264 



R. G. Stress et al. 



PREDATOR web: 



®- 



•® 



(a) is eaten by (§) 



adults 



First 

 instar 



DophniQ 

 middendorffiono 



nauplli 



metanauplii 



pre-adults 



Branchinecta paludoso 

 Polyartemiella hozeni 



copepodids 



i. 



odults 



nauplli h. 



10 



Cyclops 

 vernalis 



nouplii and 

 copepodids I 



copepodids 



iL!r 



Heterocope 

 septentrionalis 



Time 



FIGURE 6-7. Predatory web of the planktonic Crustacea in Pond C as 

 constructed by Dodson (1975). 



nauplii and for the young Heterocope. All stages of the fairyshrimps were 

 eaten by the Cyclops, which seems to be a very versatile predator. We do 

 not know whether Heterocope prefers Daphnia young or Cyclops nauplii. 

 The nauplii have become rare by the time the young Daphnia hatch and 

 appear in the last 2 weeks of July. 



Some species interactions gave very low K values. For example, both 

 the fairyshrimp and Daphnia accidentally trapped Cyclops nauplii 

 (interactions 5 and 6). Others, such as C. strenuus and Diaptomus 

 alaskaensis, were not predatory. 



These experiments indicate the potential importance of predation in 

 controlling zooplankton production and perhaps even species composition. 

 From these experiments and from our observations on the Heterocope- 

 Daphnia interaction, it appears that Heterocope's success could depend 

 upon abundance of the young-of-the-year Daphnia in the July hatch. 



Production 



Estimation of production by the Crustacea is simplified in the Barrow 

 ponds because there is, with one exception, but a single generation and 

 because reproduction is restricted to specific periods. Here, we define 

 production to be the sum of biomass of eggs and individuals surviving at 

 the end of the summer and the biomass of the same lost throughout the 

 summer. In general form, production (Mg C liter ~ ') is 



P= 2 i{N, -N, + ,)iM,e""")} +NtMt + NeMe 



X 



'} 



(1) 



