Zostera beds coincident averaged O. 5 m/ sec. 111 south Florida the ~Jith blade die-offand-fncreased microbial densest stands of turtle grass and manatee activity, iipparently it was not lethal. grass with hright, long leaves are observ Productivity studies in Puerto Pico (Odum ed in the tidal channels separating the et al. 1960), Florida and Texas (Odum and i:1anarove islands. Inferential evidence Wilson 1962) showed nighttime oxygen val sug~ests that the rapid currents break ues that were typically 4 to 7 rrig 02 /1; down diffusion qradients and make more CO? the 1owes t reported va 1 ue of 2 to 3 mg and inorganic nutrients available to the 0//1 occurred on a cal111, extremely low plants (Conover 1968). In a cruise of tide in August. the Alpha Helix to Nicaragua in 1977, sam ples taken from a mangrove-lined tidal channel shovied a 1eaf standing crop of 2. 8 SOLAR RI\DIATION 262 g dry weight (d~)/m and a total bio r:iass of 4,570 gdw/m'. By comparison, san When one considers the overridinq pl •:?s from a quiescent lagoon environP1ent i1nportance of solar energy as the 11ain were 185 and 1,033 g/m/ (McRoy, Zieman and forcing function on any ecosystel71, it is Ogden, personal crnrununication). amazing how infrequently va 1 ues are re ported in the scientific literature. His Where currents are strong and persis torically there has been a consensus (even tent, crescentic features knovm as blow without adequate measurement) that sea outs are often fori11ed. These are cusp grasses require high 1 ight intensity for shaped holes that actually nigrate through photosynthesis (Zieman and Wetzel 1980). 0rassbeds in the directions of the main This is based on the ohservation that ex ~urrent flow, eroding at one edge and col tensive seagrass beds are not found deeper onizing at the other. Their significance than 10 m (33 ft). These observations are is discussed in the section on succession. cor1pl icated by evidence that there is al so 17 indication of a limitation on productivity the leaf surfaces available for desicca due to hydrostatic pressure and not merely tion. Turtle grass grows in waters nearly 1 ight limitation {Gessner and flar1r:1er as shallow as that of shoal grass. The 1961). shallowest turtle grass flats are co~monly exposed on spring low tides, frequently The maximum depth at which seagrasses with much leaf mortality. Throughout the are found is definitely correlated with range of 1 to 10 m (3 to 33 ft), all of the available light regime, provided that the species r11ay be found, singly or mixed. suitable sediments are available. Off the Turtle grass is the unquestionable domi northwest coast of Cuba, 8uesa (1975) re nant in r1ost areas, however, frequently ported maximum depths for tropical sea forriing extensive meadows that stretch for grasses as follows: turtle grass, 14 m tens of kilometers. Although the absolute (46 ft); manatee grass, 16.5 m (54 ft); depth limit of the species is deeper, Halo~hilia decipiens, 24.3 m (80 ft); and mature meadows of turtle grass are not !!_. eng_l_emanni, 14.4 m (47 ft). As plant found below 10 to 12 ~ (33 to 39 ft). At species grow deeper, the quality and quan this depth manatee grass replaces turtle tity of light changes. In clear tropical grass and forms meadows down to 15 m (50 water such as that near St. Croix, Cuba, ft). Past the maxinum depth for manatee and portions of southern waters, the light grass development, shoal grass wi 11 often is relatively enriched in blue wavelengths occur, but it rarely develops extensively. with depth. By comparison, in highly tur Past the point at which the major species bid conditions as in shallow bays in Texas occur, fine carpets of Halophila extend and in Florida Bay, blue light is scat deeper than 40 m (130 ft). tered and the enrichment is in the direc tion of the green wavelengths. In both Numerous studies confirmed the pat cl ear and turbid waters the 1onger red tern described above, or some portion of wavele~gths are absorbed in the first few it. The relative abundance of four spe r:ie ters of the water col unn. cies of seaorasses off northwest Cuba, is graphed in ~Figure 8 (Ruesa 1974, 1975). Buesa (1975) studied the effects of Halophila decipiens was the least abundant specific wavelengths on photosynthesis of with a mean density of 0.14 g/m"-. ~alo.Q.:_ turtle grass and manatee grass in Cuba. hila enqelmanni showed a mean density of Me found that turtle grass responded best o.25 g/m2. Manatee grass was nearly 10 to the red portion of the spectrum ( 620 times denser than Halophila with an aver nanometers); the blue portion (400 nanol'le age density of 3.5 g/m 2 down to 16.5 ,~ (54 ters) was better for manatee grass. ft). Turtle grass was the most abundant seagrass, accounting for nearly 97.5% of the total seagrass biomass, with an aver 2. 9 ZONATION age of 190 ~/rn 2 down to its maximum depth of 14 r, (46 ft). This area is uniqoe in A1though seagrasses have been re that there is little or no shoal qrass corded fr01:1 as deep as 42 m (138 ft), ex which normally is eitrer the secon-d or tensive development of seagrass beds is third most abundant species in a region. confined to depths of 10 to 15 m (33 to 49 ft) or less. Principal factors determin In St. Croix, turtle grass had the ing seagrass distribution are 1 ight and shallowest range, occurring down to 12 m pressure at depth, and exposure at the (39 ft) on the west side of Buck Island sha1 low end of the gradient. A general (Wiginton and Md'illen 1979). Shoal grass pattern of seagrass distribution in clear and manatee grass showed progressively waters of south Florida and the Caribbean greater depth, occurring to 18 m (59 ft) was presented by Ferguson et aJ. {1980). and 20 ~ (65 ft), respectively, while Shoal grass usually grows in the shallow Halophila decipiens occurred to 42 m (138 est water and tolerates exposure better ft). All the species were found in less than other species. The relatively high than 1 m (3.3 ft) of water in St. Croix. flexibility of its leaves allows it to confonn to the damp sediment surface dur Because of the variety of rocky and ing periods of exposure, thus minimizing sedimentary patterns in the 1 agoons and 18 10 ----- E N 15---- .c. a. -Q) 0 20t----111t------"------~ 25 0 20 0 20 0 20 0 150 I I I I I I I I I -2 I _J I g m g m-2. gm-2. gm 30 Figure 8. Depth distribution of four seagrasses on the northwest coast of Cuba. 1 = Thalassia testudinum, 2 = S!ringodium filiforme, 3 = Halo~hila decipiens, 4 = H. ensel manni (from Busea 1975). A though Syringodium is quite a undant in certain localities, note the preponderance of Thalassia biomass and the absence of Halodule on the Cuban coast. bays of south Florida, the turbidity and exposure well. Exposed leaf surfaces will therefore the maximum depth for rooted lose water constantly until dry, and there plants can vary over short distances. is no constraint to water loss that would Phi 11 i ps ( 1960) recorded turtle grass limit drying (Gessner 1968). Although ranging from 10 to 13 m (33 to 43 ft) in exposure to the air definitely occurs at depth. In the relatively clear waters of certain low tides on shallow turtle grass the back reef areas behind the Florida or shoal grass flats, unless it is Keys, turtle grass is common to 6 or 7 m extremely brief, the exposed leaf surfaces (20 or 23 ft) and occurs down to 10 m (33 will be killed. ft); by contrast, in the relatively turbid portion of the "1 akes II of Florida Bay, maximum depths of only 2 m (7 ft) are Fol lowing exposure, the dead leaves common. are commonly lost from the plant. Rafts of dead seagrass leaves may be carried 2.10 EXPOSURE from the sh-allow flats fo11owing the spring low tides. Normally the rhizomes The seagrasses of south Florida are are not damaged and the plants continue to all subtida1 plants that do not tolerate produce new leaves. 19 CHAPTER 3 PRODUCTION ECOLOGY The densities of seagrasses can vary (1977) and Zierian and Wetzel (1980). Be widely; under optirium conditions they form cause these studies represent a variety of vast meadows. The literature is becoming habitats, different sampling times and extensive and often bewildering as density seasons, wide variation in sample repli values have been reported in many forms. cates (if any), as well as the diverse For consistency, the terms used here con reasons for which the investigators col form to those of Zieman and 1-letzel lected the sa111pl es, it becomes difficult (1980): standing crop refers to above to draw meaningful patterns frOPJ these ground (above-sediment) material, whereas published results. biomass refers to the weight of all living p1 ant material, including roots and rhi ~lhile the standing crop of leaves is zomes. 80th quantities should be expressed significant, the majority of the biomass in terms of mass per unit area. These of seagrasses is in the sediments, especi measurements both have valid uses, but it ally for the larger species. Although the is sometimes difficult to determine which relative amounts vary, turtle grass typi an author is referring to, because of in ca1 ly has about 15% to 22% of its biomass cornp1ete or imprecise descriptions. His in emergent leaves and the rest below the torically. standing crop has been the pri sediment surface as roots and rhi zo111es. mary measure of comparison because of the The published ranges for turtle grass, relative ease of sampling compared with however, vary from 10% to 45% for leaf the laborious methods needed to col 1ect biomass (Zieman 1975b). In central Bis and then sort belowground material. cayne Bay, Jones (1968) found a relatively consistent ratio of 3:2:2 for leaves and short shoots: rhizomes: roots. Studies 3.1 BIOMASS with turtle grass and Zostera have indi cated that the ratio of leaves to roots Seagrass biomass varies widely de increased with a shift in substrate froir pending on the species involved and the course sand substrates to fine muds (Ken local conditions. The biomass of the spe worthy 1981). This can be interpreted to cies HaloQhila is always sma1 l, whereas indicate either the positive effect of the turtle grass Fias been recorded at densi richer fine muds on more robust plant de ties exceeding 8 kg dry weight/m? (13auers velopment, or the need for a better devel fe1d et al. 1969). Representative ranges oped nutrient absorptive (root) network in of seagrass biomass tn south Florida am:! the coarser sedir,1ents that tend to be 1ow in neighboring regions are given for com er in nutrients and organic matter. Thus, parison in Table 3. Because of the ex substrate may be an important variable treme variations found in nature and re when determining pheno1ogica1 indices. flected in the 1 iterature, one must be careful not t,:) place too much value on a Structurally, turtle grass has the few measurements. Many of these studies most well-developed root and rhizmne sys have been summarized hy McRoy and McMi nan tem of all the local seagrasses. Table 4 20 2 Table 3. Representative seagrass biomass (g dry wt/m ). Species Location Range Mean Source Halodule wriqhtii Florida 10-300 50-250 Zieman, unpubl. data Texas 10-250 90 McMahan1968; McRoy1974 Morth Carolina 22-208 Kenworthy 1981 Sxringodium filifor~e Florida 15-1,100 100-300 Zieman, unpubl. data Texas 30-70 45 McMahan1968 ,_.N Thalassia testudinum Cuha 30-500 350 Buesa 1972, 1974; Buesa and Olaechea 1970 Florida Odum1963; Jones (east coast) 20-1,800 125-800 1968; Zieman 1975b Florida Bauersfeld et al. (west coast) 75-8,100 500-3,100 1969; Phillips 1960; Taylor et al. 1973 Puerto Rico 60-560 80-450 Burkholder et al. 1959; t"argalef and Rivero 1958 Texas 60-250 150 Odum1963; McRoy1974 lists conparative biomass values frrnn sev Three hasic ~ethods have been used to eral stations in Pine Chann~l in the Flor study seagrass productivity: ,,,arking, ida Keys where the three 1:1ajor species co l 11 c, and O; production. (See Zieman and exist. Shoal grass and manatee grass have ~letzel 1~1HO for a recent review of produc less well-developed root and rhizo1:1e sys tivity measure1nent techniques.) tems and consequently wi 11 generally have much more of their total biomass in leaves Many assui:1ptions are made when using than does turtle grass. Samples for these the oxygen production method, and al 1 can two species where the 1ea f cornponen t is lead to large and variable errors, pri SQl to 60% of total weight are not uncor,i marily because 1 eaves of aquatic vascular rion. Maximur1 values for the species al so plants can store gases produced during vary widely, Biomass 1•1e;1sure1~EH1ts for photosynthesis for an indefinite period. riense stands of shoal grass are typically The largest potentia1 error, however, is severa 1 hundred grams per square meter; related to the storage of metabolically manatee grass reaches 11aximur•1 development produced oxygen. To use the oxygen produc at 1,200 to 1.500 9/m/. while maxiF11.1,11 val tion technique, nne assufl'1es that oxyqen ues for turtl 22 Table 4. Comparison of biomass distribution for three species of sea9rasses from Pine Channel, June 1980 (Zieman et al. in preparation). MRindicates stations frofl1 the central portion of thli embayment, \1/hile N is from a station at the northern end of the channel. Species Component }'P, 2 ~8 3 N 1 2 2 2 OI 9/ri "'h g/m h g/m la Thalassia Leaves 206 11 58 15 267 10 Roots and rhizomes 1,669 89 321 85 2,346 90 Total biomass 1,875 379 2,613 24 2P 4.7 Syrinqodium Leaves 58 102 IC ..,, Roots and rhizomes 182 76 521 84 .) i 53 Total biomass 240 623 59 Nw Halodule Leaves 54 21 15 11 5 33 Roots and rhizomes 200 79 120 89 10 67 Total bior1ass 254 135 15 A11 species Total biomass 2,369 1,137 2,687 f Table R,epresentative seagrass ties. ics Location Productivity Source {g c1/1aay) Ha1odu1e wri.9.hti i North Carolina 0.5- 2.0 Dillon 1971 ~ri ns:o~ fi 1 i forme Florida 0.8- 3.0 Zieman, unpubl. data Texas 0.6- 9.0 OduMand Hoskin 1958; McRoy1974 Thalassia testudinum Florida 0.9-16.0 Odum1957, 1963; Jones (east coast) 1968; Zieman 1975h Cuba 0.6- 7.2 Buesa 1972, 1974 Puerto Rico 2.5- 4.5 Odum al. 1960 N et .;:.. Janaica 1.9- 3.0 Greenway 1974 Rarhados 0.5- 3.0 Patriquin 1972h, 1973 Net production measurements for most aboveground production quite accurately. seagrasses can be obtained by marking It underestimates net productivity as it blades and measuring their growth over does not account for be 1 owground produc time (Zieman 1974, 1975b). With this t ion, excreted carbon, or herbivory. Mod method, the blades in a quadrat are marked ifications of the marking method for at their base, allowed to grow for several Zostera marina have been used to estimate weeks, and then harvested. As seagrass root and rhizome production ( Sand-Jensen leaves have basal growth, the increment 1975; Jacobs 1979; Kenworthy 1981) and added below the marking plus the newly could be adopted for tropical seagrasses. emergent 1eaves represent the net above The generalization that emerges from these ground production. After collection, the various diverse studies is that seaqrass 1 eaves of most tropical species must be systems are highly productive, no matter gently acidified to remove adhered carbon what method is used for measurement, and ates before drying and weighing. under optimum growth conditions production can be enormous. Bittaker and Iverson (1976) critical ly compared the marking method with the measurement of productivity by radioactive 3.4 NUTRIENT SUPPLY carbon uptake. ~Jhen the 111 C method was corrected for inorganic losses (13'.l.!',), Seagrasses along with the rhizophytic incubation chamber light energy absorption green algae are unique in the marine envi (14%), and difference in light energy re ronment because they inhabit both the 1>1a sulting from experimental design (8%), the ter column and the sediments. There was differences in productivity were insignif previously much controversy whether the icant. These results reinforce the concept seagrasses took up nutrients through their that the l C method measures a rate near roots or their leaves. McRoy and Barsdate net productivity. In a study of turt"le (1970) showed that Zostera was capable of grass productivity near Bimini, however, absorbing nutrients either with the leaves Capone et al. {1979) found that the 1 1,c or roots. McRoy and Barsdate found that measurements yielded values nearly double Zostera could tal Species Collection value Collection site Thalassia testudinurn -10.4 4.2 -C.3 to -11.C Texas (Parker 1Q64; Calder 1969; Smith and Epstein 1971; Benedict and Scott 1976; Fry 1977} -9 .9 to -10.0 St. Croix, ti.s. Virgin Islands (Fry 1077) -10.9 Veracruz, Mexico -12.5 Long Key, Florida {Craig 1953) N 00 Halodule wrightii -10.8 4.8 -8.5 to -12.3 Texas (Parker 1964; Calder 1969; Smith and Epstein 1971; Fry 1977) -9.5 Freetown, Sierra Leone -lC.5 Gibbitt Island, Bermuda -13.3 La Pesca, Tamaulipas, Mexico Syringodium filiforme -5.0 6.5 -3.0 to -9.5 Texas (Parker and Calder 1970; Smith and Epstein 1971; Fry 1977) -4.0 -5.l St. Croix, U.S. Virgin Isalnds (Fry 1977) Ha1.£e!!.& decipiens -10.2 4.7 - 7. 7 to -12. 4 St. Croix, U.S. Virgin Islands Halophfla engelmanni -12.6 2.9 -11. 1 to -14. O Texas (Calder 1969; Fry 1977) Hal~ila johnsonii -9.8 Ft. Pierce, Florida Currently the main limitations of the epiphytes (Dawes et al. 1979) to 29.7% for carbon isotope method are equipment and leaves washed in distilled water (Walsh interpretation. It requires use of a mass and Grow 1972), although numbers typically spectrometer which is extremely costly, fall in the range of 10% to 15% of dry although today a number of 1abs wi 11 pro weight. Protein values may be suspect if cess samples for a reasonable fee. The not measured directly, but calculated by interpretation can become difficult when extrapo 1 a ting from percent nitrogen. In an organism has a o13C value in the middle grass beds north of Tampa Bay, Dawes and ranges. If the o1 3C value is at one ex Lawrence (1980) found that protein levels treme or another, then interpretation is of turtle grass and manatee grass 1eaves straightforward. However, a mid-range varied seasonally, ranging from 8% to 22% value can mean that the animal is feeding and 8% to 13%, respectively, with the on a source that has this o13C value or higher levels occurring in the summer and that it is using a mixed food source which fall. The protein content of shoal grass averages to this value. Recent studies ranged from a low of 14% in the fall up to utilizing both isotopes of carbon and sul 19% in the winter and summer. Tropical fur (Fry and Parker 1982) and nitrogen seagrasses, particularly turtle grass, (Macko 1981) show much promise in deter have been compared to other plants as mining the origin of detrital material as sources of nutrition. The protein content well as the organic matter of higher of turtle grass leaves roughly equaled organisms. Knowledge of the feeding ecol that of phytoplankton and Bermuda grass ogy and natural history of the organism is (Burkholder et al. 1959) and was two to needed, as is an alternate indicator. three times higher than 10 species of tropical forage grasses (Vicente et al. 1978). ~lalsh and Grow (1972) compared 3.6 PLANT CONSTITUENTS turtle grass to grain crops, citing stud ies in which 114 varieties of corn con Recognition of the high productivity tained 9.8% to 16% protein; grain sorghum of seagrasses and the relatively low level contained between 8.6% and 16.5%; and of direct grazing has led to questions wheat was lowest at 8.3% to 12%. Although regarding their value as food sources. several studies have included measurements Proximate analyses of seagrasses in south of carbohydrates (Table 7), it is imprac Florida, particularly turtle grass, have tical to compare much of the data because been performed by many authors (Burkholder various analytical methods were employed. et al. 1959; Bauersfeld et al. 1969; Walsh and Grow 1972; Lowe and Lawrence 1976; Studies using neutral detergent fiber Vicente et al. 1978; Bjorndal 1980; Dawes (NDF) analyses found that cell wall carbo and Lawrence 1980); their results are hydrates (cellulose, hemicellulose, and summarized in Table 7. As noted by Dawes l ignin) made up about 45% to 60% of the and Lawrence (1980), differences in the total dry weight of turtle grass 1eaves preparation and analysis of samples, as (Vicente et al. 1978; Bjorndal 1980). v1ell as low nuribers of sariples used in Dawes and Lav>1rence (1980) reported that some studies, make data comparison dif insoluble carbohydrate content in the ficult. leaves of turtle grass, manatee grass, and shoal grass was 34% to 46%. The rhizo~es The reported ash content of turtle of seagrasses are generally higher in grass leaves ranges from 45% dry weight carbohydrates than are the leaves. Dawes for unwashed samples down to around 25% and Lawrence (1980) found that soluble for samples washed with fresh water. carbohydrates in turtle grass and manatee Leaves washed in seawater contained 29% arass rhizomes varied seasonally, indicat +/- 3.5% to 44% +/- 6. 7% ash (Da1•Jes and ing the production and storage of starch Lav1rence 1980). in summer and fa 11 . These authors, how ever, were working in an area north of Values for the protein content of Tampa Bay, where such seasonal changes leaves vary from a low of 3% of dry weight would be more pronounced than in the for unwashed turtle grass leaves with southern part of Florida and the Keys. 29 Table 7. Constituents of seagrasses. Species Component Season/ %/Ref Ash Nitrogen Protein Fat Carbohydrates Ener9y Reference date (kcal/g} Thalassia Leav1es February %OW 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 \t/alsh and mean %OW 24. 5 (10.3-29. 7) Grow 1972 January %OW 29 t' 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 w 0 October 44 13 2.0 41 2. 6 Mean 36 D TT 45 2.8 ? %0\ol 47.3 11.0 0.7 38 Bauersfeld (unwashed). et al.1969 % DW 24.8 13.0 0.5 35.6 (washed) July - %D~! 24.7 9.1 2.3 63.9 Lowe and August Lawrence 1976 January- %DH Hi. 7 Rjorndal August 1980 17 Vicente et al. 1978 (continued) Table 7. Continued. Species Cor1ponent Season/ %Ref .~sh Protein Fat Carbohydrates Energy Reference date (kcal/a) Thalassia Rhizorie P,nnual row 23.8 S.8-12.2 Ll.83 t,Jalsh and mean %AFDi,J 11. 0 72.1 Gro~, 1°72 Roots %OW 50.5 19.6 Bauersfeld 24.1 15.0 et al .1969 Photo syn. January J~D\4 39 9 1.0 51 2.7 nawes and inactive part April 51 7 0.5 42 2.2 Lawrence ') ~ of short shoot July 4.p 16 0.7 35 I_• ..J 1980 October 56 u0 0.8 35 2.0 i1ean 49 To 0.2 41 2.4 ,_.w Rhizomes January %DH 26 9 o.s 65 3.2 April 24 8 1. 6 66 3.4 July 33 16 0.2 51 3.0 October 36 7 l.1 56 2.8 nean 30 10 0.9 b() TI S)'.ri ngod i UJ1l Leaves July- %OW 27.0 3.10 "•'? LI 66.3 Lmve and August Lawrence 1976 Leaves January %01,/ 30 9 1. 7 59 3.1 Dawes and Apri 1 28 8 6.2 58 2.4 La\1/rence July 33 13 4.0 50 3.2 1980 October 32 13 1.8 53 3.1 Mean 31 IT 3.4 55 3.0 Short shoots- January %!)\,./ 28 10 1. 3 61 3.2 photosyn. 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 32 12 1. 7 55" TT (continued) Ta~1e • Concluded. Species CDrip.ooent Season/ 'I/Ref /lsh Protein Fat Carbohydrates Energy Reference date (kcal/g) ___...... ,._._" Syri ng~U,JM R:-'!izo~es January %':M 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 H! 8 1.6 73 3.6 :%,DW 32 48 _,_Ha1oduie ....,..,..,-~ Leaves January 19 1.0 3.1 Oav1esand -:; ') April 25 18 ,..J,.L 54 3.5 Lawrence July 25 19 l. 2 55 3.3 1980 Octoher 26 14 1.4 59 3.3 r'ean 27 18 54 w TT 3.3 N Shcrt shoots- January %0tJ 25 5 1.1 69 3.2 photosyn. inactive April 2S 9 3.5 59 3.0 part July 36 8 0.8 55 2.9 October 34 9 l. 2 56 2.9 r-iean 3T 8 1. 7 60 3.0 Rhi.zomes January %Dt! 14 9 o. 7 76 3. 7 April 17 7 1.6 74 3.7 July 22 8 O. l 70 3.4 October 17 8 1.1 74 3.6 Mean 18 7i 0.9 74 TI CHAPTER 4 THE SEAGRASS SYSTE~1 4.1 FUNCTIONS OF SEAGRASS ECOSYSTEMS general pathways: direct grazing of organisr.1s on the living plant mate In addition to being high in net pri rial or utilization of detritus from mary production and contributing large decaying seagrass material, prinarily quantities of detritus to an ecosystem, leaves. The export of seagrass mate seagrasses perform other functions. Re rial, both living and detrital, to a cause of their roots and rhizomes, they 1oca ti on some distance from the sea can modify their physical environment to grass bed allows for further distri an extent not equaled by any other fully bution of energy away from its orig submerged organism. Phillips {1978) stated inal source. that, "by their presence on a 1andscape of relatively uni form relief, seagrasses (3) Shelter create a diversity of habitats and sub strates, providing a structured habitat Seagrass beds serve as a nursery fran a structureless one." Thus seaarasses ground, that is a place of both food also function to enhance environ~ental and shelter, for the juveniles of a stability and provide shelter. variety of finfish and shellfish of commercial and sportfishing impor Seagrass ecosystems have numerous im tance. portant functions in the nearshore marine environment. Wood et al. (1969) originally (4) Habitat stabilization classified the functions of the seagrass '?cosystem. The follov1ing is an updated Seaqrasses stabilize the secti11ents in version of the earlier classification two'ways: the leaves slow and retard scheme. current fl ow to reduce water velocity near the sediment-water interface, a (1) High production and growth process v1hich proriotes sectfr1entation of particles as 1-1el1 as inhibiting The ability of seagrasses to exert a resuspension of both organic and najor influence on the marine seacape inoraanic material. The roots and is due in large part to their ex rhizomes fom a complex, interlocking tremely rapid growth and high net matrix with which to bond the sedi productivity. The leaves grow at ment and retard erosion. rates typically 5 mm/day, but growth rates M ever 10 f';W;l/day are n0t {S) Nutrient effects unco111i:1on under favorable circum stances. The production of detritus and the promotion of sedimentation hy the (2) Food and feeding pathways 1eaves of seagrasses provide organic natter for the sedinents and maintain The photosynthetically fixed energy an active envirorn11cnt for nutrient from the seagrasses nay fo1101-1 tv✓O recyclin9. Epiphytic algae on the 33 leaves of seagrasses have been shown is a 1so the key to restoring damaged or to fix nitrogen, thus adding to the denuded sys ter1s. nutrient pool of the region. In add ition, seagrasses have been shown to pick up nutrients froM the sediments, 4.3 SPECIES SUCCESSION transporting them through the pl ant aod rel easing the nutrients into the Throughout the south Florida re!Jion, water column through the leaves, thus and most of the Gulf of Mexico and Carib acting as a nutrient punp fror11 the bean, the species of plants that partici sedfrient. pate in the successional sequence of sea grasses are remarkably few because there are so few marine plants that can colonize 4. 