The impact of ballast water effluent on the Manila clam, Tapes semidecussatus

The impact of ballast water discharge from an oil refinery in Whitegate Harbour, Co. Cork, Ireland to the Manila clam, Tapes semidecussatus, was investigated using a whole sediment bioassay. Bioassay organisms were exposed to surface sediments for a period of 2l days, including a reference and control sediment, collected from the vicinity of a ballast water discharge pipe. At the whole organism level, mortality and burrowing behaviour (assessed as time taken for organisms to burrow into the sediment) were used to determine the effects of exposure to test sediments. After 21 days, clam mortality was higher in surface sediments collected directly at the point of the ballast water discharge pipe than from all other test sediments assayed. After 10 days exposure to test sediments collected from the vicinity of the ballast water discharge pipe, the burrowing behaviour of animals was significantly different to the behaviour of animals exposed to uncontaminated sediments.