In evaluating a relatively low rate of sedimentation and predatory 

 feeding by coral (Johannes et al., 1970), we must consider that coral 

 receives the bulk of the energetic material it needs by photosynthesis 

 of zooxanthellae. The heterotrophic feeding serves corals not only as a 

 source of energy, but also as a way of supplying them with necessary 

 nutrient salts, vitamins, trace elements, as well as with some essential 

 amino acids which are not produced by the zooxanthellae. 



The digestive organs used for predatory feeding are the mesenterial 

 filaments which line the edges of the septa in the intestinal cavity. 

 These filaments Are mobile and may extend outside the oral aperture by a 

 distance of up to 10 cm, causing predigestion of large prey items 

 outside the intestinal cavity. They literally weave around the food and 

 digest it with exoenzymes. 



Experiments have demonstrated that when there is a significant 

 concentration of zooplankton, corals with large polyps (such as 

 ^bntastrea ) are capable of completely satisfying their requirements for 

 food by predatory feeding (Coles, 1969; Porter, 1974). However, 

 usually, the concentration of zooplankton over reefs is so low that it 

 cannot satisfy the energy demands of the coral (Johannes et al., 1970; 

 Johannes, 1974). Predatory feeding of coral is probably increased 

 during the period of massive development of invertebrate larvae 

 (veligers, trochophores, echiniopl uteus larvae, etc.). Calculations of 

 the difference in concentration of plankton in the lagoon and in the 

 surrounding atoll waters have shown that the consumption of plankton by 

 the coral community can cover about 5-10% of the energy expended in 

 metabolism (Johannes et al., 1970; Glynn, 1973). 



Furthermore, coral is capable of feeding effectively on organic 

 matter dissolved in the water at concentrations near the natural 

 concentration: 1-2 mg c/Z (Stephens, 1960). With this concentration 

 glucose or protein hydrolysate, the corals in our experiments 

 assimilated the dissolved organic matter in quantities sufficient to 

 cover 15% of the daily expenditure for metabolism (Sorokin, 1973a). 

 About half of the labeled organic matter consumed by the coral is 

 included in the composition of the matter of the polyps (Lewis, Smith, 

 1971). 



Experiments on Pocil lopora have shown that the rate of consumption 

 of one labeled amino acid at a concentration of 0.1 mg C/ i is not 

 reduced when other nonlabeled amino acids are added at 100 times greater 

 concentration (Sorokin, 1977). Obviously, the corals have a mechanism 

 for enzymatic (permease) transport of dissolved organic matter into 

 their cells. Effective consumption of organic matter is provided by the 

 large surface dreA in contact with the water due to the ciliated 

 epithelium and mesenterial filaments. The significance of this way of 

 feeding of corals under natural conditions requires further 

 clarification. 



The phenomenon of interspecific antagonism and aggressiveness of 

 coral species has considerable value in the population ecology of coral 

 communities (Lang, 1973). An entire hierarchy of such relationships has 

 been found between various species of coral. When two species of 



175 



