TOTAL CADMIUM, COPPER, AND ZINC IN 2 DREISSENID MUSSELS, DREISSENA-POLYMORPHA AND DREISSENA-BUGENSIS, AT THE OUTFLOW OF LAKE ONTARIO

Two closely related Dreissenid mussel species, Dreissena polymorpha an d Dreissena bugensis, both recent invaders of the Great Lakes and St. Lawrence River, have potential as biological monitors of metal contami nation. To better understand their usefulness as biomonitors, we measu red total cadmium, copper and zinc concentrations in soft tissues of b oth species at a site at the outflow of Lake Ontario. We examined tota l mean metal concentrations in soft tissues for both seasonal and inte rannual variability. Both mussel species exhibited elevated copper and cadmium concentrations compared to relatively uncontaminated waters. D. bugensis (quagga) mussels bioaccummulated higher levels of cadmium than D. polymorpha (zebra) mussels, while zebra mussels had higher con centrations of zinc and copper. Zebra mussels showed greater interannu al variability in metal concentrations than quagga mussels. Total meta l concentrations in both species were influenced by season, particular ly stage in the reproductive cycle. The two species differed in their seasonal bioaccumulation patterns for both cadmium and zinc, but were similar in their seasonal variability of copper. We did not find a con sistent pattern between shell length and total metal concentration for either species. Patterns of bioaccumulation for these species must be better known if they are to be used in biological monitoring programs to assess trends of contamination in the Great Lakes basin.