The Ecology of the Seagrasses of South Florida - USGS National ...

F WS/O&S-82/25 

September 1882 

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 Sept.ember 1985 

THE FCOLOCY OF THt SFACKASSES 

OF SOUTH F LORI DR: A CQF4FrtiriI.rY PROFILE 

Joseph C. 7 i ~ r ~ n 

Departnlcrlt of Fnvi rorrr1cntal Sciences 

University of Virginia 

Charlottesvil le, VA ??PO3 

Projrct Officer 

Ken Aclarls 

Na tional Coastal Ecosystems Team 

U.S. Fish and Wildlife Service 

1010 Gausc 8oul ward 

Sl idell, I.h 70458 

Prepared for 

National Coastal Fcosystens Tean 

Office of Riologieal Services 

U.S. Department of the Interior 

Washington, l?C 20240

1 

DISCLAIMER 

The findings in this report are not to be construed as an official U.S. 

Wildlife Service position unless so designated by other authorized documents. 

Fish and 

Library of Contress Card Number 82-606617. 

This report should be cited as: 

Ziema~, J.C. 1982. The ecology of the seagrasses of south Florida: a cornunity 

profile. U.S. Fish and Wildl,ife Services, Office of Biological Services, 

Mashington, D.C. ~~s/ms-82/25. 158 pp.

PREFACE 

This profif e of the seagrass community 

of south Florida is one in a series of 

comuni ty profiles that treat coastal and 

marine habitats important to humans. Seagrass 

meadows are highly productive habitats 

which provide 1 iving space and protection 

from predation for large populations 

of invertebrates and fishes, many of 

which have commercial value. Seagrass 

also provides an important henefit by 

stabilizing sediment, 

The information in the report can 

give a basic understanding of the seagrass 

community and its role in the regional 

ecosystem of south Florida. The primary 

geographic area covered 1 ies along the 

coast between Biscayne Bay on the east 

and Tampa Bay on the west. References 

are provided for those seeking indepth 

treatpent of a specific facet of seagrass 

ecology. The format, style, and level of 

presentation make this synthesis report 

adaptable to a variety of needs such as 

the preparation of environmental assessment 

reports, supplementary readina in 

marine science courses, and the education 

of participants in the democratic process 

of natural resource management. 

Any questions or comments about, or 

requests for publications should be directed 

to: 

Information Transfer Speci a1 i st 

National Coastal Ecosystems Team 

U.S. Fish and Wildlife Service 

NASA/Sl 1 dell Computer Complex 

1010 Gause Boulevard 

Sl idel 1, Louisiana 70458

CONTENTS (continued ) 

Page 

CHAPTER 5 . THE SEAGRASS COMMUNITY . COMPONENTS. STRUCTURE. AND FUNCTION .... 41 

5.1 Associated A1 gae .......................... 42 

Benthic A1 gae .......................... 42 

Epiphytic A1 gae ......................... 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 Manmals ............................... 56 

CHAPTER 6 . TROPH IC RELATIONSHIPS IN SEAGRASS SYSTEMS .............. 57 

6.1 General Trophic Structure ...................... 57 

6.2 Direct Herbivory .......................... 59 

6.3 Detrital Processing ......................... 69 

Physical Breakdown ........................ 70 

Ficrobial Colonization and Activities .............. 71 

Microflora in Detri tivore Nutrition ............... 72 

Chemical Changes During Decomposition .............. 73 

Chemical Changes as Indicators of Food Value ........... 73 

Re1 ease of Di ssol ved Organic Matter ............... 74 

Role of the Detrital Food Web .................. 74 

CHAPTER 7 . INTERFACES WITH OTHER SYSTERS .................... 75 

7.1 Mangrove .............................. 75 

7.2 Coral Reef ............................. 75 

7.3 Continental She1 f .......................... 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 DredgingandFilling ........................ 84 

8.2 Eutrophication and Sewage ...................... 86 

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

8.3 Oil 

8.4 Temperature and Sa 

8.5 Disturbance and Re 

8.6 The Lesson of the 

8.7 Present. Past. and 

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

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

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

...... 

REFERENCES 96 

APPENDIX A-1 

Key to Fish Surveys in South Florida 

A-l 

List of Fishes and their Diets from Collections in South Florida A-2 

v

FIGURES 

. Number 

Page 

1 Panoramic view of a south Florida turtle grass bed ......... 2 

2 Map of south Florida ........................ 3 

3 Average monthly terrperatures 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 Ideal ized 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 Thal assi a 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 habi tats ................. 49 

19 Small groupei (Serranidae) foraging in seagrass bed ......... 52 

20 Seagrass bed following grazing by green sea turtle ......... 53 

21 Shal low 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 Florida 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 

v i

TABLES 

Number 

Temperature, salinity, and rainfall at Key West . . . . . . . . . . . 5 

Seagrasses of south Florida . . . . . . . . . , . . . . . . . . . . . 8 

Representative seagrass biomass . . . . . . . . . . . . . . . . . 21 

Compari son of biomass distribution for three 

species of seagrasses . . . . . . . . . . . . . . . . . . . . . . . . 23 

Representative seagrass productivi ties . . . . . . . . . . , . . . . 24 

C values for gulf and Caribbean seagrasses . . . . . . . . . . . . 28 

Constituents of seagrasses . . . . . . . . . . . . . . . . . . . . . 30 

A gradient of parameters of seagrass succession . . . . . . . . . . . 40 

Birds that use seagrass flats in south Florida . . . . . . . . . . . 55 

Direct consumers of seagrass . . . . . . . . . . . . . . . . . . . 60

ACKNOWLEDGMENTS 

In producing a work such as this profile, 

it is impossible to catalog fully 

and accurately the individuals that have 

provided either factual information or 

intellectual stimulus. Here much of the 

credit goes to the mutual stinulation provided 

by my colleagues in the Seagrass 

Ecosystem Study of the International 

Decade of Ocean Exploration. Special 

recognition must be given to the magus of 

seagrass idiom during those frantic and 

mc~iorable years, Peter McRoy . 

At one stage or another in its gestation, 

the manuscript was reviewed and comments 

provided by Gordon Thayer, Richard 

Iverson, James Tilmant, Iver Brook, and 

Polly Penhal e. Other information, advice, 

or c;elcomed criticism was provided by John 

O~den, Ronald Phillips, Patrick Parker, 

Robin Lewis, Mark Fonseca, Jud Kenworthy , 

Brian Fry, Stephen Macko, James Kushlan, 

Rill iam Odum, and Aaron Flills. 

Two of the sections were written by 

my students, Vichael Robhlee and Park 

Robertson. To thec and other students, 

present and past, I PUS^ give thanks for 

keeping life and work fresh (if occasional 

ly exasperating). The numerous drafts 

of this manuscript were typed by Deborah 

Coble, who also provided much of the editing, 

rvlarilyn frlcLane, and Louise Cruden. 

Original drafting was done by Rita Zieman, 

who also aided in the production of Chapter 

8, and Betsy Blizard. I cannot thank 

enough Ken Adams, the project officer, for 

his patience and help in the production of 

this work, which went on longer than any 

of us imagined. 

Thanks are also expressed to Gay 

Farris, El izabeth Krebs, Sue Lauritzen, 

and Randy Smith of the U.S. Fish and 

Wildlife Service for editorial and typing 

assistance. Photographs and figures 

were by the author unless otherwise noted.

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 proplant 

that has totally returned to the 

sea. Salt marsh vegetation and mangroves 

ductivity of the abundant fisheries and 

wildlife of the region. Earlier studies 

are partially submerged in sa1 t water, but describing the 1 ink between estuarine systhe 

seagrasses llve 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 obl igately in sea water (Fig- Everglades (W,E, Odum et al, 1982), alure 

l). 

though the seagrass beds of Florida Bay 

and the Florida Keys have been identified 

Seagrass meadows are highly produc- as habitats for commercial 1y valuable spetive, 

faunally rich, and ecologically cies, as well as for organi$ms that are 

important habitats within south Florida's important trophic intermediaries. Many 

estuaries and coastal lagoons (Figure 2) species are dependent on the bays, laas 

we11 as throughout the world. The com- goons, and tidal creeks for she1 ter and 

plex structure of the meadow represents food during a critical phase in their life 

l iving space and protection from predation cycle. 

for large populations of invertebrates and 

fishes. The combination of plentiful shelter 

and food results in seagrass meadows' 

Many organisms that, are primarily 

characterized by their presence and abunbeing 

perhaps the richest nursery and 

feeding grounds in south Florida's coastal 

dance over coral reefs, such as the errormous 

and colorful schools of snappers and 

waters. As such, many commercially and grunts, are residents of the reef only by 

ecological ly significant species within 

mangrove, coral reef, and continental 

day for the shel ter its camp1 ex structure 

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 

barrfer reefs or surrounding patch reefs, 

A1 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 (119181 in the the grass bed. The juveniles of many 

Baltic Sea, it is only in the past 10 to Pomadasyid species are resident in the 

15 years that seagrasses have ~E?CO?W wfde- grass beds* As they grow, however, their 

ly recognized as one of the richest of increasing size will no longer allow them 

ecosystems, rivaling cu1 tivated tropical Po seek shel ter in the grass and they move 

agriculture in productivitY ((Westlake on to the more complex structure of the 

1963; Wood et a1. 1969; McRoy and McMillan reef for better protection (Qgden and 

1977; Zieman and Wetzel 1980)~ Zieman 1977), 

1

Mangroves and coral reefs are rarely, When assessing the role of seagrassif 

ever, in close proximity because of es, sediment stabilization is also of key 

their divergent physio-chemical require- importance. A1 though the seagrasses themments, 

but seagrasses freely intermingle 

with both communities. Seagrasses also 

selves are only one, or at most three species, 

in a system that comprises hundreds 

form extensive submarine meadows that fre- or thousands of associated plant and aniquently 

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 

mangrove-1 ined hays 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 

small proportion of the total bottom cov- they inhabit would be a seascape of unerage 

of these bays, are the primary zones stable shifting sand and mud. Production 

where important juvenile organisms, 

as shrimp, are found. 

such and sediment stabil ization would then be 

due to a few species of rhizophytic oreen 

a1 gae. 

There are two major internal pathways 

along which the energy from seagrasses is 

made available to the community in which 

they exist: direct herbivory and detri tal 

1.2 CLIMATIC ENVIRONMENT 

food webs. In many areas a significant South Florida has a mild, semitropiamount 

of material is exported to adjacent cal maritime cl imate featuring a small 

communities. daily range of temperatures. The average 

Direct grazing of seagrasses is conprecipitation, 

air temperature, surface 

water temperature, and surface water safined 

to a small number of species, al- linity, for Key Mest are given in Table 1. 

though in certain areas, these species may Water temperature and salinity vary seahe 

quite abundant. Primary herbivores of sonal ly and are affected by individual 

seagrasses in south Florida are sea tur- storms and seasonal events. Winds affecttles, 

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 

varies greatly, as many of these herbiair. 

Occasional major storms, usually 

hurricanes, affect the region on an avervores 

are at or near the northern 1 imit 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 

Iay the sea turtles, Today turtles are 

scarce and consume a quantitatively insigthe 

winter, cold fronts often push through 

the area causing rapid drops in temperanificant 

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 Flulter 1977). 

vast, being 100 to 1,000 times - if not In general, sumner high temperatures are 

greater - than the existing population. no higher than elsewhere in the State, hut 

winter 1 ow temperatures are more moderate 

Some grazers, such as the queen (Figure 3). 

primarily scrape the epiphytic algae on Water temperatures are 1 east affected 

the leaf surface. Parrotfish preferen- on the outer reef tract where surface waconch, 

appear to graze the leaves, but 

tially graze the epiphytised tips of sea- ters are consistently mixed with those 

grass leaves, consuming the old portion of 

the leaf plus the encrusting epiphytes. 

from the Florida Current. By contrast the 

inner regions of Florida Bay are shallow 

and circulation is restricted. Thus water 

The rletri tus food web has classical 12 te~pwatures here change rrzpldly wi tk sudbeen 

considered the main path by which the den air temperature variations and rain. 

energy of seayrasses makes its way through 

the food web. Although recent studies 

Water temperatures in Pi ne Channel dropped 

from 2Qo to 12OC (68' to 54OF) in 1 day 

have painted to increased importance of 

grazing in some areas (Ogden and Zienan 

the passage of a major winter 

::Azin?Zieman, personal observation). 

1977), this genera? ization contl'nucs to be These stows cause rapid increases in sussupported. 

pended sediments because of wind-i nduced 

4

Key Went St Pstarobur~ Cedor Key Panaocola 

J F M A M J J A $ O N D J F M ~ M J J A ~ ~ O N D J F M A M J J A S O N D J ~ . M A M J J A S ~ , N C 

-"- 

-, , 

Flgura? 3. Average monthly temperatures in Florida, 1965 (McNul ty et a1 . 1972). 

turbulence and occasional ly reduced sa1 in- 1.3 GEOLOGIC ENVTRQMl4ENT 

Ottes, all sf whlch stress the local shallaw 

wader cmunities. Et is thought that The south Florida mainland is lowthe 

rapid influx of this type of water lying 1 imestone rock known as Miami 1 ime- 

Prom Florida Bay through the relatively stone. For descriptive purposes the region 

open passages of the central Keys, when can be broken into four sections: the 

puohsd by strong northwesterly winter south peninsular main1 and (including the 

wlnds, is the majar factor in the reduced Everglades), the sedimentary barrier 

abundance of coral reefs in the central islands, the Florfda Keys and reef tract, 

kys (Warszalek et 81, 1977). 

and Florida Bay. 

Tides are typically about 0,75 m (2,s The sedfmentary barrier islands of 

ft) at the MJarni harbor muth. Thfs range north Biscayne Bay, Mr'ami Beach, Virginia 

is reduced to (I6, 5 m (1,6 ft) f n the embay- Key, and Key Biscayne are unique for the 

ntents such as South Biscayne Bay and to area because they are composed largely of 

O,3 m (I ft) in restricted mbaylents like quartz sand, The islands are the southern 

Card Sound (Van de #reeke 1976). The mean terminus of the longshore transport of 

range decreases to the south and js 0.4 m sand that moves down the east coast and 

(1.3 ft) at Key Mest Harbor, Tidal hejghts ultimately out to sea south of Key Bisand 

velocities are extrmely complex in cayne. All other sediments of the region 

south Florida as the Allantl'c tides are are primarily biogenic carbonate. 

aemidiurnal , the gulf tides tend to be diurnal, 

and much of this regSon is between The Florida Keys are a narrow chain 

these two regimes. Neither tidal regime of islands 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, coupled with the baffl Jng (563 mi) to Key Mest and ultimately to the 

effects of mudbanks, channels, and keys, Marquesas and the Dry Tortugas some 110 km 

create an exceedingly complex tidal cSrcu- (69 mi) further west, The upper keys, 

1 ation. from Big Pine no~thward, are composed of 

6

ancient coral k'town as Key largo licx- this 13i.ea (gittdk~r and Iverson, in 

stone, ~hcrens the lowo- keys frot:~ [iict press). In an inventory of ttlc estuaries 

Pine \vest are corlposcd of oolitic fdcies of the glal f coast of Florida, pkc~iulty 

of the i4iami 1 ir71estonc;. (A note to boaters et a]. (1?72) estjfjjated that over &fix of 

and researchers in these shallow waters: the total area In the region of Florida 

thc 1 irrestene of the lower keys is ~uch Ray west gf the Keys and landward to the 

hdrdcr than in tile upper keys, and occa- freshwater line to Cape Sable was subs 

ional brushes with the b0tt0~1, which tnerged vegetation, Sy comparison, manwould 

be r.linor in the upper keys, will :Trove vegetation coti~priseii less than 7% of 

~nanqle or destroy otltboard propellers and the areta. 

lower drive units.) 

The amaunt of seagrass coverage drops 

The Florida reef tract is a shallow off rapidly to the nortli of this area on 

hdrrierm-type. reef and 1 agoon extending botb coasts, nn the At1 antic coast, the 

east and sotrt? tf the Florida Keys. It shifting sand beachcs signal a chancy to a 

averages 6 to 7 km (4 to 4.4 mi) in width high-energy coast that is unprotected from 

with an irrcytrl ar surface and depths vary- naves and has a relatively unstable subing 

fro- 0 to 17 11 (56 ft). The outer strate, coupled with the littoral drift of 

reef tract is not cnntinuouc, hut consists sand fronr the north. Thraughor~t this area 

of varioirs reefs, often with wide gaps be- seagrasses are i~stlally found only in small 

twccrn thcr~. The developnent is greatest pockets in protacteti inlets and 1 acroons. 

in the upper keys. The patch reefs are On the Gul F of tviexico coast north of Cape 

irregular kt101 1 s rising fro!-1 the 1 illlcstone Sable, seagrasses are virtually el ininatcd 

platforfrr in the area between the outer hy drdinage fr0r.r tho Everglades with its 

reef and the keys. Rehind the outer reef, increased turbidity and reduced salinity. 

the back reef zone or layoonal area is a Seagrasses are then found only in relarqosaic 

of patchreefs, 1 incs tone bedrock, tively spa1 1 beds within hays and cs tuarand 

grass-covered sediiwntcd areas. 

ies until north of Tarpon Springs, where 

an caxt~nsive (3,000 krn' or 1,158 mid') bed 

Florida Ray is a triangular region exists on the extrmely broad shelf of the 

lying west of the upper keys and south of northern qul f. Several bays on the gulf 

the Everglade.;. This large (226,000 ha or coast, including Tampa Bay and Roca Clcga 

558,220 acres), extremely shallow basin nay, forrnerly possesself extensive seagrass 

reache5 a maxirftun depth of only 2 to 3 m resources, htlt drcdpe and fill operations 

(7 to 10 ft), but averages less than 1 n and other human perturbations have greatly 

(3.3 ft) over a great area. Surface wdi- reduced the extent of these beds. 

~nents of fine carbonate ntrd OCCJI- in windiyg, 

anartorlos ing rtud banks, seagrass- This profile Is prin~arily directed at 

f11lt.d "lakes" or basins, and nanarove the seagrass ecosysteirl of southern Florislands. 

ida. It is neccssdry, however, to draw on 

the pertinent work that bas been done in 

other scaqrass systems, 

1.4 REGIDfiAL SEACRASS DISTRIRUTIOP4 

Florida possesses one of the largest 1.5 SEAGRASSES OF SOUTH FLORIDA 

reagrass resources on earth. Of the 

10,000 km*' (3,860 mi') of seagrasses in Plants needed five properties to sucthe 

Gui f of Hcxico, over 8,500 knz' (3,280 cessful ly colonize the sea, according to 

mii) are in Florida waters, prirqarily in Arbcr (1920) and den Hartoq (1970): 

two major areas (8ittdker and fverson, ffl 

pr~ss). The southern seagrass bed, which (1) The ability to live in a sal' 

is bounded by Cape Sable, north Biscayne 

ned i urn. 

Bay, and the Dry Tortugas, and includes 

the warm, shallow waters of Florida R ~ Y (2) The ability to function while 

and the Florida coral reef tract, e~t@nds fully suhl~erged. 

over 5,500 kmL (2,120 mi* ), though coyerage 

is brokers in nurnerous places, over (3) A we1 1 -developed anchoring sys- 

80% of the sea hottom contains seagrass in tern. 

7

(4) The ability to complete their systematic treatments such as den Hartog 

reproductive cycle while fully (1970) and Tomlinson (1980) should be consubmerged 

. sulted, however, when comparing the seagrasses 

of other areas. The best descrip- 

(5) The ability to compete with 

other organism in the narine 

tions of the local species are still to he 

found in Phil1 ips (1960). 

environment. 

Turtle grass (Thal assia testudinum) 

Only a small, closely related group of is the largest and most robust of the 

monocotyledonous angiosperms have evolved south Florida seagrasses. Leaves are riball 

of these characteristics. bon-like, typically 4 to 12 rnm wide with 

rounded tips and are 10 to 35cm in length. 

h'orldwide there are approximately 45 There are commonly two to five leaves per 

species of seagrasses that are divided short shoot. Rhizomes are typically 3 to 

between 2 famil ies and 12 genera. The 5 m 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 Hydrochari taceae 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 f il ifome) 

(Table 2). The two genera in the family is the nost unique of the local seagrass- 

Potanogetonaceae have been reclassified es, as the leaves are found in cross seccomparatively 

recently and many of the tion, There are commonly two to four 

widely quoted papers on the south Florida leaves per shoot, and these are 1.0 to 1.5 

seagrasses show Qmodocea for Syrinaodiurn mm in diameter. Length is highly variand 

Dipfanthera for Halodule. Recent dis- able, hut can exceed 50 cm (20 inches) in 

cussion in the literature speculates on some areas, The rhizome is less rohust 

the possibility of several species of than that of Thalassia and more surfici- 

Halodule in south Florida (den Hartog ally rooted. Syringodium is covmonly 

=70), but the best current evidence mixed with the other seagrasses, or in 

(Phillips 1967; Phillips et al. 1374) in- small, dense, monospecific patches, It 

dicates only one highly variable species. rarely foms the extensive meadows 1 ike 

Thal assi a. 

The small species numher (six) and 

di sti nctivc appearance of south Florida Shoal grass (Halodule wrightii) is 

seagrasses make a standard dichotonous key extremely important as an early colonizer 

generally unnecessary (Figure 4). General of disturbed areas. It is found primarily 

Table 2. Sea?rasses of south Florida. 

-.- -- 

Family and species 

Hydrochari taceae 

Conmon name 

-....-- . ---- --- -

Halodula wrightii 

Syringodium filiforme 

Figure 4. 

Tcagrdsses of sout'~ Florida,

in disturbed areas, and in areas where 

----- Thalassia or Syringodium --- are excluded 

because of the prevail ing conditions. 

Shoal grass grows commonly in water either 

too shallow or too deep for these seagrasses. 

Leaves are flat, typically l to 

3 mr,i wide and 10 to 20 cm long, and arise 

froin erect shoots. The tips of the leaves 

are not rounded, but have two or three 

points, an important recognition character. 

----- Hal odule is the most tolerant of a1 1 

the seagrasses to variations in temperature 

and sal ini ty (Phil 1 ips 1960; r4cf4il lan 

and Floseley 1967). In low sa1 inity areas, 

care must be taken to avoid confusing it 

w i t h Rupp-G.. 

Three species of Halo hila 11 small 

and delicate, are sparse y istributed in 

south Florida, Halophila engelmanni is 

the most recognizable with a whorl of four 

to eight oblong leaves 10 to 30 mm long 

borne on thc end of a stem 2 to 4 cm long. 

This spccies has been recorded frorn as 

deep as 90 m (295 ft) near the Dry Tortugas. 

&il+&ihia kcipiens has paired 

oblong-e 1 ~ p t ~ leaves c 10 to 25 lnrn long 

and 3 to 6 mn wide wising directly fro17 

the node of the rhizome. A nevJ species, 

- H. johnsonii, was described (Eisernan and 

t4cMillan 1980) and could be easily confused 

with H. decipiens. The most obvious 

differences are that N. johnsoni i 1 acks 

hairs entirely on the leaf surface and the 

veins emerge from the midrib at 45O angles 

instead of 60". The initial description 

recorded H. johnsonii fron Indian River to 

Riscayne Bay, hut its range could ul timately 

be rnuch wider. 

The najor problem in positive identification 

of seagrasses is between Npd1~1e 

and Ruppia mariti*, com~nonly known as 

widgeongrass.~thougti typical ly found 

alongside tialodule, primarily in areas of 

reduced sarnity, Ruppia is not a true 

seagrass, but rather a freshwater plant 

that has a pronounced sal ini ty to1 erance. 

It is an extremely important food for 

waterfowl and is widely distributed. 

Where it occurs, it functions similarly to 

the seagrasses. In contrast with Halo- 

- dule, the leaves are expanded at the base 

and arise a1 ternately from the sheath, and 

the leaf tips are tapered to a long point. 

It should he noted, however, that leaf 

tips are cor~r~only missins fro(. older 

leaves of both species.

2.1 GROWTH in the denser grass beds east of the Flor- 

A remarkable sir-ilarity of vegetative 

ida Keys. Short shoots in areas exposed 

to heavy waves or currents tend to have 

appeardnce, yrowtf7, and morphology exists fewer leaves. 

among the seagrasses (den Hartog 1970; 

Zienan and k'etze? 19g0). Of the local The growth of individual leaves of 

species, turtle grass is the R O S ~ abun- turtle Grass in Biscaync Ray averages 2.5 

dant; its growth and clor~holog~ provide 

a typical scheme for seagrasses of the 

mv/c!ay, increasing with leaf width and 

robustness. Rates of up to 1 cmlday were 

area. 

observed for a 15- to 20-day period (Zieman 

1P75b). Leaf growth decreased exponen- 

Tot7linson and Vargo (1966) and Torn- tially with aqe of the leaf (Patriouin 

1 inson (1969a, 1?69b, 1972) described in 1973; Zielqan 1975h). 

detail the rnorphology and anatomy of turtle 

grass. The round-tipped, strap-1 i ke Leaf width increases with short shoot 

leaves ernanate fro17 vertical short shoots aae and thus with distance frorl the rhiwhich 

branch 1 atera1 1~ frop the horizontal zorne ~veri s tell, reaching the colnmuni ty paxrtiizorrlcs 

at regular intervals. Turtle imur? 5 to 7 short shoots back from the 

grass rhizomes are buried in 1 to 25 Cn growin2 tip (Figure 5). The short shoot 

(0.4 to 10 inches) of sedillent, although has an average 1 ife of 2 years (Patriquin 

they usually occur 3 to 10 cn (1 to 4 1975) and nay reach a length of 10 cr! 

inches) below the sediment. In contrast, (iorqlinson and Vargo 1966). A nxw short 

rhizomes of shoal grass and Flalophilr! are shoot first pots out a few small, tdp>red 

near the surface and often exposed, while leaves about 2 cm wide before producinq 

manatee grass rhizones are most typically the regular leaves. New leaves are producfound 

at an intermediate depth. Turtle ed throughout the year at an avera~e rate 

grass roots originate at the rhizoi~es or of one new leaf per short shoot every 14 

less frequently at the short shoots. They to 16 days, and tirnes as short as 10 days 

are r;lucti smaller in cross section than the have been reported. In south Florida the 

rhizomes, and their length varies with rate of leaf production depended on tempsediment 

type, organic matter, and depth erature, with a rate decrease in the coolto 

bedrock. er winter months (Zieman 1975b). The rate 

of leaf production varies less throughout 

On a turtle grass short shoat, new the year in the tropical waters of Barbaleaves 

grow on a1 ternating sides from a dos and Jamaica, accordinf! to Pztriqui 

central ncristern which is enclosed hy 016 (1973) and Greenway (19741, respectively. 

leaf sheaths. Short shoots typically 

carry two to five leaves at a time; in 

south Florida, Zieman (1915b) found an 2.2 REPPOOUCTIVE STRATEGIES 

average of 3.3 leaves per shoot in the 

less productive inshore areas of Biscayne Seaorasses reproduce vegetati vely and 

6ay, and 3.7 leaves per shoot at stations sexually, but the infornation on sexual 

11

AVERAGE 

LEAF WIDTH 

I 

DISTANCE BETWEEN BRANCHES (CM) 

Figure 5. Diagram 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 typiamount 

of information exists for turtle cally 26" to 30°C (79" to 86OF), 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 

1 arge and easily identified for seagrass- tropical organisms 1 ed many otherwise capes. 

In south Florida buds develop in Jan- able scientists to view the tropics and 

uary (Moffler et al. 1981); flowers, from 

mid-April until August or September (Orsubtropics 

as simply warmer versions of 

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 tolpermanent1 

y marked quadrats, Zieman noted erances; the upper thermal l imi t of tropithat 

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 refruits 

appeared from 2 to 4 weeks later. 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 

2.3 TEMPERATURE 

the surrounding waters. At 40" north latitude, 

the seasonal temperature range of 

oceanic surface water is approximately 

One of the first mental images to 10°C (5O0F), while at 20° north, the range 

be conjured up when considering the trop- is only 3OC, reaching a low of only 1°C 

ics is that of warm, clear, calm water, (33.8OF) at about 5" north. However, beabounding 

with fish and corals. This image cause of the extensive winter cooling and 

12

sumer heating of shal low coastal water, 

Moore (1963a) found that the ratio of mean 

tmptrrature range (30° to 50" N) to mean 

tropical range (20' M to 20° S) to be 

2.5:l for oceanic waters, but increased to 

4.2: 1 for shallow coastal waters, 

Because of thermal tol erance reduction 

in the tropics, the biological result 

is a loss of cold tolerance; that is, the 

range of thermal tolerance of tropical 

organisms is about hat f that of temperate 

counterparts, whereas the upper to1 erance 

limit is similar (Zlenan and Wood 1975). 

Turtle grass thrives best in temperatures 

of 20' to 30°C (68" to 86OF) in 

south Florida (Phillips 1960). Zieman 

(1975a, 1975b) found that the optimum 

temperature for net photosynthesis of 

turtle grass in Biscayne Bay was 28' to 

30°C (82' to 86OF) and that growth rates 

declined sharply on either side of this 

range (Figure 6). Turtle grass can tolerate 

short term emersion in high temperatures 

(33' to 35'C or 91" to 95'F), but 

growth rapidly falls off if these temperatures 

are sustained (Zieman 1975a, 1975b). 

In a study of the ecalogy of tidal 

flats in Puerto Rico, Glynn (1968) observed 

that the leaves of turtle grass were 

killed by temperatures of 35' to 40°C (95" 

to 104OF), but that the rhizomes of the 

plants were apparently unaffected. On 

shallow banks and grass plots, temperatures 

rise rapidly during low spring 

tides; high temperatures, coup1 ed with 

desiccation, kill vast quantities of 

leaves that are later sloughed off. The 

process occurs sporadically throughout the 

year and seems to pose no long-term problem 

for the plants. Wood and Zieman (1969) 

warn, however, that prolonged heating of 

substrate could destroy the root and rhizome 

system. In this case, recovery could 

take several years even if the stress were 

removed, 

The most severe mortalities of organisms 

in the waters of south Florida are 

usually caused by severe cold rather than 

heat, as extreme cold water temperatures 

are more irregular and much wider spaced 

phenomena than extreme high temperatures, 

McMi1 lan (1979) tested the chi1 1 to1 erance 

of populations of turtle grass, manatee 

Figure 6.

grass, and shoal grass in various 10cations 

from Texas to St. Croix and Jamaica. 

embayments with restricted circulation, 

such as southwest Biscayne Bay, nany 

Populations from south Florida were inter- algal species are reduced during summer 

mediate in tolerance between plants from high temperatures and some of the nore 

Texas and the northern Florida coast sensitive types such as Cauler a 

and those from St. Craix and Jamaica in hora and Laurencia nay d9F@= 

e ki ed Zienan 

the Caribbean. In south Florida, the 1975a). 

most chill-tolerant plants were from the 

shallow bays, while the populations that 

were least tolerant of cold temperatures 2.4 SALINITY 

were from coral 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 to1 erate considerable saern 

winds quickly cool off the shallow linity 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 Fay. The deeper waters, however, tion of oceanic water. The dominant seain 

the area below the Keys and the reef grass, turtle grass, can survive in sal inline 

(up to 15 m or 50 ft) not only have a ities fron 3.5 ppt (Sculthorpe 1967) to 60 

much greater mass to be cooled, hut are ppt (McVillan and Moseley 1967), but can 

also flushed daily with warmer Gulf Strea~t tolerate these extremes for only short 

water which further tends to buffer the periods. Even then, severe leaf loss is 

envi ronmental fluctuations. common; turtle grass lost leaves when 

sa1 inity was reduced below 2C ppt (den 

The anount of direct evidence for the Warton 1970). The optimuin sal ini ty 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 

grass, Phil 1 Ips (1960) suggested that 

(Phil1 ips 1960; HcMillan and Poseley 1Q67; 

Zieman 1975h). Turtle grass showed maxinum 

shoal grass generally prefers temperatures photosynthetic activity in full -strength 

af 20 to 30°C (68' to 86aF), but that it seawater and a linear decrease in activity 

is somewhat marc ecrrythermal than turtle ti th decreasing sal ini ty (Hammer lP68b). 

grass, This fits its ecological role as a At 5QX strength seawater, the photosynthepioneer 

or colonizing species. Shoal grass tic rate was only one-third of that in 

is comnonly Found in shallower water than full-strength seawater. Fo1 lowing the 

either turtle grass ar manatee grass, passage of a hurricane in south Florida in 

wherc then~al variation would tend to be 1960, Thornas et a1 . (1951) considered the 

greater, FAcP"i1 lan (1979) found that shoal damage to the turtle grass hy freshwater 

grass had a greater chill tolerance than runoff to have been more severe than the 

turll~ grass, while manatee grass showed 

less resistance to chi1 I ing, 

pl~ysical effects of the high winds and 

water surge. 