2 SUCCESS ION AND ECOSYSHM DEVELOPMENT unconsolidated sediments. In addition to the seagrasses, one other group, the rhi In conventional usage, succession zophytic green algae, has this capability. referf, to the orderly development of a These algae, however, have only limited series of com1:mnities, or seral stages. rhizoidal development and never affect an which result in a c1 imax stage that is in area greater than a few centimeters from t:quil ibrium with the prevailing environ their base. mental conditions. In inore contemporary usage. t1owt?ver. succession is more br()adl y The 1:iost conmon illustration of suc used tt1 ,11ean the succession of species. cession in seagrass systems is the recolo structure, and functions within an ecosys nization following a "blowout." This loc t;1}tl, Odum (1969) stated the contemporary alized disturbance occurs in seagrass beds concept as fo11ows: throughout Florida and the Caribbean where there is sufficient current movement in a (1) Succession is an orderly process dominant direction (Figure 9). Usually a of community d€we1opment th,,t in disruption, such as a major storm, over volves changes in species structure grazing caused by an outbreak of urchins, and comrlllnity processes with time; it or a major ripping of the beds caused by ts reasonable, directional, and dragging a 1arge anchor, is required to therefore predictable. initiate the blowout. Once started, the holes are enlarged by the strong water (2} Succession results from 1•1odifi• flow which causes erosion on the down cur cotfo11 of th(• physical environment tiy rent side. Slowly a crescentic shape a the corw,1mity; that is, succession is fow meters 1vide to tens of rieters wide is conuunl ty~contro11 ed even thouqh the fanned. A sample cross section in Figure physical environment determines the 10 shows a riature turtle grass cor1rnunity puttern and the role of chaMt~, and that has been disrupted and is recovering. often sets linlts as to h~w far The reg ion at the hase of the erosion c1ev(' lopment Ci:H1 90. scarp is highly agitated and contains large chunks of consolidated sediment and (3) Succession culminates in a sta occasional rhizome fragr.ients. With in h11lzed ecosystem in which maximum creasinq distance from the face of the hion IDEALIZED SEQUENCE THROUGH A SEAGRASS BLOWOUT 5cm PENl~l~LUS HMIM(QA ~ Dominanl Wofer Flow --~ R:~::IVS::~:!A_ss_ _,[J.,.__ __...,,8----~--~. __ _ .. 1 Below Sediment 2 Cl, 10 GMtM Halimeda Penicillus Figure 10. Idea 1 ized sequence through a Figure 11. Re pres en tat i ve ca 1 careous seagrass blowout. Note erosion and recov- green algae from seagrass beds. Note the ery zones moving into the dominant water binding action of the rhizoids in forming flow. small consolidated sediment ba11 s. 35 composition of marine sediments in south The pioneer species of the Caribbean Florida as taken from Ginsburg (1956) are seagrasses is shoal grass, which colonizes illustrated in Figure 12. Behind the reef readily either from seed or rapid vegeta tract over 40% of the sediment was gener tive branching. The carpet laid by shoal ated from calcareous algae. Penicillus grass further stabilizes the sediment sur capitatus produced about 6 crops per year face. The leaves fonn a better buffer in Florida Bay and 9. 6 crops per year on than the algal communities and protect the the inner reef tract (Stockman et al. integrity of the sediment surface. In 1976}. Based on the standing crops, this some sequences manatee grass will appear would produce 3.2 g/m 2 /yr on the reef next, intennixed with shoal grass at one tract which could account for one-third edge of its distribution and with turtle of the sediment produced in Florida Bay grass at the other. Manatee grass, the and nearly all of the back-reef sedi least constant member of this sequence, ment. Similarly, Neuman and Land (1975) is frequently absent, however. estimated that Halimeda incrassata pro duced enough carbonate to supply a 11 the Manatee grass appears more commonly sediment in the Bight of Abaco in the in this developmental sequence in the Car Bahamas. ibbean islands and in the lower Florida SE REEF TRACT FLORIDA BAY NW Back Reef w z LL.Q WI W Cl) cr::w ~ W- z ..J w <..>o 0(!) I- et: ~<{ W..J ..J a..>- w ::t:: Figure 12. Origin of sedimentary particles in south Florida marine waters (modified from Ginsberg 1956). 36 Keys waters. Where the continental influ restabi1 ized within 5 to 15 years (Patri ence increases the organic matter in the quin 1975). During the study of Patriquin sediments, manatee grass appears to occur (1975) the average rate of erosion of the less commonly. Lower organic matter in blowout was 3. 7 mm/day, while the rate of Caribbean sediments, due to the lack of colonization of the middle of the recovery continental effect, may slow the develop slope by manatee grass was 5 mm/day. Once mental process. recolonization of the rubble layer began, average sediment accretion averaged 3.9 As successional development proceeds mm/yr. in a blowout, turtle grass will begin to colonize the region. Because of stronger, With the colonization of turtle strap-like leaves and massive rhizome and grass, the normal al gal epiphyte and root system of turtle grass, particles are faunal associates begin to increase in trapped and retained in the sediments with abundance and diversity. Patriquin (1975) much greater efficiency and the organic noted that the most important effect of matter of the sediment will increase. The the instability caused by the blowouts is sediment height rises (or conversely the to "limit the sera1 development of the water depth above the sediment decreases) community. The change in the region of until the rate of deposition and erosion the blowouts of a well-developed epifauna of sediment particles is in balance. This and flora, which is characteristic of process is a function of the intensity of advanced stages of seral development of wave action, the current velocity, and the the seagrass community, is evidence of density of leaves. this phenomenon." The time required for this recovery In areas that are subject to contin will vary depending on, among other fac ued or repeated disturbances, the succes tors, the size of the disturbance and the sional development may be arrested at any intensity of the waves and currents in point along the developmental gradient the region. In Barbados, blowouts were (Figure 13). Many stands of manatee grass SOLID =====8> EPILITHIC ===::::;C> CORALLINE ALGAE SUBSTRATE ALGAE t!AL.JM.f.M ~ I HALAS SIA S,XRINGODIUM SANDY SUBSTRATE RHIZOPHYTIC / ALGAE ===::::::C> t:LA~QDUL~ =::::;::::::;::----- MUDDY SUBSTRATE ECOSYSTEM DEVELOPMENT Stable Environmental Conditions ~------Oistur bance Figure 13. Ecosystem development patterns in south Florida marine waters. This is a generalized pattern, and a11 stages may not _be p~esent. Note that in the absence of disturbance that the tendency is to a Thalass1a climax. 37 are present because of its ability to tol organisr.is with their widely differin~1 erate aerobic, unstable sediments and to requirements and interactions functioned rapidly extend its rhizo1qe systetn under as a highly intricate weh structure that these conditions. This is especially evi made each individual or each link less dent in back-reef areas. Patriquin (1975) necessary to the maintenance of the total at tributes the persistence of c1ana tee system. There was much natural redundance grass in areas around Barbados to recur built into the system. For certain seg rent erosion in areas where the bottom was ments of the comr11 unity this may be true. never stable for a sufficiently 1ong time The problem is that at climax there is one to allow turtle grass to colonize. Mana species for vihich there is no redundancy : tee grass can have half of its biomass as the seagrass. Irt some cases. if the sea leaves (Table 4). Thus, while manatee grass disappears, the entire associated grass is colonizing aerobic disturbed sed conmunity disappears along with it; there iments, which would he areas of low nutri is no other organisr1 that can sustain and ent supply and regeneration, the amount of support the syste11. its root surface available for nutrient uptake would be reduced, and correspond This is shown in a srr1al1 way when i ng1y leaf uptake would become a major mi nor disturbances occur as was described source of nutrients. If this is the case, with the blowouts. As the crass beds in the higher agitation of the water column these areas are eroded away, the entire \,mu1 d be of benefit tiy reducing the grad seagrass system disappears, including the ients at the leaf surface. top 1 or 2 in of sediment. These features are small and readily repaired, but give an indication of what could happen if 4. 4 THE CENTRAL POSITION OF THE SEA- there was widespread damage to the sea GRASSES TO THE SEAGRASS ECOSYSTEM grasses. Seagrasses are vital to the coastal The largest contribution to the di ecosystem because they fonn the basis of a versity of the syste1:1 is comnonly made by three~dimensiona1, structurally co111pl ex the coi'1plex communities that are epiphytic habitat, In modern ecology there has h,}en on the seagrass leaves. \·!hen defoliation a shift from the autoecolo9ical approach of the seagrasses occurs, 111ost of this of studying individual species independ community disappears. either by bei n9 car ently, to the community or ecosystem ap ried out as drifting leaves or becoming proach where the focus is the 1a rqer i nte part of the 1 itter layer and ultimately grated entity. With that realization, one the surface sediments. With the 1eaves cou 1d wonder. "Why spend so nuch effort on gone, the current baffling effect is lost ,, few species of marine plants, even if and the sediment surface begins to erode. they are the most abundant, in a sys te1:1 Al9al mats that may fonn, have minimal that has thousands of other species?" The stabilizing ability; however, the dead reason is that these plants are critical rhizor:ies and 1:1ats will continue to bond to most other species of the systeP1, both the sediments, in some cases for several plant and animal. There are few other years (Patriquin 1975; Scoffin 1970). syste1:1s which are so dominated and con trolled by a single species as in the case In south Florida the disappearance of of a cl irnax turtle grass or Zostera mea seagrasses would yield a far different dow. H. T. Odum (1974) classified-turtle seascape. Much of the region would be grass beds as 11 natural tropical ecosystems shifting mud and mud banks, while in r1any with high diversity. 11 Taken as a total areas the sediments would be eroded to system, tropical seagrass beds are regions bedrock. Based on the communities found of very igh diversity, but this can be in such areas today, primary production misleading. Comparisons between tropical and detrital production would be dramati and temperate systems were made at a time cally decreased to the point that the when high diversity was equated with hiqh support base for the abundant co1m:1ercial biological stability. The prevailing con fisheries and sport fisheries wou1 d shri nr. cept was that the mu1 titude of different if not disappear. 38 4.5 STRUCTURAL AND PROCESS SUCCESSION IN stages are often characterized by a low SEAGRASSES supply of organic matter in the sediment and open nutrient supply; that is, the As species succession occurs in a community relies on nutrients being shallow marine system, important struc brought in from adjacent areas by water tural changes occur. Because seagrass movement as opposed to in situ regenera systems do not have woody structural com tion. With the development from rhizophy ponents and only possess relatively simp- tic algae to turtle grass, there is a pro 1is tic canopy structure, the main s truc gressive development in the helowground tura l features are the leaf area and bio biomass of the community as well as the mass of the leaves as well as the root and portion exposed in the water column. With rhizome material in the sediment. The the progressive increase in leaf area of most obvious change with community devel the plants, the sediment trapping and par opment is the increase in leaf area. This ticle retention increase. This material provides an increase in surface area for adds orqanic riatter to further fuel the the colonization of epiphytic algae and sedimentary microbial cycles. Although fauna, with the surface area of the climax various segments of this successiona1 community being many times that of either sequence have been measured by numerous the pioneer seagrass, shoal grass, or the authors, the most complete set of data has initial algal colonizers. In addition to recently been cornpil ed by \Ji1 l i ams ( 1981) providing a substrate, the increasing leaf in St. Croix (Table 8). In St. Croix, area also increases the current baffling where the data were co 11 ected, as on many and sediment-trapping effects, thus en low, small islands with little rainfall, hancing internal nitrogen cycling. the cl iriax is cor1111only a mixture of turtle grass and manatee grass. In south Florida, As organisms grow and reproduce in with its higher rainfall and runoff, the the environment, they bring about changes climax more commonly is a pure turtle in their surroundings. In doing so these grass stand. In turtle grass beds in organisms frequently riodify the environ south Florida, Capone and Taylor (1977, ment in a way that no longer favors their 1980) found that nitrification was highest continual orowth. McArthur and Connell on the developing periphery of the beds (1%6) stated that this process "gives us and lower in the centers where particulate a clue to all of the true replacements of trapping and retention were greater. Add succession: each species alters the envi itionally, mature ecosystems, both marine ronment in such a way that it can no and terrestrial, seem to be based primar 11 1onger grow so successfully as others • ily on the ctetrital food weh which aids in conserving both cnrhon and nitrogen, as In a shallow ,vater successional se direct grazing is quantitatively low in quence leading to turtle grass, the early these systems. 39 Teble n. of ters of seagrass succession frOJ'i Tague Bay Lagoon, St. Croix, lJ. S. I. fod ica tes no data; ues shown are averages. Paraf'let1;rs Bare Rhi zoptiyt ic Colonizing !mature Thalassia sediments a 1ga1 seagrass seagrass seagrass C~tmity bed hed climax ') No. p1ants/~'· C 254 981 3,089 1,533 3io:riass ,, '-" 185 89 1,244 2,241 ( g dry wt/t~L I No. Thal~ssia: No. Syri 'l2_~_fom: Mo. ----·----Halodule 0:0:D 0:0:0 1:17:33 1:2:2 1:1:0 ,.,,,. 0 NH 304 6-200 Interstitial 4 ri. 0 1.0 3-39 ~:·1icror1oles N) NH 2.50 3.fl5 12.82 Adsorbed 4 - 0.63 {Micror,ole 14/g dry sedii1ent} Tnalassia blade length - - 14.08 16.25 22.37 (cr:1) ~-Thalassia blade width - - 8.33 10.17 10.87 Sediment deposit ion 240 - 2,168 - 2, q41 {g dry wt/ri/day) '.:letri tal seaqrass - - 25.21 - 252.10 (g dry wt/ni/'neek) CHAPTER 5 THE SEAGRASS COMMUNITY - COMPONENTS, STRUCTURE, AND FUNCTION Seagrass-associated communities are The term epiphytic organisms is used determined by species composition and den here the sane as that of Harlin (1980) and sity of seagrass present, as well as abi means any organism growing on a plant and otic variables. These communities ranae not just a plant living on a plant. Epi from monospecific turtle grass beds in the benthic organisms are those organisms that cl ear, deep waters behind the reef tract live on the surface of the sediment; in to the shall ow, muddy bottoms of upper its broadest sense, this includes inotile Florida Bay where varying densities of organisms such as large gastropods and sea shoal grass are intermixed with patches of urchins, as we 11 as sess i1 e forms such as turtle grass. sponges and sea anemones or macro a1 gae. Infaunal organisms are those organisms Turney and Perkins ( 1972) divided that live buried in the sediments. Organ Florida Bay into four regions based large isms such as penaeid shrimp, however, that ly on temperature, salinity, circulation, lie buried part of the day or night in the and substrate characteristics. Each of sediments, but are actively moving on the these regions proved to have a distinctive sediment surface the rest of the time molluscan assemblage. would not be included as part of the infauna. The infauna would include orqan Studies have also shovm that great isms such as the relatively immobile diversity in species number and abundance sedentary polychaetes and the relatively exists even within communities of similar mobile irregular urchins. Nektonic organ seagrass composition and density, and isms, the highly riobile organisms living within comparatively small geographical in or above the plant canopy, are largely regions. Brook (1978} compared the macro fishes and squids. faunal abundance in five turtle grass con muni ties in south Florida, where the blade Kikuchi {1961, 1962, 1966, 1980) density was greater than 3,000 blades/m 2• originally proposed a functional classi Total taxa represented varied from a low fication scheme for the utilization of of 38 to a high of 80, and average abun Japanese seagrass beds by fauna that has dance of individuals varied from 292 to wide utility. This classification, mod- 10,644 individuals/m 2• ified for tropical organisms, would include (1) perrianent residents, (2) The biota present in the seagrass seasonal residents, ( 3) temporal mi grants, ecosystem can be classified in a scheme (4) transients, and (5) casual visitors. that recognizes the central role of the The third category is added here to seagrass canopy in the organization of the include the organisms that daily migrate system. The principal grou)s are (1) epi between seagrass beds and coral reefs. phytic organisms, (2 epibenthic These were not inc 1uded in the original organisms, (3) infaunal organisms, and {4) classification which was based on tem the nektonic organisms. perate fauna. 41 their h,Jldfast. Pri1nary substrate for algae will include (1) the sediments, (2) Major so1Arces of primary product ion the seagrasses ther~selves, ;ind (3) occa for coastal and estuarine areas are the sional ~ocks or outcrops. In addition fo11 ovd ng: many macroalgae in south Florida form large unattached masses on the sea botton, (1) ~1acrophytes ( seagrasses, rian- collectively known as drift algae. groves, macroalgae, and marsh grasses) Althouoh much of south Florida offers sufficient "hard substrate for alqa1 at {2) Benthic microalgae (benthic and tach111ent, notably the reef tracts and the epiphytic diato~s. dinoflagel- shallow zones bordering r~any of the keys, 1ates. fil arientous qreen and the dominant subs tra tc type is not solid. bluegreen algae) · In many areas mangrove prop roots, oyster base'>, and scattered rocks or shells and (3) Phytoplanktun to man~ade structures such as bridge sup ports and canal ~Jal ls offer the primary algal substrates. Al though in deep, turbid northern estuaries, such as the Chesapeake or Dela The only algae able to consistently \vare Says. phytoplankton may be the domi use sediments as substrate are (1) the nant producer. in most areas that have mat-fon11ing algae and (2) fl1embers of the b(ien investigated the macrophytes are the order Siphonales (Chlorophyta) which 1nost imp 42 Figure 14. Calcareous algae(~ sp.) from the fringes of a seagrass bed. 43 of Rhieocephalus, Udotea, and Acetabularia emerge, the study of epiphytes has suf produced at 1east as much mud as Penicit fered from what Harlin (1980} described as lus in the same locations. the "bits and pieces" approach. In the Bight of Abaco, Neumann and An annotated 1 i st of 113 species of Land (1975) calculated that the growth of algae found epiphytic on turtle grass in Penici11us, Rhi2ocefihalus, and Halimeda south Florida was compiled by Hur,im (1964}. produced 1. 5 to3 t mes the ariount of mua Of these only a few were specific to sea and Halimeda sand now in the bas in and grasses; most were also found on other that fo a typical Bahamian Bank lagoon, plants or solid substrate. Later, Ballan calcareous green algae alone produced more tine and Humm (1975) reported 66 species sediment than could be accommodated. Bach of benthic algae which were epiphytic on {1979) measured the rates of organic and the seagrasses of the west coast of Flor inorganic production of calcareous siphon~ ida. Rhodophyta comprised 45% of the ates in Card Sound, Florida, using several total, Phaeophytas were only 12%, and techniques. Organic production was low in Chlorophytas and Cyanophytas each repre this lagoon, ranging fr9m 8,6 to 38.4 g sented 21% of the species. Harlin (1980) ash free dry weight /m 2/yr, and 4.2 to compiled from 27 published works a species 16. 8 g CaCO:/m 2/yr for al 1 the species list of the microalgae, macroalgae, and combined. animals that have been recorded as epiphy tic on seagrasses. The al gal 1 i sts are In addition to the calcareous a1 gae, comprehensive, but none of the reports several algae are present In grass beds as surveyed hy Hul:ft11 1 ist the epiphytic inver large clumps of detached drift algae; the tebrates froc1 south Florida. rriost abundant belongs to the genus Lauren clt• The areal production of theseai gae Harlin (1975) listed the factors is low compared with the seagrasses. Jos influencing distribution and abundance of selyn (1975) estimated the production of epiphytes as: Laurencia in Card Sound to averaoe about s:~r"g-· Seagrass 1 eaves are more heavily epi In some areas there are few epiphytes and phyti zed at their tips than their bases little contribution, but in places the for various reasons. For the snall algae, amount of production is high. Jones (1968) being on the 1eaves has the advantage of estimated that in northern Biscayne Bay raising them higher in the photic zone. epi phytes contributed from 25% to 33% of The shading effect produced by epiphytic the community metabolism. Epiphytes con organisms on seagrass leaves decreases tributed 18¾ of productivity of Zostera photosynthesis by 31% (Sand-Jensen 1975). meadows in North Carolina (Penhale 1977). In addition, the upper leaf surface exper The trophic structure of these leaf com iences much greater water motion than the munities can be quite complex and will be lower surface. This not only provides a discussed later. Much of the epiphytic r,iuch greater volume of water to be swept material, both plant and animal, ultimate by suspension-feeding animals, but also ly becomes part of the litter and detritus reduces the gradients for photosynthetic as the leaf senesces and detaches. organisns. Studies have shown that there is transfer of nutrients from seagrasses to epiphytes. Harlin (1975) described the 5.2 INVERTEBRATES uptake of PO,, translocated up the leaves of Zostera. and Phyllosoadix. Epiphytic Composition b1 ue-green a 1gae have the capacity to fix molecular nitrogen, and Goering and Parker The invertebrate fauna of seagrass (1972) showed that soluble nitrate fixed beds is exceedingly rich and can only be in this r.1anner was utilized by seagrasses. characterized in broad terms unless one is dealing with a specific, defined area. Epiphytes also contribute to the pri- This is because the fauna of the grass mary production of the seagrass ecosystem. beds is diverse, with many hundreds of 45 species being represented within a small providing a substrate for attachment (Fig area, and variable, with dramatic changes ure 17). The most prominent of these epi occurring in the faunal composition and faunal organisms in south Florida are the density within relatively small changes of gastropods. Cerithium mascarum and C. time or di stance. If one does not 1ose eburnum, Anachis sp., Astrea spp., ~odulus sight of these facts, it is possible to modulus, Mitrella lunata, and Bittium list various organisms that are represent varium are characteristic in turtle grass ative of seagrass meadows over large dis and shoal grass habitats throughout south tances. Florida, as is the attached bivalve Cardita floridana. The most obvious invertebrates of many of the seagrass beds of south Florida Small crustaceans are also common in are the large epibenthic organisms (Figure seagrass beds where they live in tubes at 16). The queen conch (Strombus ~) tached to the leaf surface, move freely feeds primarily on epiphytes it scrapes along the blades, or swim freely between from turtle grass blades, while the Baham the blades, the sediment surface, or the ian starfish (Oreaster reticulata) and the water column above the blades. Common am gastropods Fascioiaria tulipa and Pleuro phipods are Cymadusa compta, Gammarus muc ploca gigantea prey largely on infauna. ronatus, Melita nitida, and Grandidiereila Numerous sea urchins, such as Lytechinus bonnieroides, while the caridean shrimps variegatus and Tripneustes ventricosus, Palaemonetes ~. f. vulgasis, and f. are found throughout the beds. Juven i 1es intermedius, Periclimenes lonoicaudatus, of the long-spined urchin Diadema antil and P. americanus, Thorfloridanus, Tozeuma larum are common, but the adults seek the carofinense, Hippolyte pleuracantfia, shelter of rocky ledges or coral reefs. Alpheus normanni, and fl. heterochaelis are The deposit-feeding holothurians Actino abundant within the grass beds. Hermit ~ agassizi and Holothuria floridana may crabs of the genus Paourus are numerous be found on the surface, while the large and at night cra\vl up the blades to graze sea-hare, the nudibranch Aplysia dactylo on epiphytic material. When they reach mela, may be found gracefully gliding over the end of the blades, they simply crawl the grass canopy. At night pink shrimp off the end, fall to the sediment, scuttle (Penaeus duorarum) and spiny lobster to another blade, and repeat the process. (Panul irus argus) may be seen foraging in the seagrass along with the predatory Structure and Function Octop~ bri areus. The structure of the grass carpet On shallow turtle grass flats the with its calm water and shaded microhabi corals Manicinia areolata and Porites tats provides living space for a rich epi furcata are com~on, while in somewhat fauna of both mobile and sessile oroanisms deeper waters sponges such as Ircinea, (Harlin 1980). It is these organisms which TetQ.Y_~~ and Spongia may be found. are of greatest ir:1portance to higher con sumers within the grass hed, especially The infauna can be di verse, but are the fishes. When relatively small quanti not visually obvious. The rigid pen shell tative samples are used in estimating pop (Atrina rigida) is a common filter-feeder ulation sizes, gastropods, amphipods, and in many grass beds, along with numerous polychaetes are typically most numerous, bivalve molluscs such as Chione cancel while isopods can he i1nportant (Na9le lata, Codakia orbicu1aris, Tellina radi 1968; Carter et al. 1973; Marsh 1073; Ki at~; LuclnaEQ_~l vani ca, and ·1:aev~ kuchi 1974; Brook 1975, 1977, 1978). In a di um l aevJ.g_atum. A variety of annelid Card Sound turtle grass bed, Rrook ( 1975, worr1s are in the infauna, notably Areni 1977) estinated that a~phipods represented col a cri_s_~~ta, Onuphi s maqna, Te rebel 1 ides 62. 