EXPERIMENTAL CULTURE OF BLUE MUSSELS Mytilus edulis L. IN HEATED EFFLUENT WATERS OF A NUCLEAR POWER PLANT

Growth, mortality, and recruitment of blue mussels (Mytilus edulis L.) at varying distances from the heated effluent waters of a nuclear power plant were monitored using experimental rafting techniques Data were obtained at monthly intervals from April through November over a 3‐year period (1973 to 1975). Highest growth rates during April (surface water temperatures less than 25 C) were observed in the immediate vicinity of the effluent. Nortality during April was negligible and growth rates at other stations were negatively correlated with linear distance from the discharge. During May of both 1973 and 1974, with surface water temperatures rising above 25 C, growth rates in the effluent waters declined sharply and by the end of June, mortality ranged from 89% to 100%. Growth rates and survival at other stations from May through November were positively correlated with linear distance from the effluent. With the discontinuation of heated discharge from the plant in May 1975, mortality by November at the “effluent” station was 17% (only slightly greater than control sites). The number of Mytilus edulis spat attached to experimental collector ropes in, and adjacent to, the effluent waters was several orders of magnitude less than that found at control sites during each of the 3 years. Results suggest that, for optimum growth of this species, cultivation operations should probably be restricted to environments in which the upper limit of annual temperature ranges does not exceed 20 c.