Chapter 65 



On the Quantitative Significance of 



Microorganisms in Nutrition of 



Aquatic Invertebrates 



A. I. Zhukova 



jl\ rather large number of works have been dedicated to the 

 study of the question under consideration. It was repeatedly ob- 

 served that zooplankton are concentrated where microorganisms 

 are abundant, the number of the latter being reduced on account 

 of consumption (11, 16, 20, 28). The absence of microorganisms 

 in the environment affects the normal development of animals 

 (2, 17). Numerous experiments carried out by Gayevskaya (4) 

 and Rodina (23) proved convincingly that microorganisms form 

 a necessary component of the nutriment of aquatic invertebrate 

 animals. Vegetable remains, devoid of bacterial cells, lose their 

 nutrient value. On the other hand, pure bacterial cultures can 

 serve as the sole source of nutriment of aquatic animals (1,7, 18, 

 25, 26, 27, 31). 



However, a number of authors suggest that the nutrient 

 value of microbial cells cannot be important because of the small 

 size of microorganisms and their low concentration in natural 

 conditions (3, 12). But there are no good reasons for that sug- 

 gestion. 



Microorganisms occur in the seas and oceans in great quan- 

 tity and despite the minute volume of the cells, their biological 

 mass is considerable. As a rule, the number of bacteria (by direct 

 microscopic counting) per ml of sea water amounts to tens and 

 hundreds of thousands, and the biological mass up to some mg 

 per cubic meter (Table 1). In tlie surface strata of sediment de- 

 posits the number of microbial cells is still greater, tlieir biologi- 

 cal mass reaching, in indi\'idual cases, up to some tens of grams 

 per square meter. Under most favourable conditions tlie fission 



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