in the final analysis, by the varying stability of the communities which, 

 according to MacArthur (1955), increases as the number of links in the 

 food chain increases. High stability of a community, according to 

 Margalef (1968), allows it to exist with a lower specific quantity of 

 energy entering the system, i.e., with more limited food resources. 



In the oligotrophic tropical or deep-water communities, the number 

 of trophic levels is high, while in regions with a high level of primary 

 production, the food chains of the communities are very short. For example, 

 in the ultraeutrophic waters of the Peruvian coastal upwelling, the trophic 

 chain of the pelagic zone community consists of only two main links: the 

 phytoplankton and the anchovies. The presence of mass species of fish 

 feeding directly on the phytoplankton is also characteristic for other 

 subtropical, highly productive upwellings. During certain periods, 

 phytoplankton dominates in the food of Sardinella aurita in the upwelling 

 off northwest Africa, for Sardinops melanosticta and Engraul is japonicus 

 off the Pacific coast of Japan, and for Sardinops caerulea in the Oregon 

 upwelling, etc. 



The trophic structure of communities in various climatic zones . The 

 basic differences between subpolar and tropical regions of the ocean is 

 that in the former there are great seasonal changes in the environmental 

 conditions--the intensity of solar radiation, temperature, stratification 

 of surface waters--whereas in the tropics, these factors change little. 

 These planetary distinctions, in the final analysis, also determine the 

 difference in the trophic structure of communities. 



The trophic systems of communities in cold water and temperate to 

 cold water regions are adapted to achieve the most effective utilization 

 of the comparatively brief but clearly expressed spring maximum in biomass 

 of phytoplankton, whereas in open regions in the tropical ocean, the 

 system is adapted to achieve most complete utilization of the relatively 

 low, but little changing level of production of phytoplankton throughout 

 the year. 



In Arctic, boreal and Antarctic regions, the main producers are the 

 diatoms. Their primary consumers are copepods, euphausiids and (in certain 

 regions) pteropod mollusks. Zooplankton is consumed by coelenterates , 

 carnivorous copepods, hyperiids, chaetognaths , baleen whales and plankto- 

 phagous fish. These fish, in turn, are eaten by predatory fish and squids 

 (Fig. 2, A). 



In the open regions of the ocean at low latitudes, the picture of 

 trophic interactions in a community is much more complex (Fig. 2. B). The 

 primary sources of food are phytoplankton and bacteria. In addition to 

 the small phytophagous plankton, macroplanktonic predators are very 

 important, serving as the primary food of planktophagous fish which, in 

 turn, are eaten by larger predaceous fish, while these, in turn, are eaten 

 by tuna and sharks (Parin, 1968, King, Ikehara, 1956, etc.). 



39 



