AN IN SITU STUDY OF CADMIUM STRESS 



325 



TABLE 3 



RESULTS OF T-TESTS OF DIFFERENCES BETWEEN 



MEAN NUMBERS OF VARIOUS CRUSTACEANS IN 



INCUBATED CONTROL SAMPLES AND UNINCUBATED 



SAMPLES TAKEN AT INITIATION AND TERMINATION 



OF IN SITU INCUBATION* 



*The number of tests with no significant differences are shown as 0; those 

 with a significant difference (P < 0.05) are shown as — for decrease or + for 

 increase of the incubated control populations. 



fD. oregonensis, D. minutus, D. ashlandi, and D. siciloides. 



direct effects on growth, survival, or reproduction of the sensitive 

 species. He also stated that toxicity is the parsimonious explanation 

 for any population decline that is demonstrated to result from 

 exposure. 



The observed differences in apparent cadmium toxicity to the 

 different major groups of zooplankton and the similar sensitivities of 

 species within each major group are in agreement with the results of 

 previous studies of heavy-metal toxicity to zooplankton. Mcintosh 

 and Kevem (1974) found that in copper- treated ponds both 



