2. The Communities of Coral Reefs . (Yu. I. Sorokin) 



The biogeocenoses of coral reefs represent one of the most active 

 biologic systems in the world ocean, and in fact, on the planet as a 

 whole. The area occupied by coral reefs only in the Pacific Ocean is 

 comparable to the area of the continent of Australia. The biological 

 activity of the coral biogeocenoses, per unit area, is 20-100 times 

 greater than in the pelagic areas of the tropical zone of the oceans. 

 For example, the daily primary production of photosynthesis in the 

 coastal waters is 0.15-0.30 g C/mS whereas in coral communities of the 

 phytobenthos, periphyton and symbiotic zooxanthel lae, it is 5-20 g 

 C/mS The activity of the microflora, characterized by its destructive 

 activity and heterotrophic production in the coral biogeocenoses is 10- 

 20 times higher than in the surrounding oligotrophic tropical waters. 



The processes of biogeochemical circulation of matter occur in 

 coral reef ecosystems much more intensively than in the surrounding 

 tropical waters and on the ocean floor. It is quite probable that it is 

 in the coral communities that microbial oxidation of the fraction of 

 organic matter resistant to sea water occurs (Sorokin, 1971a). Due to 

 the high productivity, optimal oxygen mode and high temperature of the 

 water in coral communities and in the regions of the surrounding shelf, 

 optimal conditions are created for the breeding and feeding of many 

 species of commercial animals. 



Coral reef communities in and of themselves represent a classic 

 example of a biogeocenosis as a self-supporting community, which creates 

 its own physical substrate and chemical medium. At the same time, coral 

 biogeocenoses are distinguished from the surrounding oligotrophic waters 

 and exist basically on the energy of autochthonous primary production. 

 The system is organized so that the absolute concentration of nutrients 

 is maintained at a high level, in spite of an intensive exchange with 

 the surrounding oligotrophic waters of the ocean. The biological 

 mechanisms which maintain the reserves of nutrients and a high 

 productivity of the coral communities--conditions of an intensive 

 physical contact with the oligotrophic waters which pass over the reef-- 

 represent an interesting problem. Its interpretation will doubtless be 

 of important significance in the creation of a theory of marine 

 aquaculture and will thereby assist in the solution of one of the key 

 problems of modern hydrobiology. 



Primary production in coral communities is basically created by the 

 photosynthesis of hermatypic reef-forming organisms. The processes of 

 sedimentation of CaCOo and MgCOj on the reefs and, consequently, the 

 processes of formation of the reefs themselves and the sediments 

 surrounding them, are directly functionally related to the production 

 processes in the coral communities (Goreau et al., 1972). Therefore, 

 the study of the regularities of functioning and the production 

 processes of coral biogeocenoses provide the necessary basis for the 

 creation of the theory of growth of the reefs as the facies of 

 sedimentary rock of the earth's crust. 



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