PHYSIOLOGICAL AND TAXONOMIC SEPARATION OF 2 DREISSENID MUSSELS IN THELAURENTIAN GREAT-LAKES

Physiological techniques were used to separate two related Dreissena s pecies initially established by electrophoretic and morphological char acteristics (May and Marsden. 1992. Can. J. Fish. Aquat. Sci. 49: 1501 -1506). Samples of zebra mussels (Dreissena polymorpha) and ''quagga'' mussels (provisionally either Dreissena polymorpha andrusovi or Dreis sena rostriformis bugensis) of the same size growing side by side were collected in Lake Erie, thereby ensuring that they had identical ther mal histories. Upper lethal temperatures of zebra mussels were signifi cantly higher than those of quagga mussels. The critical thermal maxim a of zebra mussels acclimatized at 20-degrees-C were half a degree hig her than those of quagga mussels. The average survival times of zebra mussels held at a constant lethal temperature were also significantly longer. These results indicate that in addition to differences in allo zyme loci and shell morphology, these two dreissenids may be distingui shed by important physiological differences in their thermal resistanc e; moreover, there may be important ecological differences associated with the different species of dreissenids in North America.