significance of temperature, salinity and zinc as lethal factors for the mussel Mytilus edulis in a polluted estuary

Mussels, Mytilus edulis L., were subjected to high temperatures, low salinities and dissolved zinc in order to investigate possible environmental hazards of a discharge of heated effluent near Newport on the Yarra River estuary, Victoria, Australia. Exposure to zinc at 0.8 mg l super(-4) for 14 d in otherwise favourable conditions significantly increased mortality resulting from subsequent exposure to temperatures between 29 degree to 31 degree C for 24 H without added zinc. Mussels collected from water of temporarily lowered salinity (8ppt. - 16ppt. S) showed significantly lower thermal resistance than controls collected from marine salinities (35ppt. S). Mussels taken from a marine environment and exposed to 10ppt. S died at a rate which increased with temperature. Mussels acclimated for 14 d to combinations of 10 degree , 16 degree and 22 degree C and 22ppt. and 35ppt. S, and subsequently exposed to increased zinc concentrations accumulated zinc to levels which were independent of temperature and salinity. The zinc was lethal more quickly at 22 degree C and 35ppt. than at the lower temperatures and salinities.