Twenty five years of changes in Dreissena spp. populations in Lake Erie

Lake Erie has the longest history of colonization by both Dreissena polymorpha and Dreissena rostriformis bugensis in North America and is therefore optimal for the study of long-term dynamics of dreissenid species. In addition, the morphometry of Lake Erie basins varies dramatically from the shallow western to the deep eastern basin, making this waterbody a convenient model to investigate patterns of Dreissena distribution, as well as interspecies interactions among dreissenids. We compare our data on the distribution, density and wet biomass of both dreissenid species in Lake Erie collected in 2009 and 2011-2012 with previous data. We found that Dreissena spp. distribution in Lake Erie varied depending on the time since the initial invasion, collection depth, and lake basin. In 2009-2012, zebra mussels were smaller than in 1992 and were consistently smaller than quagga mussels. During 2009-2012, quagga mussels were found at all depths and in all basins, while zebra mussels were common in the western basin only, and in the central and eastern basins were limited to shallow depths, resulting in an almost complete replacement of D. polymorpha with D. rostriformis bugensis. In the shallowest western basin of Lake Erie, zebra mussels represented > 30% of the combined dreissenid density even after more than 20 years of coexistence, providing strong evidence that, even in lakes as large as Lake Erie (or at least its western basin), D. polymorpha may sustain a significant presence for decades without being displaced by quagga mussels.