Control of Brackish Water Fouling Mussel, Mytilopsis leucophaeata (Conrad), with Sodium Hypochlorite

Though the Conrad's false mussel, Mytilopsis leu- cophaeata, is an important fouling animal in industrial cooling water systems, there are no published reports on the tolerance of this species to chlorination. A series of experiments was conducted to determine the effects of mussel size (2-20 mm shell length), season (breeding versus nonbreeding), nutritional status (fed versus starved) and acclimation temperature (5- 30°C) on the mortality pattern of M. leucophaeata under con- tinuous chlorination (0.25-5 mg/L). The effect of mussel size on M. leucophaeata mortality in the presence of chlorine was significant, with 10 mm size group mussels showing greater resistance. At 0.25 mg/L residual chlorine, 2 mm size group mussels took 89 days to reach 100% mortality, whereas 10 mm size group mussels took 109 days. M. leucophaeata collected during nonbreeding season (December-April) was more toler- ant to chlorine than those collected during breeding season (June-October). Nutritional status of the mussel had no signif- icant influence on the chlorine tolerance of the mussel: fed and starved mussels succumbed to chlorine at equal rates. The effect of acclimation temperature on M. leucophaeatamortality in the presence of chlorine was significant. At 0.5 mg/L resid- ual chlorine, mussels acclimated at 5°C required 99 days to reach 95% mortality, whereas mussels acclimated at 30°C required 47 days. A comparison of present data with previous reports suggests that resistance of M. leucophaeata to chlori- nation is higher than other mussel species causing fouling problems in The Netherlands (Mytilus edulis and Dreissena polymorpha).