176 



BIOLOGY OF THE SEAS OF THE U.S.S.R. 



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, 

 in the coastal region the boundary of the 

 Arctic fauna recedes along the coast far to the east. Finally, as has been 

 mentioned above, high Arctic fauna concentrate in the cold bottom water 

 of some stagnant hollows of some sections of inlets on the Murman coast, 

 even in its western parts. Thus a vertical change of the fauna from boreal to 

 high Arctic may be observed within the same region as we proceed from 

 the littoral to the depths. 

 The Barents Sea fauna thriving in an area where the warm Atlantic waters 



700 

 80 



60 



BOREAL SPECIES 



ARCTIC SPECIES 



ARCTIC -BOREAL 



SPECIES 



Fig. 74. Relationship between 

 Arctic, boreal and Arctic- 

 boreal species per cent in bot- 

 tom fauna biocoenoses of 

 southwestern part of Barents 

 Sea from west to east (Fila- 

 tova, 1934). 



