Temperature plays an important role in the seasonal life cycle and physiology of zebra mussels. Particular temperature regimes cue major life cycle events.
Effect of Temperature on Spawning
A female D. polymorpha releases eggs, visible as tiny white dots, into the water column via the exhalant siphon.
Zebra mussel spawning (release of gametes into the water column) will not generally occur at temperatures below about 12 °C for either North American (Claudi and Mackie 1994) or European (Kornobis 1977, Stanczykowska 1977, Borcherding 1991, Sprung 1991) populations. Waters above this temperature coincide with June-September in most of the North American temperate freshwater systems. As temperatures decline in the fall, zebra mussels begin gametogenesis (development of sperm and eggs) while food supplies are still adequate, and then accelerate this process with rising temperatures in the spring (Borcherding 1991). There is evidence, however, that quagga mussels in deep waters of the Great Lakes are capable of spawning at temperatures near 5 °C (Roe and MacIsaac 1997) and 9 °C (Claxton and Mackie 1998), and this may explain in part why quagga mussels are proliferating in the hypolimnion of the Great Lakes.
Effect of Temperature on Survival
Since zebra mussels cannot withstand freezing temperatures, their lower temperature limit is 0 °C (Paukstis et al. 1997). Although they can survive temperatures slightly in excess of 30 °C for short periods, optimum temperatures are generally less than 25 °C. In European waters, the upper temperature limit for D. polymorpha has been reported to be about 32-34 °C (Karatayev et al. 1998). In a Louisiana field study (Mihuc et al. 1999), increasing temperatures (and decreasing dissolved oxygen levels) correlated with adult zebra mussel mortality; in May-August, minimum daily temperature warmed above 29 °C in a floodplain and 32.5 °C in riverine sites. It is important to realize, however, that once these southern populations become acclimatized to warmer habitats, the upper thermal tolerances could shift after years of selection pressure.
Effect of Temperature on Growth
Temperature also has a significant effect on mussel growth. The minimal temperature for growth and development in D. polymorpha is approximately 10 °C (Karatayev et al. 1998). High feeding rates lead to high growth rates, and Aldridge et al. (1995) reported that: 1) the feeding rates of D. polymorpha declined by 73 percent as temperatures rose from 20 to 32 °C, and 2) above 28 °C, D. polymorpha was unable to match energy expenditures with concurrent food intake and was forced to rely on stored fuels.