816 



BUIKEMA et al. 



TABLE 2 



LONG-TERM BIOLOGICAL EFFECTS OF ENTRAINMENT 

 STRESSES ON Daphnia pulex 



*No significant differences noted; test terminated after 8 days, 

 t Average over first 15 instars after stress. 

 :|:Control data for all experiments were combined. 



cantly depressed individual growth, number of eggs produced, and 

 number of live young. 



A 10° C thermal stress caused all young cladocerans to become 

 primaparous one instar earlier, whereas only 40% of the controls 

 were primaparous one instar early. Consequently, thermally shocked 

 animals produced an average of one more brood than did controls 

 during the observation period. 



Adult animals exposed to temperature and chlorine stress had 

 depressed rates of oxygen consumption, but animals exposed to 

 mechanical and combined stress had increased rates of oxygen 

 consumption. Only a 14°C thermal shock significantly reduced 

 oxygen consumption in adults, but mechanical stress significantly 

 increased oxygen consumption (Table 4). A 10°C thermal shock 

 caused a significant reduction in oxygen consumption of first instar 

 animals, and the effect was significant 48 hr after exposure. 



Within 24 hr after thermal stress, there were significant decreases 

 in filtering rate (Table 5). The negative filtering rates were obtained 

 because algal growth rate during the test exceeded removal rate. 

 Chlorine and mechanical stresses had no significant effects, and no 

 data were available for the effect of combined stress. 



Chlorine and combined stresses significantly reduced ATP levels 

 in adult organisms, and other stresses had no significant effect 



