U.S. Department of Commerce


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Proceedings of the Colorado River Basin Science and Resource Management Symposium. Coming Together, Coordination of Science and Restoration Activities for the Colorado River Ecosystem. Melis, T.S., Hamill, J.F., Bennett, G.E., Coggins, L.G., Jr., Grams, P.E., Kennedy, T.A., Kubly, D.M., and Ralston, B.E., eds. November 18–20, 2008, Scottsdale, Arizona: U.S. Geological Survey Scientific Investigations Report 2010–5135, 372 pp. (2010).


The quagga mussel (Dreissena rostriformis bugensis) was first found in the Great Lakes in 1989 and has since spread to all five lakes. Although its spread through the system was slower than that of the zebra mussel (Dreissena polymorpha), once established, it replaced zebra mussels in nearshore regions and is colonizing deep regions where zebra mussels were never found. Outside the Great Lakes Basin, quagga mussels do not appear to be increasing to any extent in the Ohio and Mississippi Rivers, even after being present in these rivers for over a decade. In contrast, numbers in the Colorado River system have continued to increase since the quagga mussel was first reported. It will likely become very abundant in all the reservoirs within the Colorado River system, but attain limited numbers in the mainstem. Ecological impacts associated with the expansion of quagga mussels in the Great Lakes have been profound. Filtering activities of mussel populations have promoted the growth of nuisance benthic algae and blooms of toxic cyanobacteria. In addition, the increase in quagga mussels has led to a major disruption of energy flow though the food web. An understanding of food webs in the Colorado River system, particularly the role of keystone species, will help define future ecological impacts of quagga mussels in this system.