BACKGROUND

The zebra mussel (Dreissena polymorpha), native to southern Russia, was introduced to the Great Lakes in 1985 or 1986 via ballast water from foreign ships. Since then it has spread quickly and caused dramatic economic and ecological effects. Zebra mussels now exist in many aquatic systems in the eastern US and are expected to invade freshwaters throughout the nation in about 20 years. The mussel can reach densities of up to 700,000 individuals/m². It outcompetes other filter feeders for food, smothers clams, native mussels and snails, and clogs water intake and exit pipes for facilities such as electric generating plants. Pimentel et al. (2000) estimate annual damage for U.S. utilities at about $100 million.

Lack of predators and parasites are partly responsible for the success of the zebra mussel in the U.S. Availability of space is another reason. Hard substrates such as pipes appear to be an open niche for the mollusk; several publications include striking photographs of cars and barrels completely covered with zebra mussels. Its physiological plasticity and human transport in ballast and other water also contribute to the mussel’s spread.

The biology of the zebra mussel predisposes D. polymorpha to be a successful invader. For instance, the free-swimming veliger larva can disperse widely. Females are also extremely fecund. This exercise will help students understand the several life history and ecological characteristics of the mussel that contribute to its ability to invade freshwaters so successfully.

References

• Herbert, P. D. N., B. W. Muncaster, and G. L. Mackie. Ecological and genetic studies on Dressena polymorpha (Pappas): a new mollusk in the Great Lakes. Canadian Journal of Fisheries and Aquatic Science 46: 1587-1591.


• Johnson, L. E., and J. T. Carlton. 1996. Post-establishment spread in large-scale invasions: dispersal mechanisms of the zebra mussel Dreissena polymorpha. Ecology 77: 1686-1690.


• Ludyanskiy, M. L., D. McDonald, and D. MacNeill. 1993. Impact of the zebra mussel, a bivalve invader. BioScience 43: 533-544.
• Neary, B. P., and J. H. Leach. 1992. Mapping the potential spread of the zebra mussel (Dreissena polymorpha) in Ontario. Canadian Journal of Fisheries and Aquatic Science 49: 406-415.


• Mills, E. L., J. H. Leach, J. T. Carlton, and C. l. Secor. 1994. Exotic species and the integrity of the Great Lakes. BioScience 44: 666-676.


• Pimentel, D., L. Lach, R. Zuniga, and D. Morrison. 2000. Environmental and economic costs of nonindigenous species in the United States. BioScience 50: 53-65.


• USGS. 2003. Zebra Mussel Information: U.S. Distribution Maps. (nas.er.usgs.gov/zebra.mussel/)