598 



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



A remarkable coincidence between quantitative development of zoo- 

 plankton and of bacterial flora is evident from the data gathered by Kusmor- 

 skayr (1938). On the cross section Volga delta-Mangistau maximum numbers 

 of micro-organisms and zooplankton are found together, falling exactly within 

 the area of confluence of river and sea waters (Fig. 283). The same coin- 

 cidence was recorded for Mertvyi Kultuk and Kaidak. It might reflect both 



MICRO- 

 ORGANISMS 



160000- 



140000- 



120000- 



WO 000 



80000 



60000 



40000 



20000 

 10000 



ZOOPLANKTON 



70 



NUMBER OF MICRO-ORGANISMS (COLONIES) 

 ZOOPLANKTON BIOMASS mg/m 



60 



50 



ч 



30 



20 



10 



Fig. 283. Quantitative distribution of bacteria and zooplankton along the cross 

 section Volga delta-Mangistau (Kusmorskaya). 



an indirect and a direct dependence of zooplankton on micro-organisms. 

 Micro-organisms decompose organic matter and enrich the waters with 

 plant food. The development of phytoplankton biomass is due to it ; this in its 

 turn serves as food for zooplankton. Moreover plankton Copepoda feed 

 directly on micro-organisms, and bacterial flora is used to feed zooplankton. 

 Taking Knipovitch's value of 793 km 3 as the volume of the Northern 

 Caspian, Kusmorskaya calculated the absolute amounts of zooplankton bio- 

 mass and has obtained indices for the whole Northern Caspian as given in 

 Table 246. 



Zooplankton biomass of Central and Southern Caspian. Quantitative data on 

 Central and Southern Caspian zooplankton are contained in the works of 

 M. Idelson (1941) and V. Jashnov (1938, 1939). According to Idelson the 

 largest zooplankton biomass is found in the to 100 m layer; below that it 

 decreases regularly with depth (Table 247). 



The relationship between separate groups changes simultaneously (Fig. 

 284). Copepoda are the dominant groups in the to 100 m layer, comprising 

 96 to 99 per cent of the total biomass in the Central Caspian and 71 to 95 per 