Seagrasses are partially huf'fercd The tolerance of local seagrass spefral 

tetnpcrdture extrelscs in the overlying cies to sal a'nity variation is simildr to 

water because of the scctir~en ts covcring their temperature to1 erances. Shoal Grass 

the roots and rhizotiles. Sedi~?cnts are is thc nost broadly euryhaline, turtle 

poorer conductors of heat than seawater grass is intermediate, and vanatee grass 

and they absorb heat morc slowly. In a and - fJalophi1a -- have the narrowest tolerance 

study by Redfield (19651, changes in the ranges, with -- tialghila being even rqore 

ter:;perature of the water cel urnn decrease stenohal ine than manatee grass (F-?clJil 1 an 

exponent? at ly ni th depth in sedir??n ts. 1979). 

Hxtroa? ~ ae assaci;tcd wi kt? grass beds 

exist totally it? the water coluinn, and 2.5 5EDIYCP!TS 

thus will be af fccted at a rate thdt is 

dcpcndent upon their indivitlual tellper- Scagrassec qrow in a wide variety of 

attlrc tolerances. Ilost algae associated sediments froir fine mud.; to coarse sands, 

with tropical seagrass beds are more depending on the type of source rf?ateriii'I, 

sensitive to t"n~7tii stress than the the prevailing physical flaw regi4n@, and 

.;@itgrasses (Zieman lQ75a). Ira shallow the density of the Seagrdss blad~s. AS 

14

ooted plants, seagrasses require a sufficient 

depth of sediment for proper 

development. The sediment anchors the 

plant against the effects of water surae 

and currents, and provides the matrix for 

regeneration and nutrient supply. Runners 

occasionally adhere directly t~ a 

rock surface, with only a thin veneer of 

sediment surrounding the roots, but this 

happens sporadical ly and is quantitatively 

insignificant. The single most important 

sediment characteristic for seanrass 

growth and development is sufficient sedi - 

ment depth. 

Depth requirements a1 so vary with the 

different species. Because of its shallow, 

surficial root system, shoal grass 

can colonize thin sediments in an area of 

mininal h draul ic stabil i ty (Fonseca 

et a,. 19813. Turtle Srass is more robust, 

requiring 50 cn (20 inches) of sediment to 

achieve lush growth, although meadow formation 

can begin with a lesser sedinent 

depth (Zieman 1972). In the Bahamas, 

Scoffin (1970) found that turtle grass dld 

not appear untiP sediment depth reached cat 

least 7 cm (3 inches). 

The density of turtle grass leaves 

greatly affected the concentration of 

fine-grained (less than 63~) particles Sn 

sediments. Compared with hare sedinent 

which showed only 1% to 3% fine-grained 

material, sparse to medium densities of 

turtle grass increased the fine percen tags 

from 3% to 62 and dense turtle grass 

increased this further to over 15%. 

The primdry effects of thc grass 

blades are the increasing of scdimen ta tion 

rates in the heds; the cancentr3tin~~ of 

the finer-sized particles, hoth inorganic 

and organic; and the stabilizing ?F the 

depori ted sedirlents (Fonseca, irl press d:, 

h; Kenworthy 1321). Burrell and Schubcl 

j 1977) described three effects produced by 

these cwchsan i srns: 

(1) Direct and indirect extraction 

and entrapment of fine dateri~orne 

~tdrticles by' tkc sasl?ras% 

1 c;ivr?s. 

Forn:ation and retention of Particles 

nroduced within the grass 

(3) Binding and stabilizina of the 

substrate by the seagrass root 

and rhizome syste~. 

One of the values of the seagrass 

system is the ability to create a relatively 

low energy environment in regions 

of hipher energy and turbulence. In addition 

to the fine particle extraction due 

to decreased turbulence, the leaves trap 

and consol idate particles of passing sedicent 

which adhere to the leaf surface ar 

become enmeshed in the tangle of epiphytes 

sf older leaves. As the older portion of 

the leaves fragment, or as the leaves die 

and fall to the sediment surface, the organic 

portions of the leaves decay and the 

inoraanic particles become part of the 

sediment. The continued presence of the 

growinp 1 eavcs reduces the water velocity 

and increases the retention of these 

particles, yielding a net increase in 

sedinent. 

Key elements in a plant's efficiency 

of sedinent stabilization are plant species 

and dens1 ty of leaves. From observational 

data in Bermuda, researchers found 

open sand areas had 0.1% to 0.2% fine particles 

(less than 63~1). In manatee grass 

Seds this increased to 1.9% fines, while 

turtle grass heds had a.P% to 5.4% fine 

material (Wood et al. 1969). In the same 

study organic natter (% dry weight) was 

2.5% to 2.6% in open sand areas with similar 

values in inanatce grass heds; the 

organic matter in turtle grass beds was 

3.5% to 4.91, demonstrating the increased 

stabilization and retention power of the 

more robust turtle grass. 

Seagrasses not only affect mean grain 

sire of particles, but other geologically 

important parameters such as sorting, 

skcwnclss, and shape (Burrel? and Schuhel 

1977). St~inchatt 61965) qound that the 

mean site of sand fraction particles, the 

relative abundance of Fines, avd ttlc standard 

dinension all increased with an 

increase in blade dcnqity near a Florida 

reef traet. T!?? fl:td'ttit+?tiu? eefferf nf 

the trapping and honding was discussed in 

scveriil studies (Ginsberg and Lov!enstar? 

1958; Wood ct aS. 1969; Fnnscca in precs 

a, h) and is st-sovrn qraphical ly in Finure 7 

(Zieman 1072). 

5

Sediment 

Elevation 

(c m) 

Leaf 

Density 

( leaves / 

100crn2) 

Leaf 

Length 

(cm) 

Sediment 

Depth 

(em 

0 

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 1 ocal ly 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 coral 1 ine The microbially mediated chemical 

algae such as Melobesia or Fosliella. It processes in marine sediments provide a 

has been estimated that these encrusting 

algae produce from 40 to 180 g/rnvyr of 

major source of nutrients for seagrass 

growth (Capone and Taylor 1980). Bactecal 

ciurn carbonate sediment in Jamaica ri a1 processes convert organic nitrogen 

(Land 1970) and upwards to 2,800 g/m2/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 sediaffect 

the production of inorganic partic- ment surface. The ammonia that is not 

ulates a1 so. Cloud (1962) estimated that rapidly util ized will diffuse upward to 

75% of aragonitic mud in a region of the 

Barbados was due to direct precipitation 

the aerobic zone where it can either 

escape to the water column or be converted 

of carbonate when the seagrasses had 

removed C02 from the water during periods 

to nitrate by nitrifying bacteria in the 

presence of oxygen. Endobacteria were 

of extremely high primary productivity. found in the roots of the seagrass Zostera 

Zieman (19756) also noted the ability marina (Smith et a1. 1981a), and were 

of seagrasses under calm conditions to associated with nitrogen fixation mi th 

16

et a1. 1361b). The anount of nitrate is 2-7 OXYL'EN 

usually low or ahsent in sediments ds it 

is either rapidly rietabol izcti or converted 

to dinitrogen (M ) via deni trifyilly tjac- 

Post seagrass meadows have sufficient 

oxygen in the water coluinn for survival of 

teria. the associated plants and animals. Often 

the shallow beds can be heard to hiss Fron 

Sulfur bacteria are primarily respon- the escaping 0 bubbles in the late aftersible 

for riaintaining conditions necessary noon. Dense beds in shallow water with 

for the remineralization of nutrients in restricted circulation can show extrerlcly 

the sedirnent. By reducing sulfate to sul- reduced 0, levels or even anoxia late at 

fide, these bacteriamaintain the environ- night on a slack tide. This can be a 

rFiental conditions (Eh and pH) at a Icvcl greater problerl if there is a heavy load 

where the ni trogeri mineral iza tion proceeds of suspended organic sedirnent that would 

at a rdte gredter than its utilieatiarl by also corisulne oxygen. Generally the wind 

the rvicrobi a1 col-unurri ty . This produces rcqtl i red to

indication of a 1 ini tation on productivity the leaf sqrfaces available for desiccadue 

to hydrostatic pressure and not merely tion. Turtle grass grows in waters nearly 

light limitation (Gessner and Harimer as shallow as that of shoal grass. The 

1961). shallowest turtle grass flats are covmonly 

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 

suitable sediments are available. Off the 

the species may be found, singly or mixed. 

Turtle grass is the unquestionable dominorthwest 

coast of Cuba, Buesa (1975) re- nant in nost areas, however, freauently 

ported maxiisurn depths for tropical sea forming extensive meadows that stretch for 

rasses as follows: turtle grass, 14 m tens of kilometers. A1 though the absolute 

446 ft); manatee grass, 16.5 m (54 ft); depth limit of the species is deeper, 

I-(alophilia deci iens, 24.3 m (80 ft); and mature ~rleadows of turtle grass are not 

- ti. enslemanni - 1 4 rn (47 ft). As plant found below 10 to 12 R (33 to 35, ft). At 

species grow deeper, the qua1 ity 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 1 ight grass development, shoal grass will often 

is relatively enriched in blue wavelengths occur, hut it rarely develops extensively. 

with depth, By comparison, in highly tur- Past the point at which the raajor species 

bid conditions as in shallow bays in Texas occur, fine carpets of Halophila extend 

and in Florida Ray, blue 1 ight is scat- deeper than 40 m (130 ft). 

tered and the enrichment is in the direction 

of the green wavelenpths. In hoth Numerous studies confirmed the patclear 

and turbid waters the longer red tern described above, or some portion of 

wavelengths are ahsorbed in the first few it. The relative abundance of four spencters 

of the water colunn. 

cies of seagrasses off northwest Cuba, is 

graphed in Figure 8 (Ruesa 1374, 1975). 

Ruesa (1575) studied the effects of - Halophila decipiens was the least abundant 

specific wavelengths on photosynthesis of with a mean densi t.y of 0.14 g/~2. Halopturtle 

grass and rnanatee grass in Cuba. hila aelmanni showed a mean density of 

Ile found that turtle grass responded best 

to the red portion of the spectrum (620 

g/m?=atee grass was nearly 10 

times denser than Halophila with an avernanorrletcrs); 

the blue portion (400 nanome- age density of 3.5 g/m2 down to 16.5 t" (54 

ters) was better for manatee grass. ft). Turtle grass was the vost abundant 

seagrass, accoi~nti ng for nearly 07.52 of 

the total seaqrass biomass, with an aver- 

2.3 ZONATION age of 190 q/17j down to its maximum depth 

of 14 m (46 ft). This area is unique in 

Although seagrasses have been re- that there is 1 ittle or no shoal grass 

corded fran as deep as 42 rn (138 ft), ex- which normal ly is eitber the second or 

tensive develop~nent of seagrass beds is third most abundant species in a region. 

confined to depths of LO to 15 m (33 to 49 

ft) or less. Principal factors determin- In St. Croix, turtle grass had the 

lng seagrass distribution are light and shallowest range, occurring down to 12 m 

pressure at depth, and exposure at the (39 ft) on the west side of Ruck Island 

shallow end of the gradient. A general (Uiginton and McP"i1len 1970). Shoal grass 

pattern of seagrass distribution in ct ear and manatee grass showed progressively 

waters of south Florida and the Caribbean greater depth, occurring to 18 m (53 ft) 

uas presented by Ferguson et 31. (1980). and 20 n (65 ft), respectively, while 

Shoal grass usually grows in the shallow- Halo hila decipiens occurred to 42 m (13% 

est water and tolerates exposure better & 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 

confons to the damp sediment surface dur- Because of the variety of rocky and 

ing periods of exposure, thus minimizing sedimentary patterns in the lagoons and 

18

0 

5 

10 

E 

d 

N 15 

f a 

a 

0 

20 

25 

30 

Figure 8. Depth distribution of four seagrasses on the northwest coast of Cuba, I = 

Thalassia testudinum, 2 = S rin odium filiforme, 3 = Halo hila decipiens, 4 = H. :nye1- 

m o m Susea 1g75). *r7nqodium is yi&nt in certain IoFal~t~es, 

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 ips (1960) recorded turtle grass 1 imi t drying (Gessner 1968). A1 though 

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 rn (33 will be killed. 

ft); by contrast, in the relatively turbid 

portion of the "lakes" 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 frm the shallow flats following the 

spring low tides. Normally the rhizomes 

The seagrasses of south Florida are are not damaged and the plants continue to 

all subtidal plants that do not tolerate produce new leaves. 

19

CHAPTER 3 

PRODUCTION ECOLOGY 

The densities of seagrasses can vary (1977) and Zienan and Wetzel (1980). Bewidely; 

under optinvrn conditions they fom cause these studies represent a variety of 

vast rrleadows. The 1 i terature is becoming habitats, different sampling times and 

extensive and often bewif dering as density seasons, wide variation in sample rep1 i- 

values have been reported in many foms. cates (if any), as well as the diverse 

For consi~tency, the terms used here con- reasons for which the Snvestigators colfarm 

to those of Zieman and tletzel lected the samples, it becomes difficult 

(1980): standing crop refers to above- to draw meaningful patterns from these 

ground (above-sedf ment) material, whereas pub1 i shed resul ts. 

bionass refers to the weight of all 1 lving 

plant material, including roots and rhi- While the standing crop of leaves is 

romes, Both quantities should be expressed significant, the cnajority of the biomass 

In terms of mass per unit area. These of seagrasses is in the sediments, especimeasurements 

both have valid uses, but it ally for the larger species. Although the 

3s samatfrnes dlfficul t to determine which relatfve amounts vary, turtle grass typian 

author is referring to, because of' in- cally has about 15% to 22% of its biomass 

catnplet@ or imprecise descriptions. His- in emergent leaves and the rest below the 

torlcally, standing crop has been the pri- sediment surface as roots and rhizomes. 

mary measure of cmparisnn because of the The pub1 ished ranges for turtle grass, 

relative ease of sampling conpared with however, vary from 10% to 45% for leaf 

the laborjous methods needed to callect biomass (Zleman 197%). In central Bisand 

then sort belowground material. 

cayne Bay, Jones (1968) found a relatively 

consistent ratio af 3:2:2 for leaves and 

short shoots: rhizomes: roots. Studies 

3.1 RIOFlASS with turtle grass and Zostera have indicated 

that the ratio o m e s to roots 

Seagrliiss biomass varies widely de- increased with a shift in substrate froir 

pending on the species involved and the course sand substrates to fine muds (Kenlocal 

condflions. Tho biomass of the spe- worthy 1981). This can be interpreted to 

cies Halophila is alwinys small, whereas indicate either thc positive effect of the 

turtle grass Kas been recorded ,at densi- richer fine muds on more robust plant deties 

exceeding 8 kg dry weightlm- (Oauers- velopment, or the need for a better develfeld 

et al. 1369). Representative ranges oped nutrient ahsarptive (root) network in 

of seagrass tsiasirass ttt south FTorida and the coarser seditwsts that tend to be f o 

in neighboring regions are given for con- er in nutrients and organic matter. Thus, 

parison in Table 3. Because of the ex- substrate may he an important variable 

trerne variatiions Found in nature and re- when determining phenol ouical indices. 

flected in the literature, one must be 

careful not ta place too muck value on a Structural fy , turtle grass has the 

few measurements. Many of these studies zwst well-developed root and rhizome syshave 

been su~~bctarized hy FFScRay and McMil lan tem of all the local sea9rasses. Table 4 

20

2 

Table 3. Representative seagrass hionass (g dry wt/m ). 

Species 

Location Range Mean Source 

-- Halodule wriahtii 

Fl orida 

Zieman, unpuhl . data 

Texas 

N 

w 

Syringodium filifor~e 

-- 

Thal assia testudinuw 

- 

North Carol ina 22-208 Kenworthy 1981 

F1 orida 15-1,100 100-300 Zi eman, unpubl . data 

Texas 30-70 4 5 Vctlahan 1368 

Cu ha 30-50C 35@ Buesa 1972, 1974; 

Buesa and Olaechea 

1970 

Florida 

Odum 1963 ; Jones 

(east coast) 20-1,800 125-800 1968; Zieman 1975b 

Fl or i da Bauersfeld et a1 . 

(west coast) 75-8,100 500-3,100 1409; Phillips 

1960; Taylor 

et al. 1973 

Puerto Rico 60-560 80-450 Rurkholder et al. 

1953; Pargal ef 

and Rivero 195e 

Texas 60-250 150 Odum 1963; 

PcRoy 1974

1 isl;s conpdratiue Piorrlass values frow sev- Threp basic .~ethods have been usc:f to 

era1 stations .in Pine Channsf in the Faor- study scagrass productivity: rwrkin~;, 

ida Keys where the three islador species CO- and 0, production. (~ec Tienan and 

exist. Shoal grass and mandtee grass have Wetzel 1980 for a recent reuietg of producless 

well -devehoi~cd root and rhizoa~e sys- tivi ty rteast~reinerllt, techniques. ) 

teiris and conscquen tly wi 11 general Iy have 

I~IUC~ more of their total biornass in leaves Many assur,lptions are xade when tising 

than does turtle grass;. Samples for these the oxygen production method, am! all can 

two species where the leaf caiiaponent is lead to large and variable errors, pri- 

59% to GOY of total weight are not erncorn- fzarily becausc leaves of aquatic vasctrlar. 

mori. Flaxl'rrrurr6~ values for the species also plants can stare gastls pro+rrc~rj during 

vin,-;y wideby, t3iur~ar;s mcdsuremeftts for photosyntilesis For an incfeFini te period. 

dense stands of shoal grass are typ4cally The largest potential error, boudcver, is 

several hundred yrarls per square meter; related to the staraqe of r~ctahol ically 

~fidnintec cjrass rcachrs rqaxicrrurts devefoprner~t produced ~xygbr~. To u5i. tile oxygefl producat 

'1,200 to 2,500 :r/rfrd, while maxl'r trvr ual- tr'on technique, one assumes that oxvcen 

ctes for turtl~ ~F'~CXSC are c~v~r 8,fSOO g{v~ . pr~duced in photosynthesis diffuses ra?- 

idly into the surroundinq water where IC 

can be r~adil y twdsurcd. bfi th scar~rasses , 

3,'d PMOUI~GfIt'XTY as HI th oth~r- subinergell rlacraphytas, however, 

this gas cannot diffuse otltwarh at 

%eagra~,res hdv~ the potr~ntinl for the rat? at which it is produced and so it 

c"xtreir1~1y hTyf1 1br4raar.y productivity. Re- rtccuqula tes in the intcrsl i tial lacunae of 

corded value% for seatjrass product ivi ty the 1 eaves (Ctartrlan and Prawn 1966). Revary 

arlurrxlclusly dcpttrdl ng on species, den- cent work with frcshu~ater rlacrophy tcs has 

si ty, saaa;on, erld rrreasurei~rexrt: techniques. suyc;ested that under we1 1 -stirred condi- 

Pvnsr, studfes use turtle grass witla orsly a L4or.r~ only a short period is rc~quired far 

few ~r&Ftsred values t"sr shoal grass and eauil ibrat-ion fb!estla\te l?78; Kelly et al, 

tqBnrdfPt! 9~i&%%* 

1"PO); howcver, this has not been veri fie4 

For seaqrasses. As the gas a~cur?u1ates, 

!-or roaiitlt Ilardda, turtle grass pro- seagrass lcaves swell up to 252% of their 

ductlvity valuec of 0.9 to 16 g Clr~ /day original volume (Zianan 1975b). Some of 

heve kaeQu reported (Table 51, The highest the? oxygen produced l's iisud metabolically, 

rtlyjarlo;i values (e.q. (ddufrt 1243) represent while the re-iainder either diffuses out 

sairrrurxri ty :tet;dB,al.is~rr and reflect the pro- slowly or, if production is sufficf ent, 

darcts of thc zeaurassaq, epigrhytic algae, will burst frorq the leaves in a strear? of 

nfrd bealtiric ~nlgae, Peasurerncnts; of sea- harh!?l~s. 

grass production indicnte that the net 

ahnvegruond praductflrn is corlirlctrrt y 1 to !*easwre.rent of seagrass productivity 

4 g I:frru ./$BY, dl Chot~~~h the nrdxiil~~ rates hy r*adt'oactive carbon uptake has the adcdn 

he sevcral liartrs thwc values flien\an vanta~e of high s,cnsl'livj.t;y, brief incubdarid 

get261 InPI?), Tltc ir~portance of the tian periods, and the ahil ity to partition 

R-Sgir stirti ined Icve? rtf przjdtrction of sea- out the productivity associated with the 

cjrdsses 14 kspectal ly djlpdr~tlt kq-llh~~ condi ff ercnt morp\~u?ogical parts of the 

~idt*ed with the Praductiort valblec of the plant? as well as productivity of the 

ennl J yuous uf f sklure wnters , attendant epiphytes and macroalgae. A? - 

thougl.~ thi s 11edsurei.tent technique requires 

sophl sticated and expensive laboratory and 

3.3 PROOUCTIVXTY bfEA%U9fVE!iT field ecgiiipment, and vav have errors associated 

with COA storage, it apparently 

Frm the earl test seayrass sl.udies, yields a value near to net productivity 

t%seea~Ck%7~5 itave' ~urr. t irluill i y noted tile an6 pra6uces; vai ues co12parab'te to rlark and 

hlgl\ pradlactlivi ty of seagrasses, arid their recovery techniques. The appl ication of 

u'ltlm$'ce value as Food for tropha'cally the 14C technique Lo seagrasses is dishl'gher 

organfssrs. As a rcsul t, nuch study cussed in detail by Penhale (lQ75), Rithas 

been devoted to rsethods for detennin- taker arld Xverson (19761, and Cayone 

trig the pr'oduetivl't~t of seayrass beds. art sl. (19711). 

22

s= VI 

L n3 

E: 

w 0 

I; 'C 

rdn 

V) 

C) m- 

>+J a 

(6 Oc' 

moo 

J C c b

Net production measurements for ~10s t 

seagrasses can be obtained by marking 

blades and measuring their growth over 

tine (f ienan 1974, 1975b). With this 

nethod, the blades in a quadrat are marked 

at their base, allowed to grow for several 

weeks, and then harvested. As seagrass 

leaves have basal growth, the increment 

added below the marking plus the newly 

emergent leaves represent the net aboveground 

production. After collection, the 

leaves of most tropScal species must be 

gently acidified to remove adhered carbsnates 

before drying and weighing. 

Bi ttaker and Iverson (1976) ct-i tical - 

ly compared the marking method with the 

measurement of productivity by radioactive 

carbon uptake. When the li+'C method was 

corrected for inorganic 1 osses (1351, 

incubation chamber light energy absorgtion 

(14Y), and difference in light ener y resul 

tin9 from experinental design (8x3, the 

differences in productivity were insignificant. 

Thcse rcsul ts reinforce the concept 

that the 1*C method rneasurcs a rate near 

net productivl'ty. In a study of turtlc 

grass productivity near Oimini , however, 

Cap~ne et al. (1979) found that the 

neasurer~ents yielded values near1 y double 

that of the marking methods. 

A neth hod developed by Patriquin 

(1373) uses statistical estimates based on 

the length and width of the longest 54 

of the leaf population of a given area. 

Capone et a1 . (1979) used this method; it 

aclreed +J-15X with the staple ~iarkfng 

rlethod. Indications arc that this nethod 

is very useful for a first order e~;tir?at~, 

but rorc comparative studies arc st311 

neecicd. 

SOIT form of oxygen r.leasurer.ient vias 

used to attain the highest production 

values recorded in the 1 iterature for turtle 

grass and --- Zostcra. Recently Kemp 

et al. (19el) surveyed nuperous productivity 

measurervnts from the litcratt~re and 

ccnnf irned that for seagrasses an& several 

freshwater rlacrophytcs, the oxygen wthad 

$l?t?k:etl !?rq!~est p-~brlrlt jt!ity v*'fur?c; r7;lk-I.- 

in5 r'rethohr, the lowert; and 1'" dallies 

verr lintcrr~e,iate, A1 thocigh thesc coflpari 

sot>j; rcqlri rcd nUi?CrQuS assurGpt 

resill ts show the need for furti..acr 5L"d.Y. 

The iiarkinsj metbod probdt.ily qivci~ ~ F I C 

'I east ai-higuous ariswcr.5, s'lnv!in:; 

i.jncj, tla~ 

25 

aboveground production quite accurately, 

It underestimates net productivity as it 

does not account for belowground produc- 

tion, excreted carbon, or herbivory. Wodifications 

of the marking method for 

lostera marina have been used to estimate 

root anmome production ( Sand-Jensen 

1975; Jacobs 1979; Kenworthy 1981) and 

could be adopted for tropical scagrasses. 

The generalization that energes fron these 

various diverse studies is that seagrass 

systems are highly productive, no matter 

what method is used for measureraent, and 

under optimur;~ growth conditions production 

can he enormous. 

3.4 NUTRIENT SLIPPLY 

Seagrasses along with the rhitophytic 

green algae are unique in the marine environnent 

hecause they inhabit both the water 

colunln and the sediments, There was 

previously much controversy whether the 

seagrasses took up nutrients throuph their 

roots or their leaves. McRoy and Barsdate 

(1970) showed that Zostera was capable of 

absorbing nutrients either with the leaves 

or roots. FlcRoy and Barsdate found that 

Zostera could take up ammonia and phos- 

phate from the sediments through their 

roots, translocate the nutrients, and puvp 

than out the leaves into the surrounding 

water. This process could profoundly 

affect the productivity of nutrient-poor 

wa tcrs. 

Sediment depth directly affects seagrass 

development f Figure 7). The imp1 ication 

is that the deeper s~dinent is required 

to al law sufficient root developnent 

which would in turn increase the 

nutrient absorptive capabil ities of the 

roots. Thus to sustain growth, the plants 

would need greater nutrie~t absorptive 

tissue in sediments that contained less 

nutrients. Whilc studying turtlc grasq 

in Puerto Pico, Rurkhof der et al. (1051) 

founcl a change in the 'leaf to root and 

rhiznr.rc ratios of tho plants as the scdiinent 

type changed. Thc ratio of leaf 

to root and rhiznrqc of turtl~ crass ~ias 

1:3 4n fine nud, 1:5 in riid, and 1:7 in 

cnarsc sand. Kevk~nrtkry ( 3 noted a 

5imilar chancjr! in -- 7ostrra in 8orth Carolina. 

Thfa plants frur~ sirrdy arcar had 

over tvrice the root tissue per uvi? 1caf 

tissue, possihly indicatirl~ I,+ir nrcd fnr

algt.icfit dbsorptive area or greater and riiizomcs was 30% greater than tile cnnancijorjfiy 

capnci ty in tile coarser sedi- trolc;, and the standing crop of Icaves ha? 

r:enes7 Altr:rnativcly, the decrease in increased by a factor of thrce to fr~ur. 

root ~qdterial in f ir~e sodii1)ent.s c~i~ld Sea(?rasst?$ seer! to he' cxtre?lc?y eff icient 

tesu\t frcnn9 a ncqative effect frorri anae- at capturing and utilizina ncrtrients, arid 

rohlns1s or i~icrobial netatrol i tcs. 

this is a najor factor in their ability to 

rviaintain high productivity evert in a rela- 

A l ttiou?lt scagrasscts require a variety ti vely low nrr trient envi ronmcnt. 

uF rrracro- carrel r~icronutriertts for nutritinn, 

nost, research effort !ids hcan dirc?clecf 

to tile source and rate ef supply of 3.5 SEACRASS 13t(YS1131.1?CY 

111 trogcn, Whilc? phosphorous is in very 

law cr~rrcentration in tropical waters, it 5cagrasses haw evofveri a ~)l.~ysiolu~y 

is re1 atively ahurtdant in the scdir~ents, thdt often di s tiny$ shes thein frsur.? tilcir 

drrd ~5tiiq~tci; 011 turnover time ranqe Frmn terrestrial counterparts. Since water has 

rrrrc tw two turnovers per yedr to once ratcs of Gaseous diffusion thdt arc suvevery 

f-PW tars (i4cRoy et al, 1972; Patri- era1 orders of tqagnitude lower than air, 

qui~~ 1912hj piitragen, howevrr, is necdcd nluch af this physiological codi fica tion is 

in I \ ~ ~ z J I ijreattlt- rlclantf tie5 and its source a response to the Itwet-~r! gas cotieentra- 

4s rwrQ shsc.ura (!/tcRoy and Mctfiillan 1Vl). tlon and the slowet. ratcs of rfi fftlsiorl 

Fi&tr.iqul'n (IS??b) csti~rratcs tt~t 

Lhcrc when coi.nllclrsej with the terrestt-id7 crlviotrly 

4 5- tn 15-day supply of inarydrric rsnttient. It is cora~only thouiyht tht henllrugi:tr 

avafldtle irr the sctfir~tents. This cause of the ahurltlatlce of itr:~t.cnanic citr-klara 

castiriatc lid not accctrdr~t for cc,rttinuour in seawater in the carhenate buffer sysrecys 

l i ng, herwevct.'. 

ten, n;arine plants are nut carlr~n limited. 

Pcaring active photosynthesis, howcver, in 

Sr~~tgrc\ss~s have tlzrec po fenki a1 ni- skal f ON grass beds wlra?n tidal curreri ts are 

t~ocit?rt SOU~CCS: recycled nitvogen in tttc slow, the pf-l may rise Prom the nor~~al scasctiitlrcrat%, 

rtit;roge,xri in the water columrt, water ptl of 8.2 to 8,Q, at which point the 

~rld rrt tragcra f'.ixdlion. Pjitrogcn fixation frec CO, is greatly reduced in the water. 

cdrr BCC~~P clther ln the rhhI~o~phert? or 1'11 values of "-4, d floir~t at whjc4 hiocdryt~ylsspktrc, 

Trarrsfers bctwaen leaf and tsona te is hrdrdly present, have \~ccri recpiphy 

tr,p fravc al so been dctnonstra tcld (tlar- coreled aver qrass herds. 

