reefs and elongated parallel to the 

 reef tract's outer reefs. They 



possess a well-developed reef flat 

 and rudiments of spur and groove 

 formations of Acropora palmata on 

 the seaward slope (Jaap 1982). 

 Colonies of Acropora palmata also 

 occur on the reef flat, usually in 

 association with the fire coral 

 Millepora complanata , the alcyona- 

 rian sea fan Gorgonia ventalina , the 

 encrusting brain coral Diploria 

 clivosa , and the staghorn coral 

 Acropora cervicornis . In addition 

 to the numerous coelenterates, the 

 organisms commonly found in both 

 types of patch reefs include the 

 algae Goniolithon sp. and Halimeda 

 opuntia , occasionally the seagrass 

 Thalassia testudinum , numerous erect 

 sponges, e.g. Ircinia sp., the 

 bivalves Area sp., Lithophaga sp., 

 and Barbatia sp., the gastropods 

 Strombus gigas and Corallophila 

 abbreviata , the arthropods spiney 

 lobster Panulirus argus and stone 

 crab Menippe mercenaria , the echi- 

 noids Diadema antillarum and Echino- 

 metra lucunter , and numerous fora- 

 minfera, fishes, ostracods, and 

 bryozoans (Enos 1977, Multer 1977, 

 Jaap 1982). 



Outer Reef 



Outer reefs or reef banks are 

 located very near or at the shallow 

 shelf break along the seaward edge 

 of the shelf margin. Typically 



elongated, these reefs form a nar- 

 row, linear, discontinuous belt 

 which is best developed seaward of 

 Key Largo and the lower Keys (Sugar- 

 loaf to the Marquesas Keys). The 

 outstanding features of these outer 

 reefs are: (1) the occurrence of 

 the moosehorn coral Acropora palm - 

 ata ; (2) the vertical coral zonation 

 off the terraced reef front; and (3) 

 the distinctive seaward spur and 

 groove formation (Multer 1977). 

 Table 40 shows two zonation schemes 

 developed from studies of the lower 



Table 40. Bank reef zonation. 



reef tract (Kissling 1977) 

 primarily, the upper reef 

 (Jaap 1982). 



and, 

 tract 



Flora and fauna characertistics 

 of these sub-zonations on the outer 

 reef are difficult to pinpoint 

 because of the apparent assemblage 

 variation from one area to the next. 

 It is not unusual to find an organ- 

 ism identified as the most signifi- 

 cant member of a class (e.g., based 

 on size and abundance) reported from 

 one reef system to be absent or 

 negligible on another (Enos 1977, 

 Kissling 1977, Jaap 1982). As a 

 result, those mentioned below are 

 simply the most commonly observed 

 (probable) organisms. 



On the shallow reef flat the 

 organisms include the stony corals, 

 such as porous coral Porites astre- 

 oides , lettuce coral Agaricia 



agericites , clubbed finger coral 

 Porites porites , and brain coral 

 Diploria clivosa ; the alcyonarians 

 Plexaura flexuosa , Pteroqorqia 



citrina , and Eunicea mammosa ; the 

 hydrozoan Millepora complanata 

 (stinging coral); the green algae 

 Halimeda opuntia ; and encrusting and 

 branches coralline algae. 



The reef butress commonly in- 

 cludes one or two sets of spur and 

 groove terraces providing a variety 

 of micro-environments within which 

 are usually found the scleractinians 

 Agancia agericites , Porites astre- 

 oides , P. porites , and Siderastrea 



195 



