CHAPTER II. PELAGIC COMMUNITIES AND THEIR STRUCTURAL 

 AND FUNCTIONAL CHARACTERISTICS 



1 . Trophic Relationships in the Pelagic Zone 



(M. E. Vinogradov, N. V. Parin, A. G. Timonin) 



P rimary sources of matter and energy . The trophic relationships in 

 the pelagic zone of the ocean, in spite of their great importance for an 

 understanding of the functioning of communities, have been quite insuffi- 

 ciently studied. Even such a basic problem as the primary sources of 

 incoming organic matter (energy) entering the food chain of the communities 

 which; in the final analysis, determines their total productivity, 

 functioning and structure, is still a subject of lively debate. 



The primary organic matter in the pelagic zone is formed by the 

 photosynthetic activity of phytoplankton. It is thought that the entire 

 food pyramid is constructed on this basis. The flow of energy passes 

 through the phytoplankton to the herbivorous zooplankton, then to the 

 carnivorous plankton and nekton (Fig. la). However, attempts at quantitative 

 estimation of the energy flow and energy balance of the various trophic 

 levels have shown that over broad expanses of water in the oligotrophic 

 regions of the tropical ocean, this path cannot support the energy demands 

 for existence of the communities. At least in these regions, obviously, 

 another path of arrival of energy is no less 1mportant--through autochthonous 

 and al lochthonous dissolved organic matter to bacteria, protozoa, then 

 filtering and predaceous invertebrates (Fig. lb). It is assumed here 

 (Sorokin, 1971a) that the dissolved organic matter is formed in excess in the 

 highly productive cold regions of the ocean, descends together with the 

 descending flows of water into the deep layers where, due to the low tem- 

 perature, its decomposition is retarded, then returns to the surface in 

 the equatorial regions in the areas of quasi-stationary upwelling of water 

 where, at the high temperatures reached in the surface layers, it becomes 

 available for bacterial destruction. Thus, the bacteria in these tropic 

 communities act as local "producers." Yu. I. Sorokin (1971a) believes 

 that the bacterial path of inclusion of organic matter in the food chain 

 in tropical communities is equal. In terms of energy flux, to the classical 

 phytoplankton path, or even exceeds it. This high evaluation is not agreed 

 with by all (Steemann Nielsen, 1972; Banse, 1974), but, nevertheless, the 

 significance of the role of arrival of energy in the community through 

 dissolved organic matter and bacterioplankton is obvious. 



T he trophic network of the community . The distribution of matter and 

 energy among trophic groups in the community follows a complex network of 

 trophic connections. Connections at the higher trophic levels may be 

 comparatively easily traced by examining the contents of the guts of 



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