2% of al 1 crustaceans. When the tra1 Roessler and Tabb 1974; Bader and Roessler It is a long standing assumption that 1971; Tabb et al. 1962; Tabb and Manning the grass carpet represents protection 1961). Faunal differences among studies from predation for the animals living in reflect sampling gear selectivity, but it. The dense seagrass blades and rhizomes typica11y penaeid and caridean shrimp are associated with the grass carpet provide less numerous than the smaller macrocrus cover for invertebrates and sma 11 fishes taceans (i.e. amphipods, isopods). yet while al so interfering v-li th the feeding represent a larger biomass within the bed, efficiency of their potential predators. For example, data from Brook (1977) for a Experimental evidence suggests that grass Card Sound turtle grass grass bed indi bed invertebrates actively select vege cated that ampMpods and caridean shrimp tated habitat rather than bare sand indi represent respectively 5.8% and 23.3% of cating that habitat preference is an estimated biomass of principal taxa col important force contributing to observed lected and 12.4% and 50.31 of crustacean fauna1 densities in grass beds (Heck and biomass. Demonstrating the importance of Orth 1980). Selection appears to be based the ohvs ica1 structure of the arass car~ on the fonn or structural c.haracteri sties pet,· Yokel {1975a) reported -that the of the seagrass (Stoner 1980a}. · standing crop of crustaceans (estiFiated using a trawl} was 3. 9 times 1arger in It is speculated from experimental mixed seagrass and alga, flats than on work using shapes that the carldean nearby unvegetated bottoms {see Figure shrimp, HlEJ>J!lX1~ ca1iforniensis, locates 18). its host plant, Zostera marina, visually 48 100 (f) Fish a::: w 75 Invertebrates (l) D z :::> z 50 _j <( I- 0 I- 25 0~ HEAVY THIN SANO/ MUD/ SEAGRASS SEAGRASS SHELL SAND/ ( Halodule 8 ( Halodule) SHELL Thalassia) Figure 18. Relative abundance of fishes and invertebrates over seagrass beds and adja cent habitats (after Yokel 1975a). by discriminating on the basis of form fish species that will ultir.iately be of (Barry 1974). Stoner (1980a) demonstrated commercial or sport fishery value. The that common epifaunal amphipods were cap classification created by Ki l in controlling abundances and species com into the beds at night when predation is position within sea grass beds (Nelson less intense (Ogden and Zieman 1977; Ogden 1979a; Stoner 1979). 1980). The size of the individuals in these groups is a function of the length Little is known about how fishes and density of the grass beds. In Fl or respond to the structural complexity of ida, where the seagrasses are typically the grass canopy. Noting the size distri larger and denser, the grass beds offer bution of fishes typically inhabiting sea shelter for much larger fish than in St. grass beds, Ogden and Zieman (1977) specu- Croix, where the study of Ogden and Zieman 1 ated that large predators, such as bar {1977) was done. racudas, jacks, and mackerels, may be responsible for restricting permanent Heck and Orth (1980a) hypothesized residents to those smal 1 enough to hide that abundance and diversity of fishes within the grass carpet. For fishes larger should increase with increasing structural than about 20 cm (8 inches) the grass bed complexity until the feeding efficiency of can be thought of as a two-dimensional the fishes is reduced because of interfer · environment; these fishes are too large to ence with .the~grass blade:S ..... or because find shelter within the grass carpet. conditions within the grass canopy become Mid-sized fishes (20 to 40 cm or 8 to 16 unfavorable (i.e., anoxic conditions at inches) are probably excluded from the night). At this point densities should grass bed by occas i ona 1 large predators. drop off. Evidence indicates that feeding Mid-size fishes are apparently restricted efficiency does decline with increasing to sheltered areas by day and may move structural complexity. 52 The pinfish's predatory efficiency on Caribbean, the green sea turtle (Chelonia amp hi pods decreases with increasing den ~) is the only herbivorous sea turtle sity of Zostera marina blades (Nelson (Figure 20). In the Caribbean, the main 1979a). Coen (1979) found in single food of the green turtles are sea grasses species experiments (one shrimp species at and the preferred food is Thalassia, a time) that with increasing cover of red hence the .name turtle grass (see section algae (Digenia simplex, Laurencia spp., 6. 2). Gracilaria spp. and others) the pinfish's foraging efficiency on Palaemon floridanum Green turtles were formerly abundant and Palaemonetes vulgaris was reduced. throughout the region, but were hunted The ki 11 ifi sh ( Fundul us heterocl itus) fed extensively. Concern over the reduced less efficiently on the grass shrimp populations of green turtles dates back (Palaemonetes ~) in areas of densest to the previous century (Munroe 1897). artificial seagrass. Virtually nothing is Although limited nesting occurs on the known about the relation of typical grass sma 11 beaches of extreme south Florida, bed fishes and their predators; research the region has almost certainly been pri on this topic would be fruitful. marily a feeding rather than a nesting site. Turtle and manatee feeding behavior are described in Chapter 6. 5.4 REPTILES The American crocodile (Crocodylus Although there are several species acutus) occurs in the shallow water of sea turtles in the Gulf of Mexico and of Florida Bay and the northern Keys. Figure 20. Seagrass bed following grazing by green sea turtle. Note the short, evenly clipped blades. The scraping on the Thalassia blade in the center is caused by the small emerald green snail, Smaragdia vir1d1s. 53 Although crocodiles undoubtedly feed in from some distance in the air to sieze sha 11 ow grass beds, 1 i tt 1e is known of prey. The most common of the swi mrrii ng their utilization of this habitat. birds is the double-crested cor~orant which pursues fish in the water column. 5. 5 Birds Cormorants may be found wherever the water is sufficiently deep for them to swim, and The seagrass beds of south Florida cl ear enough for them to spot their prey. are used heavily by large numbers of The osprey and the bald eagle sieze prey birds, especially the wading birds, as on the surface of the water with their feeding grounds. This heavy utilization claws, while the brown pelican pluges from is possible because of the relatively high some distance in the air to engulf fishes proportion of very shallow grass bed habi with its pouch. The value of the seagrass tat. There are few studies of the uti1 i meadows to these birds is that prey are zation of seagrass beds by birds, al more concentrated in the grass bed than in though there are extensive lists of birds the surrounding habitit, thus providing an using temperate seagrasses and aquatic abundant food sourer. plants (McRoy and Helfferich 1980). Birds known to use the seagrass habitat of south The extensi•e shallow grass flats are Florida and their modes of feeding are excellent forar ing grounds for the larger listed in Table 9. wading birds :rigure 21). The great white heron is c,mmon on the shallow turtle Three common methods of feeding in grass flats on the gulf side of the lower birds are wading, swimming, and plunging Keys. The great blue heron is comr1on Figure 21. Shallow seagrasses adjacent to red mangrove roots. This is a common feed ing area of small and medium sized wading birds. 54 Table 9. Birds that use seagrass flats in south Florida (data provided by James A. Kushlan, Evergaldes National Park). Preferred Common name Species name feeding tide Waders-primary Great blue heron Ardea herodias Low Great white heron A.herodias LO\'I Great egret Casmerodius albus Low Reddish egret Egretta rufesceris Low Waders-secondary Louisiana heron E. tricolor Low Little blue heron r. caerulea Low Roseate spoonbill !Jaia ajaja Low Will et Catoptrophorus semipalmatus Low Swimmers Double-crested Phalacrocorax auritus High cormorant White pelican Pelecanus erythrorhynchos High (winter only) Crested grebe (winter) Red-breasted merganser Mergus serrator (winter) Flyers-plungers Osprey Pandion haliaetus High Bald eagle HaliaeetusTe"'ucocephalus High Brown pelican Pelecanus occidentalis High 55 throughout south Florida, but is sometimes sighted in Whitewater Bay, 20% in the Gu1f found in greatest numbers on the shallow of Mexico, 23% in inland waters, and only grass flats in Florida Bay. Small egrets 1% in Florida Bay. A later study (Odell and herons probably all feed occasionally 1979) reported no manatee sightings in on the shallowest, exposed flats, but are Biscayne Bay. generally 1 imited by water too deep for them to wade. The ecology of wading birds The bottlenose dolphin is the most and their feeding behavior have been re common marine mammal in south Florida viewed by Kushlan (1976, 1978). Odum waters and feeds over qrass flats, even et al. {1981) reviewed the extensive avi those less than 1 m (3.3-ft) deep. In the fauna of the mangrove regions of southern Everglades National Park region, Odell Florida. (1976) reported that 36% of the animals seen were in the Gulf of Mexico, 33% were in Whitewater Bay, 20% were in inland 5.6 MAMMALS waters, and 11% in Florida Bay. The rela tively low numbers in Florida Bay were Some marine maro.als also feed in sea probably due to the extreme shallowness grass beds. Odell (1979) reported that which would preclude swimming for this a1 though 27 species of marine mar1r1al s were large mar:imal. Bottlenose dolphin are either sighted alive or reported stranded opportunistic feeders, primarily on fish. on beaches in south Florida in recent Their diets are not well known, but they years. only 2 were common:· the rianatee consume large quantities of mullet in (Trichechus manatus) and the bottlenose Florida Bay. doTphTn-TTursTopstrunca tus). By comparison with the Everglades A1 though the range of the manatee was region, Biscayne Bay had a low dolphin formerly much larger, now it seems largely density. Odell (1979) found that in confined to the protected regions of aerial surveys of the two regions, 11.4 Everohdes National Park. Odell (1976) animals were sighed per flight hour in the surveyed the manatee distribution in Everglades area, while only 1.25 animals the Everg1 ades region. Of a total of per hour were seen in Biscayne Bay. herds with 772 individuals, 46% were 56 CHAPTER 6 TROPHIC RELATIONSHIPS IN SEAGRASS SYSTEMS 6.1 GENERAL TROPHIC STRUCTURE than previously suspected; however, it stil 1 appears that the detrital food web Seagrasses and associated epiphytes is the primary pathway of trophic energy provide food for trophically higher organ transfer (Zieman et al. 1979; Kikuchi isms by (1) direct herb ivory, (2) detrita1 1980; Ogden 1980). food webs within grass beds and (3) ex ported material that is consumed in other Studies have attempted to measure the systems either as macroplant material or proportion of daily seagrass production as detritus (Figure 22). Classically the which is directly grazed, added to the detrital food web within the grass beds 1 itter layer, or exported. Greenway has been considered the primary pathway, (1976) in Kingston Harbor, Jamaica, esti and in most cases is probably the only mated that of 42 g/m 2/wk production of significant trophic pathway. During the turtle grass, 0.3% was consumed by the past few years, new information has been small bucktooth parrotfish, Sparisoma rad gathered on the re 1at i ve ro 1 e of the other ians; 48.1% was consumed by the urc"fiTn':" modes of uti1 ization. The picture emerg lytechinus ariegatus; and 42.1% deposited ing is that in many locations both the on the bottom and available to detriti direct utilization pathway and the export vores. The rest of the production was of material mav be of far more importance exported from the system. This study may ·--·------.~·~--=---..-,::------,h:--~ rlF~:~E::: V\J ~JGRAZING nn DECAY, - ..... flI I' /I I SINKING PLANT CANOPY -...... I , 1 STRUCTURE \: ' II -~. ~·· i I II ········\ ~·· . l PRODUCTION _.: : UTTER ORGANIC DETRITUS ';~<.i~~~o ti _,t ,') o , .. .. ·•.•,,•.• .. ················,·.·.·.·.··············-···· .·•:.•-•·,• . , . ' .. ·, .. •.•· ·...... ·..... · ...... ~· ·. -·~. -·.•,··~--- Figure 22. Principal energetic pathways in seagrass beds. 57 overemphasize the quantity of seagrass Biscayne Bay, turtle grass formed the most material entering the grazing food chain important constituent of the detritus since urchins are not typically found at present (87.1%), wliile other portions densities of 20 urchins/rn 2 as was the case included 2.1% other seaarasses, 4.6% in Kingston Harbor (Ogden 1980). In St. algae, 0.4% animal remains,-3.3% nanqrove Croix, it has been estimated that typi leaves and 2.5% terrestrial r,,aterial cally between 5% and 10% of daily produc (Fenchel 1970). The microbial comi:1unity tion of turtle grass is directly consumed, living in the detritus collected consisted primarily by Sparisoma radians and second mainly of bacteria, sr.iall zooflagellates, arily by the urchins 1iTadema ant ill arum diatons, unicellular alciae, and ciliates. and Tripneustes ventricosus. Averaged over It is these types of or'ganisms which form the day, turtle grass production was the major source of nutrition for detrital 2.7 g dw/m 2/day of which only about 1% feeders. Bloom et al. (1972), Santos was exported, while 60% to 100% of the a.nd Simon (1974), and Young and Young 0.3 g dw/m 2/day production of manatee (1977) provided species 1 ists annotated grass was exported (Zieman et al. 1979). with feeding habits for molluscs and From these figures it is conservatively polychaetes, many of v1hich ingest detri estimated that about 70% of the daily tus. production of seagrasses was available to the detrital system. Typically penaeid and caridean shrimp are considered to be omnivores. The pink Many of the small organisms in grass shrimp (Penaeus duorarum), in addition to beds use algal epiphytes and detritus as organic detritus and sand, ingests poly- their food sources. The gastropods are chaetes, nematodes, caridean shrimp, the most prominent organisms feeding on mysids, copepods, isopods, arnphipods, epiphytic algae in seagrass beds. Amphi ostracods, moll uses and forarr:iniferans pods, isopods, ·crabs, and other crusta (Eldred 1958; Eldred et al. 1961). These ceans ingest a mixture of epiphytic and consumers strip the bacteria and other benthic algae as well as detritus (Odum organisms from the detritus, and the fecal and Heald 1972). As research continues, pellets are subsequently reingested fol it is becoming apparent that the util iza lowing recolonization (Fenchel 1970). t ion of this combination of rni c roa 1ciae and Some fishes, notably the mullet (Muail detritus represents one of the· major ceo/halus), are detrital feeders (Odum energy trans fer pathways to higher organ 19 0). Several large invertebrates such isms. as the gastropod Strombus aia~ (Randall 1964) and the asteroid Oreaster reticula N1tabl e by their absence are the tus (Scheibling 1980) take detritus as a 1 arge flocks of ducks and related water pa rt of their food. To emphasize the fowl found on te1nperate Zostera beds and importance of detritL1s to higher trophic especially the freshwat~uppia beds levels within the grass, the work of Carr (Jacobs et al. 1981). McRoy and Helfferich and Adams (1973) should be noted. They (1980} list 43 hird species that consurie found that detritus consumers were of seagrass primarily in the temperate zone. major frlportance in at least one feeding Relatively few species of birds ingest stage of 15 out of 21 species of juvenile seagrass species of the tropics or forage marine fishes studied. for prey in the sediments of shallow grass beds. It is well documented that fishes feed while occupying grass beds (Carr and Detritus undoubtedly serves as the Adams 1973; Adams 1976b; Brook 1975, 1977; base of a major pathway of energy fl ow in Robertson and Howard 1978), as opposed to seagrass meadows. A significantproportion simply using their for shelter. Typically, of net production in the seagrass bed re seagrass-associated fishes are small, gen sults in detritus either by dying in place eralist feeders, tending to prey upon epi and being broken down over a period of faunal organisms, primarily crustaceans. months by bacteria, fungi and other organ lnfaunal animals are under used in propor isms (Robertson and Mann 1980) or by being tion to their abundance as few fishes consumed by 1arge herbivores, fragmented. resident in the grass heds feed on them or and returned as feces ( Ogden 1980). In on other fishes (Kikuchi 1980). 58 Numerous fishes inqest some plant epifauna, tne inpact of blue crab pre material, while relativeiy fev1 of these dation may be greatest on epihenthic species are strict herbivores; exceptions fauna. are the Scarids and Acanthurids already rnentioned. Most plant and detrital mate The majority of fishes within the rial is probably taken incidentally v1hile grass bed feeds on small, mobile epifauna feeding on other organisrns. Orthopristis including copepods, cuo.1aceans, ariphipods, chrys92-tera and Laqodon rhoi11boides are two isopods, and shrimp. Fishes feeding in very abundant grass bed fishes in south this manner include all the seasonallv Florida and apparently during soi'.le feeding resident fishes of the south Florida arasi stages are ,wmivores, ingesting substan beds, such as the Sciaenids, Pomadasyids, tial amounts of epiphytes, detritus and Lutjanids, and Gerrids, as well as ~anv of seagrass (Carr and Adams 1973; Adams the permanent residents, 1 ike Syngnatr;ids, 1976a, 1976b; Kinch 1979). Other omnivores and Cl in ids. As such, they are deriving include some filefishes, porgies, blen much of their nutrition indirectly fror, nies, and gobies. seagrass epiphytes and the detrital com munity present in the grass bed rather Gastropods are fed upon by a variety than the grasses thernselves. Many of these of fishes including wrasses, porcupine fishes, as adults, will feed on other fishes, eagle rays, and the permit Trach fishes; however, as juvenile residents in notus folcatus. Randall (1967) listed 71 the grass beds, their sr'lall size limits species o(--:fi shes that feed on gastropods, them to eating epifauna. 25 ingesting 10% or more by volume. Most species crush the shell while ingesting, Important pi sci vores are present in but a few swallow the gastropod whole. south Florida grass flats. These include The white grunt (Hacmulon plumeri) appears the lemon shark (Ne a1rion brevirostires) to snap off the extended head of Cerith and the bonnethea shark Sphyrna tib~ro}, ium, ignorinq the shell. The southern the tarpon (Megalops atlantica), the liz stingray (Oasyatus americana) has been ardfish (Synodon foetens1, the coronet observed turning over the queen conch fish (Fistularia tobacaria}, the harracuda (Strombus ~) and wrenching off the (~t.!i'.r_aena barracucial-;""carangids, the grey conch's extended foot with its jaws as snapper (Lutjanus ~~~~). and the spot the conch tries to right itself (Randal ted seatrout TCfri""oscion nebulosus). 1964). The spiny lobster (Panulirus argus) is an active predator on seagrass 111011 uses. 6.2 DIRECT HERBIVORY The southern stingray and the spotted Caribbean grass beds rnay be unique eagle ray (Aetobatis narinari) are two of for the numbers and variety of direct con a relatively few number of fishes that sumers of blade tissue (Ogden 1q8Q) as feed on infauna within the grass bed. relatively few species ingest green sea These fishes excavate the sediments. grass in significant quantities (Table Other similar feeders are wrasses, goat 10). Prominent herbivores include urchins, fishes, and rnojarras. Adult yellowtail conch, fishes, as well as the oreen tur snapper (Oryhurus chrysurus) have been ob tle, Chelonia mydas, and Caribbean manatee served foraging in bacl Herbivore Part of Seagrass Location scienti fie Cormnon Seagrass seagrass in diet of name nane eaten eaten (%) population Reference ANNELIDS Arenicola cristata Lugwom Thalassia Detritus Max. 100 Florida D1 Asaro and Chen ---·-- Ha1odu1e 1976 S~odium MOLLUSCS Strombus giga~ ~een conch Thalassia Leaf West Indies Randall 1964 S.}'.ringodium Leaf Halodule Leaf ~ CRUSTACEANS Callinectes sapidus Blue crab Zostera Leaf U.S. Atlantic Hay 1904 Tha1assia Leaf Coast Pull en 1960 Ruppia Leaf Texas Uca sp. Fiddler crab Thalassia Leaf (wrack) Texas T. McConnaugher, pers. comm. ECHINODERMS Diadema antillarum Sea urchin Thalassia Leaf West Indies Ogden et al. 1973 S.}'.ringodium Leaf Diadema setosum Sea urchin Thalassia 12 West Indies Lawrence 1975 Zanzibar Echinornetra 1acunter Sea urchin Thalassia Leaf 10.2 Caribbean Abbott et al. 1974 Sj!ringoctium Leaf 8.9 Alaska Halodule Leaf 7.9 Alaska --·--Eucidaris tribuloides Sea urchin Thalassia Leaf Caribbean t,1c Pherson 1% 4 (continued) Table 10. Continued. Herbivore Part of Seagrass Location scientific Comrion Seagrass seagrass in diet of nal'le name eaten eaten (%) population Reference ECHINODERMS(continued) Lytechinus variegatus Sea urchin Thalassia Leaf Florida Campet al. 1973 Thalassia Leaf Max. 100 Jamaica Greenway 1974 Thalassia Leaf Caribbean ~oore et al. 1963a Thalassia Leaf Lawrence 1975 Syringodium Leaf Tripneustes esculentus Sea urchin Thalassia Leaf Florida Moore et al. 1963b Smaraydia viridis Emerald Thalassia Leaf Florida J. Zieman and R. nerite West Indies Zieman per. obs. Sea Max. 100 Lawerence 1975 01 Tripneustes ventricosus urchin Thalassia Leaf Florida ...... VERTEBRATES FISHES Acanthostracion Cowfish Thalassia Leaf 3 West Indies Randall 1967 guadricorn1$ Acanthurus bahianus Ocean surgeon Strinqodium Leaf 8.2 West Indies Randall 1967 Halophila Thalassia Leaf 40-80 (T.) Randall 1965 Syri ngodi um Acanthurus chir?rgus Doctor fish Thalassia Leaf 5.7 West Indies Randal 1 1965 Syringodium Thalassia Leaf 25 ~Jest Indies Randall 1967 Syrin~odium Acanthurus coeruleus Blue tang Halop ila Leaf 6.8 West Indies Randall 1967 ----- S,tringodium Alutera schoepf1 Orange Syringodiurn Leaf 67 West Indies Randall 1967 filefish Tha1assia (continued) Table 10. Continued. Herbivore Part of Seagrass Location scientific Comr,on Seagrass seagrass in diet of name name eaten eaten ( %) population Reference FISHES (continued) Alutera scri pta' Scrawled S_yringodium Leaf 9 West Indies Randall 1967 filefish Thaiassia Archosar~us · Sea brear.i Thalassia Leaf 44.6 \Jest Indies Randall 1967 rhombo1da1is Syringodium Cantherhines pu11us Orange-spotted Thalassia Leaf 4.6 West Indies Randall 1967 fil efi sh Halophila Canthigaster rostrata Sharp-nose Stringodium Leaf 16.1 West Indies Randall 1967 puffer Ha1ophila N°' Chaetodi pterus faber Spadefish Syringodium Leaf 2.3 West Indies Randal 1 1967 Diapterus plumieri Striped Thalassia Leaf Max. 33 Puerto Rico Austin and Austin 1971 juvenile) mojarra Diapterus rhombeus Sand mojarra Thalassia Leaf Venezuela Cervigon 1966 Ruppia Leaf Max. 16. 7 Puerto Rico Austin 1971 Thalassia Leaf Max. 32. 5 Puerto Rico Austin and Austin 1971 Ruppia Leaf Halophila Leaf Diplodus holbrooki Spottail Florida pinfish Hildebrand 1941 Halichoeres Slippery dick Thalassia Leaf 5 West Indies Randall 1967 bi vi ttatus Haren~ humerallis Red-ear Thalassia Leaf 2.5 West Indies Randall 1967 sardine Syringodium HernirarnThus Hal fbeak, iiialassia Leaf 81 West Indies Randall 1967 brasi lensis ballyhoo String_odium (continued) Table 10. Continued. Herbivore Part of Seagrass Location scientific Common Seagrass seagrass in diet Peference name name eaten eaten (%) population Reference FISHES (continued) Hyhorhamphus .. Ha1fbeak 1-lalodule Leaf Texas Carangelo et al. 1975 nae6rancli · Hyporhamphus Halfbeak Thalassia Leaf 49 Florida Carr and Adams 1973 unifasciatus Kyphosus incisor Paddlefish Thalassia Leaf !~est Indies Randall 1967 cr, Kyphosus sectatrix Rudderfish, Syringodium Leaf 0.5 West Indies Randal 1 1967 w Bermuda chub Lacto~ bicaudalis Spotted Syr i ngodi um Leaf 8 West Indies Randall 1967 trunkfish Lacto~ trigonus Trunkfish Syri ngodi um Leaf 3 West Indies Randall 1967 Tha1assia Lacto~ triguetar Smooth Thalassia Leaf 1. 3 ~lest Indies Randal 1 1967 trunkfi sh Halophila Lagodon rhomboides Pinfish Rutpi a Leaf Gulf of Mexico Carr and Adams 1973; Haodule Darnell 1958; Springer and Woodburn 1960 41 Florida Hansen 1969 Melichth.