Zebra mussel feeding relationships and their implications for native unionids

Abstract

Human impacts have altered many Great Lakes ecosystems. The human-induced appearance and spread of invasive zebra mussels (Dreissena polymorpha) has accompanied a remarkable decline in the population sizes of North American unionid mussel species, most of which are now endangered. Despite conclusive evidence that zebra mussels kill native unionid mussels in the areas they invade, the mechanism by which they do so is uncertain. Studies suggest that zebra mussels may kill unionid mussels by latching onto their shells and then out-competing them for food resources. To model the effects of zebra mussel infestation and food resource competition on scarce, endangered unionid mussels, we examined the 13C and 15N isotope compositions of zebra mussels found attached to other zebra mussels (i.e. “parasite” zebra mussels) and zebra mussels found with other zebra mussels attached to them (i.e. “host” zebra mussels) in Douglas Lake, Cheboygan County, Michigan. Results indicated that attached zebra mussels do not, in fact, out-compete their “hosts” for food. Tentatively, this also suggests zebra that mussels do not out-compete unionids for foo