THE BARENTS SEA 



93 



In the spring the diatoms are most important, developing rapidly and giving 

 an appearance of ' bloom ' in some parts of the Sea. In the autumn diatoms 

 are superseded in importance by the peridinean 

 mass, then showing maximum development. 



The course of phytoplankton development, 

 with its two maxima, which is characteristic of 

 the whole temperate zone of the oceans of the 

 world, is well defined in the southwest of the 

 Barents Sea (Fig. 32). The first maximum in the 

 coastal waters is in May and is connected with 

 the mass bloom of Phaeocystis (Crypto- 

 monidinae) and to a much lesser degree with 

 that of the diatomaceous Chaetoceras and 

 Sceletonema. The second, smaller maximum 

 (July to September) is conditioned by the mass 

 development of peridineans. 



Composition of zooplankton. Zooplankton in 

 the Barents Sea (V. Bogorov, 1946) is fairly poor 

 in its numbers; of the groups composing it only 

 Infusoria, Copepoda and Coelenterata {Table 

 32) stand out. 



The Barents Sea zooplankton contains the 

 oceanic and neritic forms and forms distributed 

 equally in the coastal areas in the open sea. 

 M. Virketis (1928) includes in the first category 

 the main forms of Copepoda genera — Calanus, 

 Pseudocalanus, Metridia, Oithona, Euchaeta, 

 Microsetella ; salps — Oikopleura medusa, Aglanta 

 digitalis: and in the second the Daphnidae 

 Evadne and Podon, the Copepod Temora longi- 

 cornis, and the salps Fritillaria borealis and F. 

 medusa Rathkea octopunctata. 



On the other hand the permanent inhabitants of the Barents Sea may be 

 distinguished from the more or less temporary visitors. The latter forms of one 

 origin or another may often appear in large numbers carried in by the waters, 

 and rapidly disappear with a change of hydrological conditions. Thus it is 

 possible to observe the seasonal change of zooplankton composition, which 

 is not possible with benthos forms. Virketis includes Calanus finmarchicus, 

 Metridia longa, Oithona similis and others among the main permanent in- 

 habitants of the Barents Sea. 



The more thermophilic forms of western origin keep mostly in the warm 

 streams of the North Cape current. They move eastward in summer and west- 

 ward in winter. Their numbers are higher in warmer years than in colder. 



In contrast to the thermophilic forms, the arctic ones attain their highest 

 development in winter and spring. In summer they travel far to the north, or 

 keep to the cooler abyssal layers or the colder waters remaining over the 



V VI VII VIII IX X 



MONTHS 



Fig. 32. Quantitative altera- 

 tion of phytoplankton from 

 May to October 1932, in one 

 of the Gubas of western 

 Murman Peninsula (Man- 

 teufel, 1939). The ordinate 

 gives the number of cells in 

 millions in a 40 m column 

 of water of 50 cm 2 cross 

 section. 