¥2_niger Black durgon Syri ngodi um Leaf 4.4 West l!1dies Randall 1967 Me1ichthll radula Trigger fish Syri ngodi um Leaf West Indies Randall 1965 Monocanthus ciliatus Fringed Thalassia Leaf 15.4 \~est Indies Randall 1967 filefi sh Monocanthus setifera Speckled Thalassia Leaf West Indies Greenway 1974 filefish (continued) Table 10. Continued. Herbivore Part of Seagrass Location scientific Co1TIP1on Seagrass seagrass in diet of name name eaten eaten {%) population Reference FISHES (continued) Mugi1 cure1:1a \.Jhite mu11et Thalassia Leaf West Indies Randall 1967 Pogonias chromis Black drum Halodule Leaf Texas Carangelo et al. 1975 Pol,¥da~t,};lus Thread fish Thalassia Leaf 17 Puerto Rico Austin and Austin 1971 v1 rg1n1cus ~ia Pomacanthus Grey Sy_ringodium Leaf West Indies Earle 1971 0-, arcuatus angelfish ~ia 0.1 West Indies Randall 1967 .i::,. Pomacanthus paru French Syringodium Leaf 0.1 West Indies Randall 1967 angelfish Halo[!hila Pornacentrus fuscus Dusky Syringodium Leaf 1.6 West Indies Randall 1967 damselfish Pornacentrus Three-spot Thalassia Leaf 3.9 \fast Indies Randall 1967 gl ani frons damsel fish Rhinootera quadriloba Cownose ray Thalassia Leaf Texas Carangelo et al. 1974 Halodule Scarus coelestinus Midnight Thalassia Leaf 1. 3 West Indies Randall 1967 parrotfish Scarus gua~ainaia Rainbow Syri ngodi um Leaf 95 West Indies Randall 1967 parrotfish Syringodium Leaf 8 West Indies Randall 1967 Thalassia Scarus retula ('ueen Thalassia Leaf 3.2 West Indies Randall 1967 parrotfish (continued) Table 10. Continued. Herbivore Part of Seagrass location scientific Cornrion Seagrass seagrass in diet of name narie eaten eaten (%) population Reference FISHES (continue~) Scarus taeniopterus Painted-tail Thalassia leaf 17.3 West Indies Randall 1967 parrotfish Sparisoma Redband Syringodium leaf 1.3 West Indies Randall 1967 aurofrenatum parrotfish Sparisona Redtail Thalassia leaf 16.8 West Indies Randall 1967 chrysopterum parrotfish ~ Soarisoma rubripinne Redfi n Thalassia leaf 7 West Indies Randall 1967 u, parrotfish Sparisoma radians Bucktooth Thalassia leaf 88 West Indies Randall 1967 parrotfish Jamaica Greenway, pers. comm. Sparisorna viride Spotlight Thalassia leaf 2.5 West Indies Randall 1967 parrotfish Sphaeroides Banded Halophila leaf 5. 3 vlest Indies Randall 1967 spengl eri i pufferta i 1 Thalassia Strongy1ura marina Atlantic ..!3Qp_Qia leaf Darnel 1 1958 neddlefish Symphurus .P.J.M_iusa Blackcheek Ruppia leaf tips 19 Puerto Rico Austin and Austin 1971 tonguefish Halodule Leaf tips REPTILES Caretta caretta Loggerhead Leaf Rebel 1974 turtle (continued) Table lC. Concluded. Herbivore Part of Seagrass Location scientific Cofl1111on Seagrass seagrass in diet of name narne eaten eaten (%) population Reference REPTILES(continued) Chelonia mydas Green sea Thalassia Leaf Max. 100 Inda-Pacific Bustard 1969 (adult) • turtle Enhalus Red Sea Hirth et al. 1973 Posidonia Halodule Caribbean Carr 1954 Eretmochelys Hawksbill Leaf Max. 100 Rebel 1974 imbricata turtle (juvenile} g: MAMMALS Trichechus manatus Manatee Ruppia Leaf Florida Hartr1an 1971 Zostera (captive) Syringodium, Halodule, Thalassia implicated The herbivory of parrotfish and sea ur in many areas because of its high food chins may be important in the back reef value ancl ease of capture by man. Conchs areas and in Hawk Channel; but, with the are found in a variety of grass beds, from exception of sporadic grazing by passing dense turtle grass to sparse manatee grass turtles, herbivory is low or non-existent and Halophila. When in turtle grass beds in the areas to the west of the Florida conchs primarily feed by rasping the epi Keys (J.C. Zieman, personal observation). phytes fr0rn the leaves as opposed to eat ing the turtle grass. In sparse grass Parrotfish typically move off the beds, however, conchs consumed large quan reef and feed during the day (Randall tities of manatee grass and Halophila 1965). Spar1_~oma radians, 2· rubripinne, (Randall 1964}. A maximum of 20% of the and 2· chrysopterum are known to feed on stomach contents of conchs at St. John, seagrass and associated algae (Randall U.S. Virgin Islands, was comprised of tur 1967). The bucktooth parrotfish (S. radi tle grass. In manatee grass (Cymodocea) ~) feeds almost exclusively on turtle beds, conchs consumed mostly this seagrass grass. Other fishes that are important along with some algae. The rllaximum quan seagrass consumers are suraeonfishes tity of seagrass found was 80% Ha 1ophil a (Acanthuridae) (Randall 1967 ;- Clavijo from the gut of four conchs froin-Puerto 1974), the porgies (Sparidae) (Randall Rico. 1967; Adams 197Gb}, and the halfbeaks (Hemiramphidae). The emerald neri te (Smaragdia v1r1- di s), a small gastropod, commonly~ Fishes in the Caribbean seagrass beds 8 mm long, can be numerous in turtle grass tend to be generalist herbivores, select beds although it is difficult to see be ing plants in approximate relation to cause its bright green color matches that their abundance in the field (Ogden 1976; of the lower portion of the turtle grass Ogden and Lobel 1978). Some deqree of blades. It is a direct consumer of turtle selectivity is evident, however. Sparisoma grass where it roams about the lower half chr so terurn and i, radians, when given a of the green b1 ades; the snail removes a c oice, wi select seagrass with epiphy furrm,, about 1 mm wide and half the thick tes (Lobel and Ogden, personal communica ness of the blade with its radula (J.C. tion). Seagrasses (turtle grass, manatee Zieman and R.T. Zieman, personal observa grass, and shoal grass) ranked highest in tion). preference over common al gal seagrass associates. ~iost studies (for review, see Law rence 1975) indicate that the majority of Urchins that feed on seagrass include seagrass consumers have no enzymes to di Eucidaris tribuloides, Lytechinus varieaa gest structural carbohydrates and that, tus, Diadema antillarur.1 and Tripneustes with the exception of turtles and possibly ventricosus (McPherson 1964, 1g68; Randall manatees, they do not have a gut f1 ora et al. 1964; Kier and Grant 1965; Moore capable of such digestion. Thus, most and ~cPherson 1964; Prim 1973; Abbott macroconsumers of seagrasses depend on the et al. 1974; Ogden et al. 1973; Moore eel 1 contents of seagrasses and the at et al. 1963a, 1963b; Greenway 1976). The tached epi phytes for food and must have a latter two urchins feed in approximate mechanism for the efficient maceration of proportion to food abundance in the area. the material. The recent work of Weinstein Where present in seagrass beds, T. ventri et a 1. (in press), however, demonstrated ~ and Q_. antillarum feed on seagrasses that the pinfi sh was capable of digesting with epi phytes exclusively (Ogden 1980). the structural cellulose of detrital mat Lytechinus varie atus is largely a detri ter or green seagrasses. Feeding rates tal feeder Ogden 1980), b-ut has denuded are Jtigh Jor urchins and parrotfi shes, large areas in west Florida (Camp et al. while absorption efficiency E around 50% 1973). (Moore and McPherson 1965; Lowe 1974; Ogden and Lobel 1978). Assimilation effi The queen conch (Strombus ~). ciencies for T. ventricosus and L. varie once a cor.mon inhabitant of Caribbean sea aatus are refative1y low, 3.8% and 3.0% grass beds, has been dramatically reduced ~ctively (Moore et al. 1963a, 1963b). 67 The result of macroherbivore grazing There is little doubt that the struc within the grass bed can be dramatic (Camp ture of many grass beds was profoundly et al. 1973). Of greater overall signifi different in pre-Columbian times when tur cance, however, is the fragmentation of tle populations were 100 to 1,000 times living seagrass and production of particu greater than those now. Rather than ran late detritus coincident with feeding. domly cruising the vast submarine meadows, Further, the nature of urchin and parrot grazing as submarine buffalo, turtles fish feeding results in the 1 iberation of apparently have evolved a distinct feeding living seagrass and its subsequent export behavior. They are not resident in sea from the bed (Greenway 1976; Zieman et al. grass beds at night, but live in deep 1979). Zieman et al. (1979) observed that holes or near fringing reefs and surface manatee grass blades floated after detach about once an hour to breathe. During ment, whereas turtle grass tended to sink; morning or evening the turtles will swim the result was that turtle grass was the some unknown distance to the seagrass beds primary component of the litter 1ayer to feed. What is most uniaue is that they available for subsequent utilization by return consistently to the same spot and detritivores. regraze the previously grazed patches, maintaining blade lengths of only a few Many of the macroconsumers, such as centimeters (Bjorndal 1980). Thayer and Acanthurids, ~- rubri}inne and~- chrysop Engel (',1S in preparation) calculated that terum (Randall 1967 , ingesting 1 iving an intermediate-sized Chelonia (64 kg or seagrass take in only small amounts, the 141 lb) consumes daily a dry weight of majority of their diet consisting of epi blades equivalent to 0.5 m2 of an average phytic algae. Species primarily ingesting turtle grass bed (500 g dw of leaves). seagrass (i.e., S. radians) typically pre Since the regrazed areas do not contain as fer· the epiphyfized portion of the sea heavy a standing crop as ungrazed grass grass blade. These observations suggest beds, it is obvious that their grazing that seagrass epiphytes are important in plots must be considerably larger. The the flow of energy within the grass car maximum length of grazing time on one dis pet. Many of the small, mobile epifaunal tinct patch is not known, but J.C. Ogden species that are so abundant in the grass (personal communication) observed patches bed and important as food for fishes feed that persisted for up to 9 months. at least in part on epiphytes. Typically, these animals do not feed on living sea The first time turtles qraze an area grass, but often ingest significant quant they do not consume the entire blade hut ities of organic detritus with its asso bite only the lower portion and allow the ciated flora and fauna. Tozeuma carol in epiphytized upper portion to float away. ense, a common caridean shrimp, feeds on This behavior was recently described in epiphytic algae attached to seagrass some detail by Bjorndal {1980), but the blades but undoubtedly consumes coinciden earliest description was from the Dry tally other animals (Ewald 1969). Three Tortugas where John James Audubon observed of the four seagrass-dwelling amphipods turtles feeding on seagrass, "which they common in south Florida use seagrass epi cut near the roots to procure the most phytes, seagrass detritus, and drift algae tender and succulent part" (Audubon 1234). as food, in this order of importance {Zim merman et al. 1979). Epiphytic algae were It was previously thought that there the most important plant food sources was an advantage for grazers to consume tested since they were eaten at a high the epiphyte complex at the tip of sea rate by ~ymadusa compta, Gammarus mucro grass leaves, as this complex was of natus, an Melita nitida. Epiphytic algae higher food value than the plain seagrass were also assimilated more efficiently by leaf. Although this seems logical, it these amphipods (48%, 43% and 75%, respec appears not to be so, at least not for tively) than other food sources tested, nitrogen compounds. While studying the including macrophytic drift algae, live food of turtles, Mortimer (1976) found seagrass, and seagrass detritus. Live that entire turtle grass leaves collected seagrass had little or no food value to at Seashore Key, Florida, averaged l.7%N these amphipods. on an ash free basis, while turtle grass 68 leaves plus their epiphytes averaged 1.4% common throughout the Caribbean, espec N. Bjorndal found that grazed turtle ially in the mainland areas, but is now grass leaves averaged 0.35% N (AFDW) greatly reduced in range and population. higher than ungrazed leaves, and Thayer Manatees live in fresh or marine waters; and Engel (MS. in preparation) found a and in Florida, most manatee studies have nitrogen content of 1.55% (DW) in the focused on the manatee's ability to con esophagus of Chelonia. Zieman and Iverson trol aquatic weeds. r~anatees, which weigh ( in preparation) found that there was a up to 500 kg (1,102 lb), can consume up to decrease in nitrogen content with age and 20% of their body weight per day in aqua epiphytization of seagrass leaves. The tic plants. basal portion of turtle grass leaves from St. Croix contained 1. 6% to 2.0% N on a When in marine waters, the manatee dry weight basis, while the brown tips of apparently feeds much like its fellow these leaves contained 0.6% to 1.1% N, sirenians, the dugongs. The dugongs use and the epi phyt i zed tips ranged from O. 5% their rough facial bristles to dig into to 1.7% N. Thus the current evidence the sediment and grasp the pl ants. These would indicate that the green seagrass are uprooted and shaken free of adhered leaves contain more nitrogen than either sediment. Husar (1975) stated that feed the senescent 1eaves or the l eaf-epi phyte ing patches are typically 30 by 60 cm (12 complex. By successively recropping by 24 inches) and that they form a conspi leaves from a plot, the turtle main cuous trail in seagrass beds. This author tains a diet that is consistently higher has observed manatees feeding in Thalassia in nitrogen and lower in fiber content beds in much the same manner. The patches than whole leaves (Bjorndal 1980). cleared were of a similar size as those described for the dugongs, and rhizome Grazing on seagrasses produces removal was nearly cornpl ete. The excess another effect on sea turtles. In the sediments from the hole were mounded on Gulf of California (Felger and Moser 1973) the side of the holes as if the manatee and Nicaragua (Mortimer, as reported by had pushed much of it to the side before Bjorndal 1980), witnesses reported that attempting to uproot the plants. turtles that had been feeding on sea grasses were considered to be good tast Mana tees would seem to be more ing, while those that were caught in areas limited in their feeding range because of where they had fed on algae were cons id sediment properties, as they reauire a ered to be "stinking" turtles with a defi sediment which is sufficiently unconsol i nite inferior taste. dated that they may either root down to the rhizome or grasp the short shoot and Thayer and Engel (MS. in preparation) pull it out of the sediment. Areas where suggested that grazing on seagrasses can manatee feeding and feeding scars were short-circuit the time frame of decomposi observed were characterized by soft sedi tion. They showed that an intermediate ments and lush growth of turtle grass and sized green turtle which consumes about Halimeda in mounded patches. Nearly al 1 300 g dry weight of 1eaves and defecates areas in which sediments were more consol about 70 g dry weight of feces daily, does idated showed no signs of feeding. In the return nitrogen to the environment at a areas where the manatees were observed, more rapid rate than occurs for the decom the author found that he could readily position of a similar amount of leaves. shove his fist 30 cm (12 inches} or r1ore They point out that this very nutrient into the sediments, while in the adjacent rich and high nutritional quality fecal ungrazed areas, maximum penetration was matter should be readily available to only a few centimeters and it was impos detritivores. It is also pointed out that sible to remove the rhizomes without a this matter is probably not produced shovel. entirely at the feeding site and thus provides an additional interconnection between grass beds and adjacent habitats. 6.3 0ETRITAL PPOCESSING Like the turtles, the Caribbean For the majority of aninals that r.1anatee (Trichechus manatus) formerly was derive all or part of their nutrition from 69 seagrasses, the greatest proportion of Microorganisms, because of their di fresh plant material is not readily used verse enzymatic capabilities, are a neces as a food source. For these animals sea sary trophic intermediary between the sea grass organic matter becomes a food source grasses and detritivorous animals. Evi of nutritional value only after undergoing dence (Tenore 1977; Ward and Cummins 1079) decomposition to particulate organic suggests that these animals derive the detritus, which is defined as dead organic 1argest portion of their nutritional re riatter alonq with its associated micro quirements from the microhial component of organisms (Heald 1969). detritus. Detritivores typically assimi late the microflora compounds with effi The nonavailability of fresh seagrass ciencies of 50% to almost 100%, whereas r:iaterial to detritus-consuming animals plant compound assimilation is less than (detritivores) is due to a complex combi 5% efficient (Yingst 1976; Lopez et al. nation of factors. For turtle grass 1977; Cammen 1980). leaves, direct assays of fiber content have yi e 1 ded va 1 ues up to 59% of the dry During seagrass decomposition, the weight (Vicente et al. 1978). Many ani size of the particulate matter is decreas mals lack the enzymatic capacity to assim ed, making it available as food for a wid ilate this fibrous material. The fibrous er variety of animals. The reduced parti components also make fresh seagrass resis cle size increases the surface area avail tant to digestion except by animals (such able for microbial colonization, thus in as parrotfishes and green turtles) with creasing the decomposition rate. The abun specific morphological or physiological dant and trophically important deposit adaptations enabling physical maceration feeding fauna of seagrass beds and adja of pl ant material. Fresh sea grasses al so cent benthic communities, such as poly contain phenolic compounds that may deter chaete worms, amphipods and isopods, ophi herbivory by some animals. uroids, certain gastropods, and mullet, derive much of their nutrition from fine During decomposition of seagrasses, detrital particles. numerous changes occur that result in a food source of greater value to many con It is important to note that much of sumers. Bacteria, fungi, and other micro the contribution of seagrasses to higher organisms have the enzymatic capacity to trophic levels through detrital food webs degrade the refractile seagrass organic occurs away from the beds. The more matter that many animals lack. These decomposed, fine detrital particles (less microorgan 1Sri1s co 1oni ze and degrade the than O. 5 mm) are easily resuspended and seagrass detritus, converting a portion of are widely distributed by currents (Fisher it to microbial protoplasm and mineraliz et al. 1979). They contribute to the ing a large fraction. Whereas nitrogen is organic detritus pool in the surrounding typically 2% to 4% dry weight of seagrass waters and sediments where they continue es (Table 7), microflora contain 5% to 10% to support an active microbial population nitrogen. Microflora incorporate inorganic and are browsed by deposit feeders. nitrogen from the surrounding medium- either the sediments or the water column- Physical Breakdown into their eel ls during the decomposition process, enriching the detritus with pro The physical breakdown and particle teins and other soluble nitrogen com size reduction of seagrasses are important pounds. In addition, other carbon com for several reasons. First, particle size pounds of the microflora are much less is an important variable in food selection resistant to digestion than the fibrous for a wide range of organisms. Filter components of the seagrass matter. Thus. feeders and deposit feeders ( po lychae tes, as decompos it; on occurs there wi 11 be a zooplankton, gastropods) are only able to gradual mineralization of the highly ingest fine particles (1 ess than 0. 5 mm resistant fraction of the seagrass organic diameter). Second, as the seagrass mate matter and corresponding synthesis of rial is broken up, it has a higher surface microbial biomass that contains a much area to volume ratio which allows more higher proportion of soluble compounds. microbial colonization. This increases 70 the rate of biological breakdown of the rapidly, although this may inhibit micro seagrass carbon. Physical decomposition bial growth (Josselyn and Mathieson 1980). rate is an approximate indication of the rate at which the plant material becomes Biological factors also affect the available to the various groups of detri rate of physical decompositon. Animals tivores and how rapidly it will be sub grazing on the microflora of detritus dis jected to microbial degradation. rupt and shred the plant substrate, accel erating its physical breakdown. Fenchel Evidence indicates that turtle grass (1970) found that the feeding activities detritus is physically decomposed at a of the amphipod Parahyella whelpYi dramat rate faster than the marsh grass, Spartina ically decreased the particle size of alterniflora, and mangrove leaves. Zieman turtle grass detritus. (19756) found a 50% loss of original dry weight for turtle grass leaves after 4 Microbial Colonization and Activities weeks using sample bags of 1-mm mesh size (Figure 23). Feeding studies performed with vari ous omnivores and detritivores have shown Seagrass leaves are often transported that the nutritional value of macrophyte away from the beds. Large quantities are detritus is 1imited by the quantity and found among the mangroves, in wrack lines quality of microbial biomass associated along beaches, floating in large mats, and with it. (See Cammen 1980 for other stud collected in depressions on ·unvegetated ies of detrital consumption.) The micro areas of the bottom. Studies have shown organisms' roles in enhancing the food that the differences in the physical and value of seagrass detritus can be divided biological conditions in these environ into two functions. First, they enzymati ments resulted in different rates of phys cally convert the fibrous components of ical decomposition (Zieman 1975b). Turtle the plant material that is not assimilable grass leaves exposed to alternate wet by many detritivores into microbial bio ting and drying or wave action breakdown mass which can be assimilated. Second, 100 C) z 90 -z 80 -,c( 70 ~ w 60 °'.... 50 :c 40 C) -LU 30 ~ 20 ~ 10 0 1 2 3 4 5 6 TIME IN MONTHS Figure 23. Comparative decay rates showing the rapid decomposition of seagrasses com pared with other marine and estuarine plants (references: Burkholder and Bornside 1957; de la Cruz 1965; Heald 1969; Zieman 1975b). 71 the microorganisr1s incorporate constitu sediment particles by removal of the ents such as nitrogen, phosphorous, and microorganisms but did not measurably dissolved organic carbon compounds from reduce the total organic carbon content of the surrounding mediur:i into their cells the sediments which was presuriably dol".'i and thus enrich the detrita1 complex. The nated by detrital plant carbon. When the microorganisms also secrete large quanti nitrogen-poor, carbon-rich feces were ties of extracellular materials that incubated in seawater, their nitrogen con change the chemic a1 nature of detritus and tent increased because of the growth of may be nutritionally available to detriti attached microorganisms. A new cycle of vores. After initial leaching and decay, ingestion by the animals again reduced the th~se processes make microorganisms the nitrogen content as the fresh crop of prnnary agents in the chemical changes of microorganisms was digested. In a study detritus. of de tr ital leaf material, Morrison and White (1980) found that the detritivorous The microbial component of macrophyte amphipod Mucrogammarus sp. ingested the detritus is highly complex and contains microbial component of 1 ive oak ( Q.Jercus organisms from many phyla. These various virginica) detritus without altering or components interact and influence each consuming the leaf matter. other to such a high degree that they are best thought of as a 11 decomposer commun While the importance of the microbial ity" (Lee 1980). The structure and activ components of detritus to detritivores is ities of this community are influenced by established, some results have indicated the feeding activities of detritivorous that consumers may bf! capable of assimi animals and environmental conditions. lating the plant carbon also. Cammen (1980) found that only 26% of the carhon !1,fil9Jlora in !Jetritivore Nutrition requirements of a population of the deposit-feeding polychaete Nereis succinea Microbial carbon constitutes only 10% would be met by ingested rnicrob1al bio of the total organic carbon of a typical mass. The rnicrobi al biomass of the in detr1ta1 particle, and microbial nitrogen gested sediments cou1 d supply 90% of the constitutes no more than 10% of the total nitrogen requirements of the studied poly ni trogcn (Rub1ee et al. 19713; Lee et al. chaete population. The mysid Mysis steno- 1980). Thus t 111ost of the organic compo 1epsis, conimonly found in Zostera beds, nents of the detritus are of plant oriqin was capahle of digesting ce11-wa11 com and are limited in their availability~to pounds of plants {Foulds and Mann 1978). detritivores. These studies raise the possibility that while microbial bio1:1ass is assimilated at Carbon uptake from a macroalga, high efficiencies of 50% to 100% (Yingst Graci1 aria, and the seaorass Zostera 1976; Lopez et al. 1977) and supplies -,la~ by the deposit.feeding polychaete, proteins and essential growth factors, e J,,! ca..E.1!:,ill, was measured l:ly Tenore the large quantities of plant material ~ • Uptake of carbon by the won11s was that are ingested may be assi1nilated at directly proportional to the microbial low efficiencies (less than 5%) to supply activity of the detritus (measured as carbon requirements. Assimilation at this oxidation rate). The MaxiMum oxidation low efficiency would not be readily quan rate occurred after 14 days for Gracilaria tified in most feeding studies (Cammen detritus and after 180 days for Zostera 1980). detritus. This indicates that the charac teristics of the original plant matter The microbial degradation of seagrass affect its avai1abil ity to the microbes, organic matter is greatly accelerated by which in turn 1 imits the assimilation of the feedinq activities of detritivores and the detritus by consumers. microfauna: a 1though the exact nature of the effect is not clear. Microbial res- Most of the published evidence shows piration rates associated with turtle that detritivores do not assimilate grass and Zostera detritus were stimulated significant portions of the non-microbial by the feeding activities of animals, component of macrophytic detritus. For apparently as a result of physical frag- examp1e, Newell {1965) found that deposit- mentation of the detritus (Fenchel 1970; feeding ~olluscs removed the nitrogen fron Harrison and Mann 1975a). 