A REVIEW OF THE BIOLOGY AND ECOLOGY OF THE QUAGGA MUSSEL (DREISSENA-BUGENSIS), A 2ND SPECIES OF FRESH-WATER DREISSENID INTRODUCED TO NORTH-AMERICA

North America's Great Lakes have recently been invaded by two genetica lly and morphologically distinct species of Dreissena. The zebra musse l (Dreissena polymorpha) became established in Lake St. Clair of the L aurentian Great Lakes in 1986 and spread throughout eastern North Amer ica. The second dreissenid, termed the quagga mussel, has been identif ied as Dreissena bugensis Andrusov, 1897. The quagga occurs in the Dni eper River drainage of Ukraine and now in the lower Great Lakes of Nor th America. In the Dnieper River, populations of D. polymorpha have be en largely replaced by D. bugensis; anecdotal evidence indicates that similar trends may be occurring in the lower Laurentian Great Lakes. D reissena bugensis occurs as deep as 130 m in the Great Lakes, but in U kraine is known from only 0-28 m. Dreissena bugensis is more abundant than D. polymorpha in deeper waters in Dneiper River reservoirs. The c onclusion that North American quagga mussels have a lower thermal maxi mum than zebra mussels is not supported by observations made of popula tions in Ukraine. In the Dnieper River drainage, quagga mussels are le ss tolerant of salinity than zebra mussels, yet both dreissenids have acclimated to salinities higher than North American populations; event ual colonization into estuarine and coastal areas of North America can not be ignored.