coarse filter feeders, which filter out primarily bacterial aggregates 

 measuring more than 5 m in diameter, bacterioplankon makes up only a 

 portion of their daily ration. For example, the coral Pocillopora . by 

 feeding on bacterioplankton and dissolved organic matter with a 

 concentration near the natural concentration, can compensate for about 

 1/4 of the metabolic expenditures. It must be considered that the value 

 of the bacterioplankton for the corals could be more in the nutrients 

 they contain than in the energy which they receive in sufficient 

 quantity from the symbiotic Zooxanthel 1 ae. 



Phytoplanktcn, as a source of food for filter feeders, in most 

 cases plays a much less significant role than does bacterioplankton. 

 Its biomass in the water of coral biogeocenoses is usually 5-10 times 

 less than that necessary for the normal nutrition of the reef 

 organisms. Only in the productive zones of the ocean or during periods 

 of the maximum development of phytoplankton in oligotrophic waters can 

 we expect participation of phytoplankton in the nutrition of benthic 

 filter feeders and sediment feeders of the reef to be significant. The 

 question of the value of phytoplankton as a source of food for the coral 

 has not yet been answered. The available data indicate that the 

 madreporarians practically do not consume it and are not capable of 

 digesting the plant cells (Yonge, 1931; Sorokin, 1973a). However, the 

 alcionarians and zoantharians can feed on phytoplankton (Sorokin, 

 1973e). 



We can also suppose the microzooplankton has to be a significant 

 component in the trophic connections of the reef. However, there dre no 

 quantitative data available on this question. The mesozooplankton of 

 the reef is consumed both by the corals themselves (Porter, 1974) and by 

 the hydroids, Zoantharia, Actinia, Gorgonaria, Calani and Polychaeta. 



Attempts to estimate the food value of net zooplankton for the 

 coral have been made on the reefs off the Bermuda Islands (Johannes et 

 al., 1970). It was found that even with complete consumption of the 

 zooplankton carried above the reef by currents by the coral (Pi ploria ) , 

 it could compensate for only about 5% of the expenditure of the coral 

 community for metabolism. However, the biomass of zooplankton on the 

 reefs in eutrophic regions off Florida and the Laccadive Islands is 

 quite high--up to 0.2-0.5 q/m^ (Emery, 1968; Tranter, A. Jacob, 1969). 

 The meroplankton is also quite numerous, particularly at night. 



The food resources created by benthic algoflora and the bacterial 

 population of the sediment and reef periphyton are used by many benthic 

 invertebrates and fish. Many of them take in the bottom sediment 

 nonsel ectively : coral sand, detritus, regeneration sediment, formed 

 among accumulations of dead colonies of coral (Bakus, 1973). As was 

 shown earlier, the bottom sediments of the reef contain an exceptionally 

 rich microflora and phytobenthos. It is therefore not surprising that 

 even nonselective consumption is energetically expedient for animals. 

 Experiments using C^^ have shown that the Holothurioidea Ophiodesma and 

 Gastropoda Nerita digest the microflora contained in the sediment and 

 can fully satisfy their nutient requirements with it alone (Sorokin, 

 1973e). The quantity of bottom soil consumed per day by these animals 

 frequently exceeds their own weight. In a year, the entire upper layer 

 of sand, several centimeters thick, passes through the intestines of the 



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