72 Chemical Changes During Decomposition of detritus and has been assumed to repre sent protein content (Odum and de la Cruz The two general processes that occur 1967). Subsequent analyses of detritus during decomposition, loss of plant com from many vascular plant species, however, pounds and synthesis of microbial biomass, have shown that up to 30% of the nitrogen can be incorporated into a generalized is not in the protein fraction (Harrison model of chemical changes. Initially, the and Mann 1975b; Suberkropp et al. 1976; leaves of turtle grass, manatee grass, and Odum et al. 1979). As decomposition pro shoal grass contain 9% to 22% protein, 6% gresses, the non-protein nitrogen fraction to 31% soluble carbohydrates, and 25% to as a proportion of the total nitrogen can 44% ash (dry weight basis), depending on increase as the result of several process species and season (Dawes and Lawrence es: complexing of proteins in the lignin 1980). Direct assays of crude fiber by fraction (Suberkropp et al. 1976); produc Vicente et al. (1978) yielded values of tion of chitin, a major cell wall compound 59% for turtle grass leaves; Dawes and of fungi (Odum et al. 1979b); and decompo Lawrence (1980) classified this material sition of bacterial exudates (Lee et al. as "insoluble carbohydrates" and calcu 1980). As a result, actual protein con lated values of 34% to 41% for this spe tent may be a better indicator of food cies by difference. Initially, losses value. Thayer et al. ( 1977) found that through translocation and leaching will the protein content of Zostera leaves lead to a decrease in certain components. increased frol'1 standing dead to detrital Thus, the organic carbon and nitrogen con fractions, presumably due to microbial tent will be decreased, and the remaining enrichment. The role of the non-protein material will consist primarily of the and protein nitrogen compounds in detriti highly refractive cell wall compounds vore nutrition is not presently well (cellulose, hemicellulose, and lignin) and understood. ash (Harrison and Mann 1975b; Thayer et al. 1977). Like many higher plants, tropical seagrasses contain phenolic acids known as As microbial degradation progresses, allelochemicals. These coMpounds are known the nitrogen content will increase through to deter herb ivory in many pl ant groups two processes: oxidation of the remaining (Feeny 1976). Six phenolic acids have nitrogen-poor seagrass compounds and syn been detected in the leaves, roots, and thesis of protein-rich microbial cells rhizomes of turtle grass, manatee grass, (typically 30% to 50% protein) (Thayer and shoal grass (Zapata and l"'lcMil 1an et al. 1977; Knauer and Ayers 1977). The 1979). In laboratory studies two of these accumulation of microbial debris, such as compounds, ferulic acid and p-coumaric the chitin-containing hyphal walls of fun acid, when present at concentrations found gi, may al so contribute to the increased in fresh leaves, inhibited the feedinq nitrogen content (Suberkropp et al. 1976; activities of detritivorous aMphipods and Thayer et al • 1977). Nitrogen for this snails grazing on l• alterniflora detri process is provided by adsorption of inor tus. During decompositon the concentra ganic and organic nitrogen from the sur tions of these compounds decreased to rounding medium, and fixation of atmos levels that did not significantly inhibit pheric NL. For tropical seagrasses, in the feeding activities of the animals particular, there is an increase in ash {Valiela et al. 1979). content during decomposition because of deposition of carbonates during 111icrobial respiration and growth of encrusting algal Seagrass leaves May also contain com species, and organic carbon usually con pounds that inhibit the growth of microor tinues to decrease (Harrison and Mann ganisms; this in turn would decrease the 1975a; Knauer and Ayers 1977; · Thayer ·· usable ·· nu tr Hi ona l · value of the detritus . et al. 1977). Water soluble extracts of fresh or re cently detached Z. marina leaves inhibited Chel1}_ical Changes as Indicators of Food the growth of dlatoms, phytoflagellates, Value and bacteria (Harrison and Chan 1980). The inhibitory compounds are not found in Nitrogen content has long been con- older detrital leaves or ones that have sidered a good indicator of the food value been partially desiccated. 73 Release of Dissolved Organic Matter carbon than did the particulate carbon fraction (Robertson et al. 1982). Seagrasses release substantial DOC may also become available to con amounts of dissolved organic carbon (DOC) sumers through incorporation into particu during growth and decomposition. The DOC late aggregates. Microorganisms attached fraction is the most readily used fraction to particles will assimilate DOC from the of the seagrass organic matter for micro water column, incorporatin§ it into their organisms and contains much of the soluble cells or secreting it into the extracellu carbohydrates and proteins of the plants. lar materials associated with the parti It is quickly assimilated by microorgan cles (Paerl 1974, 1975). This microhially isms, and is available to consumers as mediated mechanism also makes seagrass DOC food in significant quantities only after available for consumers. this conversion to microbial biomass. Thus, the utn ization of seagrass DOC is In most marine systems the DOC pool functionally similar to detrital food webs contains 100 times more carbon than the based on the particulate fraction of sea particulate organic carbon pool (Parsons grass carbon. Both epiphytes and leaves et al. 1977; references therein). The of Zost~.rl, are capable of taking up label- cycling of DOC and its utilization in de 1 ed organic compounds {Smith and Penhal e trital food webs are complex. The highly 1980). labile nature of seagrass DOC suggests that it may play a significant role in Experiments designed to quantify the supporting secondary productivity. release of DOC from growing seagrasses have yielded a wide range of values. The Role of the Oetrital Food Web short-term release of recently synthesized photosynthate from blades of turtle grass The detrital food web theory repre was found to be 2% to 10%, using radio- sents our best understanding of how the 1abelled carbon (Wetzel and Penhal e 1979; major portion of seagrass organic carbon Brylinsky 1977). Losses to the water col contributes to secondary productivity. The umn from the entire community, including organic ~atter of fresh seagrasses is not belowground biomass and decomposing por commonly utilized by many animals hecause tions, may be much higher. Kirkman and of various factors, including their low Reid (1979) found that 50% of the annual concentrations of readily available nitro 1oss of organic carbon from the Pos idoni a gen, high concentrations of fiber, and the J!!ttr!lli seagrass coMmunity was in the presence of inhibitory compounds. The par form of DOC. ticulate and dissolved fractions of sea grass carbon seem to become potential food Refoase M DOC from detrital leaves for animals primarily after colonization may al so be substantial. In freshwater by microorganisms. Ouri ng decomposition macrophytes. leaching and autolysis of DOC the chemical nature of the detritus is lead to a rapid 50% loss of weight {Otsuki changed by two processes: loss of plant and Wetzel 1974). In laboratory experi compounds and synthesis of microbial pro ments dried turtle grass and manatee grass ducts. leaves released 13% and 20%, respectively, of their organic carbon content during The decomposer comr.iunity also has the leaching under sterile conditions {Robert enzymatic mechanisms and abi1 ity to assim son et al. 19£2). ilate nutrients from the surroundinq med iun, leading to the enrichment of the de tritus as a food source. As a result, the The carbon released as DOC is ex decomposer community represents a readily trc::-:e1y labfle and is rapfd-1y assimilated usable troµhic level between the produc by microorganisms {Otsuki and l,,/etze1 1974; ers and 1:1ost aniinal consumers. In this Brylinsky 1977), which leads to its immed food web, the consumers derive nutrition iate avai1abi1 ity as food for secondary largely from the microbial components of consumers. In 14-day laboratory incuba the .. detritus. This decomposer community tions, the DOC released by turtle grass is influenced by environmental conditions a~d manatee 9rass. leav~s supported 10 and biological interactions, including the t1mes more 1n1crob1al b1onass per unit feeding activities of consw11ers. 74 CHAPTER 7 INTERFACES WITH OTHER SYSTEMS 7.1 MANGROVE 7.2 CORAL REEF Mangroves and seagrass beds occur Coral reefs occur adjacent to exten close to one another within the estuaries sive turtle grass-dominated grass beds and coastal lagoons of south Florida along the full extent of the oceanic mar especially in the clear waters of th; gin of the Florida Keys. The 1'10St promi Florida Keys. While the importance of nent interaction involves nocturnally r1angrove habitat to the estuary has been active coral reef fishes of several farni- established (Odum and Heald 1972, 1975; 1ies feeding over grass beds at night. Odum et al. 1982), its faunal interactions Randall (1963) noted that grunts and snap with adjacent seagrass beds are poorly pers were so abundant on some isolated understood. patch reefs in the Florida. Keys that it was obvious that the reefs could not pro Like the seagrass meadow, the man vide food, nor possibly even shelter, for grove fringe represents shelter; fishes all of them. lonoley and Hildebrand and invertebrates congregate within the (1941) also noted "the dependence (for P:otection of mangrove prop roots. Game food) of pomadasyids and lutjanids on fish found in mangroves include tarpon areas adjacent to reefs in the Tortugas. (Megalo~ atlanticus). snook (Centro omus undecirnalis}. ladyfish (E)ops saurus , Typically, both juveniles and adults crev~lle jack (Caranx_~, gafftopsail form large heterotypic resting schools catf1 sh (Bagre mar mus), and jewfi sh (Ehrlich and Ehrlich 1973) over proMinent (E ine helus itajara) (Heald and Odum coral heads or find shelter in caves and 1970 . Undoubtedly, when mangroves and crevices of the reef (Figure 24). At dusk seagrass meadows are in proximity, these these fishes migrate (Ogden and Ehrlich fishes \tli 11 forage over grass. Grey 1977; MacFarland et al. 1979) into adja snapper (lutjanus gri seus), sheepshead cent seagrass beds and sand flats where Archosar us probatocephalus), spotted they feed on av a i1 ab 1 e invertebrates sea trout Cynosc ion nebulosus), and the (Randall 1967, 1968), returning to the red dru~ (Sciaenops ocellota) recruit into reef at dawn. Starck and Davis (1966) seagrass habitat initially, but with list species of the Holocentridae, lutjan growth move into the mangrove habitat for idae, and Pomadasyidae families as occur the next several years (Heald and Odum ring diurnally on Alligator Reef off Mate 1970). All of these fishes have been col cumbe Key in the Florida Keys, and feeding lected over grass. Little .work has been nocturnally in adjacent grass beds and done, however, to explore the possible sand flats: ·· As such, these fishes epito mize what Kikuchi and Peres (1977) defined interactions between Qangroves and sea as temporal visitors to the grass bed, grass beds. For a detailed review of the which serves as a feeding ground {Hobson mangrove ecosystems of south Florida see 1973). Starck (1968) discussed further Odum et al. (1982). 75 Figure 24. Grunt school over coral reef during daytime. At night these schools will disperse over seagrass beds and adjacent sand flats to feed. the fishes of Alligator Reef with brief distances as great as 2.7 km (1.7 mi) in notes on their ecology, while Davis (1967) the U.S. Virgin Islands (Ogden and Ehrlich described the pomadasyids found on this 1977). reef and their ecology. It is interesting to speculate on the little is known about the ecology of possible role that habitat partitioning these nocturnal coral reef fishes while on plays in reducing competition for food the feeding ground. These fishes poten over the feeding ground. Competition is tially can range far from their diurnal important in structuring other fish com resting sites. lutjanus griseus and munities, such as Centrachidae (Werner and Haernulon f1avolineatum range as far as Hall 1977), Embiotocidae (Hixon 1980) and 1. 6 km l'l ml} from Alligator Reef (Starck Scorpaenidae (Larson 1980). Starck and and Davis 1966). Haemulon plumeri and!!• Davis (1966) reported that 11 of 13 pom fl avol ineatum typically migrate di stances adasyids found in durnal resting schools of 300 m (984 ft) to greater than 1 km on Alligator Reef disperse at night to (0.6 mi) over the grass beds in Tague Bay, feed. The 1 ighter colored grunts (seven St. Croix (Og('fen and Ehrlich 1977; Ogaen species) move off the reef and generally and Zieman 1977). Tagged!!• plumeri were distribute themselves along a sand flat repeatedly captured on the same reef and grass bed back reef continuum. Snappers when transplanted exhibited a tendency to (lutjanidae) follow a similar pattern with home (Springer and McErlean 1962a). So~e !:_. ariseus and !:_. s~nagris moving into lf. plumeri and!!• flavolineatum success mi xe sand, grass an rubble back reef fully home to original patch reefs over habitat. The nocturnal distribution of 76 grunts over the grass beds of Tague Ray, current hypotheses, the structuring of St. Croix, is similar to those reported in coral reef fish comr1unities is probably the Florida Keys. The French grunt, largely controlled by their physical Haemulon flavolineatum, was most abundant requirements for living space. Sale over sparse grass or bare sand botto1n, (1978) speaks of a lottery for living while the v1hite grunt .t!_. plumeri was usu space among cora 1 reef fish communities ally observed in dense grass. Numbers of composed of groups of fishes with similar coral reef fishes {grunts and squirrel requirements ( the representatives on any fishes) feeding nocturnally over seagrass one particular reef being determined hy were positively correlated with a measure chance recruitment). Alternatively, Smith of habitat co111plexity. This correlation (1978) advocated the ordered view that implies organization of the fish assem recource-sharing adaptations determine blage while feeding {M.B. Robblee, in pre which species can live together. Resources paration). Lutjanids were not found in external to the reef influence the species significant numbers either on the reef or composition and abundances of at least in the grass beds. nocturnally feeding, supra-benthic species (grunts and snappers), and perhaps several These observations on the distribu of the holocentrids. tion of fishes over the feeding ground suggest that the nature and quality of It has been hypothesized that the grass bed and sand fl at habitat adjacent diel activity patterns exhibited by these to a coral reef may influence both the fishes contribute to the energy budget of composition and abundance of these noctur the coral reef. Billings and Munro (1974) nal fishes on a reef. Randall (1963) and Ogden and Zieman (1977) suggested, as stated that whenever well-developed reefs originally proposed by Johannes (personal 1 ie adjacent to flats and these flats are comriunication), that migrating pomadasyids not shared by many other nearby reefs, the may import significant quantities of grunts and snappers on the reef may be organic matter (feces) to the reef. expected to be abundant. Starck and Davis Thayer and Engel {in preparation) have {1966) and Robins (1971) also noted that also postulated a similar mechanism for it is understandable, given the require green turtles, whose contribution to reef ment of most pomadasyids and several nutrient budgets may al so be important. lutjanid species for back-reef forage These assertions are open to investiga area, that these fishes are a 1rnos t corn tion. pl etely absent from certain islands in the Caribbean which have fringing reefs with Temporary visitors from the coral only narrow shelf and very 1 irnited back reefs are not limited to fishes. The reef habitat. Conversely, grunts and urchin Diadema antillarum moves off patch snappers form resting schools over char reefs at night into the turtle grass acteristic coral heads, most commonly dominated grass bed immediately adjacent Acropora palamata and Porites porities in Tague B~y, St. Croix {Ogden et al. {Ehrlich and Ehrlich 1973; Ogden and 1973). The prominent halo feature asso Ehrlich 1977), which also influences their ciated with many patch reefs is attributed population size. Starck and Davis (1966) to the nocturnal feeding forays of these commented that these species are excluded longspine urchins. Of greater signifi- from many suitable forage areas by the cance, the spiny lobster (Panulirus absence of sheltered locations for diurnal argfs), is known to move onto offshore resting sites. When artificial reefs were ree s as adults in the Florida Keys, seek established in the Virgin Islands (Randall ing shelter in caves and crevices (Simmons 1963; Ogden, personal communication), 1980). Lobsters remain in their dens dur rapid colonization by juvenile grunts tng daylight; at or after sunset they move occurred, indicating the importance of onto adjacent grass beds to feed solitar shelter to these fishes near their poten ily, returning to the reef before dawn tial feeding grounds. (Hernkind et al. 1975). While farther from the reef, the spiny lobster ranges Much of the interpretation given over considerable distances, typically above is speculative, but in 1 ight of several hundred meters. 77 Use of adjacent grass and sand flats 7.4 EXPORT OF SEAGRASS by coral reef creatures is not strictly a nocturnal phenomenon, but seems to be the The most recently recognized function dominant pattern. Only large herbivores of seagrass beds is their ability to (e.g., Chelonia my~as, Scarus guacamaia) export large quantities of organic r,atter venture far into t e grass bed away from from the seagrass meadows for utilization the shelter of the reef. Mid-sized herbi at some distant location (Zieman et al. vores are apparently excluded by predators 1979; Wolff 1980). This exported material and feed only near the reef (Ogen and Zie is both a carhon and nitroqen source for man 1977). Randall (1965) reported parrot benthic, mid-water, and surface-feeding fishes (Scarus and S arisoma) and surgeon organisms at considerable distances from fishes (Acanthurus eeding on seagrasses the original source of its formation. The (Thalassia and manatee grass) closely abundance of drifting seagrass off the adjacent to patch reefs in the Virqin west Florida shelf is illustrated in Islands during the day. He attributed the Figure 25 (Zieman et al., in preparation). formation of halos around patch reefs in This material originates on the shallow St. John to this grazing. grass flats and is transported westward by the prevailing winds and tides. 7.3 CONTINENTAL SHELF leaves and fragments of turtle grass were collected by Menzies et al. (1967) Recently interest has been sparked in off the North Carolina coast in 3,160 r, estuarine-Continental Shelf interactions (10,368 ft) of water. Although the near (Darnell and Soniat 1979). The seaarass est source of turtle grass was probably meadow represents a highly productive, 1,000 km (625 mi) away, blades were found faunally rich habitat within south Fl or at densities up to 48 b1 a des per photo ida 's estuaries and coastal lagoons. Many graph. Roper and Brundage (1972) surveyed species are dependent on the seagrass bed the Virgin Islands basin photo9raphically and estuary. The pink shrimp Penaeus and found seaarass blades in most of so111e duorarum, the lobster Panulirus a~gus, 5,000 photographs taken at depths averag and the grey snapper lutjanus gr1seus ing 3,500 m (11,484 ft). Most were clearly may serve as examples of estuarine or recognizable as turtle grass or manatee lagoonal dependent fauna which at one life grass. Seagrasses were collected by trawl stage or another are found in seagrass ing in three Caribbean trenches and sea meadows. grass material was found in all the trenches sampled (Wolff 1976). Most of In south Florida, pink shrimp spawn the material collected was turtle qrass, in th~ vicinity of the Tortugas Bank, the and there was evidence of consumotfon bv pelagic larvae returning to the estuary deep-water organisms. Intere.stingly~, and perhaps the seagrass bed (Yokel some grass blades collected from 6,740 m 1975a). Eventually mature individuals re (22,113 ft) in the Cayman Trench showed turn to the spawning grounds. Similarly, the distinctive bite marks of parrot the lobster matures in inshore seaorass fish which are found only in shallovJ nursery grounds and as a sub-adult resides waters. on inshore reefs while continuing to feed within the grass bed at night. As sexually The priMary causes of detachment are mature adults, female lobsters move to grazing by herbivores, mortality on shal deep offshore reefs and spawn. The grey low banks caused by low tides, and wave snapper initially recruits into crass and induced severing of leaves that are becom 1-1ith growth moves into mangrove habitat ing senescent. In addition, r.ajor storms and eventually on to coral reefs and deep wi11 tear out livina leaves and rhizomes er shelf waters. Coming or going, these (Tho!'las et al. 196-1). 1,.Jhich mode of organi srns and others like them serve to detachment will be r1ost important in a trans fer energy from the sea grass bed to particular area will be largely deter offshore waters (see section 7.5), as has mined by physical conditions such as been shown by Fry (1981) for brown shrimp depth and wave exposure. Reduced sal in (P.- ---·--aztecus) in Texas waters. ity or extreMe te111perature variation wil 1 78 83° 82° 81° TOTAL SEAGRASS, G M.2 26° !)000 • .0009 .IOOO • .9000 I 26° .OOIO • .0090 > .9000 .OIOO • .0900 25'' 1"'.> ... 82° 81° Figure 25. Seagrass export from south Florida to the eastern Gulf of Mexico. In cer tain areas there is a substantial subsidy to the local carbon and nitrogen budgets by material exported from nearby seagrass beds. limit the herbivores responsible for de whole turtle grass blades during initial tachment (primarily parrotfish, urchins, grazing. and turtles). Because of this difference in re Freshly detached, healthy blades of sponse to grazing, Zieman et al. (1979) all species float better than senescent found that in Tague Bay 60% to 100% of the ones. Because of the difference in size daily production of manatee grass was de and shape of turtle grass and manatee tached and exported, whereas only 1% of grass blades, the effect of direct herbi turtle grass was exported, and this was vory on the two species is quite differ primarily as bedload. This also indicates ent. When a parrotfi sh or urchin bites a the relative successional status of these turtle grass bJade, it usuiilJy reITIO\IE!S spec:j e_s. Jµrtl EL gra.ss reta.Jns Jll()re 9f j ts only a portion of the blade, which remains 1eaves within the bed, which thus become attached. However, a manatee grass blade part of the litter layer, pronoting carbon is typically only 1 to 1.5 mm wide and and nitrogen recycling in the seagrass bed one bite severs it, allowing the upper and enhancing its performance as a climax portion to float away (Zieman et al. species. By contrast, relatively 1 ittle 1979). Similarly, green turtles sever of the leaf production of manatee grass is 79 retained in the bed to contribute to fur Many species of fishes and i nverte ther development of the little layer brates use south Florida grass beds as (Zieman 1981). nurseries. Approximately one-third of the species collected at Matecumbe Key, It is possible that in certain re including all grunts, snappers, file gions, exported seagrass could be an fishes, and parrotfishes, occurred only as important food source. Sediment collected young, indicating that the grass-dominated from the bottom of the Tongue of the Ocean shore area was a nursery ground (Springer that was not associated with turtle grass and Mc Erl ean 1962b). In Tampa Bay, 23 patches had carbon and nitrogen contents species of finfish, crab, and shrimp of of 0.66% and 0.07%, respectively (Wolff major importance in Gulf of Mexico fisher 1980). Turtle grass blade and rhizome ies were found as ir.11'1ature forms (Sykes samples had a carbon content of 20% and a and Finucane 1966). Comparatively little nitrogen content of 0.77%. is known concerning invertebrates other than those of com~ercial value. 