TABLE 1 



Average rates of biomass contents (%) of dead organisms in populations of dominant species of zooplankton 

 in the Bering and Chukchi Seas. [( ) - data gathered at one station of the area.] 



of dead to living species types depends upon the degree of 

 development of the population. In the upper deep-water 

 regions in the Bering Sea, as well as the outer zone of the 

 northeastern shelf, the size of the dead population of O. similis 

 averaged 80% of the total number of necrozooplankton, while 

 the size of the dead population of P. ininutiis was only 6%. The 

 shoal waters in the shelf of the Bering Sea contained 49% and 

 27%, respectively, of these dead organism types. In the 

 Chukchi Sea, dead populations of P. mimitiis predominated 

 (61%). A number of other major types, such as Eucalanus 

 bungii (juveniles), Microcalanus pygmaeus. Metridia pacifica. 

 and Acartia sp., also contributed significantly to the fomiation 

 of zooplankton accumulation; in higher latitudes, Onacea 

 borealis made up about 10% of the total number. At the 

 stations listed above, the structure of the necrozooplankton was 

 destroyed and dominance was gained from types whose dead 

 species were rarely found. In the western part of the Chirikov 

 basin (Station 96), 73% of the dead portion of organisms were 

 echinoderm larva; in the Gulf of Anadyr (Station 27), 36% 

 were dead specimens of the neritic copepod. Acartia tiimida. 

 Data collected on the death of specific populations of 

 marine organisms will enable understanding of certain features 

 of ecological relations in the study areas of the Bering and 

 Chukchi Seas. These data are connected with the inass 

 destruction as a result of the influence by negative external 

 factors. In our opinion, the population condition of major types 

 in the deep-water regions of the Bering Sea was favorable. 

 There was a comparatively low population of dead organisms 

 found in these areas, 5% on the average. The exception was a 

 number of neretic copepods./lcnrrfV/ sp., that constituted about 

 half of the dead organisms in the biomass. High mortality was 

 found in O. Iwrealis and O. similis — 23% and 30%, respectively. 

 Similar situations to the two species noted were found in the 

 middle front zone of the northwestern shelf of the Bering Sea 

 ( 100 m). The western part of the Chirikov and the Gulf of 

 Anadyr was the area of highest mortality. The high content of 



dead organisms belonged to populations such as Eucalanus 

 bungii. Microcalanus pygnwnus. Centropages memurrichi. 

 Acartic tumida, and Frilillaria borealis. At Station 96, the 

 dead population was 76% E. nordmanni. 43% O. similis. 73% 

 O. borealis. and 95% echinoderm larvae. Populations of major 

 oceanic types were affected by the strong influence of 

 illumination in the total area northern shelf of the Bering Sea. 

 The high mortality level, up to 14% inareasof shelf water 

 mass (central shelf area and eastern part of the Chirikov basin), 

 is a characteristic feature of populations of P. minutus. The 

 shallow shelf of the Chukchi Sea had low averages of 

 necrozooplankton. The only high mortality rates found in this 

 area were for Metridia pacifica. 87% (Station 55); Eucalanus 

 buugii. 50% (Station 55); and Oithona similis. 17% 

 (Station 45). 



Conclusions 



During the investigation, the number and biomass of dead 

 organisms varied widely, from to 7.500 ind/m- and 

 100.3 nig/m\ respectively. The content of zooplankton 

 communities reached 44.3% in number and 46.9% in biomass. 

 The nature of the vertical distribution of necrozooplankton 

 depended on the position of the stations. At deep-water stations 

 (more than 2,500 m), dead remains of organisms accumulated, 

 through the process of biosedimentation; in colder deep layers, 

 these remains were from animals that died in the upper warm 

 layer, the layer of highest concentration of living organisms. 

 At the majority of the stations situated on the outer shelf of the 

 eastern and northwestern Bering Sea, necrozooplankton 

 concentrated in the horizons where mortality occurred. The 

 reasons for this may be low biosedimentational rates or the high 

 intensity of organism death. In the stratified waters of the 

 shallow shelf regions of the Bering and Chukchi Seas, the ratio 

 of dead animals was related to water mass boundaries, due to 

 the absence of near-bottom horizons. Highest levels of 



176 



