ABUNDANCE AND DISTRIBUTION 

 OF ZOOPLANKTON 



Sixty-three categories of zooplankton, including 

 separate larval stages for some species, were identified 

 in the samples from the 39 stations (Table 2). Among 

 the categories, 18 occurred at only one station each 

 and 12 occurred at more than half of the stations 

 (Table 2). The number of categories identified at each 

 station varied from 6 at station 86 to 29 at station 55; 

 the average number of species per station was 13 

 (Table 1, Fig. 1). In general, the stations with the 

 greatest number of species were northwest of Cape 

 Lisburne and those with the least were between Cape 

 Lisburne and Point Lay. 



The numbers of individuals in each category at each 

 station varied greatly (Table 2). I calculated the aver- 

 age number for the two samples at each station for the 

 purpose of comparing abundance of the categories. 

 Aglantha digitale was the predominant zooplankter 

 and the only one that occurred at all of the stations. 

 The average number per 1(X) m^ (i.e.. the average of 

 the two samples) among the stations ranged from 2(X) 

 to 22.516. Calanoid copepods. the second most abun- 

 dant zooplankters, ranged from 27 to 3.146 per 100 m^. 

 C alanus finmarchiciis was the most abundant calanoid 

 (up to 2,299 per 100 m^) and also occurred the most 

 frequently (29 stations). Larvae of polychaetes, barna- 

 cles, oxyrhynchid crabs, hermit crabs, and sea urchins 

 in aggregate were more abundant than calanoid 

 copepods at 18 stations. The large proportion of mero- 

 plankton to the total zooplankton is characteristic of 

 the shallow areas of the eastern Chukchi Sea (John- 

 son. 1956). 



Even though two samples were available from most 

 stations, no rigorous statistical comparisons were 

 made between samples or stations because of the low 

 counts and the high frequency of zero counts in the 

 samples. Frequently one sample of a pair would have a 

 raw count four times or more the count of its mate. 

 The extreme case was station 63 where one sample 

 contained a single Clione limacina and its mate con- 

 tained 38. The presence of one or more individuals of a 

 species in one sample of a pair was often accompanied 

 by the absence of individuals in the other sample. 

 Extreme cases of absence and presence were and 

 32 Aglantha digitale in the samples from station 86 

 and and 20 plutei of Echinoidea in the samples from 

 station 54. 



RELATIONSfflPS BETWEEN ZOOPLANKTON 

 AND CHARACTERISTICS OF WATER 



The distribution and abundance of zooplankton are 

 in part dependent on characteristics of the water be- 

 fore and at the time of sampling. In discussing the 

 distribution and abundance of species within the area 

 covered by the Glacier, it must be remembered that 

 the survey was extended over a month; during this 



time marked chemical and physical changes in the 

 water were caused by surface freezing, wind mixing, 

 and the southward movement of the ice front (Ingham 

 and Rutland. 1972). Despite the extended period, 

 comparison of the contours of plankton abundance 

 (Fig. 2 to 10) with contour plots of temperature, salin- 

 ity, and dissolved oxygen (Fig. 1 1 to 13) are useful for 

 an understanding of the area. 



The similarity of the density distributions of zoo- 

 plankters in the nine categories (Fig. 2 to 10) selected 

 for comparison suggests that the abundance of all ex- 

 cept ^cflrr/a longiremis (Fig. 5) were being influenced 

 by a common set of environmental factors. The area 

 appeared to be subdivided into three parts: a west area 

 (stations 40-60, 64, 90, and 91), a north area (stations 

 8-39 and 69), and a south area (stations 62. 63. and 

 72-87). To test the reality of this subdivision. I com- 

 puted means and variances for each area from the sta- 

 tion means. The variances were high and increased as 

 the means increased, which indicated that the data 

 were not normally distributed and required transfor- 

 mation. Plots of variances and standard deviations 

 against the means indicate d that the square root trans- 

 formation (A" = \X -1-0.5) could be used. The original 

 means and transformed data are given in Table 3. 



The square root transformation did not fully nor- 

 malize the data but did reduce variances enough for 

 me to test for differences of means and variances 

 among the three areas. To test for equality of trans- 

 formed means (Table 4). I used either a r-test assuming 

 equal variance or a ?'-test assuming unequal variance 

 (Ostle. 1963). The choice of whether to use the f-test 

 or the /'-test depended on the results of an F-test for 

 equality of variances (Ostle. 1963) (Table 5). The 0.05 

 level of significance was used in all cases to accept or 

 reject the assumptions of equal means or variances. 

 Although they were not always statistically different, 

 the higher variances were usually associated with the 

 higher means. Because the north and south areas ap- 

 peared to have equivalent means but differing var- 

 iances in several cases. I combined the north and 

 south areas into an east area for fiirther testing against 

 the west area (Tables 4 and 5). 



Aglantha digitale (Fig. 2) was least dense in the 

 south area and had significantly higher variance in the 

 north area than in either the west or south areas. 

 Sagitta elegans (Fig. 3) had significantly different 

 mean densities in all three areas: the west was highest 

 and the north lowest. 



Clione limacina (Fig. 4) was the only species in 

 which no statistical difference among means was 

 found. The variance about the mean was highest in the 

 south area because of the exceptionally high count of 

 juveniles at station 63. Deleting station 63 from the 

 statistics left the north area separable from the other 

 areas by reason of higher variance (Table 5). 



The mean density oiAcartia longiremis in the south 

 area was significantly lower than in the west area but 

 not lower than in the north area. The variance for the 