7.5 NURSERY GROUNDS Shrime Grass beds serve as nursery grounds Pink shrimp (Penaeus duorarum) occupy where post larval stages of fishes and south Florida grass beds as Juveniles invertebrates concentrate and develop and (Tabb et al. 1962; Costello and Allen also as spawning grounds for adult breed 1966). Penaeus aztecus and P. brasilien ing populations of some species. To be of sis are alsopresent, but never as abun significance as a nursery, a habitat must dantly as the pink shrimp (Tabb and Man provide protection from predators, a sub ning 1961; Saloman et al. 1968; Bader and strate for attachment of sessile stages, Roessler 1971). Shrimp spawn on the Tor or a plentiful food source (Thayer et al. tugas grounds, probably throughout the 1978b). Seagrass habitats fulfill all of year (Tabb et al. 1962; Munro et al. these criteria with their high productiv 1968). Roessler and Rehrer (1971) found ity, surface areas. and blade densities, post1 arva1 pink shrimp entering the estu as well as a rich and varied fauna and aries of Everglades National Park in all flora. Seagrass provides abundant nursery months of the year. habitat and is often preferred, based on abundance and size data, over available Pink shrimp were distributed through alternatives. in the estuaries and coastal out Rookery Bay Sanctuary in southwestern lagoons, by many commercially or eco1ogi Florida, but were most abundant at sta ca11y important species (Yokel 1975a). tions with grass-covered bottoms (shoal grass and turtle grass), and within these The importance of grass bed habitat stations were 1:1ost abundant where benthic as a nursery has been historically demon vegetation was dense (Yokel 1975a). Pink strated and should not he minimized. Fol shrimp were also abundant in grass habitat lowing the decline of Zostera marina along at Marco Island and Fakahatchee Bay, also the east coast of the United States in the in southwestern Florida (Yokel 1975b). early 1930 1 s, the sea brant, a variety of Postlarval pink shrimp with carapace goose dependent on eel grass for food (as length less than 3 mm were taken only at are many waterfowl; McRoy and Helffrich stations where shoal qrass and turtle 1980), was reduced in numbers to one-fifth grass were present in Rookery Bay Sanc its former levels (Moffitt and Cottaf'1 tuary, while other stations without grass 1941}. Pronounced decreases in abundance always had larger mean sizes. These ob of bay scallops (~_~cten irradians} servations are in accordance with Hilde were al so noted following the disappear brand {1955} and WilJiams (1965), who ance of eelgrass (Stauffer 1937; Dreyer noted that very small pink shrimp prefer and Castle 1941; Marshall 19t.7). The grassy areas and with increasing size are post-veliger larval stage of the scallop found in deeper water. In terris of the depends on eel grass to provide an above functioning of the grass bed as a nursery sediment surf a cf; for attachment. Di srup ground, it is interesting to speculate tion of eelgrass beds resulted in lowered whether this distributional pattern repre numbers of bay scallops (Thayer and Stuart sents a preference on the part of pink 1974). shrimp postlarvae for grass bed habitat 80 (associated characteristics) or is the while still returning the larvae to south result of differential mortality within Florida waters (Menzies and Kerrigan the estuary. 1980). It has also been sug9ested by Sims and Ingle (1966) that larvae recruited to ~iny Lobster south Florida nursery areas 1nay have been spawned in locations south of the Yucatan Juvenile spiny lobsters (Panulirus Channel, perhaps as distant as the Leser ar~us) are commonly found in nearshore Antilles or Brazil, and deposited ready seagrass nursery areas of Biscayne Bay, for settlement by oceanic currents in Florida (Eldred et al. 1972); the Carib south Florida waters. Ongoing studies of bean (01 sen et al. 1975; Peacock 1974); protein variation as a reflection of gene and Brazil (Moura and Costa 1966; Costa tic variation hetween adult populations et al. 1969). In south Florida these and puerili postlarvae are designed to inshore nursery areas are largely 1 imited determine if Florida spiny lobsters origi to clear, near-normal oceanic salinity nate within Florida's waters or are re waters of the outer margin of Florida Bay, cruited fron adult population centers the Florida reef tract, and the coastal e 1 sewhere (Menzies and Kerrigan 1973, lagoons. Tabb and Manning (1961) noted 1979, 1980). that the spiny lobster is rare on the muddy bot to;ns in northern Florida Bay. Phyllosomes that survive their plank tonic existence recruit into the nurser_y Residence time in shallow grassy areas as puerulus lobsters (postlarvae) areas is estimated at about 9 to 12 months that resemble adults in forr,, but are (Eldred et dl. 1972; Costa et al. 1969) transparent. The postl arvae swirP toward after which time the small lobsters (cara shore at night and burrow in the bottom by pace length typically less than 60 mm) day until they reach inshore seagrass nur take up residence on small shallow water series, where they gradually becor1e pig patch reefs. On the reefs, the lobsters mented (Johnson 1974; Serfl i no and Ford live gregariously during the day while 1975; Simmons 1980). Recruitment takes foraging at night over adjacent grass and place throughout the year in south Florida sand flats. With maturity (1.5 to 2.0 with peak influxes usually between Febru years, Peacock 1974; up to 3 years in ary and June and between Septeriber and Florida, Simmons 1980) mating occurs and December (Eldred et al. 1972; Witham females r:,igrate to deeper offshore reefs et al. 1968; Sweat 1968). This pattern to release larvae (Little 1977; Cooper may be less pronounced in the lower Fl or et al. 1975) and then return. Reproduc i da Keys where high summer influxes have tive activity occurs throughoL1t the year also been noted (Little 1977). A summer in Florida waters, but is concentrated peak in abundance was a1 so noted in the during March through July (Menzies and Less Antilles (Peacock 1974). Greatest Kerrigan 1980). monthly recruitment takes place between new and first quarter moon {Little 1977}. Theories differ about where the lar vae which recruit into south Florida There is some evidence to suggest inshore nurseries originate. The question that puerul i first settle temporarily is of great importance to the manager:1ent above the bottom on al gal mats, r1angrove of this fishery. Once released alona prop roots, or on floating algal rafts Florida's offshore reefs, the larvae (Smith et a1. 1950; Lewis et al. 1952; ( phyll osomes) drift with the current dur Witham et al. 1968; Sweat 1968; Little ing a planktonic stage of undetermined 1977). Peacock (1974), working in Antiqua length; estimates range from 3 months to 1 and Barbados, noted that no puerul i were year (Simons 1980). ControHed verHc-al collected fro111 within the grass hed in movements in the water column may allow the lagoon where juveniles were present, the larvae to remain in the area of hatch but were co 11 ected corirnon l y from the ing via eddies, layered countercurrents prop roots of r:iangroves 1 i ni ng its en or other localized irregularities in the trance. After the puerulus molts, the movements of the water (Simmons 1980). Al body of the young lobster is heavily pig ternatively, larger scale countercurrents mented. At this ti111e it assumes a derier and gyres may allow for larval development sal behavior in the nursery (Eldred et al. 81 1972). Similar habitat use by juvenile P. and Phi tewa ter Bays and then 1:1ove into the ~ has been reported in Cuba (Buesa ~anqrove habitat for the next several 1%9). the Virgin Islands (Olsen et al. years (Heald and Odum 1970). 1975), the lesser Antilles (Peacock 1974), and in Brazil (Costa et al. 1969). Degra The pinfish (Lagodon rhomboides) was dation of this habitat would certainly the most abundant fish collected and was threaten lobster productivity (Little taken throughout the year in the turtle 1977). grass beds of Florida Ray (Tabb et al. 1962), as is generally true for southwest ern Florida (Weinstein and Heck 1979; Weinstein et al. 1977; Yokel 1975a, In south Florida it appears that con 1975b). Yokel (1975a) in Rookery Bay and tinental fish faunas and insular fish Yokel (1975b) in Fakahatchee Bay, both of faunas mix. Continental species require the Ten Thousand Isl and reg ion of south changing environments, seasonally shifting Florida, noted a strong preference of estuarine conditions, high turbidities, juvenile pinfish for vegetated areas. The and muddy bottocis (Robins 1971). South sheepshead (Archosargus _E!Qhatocephalus), western Florida and northern Florida Bay another sparid, initiall.Y recruit's into typify these conditions and their fish grass beds hut quickly moves into mangrove asse,:iblages ore characterized by t7any hahitats (Heald and Odum 1970) or rocks sciaenid species (drums) and the prominent and pilings (Hildebrand and Cable 1938). scarid, Lato~on rhomboides, which is also the most a undantrTsfi'Tn""clearwater sea The snappers, ~_us gri seus and .h_. grass areas of Biscayne Bay and Card Sound synagri s, are cor:1mon fnroughout south (I. Brook, personal communication). Insu Florida. ,J1Jvenile gray snapper {L. aris lar species require clear water, buffered eus), are often the most common snapperin environmtmtal conditions, and bottorn sedi- lforthern Florida and Whitewater 8ays, 1nents composed largely of calcium carbon including freshwater regions (Tabb and ate (Robins 1971}. These conditions are Manning 1961). The gray snapper is con found within the grass beds of the F1 orida sidered to recruit into grass beds and Keys and outer 11arrins of Florida Bay. then after several weeks riove into man Representative species of fami1 ies Poria grove habitat (Heald and Odur:1 1970). The dasyidaP., Lutjanidae, and Scaridae are lane snapper (.h_. synagris), never reaches rri 83 CHAPTER 8 HUMAN IMPACTS AND APPLIED ECOLOGY Si nee the days 1-1hen Henry Fl ag l er I s acres of adjacent habitats. The impact of railway first exposed the lush subtropical dredging can be long-lasting since such environment of south Florida to an influx disturbance creates sediment conditions of peop 1e from outside the reg ion, the unsuitable for seagrass recolonization for area has been subjected to great change at a protracted period (Zieman 1975c). the hands of man. Through the 1950' s, boom1ng development precipitated the Of the Gulf Coast States, Florida destruction of many acres of submerged ranks third, behind Texas and Louisiana, land.s as demands for industrial, residen in amount of submerged land that has been tial, and recreational uses in this unique filled by dredge spoil (9,520 ha or 23,524 part of the Nation increased. While sea acres). In Texas and Louisiana, however, grass beds generally have experienced less most of the spoil created came from d1rect damage than have the mangrove dredged navigation channels, while in shorel foes, sea grasses have not been Florida this accounts for less than 5% of tota11y spared the impact of development. the State total. Not surprisingly, the Environmental agencies receive permit majority of filling of land in Florida, requests regularly, many of which would about 7,500 ha {18,525 acres), has been to directly or indirectly impact seagrass create land for residential and industrial beds. Because of the concern for these development (Figure 26). In addition to bio1ogica11y important habitats several the direct effect of burial, secondary articles have been pub1 ished which docu effects from turbidity may have serious ment their importance and man I s impact consequences by restricting nearby produc (e.g. Thayer et al. 1975b; Zieman 1975b, tivity, choking filter feeders by exces 1S75c, 1976; Phillips 1973; Ferguson sive suspended matter, and depleting oxy et al. 1980). gen because of rapid utilization of sus pended organic matter. The dredg~d sedi ments are unconsolidated and readily sus 1 DHEOGING AND FILLING pended. Thus a spoil bank can serve as a source of excess suspended matter for a Probohly the greatest amount of protracted time after deposition. Zieman destruction of seagrasses in south Flor (1975b) noted that in the Caribhean ida has resu1 ted from dredging practices. dredged areas were not recolonized by tur Whether the objective is landfill for tle grass for many years after operations causeway and waterfront property con ceased. Working in estuaries near Tampa structf on, or deepening of water's for and Tarpon Springs, Godcharles (1971) channels and canals, dredging operations found no recovery of either turtle grass typically invo1 ve the burial of portions or manatee grass in areas where commercial of an estuary with materials from nearby hydraulic cl arn dredges had severed rhi locations. Such projects therefore can zomes or uprooted the pl ants, al though at involve the direct destruction of not one station recolonization of shoal grass only the construction site, hut al so 11any was observed. 84 Figure 26. Housing development in south Florida • Portions of this development were built over a dredged and filled seagrass bed. This has historically been the most common form of man-induced disturbance to submerged seagrass meadows. Van Eepoel and Grigg (1970) found Reduced light penetration was obser that a decrease in the distribution and ved in grassflats adjacent to the dredging abundance of seagrasses in Lindbergh Bay, site of an intracoastal waterway in Red St. Thomas, U.S. Virgin Islands, was re fish Bay, Texas (Odum 1963). Odum sug lated to turbidity caused by dredging. In gested that subsequent decreases in pro 1968 lush growths of turtle grass had been ductivity of turtle grass reflected the recorded at depths up to 10 m (33 ft), but stress caused by suspended silts. Growth by 1971 this species was restricted to increased the following year and Odum sparse patches usually occurring in water attributed this to nutrients released from 2.5 m (8 ft) deep or less. A similar pat the dredge material. While dredging tern of decline was observed by Grigg altered the 38-m {125-ft) long channel and et al. (1971) in Brewers Bay, St. Thomas. a 400 m (1300 ft) zone of spoil island and In Christiansted Harbor, St. Croix, U.S. adjacent beds, no permanent damage occur Virgin Islands, removal of material for red to the seagrasses beyond this region. dredging of a ship channel combined with 1 andfi11 projects increased the harbor ts · Studies of Boca. Ciega Bay, Florida, volume by 14% from 1962 to 1971. Silta reveal the l ong-tem impact of dredging tion in areas adjacent to the channel activities. Between 1950 and 1968 an caused extensive suffocation; and where estimated 1,400 ha {3,458 acres) of the deeper water resulted, sediment and light bay were filled during projects involving conditions became unsuitable for seagrass the construction of causeways and the growth. creation of new waterfront homesites. 85 Taylor and Saloman (1968) contrasted the roots, a moderate anount of enrichment undisturbed areas of the bay, where 1uxu may actually enhance productivity, under ri ant grass grew in sediments averaging certain conditions where waters are we11- 94% sand and shel 1, with the bottom of mixed, as observed by this author in the dredge canals, where unvegetated sediments rich growt~ of turtle grass and associated averaged 92% silt and clay. While several epiphytes in the vicinity (within 1 km or studies of Boca Ciega Ray collectively 0.6 mi) of Miami's Virginia Key se11age described nearly 700 species of plants and plant. This discharge is on the side of animals occurring there, Tay1 or and Salo the key open to the ocean. In the imme man ( 1968) found only 20'% of those same diate area where these wastes are dis species in the canals. Most of those were charged, however, water quality is so fish that are highly motile and thus not reduced that seagrasses cannot grow. Stim restricted to the canals during extreme ulation of excess epiphytic production may conditions. Interestingly, while species adversely affect the seagrasses by persis numbers \/Jere higher in undisturbed areas, tent 1 ight reduction. Often the effects 30% more fish were found in the can a1 s, of sewage discharge in such areas are com the most abundant of which were the bay pounded by turbidity from dredging. In anchovy, the Cuban anchovy, and ttie scaled Christiansted Harbor, St. Croix, where sardine. The authors noted that in the turtle grass beds were subjected to both few years since the initial disturbance, forms of pollution, the seagrasses decl in colonization was negligible at the bottom ed and were replaced by the green al 9a, of the canals and concluded that the sedi Enteromoi:.eb.a. In a 17-year period, the ments there were unsuitable for most of grassbeds 1r1 the emba.y111ent were reduced by the bay's benthic invertebrates. Light 66% (Dong et a1. 1972). transmission values were highest in the open bay away from landfills, lowest near Phytoplankton productivity increased the fi1 Ied areas t and increased sorttewha t in Hillsborough Bay, near Tampa because of 1n th1? quiescent waters of the canals. nutrient enrichment for domestic sewaqe Because of the depth of the canals, how and phosphate mining discharges (Taylor ever, 1 ight at the bottom was insufficient et al. 1973). Phytop1 ankton blooms con for seagrass growth. Taylor and Saloman tributed to the problem of turbidity, (1968), using conservative and incomplete which was increased to such a level that fipures, e~tt~ated that fill operations in sea grasses persisted only in sma11 sparse th11 bay resulted in an annual 1oss of 1. 4 patches. The only important r:1acrophyte 11 ion do 11 ars for fisheries and recrea found in the bay was the red a 1qa, Grae i1 - t ton. laria. Soft sediments in combi11atiMwrffi low oxygen levels 1 imited diversity and if seagrasses are on1y lightly abundance of benthic invertebrates. covered and the rhizome systeE1 is not changed, regrowth through the sed imcnt is Few seagrasses grow in waters of sorneti111es possible. Thorhaug et al. Biscayne Ray that were po 11 uted by sewage (1973) found that construction of a canal discharge in 1956 (McNulty 1970). Only in Card Sound temporarily covered turtle shoal grass and Ha1ophi1a grew sporadi s in M area of 2 to 3 ha ( 5 to 7 cally in small patches within l km (C.6 acres) with up to. 10 cm ( 4 inches) of mi) of the out fa 11. Post-abatement stud sedir~ent, killing the leaves, hut not the tes in 1960 showed seagrasses in the area rhizome system. Regrov,th occurred when had actually declined, probably because of the dredging operations ceased and cur the persistent resuspension of dredge rents carried the sediment away. materials resulting from the construction of a causeway. 8. 2 EUTROPH ICAT ION ANO SEWAGE Physiological studies reveal that seagrasses are not only affected by low Seagrass comr1unities are sensitive to levels of light, but also suffer when dis additions of nutrients from sewage out solved oxygen levels are persistently low, falls or industrial wastes. Because a situation encountered where sewage addi seagrasses have the ability to take up tions cause increased microbial respira nutrients through the 1eaves as wen as tion. Hammer (1968a) compared the effects 86 of anaerobiosis on photosynthetic rates of refined oils were evaluated for six spe turtle grass and Halo~hila deci_Q_iens. cies of estuarine crustacea and fishes \4hi1 e photosynthesis v1as epress~in both from Galveston Bay, Texas (Anderson et al. species, Halophila did not recover after a 1974). The refined oils were consist 24-hour exposure, whereas the recovery of ently more toxic than the crude oils, and turtle grass was complete, possibly be the three invertebrate species stu 88 reached 35° to 40°C (95° to 104°F). had increased to 40 ha (99 acres) with a Planktonic species are probably less zone of lesser damage extending to include affected by high temperatures than are about 120 ha (297 acres). In 1971 the sessile populations since larvae can effluents were further diluted by using readily be imported from unaffected areas. greater volumes of ambient-temperature bay waters. The net effect, however, was to Time of exposure is critical in expand the zone of thermal stress. One assessing the effect of thermal stress. station 1,372 m (4500 ft) off the canal Many organisms tolerate extreme short-term had temperatures of 32.2°C (90°F) only 2% temperature change, but do not survive of the tirie in July 1970, but this in chronic exposure to smaller elevation in creased to 78% of the time in July 1971 temperature. For seagrasses that have (Purkerson 1973). buried rhizome systems, the poor thermal conductivity of the sediments effectively Temperatures of 4°C or more above serves as a buffer against short-term ambient killed nearly all fauna and flora temperature increases. As a result, the present (Roessler and Zieman 1969). A seagrasses tend to be more resistant to rise of 3°C above ambient damaged algae; periodic acute temperature increase than species numbers and diversity were de the algae. Continued heating, however, creased. The optimum temperature range can raise the sediment temperature to for maximal species diversity and numbers levels lethal to plants (Zieman and Wood of individuals was between 26° and 30°C 1975). The animal components of the sea (79° and 86°F) (Roessler 1971). Tempera grass systems show the same ranges of tures between 30° and 34°C (86° and 93°F) thermal tolerances as the plants. Sessile excluded 50% of the invertebrates and forms are more affected as they are unable fishes, and temperatures between 35° and to escape either short-term acute effects 37°C (95° and 99°F) excluded 75%. or long-tenn chronic stresses. The effects recorded above resulted The main source of man-induced ther from operation of two conventional power mal stress in tropical estuaries probably generators which produced about 12 m3/sec has been the use of natural waters in of cooling water heated about 5°C (41°F). cooling systems of power plants. Dariage Using this cooling system, the full plant, to the communities involved has been which was two conventional and two nuclear reported at various study sites. In Guam generators, would produce 40 m3/sec of characteristic fish and invertebrates of water heated 6° to 8°C above ambient. The the reef fl at comriuni ty disappeared when plant had begun operations in spring 1967 heated effluents were discharged in the with a single conventional unit, and a area (Jones and Randall 1973). Virnstein year later a second unit was added. Stud (1977) found a decrease in density and ies at the site began in May 1968 when the diversity of benthic infauna in Tampa Bay area was still relatively undisturbed. in the vicinity of a power plant, where Except for a few hectares directly out temperatures of 34° to 37°C (93° to 99°F) from the effluent canal, the communities were recorded. in the vicinity were the same as in adja cent areas to the north and south. As The riost thorough investigations of temperatures increased throughout the sum thermal pollution in tropical or semitrop mer, however, damage to the benthic com ical environments have centered around the munity expanded rapidly. Miami Turkey Point power plant of Florida Power and Light (see review by Zieman and Because of the anticipated impact of Wood 1975). Zieman and Wood (1975) found the nuclear powered units, a new 9-r.m that turtle grass productivity decreased (5.6-mi) canal emptying to the south in as tempera tu res rose and showed the rcla Card Sound v1as dredged~ Fears that this t ions hip between the pattern of turtle body of water al so wou 1d be damaged per grass leaf death and the effluent plume, s is ted, and as a final solution to the reporting by late September 1968, that problem a network of 270 km (169 mi) of 14 ha (35 acres) of grass beds had been cooling canals 60 m {197 ft) wide was con destroyed. Purkerson (1973) estimated structed. Heated water was discharged that by the fall of 1968, the barren area into Card Sound until the completion of 89 the closed sys tern, however. Thorhaug seagrass beds. The eastern regions of et a1. {1973) found little evidence of Florida Bay were formerly characterized by damage to the biota of Card Sound, partly 1ow salinity, nuddy bays with sparse because effluent te111peratures there were growths of shoal grass. Fishing here was lower than those experienced in Biscayne often excellent as a variety of species Bay. and even before the thermal addi such as mul 1et and sea trout foraged in tions, tlie benthic community of the af the heterogenous bottom. One of the Main fected portion of Card Sound was rela stays of the fishing guides of this area tively depauperate compared to Biscayl'Je was the spectacular and consistent fishing Bay. for redfish. In recent years the guides have complained that this fish population The temperatures and salinities of has become reduced, and it is not worth the bays and lagoons of south Florida show the effort to bring clients to this area. much variation, and the fauna and flora In January 1979 this author took a trip must have adequate adaptive capacity to through this region and found that much of survive. Al though the heated brine ef the formerly mud and shoal grass bottom fluent from the Key West desalination that he had worked on 10 to 12 years prior plant caused marked reduction in the was now lush, productive turtle grass diversity in the vicinity of the outfall, beds. Where the waters were once muddy, nearly all beds of turtle grass were unaf they were now, according to the guide, fected (Chesher 1975). Shoal grass is the much clearer and shallower, but provided most euryha1 ine of the local seagrasses less sea trout and redfish. Why? The (McMillan and Moseley 1967). Turtle grass following hypothetical scenario is one and manatee qrass show a decrease in explanation. photosynthetic" rate as salinity drops below fu11 strength seawater. The season ln the late sixties the infamous al Hy of seagrasses in south Florida is C-111 or Aerojet-General canal was built lar~1ely explained by ternperature and in south Dade County, on which Aerojet salinity effects (Zieman 1974). The hoped to barge rocket motors to a test greatest decl ir,e in pl ant populations was site in south Dade. The contracts failed found when combinations of high tempera to materialize and the canal, although ture and low sa1 ini ty occurred simul tan completed, was left plugged and never eously. Tabb et al. (1S62) stated: "Most opened to the sea. Its effect, however, of the effects of man-made changes on was to intercept a large part of the over plant and animal populations in Florida land freshwater flow to the eastern Ever estuaries (and in many particulars in glades and ulti1nately to eastern Florida estuartes in adjacent