the shallow hardground environment, 

 adjacent and seaward to most of the 

 Florida Keys, the currents are more 

 moderate. Both habitats experience 

 relatively large temperature and 

 salinity variations, although for 

 two different reasons. As metioned 

 earlier, the tidal channel environ- 

 ment is exposed to the temperature 

 and salinity regemes of both the 

 Gulf/Bay and the Atlantic water 

 bodies corresponding to the daily 

 tides. Adjacent to the Florida 



Keys, the salinity and temperature 

 variations are again large but this 

 time they are related to the shal- 

 low, restricted circulation. The 

 former is controlled by "imported" 

 variations; the latter by "endemic" 

 variations. 



The origin of the rock surface 

 exposures is not always clear. The 

 nearshore subtidal hardgrounds bor- 

 dering the emergent Florida Keys may 

 represent: (1) former subaerially 

 exposed and lithified sediment or 

 limestone bedrock highs; (2) subma- 

 rine cementation and/or the product 

 of encrusting organisms, e.g., cor- 

 alline algae; or (3) former coral 

 rubble surfaces, welded together 

 (Multer 1977). 



The flora and fauna here are 

 generally similar to the current- 

 swept hardground community. Various 

 organisms inhabiting the surface 

 or the sediment-filled fractures 

 include alcyonarians, sponges, 



encrusting foraminifera, boring mol- 

 lusks and worms, crustose coralline 

 algae, and sea urchins. The more 

 common alcyonarians observed include 

 the plume-like Antillogorqia acre- 

 rosa and Plexaura vermiculata . The 

 sea fan Gorgonia flabellum may occur 

 but not too frequently. The number 

 of stony coral (scleratinian) spe- 

 cies increases with the addition of 

 Solenastria hyades , Siderastrea 

 radians, Porites divaricata, and 



Oculina diffusa . The bivalve Pteria 

 colymbus , two gastropods of the 

 genus Cyphoma , and the basket star- 

 fish Astrophyton muricatum are usu- 

 ally found on Antillogorqia colo- 

 nies. The flora speciation is 

 reduced, and composed primarily of 

 the green algae Halimeda opuntia and 

 Cladophora sp.; a blue-green algal 

 scum over some surfaces; and the red 

 algae Jania sp. and Gonolithon sp. 

 (Voss and Voss 1955, Enos 1977). 



The second belt of rocky or 

 dead-reef bottoms lies near the 

 shelf break as elongated areas of 

 dead and partly eroded coral reefs 

 which form a relatively hard sub- 

 strate. These dead reefs range in 

 depth from near sea level to at 

 least 30 m (33 yd). Located seaward 

 of the outer reef, this habitat 

 experiences open marine circulation, 

 minimal salinity and temperature 

 variation, and low turbidity. The 

 floral and faunal assemblages are 

 generally similar to the nearshore 

 hardground habitat, dominated by 

 alcyonarians (octocorals) , sponges, 

 algae, and smaller hardy stony coral 

 (scleractinians) species (Enos 1977, 

 Jaap 1982). Brown algae include: 

 Sargassum polyceratum , Turbinaria 

 turbinata , Padina sp., and Stypopo - 

 dium zonale . These represent the 

 most dramatic addition to the floral 

 community. Relatively few sponges 

 are present, mainly the large 

 loggerhead sponge Spheciosponqia 

 vesparia , and Clione lampa . The 

 hydrozoan fire coral Millipora 

 alcicornis flourishes in these sea- 

 ward communities. The alcyonarians 

 are dominated by the sea fan Gorgo- 

 nia flabellum , two species of the 

 genus Muricea , and other octocorals 

 common to the nearshore habitat. 

 The more commopn scleractinians 

 (stony corals) include Diploria 

 clivosa , Porites (Holothurians) , 

 starfish, and several gastropods are 

 typically absent in the seaward 



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