Vfithin the individual trophic regions, we see medium-scale and 

 small-scale changes in feeding conditions, resulting from the influence 

 of bottom topography and hydrodynamics on sedimentation and the content 

 of organic matter in the sediment. These changes lead to unevenness in 

 the distribution of the population of deposit-feeders within the range 

 of distribution of a species. 



With various rates of sedimentation, the influence of bottom 

 topography on the redistribution of nutrient material in the sediment 

 varies; where the rates are minimal, the influence is least (due to the 

 paucity of nutrient material). Therefore, in oligotrophic areas the 

 bottom topography is much less important as a factor changing the 

 feeding conditions for the macrobenthos than in the eutrophic areas 

 (Sokolova, 1969). In the eutrophic areas on elevations and protrusions 

 of the sea floor, the quantity of soft sediment usually decreases as a 

 result of slower sedimentation or erosion due to greater mobility of the 

 near-bottom waters (shielding effect); frequently, soft sediments are 

 totally absent. The accumulation of sediments is observed in 

 depressions and on flat bottom surfaces (Lisitsyn, 1974). When the 

 layer of soft sediment is thinned or disappears completely, the 

 macrobenthic suspension-feeders predominate, while deposit-feeders 

 become secondary in importance or disappear. When the sediments 

 accumulate, deposit-feeders predominate. Naturally, changes in the 

 feeding conditions under the influence of bottom topography are less 

 significant than changes with replacement of the eutrophic conditions by 

 oligotrophic conditions. 



Within the large-scale forms of bottom topography (continental and 

 island slopes, underwater mountain ranges, basins of the ocean floor), 

 we can observe medium-scale variability of the feeding conditions of the 

 macrobenthos, while within the limits of smaller relief forms (e.g., 

 abyssal hills), we see small-scale changes. These large-, medium-, and 

 small-scale changes in feeding conditions are based on changes in the 

 accessibility of organic matter in the surface layer of sediment, 

 necessary for the nutrition of deposit-feeders, correlated to the 

 thickness of the sediment layer. Under oligotrophic conditions, absence 

 or an insufficiency of food for deposit-feeders, limiting their 

 distribution and preventing their dominance in the macrobenthos, is 

 related to a loss of the nutritive value of organic matter, which is 

 deeply transformed on the surface of the sediment before it is buried, 

 while its supply to the bottom is minimal, sedimentation rates as well 

 as phytoplankton production are lowered. Under eutrophic conditions, 

 absence or insufficiency of food for deposit-feeders is caused by local 

 absence of deposits or erosion of soft sediments and the organic matter 

 they contain when the supply of sedimentary material and organic matter 

 to the bottom is significant and the production of the phytoplankton is 

 high. 



The concept of the trophic zone, which we introduced (see II 1. 5), 

 allows us to characterize the trophic structure of the deep-water 

 macrobenthos in various scales. The medium-scale zonality refers to the 

 distribution of feeding groups within the limits of the main large forms 

 of bottom topography, while the small-scale zonality refers to the 

 limits of medium and smaller forms of relief. Within the limits of the 



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