regions of the Gulf flay. of Mexico and south Atlantic) are a result of a1 terations in salinity and turbidity. The interception of this water is H1gh saltntttes (30-40 ppt) favor the sur thought to have created pronounced changes vival of certain species like sea trout, in the salinity of eastern Florida Bay, red fish and other r:1arine fishes, and allowing for much greater saltwater pene therefore improve an9l ing for these spe tration. As the salinity increased, tur cies. On the other hand these higher tle grass, which had been held in check by in1ties reduce survival of the young lowered salinity, may have had a competi stages of such i111portant species as com tive advantage over shoal grass and mercial penaeid shrimp, menhaden, oysters increased its range. The thick anastomos and others. It seems clear that the ing rhizome mat of turtle qrass stabilized balance favors the low to moderate sal in sediments and may have made foraging dif ity situation over the high salinity. ficu1 t for species that normally grub Therefore, control in southern estuaries about in loose mud substrate. A1 so the should be 111 the direction of 111alntaTrilnci greater~sediment stabiiizi11g capacity of the supply of sufficient quantities of turtle grass may have caused rapid filling fresh water which would result in estua in an environment of high sediment supply rine salinities of 18 to 30 ppt." and low wave energy. Perhaps reduced water fl ow in the This scenario has not been proven; Everg1 ades has had unexpected ir1pac ts in thus it is hypothesis and not fact. It 90 points out, ho~~ever, the conceivability of ~1ost cdses of restoration in south how a manmade modification at some dis Florida involve turtle orass because of tance may have pronounced effects on the its value to the ecosyste~ and its spatial life history and abundance of organisms. dominance as well as its truculence at recolonizing a disturbed area. Recoloni It is interesting to note that the zation by shoal grass is not frequently a fishing guides regarded the lush, produc probleJ11. The plant has a surficial root tive turtle grass beds as a pest and much and rhizome system that spreads rapidly. desired the muddy, sparse shoal grass. It grows from remaininCJ fragments or from What this really illustrates is that quite seed and can recolonize an area in a short different habitats may be of vital impor time. tance to certain species at specific points in their life cycle. Those fea By conparison, turtle grass is much tures that make the turtle grass beds good slower. Fuss and Kelly (1969) found 10 nurseries and important to these same car months were required for turtle grass to nivores when they are juveniles restrict show new short shoot development. The their foraging ability as adults. It short shoots seem to be sensitive to envi should be noted in passing that while ronmental conditions al so. Kelly et al. lamenting the encroachment of turtle grass ( 1971) found that after 13 months 40% of into this area, the guides still hailed the trans pl ants back into a central area the shallow turtle grass beds to be super had initiated new rhizome growth, while ior bonefish habitat. only 15% to 18% of the pl ants showed new growth initiation when transplanted to disturbed sediments. Thorhaug (1974) 8.5 DISTURBANCE AND RECOLONIZATION reported success with regeneration from turtle grass seedlings, but unfortunately The rate at which a disturbed tropi seeding of turtle grass in quantity is a cal grass bed may recolonize is still sporadic event in south Florida. largely unknown. Fuss and Kelly (1969) found that at 1east 10 months were re If one accepts the concept of ecolog quired for a turtle grass rhizome to ical succession, there are two basic ways develop a new apex. to restore a mature community: (1) estab lish the pioneer species and allow succes The most common form of disturbance sion to take its course, and (2) create to seagrass beds in south Florida involves the environmental conditions necessary for cuts from boat propellers. Although it the survival and growth of the climax spe would seem that these relatively small cies. Van Breedveld (1975) noted that scale disturbances would heal rapidly, survival of seagrass trans pl ants was typically it takes 2 to 5 years to recolo greatly enhanced by using a "ball" of sed nize a turtle grass bed (Zieman (1976). iment, sirnil ar to techniques in the ter Although the scarred areas rapidly fill in restrial transplantation of garden pl ants. with sediment from the surrounding beds, He also noted that transplantation should the sediment is slightly coarser and has a be done when the pl ants are in a semi dor 1 ower pH and Eh. mant state (as in winter) to give the plants time to stabilize, again a logical In some regions, disturbances become outgrowth of terrestrial technique. nearly permanent features. Off the coast of Belize aerial photographs show features Al though numerous seagrass trans in the water that appear as strings of plantings have been performed in south beads. These are holes resulting from Fl or i da, the recent study by Lewis et a 1 • seismic detonation; some have persiS-ted ( 1981) is the first to use an major sea for over 17 years (J.C. Ogden, personal grass species in a comprehensive experi communication) with no recolonization. mental design that tests each of the tech This is not just due to problems associ niques previously described in the litera ated with explosions, as Zieman has obser ture. The study site was a 10-ha (25-acre) ved blast holes from bombs on a naval borrow pit on the southeast side of Craig bombing range in Puerto Rico where some Key in the central Florida Keys, which was recolonization occurred within 5 years. studied from February 1979 to February 91 1981. The pit was created over 30 years The transplants using short shoots of ago as a source of fill material for the the various species were not nearly as suc overseas highway. The dredged site is 1.3 cessful. Al though some of the treatments to 1.7 m (4.3 to 5.6 ft) deep and is cov showed short-tenn growth and survival, ered with fine calcareous sand and silt. none of the treatments using short shoots The surrounding area is 0.3 to 0.7 m (1 to survived in significant quantitites. Sim 2 ft) deep and is well vegetated, primar ilarly, the freshly collected seeds and ily with turtle grass, and portions of the seedlings of turtle grass showed no long borrow pit were gradually being revege term survival at the barren transplant tated. site, and showed only 4% survival when planted into an existing shoal grass bed. The experimental design used a total Seeds and seedlings that had been raised of 22 combinations of pl ant species and in the laboratory showed a modest survival transplantation techniques. Bare single of 29% when transplanted to the field, but short shoots and plugs of seagrass pl us even the survivors did not spread signifi sediment (22 x 22 x 10 cm) were used for cantly. turtle grass, manatee grass, and shoal grass. Seeds and seedlings of laboratory Al though several of the restoration raised and field-collected turtle grass techniques used by lewis et al. (1981) were planted, but seeds and seedlings of proved to be technologically feasible, the other species proved impossible to there are still major logistic and eco find in sufficient quantity. Short shoots nomic problems remaining. The plug tech were attached to smal 1 concrete anchors nique showed the highest survival rate, with rubber bands and pl aced in hand-dug but the cost estimates ranged from $27,000 holes l to 3 cm deep, which were then to 86,500/ha. Because of the large volume filled with sediment. Seeds and seedlings and weight of the plugs, this method were planted by hand without anchors after requires that large source beds be close it was determined that anchors were to the transplantation site. The removal detrimental to the survival of the seed- of large quantities of plugs can represent 1 ings. The large sediment plugs with a major source of disturbance for the seagrass were placed in similar sized source bed, as the plug holes are as slow holes made with another plugging device. to recolonize naturally as propeller cuts Plugs and short shoots of all species were and other similar disturbances. Despite planted with both 1- and 2-m spacing, the spreading recorded at the trans pl ant while the seeds and seedlings of turtle site, the source holes for the plugs did grass were planted using 0.3-, 1-, and 2-m not show any recolonization at the end of spacings. the 2-year period. If source naterial was required for a 1 arge seal e revegetation Of the 20 manipulations of species, project, the disturbance caused by the planting techniques, and spacings, only acquisition of the plugs could be a major three groups survived in significant num impact itself. For this reason lewis bers for the fu11 2 years: manatee grass et a1. (1981) suggested that this method plugs with 1-m spacing, and turtle grass be mainly used where there are source beds plugs with both 1- and 2-m spacin~J. Tur that are slated for destruction because of tle grass plugs showed the highest sur some devel oprnental activity. vival rate (90% to 98%), but did not expand much. increasing their coverage by The on1y other technioue that showed a factor of only 1.6 during the 2 years. any significant survival was the uti1 i Manatee grass spread rapidly from plugs zation of laboratory cultivated seeds under the prevailing conditions and had anct seedlings. This method was prohibi increased itS-.area hv a factor of ll.4 in tively . expensive with costs estimated the 2-year period. -The initial planting at $182,900/ha, largely due to cultiva of shoal grass. however, died out com tion costs; survival was stil1 below pletely after only a few months, and a 30%. Seeds and seedlings are a 1so suit second planting was made with larger, more able only in areas where the water r,iotion robust plants from a different site. This is relatively quiescent, as their abi1- planting survived sufficiently to increase i ty to r-errta in rooted at this stage is its area by a factor of 3. 4 after 1 year. minimal. 92 Transplants of tropical seagrasses In the early 1930 1 s, Zostera marina, may ultimately be a useful restoration a widespread northern temperate seagrass technique to reclaim damaged areas, but at disappeared from a large part of its this time the results are not consistent range. In North America, it virtually van or dependable, and the costs seem prohibi ished from Newfoundland to North Carolina, tive for any effort other than an experi and in Europe from Norway and Denmark mental revegetation, especially when the south to Spain and Portugal. The outbreak relative survival of the plants is consid began on the open marine coasts and spread ered. Sufficient work has not been done to the estuarine regions. to indicate whether tropical pl ants are really more recalcitrant than temperate Many changes accompanied this distur ones. It is likely that continued re bance. Sandy beaches eroded and were re search will yield more successful and pl aced with rocky rubble. The protective cost-effective techniques. effects of the grass beds were removed. The fisheries changed, although slowly at first, as their detrital base disappeared. 8.6 THE LESSON OF THE WASTING DISEASE Noticeable improvement did not become widespread until after 1945 (Rasmussen The information overload that we are 1977), and full recovery required 30 to subjected to daily as members of modern 40 years. It should be emphasized that society has rendered us immune to many of this was a large-scale event. )n Denmark the predictions of doom, destruction, and alone over 6,300 km 2 (2,430mF) of eel catastrophe with which we are constantly grass beds disappeared (Rasmussen 1977). bombarded. On a global scale, marine By comparison, south Florida possesses scientists recently feared the destruction about 5,000 km 2 (1,930 mi 2 ) of submerged of a major portion of the reefs and atolls marine vegetation (Bittaker and Iverson, of the Paci fie by an unprecedented out in press). Originally the wasting disease break of the crown-of-thorns starfish was attributed to a parasite, Labyrithula, (Acanthaster planci). The outbreak spread but now it is felt that the cause was rapidly and the devastation was intense in likely a climatic temperature fluctuation the regions in which it occurred. Yet, (Rasmussen 1973). As man's role shifts within a few years Acanthaster populations from that of passive observer to one of declined. The enormous reef destruction responsibility for large-scale environ that was feared did not occur and recovery mental change, basic understanding of the commenced. fundamental processes of ecosystems is necessary to avoid his becoming the cause In south Florida in 1972-73 there of associated large-scale disturbance com appeared to be an outbreak of the isopod, parable to the wasting disease. Sphaeroma terebrans, which it was feared would devastate the Florida mangroves. This devastation never materialized, and 8.7 PRESENT, PAST, AND FUTURE it now appears that the episode repre sented a minor population excursion (see Increasingly, studies have shown the Odum et al. 1981 for complete treatment). importance of submerged vegetation to major commercial and forage organi srns These episodic events proved to be (Lindall and Saloman 1977; Thayer and short term and probably of 1 ittle long Us tach 1981; Peters et a 1 • 1979; Thayer range consequence, yet the oceans are not et al. 1978b). Peters et al. (1979) found nearly as immune to perturbations as many that in the Gulf States the value of the have cone to think. We witness climatic recreational salt water fish catch exceed changes having major effects and causing ed $168 mill ion in 1973,whJcb represents large-scale famine on land, but few think about 30% of the total U.S. recreational this can happen in the seemingly infinite fishery (Lindall and Sa10!".1an 1977). Of seas. However, one such catastrophic dis this, 59% of the organisms caught were turbance has occurred in the seas, and it dependent on wetlands at sorne stage of was in this century and induced by a their life cycle. Lindall and Salornan natural process. (1977) estimated an even higher dependency 93 with over 70% of gulf recreational fish corrnner-cial species--pi nk shrimp and eries of the reqion being estuarine lobster--already intense, will inevitahly dependent. • increase. The Rahar.iian waters, formerly open to U.S. lobsterrnen, are now closed The value of the estuarine regions to putting more pressure on the already important comrnercial fisheries is even depleted stocks. In the past about 12% nore striking. The Gulf of Mexico is the of the shrimp 1 anded on the Florida gulf leading region of the United States in coast was caught in Mexican waters. Re terms of both landings (35% of the U.S. cently the Mexican governr1ent announced total catch) and value (27% of U.S. total that the enabling treaty would not be fishery value), according to Lindall and renewed. These actions will put increas Sa1oman (1977), who also determined that ing pressure on domestic stocks. As this about 90% of the total Gulf of Mexico and is happening, development in the region is south Atlantic fishery catch is estuarine dramatically escalating. In the eyes of dependent. many, the main limitations to further development in the Florida Keys were fresh The pink shrimp fishery, largest in water availability and deteriorating the State of Florida, is centered around access highways. All of the bridges in the the Tortugas grounds where 75% of the Keys are now being rebuilt and a referen shrimp caught in Florida waters are taken. dum was recently passed to construct a. Kutkuhn (1966) estimated the annual con 36-inch water pipeline to replace the old tribution of the Tortugas grounds to be Navy 1 ine. The price of building lots 10% of the bltal gulf shrimp fishery, took a 30% to 50% jurnp the day after the which in 1979 was worth $378 million water referendum passed and in many areas (Thoripson 1981). The vast seagrass and had doubled 6 months after the passage. nangrove regions of south Florida are the nursery ground for this vitally important It is depressiniJ to read, "Today the co1111111:1rcial fishery. mackerel and kingfish are so depleted that they have almost ceased to be an issue In the United States, 98% of the com- with the professional fisherman," or "The 11\ercia1 catch of spiny lobsters coine from luscious crawfish, however, is now in a habitats -,ssoc1ated with the Florida Keys crucial stage in its career. largely gone (1411 l ia1:1s and Prochaska 1977; Prochaska from its more accessible haunt,;, it has and Cato 1980}. In terms of ex-vessel been preserved so far on the reef., •• Eco valu~, the spiny lobster fishery is second nomic pressure and growing deriand however, on1y to the pink shrimp in the State of have developed more intensive and success Flor'ida (Prochaska 1976). Labi sky et al. ful methods of catching them, and though a (19C0) reported that the high in lobster closed season has been put on them, in the landings. 11. 4 million 1b, vMs reached in open months uncalculable thousands are 1SJ72, and the rnaxi1:1urn ex-vessel value of shipped to market and they are rapidly Sl 4 million recorded in 1974. These disappearing. 11 Today we find 1ittle sur fi~JUr(:S include 1ohsters taken by Florida prise in these sta ternents, having cor1e to fish~n~en fr~, international waters which expect this sort of natural decline with encompass the Eahamian fishing grounds. increasing development. What is surprising Since 1975 the Bahamian fishing grounds is that this statement is taken from a have been closed to foreign fishing, plac chapter entitled, "Botany and Fishing; ing greater pressure on domestic stocks 1885-6," from the story of the founder of (Labisky et al. 1980). Coconut Grove, Ralph M. Monroe (Munroe and Gilpin 1930). There is an increasing need for more precise information to Ur5-t understand Today we see south Florida as a tan and then to manage these resources inte1- ta1 i zing portion of tne lush tropits, 1 igently. Al though south Florida has tucked awav on the far southeast coast been late in developing compared with of the United States. It is not insignif most other regions of the United States, icant in size~ and its natural produc the pressures are becoming overwheli:iing. tivity is enormous. Although the waters The fishery pressure on the two leading stil 1 abound with fish and shel 1fi sh, in 94 quantities that often amaze visitors, it consecutive years during 1972 and 1977, is useful to think back to how productive but significant change between 1972 and these waters must have been. 1975 (or between 1973 and 1976). In other words, south Biscayne Bay was signifi Their future productivity remains to cantly more turbid in 1977 than 1972, but be determined. Present productivity can a 2-year study would not have uncovered it be maintained, although that will not be (J. Tilmant, National Park Service, Home easy considering the ever-increasing stead, Florida; personal communication). developmental pressures. A catastrophic To properly manage the region, we must decline is certainly possible; merely understand how it functions. Decades ago maintaining the current economic and it would have been poss i b1 e to maintain development growth rates will provide that productivity just by preserving the area ef feet. This po int was we 11 made by one and restricting human influence. Now of the reviewers of this manuscript whose water management decisions a 100 miles comments I paraphrase here: Insidious away have profound changes on the fisher gradual change is the greatest enemy, ies. Enlightened multi-use management s i nee the observer is never aware of the will require a greater knowledge of the magnitude of change over time. A turbid complex ecological interactions than we ity study in Biscayne Bay showed no sig possess today. nificant differences in turbidity between Figure 27. Scallop on the surface of a shallow Halodule bed in Western Florida Bay. 95 REFERENCES Abbott, O.P., J.C. Ogden, and I.A. Abbott, Arber, A. 1920. Water plants: study of eds. 1974. Studies on the activity aquatic angiosperms. 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(Konig), with reference to tempera ture and salinity effects. Aquat. Yokel, B.J. 1975a. Rookery Bay land use Bot. 1:107-123. studies: environmental planning strategies for the deve 1opment of a Ziernan, J.C. 1975b. Cuantitative and mangrove shoreline, No. 5. Estuarine dynamic aspects of the ecology of biology. Conservation Foundation, turtle grass, Thalassia testudinurn. Washington, D.C. Pages 541-562 in L.E. Cronin, ed. Estuarine research. Vol. I. Academic Yokel, B.J. 1975b. A comparison of ani Press, New York. mal abundance and distribution in similar habitats in Rookery Bay, Zieman, J.C. 1975c. Tropical sea orass Marco Is 1and and Fahkaha tchee on the ecosystems and pollution. Chapter 4 southwest coast of Florida. Prelimi in E.J.F. Wood and R.E. Johannes, nary rep. from Rosentiel School of eas. Tropical marine pollution. Marine and Atmospheric Science to the Elsevier Oceanography Series 12. Deltona Corp., Mi arni, F1 a. Elsevier Publ. Co., New York. Yokel, B.J., E.S. 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Garland Young, D.K., M.A. Buzas, and M.W. Young. STMP Press, New York. 1976~ . Species densities of ff!acrohen thos associated with seagrass: a Zieman, J.C., and E.J.F. Hood. 1~75. Ef field experimental study of preda fects of thermal pollution on tropi tion. J. Mar. Res. 34(4):577-592. cal-type estuaries, with emphasis on Biscayne Bay, Florida. Chapter 5 .i!l Zapata, 0., and C. McMillan. 197c:i. Phe- E.• J. F. Wood and P.. E. Johannes, eds. nolic acids in seagrasses. t\quat. Tropical marine pollution. Elsevier Bot. 7:307-317. Oceanoqraphy series 12. 122 Zieman, J.C., G.ltJ. Thayer, M.B. Robblee, Zimmerman, R., R. Gibson, and J. Harring and R.T. Zieman. 1979. Production ton. 1979. Herbivory and detri tivory and export of seagrasses from a among 9ammavidean amphipods from a tropical bay. Pages 21-34 in R.J. Florida seagrass comriunity. Mar. Livingston, ed. Ecological processes Biol. 54:41-47. in coastal and marine systems. Marine Sciences 10. Plenum Press, New York. Zischke, J.A. 1977. A.n ecological guide to the shal 1ow-water marine communi Zieman, J.C., R. Orth, R.C. Phillips, G.W. ties of Pigeon Key, Florida. Pages Thayer, and A.. Thorhaug. In press. 23-30 in H.G. Multer, ed. Field quide The effects of oil on seagrass eco to some carbonate rock environments, systems. In J. Cairns and A. Buykema, Florida Keys and Western Bahamas. eds. Recovery and restoration of Kenda11/Hunt Publ .Co., Dubuque, marine ecosystems. Proceedings of a Iowa. conference at V.P.I. and S.U. Ann Arbor Press, Mich. 123 APPENDIX KEY TO FISH SURVEYS IN SOUTH FLORIDA Survey Location Reference number 1 North Biscayne Bay Roessler 1965 2 South Biscayne Bay Bader and Poessler 1971 3 Card Sound Brook 1975 4 Metecumbe Key Springer and McErlean 1962b 5 Porpoise Lake Hudson et al. 1970 6 Whitewater Bay Tabb and Manning 1961 7 Fa kaha tchee Bay Carter et al. 1973 8 Marco Island Weinsteain et al. 1971 9 Rookery Bay Yokel 1975a Hl Charlotte Harbor Wang and Raney 1971 r >l: rare p present C "' common a abundant List of fishes and their diets from collections in south Florida. Species Abundance by s~urvey nu1~ber Diet Source 1 2 3 4 5 6 7 8 9 10 Orectolobidae/nurse sharks Ginolymostoma cirratum r r p Fish: Acanthurus sp., clupeids, sea.rids Randall 1967; Cl ark nurse shark Mucdl sn., ,Jenkinsia sp., Cantherhines and von Schmidt 1965 ~; molluscs; cephalopods Carcharhinidae/requiem sharks Negeprion brevirostris p Fish: Ragre marinus, Chil~mycterus Clark and von Schmidt l emon sliark schoepfi, GaTeTclitFlys felis, Mugil sp. 1965; Randall 1967 Rhinobatos 1entiginosus; octopods Sphyrnidae/hammerhead sharks Sphyrna tiburo p Crabs: Callinectes sapidus, stomatopods; Bolke and Chaplin 1968 bonnethead shrimp; isopods; barnacles; bivalves; Clark and van schnidt cephalopods; fish 1965 ~ Pristidae/sawfishes Pristis pectinata p ~ltooth sawfish Rhinobatidae/guitarfishes Rhinobatus lentiginosus r atlantic guitarfish Torpedinidae/electric rays Narcine brasiliensis r r r --iesser electric ray Rajidae/skates Raja texana r Annelids; crustacea; fishes {eid 1954 rouiidel skate Oasyatidae/stingrays Urolophus jamaicensis r r yellow stingray Gymnura micrura r r Fish: Centropristis striata, molluscs: Peterson and Peterson srnoothbutterfly ray Solemya sp.; annelids; shrimp; small 1979 crustaceans list of fishes and their diets froo collections in south Florida. Species Abundance by survey number Diet Source 2 3 4 5 6 7 8 9 ID Dasyatidae/stingr~ys (continued) Dasya_tis americana p Fishes; sipunculids; crabs; polychaetes; Randall 1967 southern stjngray shrimp; hemichordates; stomatooods Dasyatis sabi nt r atl antic st mg ray El opidae/tarpons Elops ~l!.