and calanoid copepods. Stations west of Icy Cape had 

 alternating areas of low and high oxygen concentration 

 and corresponding areas of high and low zooplankton 

 abundance respectively. 



COMPARISON OF ABUNDANCE 



AND DISTRIBUTION 



OF ZOOPLANKTON IN 1970 AND 1947 



The eastern Chukchi Sea fauna is a continuation of 

 the fauna of the eastern Bering Sea (Johnson, 1953, 

 1956: Johnson and Brinton, 1963). Of the 32 kinds of 

 zooplankters from the eastern Chukchi Sea identified 

 to species, only the copepod Dcrjiiginia tolli has not 

 been previously recorded in the eastern Bering Sea; it 

 appears to be restricted to the polar seas (Brodskii, 

 1950; Johnson, 1963). 



In this section I compare the results of sampling by 

 the Glacier in the fall of 1970 with the results of sam- 

 pling by the Nere/zi in the summer of 1947. Others have 

 studied zooplankton in the Chukchi Sea, but the 

 Nereiis cruise was the only one that collected data in 

 the same area and used similar sampling techniques as 

 the Glacier. Because an east-west change in zooplank- 

 ton composition and abundance has been demon- 

 strated (Johnson, 1936, 1953; English, 1966), 1 com- 

 pare my data with Johnson's only for the most approx- 

 imate of the two sets of stations — Nereus stations 12, 

 13, 14, and 21; and Glacier stations 43, 44, 49, and 90 

 (Fig. 1, Table 6). The comparative data in Table 6 are 

 drawn from Table 1 of Johnson (1953) and my Table 2 

 in this paper. The data from both sources were ad- 

 justed to number of zooplankters per 100 m^. The dif- 

 ferences between the zooplankton catches of the two 

 cruises may have been due to differences in the years 

 of sampling, the season, or the size of the mesh in the 

 sampling net used. Also, because most of the Glacier 

 stations were inshore of the Nereus stations, they 

 were shallower and less saline. 



Johnson (1953) did not list Hydromedusae in any of 

 his samples, but the hydromedusan Aglantha digitale 

 was the predominant zooplankter in my samples and 

 occurred both as juveniles and adults. MacGinitie 

 (1955) and Hand and Kan (1961) found this species to 

 occur consistently off Point Barrow, and Hand and 

 Kan noted large yearly variation in its abundance. 

 Considering the ubiquity of the distribution oi A. 

 digitale in 1970 (Fig. 2), 1 believe it likely that 1947 

 was a year of low abundance and 1970 one of very high 

 abundance. 



Polychaete larvae were more numerous In 1947 than 

 in 1970. Among all of the stations sampled in 1970, the 

 counts at only two approached the magnitude of 

 Johnson's counts. The 1947 samples were taken with a 

 finer meshed net, which would account for part of the 

 difference, and also they were taken earlier in the 

 year. Many of the larvae I examined were approaching 

 a size and state at which they settle to the bottom. 



When present, in the 1947 cruise cladocerans 

 (Evadne sp. and Podon sp.) were observed in high 

 numbers and in the 1970 cruise in low numbers. The 

 abundance of marine cladocerans varies seasonally, 

 with peaks in spring and summer (Gieskes, 1971); so 

 that the low numbers obtained on the Glacier cruise 

 could have been due to the time of year. 



Calanoid copepods dominated the zooplankton in 

 1947 but not in 1970. Except for Acartia longiremis 

 and Pseiidocalanus miniitus most species of calanoid 

 copepods were about as abundant in 1947 as in 

 1970. Acartia longiremis was much more abundant 

 in the 1947 samples, possibly because this species, like 

 the cladocerans, has peak abundance in the 

 summer. Pseiidocalanus minutus was more abun- 

 dant in the summer of 1947 than the fall of 1970 even 

 though this species probably overwinters as copepo- 

 dites (Fontaine, 1955) and should have a relatively 

 high population in the early fall. Thus, 1 think the large 

 difference in abundance oi P. minutus between 1947 

 and 1970 reflects a difference between years rather 

 than seasons. The high numbers of calanoid nauplii 

 and the cyclopoid Oithona sp. in the summer of 1947 

 versus very few in the fall of 1970 appears to be a 

 seasonal effect. Because of their small size, copepod 

 nauplii and Oithona were never sampled adequately 

 by the nets 1 used; however, few copepod nauplii and 

 Oithona were found in qualitative phytoplankton sam- 

 ples taken with finer nets at four stations. No egg- 

 bearing calanoids were found in the 1970 samples. 



Barnacle larvae were more uniformly distributed 

 than cladocerans in both years and were more numer- 

 ous in the summer of 1947 than the fall of 1970. Early 

 summer populations of barnacle larvae may be com- 

 posed of several species. Three species of Balanus 

 (MacGinitie, 1955) and one of Chthamalus (South- 

 ward and Southward, 1967) may contribute larvae to 

 the area. Some species of Balanus release only a single 

 spring or early summer brood, whereas Chthamalus in 

 the Chukchi Sea may release more than one brood per 

 summer (Southward and Southward, 1967). Although 

 large yearly variations in abundance of barnacle larvae 

 probably occur, I believe the differences between the 

 1947 and 1970 samples represent seasonal more than 

 yearly differences. 



Amphipods and euphausids were probably not ade- 

 quately represented in either the 1947 or 1970 samples 

 because of their ability to avoid the nets used. Without 

 knowledge of the identity of the amphipods taken in 

 1947, I can only note that amphipods were about as 

 abundant in 1947 as in 1970. Only larval stages of un- 

 identified euphausids were reported for the 1947 sam- 

 ples, and juveniles of Thysanoessa inermis and T. 

 raschii predominated in the 1970 samples, as one 

 would expect in the later season. 



Crab larvae were more abundant in the fall of 1970 

 than the summer of 1947. Advanced zoeae and 

 megalopa of an oxyrhynchid crab (probably Hyas 

 coarctatus) were more numerous than equivalent 



15 



