. Biology of the seas of the Marine biology -- Soviet Union; Hydrology -- Soviet Union. 176 BIOLOGY OF THE SEAS OF THE 80 ACCORDING TO TO NUMBER OF SPECIES. 100 ACCORDING TO DENSITY INDICES brought Filatova to the conclusion that the introduction of a transitional region (boreo-Arctic according to Appellof and Hofsten, or sub-Arctic according to K. Derjugin) is unnecessary. It is evident from Fig. 74 that the clearest picture is given by the biomass. The northern parts of the Atlantic trench should be included in the Arctic region, the southern ones in the boreal. Qualitative
. Biology of the seas of the Marine biology -- Soviet Union; Hydrology -- Soviet Union. 176 BIOLOGY OF THE SEAS OF THE 80 ACCORDING TO TO NUMBER OF SPECIES. 100 ACCORDING TO DENSITY INDICES brought Filatova to the conclusion that the introduction of a transitional region (boreo-Arctic according to Appellof and Hofsten, or sub-Arctic according to K. Derjugin) is unnecessary. It is evident from Fig. 74 that the clearest picture is given by the biomass. The northern parts of the Atlantic trench should be included in the Arctic region, the southern ones in the boreal. Qualitative estimation should always be corrected by quantitative analysis. As has been mentioned in our general section, Ortmann as early as 1896, and later many other zoogeographers, have pointed out the difficulty of drawing common zoo- geographical boundaries for plankton and benthos, for the shallow- and deep-water fauna. This is particularly true of the southern part of the Barents Sea since the warm-water forms are continuously drifting into it from the west. Vertically the Barents Sea is not zoogeographically homogeneous. Under the favourable conditions of the Barents Sea littoral its fauna extends almost without qualitative change from the North Sea to the White Sea; the plant and animal forms remain practically the same, individual forms and complete fauna as a whole retaining very similar relationships. Thus the Murman and White Sea littoral is populated mainly by boreal fauna and should therefore be included in the boreal region (Fig. 75). The main mass of organisms of the upper horizon of the sublittoral is also boreal in its characteristics. In the opinion of V. Zatzepin (1939), who made a special study of the Murman coastal fauna, the latter retains its boreal character up to the Gavrilov Islands. As one goes deeper, the boreal forms become less important, while the Arctic ones become predominant. However, owing to a warm, so- called Ruppin, branch of the Atlantic current,
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