upwelling is absent or where the water is descending, have low plankton 

 biomass, high specific diversity, and weakly expressed domination of 

 species. The trophic structure reaches almost its maximum possible diversity. 

 Filter feeders amount to about 20-30% of the total biomass, and more than 

 half of them are fine-filter feeders. The total quantity of predators 

 increases to 45%. Analogously, in mesopelagic macroplankton in the mature 

 communities of the central and western equatorial Pacific, the biomass is 

 less, the specific variety significantly greater, than in the more juvenile 

 communities of the eastern Pacific (Parin, 1976). 



Factors which greatly shade the typical picture of distribution of 

 trophic groups come into play in the higher levels of a trophic system. 

 This results to a great extent from the fact that in the macroplankton and 

 nekton of the open ocean, a large portion of the flow of energy is directed 

 downward and beginning as low as the second or third level of consumers, a 

 significant fraction of the total biomass is accounted for not by 

 surface-dwelling, but by deeper dwelling, primarily mesopelagic, animals. 

 The transformation of this flow on its path down into the depths has not 

 been sufficiently studied, but subsurface currents apparently are quite 

 significant in the redistribution of animals. Therefore, the spatial 

 distribution of oceanic tuna, which make up the basis of an important 

 industry, and of the toothed whales (particularly the sperm whales), feeding 

 on mesopelagic fish and squid, cannot always be given an effective causal 

 explanation from the point of view we are now considering. 



Change in trophic structure of communities with depth . The change 

 in the role of various trophic groups of mesoplankton with increasing 

 depth will be analyzed on the example of the region of the Pacific Ocean 

 near the Kuril Islands, since we have representative quantitative data on 

 the vertical distribution of the entire mass of plankton and its basic 

 taxonomic groups for this area (Table 1, Fig. 4). 



The planktonic community, rich in phytoplankton, in the upper portion 

 of the euphotic zone, is dominated by phytophagous filter feeders. In 

 the lower levels of the euphotic zone, in the cold intermediate layer 

 (100-200 m), the significance of predaceous species (primarily Sagitta 

 e legans ) , feeding on animals from the surface layer, increases rapidly. 

 The significance of filter feeders decreases, although it remains rather 

 high as far down as 500-750 m. In the 500-1000 m layer, the significance 

 of the euryphages increases, due to the development of a rather large number 

 of radiolaria from the families Aulacanthidae and Aulosphaeridae at these 

 depths, serving as a significant component of the diet of the euryphages, 

 and also acting as predators of the copepods. Below 500-1000 m, the signifi- 

 cance of the filter feeders decreases rapidly. The quantity of specific 

 deep-water filter feeders is "jery small. The interzonal filter feeders, 

 present in comparatively large numbers (primarily the copepods Calanus 

 c ristatus and C^. p lumchrus ) , feed in the producing zone and, apparently, do 

 not feed in the deeper waters. Ignoring the interzonal phytophages, in 

 the 1500-3000 m layer, the plankton consists 60-80% of zoophagous forms, 

 primarily catching zoophages. Deeper than 3000-4000 m, given the '^ery low 

 plankton biomass and its great dispersion, predation, even passive 

 predation, is apparently not energetically expedient, and the significance 

 of zoophagous forms is greatly decreased. Euryphages move into first 



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