Environmental conditions increase growth rates and mortality of zebra mussels (Dreissena polymorpha) along the southern invasion front in North America

Environmental conditions found along an invasion front can mediate spread dynamics of an invasive species. Conditions that affect survival and individual growth rates of founder propagules and the first young-of-year generation can have a profound effect on establishment dynamics. Responses of younger, more sensitive individuals to these novel conditions, in part, determine establishment success. The southern invasion front of zebra mussels in North America expanded into Texas in 2009. To determine mechanisms that could affect establishment of zebra mussel populations at low latitudes in North America, an in situ study was conducted in Lake Texoma, on the Texas-Oklahoma border. Survival and growth were measured of young-of-year juveniles at multiple sites within the reservoir. Age-specific mortality was significantly positively correlated with temperature at all sites and no mortality occurred when temperatures were <26 °C. Shell-length growth rates were the highest ever reported for lentic environments. A decrease in shell-length growth rates was associated with an increase in soft tissue mass, possibly resulting from flexible energy allocation from shell development to gametogenesis after maturation. Overall, survivorship and growth were related to water temperatures and chlorophyll-a concentrations. Warm waters found at lower latitudes along the invasion front could facilitate establishment of populations by increasing growth rates and decreasing time to maturity. However, due to extreme climate events (e.g. drought and flooding) and a strong temperature-mortality relationship, mortality likely will also be high beyond the southern invasion front, resulting in highly dynamic boom and bust cycles.