1 frl 1971; bTcRoy arrd Csering 1974), Caponc 

ot al . f 4.Cst9) cat~cluded that r11 troyen The interr~al structure of seagrasses 

fixad irr tlre phyl ltlsp!~cr-e contribute:! pri- has becrr rrtodi f ied to i?iniroi ze? the probler,:~ 

trrarily to the epiphytic c~tr~g-iuxrity &.thilc uf life in an aquatic environrqrnt. Large 

f 9 x ~ iarr t in tile rh.jrospt.\cre cantrihu tcd iriternal 1 acunal spaces have devcl oped, 

1:rdinIy to s:jacroyliyte prurluc tirart. Indi- often cot:lprising over 70% of the total 

r*car;t?y tlrc contr-ihittiotl of ni troqcn-fixing leaf valut::e, to Facil i tate interndl gas 

6:t)fphytes ic, irt~portant hacsust:, after the transport (Arlser 1?21\; Sculthorpe 1967; 

lt:avuii senrscr? and dctiltti, r1cac,t: of tilei-1 licrrlan and bletrel 19CO). Puch of tile oxydtYedy 

arid becotite part (JT the 1 itter; solnrt gen produced in photosynthesis is apparwill 

be .tlricorpat*mtcd irr thx? sedirvnts. ently retained in thc lacuna1 systetcl and 

C1thecr. suttrces of rrltrogcn to tllc srdiriict~ts diffuses throughout the plant to the refnclude 

sxrrtatiun try plants and anilwls, gions of lliah respiratory derqantf it1 the 

p.art,l"~~~lbt;e aitatker trapped by the dense rtlots and rhizorles. Sirnil arly, hecausc of 

lo;.aves, and dead root artd rhizo1.n i~latc- the general lack of stanata, the diffusion 

rial. Caponc and Ta lor (1?(3C) agreed of CO. into the seagrdsses is slot! coilwith 

Pdtriquin (1972bf that tile priliary pared with terrestrial counterparts. in 

SB'JFCri? @f ~'ftrwar? qcr let?? ;~ra&jc',io~ $5 acfdjtj~n, the f;'~i~5p+:t, +tsf,ef ;apr E~Y,L, 

recycled r+~aterial Fropi sedir.trnts, but rhi- to the leaves does not enhance diffusion 

rospherc? Fixation can supply 2Cs to 50% of of gases. 

the plar;t8s rczquireanents. Urtn ( lP77a) 

appl led coanercial fertil izcrs directly to At nar~!a: seauakr pi!, bicarbonate is 

a 9st~t bed .in Chesapeake Bay. After 2 much more abundant than 60 . Beer et a1. 

to rhtraths the length and density of (1977) showed that the talajor source of 

leaves had Increased, thc arnslrnt nf roots carbon far photosynthesis for four species 

26

of seagrasses was bicarbonate ion, which frol~ I? generd and found that 45 species 

could corltributu to the calciufn carbonate were within the range of -3 to -19 ppt, 

clock frequently observed on seagrass with only two species of -- iialophila being 

leaves (Zieman and Gktzel 198CI). At nor!ilal lower. The mean values and range for the 

reawater pi!, C02 concentrations wre so local species are shown in Table 6. Turtle 

low that the hi~h photosynthetic potential grass shows a mean value of -10.4 ppt and 

Idas lini ted by bicarborlate uptake (Beer a total range fron -3.3 to -12.5. This 

and Waisel 1979). Increasing the propor- variation included sal~iples froin Flarida, 

tion of C02 by lowering pH greatly in- Texas, the Virgin Islands, and Mexico. 

creased photosynthetic rates in ~modocea --- The mean values and ranges for shoal grass 

-- rlodosa, .- a large seagrass with high poten- and -- Halophila fror; the Gtrlf 3f Vcxico and 

tial production. 

Caribbean are also very similar with mean 

values ranging froi:, -10.7 to -12.6 ppt, 

Much recent controversy has concerned respectively. ilana tee Crass is the only 

whether the r::etabol ic pathway of sedarass 1 ocal seagrass o f sicni f icantly di fferent 

photosyqthesis utilizes the conve:~tional value with a ,?ore dif !~ted mean of -5 ppt 

Calvin cycle (called C3 as the initial and a range of -3.Q to -9.5 ppt. Irt 

fixed sugars are 3 carbon chains) or the general, tropical species bad l~iqher 6i3C 

C,, 8-cdr(~oxylative pathway. CI, pfdnts values than species from tenperate rerefix 

CO:, efficiently and little respired gioqs. There also appears to be little 

GO, is lost in the light (t'ough 1974; seasonal difference ins13C values, at 

tloffler et a1. 1981). Cq plant5 are dif- least for -- Zostcra - marina (Thayer et 81. 

ficul t to saturate wit4 1 ig4t an;f have I978a). 

high terr~perature optiinurs. Thj s pho tosynthetic 

systen wo~lld seein to he of benefit 

in regions of high temperature and light The si3C ratio has attracted tr)ucR atintensities, 

as e as marine waters tention recently because of its utility as 

(Hatch et al. 1971). Seagrasses, however, a natural food chain tracer (Fry and Parkare 

exposed to lower relative ternpera- er 1979). The sedgrasses possess a uniaue 

tures, 1 ight level s, and oxygen concentra- slk ratio for marine plants, and thus ortions 

than are terrestrial counterparts ; gani sl?s that corisu,?c signif icant portions 

and as the diffusion capacity of CO2 fro11 of seagrass in their diet will reflect 

leaves is riuch slower, metabolic C02 is this reduced ratio. The carbon in anilnals 

available for refixation regardless of the has been shown to be generally isotopicalphotosynthetic 

pathway. After much lit- ly similar to the carbon in their diet to 

erary controversy, recent evidence has within +/-2 ppt (DeNi ro and Epstein 1978; 

shown that most seagrasses, including tur- Fry et al. 1378). Careful utilization of 

tle grass, nanatee grass, and shoal grass this method can distinguish between carbon 

are C3 plants (Andrews and Abel 1979; originating frol:~ seayrasses (-3 to -15 

Benedict et a1 . 1980). ppt), marine algae (12 to -20 ppt), particulate 

organic carbon and phytoplankton 

What n~akes the photosynthetic pat$way (-18 to -25 ppt), and mangrove (-24 to 

of interest to those other than the plant -27) (Fry and Parker 1979). In Texas, orphysiologist 

is that durina photosynthesis ganic lnatter from sediments of bays that 

plants do not use the I'c and i3C isotopes have seaarasses display a significantly 

in the ratios found in nature, hut tend to reduced ratio when conpared with adjadifferentiate 

in favor of the 12C isotope cent bays lacking seagrass meadows (Fry 

which is lighter and more mobile. A11 et al. 1977). The saae trends were replants 

and photosynthetic cycles are not ported for the aninals collected fron 

a1 ike, however, and those using the con- these bays (Fry 1981). The 8l3C value for 

ventional C, ,Calvin cycle are relatively one species of worm, Oiopatra cuprea, 

poor in the 'jC isotope, while C ,., plants shifted ft-or? an average of -13.3 to -18.A 

have high ratios of ~x/~~c. The ratios ppt between seagrass- and phytoplanktonof 

13 C/I/C (called slC or de1 1°C) gener- doninated syster~s (Fry and Parker 1?73). 

ally varies between -24 to -36 ppt for C4 The average values for fish and shrimp 

plants (Bender 1971). Seayrasses have rel- show a similar trend in that the si3c 

atively high &i3c values. HcI4illan et al. ratios are reduced in organisms from the 

(1930) surveyed 47 species of seagrasses seagrass meadows. 

27

. . 

h 

L L 

a) LA.

Currently the main 1 imitations of the 

carbon isotope method are equipment and 

interpretation. It requires use of a mass 

spectrometer which is extremely costly, 

a1 though today a number of labs will process 

samples for a reasonable fee. The 

interpretation can become difficul t when 

an organism has a 613c value in the middle 

ranges. If the 613c value is at one extreme 

or another, then interpretation is 

straightforward. However, a mid-range 

value can mean that the animal is feeding 

on a source that has this sL3c value or 

that it is using a mixed food source which 

averages to this value. Recent studies 

util izing both isotopes of carbon and sulfur 

(Fry and Parker 1982) and nitrogen 

(Macko 1981) show much promise in determining 

the origin of detrital material as 

well as the organic natter of higher 

organi sms. Know1 edge of the feeding ecology 

and natural history of the organism is 

needed, as is an a1 ternate indicator. 

3.6 PLANT CONSTITlfENTS 

Recognition of the high productivity 

of seagrasses and the relatively low level 

of direct grazing has led to questions 

regarding their value as food sources. 

Proximate analyses of seagrasses in south 

Florida, particularly turtle grass, have 

been performed by many authors (Burkhol der 

et a1 . 1959; Eauersfeld et a1 . 1969; Walsh 

and Grow 1072; Lowe and Lawrence 1976; 

Vicente et a1 . 1978; Bjorndal 1980; Dawes 

and Lawrence 1980); their results are 

summarized in Table 7. As noted by Dawes 

and Lawrence (1980), differences in the 

preparation and analysis of samples, as 

well as low nunbers of samples trsed in 

sorne studies, make data comparison dif- 

Ficul t. 

The reported ash content of turtle 

grass leaves ranges fron 45% dry weight 

for unwashed samples down to around 25% 

for sanples washed with fresh water. 

Leaves wasqed in seawater contained 29% 

+/- 3.52 to r14Z +/- 6.7:; ash (Dawes and 

Larrrence 1380). 

Values for the protein content of 

leaves vary from a low of 37 of dry weight 

for unwashed turtle grass leaves with 

epiphytes (Dawes et al. 1979) to 29.7% for 

leaves washed in distilled water (Walsh 

and Grow 1972), a1 though numbers typically 

fall in the range of 10% to 15% of dry 

weight. Protein values rnay be suspect if 

not measured directly, but calculated by 

extrapol ating from percent nitrogen. In 

grass beds north of Tampa Bay, Dawes and 

Lawrence (1980) found that protein 1 eve1 s 

of turtle grass and manatee grass leaves 

varied seasonally, ranging from 8% to 22% 

and 8% to 13%, respectively, with the 

higher levels occurring in the summer and 

fall. The protein content of shoal grass 

ranged from a low of 14% in the fall up to 

19% in the winter and summer. Tropical 

seagrasses, particularly turtle grass, 

have been compared to other plants as 

sources of nutrition. The protein content 

of turtle grass leaves roughly equaled 

that of phytoplankton and Bermuda grass 

(Burkholder et a1 . 1959) and was two to 

three times higher than 10 species of 

tropical forage grasses (Vicente et al. 

1978). Wal sh and Grow (1972) compared 

turtle grass to grain crops, citing studies 

in which 114 varieties of corn contained 

9.M to 16% protein; grain sorghum 

contained between 8.62 and 16.5%; and 

wheat was lowest at 8.3% to 12%. A1 though 

several studies have included measurements 

of carhohydrates (Table 7), it is impractical 

to compare much of the data because 

various analytical methods were employed. 

Studies using neutral detergent fiber 

(NDF) analyses found that cell wall carbohydrates 

(cell ul ose, hemicell ul ose, and 

1 ignin) made up about 45% to 602 of the 

total dry weight of turtle grass leaves 

(Vicente et al. 1978; Bjorndal 1980). 

Dawes and Lawrence (1980) reported that 

insoluble carbohydrate content in the 

leaves of turt7e grass, manatee grass, and 

shoal grass was 34% to 46%. The rhizones 

of seagrasses are aenerally higher in 

carbohydrates than are the leaves. Oawes 

and Lawrence (1980) found that soluble 

carhohydrates in turtle grass and manatee 

grass rhizomes varied seasonally, indicating 

the production and storage of starch 

i~ summer and fa1 1 . These authors, however, 

#ere working in an area north of 

Tampa Bay, where such seasonal changes 

would he more pronounced than in the 

southern part of Florida and the Keys.

....I. . . . . ./ . . . . .I . 

LC' w C\' 4 r.2, P' hNCC;)e- Cr>C2arrr-. 

O ~ C ~ r3 O ,-iQ*-dm dc'?C2dd 

a' LC) 4

CHAPTER 4 

THE SEAGRASS SYSTEN 

4.1 FUNCTIONS OF SEAGRASS ECQSYSTEMS 

In addition to being high in net privary 

production and contributing large 

quantities of detritus to an ecosystem, 

seagrasses perform other functions. Recause 

of their roots and rhizomes, they 

can nlodi fy their physical environment to 

an extent not equaled by any other fully 

submerged organism. Phi 11 ips (1978) stated 

that, "by their presence on a landscape of 

re1 atively uniform re1 ief, seagrasses (3) 

create a diversity of habitats and substrates, 

providing a structured hahi tat 

fra? a structure? ess one. " Thus seagrasses 

a1 so function to enhance environmental 

stabil i ty and provide shel ter. 

Seagrass ccosys terns have numerous important 

functions in the nearshore marine 

environr?ent. Wood et al. (1969) originally (4) 

classified the functions of the seagrass 

xosystem. The following is an updated 

version of the earlier classification 

scheme. 

(1) tligh production and growth 

The ability of seagrasses to exert a 

najor influence on the marine seacape 

is due in large part to their exbrernely 

rapid growth and high net 

productivity. The leaves grow at 

rates typically 5 mm/day, but ~frowth 

,.c+~ , 8f ever fO mf.lay are nnt (5) 

uncomrlon urtder favorabl e ci rcums 

tdaces. 

2 Food and feeding pathways 

Thc photosynthetically fixed energy 

fron the scagrasscs cay fol locr tkm 

3 3 

general pathways : direct grazing of 

or$anisms on the living plant material 

or utilization of detritus from 

decayin: seagrass material, prinarily 

leaves. The export of seagrass material, 

both living and detrital, to a 

location some distance from the seagrass 

bed a1 lows for further distribution 

of energy away from its original 

source. 

She1 ter 

Seagrass beds serve as a nursery 

around, that is a place of both food 

and shel ter, for the juveniles of a 

variety of finfish and shellfish of 

commercial and sportfishing importance. 

Habitat stahil ization 

Seagrasses stabilize the sedirqcnts in 

two ways: the 1 eaves slow and retard 

current flow to reduce water velocity 

near the sedirnen t-wa tcr interface, a 

procass which promotes sedirl~entation 

of particles as well as inhibiting 

resuspension of both organic and 

inorganic material. The roots and 

rhizomes fom a complex, interlocking 

rnatrix with which to bond the sediment 

and retard erosion. 

!Ltr tr ient ef fec tz 

The production of detritus and the 

prorqotion of sedlincntation hy the 

leaves of seagrasses provide or~anic 

rlatter for the sedii:ents dnrl naintain 

an active envi ronlrent for nutrient 

reryclinl. Fpiphytic a1 gae on the

leaves oF seagrasses hav2 been shown is also the key tcl restoring dananed or 

to Fig nitrogen, thus adding to the denuded syster~s. 

r~utrrient. pool of the region. In addjtjonx 

5cagrassrs have beer1 shown to 

pick ilp qut.ricnts from the sedirilents, 4.3 SPECIES Sl+'CCESSIOpI 

transporting their1 throuqh th2 plant 

and relcaslng the nutrients into the Thro~rqhout the sout? Florida rcoion, 

water cirluinri through the leaves, thus and nost of the Gulf of Eexico and Caribdcthng 

as a nutrient puvp fror? the bean, the species of plants that particiseciis?er~l 

pate in the successional se~ucnce of seagrasses 

are remarkably few because thtirr 

are so few marine plants that can colonize 

4.2 SIICCESSICIEJ ANE! ECOSYSTEM OEVELOPMENT unconsol ida tcd sedirnents. In addition to 

the seaqrasses, one other group, the rhi- 

In eonventlonal usage, succession zophytic green algae, has this capability. 

r-csfers to the orderly development of a These algae, however, have only linited 

scrics of c~~n.j~jni ties, or sera1 stages, rhi zoidal development and never affect an 

which rc%ulb; Jn a clitaax stage that is in area greater than a few centimeter5 from 

eqrrli 1 ltlriur: with the prevail tny environ- their haw. 

rwrt tn f cond i t Jtrns . f rl wre con tei?porarSy 

u%i;nge, trowever, nuccesslion is more brtladl y The rlost cor71;ron illustration of sucxtsed 

to i*oelan the succession of ?;prcir;s, cession In scagrass systc~s is the rccolo- 

$trudture, and functfons within an ecosys- nization fallowing a "blowout." This loc- 

Leu.:, Odurtr (19654) stated contemporary al i zcd di sturhance occurs in seagrass heds 

concept 4% follows : 

througlrout Florida and the Caribbean where 

there is sufficient current movement in a 

1) Suecessiof~ $5 an orderly process domillant direction (Figure 9). Usually a 

of cry$t~t~*rtrn.i t-y devclogment; thdt in- dl srugtfon, such as a rlajor stortn, overvrrlvcr 

changes in species Structure grazing caused by an outbreak of urchins, 

and casr:nrvun!tt;y prcrccsscs with tittle; it or a trldjor rjpping of the beds caused by 

$5 rcaronirhle, directtonal, and drdgyirlg a large anchor, is required to 

truere tore [nredicldlrl e, 

initiate th~? blo~out, Once started, the 

holes are enlarged by the strong water 

(2) Sucecss?lon results fro111 plodiff- flow which causes erosion on the dovin cur- 

(:dtSof\ of tile ~3haysicill envir~~~q~ylt b~ rent side. Slowly a crescentic shape a 

the corat8urri ti; that is, sajccession .is Few nleters bride to tens of peters wide is 

cots!tioity+controI ICE^ CV~II th~tugit the Forrned. A saapl c cross section in Figure 

b~hy..;icxnf cnvirari~rienl deterinitles the 10 shows a mature turt? e grass corlnuni ty 

~t~clttt%rn and the r01~ OF chan~p, and that has been d3srupted and is recoverin$. 

t~rten sets lr";..rEts ds to haw far The region at the hasc of the erosion 

dlzvcl ikpriaent cdri qn, scarp is highly agitated and contains 

large chunks of consol idated sediment and 

63) Ssar,ee!ssinrl cuf rriiitates irr a st*- occasional rhirorile frag~ents, CIi th inbll 

cctlsystart in which ;rraxicturrt creasing distance from the face of the 

I%~PJI\~SS 

%or hfqh dnfonaiation c~ntcnt) scarp, turbulence decreases and sorne {?atedfld 

~~:thfotir: ~WIIC~~D~) bct~~en or.gan- rial is deposited. The area has hecome 

4 sF1s are ~r~ixintlsinftd per irr~it of colonizetl with rhizophytic algae; Hal imda 

avilll ablx? etrerlry Flow, 

and Penicillus are the most abundant, but 

, -tihatea, -- Rhipocephalus and 

Species ruccessfon has received by 1 lea are also comon. These algae 

far tqe R0St atreririon as it is r-tusi pi-avid+ a certain a~ount f sedirqent- 

~bviuus and easily mcasused, The study of binding capability as illustrated iq Figsracce%sion 

af pt-acesses or functions is ure II, htrt they do nut stabilize the surjust: 

ta@$jnnln?, however, Xt: nlay well 1 prove face of the sedirqents very well (Scoffin 

fl(J5t i!?partant @venire for undey- 1970). A rslajor function of these a1 gae in 

standing ecosysle;ln development. Defining the early successional stage is the con- 

PPQCESS@S is OF much greater impor- tri bu tian of sedimentary particles (Hi 1 - 

ta~c@ than raerc scietltific curiosfry. It liatns 1981)- The generalized pattern and 

34

Figure 9. 

B1 owout disturbance and recovery zones. 

I1)EALIZEC) c~EOIIFhlT,E. TWRWBGti A SEACRASS BLOWOUI 

---4 Domtnonr Wafsr Flow 

RELATIVE BIOMASS i-7 

ht;* Sp"WFt Il_a_ - -- 

Below Sed~rnent - ! 

i 

Figure 10. Ideal ized sequence through a Figure 11. Representative calcareous 

seagrass blowout. Note erosion and recov- green algae from reagrars beds. Note the 

ery zones moving into the dominant water binding action of the rhizoids in foming 

flow. 35 small conso? idatest sediment ha1 1 S.

composition of marine sediments in south 

Florida as taken from Ginsburg (1956) are 

illustrated in Figure 12. Behind the reef 

tract over 40% of the sediment was generated 

from calcareous algae. Penicil lus 

capitatus produced about 6 crops per year 

in Florida Bay and 9.6 crops per year on 

the inner reef tract (Stockman et al. 

1976). Based on the standing crops, this 

would produce 3.2 g/m2/yr on the reef 

tract which could account for one-third 

of the sediment produced in Florida Bay 

and nearly all of the back-reef sediment, 

Similarly, Neuman and Land (1975) 

estimated that Ha1 imeda incrassata produced 

enough carbonate to supply all the 

sediment in the Bight of Abaco in the 

Bahamas. 

The pioneer species of the Caribbean 

seagrasses is shoal grass, which colonizes 

readily either from seed or rapid vegetative 

branching. The carpet laid by shoal 

grass further stabilizes the sediment surface. 

The leaves fonn a better buffer 

than the algal communities and protect the 

integrity of the sediment surface. In 

some sequences manatee grass will appear 

next, intermixed with shoal grass at one 

edge of its distribution and with turtle 

grass at the other. Manatee grass, the 

1 east constant member of this sequence, 

is frequently absent, however. 

Manatee grass appears more common1 y 

in this developmental sequence in the Caribbean 

islands and in the lower Florida 

SE REEF TRACT FLORIDA BAY 

NW

Keys waters. Where the continental influence 

increases the organic matter in the 

sediments, manatee grass appears to occur 

less commonly. Lower organic matter in 

Caribbean sediments, due to the lack of 

continental effect, may slow the developmental 

process. 

As successional devel opment proceeds 

in a blowout, turtle grass will begin to 

colonize the region. Because of stronger, 

strap-1 i ke leaves and massive rhizome and 

root system of turtle grass, particles are 

trapped and retained in the sediments with 

much greater efficiency and the organic 

matter of the sediment will increase. The 

sediment height rises (or conversely the 

water depth above the sediment decreases) 

until the rate of deposition and erosion 

of sediment particles is in balance. This 

process is a function of the intensity of 

wave action, the current velocity, and the 

density OF leaves. 

restabilized within 5 to 15 years (Patriquin 

1975). During the study of Patriquin 

(1975) the average rate of erosion of the 

blowout was 3.7 mm/day, while the rate of 

colonization of the middle of the recovery 

slope by manatee grass was 5 mm/day, Qnce 

recolonization of the rubble layer began, 

average sediment accretion averaged 3.9 

mmfyr. 

With the colonization of turtle 

grass, the normal algal epiphyte and 

faunal associates begin to increase in 

abundance and diversity, Patriquin (1975) 

noted that the most important effect of 

the instability caused by the blowouts is 

to "I imit the sera1 development of the 

community. The change in the region of 

the blowouts of a we1 1 -developed epi fauna 

and flora, which is characteristic of 

advanced stages of sera1 development of 

the seagrass community, is evidence of 

this phenomenon, ' 

The time required for this recovery In areas that are subject to continwill 

vary depending on, among other factors, 

the size of the disturbance and the 

ued or repeated disturbances, the successional 

development may be arrested at any 

intensity of the waves and currents in point along the developmental gradient 

the region. In Barbados, blowouts were (Flgure 13). Many stands of manatee grass 

SOL l D 

SUBSTRATE 

EPlLlTMlC 

ALGAE 

CORALLINE 

ALGAE 

SANDY 

SUBSTRATE 

MUDDY 

SUBSTRATE 

RHlZOPHY TIC 

ALGAE 

ECOSYSTEM DEVELOPMENT 

Stable Envfranmental Conditrons 

Figure 13. Ecosystem 

general i zed pattern, 

disturbance that the 

are present hecause of its abi l i ty to to1 - 

erate aerobic, unstablc sedirqents and to 

rapldfy extend its rhizorse systen under 

these conditions. This is especially cvident 

in back-reef areas, Patriquin (19753 

attributes the persistence OF nana tcc 

grass in areas around Barbados to recurrent 

erosion in areas where the hottom was 

never stable for a sufficiently long tine 

to allow turtle grass to colonize. Manatee 

grass can have half of its biomass as 

leaves (Table 4). Thus, while manatee 

grass is col onizing aerobic disturbed sedinrents, 

vihlch would he areas of low nutricr'lt 

supply and regeneration, the arqount of 

its root surface available f ~ nutrient r 

0pt.a ke woul d he reclucetl , and correspatldingly 

ltldfp uptakc would become a major 

source of nutrients, If this is the case, 

thc higher agitdtfon of the wdter column 

would be of benefit l-ty reducl'ng the gradients 

at the leaf surfacc. 

4.4 THE CENTQAL POSITION OF THE SEA- 

GRASSES TO TMt SEAGRASS ECOSYSTEM 

orgaili sirrs t~i th their widely di fferincr 

requirements and interactions functioned 

as a hi9hly intricate v~eh structure that 

made each individual or each link less 

necessary to the maintenance of the total 

system. There was mttch natural redundance 

bull t into the system. For certain segr~ents 

of the co~qrjunity this may be true. 

The problem is that at cl irnax there is one 

species for vrhich there is no redundaricy : 

the seagrass. I0 some cases, if the seagrass 

disappears, the entire associated 

co~muni ty disappears along with it; there 

is no other orgavlisri that can sustain arid 

support the systen. 

This is shown in a sr~all way when 

mi nor di s turbanees occur as was described 

v ~ th i the hlowouts. As the yass beds in 

these areas are eroded away, the entire 

seaqrass systcrn disappears, including the 

top 1 or 2 $4 of sediinent. These features 

are siilall and readily repaired, hut give 

an indication uf whdt cotild happen if 

there was widespread danage to the scagrasses. 

Seagrasses are vital to the coastal The largest cnntribut.ion to the diccosyste~i 

because they fann the &sf'; of a versity of the systt?~: is cornr~only nade by 

three-dirilertsionali , structural ly complex the conpl ex cominrnni ties that are epiphytic 

halri tat, In inodern ecology there has heen on tho scaqrass leave?. defol iation 

a shfft Frorn the autwecolo~~ica'l, approach of the seagrasses occurs, most of this 

of studylng irrdividual specics ir~dcpcnd- cctnl~runity disappears, either by being care?t~tly, 

to the corl~iuni ty or ecosystci:~ ap- ried out as drifting leaves or becoming 

groach where the focus is the l argsr i rite- part of the 1 i tter 1 ayer and ul tirnit tel y 

yvcrted cnti ty. Uith that real ization, one the surface sediments. Rith the leaves 

caul$ wonder, "Why spend s8 riuch effort on gone, the current baffling effect is lost 

a Few ~peciefi of' rnarine plants, evctlr if and the! sedirnent surface hegins to erode. 

tiley are the most abundant, in a system A1;:al nats that nay fom have minimal 

that hds thousands of other species?'The stabilizing abi 1 ity; however, the dead 

rrrinsan is that these pldnts are critical rhizonws and [%its will continue to bond 

ta crast other species nf the system, both the sedirnerlts, it1 some cases for several 

plant and animal. There are Feu other years (Patriqtdin 1375; Scoffin 1970). 

systerqs which dre so doiqinated and controlled 

by a single species as in the case 

In south Florida the disappearance of 

of a cl inax turtle grass or Tostera mca- seagrasses would yield a far different 

dow. H.T, Odurrl (1974) class~?~~-~urtle seascape. ?!uch of the region would be 

grass beds as '"natural tropical ecosystens shifting mud and mud banks, while in [?any 

with high diversity.'Vaken as a total areas the sediments would be eroded to 

r;ystc~*r, tropical seayrass beds are regions bedrock. Based on the communities found 

of very hTgR aiversity, brit this cdn be fri such ariras tod?ry, primary prodttctiet: 

c:?isleaditrg. Conparisans betueen tropical and detri tal product ion would be dramatiand 

ternperate systems were made at a time cally decreased to the point that the 

when hl'gh diversity was equated with high support base for the abundant co~nr~ercial 

biological stability. The prevail iny can- fisheries and sport fisheries would shrink 

cept was that the multitude of different if not disappear. 

38

4.5 STRUCTURAL AND PROCESS SUCCESSION XM 

SEAGRASSES 

As species succession occurs in a 

shallow marine syste1.1, important structural 

changes occur. Because seagrass 

systems do not have woody structural components 

and only possess re1 atively sirqp- 

1 i stic canopy structure, the main structural 

features are the leaf area and biomass 

of the leaves as well as the root and 

rhizome material in the sediment. The 

most obvious change with community development 

is the increase in leaf area. This 

provides an increase in surface area for 

the colonization of epiphytic a1 gae and 

fauna, with the surface area of the cl inax 

community being many times that of either 

the pioneer seagrass, shoal grass, or the 

initial algal colonizers. In addition to 

providing a substrate, the increasing 1 eaf 

area also increases the current baffl in!: 

and sediment-trappi ng effects, thus enhancing 

internal nitrogen cycl ing . 

As orga~isms grokr and reproduce in 

the environr?erit, they bring about changes 

in their surroundings. In doing so these 

organ1 srlis Frequently nodi fy the environ- 

~wnt in a way that no longer favors their 

continual growth. McArthur and Connel 1 

(1366) stated that this process "gives us 

d clue to all of the true replacerrents of 

succession: each species alters the environnent 

in such a way that it can no 

longer grow so successfully as others". 

In a shallow hrater successional sequence 

leading to turtle grass, the early 

stages are often characterized by a low 

supply of organic matter in the sedir'lent 

and open nutrient supply; that is, the 

cornunity re1 ies on nutrients bein9 

brought in froin adjacent areas by water 

movement as opposed to in si tu regeneration. 

Mi th the development from rhizophytic 

algae to turtle grass, there is a progressi 

ve devel aprnent in the he1 owground 

biomass of the co~tmunity as well as the 

portion exposed in the water column. With 

the progressive increase in leaf area of 

the plants, the sedirnent trapping and particle 

retention increase. This material 

adds organic matter to further fuel the 

sedimentary microbial cycles. A1 though 

various segments of thi s successional 

sequence have been rr~easured by nutaerous 

authors, the most complete set of data has 

recently been compiled by Will iams (1981) 

in St. Croix (Table 8). In St, Croix, 

where the data were collected, as on many 

low, small islands with little rainfall, 

the clinax is commonly a rnixture of turtle 

grass and manatee grass, In south Florida, 

with its higher rainfall and runoff, the 

climax more commonly is a pure turtle 

grass stand. In turtle grass beds in 

south Florida, Capone and Taylor (1977, 

1980) found that nitrification was highest 

on the developing periphery of the beds 

and lower in the centers where particulate 

trapping and retention were grea ter. Addi 

tional ly , mature ecosystems, both marine 

and terrestrial, seem to he based primarily 

on the detrital food weh which aids in 

conserving both carbon and nitrogen, as 

direct grazing is quantitatively low in 

these systens.

CHAPTER 5 

THE SEAGRASS COMMUNITY - COMPONENTS, STRUCTURE, AND FUNCTION 

Seagrass-associated com~unities are 

deterrnined by species cor?posi tion and density 

of seagrass present, as well as abiotic 

variables. These communities range 

frorn monospecific turtle grass beds in the 

clear, deep waters behind the reef tract 

to the shallow, muddy bottoms of upper 

Florida Say where varying densities of 

shoal grass are intermixed with patches of 

turtle grass. 

Turney and Perki ns (1972) divided 

Florida Bay into four regions based largely 

on temperature, salinity, circulation, 

and substrate characteristics. Each of 

these regions proved to have a distinctive 

17011 uscan assec~bl aae. 

Studies have also shown that great 

diversity in species number and abundance 

exists even within cornrnunities of similar 

seagrass composition and density, and 

within comparatively small geographical 

regions. Brook (1978) compared the macrofaunal 

aSundance in five turtle grass conrnuni 

ties in south Florida, where the blade 

dens i ty was greater than 3,000 bl adeslm ', 

Total taxa represented varied frorn a low 

of 38 to a high of 80, and average abundance 

of individuals varied from 292 to 

10,644 individual s/m7. 

The biota present in the seagrass 

ecosystem can be classified in a scheme 

that recognizes the central role of the 

seagrass cai-iopy in the organization of the 

system. The principal grou s are (I) epiphytic 

organisms, (21 epibenthic 

organisns, (3) infaunal organisms, and (4) 

the nektonic organisms. 

The term epiphytic organisms is used 

here the sane as that of liarfin (1980) and 

veans any organism grok~ing on a plant and 

not just a plant living on a plant. Epibenthic 

organisms are those organisms that 

live on the surface of the sediment; in 

its broadest sense, this includes rnotil e 

organisrns such as large gastropods and sea 

urchins, as well as sessile forms such as 

sponges and sea anemones or macroalgae. 

