coarse-grained soil, due to its weakly developed apparatus for soil 

 sorting, meaning that it cannot receive a sufficient quantity of food 

 there. L. V. Sanina (1975), using the example of sestonophagous 

 mollusks of the northern Caspian, showed that their distribution also 

 depends on the ability to sort organic particles from a suspension with 

 varying contents of mineral particles. 



The use of the method of V. P. Vorob'yev, in combination with the 

 study of the ecologic habit and methods of feeding of the main species 

 making up biocenoses, has led to the conclusion that the core of a 

 biocenosis consists of minimally competitive species, (Birshteyn, 1947; 

 Vorob'yev, 1949; Ivlev, 1955; A. P. Kuznetsov, 1960; Sokolova, 1960; 

 Turpayeva, 1948, 1949; Shorygin, 1955), because of the membership of the 

 primary species of the biocenosis in different trophic groupings. The 

 simultaneous existence of representatives of various trophic groupings 

 is possible because they feed from different zones (levels) of the 

 bottom sediments. Depending on which of the feeding zones contains the 

 greatest quantity of nutrient substances in a given biotope, one or the 

 other trophic grouping will be dominant in the biocenosis. The greatest 

 competition occurs between representatives of the same trophic grouping. 



However, there are biocenoses, the core of which consists of 

 species of a single trophic grouping. Ye. P. Turpayeva (1948, 1949) has 

 suggested that there may be fine differences in the nature of feeding of 

 species of a single trophic grouping, although she had comparatively 

 little data to work with. A. P. Kuznetsov (1960, 1963) is of the same 

 opinion. At the present time, a great deal of material has been 

 accumulated concerning the composition of shelf biocenoses of the seas 

 of the USSR and other regions of the world ocean, and these statements 

 can be made specific. For example, on the shelf of the eastern portion 

 of the Bering Sea, there is an extensive zone of sedimentation at a 

 depth of 50-150 m. The conditions are right there for rapid development 

 of detritophages, particularly gatherers. Extensive areas of the bottom 

 are occupied by biocenoses of Macoma calcarea , Yoldia hyperborea , 

 Nuculana pernula and hlucula temus , and in each of the biocenoses, all 

 of these four species are included in the core of the biocenosis. They 

 are all gathering detritophages. This composition of detritophage 

 biocenosis is, obviously, a result of the abundance of food at their 

 feeding level--detritus on the surface of the bottom deposits. K. N. 

 Nesis (1965) believes that an abundance of food at a given feeding level 

 leads to the appearance of biocenoses with a trophically homogeneous 

 core. This is proved, perhaps, by the fact that these same biocenoses 

 on a narrow shelf with relatively little sedimentation, have a different 

 core composition, containing sestonophages and nonselective 

 detritophages, as can be seen in the example of the biocenosis of 

 Macoma calcarea in the eastern Bering Sea and eastern Kamchatka. 



201 



