Life after Dreissena: The decline of exotic suspension feeder may have significant impacts on lake ecosystems

It is well documented that the introduction of dreissenid bivalves in eutrophic lakes is usually associated with decreases in turbidity and total phosphorus concentrations in the water column, concomitant increases in water clarity, as well as other physical changes to habitat that may have cascading effects on other species in the invaded waterbody. In contrast, there is a paucity of data on the ecological ramifications of the elimination or decline of dreissenids due to pollution, bottom hypoxia, or other mechanisms. Using data collected by the U.S. Environmental Protection Agency Great Lakes National Program Office's Long-Term Biology and Water Quality Monitoring Programs, we analyzed the impacts of the hypoxia-induced declines in Dreissena densities in the central basin of Lake Erie on major water chemistry and physical parameters. Our analysis revealed that the decline in Dreissena density in the central basin was concomitant with a decrease in spring dissolved silica concentrations and an increase in total phosphorus and near bottom turbidity not seen in the western or eastern basins. In contrast, opposite patterns in water quality were observed in the eastern basin which was characterized by a high and relatively stable Dreissena population. We are the first to report on observations suggesting that dreissenid-related shifts in water quality may be reversible by documenting that the sharp decline of Dreissena in the central basin of Lake Erie was concomitant with a shift from clear to turbid water.