warm water boreal-arctic species (Serripes gwenlandicus. 

 Ampharete acutifrons, and Golfingia margariacea ) with limited 

 occurrence in the Arctic. 



Preclassification of the collected benthic material indicates 

 that some species that were found during the expedition had 

 never been known to inhabit the Chukchi Sea before (e.g., coat- 

 of-mail shells Hanleyella asiatica, some obelis shells, and 

 some species of echinodermata). 



Annual Variation in the Distribution of Benthic Organisms 



Although the number of samples collected is not large, it 

 allows us to compare the distribution of benthic organisms with 

 that of previous expeditions (Deriugin & Ivanov, 1937; 

 Makarov, 1937; Vinogradova. 1954; Neiman, 1963; Stoker, 

 1981; Grebmeier et ai. 1989). First of all, one can note that 

 there is a coincidence in the location of principal biocenoses 

 (i.e., Macoma calcarea, Echinarachnius parma. and sessile 

 species biocenoses in the straits). According to data from the 

 first quantitative benthos analyses in 1 933, in the central part of 

 the Gulf of Anadyr, there was a domination of Macoma 

 ca/carea (Makarov, 1937). Analysis of materials collected by 

 the Institute of Oceanology, USSR Academy of Sciences, on 

 the RA' Vityaz (1950-1952) provides a general confirmation 

 for these data (Vinogradova, 1954; Filatove & Barsanova, 

 1 964 ). We should also note that, in some works, an overemphasis 

 was given to Ophiura «7r.s/ (Vinogradova, 1 954; Zenkevitch & 

 Filatova. 1958), which entitled the biocenosis even though it 

 has a much lower biomass than that of ark shells (Vinogradova, 

 1 954). Obviously, it can be explained on the one hand by undue 

 attention being paid to the number of individuals collected in 

 a trawl ( a Sigsby trawl usually collects echinodermata, including 

 ephiurae that inhabit the surface of the sediments), and on the 

 other hand by density indices (Brotskaya& Zenkevitch, 1939) 

 used for definition of communities and groups instead of the 

 later accepted method of biocenosis definition based on biomass 

 (Petersen, 1911, 1913; Vorobyov, 1949). A number of works 

 based on the same material from the Gulf of Anadyr 

 (Vinogradov, 1954; Zenkevitch & Filatova, 1958; Filatova & 

 Barsanova, 1 964) locate biocenosis and groups with domination 

 of either Ophiura sarsi or Macoma calcarea in different 

 regions. It is interesting to note that the biomass characteristic 

 of Ophiura sarsi found in trawl catches in 1933 and 1950-52 

 in the central part of the Gulf of Anadyr was not confirmed by 

 the material that we collected in 1988. Ophiura sarsi was 

 traced only in 3 dredger samples out of 26; it constitutes from 

 2 to 10% of the total biomass of the sample. Only 3 out of 14 

 trawl samples collected in the Gulf of Anadyr at a mass scale 

 contained Ophiura sarsi. One can assume that there was a 

 decrease of habitation density of these ophiurae during the 

 recent 30-50 years, although to confirm this conclusion a more 

 detailed investigation is required. 



Alongside the above-mentioned biocenoses that had 

 inhabited the same region for many decades, new biocenoses 

 were found both in the regions that had never been investigated 

 before in the Chukchi Sea (e.g., Leionucula injlata biocenosis) 

 and in the well researched regions in the Gulf of Anadyr (e.g., 

 Nucukma lamellosa radiata biocenosis). The latter example 



requires a detailed study since it is of special importance for us 

 as a vivid example of how one biocenosis is replaced by 

 another. 



According to some authors, 28-38 years ago other 

 biocenoses were found on the site where today we ^mdNuculana 

 lamellosa radiata (Figs. 7A,B,C). For example, according to 

 the data collected by the RA' Vityaz in 1950-52 (Vinogradova, 

 1954; Filatova & Barsanova, 1958), Ophiura sarsi + Macoma 

 calcarea biocenosis was found (Fig. 7 A). According to a 

 1958-60 expedition, Neiman ( 1963) found there was a Yoldia 

 traciaeformis biocenosis wedged in between Ophiura sarsi 

 and Macoma calcarea biocenoses (Fig. 78). In addition, 

 Neiman (1963) found that the present site of the Nuculana 

 lamellosa radiata biocenosis was partially inhabited by the 

 three above-mentioned biocenoses in 1 958-60, while according 

 to the same data, biocenosis N. lamellosa radiata (probably 

 defined as N. pernula) was located in the form of two small 

 spots much farther to the south. The high degree of domination 

 of Nuculana in our samples (80-90% of the total biomass) and 

 high abundance values (up to 1 ,040-3,700 individuals m -) and 

 a low density oi Macoma (up to 10 individuals m-) leave no 

 doubt that N. lamellosa radiata biocenosis was defined correctly. 

 The earlier data mentioned above, as well as numerous old 

 shells of Macoma in our samples, testify to the fact that 

 earlier this region was inhabited by Macoma calcarea 

 biocenosis. 



It is interesting to note that according to Makarov ( 1937), 

 in 1933, the region south of St. Lawrence Island was 

 approximately the same region where, in 1958-1960, Neiman 

 ( 1 963 ) found Nuculana biocenosis with five stations dominated 

 by small Leda pemula (Nuculana lamellosa radiata). while at 

 the neighboring Station 6 (where there was a domination of 

 Macoma calcarea), the benthic community was dominated by 

 drilled shells of Leda pernula. One can assume that at least 

 from the 1930"s to the 1960"s, Nuculana biocenosis remained 

 in the same region and then started to expand, and by the late 

 1 970" s/early 1 980's (i.e., during the last decade), it reached the 

 region that we defined in 1988 where it replaced Macoma 

 calcarea biocenosis. This conclusion is supported by our data 

 where the age of Nuculana lamellosa radiata in our samples 

 does not exceed 7-8 years. The fact that the replacement of 

 Macoma by Nuculana occurred during the last decade is 

 confirmed by an extremely small number of empty Nuculana 

 shells that did not have enough time to pile up during the period 

 equal to the average lifetime of these moUusks. Most likely, the 

 northern boundary of Nuculana biocenosis that borders with 

 the Macoma biocenosis was moving to the northwest; every 

 year Nuculana biocenosis advanced into new areas, thus 

 replacing Macoma biocenosis (Fig. 7D). Data from the 47th 

 cruise of the RA' Akademik Korolev in 1984 indicated that the 

 northern border of Nuculana biocenosis had moved northwards 

 when compared to data collected in 1958-60 (Neiman, 1983; 

 Fig. 7C). 



In the Gulf of Anadyr, we observed the disappearance of 

 Cyclocardia crebricostata as described earlier by Neiman 

 ( 1 963 ). At present, this earlier biocenosis has been replaced by 

 biocenoses of Manocae and polychaetes (Figs. 3,7). 



256 



