494 Marine Microbiology 



known. All we know so far about the rate of reproduction of 

 bacteria is based on experiments with laboratory cultures. Onl)' 

 recently we have worked out a method for estimating the time 

 required for the division of a bacterial cell under natural con- 

 ditions. It is true that it is not completely flawless, but at present, 

 it is better than the methods used in hydrobiology for the quan- 

 titative estimates of the production of animal and plant organisms. 



It is now possible to determine the value for the coefficient, 

 expressing the ratio of the production of microorganisms to their 

 biomass (P:B) in the sea. Due to the differences in the condi- 

 tions existing in various parts of seas and oceans and also to fluc- 

 tuations in these conditions with the season of the year in the 

 same localities, it is necessary to carry out systematic studies 

 of the rate of reproduction of microorganisms in the coastal and 

 open areas of the seas and oceans. Such studies will clarify the 

 process of "turnover" of living matter in the form of microbial 

 cells throughout the water and on the bottom of seas and oceans 

 within an annual cycle or several years, and find out the amount 

 of mineralization of dead organic matter and of utilization of 

 microorganisms by aquatic animals. 



In this connection it is extremely important to ensure the 

 development of one of the important branches in the hydro- 

 biological sectors of marine microbiology, namely, that of 

 determining the part played by microorganisms as a direct link 

 in the food chains in the sea. Studies in this field have been 

 conducted in the field only recently. After it was demonstrated 

 that growth and reproduction of a number of aquatic animals 

 can take place exclusively on a microbial diet, a logical question 

 was raised, whether microorganisms are used as food and, if so, 

 to what extent in natural liabitats in which various food material 

 exists. 



For this purpose investigations were carried out imder 

 natural conditions with some representatives of the bottom 

 fauna in the Caspian Sea. With the aid of specially developed 

 methods it has been shown, for example, that about half the 

 microbial cells found in mud are digested by Nereis succinea 

 during the passage of the mud through the alimentary canal of 

 that worm. This case is oflered as an example of a food chain. 



