retained in the bed to contribute to fur- 

 ther development of the little layer 

 (Zieman 1981), 



It is possible that in certain re- 

 gions, exported seagrass could be an 

 important 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 0.07?, respectively (Wolff 

 1980). Turtle grass blade and rhizome 

 samples had a carbon content of 20% and a 

 nitrogen content of 0.77%. 



Many species of fishes and inverte- 

 brates use south Florida grass beds as 

 nurseries. Approximately one-third of 

 the species collected at Matecumbe Key, 

 including all grunts, snappers, file- 

 fishes, and parrotfishes, occurred only as 

 young, indicating that the grass-dominated 

 shore area was a nursery ground (Springer 

 and r^cErlean 1962b). In" Tampa Bay, 23 

 species of finfish, crab, and shrimp of 

 major importance in Gulf of Mexico fisher- 

 ies were found as immature forms (Sykes 

 and Finucane 1966). Comparatively little 

 is known concerning invertebrates other 

 than those of commercial value. 



7.5 NURSERY GROUNDS 



Grass beds serve as nursery grounds 

 where post larval stages of fishes and 

 invertebrates concentrate and develop and 

 also as spawning grounds for adult breed- 

 ing populations of some species. To be of 

 significance as a nursery, a habitat must 

 provide protection from predators, a sub- 

 strate for attachment of sessile stages, 

 or a plentiful food source (Thayer et al . 

 1978b). Seagrass habitats fulfill all of 

 these criteria with their high productiv- 

 ity, surface areas, and blade densities, 

 as well as a rich and varied fauna and 

 flora. Seagrass provides abundant nursery 

 habitat and is often preferred, based on 

 abundance and size data, over available 

 alternatives, in the estuaries and coastal 

 lagoons, by many commercially or ecologi- 

 cally important species (Yokel 1975a). 



The importance of grass bed habitat 

 as a nursery has been historically demon- 

 strated and should not be minimized. Fol- 

 lowing the decline of Zostera marina along 

 the east coast of the United States in the 

 early 1930's, the sea brant, a variety of 

 goose dependent on eel grass for food (as 

 are many waterfowl; McRoy and Helffrich 

 1980), v/as reduced in numbers to one-fifth 

 its former levels (Moffitt and Cottam 

 1941). Pronounced decreases in abundance 

 of bay scallops ( Argopecton irradians ) 

 were also noted following the disappear- 

 ance of oelorass (Stauffer 1937; Dreyer 

 and Castle 1941; Marshall 1947). The 

 post-veligor larval stage of the scallop 

 depends on eelgrass to provide cir\ above- 

 sediment surface for attachment. Disrup- 

 tion of eelgrass beds resulted in lowered 

 numbers of bay scallops (Thayer and Stuart 

 1974). 



Shrimp 



Pink shrimp ( Penaeus duorarum ) occupy 

 south Florida grass beds as juveniles 

 (Tabb etal. 1962; Costello and Allen 

 1966). Penaeus aztecus and P_. brasil ien- 

 sis are also present, but never as abun- 

 dantly as the pink shrimp (Tabb and Man- 

 ning 1^61; Saloman et al . 1968; Bader and 

 Roessler 1971). Shrimp spawn on the Tor- 

 tugas grounds, probably throughout the 

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

 1968). Roessler and Rehrer (1971) found 

 postlarval pink shrimp entering the estu- 

 aries of Everglades National Park in all 

 months of the year. 



Pink shrimp were distributed through- 

 out Rookery Bay Sanctuary in southwestern 

 Florida, but were most abundant at sta- 

 tions with grass-covered bottoms (shoal 

 grass and turtle grass), and within these 

 stations were most abundant where benthic 

 vegetation was dense (Yokel 1975a). Pink 

 shrimp were also abundant in grass habitat 

 at Marco Island and Fakahatchee Bay, also 

 in southwestern Florida (Yokel 1975b). 

 Postlarval pink shrimp with carapace 

 length less than 3 mm were taken only at 

 stations where shoal grass and turtle 

 grass were present in Rookery Bay Sanc- 

 tuary, while other stations without grass 

 alv/ays had larger mean sizes. These ob- 

 servations are in accordance with Hilde- 

 brand (1955) and Williams (1965), who 

 noted that ^ery small pink shrimp prefer 

 grassy areas and with increasing size are 

 found in deeper water. In terms of the 

 functioning of the grass bed as a nursery 

 ground, it is interesting to speculate 

 whether this distributional pattern repre- 

 sents a preference on the part of pink 

 shrimp postlarvae for grass bed habitat 



80 