Infaunal organism are those organisns 

that live buried in the sediments. Organism 

such as penaeid shrimp, however, that 

lie buried part of the day or night in the 

sediments, hut are actively moving on the 

sediment surface the rest of the time 

would not he included as part of the 

infauna. The infauna would include organisms 

such as the relatively immobile 

sedentary polychaetes and the relatively 

nobi 1 e irregular urchins. Nektonic organ- 

isms, the highly nobile organisins livino 

in or above the plant canopy, are largely 

fishes and squids. 

Kikuchi (1961, 1962, 1%6, 198C) 

original ly proposed a functional classification 

scherne for the utilization of 

Japanese seagrass beds by fauna that has 

wide utility. This classification, modi 

f i ed for tropical organi sms, woul d 

i ncl ude (1) permanent residents, (2) 

seasonal residents, (3) temporal migrants, 

(4) transients, and (5) casual visitors. 

The third category is added here to 

include the organisms that daily ini~ratt? 

between seagrass beds and corat reefs. 

These were not included in the origl'nal 

classification ~hich was based on terperate 

fauna.

theft- h~ldfas t. Prirqary strbstrd te for 

alqae will include (1) the sediments, 12) 

Major sources of prig-ary production the seagras5es themselves, and (3) occd- 

For coastal and estuarinc areas are the sl'onal rocks or orltcrops. In addition 

fa1 1 otii ng: laany intacroalgze in south Florid? Forn 

large unattached masses can the sea botton, 

(1) Eeacrnphytes; (scagrdsr;es, iwr- col lectSvely known as 3ri ft a1 gae. 

groves, rrideroalgarj, and raarsh 

grasses) 

Althouatl vuch of south Florida offers 

sufficient hard suhstratc for alqal atf 

2) Benthr'c ri~lcroialgae (benthic and tachment, notably the reef tracts and the 

epiphytic d5alorqs, dingfl age1 - shin1 I ow zones bordering rilany of the keys, 

late$, filanentous greerr and the dominant suhstratc type is not sol id. 

bluegreen a1 gae) 

In many areas inangrove prop roots, oyster 

bases, and scattered rocks or shells and 

(3) Phytoplankton to rtrannade structures such as bridge stlpport.; 

arid canal walls offer the prinary 

a1 gal substrates. 

Al thougl~ Sn deep, turln4d northern 

esluarlos, FIJC~ ns the Chesapeake or Dela- The only al~ae able to consiste~ntly 

ware gays* phytcaplanktorr may be the cdwli- usc sediments as substrate are (I) the 

nant ycaalucor, in most areas that, kt~vkt fl~at-fon~ljng algae and (2) vernbers of the 

been r'nvss tigated the tnacrrdphytcs are the order Si phonal cs (Chl orophy ta) which 

rilaasf: fmpostant primary producers, oftan by passe$s creepinl: rhizoids that provide an 

at1 overwlnclrsi f~g in~rgin. 

anchor in sedi~*~ents (Wumm 1973). A~nong 

ttte most irriportant qenera are WjncLa, 

Pruductf v l tSes of frhytopl anktcln, 

marsh grasses, and seegrasses in a North 

Carnt 4 n$ se, tuary were conipdrsd by Mf 11 .i ams 

producers of organic 

(1973); areal gxryductfon vd'lues WIVE 53, carbon; of even greater inpartance, all 

249, and 698 gltrr +&rr rel;pf;ctivel y, Mhen but La~1- prodtacc cal cl'ur? carbona te for 

the total arca of the estuwrinc sound sys- their ~ke'lcton which, upon death, becomes 

i;&a nv;alldb?~ tn phytraptankton and sea- incorporated In the sedir:ents. 

grass was cons-islerr?d, thc seagrass production 

for tale er~tire estuary was still These algae !lave 1 imi ted sedirnen t 

&bout P,5 tf~nas the annual contributSon of stahil izing properties, the main util i ty 

the phytctp'lankl,on, In the clearer waters of their rhizoidal holdfasts being to 

of the FlofiJd erlccarles and coastal rang, maintain thlvll in place. Because they do 

the k;"iffel-ence 1% c;onsfdr;rably greater. not have a larue Investiture of structure 

In Oesc~ Ctega Bay, Taylcsr and Sal~r~an in the sediraents, they can nore rapidly 

(1968) estfrnirted tirdt Gntal production, accnmclodate changes in shifting sediments, 

which was priurrarily rrracrophyter, war; six whfle still lnaintainjnp some current 

tfnrt?s thf? annual phylopl;ar~ktor.t yradmctian. buffering capacity. In this capacl ty 

"Thaycr artd Ustack (i9CIj have ertilnated they fa119 a prior SUCC~SS~O~~? stage for 

~rasrtrphytx?;~ te, account for about 45"Xaf seaqrasses (Mil 1 isms 19G1), 

the plant productfon irh the estuarinecoastal 

area of the nortitern Gulf of Production of lime mud by these algae 

Fxexica, can be enamous, Halimeda tends to break 

up Into character? stie sand-sized pl ates, 

-- Benthic- -- !la&& 

whi 1 e Pend ci 11 us produces f i ne-grai ned 

{less than isL4 j at=aponitSc md. Stock-22 

Alga1 ctarwuni tfes ora hard substrates et al. (1967) estlrnated that at the 

can consist of hundreds of species from presefat rate af production, Penicillus 

all of the major macroalgal phyla. The alone could account for all of the fine 

areas inhabited by seagrasses do not offer mud hehind the Florida reef tract and 

an optalmal habitat for most algae, which one-third of the fine mud in northeastern 

require hard substrate Tor attachiaent of Flor-ida Ray, Xn adda'tion, the covbin3iltion 

42

of *- Udotea, and Acetabuf aria emerge, the study of cpiph tes has suf- 

Pr t as much mud as Penicil- fered from what Harlin (19803 described as 

lus in the same locations. 

the "bits and pieces" approach. 

Xn tine Bight of Abaco, PIeumann and An annotated list of 113 s~ecies of 

land (19%) calculated that the growth of algae found epiphytic on turtle grass in 

-, and Hali~eda south Florida was compiled by Hum (1964). 

produced 1,s e amou Of these only a few were specific to seaand 

Walimeda sand now in the basin and grasses; most were also found on other 

ttlat T3-typical Bahamian Bank lagoon, plants or sol id substrate, later, Ball ancalcareous 

green algae alone produced more tlne and Hum (1975) reported 66 species 

sediment than could be accommodatedr Bash of benthic algae which were epiphytic on 

(1979) measured the rates of organfc and the seagrasses of the west coast of Florinorganic 

production af cal careous siphon- ida. Rhodophyta comprised 45% of the 

ntes 4n Card Sound, Florida, using several total, Phaeophytas were only 12% and 

techniques, &ganic production was 1 ow in Chl oroptrytas and Cyanophytas each reprethds 

lagoon, rangfng from &,6 to 38.4 g sented 21% of the species. Warlin (1980) 

ash free dry weight /mi/yr, and 4.2 to compfled from 27 published works a species 

16,8 g CaCO,/mi/yr Pcrr all the specles list of the! nlicroalgae, macroalqae, and 

conbf nad, 

animals that have been recorded as epiphytic 

on seaprasses. The algal lists are 

In addftian to the calcareous algae, comprehensive, but none of the reports 

several algae arc present In grass beds as surveyed by kHuw list the epiphytic inverlarge 

clumps of detached drift algae; the tebrates frnn south Florida. 

lirrnst abundant belongs to the genus Laur3n2 

cf&, Iha areal praductfon of ehesmgae llarlin (1975) If sted the factors 

?%*mlow coinpar& with .the Seagrasses. Jas- i nfluencing distribution and abundance of 

sclyn (1975) est Jmiltsd the production of epiphytes as: 

Lauren$i&- fn Card Sound to average about 

WUB %I* 

8,1 q Z$r wcfght /tn2/yr which was less (1) Physical substrate 

than 1% of the J,lOO g/mJJyr estir?al& by (2) Access to photic zone 

Pherrharrrl et 91. (1W3) for ttirtle grass (3) F free ride tt.\rough ~ovinq 

fre)~:i the $d!ile area. waters 

(4) Nutrient exchange with host 

The least studied cmnponents OF the (5) Ornanic carbon source 

algal flora! are the benthSc nicroalpae. 

In stulffer of" benthic production through- The availability of a relatively stable 

out %he CarSbbean, Runt et nl. (1971) gal- (albej t somewhat swaying) substrate seens 

c:ulatatd the productSon in Caribbean r,@di- d0 be the most fundamental sole played by 

flarpfll~ f;O average 8.1 rrg C/mt/hr (range = the seagrasses. Thc majority of the epi- 

2,5 to 13*8 mg) igsivlg uptake. Py cop\- phytic species js sessile and needs a surjrdrfson, 

sedlrnentr; frorn the Ff ar-ida Keys face far attachnent. The turnover of the 

yff?lde?d 0*3 t0 7,4 rng C/mZ'/hr Fixation, cpiphyejc cmunity is relatively rapid 

These vl;xlucs were ~q~iv~lent to the pro- since the lifetit~c of a sinqle leaf is 

L~1~tSt~lvl 4n the vcStter colug;;rn, ferguson lialited. A typical turtle Grass leaf has a 

@t $1. (19C05 hricnfly reviet~cd rsicroatgal lifetime of 30 to 60 days (Xienan 197%). 

produckfon valucs and fndjcatcd that light After a leaf cmcrqes there is a period heand 

themal Snhibf tion occur, particu- fore epiphytic organisms appear. This nay 

7 arfy in stimfiicr. be due to the relatively svoot6 surface or 

the producticn of sane antihistic colnpound 

by the leaf. On tropical seagrasses the 

&9J2!y>J~&a2 

heaviest coatings af epiphytes only occur 

after the leaf has heen colonized by the 

One of the main functions far &i@h coral l fne red algae, Fos1 fe11ii or -- !?elah@- 

%ca$grW3SS@s have been recognir~d has he@~ G. The caral'line sk~Teton of thcse algae 

the ahil ity to provlde a substrate for the may fom a protective barrier as well as a 

attachment of epiphytic organisms, Al- sui tahly roughened and adherent sttrface 

thnuqh unffyirtg patterns arc beginning to for epiphytes (Figure 15). 

44

Figure 15. Tha1 assia blades showing tips encrusted with calcareous epiphytic algae. 

Several of the larger blades show the effects of grazing on the leaf tips. 

Seagrass leaves are inore heavily epiphytized 

at their tips than their bases 

for various reasons. For the snall algae, 

belng on the leaves has the advantage of 

raising them higher in the photic zone. 

The shading effect produced by epirthytic 

organisms on seagrass leaves decreases 

photosynthesis by 31% (Sand-Jensen 12175). 

In addition, the upper leaf surface experiences 

much greater water motion than the 

lower surface. This not only provides a 

march greater voft(m of water t~ be swept 

by suspension-feeding animal 5, hut a1 so 

reduces the gradients for photosynthetic 

organisms, Studies have shown that there 

is transfer of nutrients fran seagrasses 

to epiphytes, Karl in (1975) described the 

uotake of PO, translocated up the leaves 

ni 7ost~r-a &d phyllospadix. Epiphytic 

b1 ue-qreen a1 gae have the capaci ty t;a fix 

rnol ec;l ar nitrogen , and Coeri ng and Parker 

(1972) showed that soluble nitrate fixed 

in this manner was utilized by ';Yeagrasses, 

In some areas there are few epiphytes and 

little contribution, but in places the 

amount of production is high. Jones (1968) 

estimated that in northern Riscaync; Pay 

epiphytes contributed from 25% to 33% of 

the comuni ty metabolism. Epiphytes contributed 

18% of productivity of Zostera 

rneadows in North Carol ina (~enhalem 

The trophic structure of these leaf communities 

can be quite camp'lex and will be 

discirssed later. Much of the epiphytic 

nateri a1 , both pl ant and animal, u1 timately 

becomes part of the litter and detritus 

as the leaf senesces and detaches. 

The invertebrate fauna of seagrass 

beds is exceedingly rich and can only be 

characterized in broad terms unless one is 

dealina with a specific, defined area. 

Epiphytes also contribute to the pri- This 6 because the fauna of the grass 

mary production of the seagrass ecosystem, beds is diverse, w'ith many hundreds of 

45

species being represented within a small 

area, and variable, with dramatic changes 

occurring in the faunal composition and 

density within relatively small changes of 

time or distance. If one does not lose 

sight of these facts, it is possible to 

1 ist various organisms that are representative 

of seagrass meadows over large distances. 

The most obvious invertebrates of 

many of the seagrass beds of south Florida 

are the larqe epi benthic orqani sms (Fiqure 

16). The "queen conch (s%-ombus 'gigas) 

feeds ~rimarilv on e~iohvtes it scrapes 

from turtle grass hl ad'es', while the ah amian 

starfish-(oreaster reticulata) and the 

gastropods Fasciofaria tul i pa and PI europloca 

jigantea prey largely on infauna. 

FIumerous sea urchins. such as Lvtechinus 

variegatus and ~ri~neustes verkricosus, 

are found throughout the beds. Juveniles 

of the long-spined urchin Diadema antillarum 

are common, but the adultssen 

she1 ter of rocky 1 edges or coral reefs. 

The deposi t-feeding hol othurians Actinow 

a agassizi and Holothuria floridana may 

be found on the surface, while the large 

sea-hare, the nudi branch Aplysi a dactyl o- 

mela, may be found gracefully gliding over 

the grass canopy. At night pink shrimp 

f Penaeus duorarum) and spiny 1 obs ter 

(Panu1 irus -may 

be seen foraging in 

the seagrass along with the predatory 

Octopus br i areus. 

On shallow turtle grass flats the 

corals Manicinia are01 ata and Pori tes 

-- furcata are comaon, while in somewhat 

deeper waters sponges such as Ircinea, 

- Tetb~, and Spongia may be found. 

The infatrna can be diverse, hut are 

not visually ohvious. The riqid pen shell 

(Atrina -- rigida) is a comvon f il ter-feeder 

in many grass beds, along with numerous 

bivalve molluscs such as Chione cancelmata 

Codakia orbicularis, Tell ina radi- 

,- - - 

-- ata, Lucina pennsyl vanica, and Laevicar- 

-- 

dium laevigatuni. A variety of annelid 

worms are in the infauna, notably Areni- 

- cola cri sta ta, Onuphi s magna, Terebell id-%" 

stroeni, and Eunice 16ngicer1-a ta. 

The abundance and diversity of ~piphytic 

anivals on seagrass blades are dramatic 

evidence of the effect the seagrass 

has on increasing botta? surface area and 

46 

providing a substrate for attachment (Figure 

17). The nost prominent of these epifaunal 

organisms in south Florida are the 

gastropods. Cerithium mascarum and C. 

eburnum, Anachis sp., Astrea spp., Modulus 

modulus, Witrella lunata, and Bi ttiu~ 

varium are characteristic in turtle grass 

and shoal grass habitats throughout south 

Florida, as is the attached bivalve 

Cardi ta fl oridana. 

Small crustaceans are a1 so common in 

seagrass beds where they live in tubes attached 

to the leaf surface, move freely 

along the blades, or swim freely between 

the blades, the sediment surface, or the 

water column above the blades. Common anphi 

pods are cymadysa compta, Gammarus mucronatus, 

-- 

Flel ita nitida, and Grandidierx 

bonnieroides, while the caridean shrimps 

Palacmonetes pugio, P. vulgasis, and P. 

- intermedius, Pericl imenes longicaudatus, 

and c. americanus, Thorfloridanus, Tozeuma 

carol i n v i ppolyte aura= 

A1 pheus normanni , and A. heterochael* are 

abundant within the grass beds. Hermit 

crabs of the genus Paqurus are numerous 

and at night crawl up the blades to graze 

on epiphytic material. When they reach 

the end of the blades, they simply crawl 

off the end, fall to the sediment, scuttle 

to another blade, and repeat the process. 

Structure and Function - --- 

The structure of the grass carpet 

with its calm water and shaded microhabitats 

provides 1 iving space for a rich epifauna 

of both mobile and sessile organiso~s 

(Harl in 1980). It is these organisms which 

are of greatest ir~portance to higher consumers 

within the grass bed, especially 

the fishes. When relatively ma1 1 quantitative 

samples are used in estimating populatiorl 

sizes, gastropods, amphipods, anc! 

polychaetes are typically mast nuverous , 

hi le i sopods can be important (Naole 

19-58; Carter et al. 1973; Marsh 1973; Kikuchi 

1974; Brook 1975, 1977, 1978). In a 

Card Sound turtle grass bed, Rrook (1975, 

1977) estii~aterl that amphipods represented 

62,ZY of all crustaceans. When the trawl 

is e?lployed as a sariplin~ device, dccapods, 

including penaeid and caridcap 

shrinp and true crabs, as well as ?astropods, 

are general ly most ahundant 

in i nvertehrate col 1 ections (Thorhauq 

and Rocssl~r 1977; Yokel 1?75a, 1?75h;

Fish 

I] 

lnver tebrates 

HEAVY THIN SAND/ MUD/ 

SEAGRASS SEAGRASS SHELL SAND / 

( Halodule & ( Halo dule ) SHELL 

T halassia ) 

Figure 18. Re1 ative abundance of fishes and invertebrates over seagrass beds and adjacent 

habitats (after Yokel 1975a). 

hy discriminating on the basis of form 

(~arry 1974). Stoner (1980a) demonstrated 

fish species that will ultimately be of 

commerci a1 or sport fishery value. The 

that common epifaunal amphi pods were cap- classification created by Ki kuchi (1961, 

able of detecting small differences in the 1962, 1966) was largely inspired by the 

density of seagrass and actively selected fish community found in Japanese Zostera 

areas of high blade density. When equal beds and has effectively emphasized the 

blade biomass of the three common sea- diverse character of seagrass fish and 

grasses (turtle grass, manatee grass, and major invertebrates, while a1 so serving to 

shoal grass) were offered in preference underscore the important ecol ogical functests, 

shoal grass was chosen. When equal tions of seagrass meadows within the estusurface 

areas were offered no preferences ary as nursery and feeding grounds, 

were observed, indicating that surface 

area was the grass habitat characteristic Permanently resident fishes are typichosen. 

cally small, less mobile, 

species that spend their 

more cryptic 

entire life 

within the grass bed. few, if any, of 

5.3 FISHES these species are of direct commercial 

value but are often characteristic of the 

Compos i ti on seagrass habitat. The emerald cl ingfish 

(Acyrtops beryl1 ina) is a tiny epiphytic 

Seagrass meadows have traditional JY species found only 1 iving on turtle grass 

been known to be inhabited by diverse and blades. In south Florida, members of 

abundant fish faunas, Often the grass bed families Syngnathidae, Gobiidae, and 

serves as a nursery or feeding ground for Cl inidae may be included in this group. 

49

The pipefi shes, Syngnathus scovill i, S. 

floridae, S. louisianae, and Micrognatcs 

- crinigerus, as well as the seahorses Hipocainpus 

zosterae and H. erectus are abun- 

{ant in seagrass throughout south Florida. 

The gobies and clinids are diverse groups 

and well represented in seagrass- fish 

assemblages of southern Florida. The most 

abundant- goby is Gobi soma robusturn. The 

cl inids aneear to b e e m c 1 earer 

watercof the Florida Keys and Florida 

Bay, where Paraclinus fasciatus and P. 

marmoratus are most abundant. 

-- 

Other resident fish species are characteristic 

of seagrass hahi tat. The 

inshore 1 izardfi sh (Synodus foetens) is a 

conmon epibenthic fish predator. The 

small grass hed parrotfishes -- Sparisoma 

-- rubripinn, . radians, and 2. chrysop- 

- terurn -- are found in the clearer waters 

of the Florida Keys where they graze directly 

on seagrass. Eels, including members 

of families Moringuidae, Xenocongri- 

dae, Muraenidae and Ophichtidae (Robbl ee 

and Zieman, in preparation), are diverse 

and abundant in grass beds of St. Croix, 

U.S. Virgin Islands. These secretive 

fishes are typically overlooked in fish 

south Florida, are joined by the schoolmaster 

(L. apodus) the mutton snapper (L. 

community surveys. In the grass 

+ 

beds of analis) The dog snapper (L. u), and the 

south Florida, the Ophochtid eels F1 rich- ye1 lowtail snapper (Ocycrus chrysurus). 

JA-ys- acuminatus, the sharptail eel, an !?. Thayer et al. (1978b) list several seasonoculatus, 

the olds spotted eel, can coK- ally resident fishes that are pror~inent 

~rlonly be observed moving through the grass fishes of sport or commercial fishery 

during the day whilc young moray eels, value and include the sea bream (Prchosar- 

Gymnothorax spp., are not uncomrnon at 

n ~ g h t m i n g in grass beds for molluscs. 

Seasonal residents are animals that 

spend their juvenile or subadult stages or 

their spawning season in the grass bed. 

Sciaenids, sparids, ponadasyids, l utjanids, 

and gerrids are abundant seasonal 

residents in south Florida's seagrass cornmuni 

ties. Seasonal residents use the seagrass 

meadow largely as a nursery cround. 

At least eight sciaenid species have 

been found over grass in the variable 

salinity, high turbidity waters of southwestern 

fSoridais estuaries and coastal 

lagoons. Not all of these fishes occur 

abundantly, and only the spotted seatrout 

of muddy bottoms and turbid water associated 

with grass in Florida's variable 

salinity regions (Tabh and Manning 1961; 

Tabb et al. 1962; Yokel 1975a, 1975b; 

Weinstein et al. 1977; Weinstein and Heck 

1979) and is at best rare in the Florida 

Keys. Other grunts occur over grass only 

rarely in southv~estern Florida and Florida 

Bay and include Anisotrenus vir inicus, 

Haemulon scirus, and C(. aura -i-- ineatum. 

Lagodon rhonboides, the pinfish, was the 

most abundant fish collected in these 

waters and has demonstrated a strong aff 

i ni ty for seagrass (Cunter 1945 ; Cal dwell 

1957; Yokel 1975a, 1975h). - Eucinostor~us 

araenteus are seasonally 

%da;? gzrid-most corvnon over 

grass. 

5 0 

With the exception of the pigfish, 

the pomadasyids already mentioned are 

joined by H,- fl avo1 ineatum, H. parri , and 

- 

H. carbonarium in the clearer waters of 

the Florida Keys. Snappers and arunts are 

more diverse i"n the cl karer waters of the 

Florida Keys. Lutjanus ariseus and L. 

gnqari s, which are common throuahout 

gus mhoides), the sheepshead 

batocepham the gap grouper (F" ctero 

and the redfis'- 

The subtropi ca1 seaarass system of 

south Florida appears to differ significantly 

from more temperate beds by the 

presence of relatively large nurqhers of 

prominent coral reef fishes over grass at 

night when the bed is located in the vicinity 

of coral reefs. Fishes from families 

Pomadasyidac, Lutjanidae, and Holocentridae 

find shelter on the reef during the 

day and move into adjacent grass beds at 

night to feed, This situation is typical 

of Caribbean seagrass meadows. A71 of the 

grunts and snappers mentioned above except 

- 0. chrysurus, when of appropriate size, 

will five diurnally on the reef and feed 

in the grass bed at night. Die1 visitors 

use the grass bed primarily as a feeding 

ground.

Figure 19. 

Small grouper (Serranidae) foraging in seagrass bed. 

in controlling abundances and species corn- 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 

respond to the structural complexity of 

and density of the grass beds. In Florida, 

where the seagrasses are typically 

the grass canopy. Noting the size distri- larger and denser, the grass beds offer 

bution of ffshes typically inhabiting sea- she1 ter for much larger fish than in St. 

grass beds, Ogden and Zieman (1977) specu- Croix, where the study of Ogden and Zievan 

laled 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 small enough to hide that abundance and diversity of fishes 

within the grass carpet. For fishes 1 arger 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 interferenviroment; 

these fishes are too large to ence with the grass blades or because 

find shelter within the grass carpet. conditions within the grass canopy become 

Hid-sized fishes (20 to 40 cm or 8 to 16 unfavorable i e., anoxic conditions at 

inches) are probably excluded from the night). At thts point densities should 

grass bed by occasional large predators, drop off. Evidence indicates that feeding 

Mid-si ze fishes are apparently restricted 

to she1 tered areas by day and may move 

efficiency does decl ine with increasing 

structural complexity.

The pi nfi sh's predatory efficiency on 

amphi pods decreases with increasi ng density 

of Zostera marina blades (Nelson 

1379a). ~ 1 9 ~ o u in n single- d 

species experiments (one shrirnp species at 

a time) that with increasing cover of red 

(Pal aemonetes pugio) in areas of densest 

artificial seaarass. Virtual1 y nothing is 

known about tte relation of typical grass 

bed fishes and their predators; research 

on this topic would be fruitful. 

5.4 REPTILES 

A1 though there are several species 

of sea turtles in the Gulf of lilexico and 

Caribbean, the green sea turtle (Chelonia 

m das) is the only herbivorous sea turtle 

r" Figure 20). In the Caribbean, the main 

food of the green turtles are sea grasses 

and the preferred food is Thalassia, 

hence the name turtle grass (see section 

6.2). 

Green turtl es were formerly ahundant 

throughout the region, but were hunted 

extensively. Concern over the reduced 

populations of green turtles dates back 

to the previous century (Munroe 1897). 

A1 though limited nesting occurs on the 

small beaches of extreme south Florida, 

the region has almost certainly been primarily 

a feeding rather than a nesting 

site. Turtle and manatee feeding behavior 

are described in Chapter 6. 

The American crocodi 1 e (Crocodyl us 

acutus) occurs in the shallow water 

of Florida Bay and the northern Keys. 

Figure 20. Seagrass bed fol lowing grazing by green sea turtle. Note the short, evenly 

cl i ed blades. The scraping on the Thalassia blade in the center is caused by the 

smaQf emerald green snail, Smaraqdia vir~o~s. 

53

81 though crocodiles undoubted1 y feed in 

shallat.: grass beds;, little is known of 

their utilization of this habitat, 

5.5 Birds 

The seagrass beds of south Florida 

are used heavily by large numbers of 

bjrds, especially the wading hfrds, as 

fcedf ng grounds, This heavy util ization 

3s wssibfe kcilust?. of the relatively high 

propartian of very shall ow grass bed habitat, 

Thare are few studies of the utilirat9on 

of seagrass beds by birds, although 

there are extensive lists af birds 

us f ng tempera tc seay rasses and aaua t f c 

plants (HeRoy and tiel fferich 1980). Birds 

known to us@ the seagrass habitat of south 

Florida and t;hsSr modes af Feeding are 

listed Sn Table 9, 

"Tree cmon mthods of feeddr~g in 

bi~ds are wading, swirrtniing, and plunging 

from sorne distance in the air to sieze 

prey. The most cornon of the swif:saing 

birds is the daub1 e-crested cormorant 

which pursues fish in the water co!umn. 

Cormorants may be found wherever the water 

is sufficiently deep for them to swim, and 

clear enough for them to spot their prey. 

The osprey and the bald eagle sieze prey 

on the surface of the water with their 

claws, while the brown pel ican pluges from 

some distance in the air to engulf fishes 

with its pouch. The value of the seagrass 

meadows to these birds is that prey are 

more concentrat4 in the grass bed than in 

the surrounding habi tst, thus providing an 

abundant food sourcc. 

The extensite shallow grass flats are 

excel 1 ent forar I ng grounds for the 1 arger 

wading bfrds "igure 21). The great white 

heron is c,mmon an the shallow turtle 

grass flats on the gulf side of the lower 

Keys. The great blue heron is common

Table 9. Birds that use seagrass flats in south Florida 

(data provided by James A. Kushlan, Evergaldes National Park). 

Preferred 

Cornmon name Species name feeding tide 

Waders-primary 

Great hl ue heron 

Great white heron 

Great egret 

Reddish egret 

- 

Prdea herodi as 

- A. herodias 

Casmerodius a1 bus 

Egrettaescens 

Low 

LOW 

Low 

Low 

bladers-secondary 

Louisiana heron E. tricolor Low 

Little blue heron F. caerulea Low 

Roseate spoonhi 11 qaia ajaja Low 

Millet Catoptrophorus semi palmatus Low 

Swimmers 

Doubl e-cres ted 

cornorant 

White pel ican 

(winter only) 

Crested grebe 

(winter) 

Red-breasted merganser 

(winter) 

Flyers-plungers 

Osprey 

Bald eagle 

Brown pel ican 

Phal acrocorax auri tus 

Pel ecanus erythrorhynchos 

Mergus serrator 

High 

High 

Pandian ha1 i a m 

High 

~ -- t ~ e u c o c e p hus a l High 

-- Pelecanus occidental is 

High

CHAPTER 6 

TROPHIC RELATIONSHIPS 

IN SEAGRASS SYSTEMS 

6.1 GENERAL TROPHIC STRUCTURE than previously suspected; however, it 

still 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 (I) direct herbivory, (2) detrital 1988; Ogden 1980). 

food webs within grass beds and (3) exported 

material that is consumed in other Stud1 es have attempted to measure the 

systems either as macropl ant 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 i tter layer, or exported. Greenway 

has been considered the primary pathway, (1976) in Kingston Harbor, Jamaica, estfand 

in most cases is probably the only mated that of 42 g/mL/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 radgathered 

on the relative role of the other ians; 48.1% was consumed by the urcK 

modes of utilization. The picture marg- -chinus ariegatus; and 42.1% deposited 

ing is that in many locations both the % 

on t e ottom and available to detritidirect 

utilization pathway and the export vores. The rest of the production was 

of material may be of far more importance exported from the system. This study may 

/-- -"#----'---- .-------. 

- 

i" 

LP'~ 

DRIFT €3, 

EXPORT 

DECAY, 

PLANT CANOPY 4 

STRUCTURE 

PRODUCTION 

Figure 22. 

.. . 

Principal energetic pathways in seagrass beds. 

5 7

overenphasize the quantity of seagrass Piscdync Bay, turtle grass forrred the ~iios t 

material entering the grazing food chain important constituent of the detritus 

since urchins are not typically found at present f 87. I%), wilil e other portions 

densities of 20 urchins/nz as was the case included 2.12 other seagrasses, 4.6% 

in Kingston Harbor (Ogden 1980). In St. algae, 0.4% animal remains, 3.3'lrangrove 

Croix, it has been estimated that typi- leaves and 2.5% terrestrial paterial 

cally between 5% and 10% of daily produc- (Fenchel 1970). The microbial com~~unity 

tion of turtle grass is directly consumed, living in the detritus collected consisted 

primarily by Sparisama radians and second- mainly of bacteria, small zoofl age1 1 atcs, 

arily by tile urchT17 Ti-a anti1 larup diator~s, unicell ular algae, and cil iates. 

and Tri neustes ventricosus. Averaged over It is these types of organism which forci 

the -&&- turtTii"-grass production was the major source of nutrition for detri tal 

2.7 g dw/m3/day of which only about l-eeders. R1oo1-1 et al. (1972), cantos 

was exported, while 60% to 100% of the and Simon (1974), and Young and Young 

0.3 g dw/m"day production of manatee (1977) provided species 1 ists annotated 

grass was exported (Ziernan et al. 1979). with feeding habits for r~olluscs and 

Froin these figures it is conservatively pofychaetes, many of which ingest detriestimated 

that about 70% of the daily tus. 

production of seagrasses vlas available to 

the dctri tal system. 

