Kcal/m^ day 



^:^ 



^^ 



n 



^71 



Fig. 3. Net (P„l and actual V{^J production of the plankton communities in 

 June 1981 and July 1984. 



respectively. In the waters of the Anadyr Current, the level of 

 the net production in summer increased as compared with 

 spring values by a factor of 1 .5 and that of the actual production 

 by a factor of two. 



Intensification ofdestruction in summer adversely affected 

 the efficiency of production of the autotrophic link (Fig. 4). 

 After the changeover of the community populating the epipelagic 

 region of the southwestern deep-water area of the Bering Sea 

 from the spring status to the summer one, the levels of the index 

 K(3p) decreased by a factor of two to five, which is indicative 

 of a decline in the trophic character of water, from the eutrophic 

 levelinJune 1981 tothemesotrophiconeinJuly 1984. In shelf 

 water masses, no changes in the level of trophicity occurred, 

 since an increase in the destruction was compensated by an 

 increase in primary production. In the waters of the Anadyr 

 Current, in spite of an increase in the values of the coefficient 

 on average by a factor of three, they remained at a high level, 

 which characterizes the waters of this region as hypertrophic. 



It should be noted that during both the spring and summer 

 seasons of the investigations, the energy tlux through the 

 detrital food chain played an important role primarily in the 

 functions of the plankton community populating the epipelagic 

 region of the deep-water area of the Bering Sea (Fig. 5 ). The 

 levels of the values of p, which characterized the energy 

 fraction of assimilated dead organic matter in the total volume 

 of the energy assimilated by heterotrophic elements, were 

 maximum at later stages of seasonal development of the 

 community (at the South and East Polygons). 



The trend of the seasonal succession of the Bering Sea 

 plankton communities, accompanied by a change in the structure 



June 1981 

 July 1984 

 -boundary of levels of 

 trophit uhiiiatler of 



Soutfiem Nonhem 



North 



Polygons, pans 

 are^s 



Fig. 4. Efficiency of production Pp/D„ of the plankton communities in June 

 1981 and July 1 984. P^,- production ofphytoplankton;D„- heterotrophic 

 destruction of the community. 



~~x July 1984 

 Polygons, parts 



Soulhem Northern part 

 ^ North 1 



Fig. 5. Relations between level of energy assimilated by bacteria and other 

 detritophages and level of energy of dead organic matter and 

 phytoplankton assimilated by all heterotrophs of the plankton 

 communities in June 1981 and July 1984. 



and parameters of the processes of functioning, also included 

 a reconstruction of trophic interrelations between the elements 

 of the communities in the quantitative respect. 



A decrease in the supplies of "primary food" in the 

 epipelagic region of the deep-water in the summer season has 

 led to intensification of preying of euryphages on others 

 (Fig. 6). The fraction of animal food became predominant in 

 the overall ration, of zooplankton elements in contrast to their 

 spring ration, in which vegetable food predominated. A 

 contrary tendency was observed at the North Polygon 

 where the fraction of phytoplankton in the 

 ration of zooplankton increased in a changeover to the summer 

 season. 



In conditions of a summer deficiency of easily assimilated 

 food, observed in the southwestern Bering Sea, the degree of 

 meeting nutritional requirements (5) of micro- and 

 mesozooplankton decreased appreciably as compared with the 

 levels calculated for the spring season (Fig. 7). The real 

 specific production of these elements {t,) acquired negative 

 values, which was indicative of the appearance of a tendency 

 towards a decrease in their biomass (Fig. 8). At the same time, 

 trophic tension appeared in June in the elements of 

 phyto- and bacterioplankton and, vice versa, disappeared in 

 July, and it became possible for the elements to increase their 

 biomass. 



207 



