with maximal biomass equal to or greater than 2,000 g m- 

 (Stations55, 69; Figs. 5,6). At most ofthe stations (48, 55, 57, 

 60, and others), Macoma biomass by far exceeds that of other 

 organisms of the biocenosis, equaling 60-70% of the total 

 biomass. Alongside Macoma, this biocenosis is also dominated 

 by ark shells (Leionucula inflala and Yoldia amygdala), 

 polychaetes (Nepthys caeca. Maldane sarsi, Nicomache 

 lumbricalis, and Lumhrinaris sp.), ophiurae (Ophiuni sarsi), 

 and amphipods (Ampelisca spp.). 



170 



165 



Chukchi Sea 



(1068)'°° 



Bering Sea 



Fig. 6. Distribution oi bcnthic biomass (g m -) at stations in the northeastern 

 part of the Chukchi Sea and the northern part of the Bering Sea 

 (symbols as in Fig. 4). 



In the western part ofthe region, the Macoma biocenosis 

 borders the Leionucula inflata biocenosis at a depth of 

 44-50 m. Leionucula is obviously dominant here, as its 

 biomass is 60-80% ofthe total biomass of biocenosis organisms. 

 Average benthic biomass in the Leionucula biocenosis is 

 647 g m -. 



Closer to the Soviet coastline, there is a diverse biocenosis 

 of ark shells {Mya truncata). The only bottom sample at 

 Station 44 (entrapment area, 0.1 m') only penetrated to a 

 shallow depth and cut off eight siphons of the large, deep- 

 dwelling moUusks. 



South from the Macoma biocenosis, closer to Bering 

 Strait, there is a pronounced mosaic character of benthic 

 organisms. Different bottom samples show domination by 

 various groups, including ascidiae, polychaetes, ark shells, 

 holothuria, and sipunculida. 



In the eastern part ofthe region, near the Alaska coastline, 

 at depths of 22-35 m, only an insufficient level of biocenosis 

 of Senipes groenkmdicus ark shells occurs, with an average 

 biomass of 228 g m -. The degree of domination by this species 

 is minimal in this biocenosis. Other stations were marked by 

 domination of polychaetes (Lumhrineris, Neoamphitrite, 

 Maldane. Nephtys. Cistenides, and Niomache), ark shells 

 (Leionucula, Nuculana, and Cyclocardia), numerous small 

 holothuriae {Myriotrochus), actiniae (Haliactis and Epiaciis), 

 and echiurids. 



Sessile benthic fauna was collected at Station 52 in 50 m 

 of water; the dominant species was Balanus crenatus, which 

 had a very high biomass (about 970 g m -; Fig. 6). In general, 

 we should note a striking difference between abundance of 

 benthos between the western and eastern parts of this region. In 

 the west, there is an influence ofthe Gulf of Anadyr, Bering Sea 

 Shelf waters, and waters of the Siberian shallows; in this 

 region, average benthic biomass equals 673 g m '. In the east, 

 there is an influence of depleted coastal waters of Alaska; 

 average benthic biomass equals only 315 g m- (even with a 

 relatively rich sample with Balanus), which is over two times 

 less than in the western part. 



Benthos at East and South Polygons 



At East and South Polygons, 13 samples were taken at 

 depths between 140 and 3,700 m; 8 of these samples were 

 collected with a bottom sampler. Most of the samples are 

 dominated by polychaetes ( usually from the family Maldanidae); 

 in abysses at 3,000 m, there is a domination by large monocelled 

 organisms (Komokiacea). Biomass at all stations is not large 

 and varies from 0.7 g m - (in abyss) to 14.4 g m"' (in sublittoral 

 regions); average biomass equals 7.5 g m -. 



Discussion 



Biogeographic Characteristics of Benthic Fauna ofthe Northern 

 Bering and Chukchi Seas 



In terms of biogeography. the investigated regions ofthe 

 Gulf of Anadyr, northern Bering Sea, and southeastern Chukchi 

 Sea have very few differences. There is an advantage for a few 

 species to dominate the faunal distributions in the region; 1 4 of 

 45 species that are dominant within each of these three regions 

 are common for all of the regions (Table I). Twelve of the 

 species can be found in two of the three regions. Only 19 

 species dominate in only one region. In all three regions, most 

 of the area is occupied by Macoma calcarea biocenosis. The 

 similarity of faunal characteristics between all three regions 

 can be explained by the fact that they are all situated in the arctic 

 area to the north of the Andriyashev Anadyr faunistic barrier 

 (Andriyashev, 1939); this fact determines the similarity of 

 most ofthe fauna. One can also note certain peculiarities within 

 each ofthe regions. In this respect, the most demonstrative one 

 is the southeastern area of the Chukchi Sea. The western part 

 of this region is dominated by boreal-arctic species of the 

 panarctic complex (Macoma calcarea. Leionucula inflata. 

 Yoldia amygdala. Haliactis arctica, and Epiactis levisi); a 

 narrower and relatively warmer eastern part is dominated by 



255 



