Invasion dynamics and impact of non-native molluscs in the Laurentian Great Lakes

The abundances of non-native species in invaded ecosystems can range from negligible to extremely high, and their effects include competition with and predation on native species, habitat alteration, and the transmission of diseases. Currently, 16 non-native mollusc species are established in the Laurentian Great Lakes, including 14 exotics introduced from other continents and two North American transplants. These species represent 52% of the diversity of all free-living non-native benthic invertebrates in the lakes. Early introductions ( Bithynia tentaculata, Pisidium moitessierianum, P. amnicum, and Valvata piscinalis ) arrived in the 19th century via solid ballast, whereas recent introductions ( Dreissena polymorpha, D. rostriformis bugensis , and Potamopyrgus antipodarum ) were primarily transported in ballast water. Most exotics originated from Eurasia (64%) and Asia (21%), with single species introductions from Europe and New Zealand. Mollusc densities vary greatly from rare (e.g., Corbicula fluminea and Radix auricularia ) to extremely high ( D. r. bugensis ). Non-native mollusc diversity is highest in shallow Lake Erie and lowest in Lake Huron. The ecological impact of exotic species is largely proportional to their population abundance, ranging from negligible (e.g., sphaeriids, C. fluminea , and Radix auricularia ) to the substantial effects from D. r. bugensis , which has transformed entire ecosystems in the four lower Great Lakes. We also examine potential future invaders (e.g., Limnoperna fortunei ) and project their likely distributions and impacts. Ongoing and projected temperature increases will likely enhance conditions for currently restricted species and increase the risk of new introductions from warmer regions, further accelerating ecosystem change.