Thus, the shallow northern part of the Bering Sea exhibited 

 comparatively high total numbers and biomass and moderate 

 activities of microflora and an even distribution of bacterial 

 numbers across water types. From rates of bacterial activities 

 and numbers, the microbiocenoses corresponded to mesotrophic 

 modes. 



In contrast to the Chirikov basin, low microbiocenoses 

 growth and absolutely different distribution of bacterioplankton 

 were observed in the south Bering Sea (South Polygon, see 

 Frontispiece). Total numbers and biomass of bacteria in this 

 region comprised, on average, 479 x 10' cells/ml and 

 10.78 mg C/m'. This data is similar to those obtained in 198 1 

 (Tsyban et al., 1987). The moderate concentration of total 

 bacteria and their biomass can be attributed to microorganisms 

 being grazed by protozoa and microzooplankton. According to 

 Mamae va ( 1 987 ), the evolutionary stage and metabolic activities 

 of these grazers in the Bering Sea may be high. 



The variation in bacterioplankton distribution was clearly 

 seen at South Polygon. The highest density of bacterial 

 numbers (averaging 698 x 10' cells/ml) was found at Station 

 1 08; the lowest density (1 06 x 10' cells/ml ) occurred at Station 



111. Three bacterial maxima were found in the water column. 

 The first maximum occurred in the surface microlayer. The 

 total number and biomass of bacteria in this layer averaged 

 1,027 X 10' cells/ml and 23.32 mg C/m', respectively, which 

 was 1 .4 times that in the mixed layer. Microflora nourished in 

 the surface microlayer because of various physical-chemical 

 factors (e.g., particulate aggregates, nutrients, fatty acids and 

 lipids) (Babenzien & Schwartz, 1970), from water-air 

 interaction and from high surface tension. Japanese researchers 

 (Saijo et al., 1974) have demonstrated that concentration of 

 dissolved and suspended organic substances in the surface 

 layer is 2-9 times that in the underlying layer. 



The second maximum of bacteria was found in the surface 

 mixed layer (0.5—15 m), a zone of high phytoplankton biomass 

 and photosynthesis. According to Fogg ( 1 97 1 ) and Kudryatsev 

 ( 1973), the excretion of organic matter may constitute more 

 than 20% of the total carbon produced by photosynthesis. The 

 dissolved organic substances that are released by phytoplankton 

 and other biota may be very important for bacterial growth. 



The results showed that maximum density of bacterial 

 numbers (942 x 10' cells/ml) and high biomass 

 (21.18 mg C/m') occurred at Station 1 08, and minimum numbers 

 (427 X 10' cells/ml ) and low biomass (9.62 mg C/m') at Station 



1 12. Below the euphotic zone, total number of bacteria and 

 their biomass gradually declined. 



The third layer of high concentration of bacterioplankton 

 occurred in the near bottom layers of water column. Thus, at 

 Stations 110 and 111, near bottom bacterial population and 

 biomass ranged from 510 to 761 x 10' cells/ml and 1 1.5 to 

 17. 1 mg C/m', respectively. 



Bacterioplankton activities also showed several maxima 

 in the water column. In the euphotic zone of the south Bering 

 Sea, bacteria appeared twice as active as those in the shallow 

 northern part. Daily dark CO, assimilation by bacteria at South 

 Polygon averaged 1.98 mg C/1. which is similar to bacterial 

 activities in mesotrophic waters. 



Bacterioplankton activities in euphotic zone also correlated 

 with the distribution of bacterial numbers. The highest dark 

 CO, assimilation by bacteria occurred at Stations 108 and 1 10, 

 where daily values averaged 2.43 and 2.73 /ig C/1, respectively. 

 The lowest rate, 0.95 fig C/l/d, was at Station 109. 

 Bacterioplankton activities declined with depth below the 

 mixed layer in the south Bering Sea. However, between 150 

 and 2,000 m, relatively high activity of microflora was found, 

 coupled with high dark CO, assimilation by bacteria that 

 reached 2.0-3.0 /ig C/l/d. Thus, south Bering Sea possessed 

 high bacterial activity, particularly in the euphotic zone, and 

 low density of bacteria throughout water column. In this 

 region, bacterial distribution showed considerable variation. 

 Microbiocenoses also varied vertically across water column 

 boundaries. 



Another studied region of the sea was the East Polygon 

 (see Frontispiece) located on the eastern slope. At this site, 

 depth of the water column ranged from 135 to 3,000 m and the 

 water column possessed a mixture of water types, dissolved O, 

 saturation, and temperature. All these factors undoubtedly 

 intluenced the formation and structure of microbiocenoses and 

 distribution of bacteria. Results showed relatively low activities, 

 similar to results reported earlier at this site in 1981 (Tsyban 

 etai. 1987). 



Total number and biomass of bacteria at East Polygon 

 varied considerably (Table 1). Values averaged approximately 

 1 .4 times higher than those in the south Bering Sea. Maximum 

 bacterial population (1,302 x 10' cells/ml) and high bacterial 

 biomass (29.34 mg C/m') occurred at the shallow- water Station 

 5, and minimum bacterial (873 x 10' cells/ml) and low bacterial 

 biomass ( 19.65 mg C/m') occurred at the deep-water Station 3, 

 where bacterial activities were high. The highest rates of dark 

 CO, assimilation by bacteria occurred here, averaging 

 2.94 /ig C/1, approximately 5 times higher than those measured 

 at Stations 4 and 5. 



Bacterioplankton in the eastern region declined from the 

 surface microlayer to the bottom. Maximum numbers 

 (2,174 x 10' cells/ml) occurred at Station 4 where 

 microbiocenoses showed a maximum stage of development in 

 euphotic zone. The number and biomass of bacteria at East 

 Polygon averaged 1,183 x 10' cells/ml and 26.62 mg C/m', 

 respectively. Below the euphotic zone, bacteria and their 

 biomass declined to their lowest values ( 103 x 10' cells/ml and 

 4.6 mg C/m') in near-bottom waters of 2, 700-3,000 m. Although 

 microflora activities showed little variation with depth, dark 

 assimilation of CO, by bacteria increased from surface layers 

 to the bottom at Stations 2, 4, and 5. At Station 1 , maximum 

 bacterial activity occurred in surface waters. Thus, the eastern 

 Bering Sea possessed relatively high numbers, biomass, and 

 activities of bacterioplankton in the surface microlayer and 

 euphotic zone, but values tended to decline with depth. 



Microbiocenoses in the central basin and in the Gulf of 

 Anadyr exhibit a position between northern and southern 

 regions. The central basin is relatively shallow (45-145 m), 

 with a sharp thermocline (between 25 and 45 m, temperatures 

 ranging from 6.0 to 1 .0°C at Station 9) even though dissolved 

 O, saturation remained constant with depth. 



57 



