THE BERING SEA 



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distribution of the three dominant species of Copepoda : each species is pre- 

 dominant in a certain horizon, therefore, although they feed on the same 

 species of diatoms, their competition for food is less intense since their main 

 habitats belong to different horizons. 



Eurythermic species — Oithonasimilis, Sagittaelegans, Calanus finmarchicus, 

 Parathemisto libellula — become predominant in winter as a result of the cool- 

 ing of the upper layer (down to 1,000 m) in the western part of the Sea and the 

 total zooplankton biomass is considerably reduced. It increases again by the 

 second half of the summer (Fig. 423), Eucalanus alone producing a biomass of 

 200 to 1,000 mg/m 3 . The amount of zooplankton decreases considerably 



Fig. 423. Distribution of zooplankton biomass 

 (mg/m 3 ) in the to 100 m layer in June 1952 

 (Vinogradov). 



again in autumn. In the Bay of Anadyr, however, zooplankton reaches its 

 highest development in autumn only, mainly on account of Eucalanus bungii. 

 In the north of the Bering Sea the biomass remains low throughout the year, 

 only at certain places does Calanus finmarchicus form great concentrations 

 with a density of up to 100 mg/m 3 , and 400 specimens per 1 m 2 . 



The mass forms of the plankton Calanoida multiply at different times in the 

 Bering Sea, thus making the best use of the food resources available 

 (A. Geinrich, 1955). The multiplication of Calanus finmarchicus takes place 

 at the beginning of the greatest phytoplankton development; Eucalanus 

 bungii develops somewhat later, followed by Calanus tonsus (small race). 

 The multiplication of Calanus tonsus (large race) is not connected with phyto- 

 plankton vegetation. The multiplication of Metridia pacifica proceeds 

 throughout May to November, while Calanus cristatus spawns in December 

 to February. Most of the forms mentioned produce only one generation 



3G 



