sands; and, (2) the beaches are 

 much narrower, usually less than 

 10 m (33 ft) wide between dune and 

 low water. Wave activity is low to 

 moderate except for high energy 

 storm waves. All three levels of 

 wave energy promote the heavy accu- 

 mulation of sea wrack along the high 

 tide line. 



The faunal and floral species 

 composition is much like the fine- 

 grained sand beach habitat. Upland 

 vegetation is still of a beach- 

 strand community with a noticable 

 increase in strand and saltmarsh 

 grasses, e.g., keygrass Monantho- 

 chloe littoralis and the saltmeadow 

 cordgrass Spartina patens . Near- 

 shore marine plants include the 

 seagrasses Halodule wrightii and 

 Syrinqodium filiforme . Both infauna 

 and epifauna communities exhibit a 

 species composition shift to that 

 displayed in the rock platform 

 habitat. The mole crab Emerita 



talpoida , the gastropod Batillaria 

 minima and the polychaete Nereis 

 succinea are frequently common and 

 are usually joined by several upper 

 platform species including: the 



gastropod Littorina ziczac , the iso- 

 pod Liqia baudiniana , the barnacle 

 Balanus sp., and the polychaete 

 Lumbrineris maculata . Also, the 

 infaunal clam, Anomalocardia cunei- 

 veis , is periodically found (Zischke 

 1973, Getter et al. 1981). 



Mixed Sand and Gravel Beaches 

 and Fill 



Natural occurrences of this 

 habitat are restricted to areas of 

 high wave energy which create beach- 

 es of coarse shell and coral frag- 

 ments, e.g., seaward side of Bush 

 Key, Dry Tortugas. Man-constructed 

 versions are sand and gravel fill 

 areas composed of very poorly sorted 

 mixtures ranging from mud to cobble- 

 sized sediments. This mixture can 



sometimes be very hard packed with a 

 more mobile surface layer. The wave 

 activity ranges from high to low and 

 is often unrelated to sediment grain 

 size. Typical beach slopes are 



artifically steep with the toe of 

 the beach face generally composed of 

 coarser, better sorted sediments. 



Wrack accumulations are often 

 quite significant following the 

 trend observed in other beach and 

 rocky platform habitats. Attached 

 macroalgae are more prevalent than 

 other sand beaches, corresponding to 

 the increased rock composition. The 

 most commonly found is the red algae 

 Bostrychia tenella ; others include 

 the green algae Dasycladus sp., 

 Enteromorpha liqulata and Valonia 

 ocellata ; and the red algae Lauren - 

 cia papillosa . The upland rooted 

 vegetation is that commonly associ- 

 ated with beach-strand, mangrove, 

 and salt marsh habitats previously 

 described. The variety of vegeta- 

 tion is a reflection of the (ecolo- 

 gically) random placement of these 

 man-made shoreline modifications 

 with respect to naturally occurring 

 shoreline habitats. For example, 

 along the inter- and infratidal 

 zones mangrove colonization ( Rhizo- 

 phora mangle an d Avicennia qermi- 

 nans ) is observed in areas of Flem- 

 ing Key (Key West), Boca Chica Key, 

 and Ramrod Key. Similarly, the 

 fauna of this habitat contains 

 members of various naturally occur- 

 ring communities. Usually a mixture 

 of beach and rock platform communi- 

 ties dominates. Both epifauna and 

 infauna exhibit moderate densities, 

 biomass, and species diversity. The 

 epifauna is dominated by nerite 

 snails Nerita sp., barnacles Balanus 

 sp. and Chthamalus stellatus , and 



oysters Crassostrea virqinica . 



Several species of polycheate worms 

 are the most prevalent infaunal 

 organisms, including Nereis succinea 



186 



