where 



15 

 10-* 



2 



100 



weight of bacterial biomass, jUg C/1; 

 total number of bacterial per 1 of 



water; 

 percentage of dry residue from raw 



biomass; 

 weight of 1 ^m' of raw biomass of 



bacteria (/ig) with specific weight 



equal to unity; 

 average biovolume of bacterial 



mass, jum'; 

 carbon content from dry biomass; 

 raw biomass, %. 



CO, dark assimilation by bacteria was assessed by 

 radioisotopic method (Romanenko, 1964; Romanenko & 

 Kuznetsov, 1974). To determine dark CO, assimilation by 

 bacteria, the C'^ sodium carbonate (Na, "CO,; 20.4 x 10'~) was 

 added to 100 ml of seawater. Water samples were incubated in 

 the dark for 1-3 days at sea surface temperatures. After 

 incubation, water samples were fixed with 40% formaldehyde 

 solution and filtered (pore diameter 0.45 mm). Filters were 

 exposed to 0. 1 N HCl vapors and radioactivity of bacteria on 

 filter was measured by liquid scintillation. Rates were calculated 

 by the formula 



c = *^-" ^ '■ 



Rxt 



where 



C, 



r 



R 



t 



CO, assimilation by bacteria, ^g C/1; 

 carbonates concentration (mg/1), 



determined by directly titration (0.1 



N HCl in the presence of methyl 



red indicator); 

 radioactivity of bacteria on filters 



(dpm); 

 radioactivity of isotope Na,"C03 



used in experiment, dpm; 

 incubation time. 



Results and Discussion 



Total Number. Bioma.^s. and Dark CO. Assimilaiion by 

 Bacteria in the Bering Sea 



Results are shown in Table 1 . The growth, distribution, 

 and activity of microflora varied both in time and locality in the 

 Bering Sea. Bacterioplankton numbers, biomass, and activity 

 in 1988 was generally higher than in the summers of 1981 and 

 1984(Tsybant'r«/.. 1987). In 1981 and 1984 the total number 

 of bacteria fluctuated between 19-2,799 and 

 73-380 X 10' cells/ml. On average, the population and 

 biomass of bacteria in 1988 amounted to 671 x 10' cells/inland 

 15.09 mg C/m', respectively. These values were almost twice 

 as high as those found in 1981 and 1984. 



Comparing this data to other regions of the World Ocean, 

 for instance, the total number of bacteria in the Barents Sea 

 ranged between 10 and 500 x 10' cells/ml (Baitaz & Baitaz, 

 1986); in the Scotia Sea, populations of bacterioplankton 

 reached 200-500 x 10' cells/ml (Azam et al.. 1981); in the 

 Arctic Ocean, concentrations of bacterial population varied 



TABLE 1 



Numbers, biomass and dark CO, assimilation by bacteria in the 

 Bering Sea water, summer 1988. 



Sea area 



Total bacterial Bacterial biomass 



numbers (/jgC/l) 



(10-' cells/ml) 



Dark CO, 



assimilation 



by bacteria, 



/igC/l/d 



from 40 to 440 x 10' cells/ml (Dahlback et al.. 1982); in the 

 region of Antarctic convergence, numbers varied from 200 to 

 350 X 10' cells/ml (Hanson et al.. 1983); and in oligotrophic 

 areas of the Pacific, the density of bactenal population varied 

 between 10' and 10"' cells/ml (Seki, 1986). 



Variations in the growth, number, and distribution of 

 microflora in the Bering Sea with its complex mixture of water 

 masses are specific to various areas in the basin. The maximum 

 density of bacterial population was found on the shallow shelf 

 of the Chirikov basin (Table 1). The total number and biomass 

 of bacteria here were 2.7 times those in 1981. Relatively high 

 bacterial population (1,755 x 10' cells/ml) and biomass 

 (39.5 mg C/m') in this region were recorded at Station 106, 

 located near St. Lawrence Island. In the northern part of the 

 Chirikov basin, numbers and biomass of microflora were 

 somewhat lower. Thus, at Station 96, the concentration of 

 bacterioplankton was lowest, on average 583 x 10' cells/ml. 

 Nevertheless, even though total bacterial numbers were 

 comparatively low, the microflora activities were high. Daily 

 dark CO, assimilation reached on average 1.42/igC/l. At other 

 stations the bacterial activity was much lower, suggesting 

 some bacterial cells were dormant. 



In the shallow northern part of the sea, a fairiy uniform 

 distribution of bacterioplankton and reasonably steady level of 

 acti\'ities occurred across the system. The surface microlayer 

 showed relatively low concentrations of bacterioplankton, but 

 bacterial activities were higher than in underiying waters. The 

 bacterial dark CO, assimilation in the surface microlayer was, 

 on average. I 2 1 pg C/1 daily, which corresponded to the level 

 of mesotrophic waters. 



56 



