pericontinental zones of hemipelagic-type sediment accumulation--tens or 

 even hundreds of centimeters of surface sediment are available. The 

 thickness of the surface layer of sediment which can be fed upon by 

 benthic deposit-feeders is greater, with higher rates of sedimentation 

 and greater quantities of organic matter reaching the bottom, to be 

 stored in the sediments in a form which can still be utilized. This 

 layer is thin where sedimentation rates are low and the quantities of 

 organic matter reaching the bottom are minimal, where the organic matter 

 is greatly transformed on the surface of the sediment not being buried 

 (Bordovskiy, 1964, 1966; Romankevich, 1974, 1975). A sharp decrease in 

 the thickness of the layer of sediment suitable for nutrition represents 

 an obstacle to the spreading out of macrobenthic deposit-feeders, more 

 so than for those of meiobenthos. Consequently, most macrobenthic 

 deposit- feeders cannot exist in areas with unfavorable oligotrophic 

 conditions. 



Eutrophic conditions are observed in the peripheral and equatorial 

 parts of the Pacific, Indian and Atlantic Oceans with more or less 

 significant rates of accumulation of sediment and organic matter. 

 Oligotrophic conditions are found far from the continents in the open 

 areas of the oceans with low rates of accumulation of sediment and 

 organic matter. The locations of these trophic areas in the oceans are 

 shown in Figs. 13 and 14. 



The trophic structure of the macrobenthos changes upon transition 

 from eutrophic areas to oligotrophic areas, whereas the trophic 

 structure of the meiobenthos remains unchanged. In areas with eutrophic 

 conditions, the macrobenthic deposit-feeders are ubiquitous and 

 predominate over large areas of the bottom, except the peaks of 

 underwater sea mounts and areas of erosion on their slopes. In areas 

 with oligotrophic conditions, detritophagous macrobenthos is found 

 rarely or not at all. The macrobenthos in these areas consists of a few 

 immobile suspension-feeders and nektobenthic carnivores (Sokolova, 1964, 

 1969, 1976; Dayton, Hessler, 1972; Shulenberger, Hessler, 1974). 

 Figures 15 and 16 present examples of the distribution of typical 

 taxonomical groups of macrobenthic deposit- and suspension-feeders in 

 the eutrophic and oligotrophic region of the Pacific Ocean. The total 

 quantity of macrobenthos in the oligotrophic regions is significantly 

 less than in the eutrophic regions (Table 10). 



The meiobenthos, both in eutrophic and in oligotrophic regions, 

 consists primarily of detritophagous invertebrates. Upon transition 

 from eutrophic conditions to oligotrophic conditions, the taxonomical 

 composition (Table 11) and biomass of the meiobenthos become somewhat 

 poorer (Sokolova, 1970, see also III. 5), but the trophic structure is 

 not altered (Sokolova, 1969, 1970, 1972, 1976). 



Due to this, our analysis of the influence of variations in feeding 

 conditions on individual feeding groups and the entire trophic stucture 

 will concern only the macrobenthos. 



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