Is salinity a limiting factor?
Another possible limiting factor is salinity. Quagga mussels are usually found in fresh water in salinities up to 1; they can reproduce in salinities below 2-3, and are killed by salinities exceeding 6 (Setzler-Hamilton et al., 1997). North American comparisons of salinity tolerances for both species of Dreissena revealed that neither species could survive salinity levels greater than 5; however, Dreissena in Ukraine, show greater acclimation to salinity extremes than in North America, possibly attributed to experiencing more generations in the native range, compared to the more recent colonization in North America (Mills et al., 1996). Salinity tolerances in zebra and quagga mussels increase with larval age, however, both species are negatively affected as embryos by salinities of 4 and beyond with D. polymorpha embryos and larvae demonstrating a higher degree of salinity resistance than D. r. bugensis embryos and larvae (Wright et al., 1996).
