AN IN SITU STUDY OF CADMIUM STRESS 



323 



10 



20 



30 40 10 



CADMIUM, Mg/liter 



Fig. 2 Effects of cadmium on (a) abundance of major zooplankton 

 groups, (b) species diversity, and (c) community similarity. (See text 

 for definitions of symbols.) 



Changes in relative abundance of the major crustacean groups 

 were primarily an increase in the percentage of cyclopoid copepods 

 and a decrease in that of the cladocerans. Again, these changes were 

 greatest in the lowest portion of the overall range. From to 5 /ig 

 Cd/liter, the relative abundance of cyclopoid copepods increased 

 from 43 to 70%, cladocerans decreased from 52 to 25%, and calanoid 

 copepods remained at 4 to 5%. 



The effects of cadmium on species diversity, as indicated by the 

 mean values of Hill's (1973) diversity numbers in the range of to 

 40 [Jig Cd/liter, are shown in Fig. 2(b). The mean number of 

 identification categories, Nq, decreased with increasing cadmium 

 although the means at 5 and 10 /ig/liter are not significantly different 

 from the controls. The mean diversity numbers Nj and N2 also 

 decreased with increasing cadmium but were more^ sensitive than Nq 

 in the range of to 5 )Ug Cd/liter. The values of Nj and N2 at 5 /xg 

 Cd/liter are both significantly different (P < 0.05) from the controls. 



Changes in community similarity, as measured by indexes S and 

 S', are shown in Fig. 2(c). Both S and S' decreased with increasing 



