4. Benthic Shelf Communities (A. A. Neyman) 



In this section, we shall discuss benthic shelf biocenoses beyond 

 the limits of the plant zone, i.e., at depths of over 10 m. 



The food resources of the inhabitants of this zone consist of the 

 detritus which reaches the bottom layers of water and the floor from the 

 photic layer. This greatly simplifies the composition of the benthic 

 shelf biocenoses, since producers and phytophages are absent, while the 

 detritus consumers remain (see 1 1 1. 5), along with the low-mobility 

 predaceous forms. 



Quantitative investigations of the benthos in large water areas are 

 performed using bottom samplers, which trap only the non-moving and 

 slowly moving animals. Therefore, bottom-sampler collections can be 

 used only to study the competitive relationships between animals of a 

 single trophic level. Predator-prey relationships are played out 

 between representatives of the low-mobility benthos and necton 

 (benthophagous fishes) and migrating benthos (e.g., crabs), i.e., they 

 go beyond the framework of the biocenoses which can be studied by means 

 of bottom samplers (L. G. Vinogradov, 1963; Vinogradov, Neyman, 1965). 



V. P. Vorob'yev (1949) suggested a method of differentiating 

 biocenoses according to species dominant in terms of biomass. This 

 method has been widely used in Soviet marine research. The method of V. 

 P. Vorob'yev is quite simple and, at first glance, quite formal: in a 

 bottom-sampler sample, the species which dominates in terms of biomass 

 is determined; stations at which the same dominant species is found are 

 combined into a biocenosis. If these stations are placed on a map, as a 

 rule, we find that stations relating to a single biocenosis are quite 

 regularly placed (A. P. Kuznetsov, 1963, 1970; Neyman, 1963a, 1971). 

 Station-by-station comparison of the benthos with data on the particle- 

 size distribution of the bottom deposits reveals (Neyman, 1963b) that 

 each biocenosis is characterized by its own type of particle-size 

 distribution, and the particle-size distribution differences of similar 

 biocenoses (within a single trophic zone) are quite clear, though not 

 great: The same size fraction of bottom soil predominates, but the 

 degree of dominance and fraction of the corresponding particles differ 

 (Fig. 9). Thus, a biocenosis distinguished by the method of V. P. 

 Vorob'yev is a natural formation, owing its development to fine 

 differences in the process of sedimentation within the limits of a 

 single trophic zone. 



N. P. Bubnova (1971, 1972) studied the process of nutrition of two 

 detritophagous bivalve mollusks in the White Sea— Macoma baltica and 

 Portlandia arctica- -inhabiting soils with different contents of clay 

 particles. She demonstrated that the association with different soil 

 types of these mollusks was directly related to differences in their 

 capability to sort the bottom deposits: Portlandia cannot live on 



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