Limits to tolerance of temperature and salinity in the quagga mussel (Dreissena bugensis) and the zebra mussel (Dreissena polymorpha)

The quagga mussel (Dreissena bugensis) and the zebra mussel (Dreissena polymorpha) were exposed to varied levels of salinity and temperature in the laboratory to compare the tolerance of each species to environmental stress. The zebra mussel could tolerate 30 degrees C for extended periods and higher temperatures (<39 degrees C) for a period of hours depending on the acclimation temperature and the rate of temperature change. The upper thermal limit of the quagga mussel may be as low as 25 degrees C. Mussels of both species acclimated to 5 degrees C were less able to survive at high temperatures (30-39 degrees C) than mussels acclimated to 15 or 20 degrees C. The reduced upper temperature limit of the quagga mussel implies that it will not be able to expand as far south in North America as has the zebra mussel. Both D. bugensis and D. polymorpha were exposed to three concentrations of NaCl (5, 10, and 20 parts per thousand) to test salinity tolerance. No individuals of either species survived beyond 18 days in salinities of 5 parts per thousand or higher. No interspecific difference occurred in salinity-induced mortality rate.