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



(2) The lower sub-Arctic water mass may in its turn be divided into two 

 layers — a layer (200 to 1 ,400 m) with a much lowered oxygen content, an in- 

 creased amount of nutrient salts and a higher temperature; and a lower- 

 temperature layer with an oxygen content of 32 to 46 per cent of saturation. 

 This water mass likewise may be regarded as locally modified water, which 

 enters mainly from the Bering Sea in the winter and sinks down from the 

 Sea of Okhotsk. The rate of the movement of these waters southwards 

 reaches 10 to 13 cm/sec at a depth of 600 m. 



(J) Deep Pacific Ocean water masses (below 1,400 m) and bottom water, 

 which is in constant reaction with bottom sediments. Deep water masses 

 are characterized by their great homogeneity and by their comparatively low 

 oxygen content (D. Smetanin, 1959) (3 to 4 ml of oxygen per litre as against 

 5 or more in the Atlantic Ocean) and by their increased content of plant food. 

 Smetanin considers that this phenomenon is linked with the greater age of 

 these waters as compared with those of the Atlantic. 



In Smetanin's expression (1959) the waters of the ultra-abyssal of the Kuril- 

 Kamchatka trench are, as it were, deep water spread out vertically ; they are 

 in constant movement (probably from north to south) at the same speed as 

 the waters above them (A. Bogoyavlensky, 1955). The temperature of this 

 water falls to 1 -45°, but below 4,000 m it rises to 2- 1 5° at the bottom (adiabatic 

 process) ; its salinity increases to 34-75% , its oxygen content to 3-6 ml per 

 litre and the amount of phosphates to 60 mg/m 3 in terms of phosphorus. 



IV. COMPOSITION OF FLORA AND FAUNA 



The flora and fauna of the Pacific Ocean are in general richer than those of the 

 Atlantic, and similarly the population of its northwestern part is considerably 

 richer than that of the corresponding parts of the Atlantic. 



The general taxonomic composition of the flora and fauna of the north- 

 western parts of the Pacific cannot be considered as well known ; some groups 

 have been studied in sufficient detail, others much less (Porifera, Coelenterata, 

 Gastropoda and others) ; the taxonomy of some groups — Turbellaria, Nema- 

 toda, Actinia, bottom nemertines, Harpacticoidea and others — has hardly 

 been established at all. The composition given in Table 287 should only be 

 taken as preliminary. 



The complete list of the fauna of the northwestern part of the Pacific Ocean 

 contains no fewer than 6,000 animal species. It is apparently considerably 

 richer than that of the Atlantic Ocean fauna in the same latitudes. 



The richness of the fauna of the Far Eastern Seas and the antiquity of its 

 origin is accentuated by its abundant parasite fauna, studied by V. Dogjel 

 and his pupils (A. Akhmerov, B. Bykhovsky and others). 



About 900 parasite forms are known now, and one may assume that their 

 actual number is much greater. This number is composed of species of 1 30 

 Protozoa, 400 Trematoda, 20 Cestoidea, 120 Nematoda, 80 Crustacea, 10 

 Gastropoda and 120 others. 



The richness of the flora and fauna of the northern part of the Pacific may 

 be demonstrated also from many other examples. Thus, for example, among 



