Seas (Fig. 4). The number of dead planktonic organisms at the 

 East and South Polygons changed from 33.100 to 

 93,400 ind/nr, and the average was 56,900 ind/nr. This 

 feature corresponded with the total amount (3.3%) of 

 zooplankton. Estimated biomass showed a similar percentage 

 of the necrozooplankton. 



Chukchi Sea 



(b d) * ® © 



Bering Sea 



Fig. 4. Percentage of necrozooplankton in total zooplankton community in 

 the northern Bering and southern Chukchi Seas. 



The waters of the northwestern part of the Bering Sea 

 differed widely in these characteristics. If, at Station 7, the 

 farthest from the edge of the shelf, readings of both the absolute 

 and related indices coincided with those considered at the East 

 and South Polygons, then theircharacteristics increased several 

 times in those stations situated over the slope of the continental 

 shelf. At Station 11, the number and biomass of 

 necrozooplankton reached the highest value during the period 

 of investigation, to reach 196,300 ind/m- and 1,534 mg/m-, 

 respectively, the percentage of dead organisms to total number 

 of zooplankton was 20%. 



The frontal zone, which covered water masses composed 

 of deep water and shelf water and extended over the 1 00-meter 

 isobath (Stations 9, 15; Coachman, 1990), differed by low 

 levels of absolute and high levels of relative values of 

 necrozooplankton. At the same time, when the number of dead 

 organisms was not higher than 2 1 ,600 ind/nr, their proportion 

 in the community was 8%. 



Extreme conditions inhabited by zooplankton communities 

 in the cold water masses of the central shelf region ( including 

 Stations 18, 19, 22, 35, and 36) determined levels of dead 

 organisms. Thus, the number of necrozooplankton, as a result 



of the total lack of pelagial community, was comparatively 

 low-to-medium, 12,100 ind/m-, though about 7% of the whole 

 community, both by number and by biomass, were not living. 



The content of dead organisms in zooplankton communities 

 in the waters of the Gulf of Anadyr, Chirikov basin, Bering Sea, 

 and the Chukchi Sea Shelf were negligible and, except in a few 

 individual cases, didn't exceed 5% of number or biomass. 

 Abnormally high mortality rates, with strong evidence of 

 desiccation phenomenon, were seen at Station 96 in the western 

 part of the Chirikov basin. The number and biomass of 

 necrozooplankton at this station were 22 and 19%, respectively. 

 Some increase in mortality of plankton organisms was found in 

 the Gulf of Anadyr, at Stations 24 and 4 1 . 



The lowest mean levels of indices were found in the shelf 

 waters of the Chukchi Sea. Necrozooplankton in this region 

 averaged 9,500 ind/m-, and biomass, 88 mg/m- ( 1 .7 and 1 .6%, 

 respectively). Lower total background indices were found at 

 the central meridional section line (Stations 50, 55, and 69). 

 The average number of dead organisms at these stations was 

 21,800 ind/m- (4% ), and mean biomass was 223 mg/m- (4%). 



The taxonomic composition of necrozooplankton in 

 epipelagic waters of the Bering and Chukchi Seas include the 

 major types of planktonic organisms (Table 1 ) and reflect the 

 regularity of change of the types of live mesozooplankton in the 

 study regions. A majority of the dead organisms ( approximately 

 80%) belong to two types of copepods, Oithona similis and 

 Preudocaloims minutus (Fig. 5). The correlation of the number 



% 



///// Percent of Oithona similis 



Percent of Preiidoccilonus minutus 



Areas 



I - deep water southwestern area 



and Continental Shelf 



of the Bering Sea: 

 II - northern shelf area 



of the Bering Sea; 

 III - southern area of the Chukchi Sea. 



Fig. 5. Dominating types of necrozooplankton composition. 



175 



