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



Table 248 



Layer 

 m 



0-100 



100-200 



Below 200 



in the middle part of the Central Caspian are well illustrated in Table 248. 

 As shown in this table zooplankton biomass decreases by the autumn in the 

 upper layers, and increases in the lower ones. The relationships between 

 different groups change also. In the middle part of the Central Caspian 

 Limnocalanus grimaldi is concentrated by the autumn in the lower layers (in 

 the 100 to 200 m layer it constitutes 67 per cent and at 200 m it is 54-2 per cent 

 of the total biomass) while in the upper layer, where in the spring the plankton 

 consists almost exclusively of Limnocalanus grimaldi, by the autumn it forms 

 only 9-7 per cent of the biomass. The migration of L. grimaldi to the lower 

 layers in the autumn is undoubtedly connected with the adaptation of this 

 species to relatively lower temperatures, and is caused by a considerable 

 warming of the surface layer. In the western coastal zone a large number of 

 Lamellibranchiata larvae appear by the autumn (90 mg/m 3 , comprising 

 42-2 per cent of the total biomass). Copepoda remain, however, the dominant 

 group (comprising 47-3 per cent of the total biomass, containing 11-6 per 

 cent Eurytemora, 10-6 per cent Calanipeda, 15-2 per cent Halicyclops and 

 9-2 per cent nauplii). Limnocalanus grimaldi, dominant in spring in the eastern 

 coastal zone, comprises only 6-8 per cent of the total biomass by the autumn, 

 nauplii (42-6 per cent), Eurytemora (28-5 per cent) and Lamellibranchiata 

 larvae (9-2 per cent) take precedence. Observations from the Southern Caspian 

 are shown in Table 249. 



Zooplankton biomass and composition in the upper layer did not change 

 much. However, in the 100 to 200 m layer and from 200 m to the sea-floor a 

 considerable decrease of zooplankton biomass was recorded in March 1939; 

 moreover there were some natural alterations in the relationships between the 

 separate groups: Limnocalanus was the dominant form in April 1938 (68 

 and 56 per cent) while second place was occupied by the mysids (25 and 

 39-8 per cent); in December 1938 and in March 1939 in particular these 



