produced (Pg) should be added to the primary production of the community 

 (P ) to calculate the total energy "input" of the ecosystem (Sorokin, 

 1971a, 1973c). 



The nutrient value of marine microflora for aquatic animals is 

 estimated by long-term cultivation of these animals, using a suspension 

 of bacteria as food or by quantitative counting of microflora in the 

 contents of various segments of the gut (Zhukova, 1954). However, the 

 basic data on the nutrition of marine invertebrate microflora under 

 conditions which are close to natural have been obtained in short-term 

 experiments using bacteria labeled with ^^C or ■^'^P (Marshall, Orr, 1955; 

 Sorokin, 1966, 1968). The use of -^^P can generate only qualitative 

 data, since the labeled organic phosphorus in the bacteria is rapidly 

 involved into the metabolism and is excreted from the organism of the 

 consumer in the form of inorganic phosphate. The use of ^^C allows 

 quantitative data to be generated, since ^^C is included into the carbon 

 chains of the organic matter and is thus much more slowly excreted. The 

 radiocarbon method can be used to determine the significance of bacteria 

 in the spectrum of nutrition, to determine the magnitude of food 

 rations, the assi mi lability of food by consumers, the rates of 

 filtration and the dependence of intensity of nutrition upon the 

 concentration of food (Sorokin, 1971a, b,c). 



The results of measurement of biomass, production, and metabolism 

 of a microbial community are expressed in calories under 1 m'^ per day. 

 A coefficient of 0.92 is used to convert a unit of wet biomass of 

 bacteria to calories, considering that the content of carbon in 

 microbial biomass is 10% (Troitskiy, Sorokin, 1967). 



2.2 Number, Biomass and Production of PI anktonic Microflora in 

 Communities with Various Levels of Productivity 



In the overwhelming majority of works on marine microbiology, data 

 were presented on the numbers of saprophytic bacteria growing in protein 

 media, which gave not the slightest idea of the total microbial 

 population. The available data, obtained by direct counting and by the 

 use of ATP, show that the population and biomass of the microbes in the 

 euphotic zone of unpolluted marine basins averages 1.5-2 times less than 

 in fresh bodies of water with the same trophic level. This is 

 apparently the result of the utilization by the microflora in the fresh 

 waters of significant quantities of allochthonous organic matter 

 arriving from the land. 



Summary data on the mean population and biomass of planktonic 

 microflora in various biotopes shows that in the euphotic zone of the 

 eutrophic sea basins--estuaries, shallow bays, lagoons, and also in the 

 highly productive zones of upwelling, where the primary production 

 exceeds 1 g C/m^ per day, the total population of bacteria is 1.5-5 

 million cl/ml, the biomass is 0.5-3 g/m-^ (Melberga, 1968; Karapetyan, 

 1971; Sorokin, 1971a, c, 1973a; Sorokin et al . , 1975; Fedorov, Sorokin, 

 1975). Here, as in most marine biotopes, sporeless rod- type bacteria 

 and micrococci predominate, measuring 0.3-1 x 1-2.5 um. In eutrophic 

 basins the mean volume of microbial cells is 2 to 4 times greater than 

 in oligotrophic basins--averaging 0.8-1.5 ym"^. 



260 



