THE CASPIAN SEA 



589 



green algae reach their highest development in the Northern Caspian, where 

 their summer and autumn bloom is observed and where their biomass rises to 

 0-4 to 0-7 g/m 3 , consisting mainly of Aphanizomenon flos-aquae. If the mean 

 biomass of the Caspian phytoplankton in the autumn of 1934 be taken as 1-2 



Fig. 277. Quantitative development of Rhizosolenia 

 calcar-avis in 1934 (Usachev). 



g/m 3 , then by 1935 it had increased to almost 2 g/m 3 and in 1936 to 3 g/m 3 . 

 The whole of this increase is due to Rhizosolenia. The largest plankton 

 accumulations are adapted to the Northern, and partly to the Central, 

 Caspian— mainly on the western side, where a discharge current enriches the 

 water with plant food carried down by the Volga (Figs. 278 and 279). 

 The main mass of the Caspian phytoplankton is adapted to the upper 



