Ecological and Genetic Studies onDreissena polymorpha(Pallas): a New Mollusc in the Great Lakes

Dreissena polymorpha, a bivalve mollusc endemic to Europe, has established a population in Lakes St. Clair and Erie, likely as a result of ballast water discharge. Allozyme studies showed that the Lake St. Clair population was polymorphic at 73.9% of the loci examined and that individual heterozygosities averaged 31.6%. This high level of genotypic diversity indicated that the population was founded from a substantial number of individuals and did not undergo a bottleneck subsequent to founding. The population is reproducing with peak densities in excess of 200 individuals∙m−2. Juvenile settlement occurs in late July and August with veliger larvae preferentially settling on the shells of live mussels. The species appears likely to become a dominant member of the shallow water benthos throughout the lower Great Lakes.