Species commonly associated with 

 this carpet include Cladophoropsis 

 membranacra , Cent rocerasclavulat urn , 

 Ceramium byssoideum , Herposiphonia 

 secunda, Jania capillacea , Polysiph - 

 onia sp., and Spyridia filamentosa . 

 The green algae Valonia ocellata and 

 the vermetid gastropod Spiroqlyphus 

 annulatus are as characteristic of 

 the lower platform as they are of 

 the yellow zone. Another common 

 feature of the lower platform is the 

 cushion-like masses, often extensive 

 and also quite often choked by sedi- 

 ment, of the calcareous green algae 

 Halimeda opuntia which represents a 

 landward extension of the reef-flat 

 assemblage. In some locations there 

 are patches or large areas of a 

 zoanthid coral, Zoanthus sociatus , 

 with small polyps which often expand 

 in daylight. Numerous organisms 

 'spillover' from the reef flat onto 

 the lower platform, but only a few 

 are so common as to be considered 

 characteristic of the lower platform 

 assemblage. These are usually 



observed in rock cavities and under 

 movable stones, and commonly include 

 the short-spined urchin Echinometra 

 lucunter , two species of bearded 

 mussels ( Area barbata and A. umbo - 

 nata ), and the anemones Phymanthus 

 crucifer , Bartholomea annulata , and 

 Condylactis qiqantia (Stephenson and 

 Stephenson 1950). 



The most seaward habitat zona- 

 tion described by Stephenson and 

 Stephenson (1950) is the reef flat. 

 Consistent with the more inland 

 zones, the reef flat's physical 

 configuration is quite variable. In 

 some places it lies under very 

 shallow water so that one can wade 

 out over it for a quarter of a mile 

 or more. Under similar conditions, 

 but elsewhere in the Florida Keys, 

 the reef flat slopes down so rapidly 

 that wading is restricted to within 

 a few meters of the lower platform. 

 The unifying quality is the contin- 

 uous submergence of the community by 

 marine water except for few areas 



that emerge during the lowest tides. 

 The zone therefore is considered in- 

 fralittoral and for purposes of this 

 report will be included within the 

 marine habitat zonations discussed 

 later. 



Fine Grained Sand Beaches 



In the Florida Keys the fine- 

 grained calcareous sand beaches are 

 limited in size and frequency, with 

 most occurring in the middle Keys 

 and distal islands. Typically these 

 beaches form on the island side 

 facing the Florida Straits where 

 moderate to high wave activity 

 exists. Offshore areas are general- 

 ly shallow with subtidal grass flats 

 overlying limestone bedrock. Flora 

 in this habitat is primarily the 

 pioneer beach strand community pre- 

 viously described. The more common 

 halophytic plants include the sea 

 oat Uniola paniculata and the beach 

 morning-glory Ipomoea pes-capre . 

 Farther inland the black mangrove 

 Avicennia qerminans and buttonwood 

 Conocarpus erecta transitional 



communities are often observed. 

 As with the rocky platform zona- 

 tion a heavy wrack accumulation 

 commonly forms along the high tide 

 line. 



The epifauna is characterized 

 by low specific density and diver- 

 sity, usually represented by the 

 gastropod Batillaria minima . Numer- 

 ous amphipods and insects flourish 

 within the sea wrack. The infauna, 

 like the epifauna, exhibits a depau- 

 perate species population and diver- 

 sity most commonly represented by 

 the mole crab Emerita talpoida , the 

 ghost crab Ocypode quadrata , several 

 polycheates such as Nereis succinea , 

 and a oligocheate ( Tubificidae sp.) 

 (Getter et al. 1981). 



Coarse-grained Sand Beaches 



These beaches are physically 

 quite similar to the fine-grain 

 beaches except: (1) the sands are 

 composed of coarse-grained carbonate 



185 



