THE CASPIAN SEA 



601 



Rotatoria, Lamellibranchiata (larvae), Mysidae, Amphipoda and Cumacea, 

 as well as fish-fry, are found in addition to Copepoda, which remain the pre- 

 dominant group. 



In the Central and Southern Caspian the total amount of zooplankton 

 biomass and its qualitative composition change considerably with the seasons. 



Fig. 285a. Distribution of zooplankton biomass 



of Central and Southern Caspian in autumn 



1934 (Jashnov). 



Unfortunately there is no material available for the assessment of this pheno- 

 menon. A comparison can only be drawn from the data (by Idelson) for 

 March-April and August, and for December for the Southern Caspian. This 

 comparison shows an increase of zooplankton concentration in the western 

 coastal zone of the Central Caspian by the autumn, which at that time becomes 

 richer in zooplankton (235 mg/m 3 ) than the central (86-2 mg/m 3 ) and 

 eastern coastal zones (39 mg/m 3 ). According to Jashnov's data a similar 

 distribution of plankton population was recorded in the autumn of 1934-35 

 (Fig. 285a). The seasonal changes of the vertical distribution of zooplankton 



