Changes in Benthos and Three Littoral Zone Fishes in a Shallow, Eutrophic Ontario Lake Following the Invasion of the Zebra Mussel (Dreissena polymorpha)

Abstract

ABSTRACT We assessed changes in the benthic community, and in the feeding, growth and polychlorinated biphenyl (PCB) concentrations in three littoral zone fishes (pumpkinseed, Lepomis gibbosus, bluegill, Lepomis macrochirus and yellow perch, Perca flavescens) in Rice Lake, Ontario, following the invasion of zebra mussels (Dreissena polymorpha) in 1994. Zebra mussel settling density on ceramic tiles peaked at 449,000·m−2 in 1996, and adult mussel densities averaged 854·m−2 at the Curtis Point reference site. Mean summer chlorophyll a concentrations were still high in 1995 and 1996 (14.6 μg/L), and were not significantly different than those recorded in 1986–88. Non-dreissenid benthic invertebrate biomass did not increase significantly relative to a pre-invasion year, but amphipod biomass did increase significantly. There was no evident shift in the diet of die three littoral zone fishes from zooplankton to benthic invertebrates. The pumpkinseed was the only species to have experienced an increase in growth rates following the zebra mussel invasion. Contrary to our predictions, significant declines in the concentration of PCBs were observed in the muscle of pumpkinseed, although differences in fish sizes may have confounded PCB analysis. Overall, there did not appear to be a negative impact of zebra mussel invasion on any of the three fish species, and pumpkinseeds appeared to benefit from this invasion. Our results indicate that shallow, productive lake ecosystems may either be resistant to many of the zebra mussel-induced changes experienced in deeper, less eutrophic lakes, or that such changes may take more than three years before becoming evident.