species being represented within a snail 

 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 

 list various organisms that are represent- 

 ative of seagrass meadows over large dis- 

 tances. 



The most obvious invertebrates of 

 many of the seagrass beds of south Florida 

 are the large epibenthic organisms (Figure 

 16). The queen conch ( Strombus qigas ) 

 feeds primarily on epiphytes it scrapes 

 from turtle grass blades, while the Baham- 

 ian starfish ( Oreaster reticulata ) and the 

 gastropods Fasciolaria tul ipa and PI euro- 

 pi oca gigantea prey largely on infauna. 

 Numerous sea urchins, such as Lytechinus 

 variegatus and Tripneustes ventricosus , 

 are found throughout the beds. Juveniles 

 of the long-spined urchin Diadema antil - 

 larum are common, but the adults seek the 

 shelter of rocky ledges or coral reefs. 

 The deposit-feeding holothurians Actino- 

 pyga agassizi and Holothuria floridana may 

 be found on the surface, while the large 

 sea-hare, the nudibranch Aplysia dactyl o- 

 mela , may be found gracefully gliding over 

 the grass canopy. At night pink shrimp 

 ( Penaeus duorarurn) and spiny lobster 

 ( Panulirus argus~ y~may be seen foraging in 

 the seagrass along with the predatory 

 Octopus briareus . 



On shallow turtle grass flats the 

 corals Manicinia areolata and Porites 

 furca ta are' common, while in somewhat 

 deeper waters sponges such as Ircinea , 

 Tethya , and Spongia may be found. 



The infauna can 

 not visually obvious. 

 ( Atrina rigida ) is a 

 in many grass beds, 



be diverse, but are 



The rigid pen shell 



common filter-feeder 



along with numerous 



bivalve molluscs such as Chione cancel - 

 lata , Codakia orbicularis , Tel 1 ina radi- 

 ata , Luc ina pennsyl vanica , and Laevicar- 

 dium laev ig atum . A variety of annelid 

 worms are in the infauna, notably Areni- 

 cola cri s_ta ta , Onuphis magna , Terehel 1 ides 

 stroe mi , and Eunic e longicerrata . 



The abundance and diversity of epi- 

 phytic ani:rials on seagrass blades are dra- 

 matic evidence of the effect the seagrass 

 has on increasing bottom surface aros and 



providing a substrate for attachment (Fig- 

 ure 17). The most prominent of these epi- 

 faunal organisms in south Florida are the 

 gastropods. Cerithium nascarum and £. 

 eburnum , Anachis sp., Astrea spp.. Modulu s 

 modulus , Mitrella lunata, and Bittium 

 varium 



Mitrel la lunata , 

 characteristic in 



are characteristic 1n turtle grass 



and shoal grass habitats throughout south 

 Florida, as is the attached bivalve 

 Cardita floridana . 



Small crustaceans are also common in 

 seagrass beds where they live in tubes at- 

 tached 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 an- 

 phipods are Cymadusa compta , Gammarus muc- 

 ronatus , Mel ita nitida , and Grandidierella 

 bonnieroides , while the caridean shrimps 

 Palaemonetes pugio , P_. vulgasis , and P^. 

 intermedius , Perici imenes longicaudatus , 

 and £. americanus , Thorfloridanus , Tozeuma 

 carol inense , Hippolyte pleuracantha , 

 Alpheus normanni , and A^. heterochaelis are 

 abundant within the grass beds. Hermit 

 crabs of the genus Pagurus 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 microhabi- 

 tats provides living space for a rich epi- 

 fauna of both mobile and sessile organisms 

 (Harlin 1980). It is these organisms which 

 are of greatest importance to higher con- 

 sumers within the grass bed, especially 

 the fishes. When relatively small quanti- 

 tative samples are used in estimating pop- 

 ulation sizes, gastropods, amphipods, and 

 polychaetes are typically most numerous, 

 while isopods can be important (Nanle 

 1968; Carter et al . 1973; Marsh 1973; K.i- 

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

 Card Sound turtle grass bed. Brook (1975, 

 1977) estimated that amphipods represented 

 62. 2? of all crustaceans. When the trawl 

 is employed as a sampling device, deca- 

 pods, including penaeid and caridean 

 shrimp and true crabs, as well as gas- 

 tropods, are generally most abundant 

 in invertebrate collections (Thorhaug 

 and Roessler l'^77; Yokel 1975a, 1^75b; 



46 