Typically penaeid and caridean shrimp 

are considered to be o!nnivores. The pink 

Nany of the small organisms in grass shrimp (Penaeus duorarurn), in addition to 

beds use algal epiphytes and dctri tus as organic detritus and sand, ingests polytheir 

food sources. The gastropods are chaetes, nematodes, caridean shrivp, 

the most prominent organisms feeding on rrrysids, copepods, i sooods, arnphipods, 

epiphytic algae in seagrass beds. Amphi- ostracods, molluscs and forarniniferans 

pods, i sopods, crabs, and other crusts- (El dred 1958; Eldred et a1 . 1961). These 

ceans Ingest a mixture of epiphytic and consumers strip the bacteria and other 

benthic algae as well as detritus (Odurn organisms from the detritus, and the fecal 

and Weald 1972). As research continues, pel 1 ets are subsequently reingested folit 

is becoming apparent that the util i za- 1owi ng recolonization (Fenchel 1370). 

tian of this cornbination of r?icroaJgac and Some fishes, notably the mullet (Muail 

detritus represents one of the rnajor ce halus), are detrital feeders 'a 

dr 

energy transfer pathways to hiaher organ- 

several 1 argc invertebrates such 

i sms . as the gastropod Strornhus giaas (Randal 1 

1964) and the asteroid Oreaster reticula- 

Hatable by their absence are the & (Schcibl ing lofif!) taker] tus as a 

large flocks of ducks and related water- part of their food. To emphasize the 

fowl found on ternperate Zostera beds and importance of detritus to higher trophic 

especially the freshwater Ru ia Reds levels within the grass, the work of Carr 

(Jacobs et al. 1981). IbScRoy an See Helfferich and Adams (1973) shc~ulcl be noted. They 

(1980) list 43 bird species that consune found that detritus consumers were of 

seagrass primarily in the temperate zone. majar inportance in at least one feeding 

Relatively f e ~ 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 la73; Adam 1976b; Erook 1975, 1977; 

base of a major pathway of energy flow in Robertson and Howard 19781, as opposed to 

seagrass meadows. A significant proportion simply uslng their. for she1 ter. fypicafly, 

of net production In the seagrass bed re- seagrass-associated fishes are small, gensu1 

ts in detritus either by dying in place eralist feeders, tending to prey upon epiancl 

being broken down over a ~eriod of faunal organisms, primarily crustaceans. 

months by bacteria, fungi and other organ- Infaunal animals are under used in proporisins 

(Robertson and Nann 1980) or by being tion to their abundance as few fishes 

consumed by large herbivores, fragmented, resident in the grass beds feed on them or 

and returned as feces (Ogden 1980). In on other fishes (Kikuchi 198c). 

58

I\iumcrous fishes ingest sor:e plant 

material, while relatively fev~ of these 

species are strict herbivores ; exceptions 

are the Scarids and Acanthurids already 

l~lentioned. flost plant and detri tal rnaterial 

is probably taken incidentally while 

feedin9 on other organisrqs. Ortkopristis - 

chrysoptera and Lagodon rko~rlboides are two 

very amant grass bed fishes in south 

Fl or i da and apparently during sone feeding 

stages are oliini vores, ingesting subs tantial 

arnounts of epiphytes, detritus and 

seagrass (Carr and Adam 1373; Adams 

1?76a, 1976b; Kinch 1979). Other o~iinivores 

include some filefishes, porgies, blennies, 

and gobies. 

Gastropods are fed upon by a variety 

of fishes including wrasses, porcupine 

fishes, eagle rays, and the perr~ii t Trach- 

- ~iotus ---- folcatus. Randall (1367) 1 istedx 

species of fishes that feed on gastropods, 

25 ingesting 10% or nore hy volume. !lost 

sl~ecies crush the shell while ingesting, 

but s few swallow the gastropod whole. 

The white grunt (Hacoulon pluveri ) appears 

to snap off the extended head of Ceri thiurri 

ignoring the shell. Thc southern 

-9 

stingray (Dasyatus arnericana) has been 

observed turninq over the queen conch 

(Strombus --- jigas) and wrenching off the 

conch's extended foot with its .iaws as 

the conctl tries to right itself -(~andal 

1964). The spiny lobster (Panul irus 

argus) is an active predator on seagrass 

1:1oll USCS. 

epifauna, the ir~gact of blue crab predation 

may be greatest on epibenttric 

fauna. 

The majority of fishes within the 

grass bed feeds on small, ~~obile epifauna 

including copepods, cuwaceans, anphi pods, 

isopods, and shrimp. Fishes feeding in 

this manner include all the seasonally 

resident fishes of the south Fl widd crass 

beds, such as the Sci aenids, Pomadasyids, 

Lutjanids, and Gerrids, as well as oany of 

the permanent residents, 1 i ke Syngnathids, 

and Clinids. As such, they are deriving 

!nuch of their nutrition indirectly from 

seagrass epiphytes and the detri ta1 com- 

~iiunity present in the grass bed rather 

than the grasses themselves. Many of these 

fishes, as adults, will feed on other 

fishes ; however, as juvenile reside~ts in 

the grass beds, their srqall size limits 

the^:^ to eating epifauna. 

Important piscivores are present in 

south Florida qrass flats. These include 

the lenon shark 

6.2 DIRECT HERBIVORY 

The southern stingray and the spotted Caribbean grass beds may be unique 

eagle ray (Aetobatis -- narinari) art. two of for the numbers and variety of direct cona 

relatively few number of fishes that surners of blade tissue (Ogden 1980) as 

feed on infauna withjn the grass bed. relatively feld species ingest greefl sea- 

These fishes excavate the sediments. grass in significant quantities (Table 

Other similar feeders are wrasses, goat- 10). Prominent herbivores include urchins, 

fishes, and mojarras. Adult yellowtail conch, fishes, as well as the green tursnapper 

(Oryhurus chrysurus) have been ob- tle, Chcl onia mydas, and Caribbean manatee 

served foraging in bac-f seagrass sed- (Tric-anatus). -- The elucidation of 

iments (Zieman, personal observation). the role of direct herbivory as a pathway 

That the infauna is not heavily preyed of energy flow in seagrasses has been 

upon is typical of seagrass beds (Kikuchi 

1974, 1980). Apparently the protection 

slow in developing. Until recently, it 

was assumed that few organisms consumed 

fro~tl predation afforded the i nfauna of 

grass beds is great enough that few fishes 

seagrasses directly, and that herbivory 

had substantially decreased with the 

specialize on infauna wheri feeding (Orth decline of the ~o~ulations of the green 

1977b). The blue crab (Callinectes sea turtle. Direct grazing of seaqrasses 

sapidus) has been observed toyhift its in south Florida is prohaSly of greatest 

feeding froin Zostera infauna to epibiota importance in the grass beds of the Florand 

thus, because of the protective rhizone 

layer and the accessibility of the 

ida Keys and outer margin of Florida Bay 

which are relatively Close to coral reefs. 

59 

-3

Table 10. 

Continued. 

Herbivore 

scientific 

name 

Part of Seagrass Location 

Comnon Seagrass seagrass in diet of 

name eaten eaten (%) population Reference 

0-l 

FCHIYODERMS - - 

(continued\ 

~~techinus'varie~atus Sea urchin 

Thal assia 

Thal assi a 

Thalassia 

Thalassia 

Syri ngodium 

Thal assi a 

Tri pneu_stes esculentus Sea urchin 

- Smarayd~a viridis Emeral d Thal assia 

neri te 

Tri pne~lstes vontricosus Sea urchin Thal assi a 

Leaf 

Leaf 

Leaf 

Leaf 

Leaf 

Leaf 

Leaf 

Leaf 

Flax. lG0 

Max. 1CO 

Florida Camp et a1 . 1973 

Jamaica Greenway 1974 

Caribbean Yoore et al. 1963a 

Lawrence 1975 

Florida Moore et al. 1963b 

Fl orida J. Zieman and R. 

West Indi es Zieman per. ohs. 

F1 orida Lawerence 1975 

VERTEBRATES 

Acanthostracion 

quadricornir 

Acanthurus bahianus 

--- 

Acanthurus chi rurgus 

Cowfi sh 

Ocean surgeon 

Doctor fish 

---- Acanthurus -- coeruf eus Blue tang 

-- A1 utera schoepf i 

Orange 

filefish 

Thalassia 

Syr i ngod i urn 

Halophila 

Thalassia 

Syri ngodi um 

Thal assia 

Syri ngodi urn 

Thal assi a 

$;An;y:um 

P 

Syringodium 

Leaf 

Leaf 

Leaf 

Leaf 

Leaf 

Leaf 

Leaf 

3 West Indies 

8.2 West Indies 

40-80 (T. ) 


25 West Indies 


67 Mest Indies 

Randall 1967 

Randall 1967 

Randall 1965 

Randall 1965 

Randall 1967 

Randall 1967 

Randall 1967 

(continued)

Table 1C. 

Continued. 

tlerbi vore Part of Seagrass Location 

scientific Comon Seagrass seagrass in diet of 

name nane eaten eaten (z) population Reference 

FISHES (continued) 

Rug4 I curerna White mu1 let Thalassia Leaf 

Pogonias chromis Black drum Ha1 odul e Leaf 

Po'iydactyl us Threadfish Thal assia Leaf 

virginicus 

Ruppi a 

West Indies Randall 1967 

Texas Carangelo et al. 1975 

Puerto Rico Austin and Austin 1971 

P 

Pornacanthus Grey Syri ngodium Leaf West Indies Earle 1371 

arcuatus angel fish Ruppia 0.1 West Indies Randall 1967 

Po~iacanthus paru 

Poriacentrtis fuscus 

French 

angel fish 

Du sky 

damsel fish 

Syringodium 

Hal ophi 1 a 

Syringodiurn 

Leaf 

Leaf 

West Indies 

West Indies 

Randall 1967 

Randal1 1967 

Ponlacentrus 

p1 ani frons 

Three-spo t Thal assia Leaf 

damsel f i s h 

West Indies Randall 1967 

- Leaf Texas Caranoel o et a1 . 1974 

Bhinoptera quadril oba Cownose ray Thalassia 

-- Hal odul e 

Scarus - coel estinus Midnight -- 

Thalassia Leaf 1.3 West Indies Randall 1467 

narro tf i sh 

Scarus guacainai a ~a \ nborf S rin odium Leaf 35 West Indies Randall 1967 

parrotfish Leaf 8 West Indies Randall 1967 

Thal assia 

--- Scarus - retul a 

ween Thal assia Leaf 3.2 West Indies Randal1 1967 

parrot-fi sh 

(continued)

c rc rc r c r c r c r c rc rcrc rc 

rd a a m a a m a a m 

W W w w w a , a, w w w 

J .A A A J J A 3 Ad -1

The herbivory of parrotfish and sea urchins 

[nay be important in the back reef 

areas atid in Hawk Channel ; but, with the 

exception of sporadic grazing by passing 

turtles, herbivory is low or non-existent 

in the areas to the west of the Florida 

Keys (J.C. lieman, personal observation). 

Parrotfish typically move off the 

reef and feed durinq the da.y (Randall 

1965). wi --- so~a radians, 2. rubri pinne, 

and 5. chrysopterurn are known to feed on 

seagrass and associated alqae (Randal 1 

1967). The bucktooth parrotfish (S. -- radi- 

- ans) feeds alinost exclusively on turtle 

grass. Other fishes that are important 

seaarass consumers are suraeonfi shes 

(~canthuridae) (Randal 1 1967; C1 avi jo 

lP14)ThTporgies (Sparidae) (Randal 1 

1967; Adams 1?7Gb), and the halfbeaks 

(Herniramphidae) . 

Fishes in the Caribbean seagrass heds 

tend to be general ist herbivores, selecting 

plants in approximate relation to 

their abundance in the field (Ogden 1976; 

Ogden and Lohel 1978). Some degree of 

selectivity is evident, however. ~parisoma 

chr so term and S. radians, when given a 

d c ! sel eFt seagrass with epiphytes 

(Lobe1 and Ogden, personal communication). 

Seagrasses (turtle grass, manatee 

grass, and shoal grass) ranked hishest in 

preference over conimon a1 gal seagrass 

associates. 

in many areas because of its high food 

value and ease of capture by man. Conchs 

are found in a variety of grass beds, from 

dense turtle Grass to sparse manatee grass 

and Halo hila. When in turtle grass beds 

conc fe- s prir~arily feed by rasping the epiphytes 

from the leaves as opposed to eating 

the turtle grass. In sparse grass 

heds, however, conchs consuned 1 arge quantities 

of manatee grass and Halo hila 

(Randall 1964). R maxinun of Z h 

stomach contents of conchs at St. John, 

U.S. Virgin Islands, was conprised of turtle 

grass. In manatee grass (Cymodocea) 

heds, conchs consumed [nos tly this seagrass 

alorio with some algae. The rrlaximum quanti 

ty of seagrass found was 80% Halophila 

from the gilt of four conchs from Puerto 

Rico. 

The emerald nerite (Smara dia viridis), 

a small gastropod, common y 

8 mrr long, can be numerous in turtle grass 

beds althouqh it is difficult to see because 

its bright green color matches that 

of the lower portion of the turtle grass 

blades. It is a direct consumer of turtle 

grass where it roams about the lower half 

of the green blades; the snail removes a 

furrow about 1 mm wide and half the thickness 

of the blade with its radula (J.C. 

Ziefian and P.T. Zieman, personal observation). 

- + 

Post studies (for review, see Lawrence 

1975) indicate that the majority of 

seagrass consumers have no enzymes to digest 

structural carbohydrates and that, 

with the exception of turtles and possibly 

manatees, they do not have a gut flora 

capable of such digestion. Thus, most 

macroconsurners of seaqrasses depend on the 

Urchins that feed on seagrass include 

Eucidari s -- tri buloides, Lytechinus variega- 

- tus, Diadema anti1 larun and Tripneustes 

ventricosus(14~~0~964, 1968; Randall 

et al. 1964; Kier and Grant 1965; Moore 

arid t':cPherson 1964; Prim 1973: Abbott 

et a1 . 1974; 0cjden- ct a1. 1973; Moore cell contents of seagrasses and the atet 

a1. 1963a, 1963b; Greenway 1976). The tached epiphytes for food and must have a 

latter two urchins feed in approxirqate mechanism for the efficient maceration of 

proportion to food abundance in the area. the material. The recent work of tdeinstein 

Vhere present in seagrass beds, 1.-- ventri- et a1. (in press), however, demonstrated 

- cosus and D. antillarum feed on seagrasses that the pinfish was capable of digesting 

with epiphytes exclusively (Ogden 1980). the structural celluf ose of detri tal matis 

largely a detri- ter or green seagrasses. Feeding rates 

b ~ has t denm-led are high for urchins and parrotfishes, 

large areas in west Florida (Cainp et a1. while absorption efficiency is around 50% 

1973). (fgioore and McPherson 1965; Lowe 1974; 

Ogden and Lobe1 1978). Assimilation effi- 

The queen conch (Strmbus gigas), ciencies for T, ventricosus and L. varieonce 

a comon inhabitant f Caribbean sea- gatus are rerativefy low, 3.8% and 3.0% 

grass beds, has been dramatically reduced respectively (Yoore et a1 . 1963a, 196%).

The result of macroherbi vore grazing There is little doubt that the strucwithin 

the grass bed can be dramatic (Camp ture of many grass beds was profoundly 

et a1 . 1973). Of greater overall signifi- dffferent in pre-Columbian times when turcance, 

however, is the fragmentation of tle populations were 100 to 1,000 times 

1 iving seagrass and production of particulate 

detritus coincident with feeding. 

greater than those now. Sather than randomly 

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 seafrom 

the bed (Greenway 1976; Zieman et a1 . 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 1 itter layer 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 crazed patches, 

maintaining blade lengths of only a few 

Many of the macroconsumers, such as centimeters (Bjorndal 1980). Thayer and 

Acanthurids, 2. rubri inne and 2. chrysop- Engel ('5 in preparation) calc~~lated that 

- terum (Randall -&ngesting 1 iving an intermediate-sired Chel onia (64 kg or 

seagrass take in only small amounts, the 141 1b) consumes d a i l y 7 5 weiqht of 

majorl ty of their diet consisting of epi- blades equivalent to 0.5 m2 of an avera e 

phytic alpae. Species primarily ingesting turtle grass bed (500 g dw of leavesy. 

seagrass (i.e., $. radians) typically pre- Since the regrazed areas do not contain as 

fer the epiphytized portion of the sea- heavy a standing crop as ungrazed grass 

grass blade. These observations suggest beds, it is obvious that their grazina 

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 dispet. 

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 1 iving sea- The first time turtles graze an area 

grass, hut often ingest significant quant- they do not consume the entire blade but 

ities of organic detritus with its asso- bite only the lower portion and allow the 

ciated flora and fauna. Tozeuma carolin- epiphytized upper portion to float away. 

-' ense a common caridean shr4mp, feeds on This behavior was recently described in 

epiphytic algae attached to seagrass some detail by Bjorndal (1980), b ~ the ~ t 

blades but undoubtedly consumes coincidentally 

other animals (Ewald 1969). Three 

earl iest description was from the Dry 

Tortugas where John James Audubon observed 

of the four seagrass-dwell i ng amphi pods turtles feeding on seagrass, "which they 

common in south Florida use seagrass epi- cut near the roots to procure the raost 

phytes, seagrass detritus, and drift algae tender and succulent part" (Audubon 1F34). 

as food, in this order of importance (Zirnmerman 

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 searate 

by C madusa corn ta Gammarus mucro- grass leaves, as this complex was of 

natus, a r d k &' ~ ~ EpimcT@ higher food value than the plain seaqrass 

were also assimilated more efficiently by leaf. Pllthough this seeas logical, it 

these arnphipods (48"/, 43% and 75X, respec- appears not to he so, at least not for 

tively) than other food sources tested, nitrogen compounds. While studying the 

incf uding macrophytic drift algae, 1 ive food of turtles, !.?ortimer (1976) found 

seagrass, and seagrass detritus. Live 

seagrass had little or no food value to 

that entire turtle grass 1 eaves collected 

at Seashore Key, Florida, averaged 1.7% !! 

these amphi pods. 

on an ash free basis, while turtle grass 

68

1 eaves pl us their epiphytes averaged 1.4% 

N. Bjorndal found that grazed turtle 

grass leaves averaged 0.35% N (AFDw) 

higher than ungrazed leaves, and Thayer 

and Engel (MS. in preparation) found a 

nitrogen content of 1.55% (DM) in the 

esophagus of Chelonia. Zieman and Iverson 

(in preparat'found that there was a 

decrease in nitrogen content with age and 

epiphytization of seagrass 1 eaves. The 

basal portion of turtle grass leaves from 

St. Croix contained 1.6% to 2.0% N on a 

dry weight basis, while the brown tips of 

these leaves contained O.G% to 1.1% N, 

and the epiphytized tips ranged from 0.52 

to 1.7% N. Thus the current evidence 

would indicate that the green seagrass 

leaves contain more nitrogen than either 

the senescent leaves or the leaf-epiphyte 

covpl ex. By successively recropping 

leaves from a plot, the turtle maintains 

a diet that is consistently higher 

in nitrogen and lower in fiber content 

than whole 1 eaves (6jorndal 1980). 

Grazing on seagrasses produces 

another effect on sea turtles. In the 

Gulf of California (Felger and Moser 1973) 

and Nicaragua (Mortimer, as reported by 

Bjorndal 1980), witnesses reported that 

turtles that had been feeding on seagrasses 

were considered to be good tasting, 

while those that were caught in areas 

where they had fed on algae were considered 

to be "stinking" turtles with a defini 

te inferior taste. 

Thayer and Engel (gS. in preparation) 

suggested that grazing on seaorasses can 

short-circuit the time frame of decornposition. 

They showed that an intermediatesized 

green turtle which consumes about 

300 g dry weight of leaves and defecates 

about 70 g dry weight of feces daily, does 

return nitrogen to the environment at a 

%ore rapid rate than occurs for the decomposition 

of a similar amount of leaves. 

They point out that this very nutrientrich 

and high nutritional quality fecal 

matter should be readily available to 

tritivores. It is also pointed out that 

is matter is probably not prodaced 

entirely at the feeding site and thus 

provides an additional interconnection 

between grassbeds and adjacent hahi tats. 

common throughout the Caribbean, especially 

in the mainland areas, but is now 

greatly reduced in range and population. 

Manatees live in fresh or marine waters; 

and in Florida, most manatee studies have 

focused on the manatee's ability to control 

aquatic weeds. Panatees, which weigh 

up to 500 kg (1,102 Ib), can consume up to 

20% of their body weight per day in aquatic 

plants. 

When in marine waters, the manatee 

apparently feeds much like its fellow 

sirenians, the dugongs. The dugongs use 

their rough facial bristles to dig into 

the sediment and grasp the plants, These 

are uprooted and shaken free of adhered 

sediment. Husar (1975) stated that feeding 

patches are typically 30 by 60 cm (12 

by 24 inches) and that they form a conspicuous 

trail in seagrass beds. This author 

has observed manatees feeding in Thal assia 

beds in much the same manner. The patches 

cleared were of a similar size as those 

described for the dugongs, and rhizome 

removal was nearly complete. The excess 

sediments from the hole were mounded on 

the side of the holes as if the manatee 

had pushed much of it to the side before 

attempting to uproot the plants. 

Manatees would seem to be more 

linited in their feeding range because of 

sediment properties, as they reauire a 

sediment which is sufficiently unconsol i- 

dated that they may either root down to 

the rhizome or grasp the short shoot and 

pull it out of the sediment. Areas where 

manatee feeding and feeding scars were 

observed were characterized by soft sediments 

and lush growth of turtle grass and 

Halimeda in mounded patches. Nearly a11 

areas in which sediments were more cons01 - 

idated showed no signs of feeding. In the 

areas where the manatees were observed, 

the author found that he could readily 

shove his fist 30 cn (12 inches) or more 

into the sediments, while in the adjacent 

ungrazed areas, maximum penetration was 

only a few centineters and it was impossible 

to revove the rhizomes without a 

shovel . 

Like the turtles, the Caribbean For the majority of animals that 

rlanatee (Trichechus manatus) fortnerly was derive all or part of their nutrition fron 

69

seagrasses, the greatest proportion of 

fresh plant material is not readily used 

Picroorganisms, because of their diverse 

enzymatic capabilities, are a necesas 

a food source. For these animals seagrass 

organic matter becomes a food source 

sary trophic intermediary between the seagrasses 

and detri tivorous animal s. Eviof 

nutritional value only after undergoing 

decoinposition to particulate organic 

dence (Tenore 1077; Ward and Cummins 1979) 

suggests that these animals derive the 

detritus, which is defined as dead organic largest portion of their nutritional rematter 

along with its associated micro- quirements from the microbial component of 

organisms (Heal d 1969). detritus. Detritivores typically assirnilate 

the microfl ora cor~pounds wi th eff i- 

The nonavailahil i ty of fresh seagrass ciencies of 50"/,0 almost I@(?%, whereas 

paterial to detri tus-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; Camrnen 1980). 

1 eaves, direct assays of fiber content 

have yielded values up to 59% of the dry 

weight (Vicente et al. 1S78). Many ani- 

During seagrass decomposition, the 

size of the particulate natter is decreasmals 

lack the enzymatic capacity to assimilate 

this fibrous material. The fibrous 

ed, making it available as food for a wider 

variety of animals. The reduced particomponents 

also make fresh seagrass resistant 

to digestion except by animals (such 

cle size increases the surface area available 

for microbial colonization, thus inas 

parrotfishes and green turtles) with creasing the decomposition rate. The abunspecific 

n;orphological or physiological dant and trophical ly important depositadaptations 

enabl ing physical maceration 

of plant material. Fresh seagrasses also 

feeding fauna of seagrass beds and adjacent 

benthic communities, such as polycontain 

phenol ic compounds that may deter chaete worms, amphipods and isopods, ophi- 

herbivory by sorne animals. uroids, certain gastropods, and mu1 let, 

derive much of their nutrition from fine 

During decomposi tion of seagrasses , detri tal parti cl es . 

nurnerous changes occur that result in a 

food source of greater value to many consumers. 

Bacteria, fungi, and other micro- 

It is important to note that much of 

the contribution of seayasses 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 rnore 

matter that many animals lack. These decomposed, fine detri tal particles (less 

~nicroarganisrls colonize and degrade the than 0.5 mn) are easily resuspendetl and 

seagrass cietri tus, converting a portion of are widely distributed by currents (Fisher 

it to inicrobial protoplasrn 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 79, microflora contain 5% to 10% to support an active microbial population 

nitrogen, Hicroflora incorporate inorganic and are browsed by deposit feeders. 

nitrogen from the surrounding medium-- 

either the sediments or the water column-- 

into their cells during the decomposition 

Physical Breakdown 

process, enriching the dctri tus with proteins 

and other soluble nitrogen corn- 

The physical breakdown and particle 

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 (pol ychaetes , 

as decomposition occurs there w i n be a zooplankton, gastropods) are only able to 

gradual mineral iration of the highly ingest fine particles (less than 0.5 mm 

resistant fraction of the seagrass organic diameter). Second, as the seagrass matematter 

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 

seagrass carbon. Physi cal decomposition 

rate is an approximate indication of the 

rate at which the plant material becomes 

available to the various groups of detritivores 

and how rapidly it will be subjected 

to microbial degradation. 

Evidence indicates that turtle grass 

detritus is physically decomposed at a 

rate faster than the marsh grass, Spartina 

a1 terni fl ora, and mangrove 1 eaves. Zi eman 

(197Sb) found a 50% loss of original dry 

weight for turtle grass leaves after 4 

weeks using sample bags of 1-mm mesh size 

(Figure 23). 

Seagrass 1 eaves are often transported 

away from the beds. Large quantities are 

found among the mangroves, in wrack 1 ines 

along beaches, floating in large mats, and 

collected in depressions on unvegetated 

areas of the bottom. Studies have shown 

that the differences in the physical and 

biological conditions in these environments 

resulted in different rates of physical 

decomposition (Zieman 1975b). Turtle 

grass leaves exposed to alternate wetting 

and drying or wave action breakdown 

rapidly, a1 though this may inhibit microbial 

growth (Josselyn and Mathieson 1980). 

Biological factors also affect the 

rate of physical decomposi ton. Animal s 

grazing on the microflora of detritus disrupt 

and shred the plant substrate, accelerating 

its physical breakdown. Fenchel 

(1970) found that the feeding activities 

of the amphipod Parah el la whelpyi dramatically 

decrease sY- the particle size of 

turtle grass detritus. 

Microbial Colonization and Activities 

Feeding studies performed with various 

omnivores and detritivores have shown 

that the nutritional value of macropbyte 

detritus is limited by the quantity and 

qua1 i ty of microbial biomass associated 

with it. (See Cammen 1980 for other studies 

of detrital consumption.) The microorganisms' 

roles in enhancing the food 

value of seagrass detritus can be divided 

into two functions. First, they enzymatically 

convert the fibrous components of 

the plant material that is not assimilable 

by many detritivores into microbial biomass 

which can be assimilated. Second, 

.. ..............- 

Juncus 

TIME ON MONTHS 

Figure 23. Comparative decay rates showing the rapid decomposition of seagrasses compared 

with other marine and estuarine plants (references: Burkholder and ~ornside 1957; 

de la Cruz 1965; Heald 1969; Zieman 197%). 

71

the ~~icrooryanisns incorporate cons ti tu- sed irlerlt particles by rernovsl of the 

ents such as nitrogen, phosphororis, and inicroorganisms hut did not measurably 

di ssol ved organic carbon corripounds from reduce the total orpanic carbon content of 

the surrounding ~nediun into their cells the sedinents which was presumably doriand 

thus enrich the detrital complex. The nated by dderrital plant carbon. @hen the 

raicroorgani ~ms a1 so secrete 1 arge quanti - ni trogen-poor, carhon-rich feces were 

ties of extracel 1 ular material s that incubated in seawater, their nitrogen conchange 

the chemical nature of detrittrs and tent increased because of the growth of 

inray he nutritionally available to detri ti- attached micro organ is^?^. A new cycle of 

vores. After t'nitial leaching and decay, ingestion by the animals again reduced the 

these processes rsake microorgarlisms the nitrogen content as the fresh crop of 

primary agents in the chemical changes of rnicroorganisms was digested. In a study 

detritus, 

of detrital leaf material, Morrison and 

White (1980) found that the detri tivorous 

The i:?icrobial component of rriacrophyte amphi pod Pfucroqatmnarus_ sp. ingested the 

detritus is highly complex and contains microbial co~nponent of live oak (Qercus 

organisms frm f.aany phyla. These various virginica) detritus without a1 terinp or 

eornponents interact and Influence each consurnl ng the l eaf matter, 

other tu such a high degree that they are 

best thought of as a "&composer cornrrrun- While the importance of the microbial 

j tyii (Lee 1980). The structure and active components of detri ttrs to detritivores is 

i ties of thfs cofnmuni ty are influenced by estahl ished, some results have indicated 

the feedirkg activi tfes of detrftivorous that consulners may he capable of assirni- 

&nfmalrs and envy renlnental condjtjons. latin9 the plant carbon a1 so. Cammen 

(1988) found that only 26% of the carbon 

tllcraflora in-eeJutri 

tion 

me*-- -- 

requirements of a population of the 

deposi t-feeding polychaete Hcreis succinea 

NScrobSal carbon constitutes only 10% would be rnet by ingested microbial bioaP 

the total organic carban of a typical mass, The microbial biomass of the indetrf 

tgll particle, and rrricsrotaia'l ni trogcn gested scdirnents caul d supply 90% of the 

constltutex no mare than 10% af the total nltrogen requirements of the studied polytaitrugcn 

(Rublee et al, X97R; Lee et al, chaete population. The mysid J"!ysis steno- 

1980)- Thus, most of the organic compo- le~sis, conlfqonly found in lostera= 

nents aB the detritus are of plant ~rigfn was capable of digesting 

cornand 

are lirrited in their availability to pounds of plants (Foulds and Pann 1978). 

detrftivores, 

These studfes raise the possibility that 

while microbial biomass is assimilated at 

Carbon uptake franr a friecrualga, high efficiencies of 50% to 1QO% (~ingst 

1 , and the Sed(lra5s Zocjts 1976; Lop@% et 31. 1977) and supplies 

marlrxa by the deposft-feeding polyXete, proteins and essential growth factors, 

Fkmia s&ts, was neasured by Tenure the large quantities of plant material 

q"*1977JTW Uptake of carbrsx~ by the wanrls was that are ingested flay be assiinilated at 

dl'rectly propartlonal to the illlcrobjal fow cifficiencies (less than 5%) to supply 

activl b af the detcri tus (rn@aserred as carbon requirements. Assimilation at this 

ctxfdatl'on rate). The ~qaxinui:~ c~xidatjo~ low efficiency would not be readily quanrate 

occurred after 14 days for Gracjjarja tifded in most feeding studies (cammen 

detritus and after It0 days fo-z 1980). 

detritus. This indicates that the z z 

terlstics of the original plant !flatter The microbial degradation of seagrass 

affect its availability to the mfcrabes, organic matter is greatly accelerated by 

which An turn limits the assimilation of the feeding activities of detritivores and 

the detritus by consumers. 

microfauna, awthough the exact nature of 

the effect: is not clear, Microbial res- 

Most of the published evidence shows piration rates associated with turtle 

that detritivrsres do not assfmilate grass and Zostera detritus were stimulated 

significant portions af the non-micrabiaJ by the feeding activities of anirrtals, 

conponent of r~acrophytic detritus. F O ~ apparently as a result of physical fragexample, 

Qewell (1965) found that deposit- mentation of the detritus (Fenchel 1870; 

feeding molluscs rmavcd the nitrogen from Harrison and Mann 1375a). 