~ p Fishes: lagodon rhomboides; shrimp: Gunter 1945; Reid 1954; l adyfi sh Penaeus setiferus Austin and Austin 1971; ! Odumand Heald 1972; Megalops atlantica p Fishes: Allanetta harringtonensis, Randall 1967; Austin and tarpon Atherinomorus stipes Austin 1971 Albulidae/bonefishes "'N Albula ¥~1Res p Molluscs: Codakia costata; crabs; Bolke and Chaplin 1968 ----iione 1 s shrhp; fi~ --- Muraenidae/morays Gymnothorax nigrornarginatus r blackedge moray Ophichthidae/snake eels Myrophis punctatus r r r r Crabs Reid 1954; Springer and speckled worm eel Woodburn 1960 Oph-~~ 9 mesi r r r,mp ee1 Clupeidae/herrings Harengula pend~colae r r r r C Juveniles: veliqers, crab meqaloos, Carr and Ad~m~ 1071; scaled sar ,~ amphipods, mysids, copepods, isopods, Odumand Heald 1972 chironomid larvae Harengula humeralis r Fishes; polychaetes; shrimp larvae; Randall 1967 redear sardine plants: Enteromorpha sp., Thalassia, Syringodium; crab larvae Jenkinsia sp. r ~- lamprotaenia - copepods; shrimp larvae; Randall 1967 crab larvae; amphipods; fish eggs List of fishes and their diets from collections in south Florida. Species Abundance bt survey number Diet Source 1 2 3 4 5 6 7 8 9 10 Clupeidae/herrinps (continued) Brevoortia smithi r -yefTowti n ,nennaden Opisthonema oglinum r r r Veligers; copepods; detritus; polychaetes; Randall 1967; Carr atlantic thread herring shrimp; fishes; shrimp and crab larvae; and Adams 1973 mysids; tunicates; stomatopod larvae; eggs; gastropod larvae; other rare items Sardinella anchovia r r spanish sardine Engraulidae/anchbvies Anchoa cubana r Ostracods; copepods Springer and Woodburn --cuban anchbvy 1960 )> Anchoa 1ampr_otaen i a a p w bigeye an~ Anchoa mitch il 1 i r r p C r r C Less than 23 mmSL veligers, copepods, Carr and Adams 1973; anchovy eggs; 31 to 62 mmSL, amphipods, detritus, Reid 1954; ~ ostracods, zooplankton, mysids, harpacticoid copepods, small molluscs, chironomid larvae Anchoviell a perfasciata r fl at anchovy Anchoa hepsetus r r r C Veligers; copepods; mysids; zooea; fish; Carr and Adams 1973; striped anchovy eggs Springer and Woodburn 1960 Syr1odontidae/1 i zardfi shes Fishes: gobies, killifish, silver perch, Carr and Adams 1973; Synodus ~ r r r r p C r r r r pipefish, pigfish, juvenile seatrout, Reid 1954; Randall inshore lizardfish puffer; shrimp; plant detritus 1967 Ariidae/sea catfishes Bagre marinus r Callinectes sapidus; fishes Odumand Heald 1972 gafftopsa i1 catfish Arius felis p r r r Crabs; Rhithropanopeus harrisii, Odumand Heald 1972; -sea catfish amphipods; mysids; fishes; copepods; Reid 1954 shrimp List of fishes and their' diets from collections in south Florida. Species Abundance b_z'.surve'o/ number Diet Source l z 3 4 5 5 S 9 10 Batrachoididae/toadfishes Opsanus beta C a r r 0 C C C r f.rabs; penaeid and crangonid shrimp; Reid 1954; Odumand gulf toaafish Palaemonetes sp., Alpheus heterochaelis; Heald 1972 hermit crabs; molluscs; amphipods; fish; Lagodon rhomboides Porichth_z'.s .29rosissmus r atlantic midshipman Gobiesocidae/clingfishes Acyrt~ beryl 1 i na r r emerald cl ,ngfi sh Odumand Heald 1972 ~fITetfis-h--Gobiesox strumosus r p r Anphipods; isopods; chironomid larvae ,,, -I'> Antennaridae/frogfishes Histrio histrio r r ~assumfish Ogcocephalidae/batfishes Ogcocephalus cubifrons r Ogcocephalus nasutus r Pelecypods; gastropods; Nassarius vivex; Reid 1954 shortnose batfish Cerithium mucarium; Urosalphinx tampa~ns~; Bittium sp.; 14itrella sp.; t,mdulus modulus; Olivella mutica; Haminoea Ogcocephalus radiatus elegans; Anachris avara; .2.2J..lchaetes polka-dot batfish Gadidae/codfishes Urophys~ s f1 ori danus r Shrimps; fishes; Lagodon rhonboides; Reid 1954; Springer sout ernl-,ake amphipods; copepods; crabs; gastropods and Hoodburn 1960 Ophididae/cusk-eels and brotulas Ogilbia cayo ~ r r r key brotu 1a Ophidion holbrooki r bank cusk--eel List of fishes and their diets from collections in south Florida. Species Abundance by survey nuMber Diet Source 2 3 4 5 6 7 8 9 10 Ophididae/cusk-eul5 and brotulas (continued) Gunteri~hthys 1ongipenis r gold brotula Carapidae/pearlfishes Carapus bermudensis r pear1f1 sh Exocoetidae/flying fishes and ha1fbeaks Heriiramphys brasiliensis r Seagrasses: Thalassia, Syringodiurn, Randall 1967 ballyhoo fishes: Jenkinsia sp. Chridorus atherinoides p ------iiarcthead halfheak J> (J1 Hyporhamphus unfasci a tus P r r Juveniles zoopl ankton; crab rnegalops 1 arvae, Carr and Adams 1967 ha1fbeak veligers, copepods, insect remains.Sub-adults and adults epiphytic algae and detritus, seagrasses, occasional microcrustacea Belonidae/needlefishes Strof:.9.iLura nota ta r r ;:, r r Shrimp Reid 1954 redfin needlefish Strongylura ~imucu r r r Fishes: Anchoa parva, Jenkinsia sp.; Randall 1967; Reid timucu shrimp; copepods; insects 1954; Srpinger and Woodburn 1960 .IJ.1.2.~ crocod i1 us r Fishes: Acanthurus sp., Anchoa sp., Randall 1967 houndfi sh Cetengrau1is edentulus, "'Fiarerigula humeralis, Mugil sp.; shrimp Cypri nodont i dae/kil 1Hi shes fl ord"ichthys cal]J_j__~ C a r ,'mpliipods, copepods, po1ychaetes, filamen Brook 1975; Odumand go1dspotted killifish tous algae, diatoms, detritus, ostracods·, Heald 1972 chironomid larvae, isopods, nematodes Adinia xenica r Detritus, diatoms, filamentous algae, Odumand Heald 1972 ------aTiimondkillifish amphipods, insects, copepods Lucani ~ parva a r r p r r r Amphipods, musids, chironomid larvae, Odumand Heald 1972 rainwater killifish insects, molluscs, detritus, copepods, cumaceans List of fishes and their diets from collections in south Florida. Species Abundance by survey number Diet Source ij i--2 3 ~ 5 7 (J" 9 10 Cyprinodontidae/killifishes (continued) Fundulus heteroclitus r Srna11 crustaceans: amphipods, isopods, Peterson and Peterson mumm,chog tanaids, ostracods, copepods; polychaetes, 1979 detritus, algae, insects, crabs, fish, gastropods, eggs Cyprinodon varlegatus p r Detritus, filamentous green algae, Odumand Heald 1972 sheepshead minnow filamentous blue-green algae, diatoms, crustaceans, nematodes Rivulus marmoratus r ~1 us Poeciliidae/livebearers Poecil ia latiµ,inna p r Detritus; filamentous algae; diatoms Odumand Heald 1972; :,,, sai1fin molly Springer and Woodburn 0, 1960 Gambusia affinis r Amphipods; a1gae; hydracarina; Odumand Heald 1972 mosquitofi sh chironomid larvae; insects Heterandria formosa r Chironomid larvae; copepods; green Odumand Heald 1972 least ki11ifish algae; diatoms; cladocerans; insects Atherinidae/silversides All anetta harrinJtonens is C r p Copepods: Cory aeus sp., Labidocera Randall 1967; reef silvers, e scotti, Paraca 1anus crassirostris; Brook 1975 fish larvae; polychaete larvae Atherinomorus stipes a a Day. copepods; plants; amphipods; Brook 1975; hardhead silverside tanaids; insects; polychaetes. Randall 1967 nioht- amphipods; polychaetes; cumacea; copepods; isopods; ostra- cods; nebalids; insects; plants Menidia beryllina ~water s1lverside r r C Day less than 25 mmSL; veligers; Carr and Adams 1973; detritus; copepods. Greater than 30 mm; Odumand Heald 1972 copepods; veligers; insects; chironmid larvae; amphipods; hydracarina; algae; detritus; mysids night greater than 30 mm; mysids, amphipods, copepods, chironomid larvae List of fishes and their diets from collections in south Florida. Species Abundance by survet number Diet Source 1 2 3 4 5 6 7 8 9 10 Atherinidae/silvBrsides (continued) t:embras martinica r Copepods; insects (listed under Reid 1954 ~h silverside Membras martinica vagrans) Membrasvagrans r r Syngnathidae/pipefishes and seahorses Corythoichthys albirostris r r r whitenose pipefish Corythoichthy$ brachycephalus r crested pipefi sh Hippocampus hudsonius r );> ..... Hippocampus z.osterae r C r r p r r r r Shrimp; microcrustaceans Reid 1954 dwarf seahorse Hippocampus ~rectus r r r r r r l i ned sea horse Hippocampus reidi r longsnout seahorse Syngnathus -9.unck~ri r pugnose pJpef1sh Synanathus floridae C r r r p r r r Shrimp; amphipods; tanaids; isopods; Reid 1954; Brook 1975; usky pi pef1 sh copepods; nebalids Springer and Woodburn 1960 Syngnathus louisianae r r r r r r r r Copepods; amphipods; shrimp Reid 1954 chain pipefish ~us scovel l i r r C r r C a C C C Amphipods; copepods; tanaids; isopods; Rrook 1Q75; Peid 1954 gu pfpe~ shrimp; nebal ids Springer and Woodburn 1960 Micro~nathus crinifierus a r p r Copepods; microcrustaceans Reid 1954 fringed pipefis Centropomi dae/ snooks Centropomus undecimalis p Fishes: Eucinostomus sp., Mugil cephalus, Marshall 1958; Austin snook Lagodon rhomboides, Anchoa sp., Poecilia and Austin 1971; Odum latipinna, and Gambusia affinis; caridean and Heald 1972 and penaeid shrimp; crabs; crayfish List of fishes and their diets froo co11ections in south Florida. Species Diet Source Caran:;idae/jacks and pompanos Caranx ~os r P r Fishes: Prionotus scitu1us 0 ,rnda11 1967 ~valle jack Caranx 1 atus r Fishes: atherinids, Harengula sp., Randal 1 1967 --horse-eye· jack Myripristis Jacobus; pteropods; penaeid shrimp; isopods Caranx ruber p Fishes: larval Acanthurus sp., Randa11 1967 --iiar jack Acanthurus coerulus, Anchoa hepsetus, atherinlds, engraul ids,"Eiltomarcrodus ni.9_!j_cans, Har~ula_ clueola, Jenk_mSiil sp., Monocanthus sp., mu11id, Ophioblennius atl anticus_, l>omacentrus_pl anifr..Q!lS.., !'seudupeneus macu1atus, scarids, Scarus croicfil!5Jb ~..lli.Q!M. ;,,, Sparisoma viride; syngnathid;~. shrimps; '° penaeid, Tozeuma sp.; mysids; squids; stomatopods; gastropods; crabs Trachi notus fa1catus r C Juvenile fishes; anchovies, tidewater Carr and Adams 1973; permit silversides, crabs; Petrolisthes sp.; Randall 1967 gastropods; shrimp; mysids. adults gastropods; Astraea longiseina, Cerithium sp., Columiie!Tamercator1a, 01iva sp., Strombus ™• Tegu1a 1Tv'Tdomacu1ata, Turbo castanea; echinoids: Diadema antffiarllin." Echinometera sp.; pe1ecypods; Arca zebra, Glycymeris decussata, i'rachycaraium magnum~herm1t crabs: Pauristes ~. crabs: Albunea gibbes11, porcellanids. Trachinotus caro1inus r fl orida ptn•1pano 01igop1ites ~ p r r Mysids; shrimp; ectoparasites; copepods Carr and Adams 1973; 1eatherjacket Tabb and Manning 1961; Odumand Heald 1~72 Selene vomer r Shrimp; other crustaceans, small molluscs Peterson and Peterson ------iookdovm.. 1979 List of fishes and their diets from collections in south Florida. Species Abundance by survey number Diet Source 1 2 3 4 5 G 7 C 9 10 Lutjanidae/snappers (continued) Lutjanus jocu r Fishes: atherinids, Aulostomus maculatus, Randall 1967 dog snapper Clepticus parrae, Gymnothorax moringa, Haemulon sp., Haemulon plumei;-i, Haemulon auroTineatum, Holocanthus tricolor, Holo- centrus sp., Holocentrus rufus, JenkTnsia sp., Myricfithys sp., ophichthids, Opisthonema oglinum, Pseudupeneus maculatus, scarids, serranids, Sparisoma sp.:-Spmsoma viride, Xanthihthvs ringens; crabs: Carpiliuscorallinus, Cronius ruber, Pith~ 1herminieri, portunids, Portunus sp.; octopuses: ~ctopus vulgaris; lobsters; Panulirus argus, Panu irus guttatus, gastropods: Strombus ~; squid; fish eggs; scyllarid lobsters 2: Lutjanus synagris r p c r a c r Crabs: goneplacids, Leiolarnbrus nitidus, Randal 1 1967; Reid ,_. lane snapper portunids; stornatopods: Lysiosguilla .9Jk 1954; Springer and briuscula; fish; shrimp; mysids; copepods Hoodburn 1960 Ocyurus chrysurus r r Crabs: Callappa ocellata, Mithax sp., Mithax Randall 1967 ye11owtail snapper Mithax sculptus, Pitho aculeata; shrimp: caridean, penaeidean, S1cyonia laevigata, Trachycaris restirctus; fish: Jenkinsia sp.; siphonophores; pteropods; Calvolina sp.; copepods; cephalopods; mysids; tuni cates; ctenophores; gastropods: Strombus stornatopods: Gonodactylus oerstedii, ~;Pseudosquilla ciliata; scyllarid larvae; heteropods; plecypods; eggs; euphausids; gastropod larvae; amphipods;insects Lobotidae/tripletails ~letaflsLobotes surinamensis r Gerridae/mojarras Eucinostomus argenteus r c c r p r r r r c Less than 63 mm copepods, amphipods, mysids, Odumand Heald 1972; spotfin mojarra molluscs, detritus, chironomid larvae. 75 to Randall 1967; Brook 152 mm amphipods; ~yale sp., polychaetes; 1975 eunicids, crabs; ca appids, majids, rc1n_i_nids, shrimp; alpheids, Callianassa sp., tanaids, plecypods; Tellina sp., sipunculids, copepods, gastropods List of fishes and their diets from collections in south Florida. Species Abundance by survey number Diet Source 2 3 4 5 ~~1;--9 ,~.v Haemulon sci,~rus r c r p r Crabs: portunids, xanthids; pelecypods: Randall 1967; Davis -6Yuestri ped grunt Macomacerina, Pit1 Haemulon plumeri a r a a r Less than 40 mm copepods, mysids or Carr and Adams 1973; white gru,nt shrimp, detritus. 130-279 nm crabs: Randall 1967; Reid Mithrax sp.; polychaetes; echinoids: 1954; Davis 1967 Diadema antillarum, Eucidaris tribu loides; spatangoid, s1ounculid~ AspTdosiphon sp.; gastropods: Acmaea antil larum, Strombus qi gas; shrimps; alpheids, ophiuroids: Ophiothrix sp.; fishes: hemichordates; holothurians: Thyone pseudofusus; pelecypods: Cumingia antillarum, chitons: Ischnochi ton papi llosus, amphipods, tanaids List of fishes and their diets from collections in south Florida. Species Abundance by survey number Diet Source 1 2 3 4 5 6 7 8 9 10 Sparidae/porgies Archosargus probatocephalus r p r r r Less than 50 mm amphioods, cooepods, Springer and Wno~hur~ shcepshead polychaetes; larger than 50 mm molluscs, 1960; Odur:iand Heald barnacles, algae 1972 Archosargus rhomboides r Seagrass: Syrinqodium filiforme, Randall 1967; Austin sea bream Thalassia testudinum; algae; crabs; and Austin 1971 gastropods; eggs; pelecypods: Pinctada ladiata; polychaetes; amphipods Lagodon rhomboides C C r C p a a a a a less than 35 mm copepods; amphipods; mysids; Carr and Adams 1973; pinfish epiphytes; polychaetes; crabs. SL 36-65 mm Reid 1954; Brook 1975 epiphytes; shrimps; mysids; crabs; fish; amphipods; copepods; detritus. SL greater than 65 mm shrimp, fish; epiphytes; mysids; detritus; crabs; amphipods; copepods :,,. ,.... <.rt Calamus arctifrons r r Copepods; amphipods; musids; shri,nps; Reid 1954 grass porgy pelecypods; gastropods: Mitre11a sp., Bittium sp.; polychaetes Calamus calamus r Polychaetes; ophiuroids: Ophioderma sp., Randall 1967 saucereye porgy Ophiothrix sp.; pelecypods: Codakia orbicularis, Gouldia £lrrin.a, Pinna carnea; hermit crabs; crahs: majid, echinoids: Diadema antillarum, gastropods: Nassarius albus, Tegula sp., Teg~la fasciata; chitons; sipuncul1ds: Aspidosiphon sp. Sciaenidae/drums Menticirrhus focaliger r C minkf1sh Sciae oss ocel1ata p r r SL 31-46 mm mysids; polychaetes; amphipods; Springer and Woodburn re3 rum ; shrimp: Palaemonetes intermedius. SL 59- 1960; Odumand Heald 126 mm fisht Micropogon undulatus; shrimp; 1972; crabs~ insect larvae; mysids. SL 100- 500 mm shrimp: penaeids; crabs: xanthids, Rithropanopeus harrisii, portunids Bairdiella chrysura r r C a a C C SL 25-99 mm shrimp; copepods; amphipods; Reid 1954; Odun and silver perch mollusks; fishes, polychaetes. SL 100- Heald 1972; Springer 130 mm shrimp, amphipods, crabs, mollusks, and Woodburn 1960 fish: Anchoa mitchilli list of fishes and their diets from collections in south Florida. Species Abundance by surveo/ number Diet Source 1 2 3 4 S C 8 9 10 Sciaenidae/drums (continued) Cynoscion nehulosus p r C r r r Juveniles rysirls; cnir~nn~irt larvae; ~dum and Heald 1972; spotted seatrout carideans; fishes; Gobiosoma robustum. Springer and Woodburn, Greater than 150 mm shrimp: Penaeus 1960; Tabb 1966b; duorarum, fishes: Anchoa michTI1T;"°Mugi1 Stewart 1961 ce~halus, lagodon rhomboides, Eucinostomus ~• f. argenteus, Cypr1nodon variegatus, Gob1osomarobustus Equetus acuminatus r Shrimps: alpheids, pa1emonids, Periclimenes Randa11 1967 high-hat sp., Processa sp., penaeids, crabs: Petrolisthes galathinus; fishes; isopods; stomatopods; copepods; amphipods Bairdiella batebana r ....> blue croaker O'I Odontoscion dentex r Shrimp: larvae, alpheids, carideans, Randall 1967 reef croa~ penaeids; fishes: larvae; isopo Leiostomus xanthurus C a less than 40 mm copepods; ostracods; Springer and Woodburn chaetognaths. Greater than 40 mm 1960 ~ filamentous algae; desmids; forams; mysids; copepods; amphipods; ostra- cods; isopods; chaetognaths; insect larvae; pelecypods; gastropods; polychaetes Cynoscion arenarius r r r Fishes; shrimp: Palaemonetes sp.; Springer and Woodburn sand seatrout mysids; arnphipods; crab zoea 1960; Reid 1954 Micropogon undulatus r SL 30-107 mm copepods; mysids; Sori noer and Woorlh11rn atlantic croaker caridean shrimp; polychaetes; 1960 insect larvae; isopods; pelecypods Menticirrhus americanus r r C Polychaetes; crabs; ~ysids: Emerita Springer and Woodburn southern kingfish sp. 1960; Reid 1954 List of fishes and their diets fra,~ co1lections in south Florida. Species Abundance bj'. survey nunber Diet Source I 2 ~ 4 5 6 7 8 9 10 Mu11idae/goatfistes Pseu Chaetodip~erus faber r p r r r Sponges; zoantharians; Rhodactis Randall 1967 :,,, ...... --af1ant1c s1iadefish sacntithomae, Zoanthus sp., po1ychaetes; __, Sahe11astarte magnifica, tunicates; salps, gorgonians; Kiricea laxa, a1gae; gastropod eggs; holothur1ans; corals; Ocul ina seagrasses; Syringodium filiforme, heteropods;~ crab larvae; amphipoas; hyperi ids Chaetodon ti dae/but terf1 yf i shes Pornacanthus ar·cua t1Js r Sponges, tunicates; didemnid; algae; Randall 1967 -gray angelfish- cau1erpa spp., Penicillus pxrifonnis, Oictyota spp., zoanthar,ans; Zoanthus sp., Zoanthus sociatus, gorgon1ans; Pterogorgia sp., eggs, hydroids, 5ryozoans, seagrasses; Ruppia maritima Pomacentridae/danse 1fishes ?01nacentr1Js leucostictus r Algae, eggs; mu11uscs, pomacentrid, Randall 1967 beaugregory po1ychaetes, ;;shes, coe1enterate polyps, tunicates, crabs, amphipods, corals, foraminifera, hemit crabs, shrimps, copepods, gastropods; Arene tricarinata, Crassispira nigrescens Abudefduf saxatilis p Anthozoans, copepods, algae, tunicates; Randall 1967 sergeantriajor appendicularians, opisthobranchs; Tridachia crispata, fish eggs, fishes; Jenkinsia sp., shrimp larvae, barnacle appendages, ants, polychaetes, siphonophores List of fishes and their diets fro11 collections in south Florida. Species Abundance bt survex number Diet Source 1 2 3 4 5 6 7 8 9 10 Scarioae/parrotfishes Nichlsina usta r r r emerald"pirrotfish Scarus coeleitlnus r Algae; seagrass; Thalassia testudinun, mol- Randal1 1967 ~night parrotfi sh lusks; foraminifera; coral; echinoid; sponge Scarus ·croicensis r Algae Randall 1967 ~iped parrotfish Scarus quaca1naia r /l.lgae; seagrasses; Syrinoodjuni fil iforrne, Randall 1967 rainbow parrotfish Thalassia testuctinum 2,P.ari soma chrysopterum r Algae, seagrasses; Thalassia testudinum Randall 1967 redtail parrotfish Sparisoma radians r Seagrasses; Thalassia testundinum, algae Randall 1967 ;:': bucktooth parrotfish I.O S arisoma rubripinne a r C Algae, seagrasses; Thalassia testudinum Randall 1967 re in parrotfi sh Sparisoma viride r Algae, seagrasses; Thalassia testudinum Randall 1967 stoplight.parrotfish Mugilidae/mullets Mugil cepha1 us r p a Inorganic sediments, detritus, microalgae Odum1968 striped iw.iTlet cureina r r p C Pl ants, di atoms, L~ngbya majuscul a, Randall 1967 ~ w itemuTlet Rhizoclonium ripar1um, Thalass1a testudinum, Vaucheria sp. Mugi1 trichodon fantail mollet r Sphyraenidae/barracudas Sphyraena barracuda r r r p r Fishes: Ablennes hians, Acanthurus bahianus, Randall 1967; great barracuda Allanetta harringtonensis, atherinids, Can- de Sylva 1963 thigaster rostrata, carnagids, Caranx fusus, clupeids, Oecapterus sp., -Diodon sp., Echidna catenata, Haemulon sp., Harengula slupeola, Jenkinsia sp., Ocyurus ~. Sphyraena picu- dilla, Trachinocephalus ~. octopuses, scyllarid lobsters List of fishes and their diets from collections in south Florida. Species Abundance by survey number Diet Source l 2 3 4 5 6 7 3 '; lC Gobiidae/gobies Barbu] ifer ceuthoecus r bearded goby Microgobius rn◄crolepis r p banner goby Microgobius gulosus p C r r Detritus, copepods, epiphytic algae, Carr and Adams, 1973; clown goby amphipods, polychaetes, bivalves, Reid 1954; Springer and shrimp mysids Woodburn 1960; Odumand Heald 1972 Microgobius thalassinus r Small crustaceans; amphipods, Peterson and Peterson green goby other invertebrates 1979 ► C N Bathygobius curacao ..... notchtongue goby Bathy~obi us S:'fvrator r Caridean shrimp; Palaemonetes Odumand Heald 1972 fr111 frn go y interrnedius, chironornids, amphipods Gobionellus bolesoma r darter goby Gobione11us smaragdus r emerald goby Gobionellus shufelti r freshwater goby Gobionellus s™marturus r ~TaTT go y Gobiosoma robustum a r r p C C r r r /\mphipods, chironomid larvae, mysids, Odumand Heald 1972; code goby c'adocerans, ostracods, small molluscs, Reid 1954 algal filaments, detritus, cumaceans Gobiosoma ~ala r twoscale goby Gobiosoma macrodon r r tiger goby-- Gobiosoma longum r t~h" !H!:t5 i~tfons W4:th flo.r:kfa~ Specie:; Diet Source Gobl {.cont l11u:ed} ,. fil.~~toos algae; ,and ttuhl 1972 ostracoos; hnH; cope- '"" w••· -r-··-r-~ llarristi; snaih Algile ai-,d!oo:tdtlls, ostracoos; oi:,Muroids; Randall 1967 ie,:w,,c~ls;cope~s flc1H1ttwr1dae/s;irgi::"0Ml snes Randa11 1967; Cl~vijo 1974 Randal 1967; Clavijo 1974 r ,. 1967 1<11,v:laH1967 r R,mdaH 1967 !da<;>/S!!MuhiM List of fishes and their diets from collections in south Florida. Species Abundance by survel number Diet Source 1 2 3 4 5 6 7 8 9 10 Triglidae/searobins (continued) Prionotus scitulus r r r r r r r Small molluscs: Solemya sp., Bulla sp., Peterson and Peterson l eopardsearobin Olivia sp.; shrimp; crabs; fishes 1979 Prionotus triQ!JJ_ll_~ r r C r r Shrimp; crabs; Limulus polyphemus, Peterson and Peterson Uca sp.; fishes; amphipods; copepods; 1979 annelids; bivalves; echinoids Bothidae/lefteye flounder Bothus ocel l atus r r r Fishes; Coryphopterus sp.; crabs;~ Randall 1967 flounaer ocellata; majid; shrimps; amphfpods; ~d isaeid; stomatopods: Pseudosguilla ciliata Ancylo~setta guadrocel1 ata r ocel a ted flounder l> wN Citharichthys macrops r r spotted wiff Citharichthys spi1opterus r r r r Mysids; shrimp; crabs; copepods; Peterson and Peterson bay wiff arnphipods; fishes; annelids 1979; Austin and Austin 1971 Paralichthys albigutta r r r r r r Less than 45 mmSL: amphipods, small Reid 1954; Springer gulf flounder crustaceans. Greater than 45 mm: and Woodburn 1960 fishes: Orthopristis £!l!J'.sopterus, Lagodon rhomboides, Synodus foetens, Anchoa mitch111 i, crustaceans Syacium papi11osus r dusky flounder Etropus crossbtus r Polychaetes; copepods; shrimps; amphipods Reid 1954 fringed ffourider <:ol<>i,:lBe/sol es Trinectes inscriptus r r scrawled sole · Trinectes maculatus r r r ~nphipods; mysids; chironomid larvae; Odumand Heald 1972; hogchoker polychaetes; Neris pelagica; foraminifera Carr and Adams 1973 Achirus lineatus r r r p C C r r Polychaetes; amphipods; copepods Springer and Woodburn --nried sole 1960; Reid 1954 ffs~s their-, diets froo 1ectioii, iii scuth norilla. Species 0111:t Source r r r C r Rehl 1954; ilnd V.oodhurn Austin and Austin Ba1 ,ir,d - - . r r r r r Randan 1967; Reid arnl :,, "'""' C r r ' r r i'11'ij,hi ?Ol ychae tllS Reid 1954; Mans l976a r li'a,Hf,fl 1 0$tri!!ci ld11'!!'/!Xlxfhnes r r r List of fishes and their diets from collections in south Florida. Species Abundance by survel number Diet Source 1 2 3 4 5 6 7 8 9 1G ustraci idae/boxfilshes ( continued) Lactophrys trigonus r r C r Crabs: calappid, 8nerita sp., majids, Randall 1967 trunkfish Mithrax sp., Pitho sp., portunids, xanthids; pelecypods: Atrina seminuda, Codakia costata, Musculuslateral1s, Tellina ~achycardium muricatum, polychaetes: slyerid, pectinariid; echinoids: Lytechinus variegatus; algae; tunicates; Microcosmus exas~eratus; seagrasses: S~ringodium fili orme, Thalassia testu inum; holothurians; Holothuria aren1cola; asteroids; Oreaster ret1culata; gastropods: Acmaea pustulata, Anachis sparsa, Arene sp., Bulla sp., Haminoea elegans,Tassarius sp.; ::,,. ~Elasmopus N ophiuroids; Ophiodenna brevispinum, <.f1 Ophiothrix sp., eggs; chitons: Acanthochitona sp., hermit crabs, shrimp; alpheid Lactophrhs tri~ueter r r Polychaetes; onuphid, syllid, sipuncu- Randall 1967 smoot trun fish lids: Aspidosiphon spinosscutatus; crabs: majids, pinotherid, Upogebia sp.; shrimps: alpheids, carideans, gnathophyllid; tunicates: Asidia llign. Trididemnum savignii, spon es, hemichordates; gastropods: Ba1 cis intermedia, Nitidella laevigata, Trivia sp., Turbo castanea; hermit crabs; Paguristes sp.; Spiropagurus sp.; echinoids: ~ytechinus varieaatus; pelecypods; Tell1na sp., amph1po s; seagrasses: Halophila baillonis, Thalassia testudinum; alqae: Halimeda sp., chitons, eggs, ostracods Tetradontidae/puffers Sphoeroides nephalus r r p r C r r Crabs, Callinectes sapidus, pelecypods Reid 1954; Carr southern puffer and Adams1973 Ust 1'.lf flshes a!¾! their dfots frC!!1 conectfons in south Florida. Diet Source Tetradontidae/p1.1ffers ( cont im;e r Cr--ustacea; fto:rtunid 1cw,;;:.tQ ~vv~ , 9astropnds; Austin and Austin sp. 197 l :,;, ;i,; Ofodontidae/µon;upir:&fi r r r r r r Reid Sf)., "'"' -" and Woodh11rn sp,. t =.,.~,._%...,...... r Randal J 196 7 r r R,mdal l 1967 S0::!72 •!0l REPORT DOCUMENTATION 1_1,_REPORT NO. 2. 3. Roeipient•s Acces$ion No, PAGE J FWS/OBS-82/ 25 4 .. Title and Subtitle 5. R¢pOl"'t Oate THE ECOLOGY OF THE SEAGRASSES OF SOUTH FLORIDA: September 1982 A COMMUNITY PROFILE 6. 7. Aulhor(s) 8. Performing Organl.:ation Rept. No. J. C. Zieman 10. Project/Task/Work Unit No. Department of Environmental Sciences University of Virginia U. Controct(C) or Grant(G) No. Charlottesville, Virginia 22901 (Cl (G) ~.. ~""" ____ _ 13. Type of R~port & Period Cov.,.red Office of Biological Services New Orleans OCS Office Fi sh and Wildlife Service Bureau of Land Management .... U.S. Department of the Interior U.S. Department of the Interif,-«· --.Was.hin~trui ..... Jl... i: ...202JQ __ ...... llew. ... Qr..le.ans .., .. JJLlQJJQ_____ ,_1. ______15. Supplemenbry Note$ 16. Ab•t••et (Umlt: 200 word•l A detailed description is given of the community structure and ecosystem processes of the sea9rass ecosystems of south Florida. This description is based upon a compila tion of information from numerous published and unpublished sources. The material covered includes distribution, systematics, physiology, and growth of the plants, as well as succession and community development. The role of seagrass ecosystems in providing both food and shelter for juveniles as well as foraging grounds for larger organisms is treated in detail. Emphasis is given to the functional role of seagrass communities in the overall coastal marine system. The final section considers the impacts of human development on seagrass eco systems and their value to both man and the natural system. Because seagrass systems are fully submerged and less visually obv'ious, recognition of their value as a natural resource has been slower than that of the emergent coastal communities. They must, however, be treated as a valuable natural resource and preserved from further degradation. 17. Oo-cument Aru11ly1iu IL Oescdptors Ecology, impacts, management, succession Seagrasses, ecosystem, south Florida C, COSATI Field/Group 18. AvaHabmty Statement " J, 21. No. of Pag~s Un1 imited i.. Unclassj fi ...... J.. vitL.± .150. ______20. Se,curity Cfass (rt-frs Page) ] 22.. Pric(t ! {See ANSI-Z3SU8) Se-e fos.tructions on- R(fvtftse OPTfONAL FORM 272 {4-77) (formedy NTIS-35) D•partment of Commert:l!!' •u.s. GOVERNMENT PRINTING OFFICE: 1983--769·265/129