A Review of the Biology and Ecology of the Quagga Mussel (<i>Dreissena bugensis</i>), a Second Species of Freshwater Dreissenid Introduced to North America

SYNOPSIS. North America's Great Lakes have recently been invaded by two genetically and morphologically distinct species of Dreissena. The zebra mussel (Dreissena polymorpha) became established in Lake St. Clair of the Laurentian Great Lakes in 1986 and spread throughout eastern North America. The second dreissenid, termed the quagga mussel, has been identified as Dreissena bugensis Andrusov, 1897. The quagga occurs in the Dnieper River drainage of Ukraine and now in the lower Great Lakes of North America. In the Dnieper River, populations of D. polymorpha have been largely replaced by D. bugensis; anecdotal evidence indicates that similar trends may be occurring in the lower Laurentian Great Lakes. Dreissena bugensis occurs as deep as 130 m in the Great Lakes, but in Ukraine is known from only 0–28 m. Dreissena bugensis is more abundant than D. polymorpha in deeper waters in Dneiper River reservoirs. The conclusion that North American quagga mussels have a lower thermal maximum than zebra mussels is not supported by observations made of populations in Ukraine. In the Dnieper River drainage, quagga mussels are less tolerant of salinity than zebra mussels, yet both dreissenids have acclimated to salinities higher than North American populations; eventual colonization into estuarine and coastal areas of North America cannot be ignored.