stages of hermit crabs (Paguriis sp.) At many stations 

 oxyrhynchid and Pagurus larvae were about as abun- 

 dant as many of the calanoid copepods (Table 2). 



The pteropods Clione limacina and Spiratella 

 helicina were found in the southeastern Chukchi Sea 

 in 1970 but not in 1947. Yearly variation in abundance 

 of both species may be large — ^Johnson (1953) did not 

 find pteropods in the southeastern Chukchi Sea in 

 1947, but MacGinitie (1955) reports that 5. helicina 

 were abundant at Point Barrow that same summer. 

 Spiratella spp. are the only known prey of C. limacina 

 (Lain, 1970). However, the frequent occurrence of C. 

 limacina in the absence of Spiratella (my Fig. 4: 

 MacGinitie, 1955, Table 7) suggests that Clione does 

 have alternative prey. 



Lamellibranch veligers were numerous in Johnson's 

 samples in the summer of 1947 but rarely occurred in 

 my samples in the fall of 1970. The small size of the 

 veligers precluded quantitative sampling by the nets 

 used in 1970, but 1 believe the difference is principally 

 due to the lateness of the season in which I sampled. I 

 found lamellibranch veligers at only 7 of 39 stations, 

 and then only in low abundance; Johnson encountered 

 lamellibranch veligers at 19 of 21 stations in the Bering 

 and Chukchi Seas, usually in high abundance. 



Sagitta elegans is the only chaetognath recorded 

 from the Chukchi Sea (Dawson, 1971). The stations 

 compared in Table 6 had greater numbers of S. 

 elegans in 1947 than 1970, but complete data from both 

 years show a wide variation in catch (my Table 2: 

 Johnson, 1953, Table 1). Where there is a thousand- 

 fold difference between stations, a twofold or 

 threefold difference between years (Table 6) does not 

 seem significant. 



Echinoderm larvae, like polychaete larvae, copepod 

 nauplii, Oithona sp., and lamellibranch veligers, were 

 probably underestimated in 1970, relative to estimates 

 in 1947, because my net was coarser than that used 

 aboard the Nereus. However, I think the major cause 

 of the difference between the 1947 and 1970 counts is 

 seasonal because most echinoderm larvae have a 

 pelagic life of less than 8 weeks (Thorson, 1961) and 

 would have settled out of the plankton before late Sep- 

 tember or October. If my hypothesis is correct, this in 

 combination with MacGinitie's (1955) data indicates a 

 very short spawning period for most Chukchi Sea 

 echinoderms with planktonic larvae; the peak spawn- 

 ing period is in July or August and most larvae settle 

 before September or October. 



Like echinoderm larvae, adult larvaceans (appen- 

 dicularians) may also be seasonal in abundance. This 

 seasonality may explain why larvaceans were about 

 1,000 times more abundant in the 1947 summer sam- 

 ples than in my 1970 fall samples. Neither Johnson 

 (1953) nor MacGinitie (1955) mention Fritillaria 

 horealis in their samples, but it dominated the larva- 

 ceans in my samples. I found the larger Oikopleura 

 vanhoeffeni only occasionally in 1970. Unfortunately, 

 Johnson (1953) does not identify the larvaceans found 



in the Nereus samples, although a Fritillaria sp. and 

 an Oikopleura sp. were recorded by Johnson (1936) 

 from samples taken by the U.S. Coast Guard cutter 

 Chelan in 1934 at stations west of Nome, Alaska. 



I believe the strong seasonal nature of Arctic pro- 

 ductivity accounts for most of the differences found in 

 comparing my 1970 fall data with Johnson's 1947 

 summer data, especially those larval forms which were 

 much more abundant in 1947. Large yearly variations 

 probably account for the greater abundance of some 

 larger and longer lived zooplankters in 1970. Although 

 a coarser net was used in 1970 than 1947, I feel that net 

 selectivity played a role secondary to the seasonal and 

 yearly differences. 



SUMMARY 



1. Zooplankton samples were collected at 39 sta- 

 tions in the eastern Chukchi Sea between 26 Sep- 

 tember and 17 October 1970. 



2. Sixty-three categories of zooplankton were en- 

 countered; between 6 and 29 categories occurred at 

 the individual stations. 



3. The hydromedusan Aglantha digitate was the 

 predominant zooplankter, both in numbers and 

 biomass. Calanoid copepods were the second most 

 abundant zooplankters, although meroplankters 

 equaled or exceeded copepods in numbers at one-half 

 of the stations. 



4. Contour plots of zooplankton abundance indicate 

 that three environments were sampled: I) an area of 

 high abundance and diversity northwest of Cape Lis- 

 bume, 2) an area of low abundance and diversity be- 

 tween Cape Lisbume and Point Lay, and 3) an area of 

 rapid north-south variation but generally low abun- 

 dance extending west along the 70°N parallel. 



5. Waters with temperatues below 0°C tended to 

 have lower zooplankton abundance than adjacent 

 warmer waters. In areas where the temperatures 

 changed rapidly from 1° to 3°C horizontally, the abun- 

 dance of many species changed along the gradient in a 

 parallel fashion. Broad temperature contours in the 

 area northwest of Cape Lisbume indicated some sta- 

 bility, which would be conducive to the development 

 of large zooplankton populations. 



6. Nearly no assocation was evident between zoo- 

 plankton abundance and salinity. 



7. A tendency was noted for an inverse relation be- 

 tween zooplankton abundance and dissolved oxygen 

 concentration of the water. 



8. A comparison of the 1970 data with data for 1947 

 demonstrated several differences — some appeared to 

 be differences between years and others seemed to be 

 differences due to time of year. Apparent between- 

 year differences were greater numbers of Aglantha, 

 Clione, and crab larvae, and lesser numbers of 

 Pseudocalanus in 1970 than in 1947. Differences 

 thought to be due to season were lesser numbers of 

 cladocerans, /Icarf/fl, Oithona, larvaceans, and most 



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