vertical walls and pilings generally 

 extend below the low mean tide and 

 face open ocean or open fetch areas 

 which are exposed to high energy 

 waves and/or strong currents. The 

 structures usually occur in associa- 

 tion with other shoreline modifica- 

 tions, such as riprap. The areas 

 behind the sewalls are packed with 

 sand, fill, or concrete. 



Attached macroalgae dominate 

 the habitat's flora. Generally 



there are a few abundant species 

 located within the wetter, lower 

 areas along the vertical rock face. 

 These commonly include the red algae 

 Bostrychia tennela and Laurencia 

 papillosa , and the green algae 

 Valonia acellata (Stephenson and 

 Stephenson 1950, Getter et al. 

 1981). 



In contrast, epifauna occur in 

 moderate densities with high species 

 richness and diversity (Getter et 

 al. 1981). Several species of 



nerite snails ( Nerita tessellata , 

 N. versicolor , and N. peloronta ) 

 represent the most common organisms 

 observed. Infauna and under rock 

 fauna are absent due to the lack of 

 suitable substrate. Other typical 

 organisms within this habitat in- 

 clude o.k. gastropods Nodilittorina 

 tuberculata , Littorina ziczac , and 

 Spiroqlyphus annulatus , the limpet 

 Siphonaria alternata , and the bar- 

 nacle Chthamalus stellatus (Stephen- 

 son and Stephenson 1950). 



Exposed Rocky Platforms 



The exposed rocky platform 

 habitat is the most comprehensively 

 studied intertidal/shoreline commu- 

 nity of the Florida Keys. For 

 purposes of this study the habitat 

 zonation outlined by Stephenson and 

 Stephenson (1950) is adopted. Three 

 zonations are delineated; the first 

 of which is the upper platform which 

 varies greatly in width, angle of 



slope, and pattern of its' seaward 

 termination. This zone extends from 

 the edge of the true dryland vegeta- 

 tion to the seaward edge of the 

 limerock platform. The second zone 

 is the lower platform which is occa- 

 sionally absent, and when present is 

 greatly variable in its development. 

 This zone commonly occurs as discon- 

 tinuous patches of low rock running 

 seaward from the foot of the upper 

 platform to a level only slightly 

 above the low water level of the 

 spring tides. The third zone is the 

 reef flat which is a low lying area 

 in which rocky patches alternate 

 with sand, mud, and gravel. This 

 last zonation is commonly inundated 

 at low water, while its higher parts 

 may emerge as banks at the lowest 

 tides. Because of the broad width 

 and varied environment within the 

 upper platform, Stephenson and 

 Stephenson (1950) divide it into 

 four zones named for the changing 

 coloration of the platform rock. 

 From the dryland vegetation seaward 

 these color zones are white, gray, 

 black, and yellow. The first three 

 represent subdivisions of the supra- 

 littoral fringe; the yellow zone 

 belongs to the midlittoral zone. 

 The dry land vegetation inland of 

 the rocky platform generally con- 

 sists of mangrove or strand communi- 

 ties, some of which may spill over 

 into the platform habitat. 



The white zone is more nearly 

 dry land than intertidal zone, as 

 the highest flotsom line either lies 

 within it or along its seaward mar- 

 gin. The zone's relief varies from a 

 rock surface to a gravel beach. The 

 fauna usually exists under rocks and 

 boulders, and includes terrestrial 

 forms such as ants, earwigs, scor- 

 pions, and spiders. No fully marine 

 animals inhabit the white zone, but 

 several maritime species occur, 

 including the purple-clawed hermit 

 crab Cocnobita clypeatus , the isopod 



182 



