322 



MARSHALL AND MELLINGER 



TABLE 2 



NUMBER OF ZOOPLANKTON PER LITER (x 10) IN A 



CADMIUM-ENRICHMENT EXPERIMENT WITH IN SITU 



INCUBATION IN LAKE MICHIGAN* 



♦The experiment was conducted Sept. 11—12, 1976; values are mean ± standard error. 

 fD. oregonensis. D. minutus. and D. ashlandi. 



and community similarity. The results for experiment 5 are illus- 

 trated in Fig. 2. 



Changes in total abundance of crustacean zooplankton (minus 

 copepod nauplii) and relative abundances of the major crustacean 

 groups are shown in Fig. 2(a). The relationship between total 

 abundance and added cadmium is represented by the uppermost line, 

 the slope of which decreases with increasing cadmium. Thus total 

 abundance is most sensitive to cadmium in the lowest segment of the 

 range (0 to 5 jug/liter). Total abundance at 5 )Ug Cd/Hter was reduced 

 by 42% from that in the controls, and the difference is highly 

 significant (P < 0.002); whereas, from 5 to 10 ^tg/liter, it was 

 reduced only 11% further. 



