MOVEMENTS OF DAPHNIA 251 



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in the upper parts of the lake while the adults are found at 

 lower levels (Birge, 1897). 



Juday (1904) was also unable to find a diurnal movement of 

 this species in Lake Mendota. 



The seasonal movement of Daphnia pulex pulicaria is well 

 marked in Lake Mendota. Table I, based on figures given by 

 Birge (1897), shows that in winter the species is most abundant 

 at the surface, but that as the water of the lake heats up the 

 animals move downward until in August they are most abundant 

 at depths of between 9 and 12 meters. In the fall they move 

 upward until they again appear at the surface. 



TABLE 1 



Daphnia pulicaria 



Percentage vertical distribution in Lake Mendota, Wis. 

 (From Birge, 1897, Trans. Wis. Acad. Set., Vol. 11.) 



Per cent, in each 3 meter level 



On August 26, 1985, there was an alternation of cloud and 

 sunshine over Lake Mendota and Birge (1897) observed that 

 adult and young daphnids were approximately one meter below 



