820 BUIKEMA et al. 



TABLE 5 



EFFECTS OF ENTRAINMENT STRESSES 



ON THE FILTERING RATE OF 



ADULT Daphnia pulex 



*Algal growth exceeded rate of uptake. 



undershoot in response intensity. If the animal survived the initial 

 shock, it quickly adjusted its metabolism to a new level and then 

 acclimated to the nev^^ environmental condition. This rapid type of 

 response may have occurred in 10°C stressed animals, but the 14°C 

 stress may have caused physiological damage that resulted in a 

 reduced rate of oxygen consumption. Theoretically, oxygen con- 

 sumption should have increased as temperature increased (see, e.g., 

 Schindler, 1968). 



The depressant effect of 10°C stress on filtering rate was also 

 unexpected since filtering rate usually increases with temperature. 

 Kibby (1971) and Hayward and Gallup (1976) demonstrated that 

 Daphnia filtered best at an optimum temperature dependent on prior 

 acclimation. At temperatures above the optimum, filtering rates 

 decreased. The lower filtering rate at 30° C for acchmated D. 

 sch0dleri was similar to the response observed for D. pulex stressed 

 at 30° C for 12 min. The possible mode of action for this response is 

 not known. 



If nutrition was a limiting factor, then subtle latent thermal 

 effects significantly decreased the number of live young per brood. 

 Temperature may have affected reproduction because of the reduced 