72

Chemical Changes During Decomposition 

The two general processes that occur 

during decomposition, loss of plant compounds 

and synthesis of microbial biomass, 

can be incorporated into a generalized 

model of chemical changes. Initially, the 

leaves of turtle grass, manatee grass, and 

shoal grass contain 9% to 22% protein, 6% 

to 31% soluble carbohydrates, and 25% to 

44% ash (dry weight basis), depending on 

species and season (Dawes and Lawrence 

1980). Direct assays of crude fiber by 

Vicente et al. (1978) yielded values of 

59% for turtle grass leaves; Dawes and 

Lawrence (1980) classified this material 

as "insoluble carbohydrates" and calculated 

values of 34% to 41% for this species 

by difference. Initially, losses 

through translocation and leaching will 

lead to a decrease in certain components. 

Thus, the organic carbon and nitrogen content 

will be decreased, and the remaining 

r~aterial will consist primarily of the 

highly refractive cell wall compounds 

(cell ulose, hemicell ulose, and 1 ignin) and 

ash (Harrison and Mann 1975b; Thayer 

et al. 1977). 

As microbial degradation progresses, 

the nitrogen content will increase through 

two processes: oxidation of the remaining 

ni trogen-poor seagrass compounds and synthesis 

of protein-rich microbial cells 

(typically 30% to 50% protein) (Thayer 

et al. 1977; Knauer and Ayers 1977). The 

accuslulation of microbial debris, such as 

the chi tin-containing hyphal walls of funci, 

may also contribute to the increased 

nitrogen content (Suberkropp et al. 1976; 

Thayer et al. 1977). Nitrogen for this 

process is provided by adsorption of inorganic 

and organic nitrogen from the surrounding 

medium, and fixation of atmospheric 

W,. For tropical seagrasses, in 

particular, there is an increase in ash 

content during decomposition because of 

deposition of carbonates during microbial 

respiration and growth of encrusting algal 

species, and organic carbon usually continues 

to decrease (Harrison and iSann 

1975a; Knauer and Ayers 1977; Tkayer 

et 31. 1977). 

-- Chemical Changes as Indicators of Food 

Val uc 

Nitrogen content has long been considered 

a good indicator of the food value 

of detritus and has been assumed to represent 

protein content (Odum and de la Cruz 

1967). Subsequent analyses of detritus 

from many vascular plant species, however, 

have shown that up to 30% of the nitrocen 

is not in the protein fraction (Harrison 

and Mann lS75b; Suberkropp et al. 1976; 

Odum et a1 . 1979). As decomposition progresses, 

the non-protein nitrogen fraction 

as a proportion of the total nitrogen can 

increase as the result of several processes: 

complexing of proteins in the lignin 

fraction (Suberkropp et a7. 1976) ; production 

of chitin, a major cell wall compound 

of fungi (Odum et al. 1979b); and decomposition 

of bacterial exudates (Lee et al. 

1980). As a result, actual protein content 

may be a better indicator of food 

value. Thayer et a1 . (1977) found that 

the protein content of Zostera 1 eaves 

increased from standing dead to detrital 

fractions, presumably due to microbial 

enrichment. The role of the non-protein 

and protein nitrogen compounds in detri tivore 

nutrition is not presently well 

understood. 

Like many higher plants, tropical 

seagrasses contain phenol ic acids known as 

a1 1 el ochemical s. These compounds are known 

to deter herbivory in many plant groups 

(Feeny 1976). Six phenolic acids have 

been detected in the leaves, roots, and 

rhizomes of turtle grass, manatee grass, 

and shoal grass (Zapata and WcKillan 

1979). In laboratory studies two of these 

compounds, ferulic acid and p-couwaric 

acid, when present at concentrations found 

in fresh leaves, inhibited the feeding 

activities of detritivorous amphipods and 

snails grazing on 2. alterniflora detritus. 

During decomposi ton the concentrations 

of these compounds decreased to 

levels that did not significantly inhibit 

the feeding activities of the animals 

(Val iela et a1 . 1979). 

Seagrass leaves nay also contain compounds 

that inhibit the growth of microorganisms; 

this in turn would decrease the 

usahta nutritfena? value cf the detritus. 

Water soluble extracts of fresh or recently 

detached 1. marina 1 eaves inhi hi ted 

the orowth of diatoms, phytoflauel lates, 

and bacteria (Harrison and Chan 1980). 

The inhibitory compounds are not found in 

older detrital leaves or ones that have 

been partially desiccated.

Re1 ease of Dissolved Organic Matter 

carbon than did the particulate carbon 

fraction (Robertson et a1 . 1982). 

Seagrasses re1 ease subs tanti a1 DOC may a1 so become available to conamounts 

of dissolved organic carbon (DOC) sumers through incorporation into particuduring 

growth and decomposition. The DOC late agaregates* Microorganisms attached 

fraction is the most readily used fraction to particles wilt assimilate DOC from the 

of the seagrass organic matter for micro- water column, incorporating it into their 

organisms and contains much of the so1 uhf e cells or secreting it into the extracellucarbohydrates 

and proteins of the plants. lar materials associated with the parti- 

X t is quickly assimilated by microorgan- cles (Paerl 1974, 1975). This rnicrohial ly 

ism, and is available to consumers as mediated mechanism also makes seagrass DOC 

food In sfgnl ficant quanti tles only after available for consumers. 

this conversion to microbial biomass. 

Thus, the utilization 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 Zostera are capable of taking up label- cycl ing of DOC and its utilization in deledTg8c 

compounds (Smith and Penhale trital food webs are complex. The highly 

19130). labile nature of seagrass DOC sugaests 

that it may play a significant role in 

Experlrnents designed to quantify the supporting secondary productivi ty. 

release of DOC From growing seagrasses 

have ylelded a wide range of values, The Role of the Oetrital Food Wet? 

short-tern re1 ease of recently synthesized 

photosyntkatc from blades of turtle grass The detrital food web theory reprewas 

found to be 2% to la%, usfng radio- sents our best understanding of how the 

labelled carbon (Wetzel and Penhaf e 1979; unajor portion of seagrass organic carbon 

Bryl insky 1977). Losses to the water col - contri hutes to secondary productivity. The 

umn frat!! the enttre community, including organic flatter of fresh seagrasses is not 

belawground bi onass and decomposing par- cornnonly util ized by many animals hocatrse 

ltons, may &e much higher. Kirkman and of various factors, including their low 

Reid (1979) found that 50% of the annual concentrations of readily available nitroloss 

af organic carbon from the Posidon& gen, high concentrations of fiber, and the 

- 

&@st- seagrass community w a r t h e presence of inhibitory compounds. The par- 

form of: DOC, 

ticulate and dissalved fractions of seagrass 

carbon scan to become potential food 

Relcarse of DOC from detri tar leaves for animals primarily after colonization 

may a1 so be substantial. In freshwater by fnicroorganisfils. During decomposition 

macmphytes, leachlng and autolysis of DOC the chemical nature of the detritus is 

lcad ts a rapid 50% loss of weight (Otsuki changed by two processes: loss of plant 

and Wetzel 1974). fn laboratory experi- conpounds and synthesis of microbial prornents 

dried turtle grass and manatee grass ducts. 

1 eaves released 13% and 20X, respectively, 

of' thetr organfc carbon content during The deconpaser ciomuni ty also has the 

teaching under sterile candi tions (Robert- enzyrratic rnechanis~vs and abil f ty to assimson 

et at. 3.982). 

ilate nutrients from the surrounding medium, 

leading to the enrichment of the detritus 

as a food source. As a result, the 

The carbon released as DOC is ex- decomposer comm?rnity represents a readily 

tt*c:?,cly 12b.fle and ir; rapfdly assfjnj jdted t,'sdBle tropkic level Bett!cer, the producby 

microorganl"sms (Otsuki and It!et.rel 1974; ers and [nost animal consumers. In this 

Gry'iinsky 19771, which leads to its immed- food weh, the consumers derive nutrition 

iate availabil ity aas food for second at*^ largely fran Ltte nicrohial coa~ponents of 

eonsumerr. In 14-day lahoratot-y incuha.. the detritus. This decornposer co~~uni ty 

tions, the DOC released by turtle grass 1s inFluenced by crnviront~ental conditions 

and ~anatee qrass leaves supported 10 and biological interactions, including the 

Limes rnore ~nkrobial biomass per unj t feed~ng activities of cansur?ers. 

74

CHAPTER 7 

INTERFACES WITH 

OTHER SYSTEFlS 

7.1 MANGROVE 

Mangroves and seagrass beds occur 

close to one another within the estuaries 

and coastal lagaons of south Florida, 

especially in the clear waters of the 

Florida Keys. Mhi 1 e the importance of 

nanyrove habitat to the estuary has been 

established (Odun and Heald 1972, 1975; 

Odum et al. 19E2), its faunal interactions 

with adjacent seagrass beds are poorly 

understood. 

Like the seagrass r~eadow, the mangrove 

fringe represents shelter; fishes 

and invertebrates congregate within the 

protection of mangrove prop roots. Game 

fish found in loansroves include taroon 

when mansroves and 

seagrass meadows are in proxim;ty, these 

fishes will forage over qrass. Grev 

snapper (~utjanus- riseus); sheepshci 

(Archosar us robatoce eh- alus 1, spotted 

n o s ) , and the 

red drum (Sciaenops 0cetldea)recru i t in to 

seagrass habitat m y , but with 

growth rnovc into the marrgro;e habitat for 

the next several years (iieald and Odum 

1370). A1 1 of these fishes have been collected 

over grass. Little work has been 

done, however, to explore the possible 

interactions between mangroves and seagrass 

beds. For a detailed review of the 

mangrove ecosystems of south Florida see 

Odum et a1 . (1982). 

7.2 CORAL REEF 

Coral reefs occur adjacent to extensive 

turtle grass-doninated grass beds 

along the full extent of the oceanic margin 

of the Florida Keys. The most prominent 

interaction involves nocturnal ly 

active coral reef fishes of several fapilies 

feeding over grass beds at night. 

Randall (1963) noted that grunts and snappers 

were so abundant on sow isolated 

patch reefs in the Florida Keys that it 

was obvious that the reefs could not provide 

food, nor possibly even she1 ter, for 

all of them. Longley and Hildebrand 

(1941) also noted the dependence (for 

food) of pomadasyids and futjanids on 

areas adjacent to reefs in the Tartugas. 

Typical 1y , both juveni 1 es and adults 

form 1 arge heterotypic resting schools 

(Ehrl ich and Ehrl ich 1973) over proninent 

coral heads or find she1 ter in caves and 

crevices of the reef (Figure 24). At dusk 

these fishes migrate (Qgden and Ehrlich 

1977; MacFarland et al. 11179) into adjacent 

seagrass beds and sand flats where 

they feed on avai 1 ab7 e invertebrates 

(Randall 1967, 1968), returning to the 

reef at dawn. Starck and Davis, (1966) 

list species of the Wolocentridae, Lutjanidae, 

and Pornadasyidac families as occurring 

diurnally on Alligator Reef off Matecumbe 

Key in the Florida Keys, and feeding 

nocturnally in adjacent grass beds and 

sand flats. As such, these fishes e 

mite what Kikuchi and Peres (1977) de 

as temporal visitors to the grass bed, 

~hich serves as a feeding ground fflobson 

1973). Starck (1968) discussed further 

75

grunts over the grass beds of Tague Ray, 

St. Croix, is similar to those reported in 

the Florida Keys. The French grunt, 

-- Haemul on --- 

f1 avo1 ineatum, was most abundant 

over sparse grass or bare sand bottotn, 

while the white grunt H. plumeri was usually 

observed in dense grass. Numbers of 

coral reef fishes (grunts and squirrelfishes) 

feeding nocturnally over seagrass 

were positively correlated with a measure 

of habitat conpl exi ty. This correlation 

implies organization of the fish assemblage 

while feeding (M.B. Robblee, in preparation). 

Lutjanids were not found in 

significant numbers either on the reef or 

in the grass beds. 

These observations on the distribution 

of fishes over the feeding ground 

suggest that the nature and qua1 ity of 

grass bed and sand flat habitat adjacent 

to a coral reef may influence both the 

composition and abundance of these nocturnal 

fishes on a reef. Randall (1963) 

stated that whenever we1 1 -developed reefs 

lie adjacent to flats and these flats are 

not shared by many other nearby reefs, the 

grunts and snappers on the reef may be 

expected to be abundant. Starck and Davis 

(1966) and Robins (1971) also noted that 

it is understandable, given the requirement 

of ~vost pomadasyids and several 

lutjanid species for back-reef forage 

area, that these fishes are almost completely 

absent fro13 certain islands in the 

Caribbean which have fringing reefs with 

only narrow shelf and very 1 irnited backreef 

habitat. Conversely, grunts and 

snappers forrn resting schools over characteristic 

coral heads, most commonly 

Acro ora palamata and Pori tes porities 

rP- Ehrlich and Ehrl ich 1973: Oaden and 

~hrl ich 1977), which a1 so influences their 

population size. Starck and Oavis (196G) 

commented that these species are excluded 

from njany suitable forage areas by the 

absence of sheltered locations for diurnal 

resting sites. When artificial reefs were 

established in the Virgin Islands (Randal 1 

1963; Ogden, personal communication), 

rapid colonization by juvenile grunts 

occurred, indicating the importance of 

shelter to these fishes near their potential 

feeding grounds. 

Much of the interpretation uiven 

above is speculative, but in light of 

curr-en t hypotheses, the structurino of 

coral reef fish communities is probably 

1 argely control 1 ed by their physical 

requirements for 1 iving space. Sale 

(197e) speaks of a lottery for livina 

space among coral reef fish colnmunities 

composed of groups of fishes with similar 

requirements (the representatives on any 

one particular reef being determined by 

chance recruitment). A1 ternatively, Srrli th 

(1978) advocated the ordered view that 

recource-shari ng adaptations determine 

which species can 1 ive together. Resources 

external to the reef influence the species 

composition and abundances of at least 

nocturnal ly feeding, supra-benthic species 

(grunts and snappers), and perhaps several 

of the hol ocentrids, 

It has been hypothesized that the 

die1 activity patterns exhibited by these 

fishes contribute to the energy bud et of 

the coral reef. Bill ings and Munro ?1974) 

and Ogden and Zieman (1977) suggested, as 

originally proposed by Johannes (personal 

communication), that migrating pornadasyids 

may import significant quantities of 

organic iqatter (feces) to the reef. 

Thayer and Engel (in preparation) have 

also postulated a similar mechanism for 

green turtles, whose contribution to reef 

nutrient budgets nay also be important. 

These assertions are open to investigation. 

Temporary visitors from the coral 

reefs are not limited to fishes. The 

urchin Diadema anti1 1 arum moves off patch 

reefs at niahtin-e turtle orassdominated 

grass bed immediately adjacent 

in Tague Bay, St. Croix (0gden et al. 

1973). The provinent halo feature associated 

with many patch reefs is attributed 

to the nocturnal feeding forays of these 

longspine urchins. Of greater significance, 

the spiny 1 obster (Panul i rus 

ar us), is known to move onto offshore 

9f ree s as adults in the Florida Keys, seeking 

she1 ter in caves and crevices (Simmons 

1980). Lobsters remain in their dens during 

daytfght; at or after sunset they move 

onto adjacent grass beds to feed solitar- 

ily, returning to the reef before dawn 

(Hernkind et a1 . 1S75). While farther 

from the reef, the spiny lobster ranges 

over considerable distances, typically 

several hundred meters.

Use of adjacent grass and sand flats 7.4 M'ORT 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 m das, Scarus uacamaia) export large quantities of organic matter 

venture far into -%- t e grmd9mm 

from the seagrass meadows for util ization 

the she1 ter of the reef. Mid-sized herbi- at some distant location (Zieman et a1 . 

vores are apparently excluded by predators 1979; Wolff 1980). This exported material 

and feed only near the reef (Ogen and Zie- is both a carbon and nitrogen source for 

man 1977). Randal 1 (1965) reported parrot- benthic, mid-water, and surface-feedi ng 

fishes (Scarus and S arisoma) and surgeon- organism at considerable distances from 

fishes ~ = u r u feeding s ) ~ 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 Virgin west Florida shelf is illustrated in 

Islands during the day. He attributed the Figure 25 (Zieman et a1 ., 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 a1 . (1967) 

Recently interest has been sparked in off the North Carolina coast in 3,160 m 

estuarine-Continental She1 f interactions (10,368 ft) of water. 4l though the near- 

(Darnel1 and Soniat 1979). The seagrass 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 Flor- at densities up to 48 blades per photoida's 

estuaries and coastal 1 agoons. t- any graph. Roper and Brundage (1972) surveyed 

species are dependent on the seagrass bed the Virgin Is1 ands basin photographical 1 y 

and estuary. The pink shrimp Penaeus and found seaarass blades in most of some 

duorarum, the lobster Panul irus ayjus, 59000 photographs taken at depths averagand 

the grey snapper lutjanus 9r1seus ing 3,500 r (11,464 ft). Most were clearly 

rnay serve as examples of estuarine or recognizable as turtle grass or nanatee 

lagoanal dependent fauna which at one life grass. Seagrasses were collected by trawlstage 

or another are found in seagrass ing in three Caribbean trenches and seameadows. 

grass material was found in all the 

trenches sampled (Wolff 1976). Host of 

In south Florida, pink shrimp spawn the matcrfal collected was turtle grass, 

in the vicinity of the Tortugas Bank, the and dthre was evidence of c~n~~rrl~ti~n by 

pel agic f arvae returning to the estuary 

and perhaps the seagrass bed (yokel 

deep-water organisms. Interestingly, 

solrle grass blades collected from 6,740 m 

1975a). Eventually mature individuals return 

to the spawning grounds, Similarly, 

(22,113 ft) in the Cayman Trench showed 

the distinctive bite narks of parrottho 

lobster matures in inshore seagrass fish which are found only in shallow 

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 aduf ts, female lobsters move to grazing by herbivores, mortal i ty on shaldeep 

offshore reefs and spawn. The grey low hanks caused by low tides, and wavesnapper 

initially recruits into grass and induced severing of leaves that are becornwith 

growth moves into mangrove habitat 

and e~entual?~ on to coral reefs and deeping 

senescent. In addition, ~ajor storms 

will tear out 1 ivin: leaves and rhizornes 

er shelf waters. Coming or going, these (Thonas ct al. 1961). which rnode of 

organisms and others like then serve to detachment will be r.iost important in a 

transfer energy from the seagrasr bed to particu'lar area wilt he largely deteroffshore 

waters (see section 7.5), as has mined by physical conditions such as 

been shorrn by Fry (1981) for brown shrjpp depth and wave exposure. Reduced salin- 

(P. - ---- aztecus) in Texas waters. 

ity or extreme tervperature variation will 

78

Figure 25. Seagrass export from south Florida to the eastern Gulf of Mexi 

tain areas there is a substantial subsidy to the local carbon and nitroge 

materi a1 exported from nearby seagrass beds. 

limit the herbivores responsible for de- whole turtle grass blades 

tachment (primarily parrotfish, urchins, grazing. 

and turtles). 

Because of this differen 

Freshly detached, healthy blades of sponse to grazing, Zieman et 

all species float better than senescent found that in Tague Ray 60% to 

ones. Because of the difference in size daily production of manatee gr 

and shape of turtle grass and manatee tached and exported, whereas 

grass blades, the effect of direct herbi- turtle grass was exported, an 

vory on the two species is quite differ- primarily as bedload. This also In 

ent. When a parrotfish or urchin bites a the relative successional status of these 

turtle grass blade, it usually removes species. Turtle grass retains more of its 

only a portion of the blade, which remains leaves within the bed, which thus become 

attached. However, a manatee grass blade part of the litter layer, pronoting carbon 

is typic81 ly only 1 to 1.5 rnm wide and and nitrogen recycling in the seagrass bed 

one bite severs it, allowing the upper and enhancing its performance as a cl i ~ax 

portion to float away (lieman et 81. species. By contrast, relatively little 

1979). Similarly, green turtles sever of the leaf production of manatee grass is

etained in the bed to contribute to further 

develo ment of the l i ttle layer 

(Zieman 1981 $ . 

It Is possible that in certain regions, 

exported seagrass could be an 

inportant food source, Sediment collected 

from the bottom of the Tongue of the Ocean 

that was not associated with turtle grass 

patches had carbon and nitrogen contents 

of 0.66% and 0.07X, respectively (Wolff 

1380). Turtle grass blade and rhizome 

samples had a carbon content of 20hnd a 

nl trogen content of 0.77%. 

7.5 NURSERY GROUNDS 

Vany species of fishes and invertebrates 

use south Florida grass beds as 

nurseries. Approximately one-third of 

the species collected at Matecumbe Key, 

including all grunts, snappers, filefishes, 

and parrotfi shes, occurred only as 

young, indicating that the grass-dominated 

shore area was a nursery ground (Springer 

and KcErlean 1962b). In Tampa Bay, 23 

species of finfish, crab, and shrimp of 

major importance in Gulf of Pexico fisheries 

were found as immature forms (Sykes 

and Finucane 1966). Comparatively 1 i ttle 

is known concerning invertebrates other 

than those of commercial value. 

Shrimp 

Crass beds serve as nursery grounds Pink shrimp (Penaeus duorarum) occupy 

where post larva1 stages of fishes and south Florida r d as ~llveniles 

invertebrates concentrate and develop and (Tabb et a]. 1962; Costel lo and A1 len 

also as spawndng grounds for adult breed- 1966). Ma= artecus and fl. brasiliening 

pogulatlons of some species. To be of are also present, hut never as abun- 

~igndficance as a nursery, a habitat must dantly as the pink shrimp (Tabb and Flanprovide 

protec&.isn from predators, a sub- ning 1'161; Saloman et al. 1968; Bader and 

strate far attachment of sessile stages, Roessler 1971). Shrimp spawn on the Toror 

a plentiful food source (Thayer et al, tugas grounds, probably throughout the 

1978hj. Seagrass habitats fuf fill all of year (Tabb et al. 1362; rlunro et al. 

these criteria with their high productlv- 1968). Roessler and Rehrer (1971) found 

Ity, scrrfaee areas, and blade densities, postlarval pink shrirrtp entering the estuas 

well as a rich and varied fauna and arles of Everglades National Park in all 

flora, Seagrass provides ahundant nursery months of the year, 

habitat and f s often preferred, based on 

abundance and size data, over available Pink shritrp were distributed througha1 

krna tives, ln the estuaries and coastal out Rookery Ray Sanctuary in southwestern 

lagoons, by many coi%~~rcially or ecalogi- Florida, hut were most abundant at sta- 

@ally important species (Yokel 1975a). tions with grass-covered bottovs (shoal 

grass and turtle grass), and within these 

The importance of grass bed hahitat stations were most abundant where benthic 

as a nursery has bean historically demon- vegetation was dense (Yakel 1975a). Pink 

strated &nd should not be minimized, Fol- shrimp were also abundant in qrass habitat 

1 owl ng the decl ine of marina along at Marco Island and Fakahatchee Ray, also 

tha east coast; of the STa3T-in the in southwestern Fl orida (Yokel 1975h). 

csrly 1930ts, the sea hrant, a variety of Postlarval pink shrimp with carapace 

goose dependent on eelgrass Fur food (as length less than 3 mi? were taken only at 

are many waterfowl ; McRoy and Welffrich stations where shoal grass and turtle 

13r1,0), was reduced in numbers to one-fifth grass were present in Rookery Bay 5ancits 

fortwr 'icvels (Floffitt and Cottam tuary, while other stations without grass 

1941). Proneunced decreases in abundartce altrays had larger mean sizes. These obof 

hay scal 1 ops (Argppectcn i yradi ans) serva tions are in accordance with hi l dewere 

al so not& fol lawing the dtsappear- brand (1955) and Mil 1 iazs (15)65), who 

ance of ctzlgrars (StaufFer 1937; Dreyer noted that very small pink shrimp prefer 

and Castle 1941; Marshall lS47). The grassy areas and with increasin9 size are 

post-vcl iycr larval stage of trle scallop found r'n deeper water. In terms of the 

depends on cclgrass to provide an above- functionins of tile grass bed as a nursery 

scdiritcnl surface For attachr1tcnt4 Di srup- ground, it is interes tin9 to speculate 

tion of ccf grass beds rcsul ted in lowered whether this distribational pattern reprequmbcrs 

of bay scallops (Thayer afad Stuart senp a preference on the part of pink 

1974). shr1111p pastlarvae for grass bed habitat 

80

(associated characteristics) or is the 

result of differential mortality within 

the estuary. 

xiy - Lobster 

Juvenile spiny lobsters (Panul irus 

argus) are commonly found in nearshore 

seagrass nursery areas of Biscayrle Pay, 

Florida (Eldred et al. 1P72); the Caribbean 

(Olsen et a1 . 1975; Peacock 1974); 

and Brazil (Floura and Costa 1966; Costa 

et al. 1969). In south Florida these 

inshore nursery areas are largely limited 

to cl ear, near-normal oceanic sal ini ty 

waters of the outer margin of Florida Bay, 

the Florida reef tract, and the coastal 

lagoons. Tabb and Flanning (1361) noted 

that the spiny lobster is rare on the 

muddy botto~s in northern Florida Bay. 

Residence time in shallow grassy 

areas is estirrated at about 9 to 12 months 

(Eldred et dl. 1972; Costa et al. 1969) 

after which time the small lobsters (carapace 

length typically less than 60 ma^) 

take up residence on small shallow water 

patch reefs. On the reefs, the lobsters 

live gregariously during the day while 

foraging at night over adjacent grass and 

sdnd flats. With maturity (1.5 to 2.0 

years, Peacock 1974; up to 3 years in 

Florida, Simmons 1986) mating occurs and 

females rnigrate to deeper offshore reefs 

to release larvae (Little 1977; Cooper 

et a1 . 1975) and then return. Reproductive 

activity occurs throughout the year 

in Florida waters, but is concentrated 

during P?arch through July (Menzies and 

Kerrigan 1980). 

Theories differ about where the larvae 

which recruit into south Florida 

inshore nurseries originate. The question 

is of great importance to the managenent 

of this fishery. Cnce released along 

F1 orida's offshore reefs, the 1 arvae 

(phyl loso~nes) drift with the current during 

a planktonic stage of undeterrnined 

1 ength; estimates range from 3 months to 1 

year f Simnons f 980). Control 1 ed vertlcaf 

movernents in the water column may allow 

the larvae to remain in the area of hatching 

via eddies, 1 ayered countercurrents 

or other localized irregularities in the 

~novements of the water (Simmons 1980). Alternatively, 

larger scale countercurrents 

and gyres nay allow for larval development 

8 1 

while still returning t!ie larvae to south 

Florida waters (Menzies and Kerriyan 

1980). It has also been sug~ested hy

1972). Sinilar habitat use by juvenile fl. and Efhi tewatcr Bays and then move into the 

ar us has been reported jn Cuba (Buesa Pangrove habitat for the next several 

f;ift, the Virgin islands (01 sen et al. Years (Heald and 197p)* 

1375), the Lesser Anti1 las (Peacock 1374), 

and in Brazil (Costa et a1 , 1969). Degra- The pinfish (Lagodon rhomboides) was 

datjon of this habitat would certainly the most abundant fish cotlected and gas 

threaten lobster productivity (Li ttlc taken throuahout the year in the turtle 

1977). arass beds of Florida Pay (Tahh et al. 

Fish 

v 

1962), as is generally true for southwcstern 

Florida (ldeinstein and Heck 197a; 

Weinstein et al. 1377; Yokel 1975a, 

In south Florida it appears that con- 1P75h). Yakel (1975a) in Rookery Bay and 

tinental fish faunas and insular fish Yokel (1975b) in Fakahatchee Bay, bottl of 

Faunas mix. Continental species require the Ten Thousand Jsland region of south 

char~ging environinents, seasonal ly sili f ting F1 orida, noted a stronl? preference Of 

estuarine conditfons, hjgh turbfdi ties, juvcnil e pinfish for vey2tated areas. The 

and xliucidy hottoms (Robins 1971). South- sheepshead f Archosar us ro)at~ce~h&), 

western Florida and northern Florida Ray 

typfPPy these conditfons and their "fish 

another s p a r d l k recru~ ts into 

grass beds hut quickly rrloves into ilangrove 

asseiablages are characterized by many 

sclaenbd species (drunrs) and the prominent 

habitats (Weald and Odup 1370) Or rocks 

and pi1 i rigs IHildeSrdnd and Cable 1P3P). 

which is also 

cl earwa ter sea- The snappers, -"-us g r i s ~ and t ~ I. 

and Card Sound are CoInJqon firou5Ikout sotlth 

I, Brook, personal coi>monication), Insu- florida. Juvenile gray snapper (L. fis: 

sr specget; require clear water, buffered are often the most CO~nmon snapper in 

envfrgnmental conditionq, and botto~+~ ti ern Florida and Whi tewater nays, 

roefits composed largely of cat cjunt carbon- including freshwater regions (Tabb and 

at@ lRobfns 197l), These conditioris are Efanning 1261). The gray snapper is con- 

found wfthln tf\e grass beds of the Florida sidered to recruit into grass beds and 

Keys and !?arcins of florid4 nay, then after several weeks move into man- 

Reprrs~;?nt%tSve species OF Faiflilies Poma- grove hahitat (Heald and fMur;l 1970). The 

dasyidae, Lutjanidac~t, and Scaridae are 1 anc snapper (I. synagris) , never reaches 

$last nurserolls $0 these waters. This pat- sufficient sire within The bay to enter 

tern 4% n~ost eviderlt anonc; the seasonally the fishery si~nificantly. Young lane 

resident FJshes using seagrass rtleadows as snappers were abundast in turtle qrass 

nurser iars , 

hahi tat when salinities were above 30 ppt 

(Tabh et a?. 1962) in iiarthern Florida 

At least elght scfaenid species (see Bay, and were the most abundant snapper 

Appendix) have hecn associated with the taken corvtlanly within grass hahi ta t of the 

seegrass Reds in southwcrterf~ Florida Ten Thousand Island region of the southc&)$%kaf 

lagoons and estuaries, Plot all of western Florida codst (~einstein dnd Heck 

these ff~hc~~ Occur abundatltly, arid only 1979; Weinstc?in et al. 1977; Yokel 1(175a, 

the spatted sedtrout nebula- 1975b). In Whi tevtater Ray, I. yriseus and 

-- aus), the spot 

- L. were most abundant wben assothe 

sCSvcr pe ciated with benthic vegetation fprin~arily 

occur CQIMIIB~~ y 

the calcareous green algae Udotea flabellur?, 

but also with SOIW ?KZ?T- 

few 

The; sl30tted seatro~tt is one of the mark 197Q). 

larger carnivorous Pishcs present in 

south f:erida Meters that $paws -@ifbin On the reefs fringing the Florida 

the estuary (Tabb 1961, 1966a, 2966h], Keys aionr their oceanic margin, fane and 

Eggs sink to the hattom and hatching takes grey snappers are joined by up to 10 

place in bottoro vegetation or debris (Tabh additional liltjanid species (Starck and 

1(466a, 19GGb). The spotted seatrout and Davis 1?66; Starck 136e; Longley and 

another sciaenid, the red drum (Sciatlno 5 Elldebrand 1941; 8J.S. Dept, of Commerce 

oscels), spend the first fewTG&E 1980). Of these, the schoolmaster (L. 

their lives in the grass beds of Florida apodus), the putton Snapper (t. ana~isr, 

82

and the ye1 low- mentioned (except 2. chrysoptera), Haemutail 

snapper (Ocyurus chrysurus) all occur jo~ flavolineatum, H. parrai and l. carin 

low numbers, relative to the grey snapper, 

as juveniles near shore over grass in 

bonarium are also present as juvenile5 

these waters (Springer and VcErlean 1962b; 

the Florida Keys (Springer and McErlean Roessler 1965; Bader and Roessler 1971; 

1962b; Bader and Roessler 1971; Roessler Brook 1975). 

