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



biocoenoses and a large number of warm-water forms of sea-weeds and 

 invertebrates (Thalassiophyllum, Amphiroa, Acmaea pelta, Strombella, 

 Pholas crispata, Pholedidea penita, Tapes stominea, and others) and by the 

 rich development of the sublittoral fauna. 



The narrow shelf zone of the eastern shores of Kamchatka and the northern 

 Kuril Islands has also an exceptionally rich bottom fauna (Bivalvia, Poly- 

 chaeta, Crustacea, Echinodermata and others), which in the summer attracts 

 numerous shoals of commercial fish — pollack, cod, flatfish, sea bass and 

 Kamchatka crab. The intensive development of the fauna is the result of the 

 abundance of littoral vegetation and plankton. A. Kuznetzov carried out a 

 detailed investigation of these regions and established (1959) the presence of 

 16 biocoenoses; Modiolus modiolus, Mytilus edulis, Porifera, Hydroidea, 

 Echinarachnius parma, Astarte rollandi, A. alaskensis, Macoma calcarea, Car- 

 dium ciliatum, Ophiura sarsi, Ophiopholis aculeata, Pavonaria finmarchica (?), 

 Asteronyx loveni, Astarte icani, Ampelisca macrocephala, Brisaster townsendi, 

 Aci/a castrensis, Brisaster latifrons, Artacama proboscidea, Ammotrypane aulo- 

 gaster, Rhodine gracilior, Pista vinogradovi. 



The predominance of Arctic and Arctic-boreal species (30 species or 48-3 

 per cent of the 64 dominant and characteristic species) in the fauna is evident 

 from this list of the composition of the main forms and a quantitative analysis 

 of their predominance. The eastern shores of Kamchatka and of the northern 

 Kuril Islands are washed by cold waters flowing from the Bering Sea. The 

 boreal species constitute 38-8 per cent of the main species, and the cosmo- 

 politan ones 9-7 per cent (6 species). The number of subtropical-boreal species 

 among the main species is very small — only 2, or 3-2 per cent. This is in 

 strong contrast with the composition of the shelf fauna of the southern Kuril 

 Islands. Many of the above mentioned forms (9 out of 20) are mass forms of 

 the lower Arctic seas including the Barents Sea. The somewhat original verti- 

 cal distribution of the cold- and warm-water zoogeographical communities 

 corresponds to the distribution of the water masses (A. Kuznetzov, 1959). 

 Arctic-boreal biocoenoses are developed most intensely at a depth of 100 to 

 200 m (at a temperature of about 0° C) and at 500 to 1 ,200 m (at a temperature 

 of 2° to 2-5°). The water mass at to 100 m deep is considerably warmed up 

 in summer, while at 200 to 500 m the temperature remains between 3° and 4°. 



The bottom fauna of these regions is characterized by high density indices 

 (Table 288). 



The rich littoral population of the southernmost Kuril Island, Kunashir 

 (O. Kusakin, 1956), has much in common with the littoral population of the 

 southern part of the northern Japanese shore, some areas of southern Sakha- 

 lin and the shore of the southern Kuril Islands, and it can be included in the 

 south-boreal province of the boreal region, with considerable influence from 

 the subtropical littoral flora and fauna. Among the south-boreal and sub- 

 tropical species the following should be mentioned : the hydroids Campanu- 

 laria platycarpa ; the Porifera Grantessa nemurensis; the polychaetes Achisto- 

 comus sovieticus, Staurocephalus japonica, Audouinia tentaculata and Polymnia 

 trigonostoma ; the amphipod family Talitridae ; the isopods Ligia cinerescens, 

 Excirolana japonica, Dynoides denticinus, C/eantis isopus; the decapods 



