TurbindrJa ) and calcareous algae (Porol ithon , Jania , Caulerpa ) occupy a 

 significant position on the reefs. 



The R zone, as a rule, is inhabited by a varied benthic fauna. 

 According to averaged data (Glynn, 1973) on the reefs in the Caribbean 

 Sea in this zone the wet, lime-free biomass of animal matter of the 



benthos is about 4 kg/m (Table 3). If we include the skeletal mass 

 the biomass reaches 120 kg/m (Colikov et al . , 1972). This is near the 

 maximum possible biomass of the benthos in eutrophic biotopes. 



Table 3. Mean biomass of benthic fauna and flora on reefs of the 

 Caribbean basin in the R zone with predominance of the coral Porites 

 (Glynn, 1973). 



Dry matter, including Wet biomass of 

 Group of organisms skeletons living matter 



Madreporaria 12,022 2,855 



Echinodermata 263 526 



Foraminifera 136 18 



Mollusca 59 100 



Crustacea 40 149 



Sponges 12 58 



Polychaeta 7 32 



Fish 6 36 



Zoantharid and colonial sea anemones 1 4 



Zoobenthos, total 12,546 3,780 



including filter feeders - 3,000 



Massive macroalgae 1,022 325 



The fauna, in addition to coral, includes hydroids ( Pennaria ) . The 

 gastropods are numerous here, inhabiting the loose sediment between 

 reefs. These include primarily the same genera as are found in the 

 sandy lagoons, plus some others (Terebra , Cerithium , Rhinoclavis , 

 Pterygia ) . Among the large gastropods which inhabit the clastic 

 material and feed on the periphyton, Lambis , Strombus and Cassis 

 predominate. On hard surfaces and in clefts in the reef we find 

 Fissurella , Astraea , flirex . Turbo , Cypraea , Trochus , Lunella , Bursa , 

 Ctena , Chione , Diplodonta , Anodontia ), sponges ( TeThya ) , A"?c i d i a , crabs, 

 pencil sea urchins (Cidaridae), Ophiuroidea, starfishes (Culcita ) , 

 Holothuria ( Holothuria . Stichopus ), Polychaeta (Serpulidae, 

 Dendrostoma ). As to biomass and variety, the benthic population of this 

 zone is among the richest biotopes on the reef. 



The Fl (reef flat) zone is the rocky plateau of the reef, depth 

 0.5-1 m. The shallow reef flat may extend for up to 100 m or more. It 

 is subjected to strong surf action. Individual shoal sections of the 

 reef flat and the limestone rocks located on their surface (so-called 

 "niggerheads" ) extend above the water surface at low tide. The flat is 

 cut through by channels and cracks, through which the loose bottom 



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