Fast Flow May Reduce Upstream Colonies

From July 28, 1992 (update #14)

Some interesting speculation on river habitats likely to be colonized by zebra mussels appeared in a chapter on freshwater bivalves written by Robert McMahon of the University of Texas at Arlington. The chapter appears in Ecology and Classification of North American Freshwater Invertebrates, edited by J. H. Thorp and A. P. Covich, and published by Academic Press. McMahon pointed out that by comparison with native North American freshwater clams, the planktonic veliger life-stage produced by zebra mussels is poorly suited for high-flow, fast-moving rivers. In such waters, veligers would be carried downstream before settlement, eventually leading to elimination of upstream adult populations. He concluded that "downsteam veliger dispersal would appear to preclude zebra mussels from high-flow lotic (actively moving water) habitats, unless upstream impoundments provide a source of replacement stock. In fact, in Europe and Asia, this species is most successful in large lentic (still water) or low-flow lotic habitats such as canals or large rivers." This suggests that zebra mussels may not thrive in many smaller free- flowing rivers; however, all large North American rivers have numerous impoundments. Native clams either brood their young within the parent clam or produce a parasitic life stage that develops while attached to the gills of host fish. Both strategies allow native clams to remain at sites in fast-moving waters, and clams with parasitic young can move upriver as fish hitchhikers.

ID: 19920728-8.

The Zebra Mussel Update was a 4- to 8-page quarterly national newsletter published by the University of Wisconsin Sea Grant Institute from May 1990 through May 1997. The ZMU documented the spread of the zebra mussel -- an exotic nuisance mussel -- through North America's freshwater environments, especially the Great Lakes, and on efforts to control it.