and Heteromastus filiformis . Pre- 

 sence of the ghost crab Ocypode 

 quadrata , the sea cucumber Holo - 

 theria floridana , and a gastropod 

 usually associated with the reef 

 flat Alcyonaria-Sponge zone ( Bulla 

 occidentalis ) , illustrates the mix- 

 ture of habitat communities (Zischke 

 1973, Multer 1977, Getter et al. 

 1981). 



Gravel Beaches and Riprap 



All forms of this habitat 

 represent man-made modifications to 

 the natural key shorelines. The 

 primary structural units are gravel 

 to bouldersized riprap revetments 

 usually composed of local limestone. 

 Like the previous habitat, the wave 

 energy varies from one area to the 

 next, related more to the subtidal 

 sediment formations which are com- 

 monly finer grained, better sorted, 

 and naturally occurring. Shorelines 

 bordering the causeways are often 

 of this shoreline type, found in 

 association with fill areas and sea- 

 walls. 



The steep slopes generally 

 bring the three basic forms of Flor- 

 ida Key plant communities (terres- 

 trial, shoreline, marine) into a 

 spatially narrow area. The terres- 

 trial and shoreline communities are 

 similar to those described for the 

 mixed gravel and fill beaches. 

 Beach strand, mangrove, and salt- 

 marsh vegetation represent the 

 rooted flora; species of the green 

 algae (Chlorophyceae) , red algae 

 (Rhodophycea) , and brown algae 

 (Phacophycea) represent the attached 

 intertidal vegetation. The infrati- 

 dal areas commonly exhibit dense 

 growths of the seagrasses Halodule 

 wriqhtii and Thalassia testudium . 

 The most common shoreline rooted 

 vegetation is the red mangrove 

 Rhizophora mangle and sea purslane 

 Sesuvium maritima ; the red algae 

 Bostrychia sp. represents the at- 



tached flora. High density, species 

 richness, and diversity of infauna 

 and epifauna reflects the varied 

 habitat conditions. Getter et al. 

 (1981) observed 23 epifaunal species 

 and 12 infaunal species in this 

 shoreline habitat. The dominant 



epifaunal species are amphipods, the 

 snail Batillaria minima , the bar- 

 nacles Balanus sp., and the nerite 

 snails Nerite sp. The polycheate 

 worms Arenicola cristata . Nereis 

 succinca , and Lumbrineris sp. are 

 the predominant infaunal forms. 



Exposed Tidal Flats 



Because of the small tidal 

 range in the Florida Keys, the ex- 

 posed tidal flats is one of the 

 least common habitat zonations ob- 

 served. They are generally located 

 in open bays (Vaca Key Bight), in 

 the lee of offshore islands (Boot 

 Key), or near tidal inlets (Teatable 

 Channel in Upper Matecumbe Key. 

 Varying in width (up to 50 m or 164 

 ft) they are subject to moderate to 

 high energy wave activity and tidal 

 currents. Sediment composition is 

 dominated by carbonate sands and 

 some muds generally accompanied by 

 migrating carbonate sand bars on the 

 seaward limit of the flats. 



Vegetation is present in two 

 community types: ( 1 ) mangrove fringe 

 forests dominated by the red man- 

 grove Rhizophora mangle and the 

 black mangrove Avicennia qerminans ; 

 and (2) the seagrass beds, represen- 

 ted almost exclusively by the shoal 

 grass Halodule wriqhtii . 



The epifaunal community exhi- 

 bits high density, moderate species 

 richness, and low species diversity. 

 Of the five species Getter et al. 

 (1981) observed, land crabs Cardio - 

 soma guanhumi , fiddler crabs Uca 

 sp., and the batillaria snails 

 Batillaria minima are the dominant 

 forms. The infauna shows greater 



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