Zooplankton 255 



precision was better for the copepods, with only a small variance between 

 samples at the same station. The variance was greater between stations, 

 however, and there was also a tendency for the copepodids to cluster at the 

 margins of the ponds in the spring. 



In a later study of Daphnia distribution, Haney and Buchanan 

 (personal communication) showed a correlation between the location of 

 most of the D. middendorffiana in a pond and the sun on clear or hazy 

 days. The population seemed to move toward the margin of the pond 

 farthest from the sun and in midsummer actually circled the entire pond 

 margin over 24 hours. 



The cyclopoid copepods were numerically more abundant than other 

 zooplankton forms, especially early in the summer (Figure 6-2). As the ice 

 melted in 1971, the late juvenile and adult stages of Cyclops vernalis and 

 C. magnus appeared in the water. By mid-June the adults of C. vernalis 

 were carrying egg sacs and the first nauplii were seen on 21 June. By the 

 last week in June, most of the overwintering animals had been transformed 

 into adults which reached a maximum of 2.5 females and 1.7 males liter '. 

 The maximum number of nauplii, 35 liter ', were found on 1 3 July. After 

 25 July no more than 10 liter ' were collected. The copepodids began to 

 appear in early July and were most abundant during the first third of July. 

 From late July to mid-August, there was approximately 1.0 animal 

 liter " '. Other species of cyclopoid copepods were present, but the 10-liter 

 samples were not large enough to permit quantitative estimates. Although 

 the copepodids of all the cyclopoid species may enter diapause in the 

 sediment (Elgmork 1959, Szlauer 1963) their entry was not examined in 

 the ponds at Barrow. 



o 



■D 



40 



30 



20 



10 



— 



1 ^ 1 ' — r 



(I) D. bacillifer 



D. glacialis 

 D. olaskensis 



(2) 



(3) Heterocope 



~~i ' 



20 

 Jun 



— I — 

 10 



20 



Jul 



10 

 Aug 



o 



T3 



.0 * 



- 



20 



FIGURp 6-3. Densities of all stages combined of three 

 species of calanoid copepods from Pond C, 1971. 

 (Same samples as Figure 6-2.) 



