Fig. 2. Areas ot absence ( 1 ) and presence (2 ) of aggregations olorganisms in 

 the neuston layer. Isoline marks the boundary of equal distribution of 

 organisms in the near surface microhorizons. 



On characterizing the qualitative composition of 

 zooneuston represented by 47 taxa, it should be noted that the 

 greatest species diversity was found in the Chukchi Sea and 

 Chirikov Gulf (up to 38 taxa). The smallest amount of species 

 (18) was discovered in East Polygon. 



The dominating group of organisms in all regions 

 investigated in the Bering and Chukchi Seas was made up of 

 copepods (Fig. 4). Among the 14 species of copepods. a 

 significant part was played by three: Oithona similis, Acartia 

 longireniis. and Pseudocalamts niinutiis. During the summer 

 of 1 984, a similar pattern was observed, but the number of cold- 

 loving Pseudocakmus organisms was more abundant than 

 Acartiadht neritic, epipelagic species). But this was due to the 

 slight heating of surface waters in comparison to that during the 

 period of investigation. In the neuston layer, the copepods 

 were represented by all stages of development, while the ratio 

 of different age groups according to regions was about the 

 same. More than half of the number of copepods pertained to 

 earlier stages of ontogenesis (eggs, nauplii), which gives 

 evidence for their high reproductive activity corresponding to 

 the biological summer period. 



The wide shelf in the northeast part of the Bering Sea and 

 slight depths in the Chukchi Sea maintain favorable conditions 

 for the existence of bottom fauna with bivalve mollusks, 

 echinoderms, polychaetes, etc., predominating. Their larvae 



CHUKCHI 

 PENINSULA 





Fig. 3. Abundance ( Ig number/m") of zooneuston in regions investigated in 

 the Bering and Chukchi Seas. 1^ 3.4; 2—3.4-3.6; 3—3.6-3.8; 

 4— 3.8-4.0; 5—4.0^.2; 6—4.2^.4; 7-^.4-^.6; 8—4.6-4.8; 

 9—4.8-5.0; 10— > 5.0. 



make up a significant part of the total number of zooneuston in 

 the Chirikov Gulf (larvae of marine urchins, 24%; bivalve 

 mollusks, 20%; and polychaetes, 29%). In comparing the 

 Chukchi Sea to Chirikov Gulf, the role of bottom invertebrate 

 was slightly less; they make up to 30% (larvae of bivalve 

 mollusks, 26%; cirripeds, 3%; and ophiurans, 1 %). In the rest 

 of the regions of the Bering Sea, the role of sea bottom larvae 

 is insignificant. Even in East Polygon which is partly located 

 in the neritic zone over small depths, they are represented by 

 polychaetes making up only tenths of a fraction of 

 specimens/m'. Probably, larvae from these regions are carried 

 out by currents flowing from the south to the north and 

 northwest. 



Thus, on the average, copepods in the neuston layer 

 of the Bering Sea made up 77%; larvae of bottom 

 invertebrates, 12%; hyperiids, 4%; tunicates, 3%; and shell 

 infusorians, 2%. 



Many taxa are common for the fauna of zooneuston of the 

 regions investigated. When using the method of Preston 

 ( 1962), it has been established that the fauna of zooneuston of 

 the Chukchi Sea and Chirikov Gulf are identical. The index 

 (coefficient) of differences is minimum, while the high similarity 

 index gives evidence, first, to similar conditions of existence, 

 and second, to the exchange of fauna between these regions 

 (Table 9). 



189 



