Holothurioided. An individual about 30 cm long passes 100-200 g of sand 

 through its gut each day (Backus, 1973). In addition to the 

 Holothurioided and Gastropoda, the benthic sediment is also intensively 

 consumed by many species of fish. Some 25 t of calcareous material 

 passes through the intestines of fish feeding on the bottom sediments, 

 periphyton, and corals on the reef off Panama each year for each ha, 

 with a population density of these fish of 6 individuals for each 10 m^ 

 (Glynn, 1973). 



The periphyton is the main food of most of the reef Gastropoda, as 

 well as crabs, sea urchins and fish. The calcareous algae and corals 

 are eaten by the parrot fish, which use their strong jaws to scrape the 

 periphyton from the rocky base and dead corals (Randall, 1974). 



The direct consumption of macrophytes by the reef fauna is 

 relatively slight. The algae are partially utilized by certain 

 gastropods, sea urchins, fish and Chelonia. Nevertheless, the 

 macrophytes play an important trophic role in the reef community as a 

 source of usable dissolved organic matter and detritus. The massive 

 species of macrophytes ( Thalassia , Sargassum , Syringodium , Chnoospora , 

 Caul erp ) cover significant areas. Photosynthesis in their stands on the 

 reef may be as great as 10-20 g C/m^ per day (Odum et al., 1959). The 

 quantity of products of photosynthesis liberated by the macrophytes into 

 the water amounts to 10-20% of the daily production (Khaylov, 1971). 

 Consequently, the production of dissolved organic matter over the 

 underwater meadows of macrophytes may be as great as 1-3 mg C/m^ per 

 day, which is sufficient for the feeding of many species of benthic and 

 planktonic filter feeders, including corals. As a result of the death 

 of the algoflora, a mass of detritus is formed (Goreau, Goreau, 1973); 

 for example, on one island of the Great Barrier Reef, about 1 kg/m'^ per 

 yedr. The main nutrient component of the detritus consists of the 

 microflora and protozoa which inhabit it abundantly (Fenchel, 1970). 

 The detritus serves as a source of nutrition for a rich detritophage 

 fauna. Some of them collect the detritus from the bottom (gastropods, 

 Holothurioidea, sea urchins, various Crustacea, Polychaeta, many fish) 

 while others filter out the detritus stirred up by the surf from the 

 water. 



2.7 Conclusions 



The materials analyzed above, concerning the structure of modern 

 coral reefs, like the data from fossil reefs (Ladd, 1969; Copper, 1974) , 

 show that the coral community forms a clear biogeocenosis, consisting of 

 a system of specialized biotopes and their populations. This system is 

 similar, even under greatly differing conditions, e.g., on barrier 

 reefs, near large islands and continents, in highly productive waters 

 with rich terrigenous runoff and in atolls in the oligotrophic waters of 

 the trade currents. The reason for the similarity of the structure and 

 level of productivity of the reefs in these various regions is that 

 conditions in the coral communities, in contrast to communities of the 

 pelagic zone, are controlled primarily not by external physiochemical , 

 but rather by internal biological factors. The coral community 

 constructs a specific limestone structure--the reef. It might be 

 thought of as a kind of a cultivator, in which a definite spatial 



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