590 



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



25 m layer of water. There is every reason to think that phytoplankton caught 

 in deeper layers is in a moribund state. As a result, in late autumn and winter, 

 with the decrease in production on the surface, the maximum phytoplankton 

 may move to deeper layers (Fig. 280). In the Central Caspian Rhizosolenia 



Fig. 278. Total phytoplankton in autumn 1935 

 (Usachev). 



was still absent in 1934, and Exuviella was the dominant form. With the 

 appearance and prompt domination of Rhizosolenia, Exuviella had to cede 

 its place (Fig. 281). Changes in the total phytoplankton biomass and in the 

 relationship between Exuviella and Rhizosolenia in 1934 to 1936 are given in 

 Table 243. 

 The general quantitative distribution of surface phytoplankton throughout 



