Response of aerially-exposed zebra mussels (Dreissena polymorpha) Paukstis, G. L., F. J. Janzen, and J. K. Tucker. 1996. Response of aerially-exposed zebra mussels (Dreissena polymorpha) to subfreezing temperatures. Journal of Freshwater Ecology 11(4):513 519. Reprinted by U.S. Geological Survey, Environmental Management Technical Center, Onalaska, Wisconsin, September 1997. LTRMP 97-R017. 7 pp. (NTIS #PB98-104243) ABSTRACT Zebra mussels (Dreissena polymorpha) were subjected to a temperature cycle that exposed them to subfreezing temperatures over a three hour period, similar to that which may be encountered in nature. Supercooling was clearly exhibited by 16 of 17 individuals with thermocouple probes placed inside of the mantle. Cooling was continued for approximately 45 minutes after exotherms were produced to allow tissue freezing to occur. Two individuals with probes survived the cooling cycle, as did four of the 16 control animals without probes. Supercooling occurred between -1.8 C and -3.0 C ( = -2.4. n = 16) and the rebound temperature ranged from -0.1 C to -1.5 C ( = -0.6, n = 16). One of the surviving zebra mussels implanted with a thermocouple probe had a supercooling point of -2.4 C and a rebound temperature of -0.6 C. This individual, cooled for an additional 45 minutes after exhibiting an exotherm, reached - 1.7 C inside of the shell, indicating that at least some individuals can tolerate short-term freeze stress. KEYWORDS Aerial exposure, Dreissena polymorpha, freeze tolerance, Illinois, Mississippi River, supercooling Western sand darter (Ammocrypta clara) in Pool 26 of the Mississippi River