Quantification of mussel (Mytilus edulis) growth from power station cooling waters in response to chlorination procedures

The age and growth history of individual mussels collected from the cooling water culverts of a power station were determined from the growth bands present in acetate peels of polished and etched shell sections. During periods of exposure to the antifouling agent, sodium hypochlorite (0.2mgl^‐1), shell growth was severely reduced, resulting in marked changes in the structure and deposition of the shell. As a consequence of chlorination, the growth rate of the mussel population occurring within the culverts was substantially lower and the mean length‐at‐age significantly smaller than that of a naturally occurring population immediately outside the cooling water intake. The growth patterns present in the shells of mussels experimentally added to the cooling waters during chlorination were compared with, and found to be similar to, the patterns in the shells of mussels that had settled naturally in the culverts. The daily growth of the experimentally exposed mussels (1.1–5.2 μm d^‐1) is two orders of magnitude lower than the growth rate of mussels growing in untreated waters. The use of mussels for evaluating the efficiency and long‐term effects of low level chlorination is discussed.