1965). 

the dog snapper (I. m), 

Of the Pomadasvidae, .juvenile pisfish 

(Orthopri sti c chrysoptera )-are abundant on 

muddv bottoms and turbid water in Florida': 

variable sal initv reqions; adults 

and juvenil es were coi 1 ected throughout 

the year in Florida Bay (Tabb and Planning 

1961; Tabb et al. 1962) and Rookery Bay 

(Yokel 1'375a). The white ?runt (Haemulon 

pl umeri ) i s common throuahout south Fl orida, 

occurring most often over turtle 

grass beds in clear water as juveniles 

(Tabb and Manning 1961; Roessler 1965; 

Rader and Roessler 1971; Weinstein and 

Heck 1979). Adults were not found over 

grass during the day, but were abundant 

diurnally on coral reefs and at night over 

grass and sand flats adjacent to coral 

reefs (Starck and Davis 1966; Davis 1967). 

Tabb et al. (1962) lists the pigfish and 

the white grunt as typical residents of 

the turtle arass communitv of Florida Bav. 

ether grunfs, including "~ni sotremus viFginicus, 

Haemulon sciurus, and H, aurol ineatum, 

occur over grass only rarely in 

southwestern Florida and Florida Bay, 

(Tabb and Manning 1961; Weinstein and ~eck 

1973). 

Clearer water, higher and less variable 

oceanic sal ini ties, and the proximity 

of coral reefs may account for the increased 

species richness of juvenile 

pomadasyids in Florida Keys inshore grass 

beds. In addition to the species already 

In addition to lutjanids and pomadasyids, 

other coral reef fishes use seagrass 

beds as nurseries. Surgeon fishes 

are found as juveniles in grass beds: most 

commonly the ocean surgeon (Acanthurus 

~+ 

bahianus) and the doctorfish (A. chirursus).~he 

spotted goatfish (Pseudu eneus 

maculatus) and the yellow goatfish - 

1 oidicthys martinicus) occur as juveniles 

in grass beds (Munro 1976; Randall 1968). 

The spotted goatfish was taken at Matecumbe 

Key (Springer and McErlean 1962b). 

Parrotfish (Scaridae) are often the most 

abundant fishes on reefs (Randall 1968). 

Springer and IlcErl ean (1962b), using 

seines on Matecumbe Key, found eight species 

of scarids in turtle grass beds. All 

of these were juveniles; however, Spari- 

- soma radians and 2. chrysopterum are also 

small fishes which continually reside in 

seagrasses. The latter is also found on 

reefs (Randall 1967, 1968). The emerald 

parrotfish ( ~ chol i sina usta), which is 

most common in seagrass(Randal1 1968), 

was taken on Batecuvbe Kev, as we1 1 as in 

Biscavne Bay (Bader and -~oessler 1971). 

The remainino s~ecies of ~arrotfishes, 

Sparisoma viride' and 2. r;bripine and 

Scarus croicensis, 2. quacamaia, and 2. 

coeruleus, are present on reefs as adults, 

are less common in Biscayne Bay (Roessler 

1965; Bader and ~oessl& 19711, and are 

absent in Card Sound (Bader and Roessler 

2971; Brook 1975).

CHAPTER 8 

HUMAN IMPACTS AND APPLIED ECOLOGY 

Since the days when Henry Fl agler 's acres of adjacent habi tats. The impact of 

raflway first exposed the lush suhtropical dredging can be long-lasting since such 

envlron~nent of south Fl orida to an influx disturbance creates sedinent conditions 

af people fram outside the region, the unsuitable for seagrass recolonization for 

area has been subjected to great change at a protracted period (Zieman 1975~). 

the hands of man. Through the 195Q1s, 

boomf ng development precipi tated the Of the Gulf Coast States, Florida 

destruction of many acres of submerged ranks third, behind Texas and Louisiana, 

lands alp demands for industrial, raiden- in amount of sub~nerged land that has been 

ttat, and recreational uses in this unlque filled by dredge spoil (9,520 ha or 23,524 

part of the Natlon increased. While sea- acres). In Texas and Louisiana, however, 

grass bads generally have experienced less ,nost of the spoil created came from 

dlrect darsage than have the mangrove dredged navigation channels, while in 

shopel ines, seagrasses have not been Florida this accounts for less than 5% of 

totally spared the impact of development. the State total. Not surprisingly, the 

Environtnental agencies receive permit ,a-jori ty of fi 11 ing of 1 and in Florida, 

re~.tuests regularly, many of which would about 7,500 ha (18,525 acres), has been to 

dfrectly or lndlrectly impact seagrass create land for residential and industrial 

beds, R~cause of the concern for these development (Figure 26). In addition to 

biolsgfcal ly important hahi tats several the direct effect of burial, secondary 

artfcles have been published which docu- effects from turbidity may have serious 

rnent theSr ifnportance and man's ilnpac t consequences hy restricting nearby produc- 

(e,g, Thayar et a7, 1975h; Pieman 1975b, tivity, choking filter feeders by exces- 

$ 5 1976; Phil1 ips 1973; Fergus~n sive sljspended natter, and depleting oxyet 

al. 1980). gen because of rapid utilization of suspended 

organic matter. The dredged sediments 

are unctlnsolidated and readily sus- 

8.1 1lftEOGING AFdD FILLING pended. Thus a spoil bank can serve as a 

source of excess suspended ~natter for a 

Probably the greatest anount of protracted time after deposition. Zi eman 

destruction of Seagrasses in south Flor- (197521) noted that in the Caribbean 

ida has resulted from dredging practices. dredged areas were not recolonized by turbfhether 

the objective is landf 111 for tle grass for many years after operations 

catrsewtiy and waterfront property con- ceased. Working in estuaries near Tampa 

strtlction, or deepening of wdters for and Tarpoll Springs, Godchar! es (1371) 

channels and canals, dredsing operations found no recovery of either turtle grass 

typically involve the hurfal of portions or nanatec grass in areas where co~n?ercial 

of an estuary rtith inaterial5 fr~c~ nearby hydraufic clam dredges had severed rhilocations, 

Such projects therefore can zomes or uprooted the plants, a1 though at 

invo? ve tile direct destruction OF not one station recolonization of sboal grass 

only t h ~ construction site, hut 31 SO !?any Mas observed,

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 nan-induced disturbance to submerged seagrass meadows. 

Van Eepoel and Grigg (1970) found Reduced 1 ight penetration was obserthat 

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 suglated 

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 re1 eased from 

2.5m (8ft) 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 andfir1 projects increased the harbor's Studies of Boca Ciega Bay, Florida, 

volume by 14% from 1962 to 1971. Sil ta- reveal the long-term 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 1 ight bay were fil led during projects involving 

conditions became unsui tab1 e for seagrass the construction of causeways and the 

growth. creation of new waterfront homesites.

Taylor and Sa1 oqan (1968) contrasted the roots, a moderate arloifnt of enrich!i:e~t. 

uodjsturbed areas of the bay, where iuxu- nay actuatly enhance productivity, urrder 

rfant grass grew in sedialentr; averaging certain conditions where ~aters are wcl l- 

94% sand and lit~cll, with the kott~itl of mixed, as observed I?y this author in tbe 

dredge canals, where unvegetated sedirvents rich growt? of turtle grass and associated 

averaged 32% silt and clay. Hhile several epiphytes in the vicinity (within 1 krrl or 

studies of Boca Ciegai Ray collectively 

described nearly 700 species of plants and 

(1.6 mi) 

plant. 

of Pdiaami's Vir~inia Key swage 

This discharge is on the side of 

animals occurring there, Taylor and Saloman 

(1968) falrnd only 2CZ of those same 

the key open to the ocean. In tbe in~ediate 

area where these wdstes are disspecies 

in the canals.. FIost of those were 

ffsh that are highly motil~ and thus not 

charged, however, water qua1 ity is so 

reduced that seagrasses cannot grow. Stinrestricted 

to the canal s durirlg extreri~c ul ation of excess epiphytic production iy!ay 

conditions. Tntcrestingly, whi le species adversely affect the seagrasses by persi s- 

numbers were higher in undfsturbed areas, tent light reduction, Qften the effects 

30% ilrore fish were found in the canals, of sewage discharge in such areas are cornthe 

most abundant of which wer-e the bay pounded by turbidity from dredging. In 

itnckovy, thc Cubart anchovy, and the scaled Christiansttld Harbor, St, Croix, where 

sardine, The authors noted that in the turtle grass beds were subjected to both 

fey4 ycars since the in1 tial disturbance, foralis of pollution, the seaarasses decl incnlnnizatican 

was rtegll'gihle at tire botturn ed and were replaced by the green aloa, 

of thc: canals and concluded that thc sedi- acerornor_pf&. In a 17-year period, the 

rnents there were unsul'tiable For most of grasms in the crrlha ment were reduced by 

the bayg$ benthic invertebrates. Light 662 (Don:! et a1 . 19723. 

tranrfl~fssian values were highest in the 

open bay away froctx landfills, lowest near Phytoplankton productivity increased 

the fir led areas, and increasctd somewhat in i-lillsborough Bay, near Tarnpa hecause of 

4rs the quie~eettt waters of the canals, nutrient enrichment for domestic sewaae 

Because of the doytt~ of the canals, how- and phosphate mining discharges (Taylor 

ever, 1 ight dt the battoirr gas insufffcient et al. 1973). Phytoplankton blooms con- 

Par seagrass grawttt, Taylor and Salemarl trihuted to the prohle~ of turbidity, 

{f9C@), using canservlatiue and incomplete whlch was increased to such a level that 

figures, astilitated that fi 1 'I operations in scagrasses persisted only in small sparse 

the bny resul tetl in an annual lass of 1.4 patches. The only irnportant nacrophyte 

mfl'l ion r!ollars for ff sherles and recrea- found in the hay wds the red alga, Craciltfan. 

- laria, Soft sediments in combinalti~~?~ 

low oxygen levels 1 iirrited diversity and 

IP seagrasses are only 1 igt\tly abundance of benthic invertebrates, 

covered and the rhizotire systalr is not 

changed, regrowtt.~ through the scditnent is Few seagrasses grow in waters of 

stltretfmes possltslc?, Thorhatrg et a1. Dl'scayne Ray that were pol luted hy sewage 

(1973) found tht coflstructian of a canal discharge in 1956 (McNul ty 1470). Only 

In Card Sound tetnporarily ceverod turtle shoal grass and Halophilal grew sporadi- 

Z km (Q.6 

gras5 Jn nn area of 2 ta 3 ha (5 to 7 cally in small patches w~thin 

acres) w-i th up to 10 cm (4 inches) of ini) of the outfall. Post-abaterent studsedirqerrt, 

killfrzg the leaves, hut not: thc ies Jn 1960 sfro~ed seagrasses in the area 

ri1iz01"r system, Regt-owth occurred when had actual ly decl ined, probably because of 

the drcdglng operations ceased and cur- the persistent resuspension of dredge 

rents carriePl the sedlnlent away, 

materials resulting fron the construction 

of a causeway. 

6,2 EUTKQPH ICAJ ION AEC SEgAGE Physiological studies reveal that 

seagrasses are not only affected by low 

S~agrass ~0wif"~ltnities arc sensitive to levels of light, but also suffer %!hen disadd1 

tions of ntatrients from sewage out- solved oxygen levels are persistently low, 

falls or industrial wastes. Because a situation encountered where sewage addiseagsasscs 

have the ability to take up tions cause increased microbial respiranutrfents 

throtrgh thc leaves as well as tion, Hammer (1968a) compared the effects 

86

of anaerohiosi s on photosynthetic rates of 

turtle grass and Halo hila decipiens. 

I!hile photosynthesis &ess~jn both 

species, Halophila did not recover after a 

24-hour exposure, whereas the recovery of 

turtle grass was complete, possibly because 

of its greater ability ta store oxygen 

in the internal lacunar spaces. Such 

an oxygen reduction, however, will have a 

far greatsr impact on the faunal components 

than on the plants. 

8.3 OIL 

bii th the P4ation8s continued energy 

demands, the transport of petrolelrrti and 

the possibility of new offshore drilling 

operations threaten the coastal zone of 

south Florida. The impact on marine and 

estuarine cornr~uni ties of several 1 argescale 

oil spills has been investigated; 

laboratory studies have assessed the toxicity 

of oil to specific organisms. The 

effects of oil spills, cleanup procedures, 

and restoration on seagrass ecosystems 

have recently been reviewed by Zi eman 

ct al. (in press). 

Tatein et dl, (1978) studied the toxicity 

of two crude oils and two refined 

oils on several life stages of estuarine 

shri~np. iiefined Bunker C and number 2 

Fuel oil were inore toxic to all forms than 

were crude oils fran south Louisiana and 

Kuwait. The larval stases of the srass 

shrimp (Palaemonetes pu~fo) were sl ijhtly 

more resistant to the oil than the adults, 

while all forms of the oils were toxic to 

the larval and juvenile stages of the 

white shrimp (Penaeus setiferus) and the 

brown shrimp (Penaeus aztecus)l;lboth common 

grass bedmitants. Changes in 

temperature and sal ini ty, which are routine 

in estuaries, enhanced the toxic 

effects of the petroleum hydrocarbons. 

The greatest danyer to aquatic organisms 

seems to be the aromatic hydrocarbons as 

opposed to the paraffins or a1 kanes. The 

bicycl ic and polycycl ic aromatics, especially 

napthalene, are major sources of 

the observed tnor-ta? i ties (Tatem et a1 . 

1478). The best indicator of an oil's 

toxicity is probably its aromatic hydrocarbon! 

content (Anderson et a1. 1974; 

Tatem et a1 . 19783). 

The effects of oil -in-water dispersions 

and soluble fractions of crude and 

refined oils were evaluated for six species 

of estuarine crustacea and fishes 

fron: Galveston Bay, Texas (finderson et al. 

1974). The refined oils were consistently 

sore toxic than the crude oil s, and 

the three invertebrate species studied 

were nore sensitive than were the three 

fishes. 

The cf fects on seagrass photosynthesis 

of exposure to sublethal levels of 

hydrocarbons were studied by FcRoy and 

1 a s (1977). PI ants exposed to low 

1 eve1 s of water suspensions of kerosene 

and toluene showed significantly reduced 

rates of carbon uptake. Plants probably 

are not the most susceptible portion of 

the comtnuni ty; in boat harbors where seagrasses 

occur, the associated fauna are 

often severely affected. 

In the vicinity of Roscoff, France, 

den Hartog and Jacobs (1980) studied the 

impact of the 1978 "Arnoco Cadiz" oil spill 

on the Zostera marina beds. For a few 

weeks after the spill, the eelgrass suffered 

leaf damage, but no long-term effect 

on the plants was observed. bong the 

grass bed fauna, fil ter-feeding amphi pods 

and polychaetes were most effected. The 

eel grass 1 eaves were a physical barrier 

protecting the sediments and infauna from 

direct contact with the oil, and the rhizorne 

system's sediment-binding capahil i- 

ties prevented the mixing of oil with the 

sediment. Diaz-Pi fcrrer (1962) found that 

turtle grass beds near Guanica, Puerto 

Rico, suffered greatly when 10,000 tons of 

crude oil were released into the waters on 

an incoming tide. Mass mortalities of 

rqarine animal s occurred, including species 

commonly found in prass beds. Many months 

after the incident turtle grass beds continued 

to decline. 

In Karch of 3973, the tanker & 

Colocotroni s re1 eased 37,000 barrel s of 

Venezuelan crude oil in an attempt to free 

itself from a shoal off the south coast of 

Puerto Rico. The easterly trade winds 

moved the oil into Bahia Sucia and contaminated 

the beaches, seagrasses, and mangroves. 

Observations were made and samples 

collected shortly after the spill. 

By the third day following the release, 

dead and dying animals were abundant in 

the turtle grass beds; and large numbers 

of sea urchins, conchs, polychaetes, 

prawns, and holothurians were washed up

on the &ach (Radeau and Rerquisrt. 1977). sensitive to both the s~luble and insol- 

Although the rpflled Venezuelan crude oil uble fractions of ~etroieum (Figure 25)* 

Js cons'ldtered to have ?ow toxicity, the 

strong winds rand the wave action in shal- Considering the vast amount of ship 

low waters combined ta produce dissolution traffic that passes through the Florida 

and droplet entralment that yield& an Straits, it is sonewhat surprising that 

acutely toxic effect. This wave entrain- there have not been more reported oil 

mcnt carried 051 down into the turtle spll?s* Sampling of beaches throughout 

grass, kill ing the vegetatjon. Lacking the State has shown that a consfderahlf! 

the stabl"li~ing influence of the seagrass, amount of tar washes UP on Florida 

extensSve areas &.rere eroded, some dawn to beaches, and that the beaches of the 

the rhSzomc layer, Some turtle grass Florida Keys are the most contaninated 

rcjuvenatr*an was noted in January 1974, (Rarnera et al. 19813. In this study, 26 

1915 renewed seagrass growth and beaches throughout the State were sampled 

setdfmant dr?vr?l opment were observed. Sur- far recently &feposi t@d tar. The density 

veyt; of the epjhenthlc cormunities showed of ship traffic and the prevailing souths 

general dec"tne fo1 lowfng the spil I, but fsasterly 8~inds, result jn no tar xcumujalinfaund? 

sarrap"t ssire proved too small tion an many heaches on the gulf coast, 

(gadsau and Elsrquist lcf71) to yield defin- while the largest amounts are found 

itfve results, between Elliot Key and Key West. Of the 

25 san~ple stattons, 6 were in the Keys he- 

In July 1975 a tankazr discharged inn twccn ElTiot Key and Key Vest, and there 

ant'i~tatcrd 1;,5(?0 to 3,000 barrels gf an were 113 on each coast north of this 

cfluhfsn af cruds of7 and water into the region, The average for tee six Keys 

edge of the Florldaa current about 40 km stations was 17.2 gr7' tar/md of beach 

(25 mi) south-southwest: of the F"rarque5a sappled, with the seation on Sugarloaf Key 

#sy%. The p~glrrillllng winds drove the oi4 shawlng the highest mean annual anount of 

"tnot~oro &Tong a 50-km (31-~RS 1 section of a8. 5 gn/ma. By cmparl'son, the average 

tha Fl~~fdia Keys frar;i Soca Chfca $0 t,f tt;le annual arqount for the 10 east coast 

PSne Key, Chan (1977) observed no d+rect: beaches nctrth of Hiami was 2.5 ~n/m", and 

dafzage to tu~tle grass, rqanatec grass or the average for the west coast Reaches 

shaal grass, The natural sgagrass drfft north of Cape Sabel was only 0.3 gm/nL. 

rrr&tsrf&I apparently acts as an absorbent The imp1 ication of this study is quite 

drrd ~~ncentr~t(3r of! the of1, This mate- frightening, far as damaging and unsi~htly 

ds'l was deposft& fn tha Intartidal zone a?; an oil spill can be on a beach, the 

whcre thg? ally deposfts pa~slsted at least pedentfal for damage is inestimably higher 

1 month longer thian the narrnal scagrdss In a region such as the Florida Keys with 

bb~chwrd~k~ and Chan tkaught that this its I iving, hiotjc interfaces of mangrove, 

radltead det;t*l tal jnprlt lnta the depcnrfcnt: barely suifrxtidal seaqPass flats, and shal- 

~cosy~Ler?c,. The ~nphfp0d~ and crabs typi- low coral reefs. 

cdl 04 thfs sonc djd not occur in the polluted 

matcrfal. fhc author attributed 

rrass mortaliitief of the pearl oyster 8.4 TENPEPATWPF AN0 SfiLIR!ITY 

(P2nctc+d;a ~arQe!2-j & grass bed inhr?rbS dank, 

t~m*'?o~%-lllsT~b?~ fractioe of pctr~tc~m, fropfcal estiiraries are particularly 

The SCVCV~~S~; ERQ~CCS WI"C In the adjacent susceptible to damage by increased tempcrrrangrove 

and narsh cornunities where atcwes $?rice most of the comnunity's 

plants and animals were extensively dafq- a~gaflism~ flo~a%ly grow close to their 

aged, A@ong the effects natcd was the upper thcrr~al Jinits fblayer 5914, 1PZB). 

Increase in t~pet-atetre? zthove the lgthal Ihc Cm!a?iLtce can Inshore and Estuarine 

limit af masf fntt%rtidal nroanfsnr caused POI jution (E96?Q observed that a wide 

by the dark oS1 calatjng. 

variety of tropical narine araanisms could 

survive temperatures of 28°C (82°F) hut 

Frar-: various qtudies it; is (~byj~~s, hcgan dying at 33' to 34'2: (!?I0 to 33OF). 

then, tbnt cvcn wkr:! the seagrasses %her?- In Puerto Pico, Gly~n (1968) reported biqh 

selves apparently suffer 1 ittte PcnTan~nt mortal {ties of turtle grass and invertcdar7age, 

the dssaclaterf Fauna can be quite hratcs on shill TOW f69 ats when te~~peratures 

88

eached 35" to 40°C (95" to 104°F). 

PI anktonic species are probably 1 ess 

affected by high temperatures than are 

sessile populations since 1 arvae can 

readily be imported from unaffected areas. 

Time of exposure is critical in 

assessing the effect of thermal stress. 

Many organisms to1 erate extreme short-term 

temperature change, but do not survive 

chronic exposure to smaller elevation in 

temperature. For seagrasses that have 

buried rhizome systems, the poor thermal 

conductivity of the sediments effectively 

serves as a buffer against short-term 

temperature increases. As a result, the 

seagrasses tend to be more resistant to 

periodic acute temperature increase than 

the a1 gae. Continued heating, however, 

can raise the sediment temperature to 

levels lethal to plants (Zieman and Wood 

1975). The animal components of the seagrass 

systems show the same ranges of 

thermal to? erances as the pl ants. Sessile 

forms are more affected as they are unable 

to escape either short-term dcute effects 

or long-term chronic stresses. 

The main source of man-induced thermal 

stress in tropical estuaries probably 

has been the use of natural waters in 

cooling systems of power plants. Danage 

to the communities involved has been 

reported at various study sites. In Guam 

characteristic fish and invertebrates of 

the reef flat comnuni ty disappeared when 

heated effluents were discharged in the 

area (Jones and Randal 1 1973). Virnstein 

(1977) found a decrease in density and 

diversity of benthic infauna in Tampa Bay 

in the vicinity of a power plant, where 

temperatures of 34" to 37°C (93" to 99°F) 

were recorded. 

The nost thorough investigations of 

thermal pol 1 ution in tropical or semi tropical 

environments have centered around the 

Miami Turkey Point power plant of Florida 

Power and Light (see review by Zieaan and 

Wood 1975). Zieman and blood (1975) found 

that turtle grass productivity decreased 

as tetfiperatures rose and showed the relationship 

between the pattern of turtle 

grass leaf death and the effluent plume, 

reporting by late September 1960, that 

14 ha (35 acres) of grass beds had been 

destroyed. Purkerson (1973) estimated 

that by the fa11 of 1968, the barren area 

had increased to 40 ha (99 acres) with a 

zone of lesser damage extending to include 

about 120 ha (297 acres). In 1971 the 

effluents were further diluted by using 

greater volumes of ambient-temperature bay 

waters. The net effect, however, was to 

expand the zone of thermal stress. One 

station 1,372 m (4500 ft) off the canal 

had temperatures of 32.Z°C (90°F) only 2% 

of the tine in July 1970, but this increased 

to 78% of the time in July 1971 

(Purkerson 1973). 

Temperatures of 4°C or more above 

ambient killed nearly all fauna and flora 

present (Roessler and Zieman 1969). A 

rise of 3OC above ambient damaged algae; 

species numbers and diversity were decreased. 

The optimum temperature range 

for maximal species diversity and numbers 

of individuals was between 26" and 30°C 

(79" and 86°F) (Roessler 1971). Temperatures 

between 30" and 34°C (86" and 93°F) 

excluded 504 of the invertebrates and 

fishes, and temperatures between 35" and 

37°C (95" and 99°F) excluded 75%. 

The effects recorded above resulted 

from operation of two conventional power 

genera tors which produced about 12 m3/sec 

of cooling water heated about 5°C (41°F). 

Using this cooling system, the full plant, 

which was two conventional and two nuclear 

generators, would produce 40 m3/sec of 

water heated 6" to 8°C above ambient. The 

plant had begun operations in spring 1967 

with a single conventional unit, and a 

year later a second unit was added. Studies 

at the site began in May 1968 when the 

area was still relatively undisturbed. 

Except for a few hectares directly out 

from the effluent canal, the communities 

in the vicinity were the same as in adja- 

cent areas to the north and south. As 

temperati~res increased throughout the summer, 

however, damage to the benthic cornmuni 

ty expanded rapidly. 

Because of the anticipated impact of 

the nuclear powered units, a new 9-km 

(5.6-mi) canal emptying to the south in 

Card Sound was dredged. Fears that this 

body of water a1 so would be damaged persisted, 

and as a final solution to the 

problen a network of 270 km (169 mi) of 

cooling canals 60 EI (197 ft) wide was constructed. 

Heated water was discharged 

into Card Sound until the completion of 

I

the closed systerq, however. Thorhaug Seagrass beds. The eastern regions of 

ct a1 . (1973) found little evidence of Florida Bay were formerly characterired by 

Cag~age to the biota of Card Sound, partly low salinity, nudd~ hays with sparse 

because effluent temperatures there were growths of shoal yrass. fishing here was 

lower than those experienced in giscayne often excellent as a variety of species 

Bay, and even before the thennal addf- such as mullet and sea trout foraged in 

tions, tile benthic cclrrtmunity of the af- the heterogenous bottom. One of the nainfccted 

portion of Card Sound wds rela- stays of the fishing guides of this area 

tjvely dcpaupcrate cornpared to Rjscayqe was the spectacular and C O ~ stent S ~ f i sbing 

Bay. For redfisb. In recent years the guides 

have complained that this fish population 

The ternpcratures and salinities of has becorne reduced, and it is not worth 

the hays and lagoons af south Floridd show the effort to bring clients to this area. 

rtauch variation, and the fauna and flora In January 1979 this author took a trig 

orust have adequate adaptive capacity to through this region and found that much of 

survive. Although the heated brine ef- the forrnerly mud and shoal grass bottom 

Fluent frorn the Key West desalination that he had worked on 10 to 17 years prior 

plant causad rr~arked reduction in the was flow lush, productive turtle grass 

dfverslty in the vicinity of the outfall, beds. Where the waters were once rauddy, 

nearly all beds of turtle grass were unaf- they were now, according to the guide, 

Fected (Chesker 1975). Shoal grass is the much clearer and shallower, but provided 

frt~sl ec~ryhtallntl of the local seagrasses less sea trout and redfish. Why? The 

(li2cP9iI 1 an and F4oselcy 1967). Turtle grass fol lowin? hypothetical scenario is ane 

and mandtce grass show a decrease in explanation. 

photasy~tthetic rate as salinity drops 

below fill 1 strength seawater. The season- In the lake sixties the infarrrous 

ality of' ntzagrassss in south FSorjda is C-111 or Aerojet-General canal was built 

largely explatned by ttenrperature and in south Dade County, on which Aerojet 

salfnlty effects f7lcman 7 The hoped to barge rocket motors to a test 

gwatest t1e(ltl'rr1~ ln plant poplilations was site in south Dade, The contracts failed 

found when conrbinat$an% of high tmnpera- to r~aterialize and the canal, a1 though 

ture and lo# salfnf ty occurred siirlultan- completed, was left plugged and never 

eoualy. Tahb et a1. 41962) stdted: "Host opened to the sea, T ts effect, however, 

of the effects of niafl-made change5 on was to intercept a large part of the overp'lant 

and animal populations in Florida land freshwater flow to the eastern Ever- 

~stuarles (wtd in inany particulars in glades and wltirnately to eastern Florida 

estua~ies in adjacent reglons of the Gulf Ray. 

sf &xien and south Atlastic) are a result 

rtaf a? torations In aal inity and turbidity, The interception of this water is 

Hfgh sallnftfes (30-40 ppl) favor the sur- thought to have created pronounced changes 

vlvdl of certaif~ zpecias like sea trout, in the salinity of eastern Florida Ray, 

redF1sh and ott~er rrarine fishcs, and allowing for much greater saltwater penetheref~re 

i!fiprlave angling For thasc spc- tration. As the salinity increased, turcles. 

On the other hand these higher tle grass, which had been held in check by 

sal lnitfrs reduce survival of the young lowered salinity, may have had a competistages 

of such 'irtrp~rtcant species as COFII- tive advantage over shoal grass and 

r~e~cial penaeid shrirr~p~ inenhaden, oysters increased its range. The thick anastornosand 

others. f t sectrls clear that the ing rh-izome ~Qat of turtle grass stabilized 

balance favors the low to moderate salln- sediments and may have lnade foraging dif- 

Ity $ltuauatl'on over the high salinity. ficult for s~ecies that nornally grub 

Therefore, control irl southern estuaries about in loose mud substrate. Also the 

should be 4n the directjon of maintaining greater sediment stabilizing capacity of 

the supply of sufficient quantitteo of turtle grass !nay have caused rapid filling 

fresh water which wauld result in estua- in an environment of high sediment supply 

rfne salinities of 18 to 30 ppteW 

and law wave energy. 

Perhaps reduced water f l o ~ in the This ~~enario has not been proven; 

Everglades has had unexpected impacts in thus it is hypothesis and not fact. It 

90

points out, however, the conceivabil i ty of 

how a mantnade modification at some distance 

nay have pronounced effects on the 

1 i fe hi story and abundance of organisnls, 

It is interesting to note that the 

fishing guides regarded the lush, productive 

turtle grass beds as a pest and much 

desired the muddy, sparse shoal grass. 

What this really illustrates is that quite 

different habitats rnay be of vital irnportance 

to certain species at specific 

points in their life cycle. Those features 

that make the turtle grass beds good 

nurseries and important to these same carnivores 

when they are juveniles restrict 

their foraging ability as adults. It 

should be noted in passing that while 

1 arnen ti ng the encroachment of turtle grass 

into this area, the guides still hailed 

the shallow turtle grass beds to be superior 

bonefi sh habitat. 

8.5 DISTURBANCE AND RECOLONIZATION 

The rate at which a disturbed tropical 

grass bed may recolonize is still 

largely unknown. Fuss and Kelly (1969) 

found that at least 10 months were required 

for a turtle grass rhizome to 

develop a new apex. 

The most common form of disturbance 

to seagrass beds in south Florida involves 

cuts frorn boat propellers. Although it 

would seem that these relatively smallscale 

disturbances would heal rapidly, 

typically it takes 2 to 5 years to recolonize 

a turtle grass bed (Zieman (1976). 

A1 though the scarred areas rapidly fill in 

with sediment from the surrounding beds, 

the sediment is slightly coarser and has a 

1 ower pH and Eh. 

In some regions, disturbances become 

nearly permanent features. Off the coast 

of Be1 ize aerial photographs show features 

in the water that appear as strings of 

beads. These are holes resulting from 

seismic detonation; some have persisted 

for over 17 years (J.C. Ogden, personal 

communication) with no recolonization. 

This is not just due to problems associated 

with explosions, as Zieman has observed 

blast holes from bombs on a naval 

bombing range in Puerto Rico where some 

recolonization occurred within 5 years. 

9 1 

Most cdses of restoration in south 

Florida involve turtle grass because of 

its value to the ecosyste~ and its spatial 

dominance as well as its truculence at 

recolonizing a disturbed area. Recol onization 

by shoal grass is not frenuently a 

problem. The plant has a surficial root 

and rhi zorne systan that spreads rapidly. 

It grows from relnaininq fra~rnents or froln 

seed and can recolonize an area in a short 

time. 

Ry conparison, turtle grass is i3uch 

slower. Fuss and Kelly (1969) found 10 

~nonths were required for turtle grass to 

show new short shoot development. The 

short shoots seem to be sensitive to environmental 

condi tians a1 so. Kelly et a1 . 

