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.

We examined the relation between mercury levels in walleye (Stizostedion vitreum vitreum) and northern pike (Esox lucius) in Ontario lakes. Walleye and northern pike occurred together in 79 of the 346 study lakes. The length-standardized mercury concentrations in coexisting walleye and northern pike in the 79 lakes were highly correlated (r2 = 0.60). The mean mercury concentrations in walleye and northern pike of standardized length from these lakes were 0.65 and 0.52 μg/g, respectively. Lacustrine characteristics associated with lake dystrophy (dissolved organic carbon and iron) were positively correlated with mercury levels in both species. Variables associated with acidity (pH and alkalinity) and hardness (calcium, conductivity, and magnesium) were negatively correlated with mercury concentrations in northern pike but not walleye.

Biological and physical factors affecting the body burdens of hexachlorobenzene, octachlorostyrene, and four polychlorobiphenyl (PCB) congeners in freshwater mussels from Lake St. Clair, Ontario, Canada were investigated. Specimens of Lampsilis radiata (Barnes) and the non-native Elliptio complanata (Lightfoot) were deployed for forty days at four Lake St. Clair sites, to investigate whether the water or the sediment phase represented the primary source of contaminants and to examine the effect of enclosure of the mussels on contaminant uptake. No significant differences in body burdens were detected for any of the compounds between mussels placed in corrals containing uncontaminated sand and those with natural sediment, suggesting the water phase represents the xenobiotic source. Among three enclosure types of varying restriction there were no significant differences in the body burden of each compound indicating the effect of confinement on uptake is minimal. Weak negative correlations between body burden and body length existed for all compounds, although there were no significant differences between the sexes or, with the exception of PCB congener 118, among five indigenous species.

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