120 140 160 180 160 140 I» 100 80 60 40 



Fig. 16. Patterns of distribution of typical groups of suspension- 

 feeders on the Pacific Ocean floor: 1, sponges; 2, Cirripedia; 3, 

 Polichaeta of family Serpulidae; 4, None of these groups present in 

 trawl catches (Sokolova, 1972). 



The boundaries between eutrophic regions divide the areas with 

 similar trophic structure of the population, but with unequally 

 favorable feeding conditions. These differences are sufficient to limit 

 the areas of distribution of certain species of deposit-feeders, which 

 tend toward the boundary separating the eutrophic regions. An example 

 is the boundary of the pericontinental and oceanic peripheral eutrophic 

 regions in the Pacific Ocean (see Fig. 14). Near it, the subsurface 

 reducing zone in the sediment disappears, and the absolute quantity of 

 organic matter buried in the sediment decreases by a factor of 8 

 (Skornyakova, Murdmaa, 1976). In the macrobenthos, the frequency of 

 occurrence of deposit-feeders decreases--Holothurioidea, sea urchins, 

 stars, Polychaeta, Sipunculoidea, all of which prefer the sediment of 

 the pericontinental eutrophic region (Sokolova, 1976). The species of 

 the genera Travi sia and Kesun among the Polychaeta (Levenshteyn, 1970), 

 Cystocrepis , Fchinocrepis , Helgocystis and Ceratophysa among the 

 irregular urchins (A. N. Mironov, 1974) do not penetrate into the 

 organic eutrophic region. These and other similar facts explain the 

 rather good agreement of the boundaries between trophic areas and 

 between zoogeographic areas in the abyssal zones (Vinogradova, 1969; 

 Relyayev et al., 1973; Sokolova, 1969, 1972). Obviously, we see here 

 the influence of a sharp change in the feeding conditions on the range 



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