Sublethal Responses of Zebra Mussel, Dreissena polymorpha to Low-level Chlorination: An Experimental Study

Abstract

Chlorination is a widely used method to combat zebra mussel fouling in industrial cooling water systems. However, there is paucity of information on the sublethal effects of low-level chlorination on the zebra mussels. The physiological behaviour (shell valve movement, filtration rate, foot activity index and byssus thread production) and the byssus thread strength of different size groups (between 5 and 20 mm shell length) of zebra mussel, Dreissena polymorpha (Pallas), were studied at different chlorine concentrations (0.1-1.0 mg l m 1 ) in the laboratory. The results indicated that D. polymorpha was able to sense chlorine at levels as low as 0.1 mg l m 1 and this significantly reduced their physiological activities (9%-18%). D. polymorpha also showed a progressive reduction in physiological activities when chlorine concentrations were increased from 0 to 0.5 mg l m 1 . However, no significant differences in physiological activities were observed between 0.5 and 1.0 mg l m 1 chlorine residuals ( e.g. 89% and 93% reduction in foot activity index at 0.5 and 1.0 mg l m 1 , respectively). Shell opening frequencies of D. polymorpha in control experiments (0 mg l m 1 residual chlorine) were about 18 times higher than those at 0.5 mg l m 1 residual chlorine. Continuous dosing of at least 0.5 mg l m 1 residual chlorine was found to be required before shell opening was critically impaired. Therefore, 0.5 mg l m 1 residual chlorine appears to be the minimum chlorine level to be dosed continuously, for the successful control of D. polymorpha . The resistance of D. polymorpha to chlorine appeared to be lower than that for other mussel species in The Netherlands viz. Mytilus edulis L. and Mytilopsis leucophaeata (Conrad).