Tolerance of five species of tropical marine mussels to continuous chlorination

Abstract

The paper examines the relative lethal and sublethal response of five important tropical marine mussels ( Perna viridis, Perna perna, Brachidontes striatulus, Brachidontes variabilis and Modiolus philippinarum) to different chlorine concentrations varying from 0.25 to 15 mg l −1. The mussels were observed to co-exist in the cooling water circuits of a coastal power station that adopted intermittent chlorination as a fouling control technique. The five mussel species showed, in response to chlorination, 100% mortality at significantly different exposure times, indicating significant species-specific variability in chlorine tolerance. For example, at 1 mg l −1 residual chlorine, B. variabilis and P. viridis took 288 and 816 h, respectively, to achieve 100% mortality. The time taken for 100% mortality decreased with increasing chlorine residual concentration. The effect of mussel size (=mussel age) of P. viridis, P. perna, B. striatulus and M. philippinarum on mortality was significant between 1 and 5 mg l −1 residual chlorine, with larger mussels showing greater resistance than smaller ones. All mussel species showed progressive reduction in physiological activities when chlorine residuals were increased from 0 to 1mg l −1. However, species-specific differences in the relative rate of physiological activities were observed. Accordingly, relative reduction in physiological activities in response to chlorination was the lowest in P. viridis and the highest in B. variabilis. The data clearly indicate significant differences in the lethal and sublethal responses of the five mussel species to chlorination. The results, therefore, suggest that for effective fouling control, chlorine treatment against mussels has to be employed judiciously, depending on the mussel species involved.