(1971) found that after 13 months 40% of 

the transplants back into a central area 

had initiated new rhizome growth, while 

only 15% to 18% of the plants showed new 

growth initiation when transpl anted to 

disturbed sediments. Thorhaug (1974) 

reported success with regeneration from 

turtle grass seedlings, but unfortunately 

seeding of turtle grass in quantity is a 

sporadic event in south Florida. 

If one accepts the concept of ecological 

succession, there are two basic ways 

to restore a nature comuni ty: (1) establish 

the pioneer species and allow succession 

to take its course, and (2) create 

the environmental conditions necessary for 

the survival and growth of the climax species. 

Van Breedveld (1975) noted that 

survival of seagrass transplants was 

greatly enhanced by using a "hall" of sedinent, 

similar to techniques in the terrestrial 

transplantation of garden plants. 

He a1 so noted that transpl antation should 

be done when the plants are in a semidornant 

state (as in winter) to give the 

plants time to stabilize, again a logical 

outgrowth of terrestrial technique. 

Although numerous seagrass transplanting~ 

have been performed in south 

Florida, the recent study by Lewis et a1 . 

(1981) is the first to use a1 1 major seagrass 

species in a comprehensive experimental 

design that tests each of the techniques 

previously described in the 1 i terature. 

The study site was a 10-ha (25-acre) 

borrow pit on the southeast side of Craig 

Key in the central Florida Keys, which was 

studied from February 1979 to February

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 sucoverseas 

hs'ghway. The dredged site is 1.3 cessful. Although some of the treatments 

to 1.7 m (4.3 to 5.6 ft) deep and is cov- showed short-term 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, end portions of the seedlings of turtle grass showed no longborrow 

pit were gradually being revege- term survlva1 at the barren transplant 

ta ted . 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 plant species and in the lalooratory showed a modest survival 

transplantation techniques. Rare single of 29% when transplanted to the field, but 

short shoots and plugs of seagrass plus even the survivors did not spread signifisediment 

(22 x 22 x 10 cm) were used for cantly. 

turtle grass, manatee grass, and shoal 

grass, Seeds and seedlings of laboratory- A1 though several of the restoration 

raised and field-collected turtle grass techniques used by Lewis et a1 . (1981) 

were planted, but seeds and seed1 ings of proved to he techno1 ogical ly feasi bl e, 

the other species proved impossible to there arc! still major logistic and ecofind 

in sufficient quantity, Short shoots nomic problems remaining. The plug techwere 

attach& to small concrete anchors nique showed the highest survival rate, 

with rubber bands and placed in hand-dug but the cast estfnates ranged from $27,000 

holes 1 to J m deep, which were then to 86,500fha. Because of the large volume 

filled with sedlment, Seeds and seedlings and weight of the plugs, this method 

were planted by hand wf lhout anchors after requires that large source beds he close 

ft was detemined that anchors were to the transplantation site, The removal 

detrimental to the survival of the seed- af large quantitiirts of plugs can represent 

lings, The large sediment plugs with 

seagrass were placed in similar sized 

a major source of disturbance for the 

source bed, as the plug holes are as slow 

holes made with another plugging device. to recolonjze naturally as propeller cuts 

Plugs and short shaots of all species were and other simflar disturbances. Despite 

planted with both 1- and 2-m spacing, the spreading recorded at the transplant 

whdle the seeds and seedlings of turtle site, the source holes for the plugs did 

grass were planted using 0.3-, I-, and 2-m not show any recolonization at the end of 

spacq ngs . the 2-year period* If source naterial was 

required far a large scale revegetation 

Qf 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 sjgnificant nun- impact Itself. For this reason Lewis 

bers for the full 2 years: fnanatec grass et a1. (1981) suggested that this method 

plugs wl th 1-m spacing, and turtle grass be mainly used where there are source beds 

plugs with both 1- and 2-m spacing. iur- that are slated far destruction because of 

tlc grass plugs showed the hfghest sur- soine dew1 opnental activity. 

viva? rate (90% to 38%), but did not 

expand much, increasing their coverage by The anly other techniaue that showed 

a factor of only 1,6 during the 2 years. any significant survival was the utililvianatee 

grass spread rapidly from plugs zation of laboratory cultivated seeds 

under the prevailing conditions and had and seed1 ingse This ,yethod was prohibii%creihsed 

it% area by a factor of 11.4 in tively expensive with costs estimated 

the 2-year period, The initial plantt'ng at $182,900/has largely due to cuttivaof 

shoal grass, however, died aut corn- tian costs; survival was still below 

pletely after only a few months, and a 30% Seeds and seed1 ings are also suitsecond 

planting was nade with larger, more able only in areas where the water motion 

robust plants from a different site. This is retatfuel? Quiescent, as their abifplanting 

survived sufficiently to increase ity to V@qaln rooted at this stage is 

its area by a factor of 3.4 after- 1 year. minimal. 

92

may 

Transplants of tropical seagrasses 

ul timately be a useful restoration 

In the early 1930'~~ Zostera marina, 

a widespread northern temperate seagrass 

technique to reclaim damaged areas, but at 

this time the results are not consistent 

disappeared from a large part of its 

range. In North America, it virtually vanor 

dependable, and the costs seem prohibitive 

for any effort other than an experiished 

from Newfoundland to North Carolina, 

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 plants are 

real ly more recalcitrant than temperate Many changes accompanied this disturones. 

search 

It is 1 ikely that continued rewill 

yield more successful and 

bance. Sandy beaches eroded and were replaced 

with rocky rubble. The protective 

cost-effective techniques. effects of the grass beds were removed. 

8.6 THE LESSON OF THE WASTING DISEASE 

The fisheries changed, a1 though slowly at 

first, as their detrital base disappeared. 

Noticeable improvement did not become 

widespread until after 1945 (Rasmussen 

The infomation overload that we are 

subjected to daily as members of modern 

19771, and 

40 years. 

full recovery required 30 to 

It should be emphasized that 

society has rendered us immune to many of this was a large-scale event. In Denmark 

the predictions of doom, destruction, and alone over 6,300 km2 (2,430 mi') of eelcatastrophe 

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 km2 (1,930 mi') of submerged 

of a major portion of the reefs and atolls 

of the Pacific by an unprecedented outmarine 

vegetation (Bittaker and Iverson, 

in press). Originally the wasting disease 

break of the crown-of-thorns starfish was attributed to a parasite, Labyri thula, 

(Acanthaster planci). The outbreak spread but now it is felt that the cause was 

rapidly and the devastation was intense in 

the regions in which it occurred. Yet, 

1 ikely a cl imatic temperature fluctuation 

(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 

that was feared did not occur and recovery 

responsibility for large-scale environmental 

change, basic understanding of the 

commenced. fundamental processes of ecosystetns is 

necessary to avoid his becoming the cause 

In south Florida in 1972-73 there of associated large-scale disturbance conappeared 

to be an outbreak of the isopod, 

Sphaeroma terebrans, which it was feared 

parable to the wasting disease. 

would devastate the Florida mangroves. 

This devastation never materialized, and 8.7 PRESENT, PAST, AND FUTURE 

it now appears that the episode represented 

a minor population excursion (see 

Odum et al. 1381 for complete treatment). 

Increasingly, studies have shown the 

importance of submerged vegetation to 

major commercial and forage organisms 

These episodic events proved to be (Linda11 and Salonan 1977; Thayer and 

short tern and probably of little long- Ustach 1981; Peters et al. 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 exceedchanges 

having major effects and causing ed $168 million in 1973, which represents 

1 arge-scale famine on land, but few think about 30% of the total U.S. recreational 

this can happen in the seemingly infinite 

seas. However, one such catastrophic disfishery 

(Linda11 and Salonan 1977). Of 

this, 59% of the organisms caught were 

turbance has occurred in the seas, and it dependent on wetlands at sone stage of 

was in this century and induced by a their life cycle. Linda11 and Salonan 

natural process. 

(1977) estimated an even higher dependency 

93

with over 70% of gulf recreational fish- corqtoercial species--pi nk shrirnp and 

eries of the region being estuarine lobster--a1 ready intense, will inevi tahly 

dependent. increase. The Rahanian waters, Formerly 

open to U.S. lobs termen, are now closed 

The value of the estuarine regions to putting more Pressure on the already 

important cofin:rercial fisheries is even depleted stocks. In the past about 12% 

rlore striking. The Gulf of Flexico is the of the shrimp landed an the Florida gulf 

leading region of the llnited States jn coast was caught in ?%xican waters. Peterms 

of both landings (35% of the g,?. cently the Mexican governr~ent announced 

total catch) and value (27% of fII.5. total that the enabling treaty would not l~e 

Fjshery value , according to Linda11 and renewed. These actions will put increas- 

Salorran (1977 1 , who also determined that ing pressure on dornestic stocks. As this 

ahout 90% of the total Gulf of Mexico and is happening, developtnent in the region is 

south Atlantic fishery catch is estuarine drarrlatically escalating. In the eyes of 

dependent, many, the main limitations to further 

development in the Florida Keys were fresh 

The pink shrirnp fishery, 1 arges t in water avail abil i ty and deteriorating 

the State of FlorSda, is centered around access highways. All of the bridges in the 

the Tortugas grounds where 75% of the Keys are notd being rebuilt and a referenshrir?p 

crlugtrt in Florr'da waters are taken. dum was recently passed to construct a 

Kutkuhrt (1966) estimated the annual con- 36-inch water pipeline to replace the old 

Lrl'butian 09 thc Tortugas grolrnds to he Navy line, The price of building lots 

10% of the total gulf shrirnp fishery, took a 30% to 50% jump the day after the 

which in 1979 was worth $375 mill ion water referendum passed and in many areas 

(Thonpsan 1?81), The vast seagrass and had doubled 6 months after the passage. 

t?sngroua reglons of south Florida are the 

nursery grudnd for this vitally inportant It is depressing to read, "Today the 

cofsliera i a1 f S s irery .y, 

mackerel and kingfish are so depleted that 

they have alrnost ceased to be an issue 

In the Ctnl ted Statcs, 98% of the corrr- with the professional fisherman," or "The 

raarclal Cdtch of spiny lobsters cone from luscious crawfish, however, is now in a 

habitclts assac4ated with the Florida Keys crucial stage in its career. Largely pone 

(VI11 iar~s and Prachaska 1977; Prochaska frorq its inore accessible haunts, it has 

and Cats 198Q), In ternis of ex-vessel been preserved so far on the reef., . . Eco- 

UB~UF?, the spiny lobster fishery is second no~nic pressure and growf ng denand however, 

lrtlly too "ehe pink shrf~~sp in the State of have developed more intensive and success- 

F"lerida (Prachaska 1976). &.abisky et al. ful methods of catching them, and though a 

(19CO) reported that the high in lobster closed season has heen put on them, in the 

landings, lk,4 rliill ion llh, wds reached in open months uncalculahle thousands are 

1272, nr~d the r~~axilnunr ex-vessel value of shipped to market and they are rapidly 

813-19 rn4llion recorded in 1974, These disappearing." Today Me find little sur- 

Fiqut-e% include lobsters taken by Florida prise in these statements, having corqe to 

ffshe?rrnen fv.9: internalr'onal waters which expect this sort of natural decline with 

~ ~ I C O I ~ the ~ ~ SEaha~nian S fishing grounds, increasing developrfient. What is surprising 

Sincc 2975 the Fiahatr~lan fishing grounds is that this statement is taken from a 

have twn closed to foreign Fishing, plac- chapter entitled, "Botany and Fishing; 

ing greater pressure an domestic stocks 1885-6," fran the story of the founder of 

(Labisky et a7, 1980). 

Coconut Grove, Ralph M. Monroe (Wunroe and 

Gilpin 1930). 

Thcrc is an increasing need for more 

precise 4nfon.tation ta ffirst understdnd Today we see south Florida as a t 

and then to manage these resources intel- talising portion of the lusii tropi 

1 igently. Although south Florida has tucked away on the far southeast coast 

been late in developing compared with of the United States. It is not insignifmost 

other regions of the United qtates, icant in size, and its natural produc- 

the pressures are becoming overwhelnittg, ti~i t~ 1 s enormous. A1 thou@ the wid ters 

The fishery pressure on the two leading still abound with fish and shellfish, in 

94

quantities that often amaze visitors, it 

is useful to think back to how productive 

these waters must have been. 

Their future productivity remains to 

be determined. Present productivity can 

be maintained, although that will not be 

easy considering the ever-increasing 

developmental pressures. A catastrophic 

decl ine is certainly possible; merely 

maintaining the current economic and 

development growth rates will provide that 

effect. This point was well made by one 

of the reviewers of this manuscript whose 

comments I paraphrase here: Insidious 

gradual change is the greatest enemy, 

since the observer is never aware of the 

magnitude of change over time. A turbidity 

study in Biscayne Bay showed no significant 

differences in turbidity between 

consecutive years during 1972 and 1977, 

but significant change between 1972 and 

1975 (or between 1973 and 1976). In other 

words, south Biscayne Bay was significantly 

more turbid in 1977 than 1972, but 

a 2-year study would not have uncovered it 

(J. Tilmant, National Park Service, Hornestead, 

Florida; personal communication). 

To properly manage the region, we must 

understand how it functions. Decades ago 

it would have been possible to maintain 

productivity just by preserving the area 

and restricting human influence. Now 

water management decisions a 100 miles 

away have profound changes on the fisheries. 

En1 ightened mu1 ti-use management 

will require a greater knowledge of the 

complex ecological interactions than we 

possess today. 

Figure 27. 

Scallop on the surface of a shallow Halodule bed in Western Florida Bay. 

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APPEMDI X 

KEY TO FISH SUPVEYS IN S01'TH FLORIDA 

- --- ---- ------ - -- 

Survey Location Reference 

number 

-----p,----- 

-pew- 

1 North Biscayne Bay Roessl er 1965 

South Biscayne Bay 

Card Sound 

Metecumbe Key 

Porpoise Lake 

Whi tewater 6ay 

Fakaha tchee Bay 

Marcu Island 

Rookery Bay 

Charlotte ilarhor 

Oader and Poessler 1971 

Brook 1975 

Springer and McErl ean 1962b 

Hudson et al. 1970 

Tabb and Manning 1961 

Carter et al. 1973 

Meinsteain et al. 1971 

Vokcl 1375a 

Wang and Raney 1971 

Key to dhundaalse 

Y' 

p 

c 

rcarc. 

present 

a comltton 

c abuntfdnt

List of fishes and their diets from collections in south Florida. 

Species Abundance by survey nunher Diet Source 

1 2 3 4 5 6 7 8 9 1 0 

Orectol obidaelnurse sharks 

Gi nal ymostorna ci rratum r r P 

nurse shark 

Carcharhinidae/requiem sharks 

Nege rion brevirostris 

lLon STZX- 

Sphyrnidae/harnmerhead sharks 

Sphyrna tiburo 

bonnethead 

Fish: Acanthurus sp., clupeids, scarids 

Randall 1967; Clark 

Muoil 50., Jenkinsia sp., cant her hi^ and von Schmidt 1965 

n s ; mo1 luscs; cephal opods 

Fish: marinus, wpm cterus Clark and von Schmidt 

schoepfi, G a m y s fel is: blugil sg. 1965; Randall 1967 

Rhinobatos lentiqinosus; octopods 

Crabs: Callinectes sapidus, stomatopods; 

shrimp; isopods; barnacles; bivalves; 

Bol ke and Chaplin 1968 

Clark and von schriidt 

cephalopods; fish 1965 

C-' 

Pri stidae/sawfishes 

Pristis ectinata 

-'YZil-l!ooth sawfish 

Rhinobatidaelguitarfi shes 

Rhinobatus lentiginosus 

atlantic guitarfish 

Torpedini daelel ectric rays 

Narcine brasil iensis 

lesse-tric ray 

Raj idaetskates 

Ra-& texana r 

roGiX3-s kste 

Dasyatidae/sti ngrays 

Urol uphus jamnicensi s r r 

yell ovc stit'igray 

Gymnura mjcrura- r r 

smootmterfly ray 

r 

r 

Anne1 ids; crustacea; fishes 

Fish: Centropristis striata, molluscs: 

Solemya sp.; annelids; shrimp; small 

crustaceans 

Peterson and Peterson 

1979

L n 

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m 

'r .r > 

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(U > El-


Species 

Abundance by survey number 

1 2 3 4 5 6 7 8 9 1 0 

Diet 

Source 

-- 

Clupeidae/herrings (continued) 

-- Brevoortia smi thi 

y e m i n ~menhaden 

Opi sthonema ogl inum 

atlantic thread herring 

Sardine1 la anchovia 

spanish sardine 

r 

r Vel igers; copepods; detritus; pol ychaetes; Randall 1967; Carr 

shrimp; fishes; shrimp and crab larvae; and Adams 1973 

mysids; tunicates; stornatopod larvae; eggs; 

gastropod larvae; other rare items 

Anchoa cubana -- cuba-ovy 

r 

Ostracods; copepods 

Springer and Woodburn 

1960 

Anchoa lamprotaenia 

bigeye a6c- 

a 

P 

Anchoa mitchill i 

bay anchovy 

Anclioviell a gerfasciata 

flat anchovy 

Anchoa hepsetus 

striped anchovy 

Synodontidaell irardfishes 

r r p c r 

r c Less than 23 mm SL veligers, copepods, 

eggs; 31 to 62 mm SL. amphipods, detritus, 

Carr and Adams 1973; 

Reid 1954; 

ostracods, zooplankton, mysids, harpacticoid 

copepods, small molluscs, chironomid larvae 

r c Ve1igers;copepods;mysids;zooea;fish; Carr and Adams 1973; 

eggs 

Springer and 3oodburn 

1960 

Fishes: gobies, killifish, silver perch, Carr and Adams 1973; 

Synodus foetens r r r r p c r r r r pipefish,pigfish,juvenileseatrout, Reid 1954; Randall 

inshore 1 izardfish puffer; shrimp; plant detritus 1967 

Ari idaelsea catfishes 

rnari nus 

gafftopsail catfish 

r Callinectes sapidus; fishes Odum and Heald 1972 

Odum and Heald 1972; 

Reid 1954

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Species 


1 2 3 4 5 6 7 8 9 1 0 

Diet 

Source 

Ophididae/cusk-PC?~ s and brotul as (continued) 

Gunterich- longipenis r 

--- go1 d brotu'ia 

Carapidaejpearl f ishes 

Carapus bermudensi s 

pearlfish 

Exocoetidaelflying fishes and ha1 fbeaks 

Iienira~ophys brasil iensi s 

ball yhoo 

--- Chridorus - atherinoides 

* 

hardhead ha1 fheak 

D 

a7 ti orharn hus unfasciatus 

Belonidaejneedlefi shes 

Strongyl ura rtotata 

redfin neediefish 

Strongyl ura ti~nucu 

timucu 

T~losuru$ cracodi lus 

houndfish 

Cyprinodontidaelkillifishes 

Flnrd ichthys cargs 

-- 

goldspotted killifish 

Adinia xenica 

P. - 

diamond killifish 

Lucania parva -- rainwater killifish 

a r r p r 

Seagrasses: Thalassia, Syringodium, 

fishes: Jenkinsia sp. 

Randall 1967 

r Juveniles zooplankton; crab t,?egalops larvae, Carr and Adams 1967 

vet igers, copepods, insect reolains.Sub-adul ts 

and adults epiphytic algae and detritus, 

seagrasses, occasional microcrustacea 

r 

r 

Zhrimp 

Fishes: Anchoa parva, Jenkinsia sp.; 

shrimp; copepods; insects 

+ 

Fishes: Acanthurus sp., Anchoa sp., 

Ceten raul is edentul us, Harengul a 

umera 1s Mugil sp.; shrimp 

Reid 1954 

Randall 1967; Reid 

1954; Srpinger and 

Woodburn 1960 

Randall 1967 

:~~lpflipods, copepods, poTychaetes, filamen- Brook 1975; Odum and 

tous algae, diatoms, detritus, ostracods; Weald 1972 

chironomid larvae, isopods, nematodes 

Detritus, diatoms, filamentous algae, Odum and Heald 1972 

amphipods, insects, copepods 

r r Anphi pods, musids, chironomid larvae, 

insects, moll uscs, detritus, copepods, 

Odum and Heald 1972 

cumaceans

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Species Abundance by survey number Diet Source 

1 2 3 4 5 C 7 C 9 1 C 

Lutjanidae/snappers (continued) 

Lutjanus jocu 

dog snapper 

Fishes: atherinids, Aulostomus maculatus, Randall 1967 

2 Lutjanus synagris 

+ lane snapper 

Ocyurus chrysurus 

yell owtail snapper 

p c r a c r Crabs:goneplacids,Leiolarnbrusnitidus, Randal I 1967; Reid 

portunids; stomatopods: Lysiosquilla gla- 1954; Springer and 

briuscula; fish; shrimp; mysids; copepods Woodburn 1960 

Crabs: Call appa ocell ata, Mi thax sp., Mi thax 

Mi thax sculptus, Pi tho aculeata; shrimp: 

caridean, penaeidean, Sicyonia laevigata, 

Trach caris restirctus: fish: Jenkinsia 

so.: :iphonophores: pteropods; Cal vol ina 

sp.; copepods; cephal opods: mysids; tunicates; 

ctenophores; gastropods: Strombus 

w, stomatopods : ~onodactyl u s m i i , 

Pseudosquilla cil iata; scyllarid larvae; 

heteropods; plecypods; eggs; euphausids; 

gastropod 1 arvae; amphi pods; insects 

Randall 1967 

Lobotes surinamensis 

tripletaiis 

Gerridae/mojarras 

Eucfnostomus argenteus 

spotfin rntrjarra 

r c c r p r r r 

r c Less than 63 rom copepods, amphipods, mysids, Ddum and Heald 1972; 

molluscs, detritus, chirononid 1 arvae. 75 to Randal 1 1967; Brook 

152 mm amphipods; H ale sp., polychaetes; 1975 

eunicids, crabs; cakds, majids, raninids, 

shrimp; alpheids, Call ianassa sp., tanairds, 

plecypods; Tell ina sp., sipuncul ids, 

copepods , gastropods

C 

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List of gishes and their diets from co3lections in south Florida. 

Species Abundance by survey nuiqber Diet Source 

1 2 3 4 5 5 ; 2 s : G 

-- tiaecnulon -- -- sciurus 

b1 uestri ped grunt 

r c r p r Crabs: ~ortunids, xanthids: ~elecv~ods: 

Randall 1967; Davis 

1967 

tunicates; ostracods; bryozoans; 

scaphopods; Cadulus sp.; tanaids; 

hemit crabs 

Haemul on aurol i neatum 

tomta te 

Shrimps: larvae; polychetes: Chloeia 

so.: eaas: hermit crabs; larvae: 

Randall 1967; Davis 

1967 

Haelmulon P I 

white grunt 

Caduf us acus; isopods 

Less than 40 m copepods, mysids or 

shrimp, detritus. 130-279 m crabs: 

Hithrax sg.: polychaetes: echinoids: 

Diadema antillarum, Eucidaris tributoides: 

spatanqoid, si~uncul ids: 

As idosi hon sp.: gastropods: Acmaea 

* arum Strornhus w, sh- 

alpheids, ophiuroids: Qphiothrix sp.; 

fishes; hemichordates; fiolothurians: 

Thyane seudofusus: pelecypods : 

Cumin if antillarum, chitons: 

mi-57 sc noc i ton papil losus, amphi pods, 

tanaids 

Carr and Adams 1973; 

Randall 1967; Reid 

1954; Davis 1967



1 2 3 4 5 6 7 8 9 1 0 

Archosargus probatocephal us 

sheepshead 

Archosargus rh~mboides 

sea bream 

Lagodon rhomboides 

pinfish 

Cal amus arcti f rons 

grass porgy 

-- 

Calamus calamus 

saucereye porgy 

r Less than 50 mm am~hioods, co~epods, Springer and 'lno*hur~ 

polychaetes; larger than 50 mm molluscs, 1960; Odun and i-leald 

barnacles, algae 1972 

Seagrass: Syrinaodium filiforme, 

Randal 1 1967; Austin 

Thalassia testudinum; algae: crabs; and Austin 1971 

gastropods: eggs; pelecypods: Pinctada 

ladiata; polychaetes; amphipods 

c c r c p a a a a a Less than 35 mm copepods; amphipods; mysids; Carr and Adams 1973; 

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 

r Copepods; amphi pods; musids; shrimps; Reid 1954 

pelecypods; gastropods: Witrella sp., 

Bittium sp.; polychaetes 

Polychaetes; ophiuroids: Ophioderna sp., Randall 1967 

Ophiothrix sp.; pelecypods: Codakia 

orbicularis, Gouldia cering, Pinna 

carnea; hermit crabs; crahs: majid, 

echinoids: Diadema antillarum, 

gastropods:Nassarius a us equla 

sp., Tegula fasciata; &iz 

sipuncul ids : Aspidosiphon sp. 

Menticirrhus focal iger 

rninkfish 

Sciaeno s ocellata 

---TZ-buv 

P 

r r SL 31-46 mm nysids; polychaetes; amphipods; 

shrimp: Palaemonetes intermedius. SL 59- 

126 mm fish: Picropogon undulatus; shrimp; 

crabs: insect larvae: nysids. SL 100- 

500 mm shrimp: penaeids; crahs: xanthids, 

Rithropanopeus harrisii, portunids 

Springer and bloodburn 

1960; Odun and Heald 

1972: 

Bairdiella chrysura r r c a a c c SL 25-99 mm shrimp; copepods; anphipods; 

silver perch mollusks; fishes, polychaetes. SL 100- 

130 mm shrimp, amphipods, crabs, mollusks, 

fish: Anchoa mitchilli 

Reid 1954; @dun and 

Heald 1972; Springer 

and Woodburn 1960

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Species 


1 2 3 4 5 6 7 2 9 1 C 

Diet 

Source 

Gobi idae/gobies 

Barbul ifer ceuthoecus 

bearded goby 

Microgobius m3crolepi s 

banner goby 

Fli crogobi us 9111 osus Per r- Detritus, copepods, epiphytic a1 gae, 

clown goby 

amphipods, polychaetes, bivalves, 

shrimp inysids 

F:icrogohius tl~alassinus 

Small crustaceans; amphipods, 

green goby 

other invertebrates 

D Bath obius curacao 

N 

w *gut goby 

Bath obius SO o r - 

Caridean shrimp; Pal aemonetes 

---#Tim go& 

intermedius, chironomids, amphipods 

Gobionel 1us bolesoma 

darter goby 

- Gobionel lus sriaragdus 

emeraldgoby 

Cobionellus shufel ti 

freshwater goby 

Gobionellus sti marturus 

r 

---qFtm 

-- Gobiosoma robustum 

a r r p c c r r r Pmphipods,chironomid1arvae,mysids, 

code g o r cladocerans, ostracods, small moltuscs, 

algal filaments, detritus, cumaceans 

Gobiosoma longipala 

twoscale goby 

Gobioso~~a macrodon 

tiger goby 

Sobiosoma longum 

Carr and Adams, 1973; 

Reid 1954; Springer and 

Woodburn 1960; Odum and 

Heald 1972 


1979 

Odum and Heald 1972 

Odum and Heald 1972; 

Reid 1954

C C +m" 

CX r .-- 

a * 'PI 

C7 C T 4 

b T r 

2 3 2



1 2 3 4 5 6 7 8 9 1 0 

Trig1 idae/searobins (continued ) 

Prionotus gtulus 

leopard seamn 

Prionotus tribulus 

r r r r r r r %all molluscs: 5olemya sp., sp., 

Olivia sp.; shrimo; crabs; fishes 

Peterson an3 Peterson 

1979 

r r c r r Shrimp; crabs; Limulus olyphemus, Peterson and Peterson 

- Uca so.; fishes; anphip!ds; copepods; 

1979 

annel ids; hival ves; echinoids 

Bothidaellefteye flounder 

--- r r 

Bothus ocell atus r Fishes; Coryphopterus sp. ; crabs; Calappa Panda11 1967 

eyed flounder 

ocellata; majid; shrimps; amphipods; 

isaeid; stomatopods: Pseudosquilla ciliata 

E 

W 

Anc lo setta uadrocellata 

+ke'c~ fi: ounder 

Ci tharichthys macrops 

spotted wiff 

Ci tharichthys spilopterus 

bay wi f f 

r r Mysids; shrimp; crabs; copepods; 

amphipods; fishes; annel ids 


1979; Austin and 

Austin 1971 

r r r r Less than 45 mm SL: amphipods, small 

crustaceans. Greater than 45 mm: 

fishes: Orthopristis chrysopterus, 

Lagodon rhomboides, Synodus foetens, 

Anchoa mitchilli, crustaceans 

Reid 1954; Springer 

and bloodburn 1960 

Syacium papillosus 

dusky flownder 

Etropus crossotus r Polychaetes; copepods; shrimps; aqphipods Reid 1954 

fri ngedf1KiKfer 

Trinectes inscriptus r r 

scrawled sole 

Trinectes maculatus 

hogchoker 

Plnphipods; mysids; chironomid larvae; Odum and Heald 1972; 

polychaetes; Neris pel agica; foraminifera Carr and Adams 1973 

Achirus lineatus r r r p c c r r Polychaetes; amphipods; copepods Springer and I~~oodhurn 

1 i n e d r 1960; Reid 1954

-. "-1 

--- --- -- - ---- -- - - - .A - - i 

Tale and Subtttlc 

\ 3. Rac~pient's Aceerston No 

- - ------------. 

5. Repon Oete 

THE ECOLOGY OF THE SEAGRASSES OF SOUTH FLORIDA: / September 1982 

A COMMUNITY PROfILE - - -- ---. 

. 

7. Author(6) 

1 -----.-IIXI.-....l. "" -.-_^ _--" 

- J. C. lieman 

,- 

$. Performing Orgjniaetion N 

. '. -.-" 

sklWork Unit No. 

Department of f nv i ronmrttal Sciences 

University of Virginia 

Char.lottesville, Virginia 22901 

I 

.--- -" ". 

ldlife Service 

ment of the Interior 

Bureau of Land Management 

U.S. Department of the Inter 

$6. Abstract (Clmit: 200 worda) 

-"--"---- . ..".-.-..-- X 

"^ " I_. "X.I- -.,.--m--,.- 

--. -._ - 

A detailed description is given of the community structure and ecosystem processes 

of the seagrass ecosystems of south Florida. This descri~tion is based upon a compilatian 

of information from numerous pub1 ished and unpubl ished sources. 

The material covered includes dr'stri bution, systematics, physi 01 ogy , and growth 

of the plants, as well as succcssion and comiunity development. The role OF seagrass 

ecosystems in providing both food and shelter for juveniles as well as foraging grounds 

for ldrger organisms is treated in detail, Emphasis is given to the functional role of 

seaqrass cornunities in the overall coastal marine system. 

The final section considers the impacts of human development on seagrass ecosystems 

and their value to both man and the natural system. Because seagrass systems 

are fully submerged and less visually obvious, 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. 

--- *"* -- - - 

Ecology, impacts, management, succession 

f 

t, Idanlifiemlllpen Ended Termn 

I 

Seagrasses, ecosystem, south Florida 

I 

a - " - - .- - - --- - - -- 

hinl imi ted I iJnclassifig4 . - i ~iii + 15Q_-.- 

20. Securtty Ctasr (Thts Pdgei 22. Pncs 

1 

1 

" 

/ 

c COSATI Sicld/On)up 

"----.---- -. - *-- --- - - -- 

I& Availabtrt?y Strtemcnt 19. Secvrlly Cfars (Thlr Renort) 21. No of Pages 

(See &N$&-239.181 See Ins:ruct,ons on Ravarre OPTIONAL FORM 272 (4-77) 

(formerly NTIS-35) 

Department of Commerce 

*U S GOVERNMENT PRINTING OFFlCE 1983 769-265i129

The Ecology of the Seagrasses of South Florida - USGS National ...

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