Effects of copper and zinc on two planktonic ciliates

Abstract

The interactive effects of copper and zinc on two estuarine planktonic ciliates, Favella sp. and Balanion sp., were determined in seawater media in which the free metal ion activities were controlled by nitrilotriacetic acid (NTA) trace metal ion buffer systems. Cupric ion activities of 10-10 M caused abnormal motility in both ciliates in shortterm (5 h) tests, and cupric ion activities as low as 10-12.8 M decreased the growth rates of both species in longer-term experiments. In the short-term tests, zinc ion activity by itself did not affect the motility of the ciliates, but there were significant interactions between copper and zinc. In the longer-term experiments, the growth of Favella sp. was optimal at the lowest cupric ion activity (10-13 M) and the two lowest zinc ion activities (10-12 and 10-13 M) and the two lowest zinc ion activities (10-12 and 10-11 M), and copper and zinc inhibited growth at activities above these values. By contrast, optimal growth rate of Balanion sp. occurred at the highest zinc ion activity (10-10 M) and the lowest cupric ion activities (10-13 to 10-12 M) and growth rate was reduced at zinc ion activities ≦10-11 M. There was an antagonism between copper and zinc which was particularly pronounced in Balanion sp.