Relationships between Buffering Capacity of Water and the Size and Calcium Content of Freshwater Mollusks

The size, weight and calcium content were determined for fifteen species of mollusks in 53 freshwater habitats between the limestone formations near Guelph and the granite basement rock in the Sudbury district of Ontario. These morphological variables were related to four buffer variables of water using a canonical correlation analysis. Results showed that the main effect of a decrease in buffering capability and an increase in noncarbonate anion content is a short but heavily calcified shell in Amnicola limosa, Valvata tricarinata, Campeloma decisum, Pisidium casertanum, Pisidium variabile, Sphaerium simile, Sphaerium striatinum and Anodonta grandis grandis. Waters with increasing buffering capability relative to calcium hardness result in short, heavily calcified shells in Elliptio complanata and longer shells with increases in tissue calcium relative to weight in Helisoma anceps and Musculium secris. The latter effect is also found in Pisidium compressum but increasing calcium concentration is more important. Short shells with decreasing calcium content relative to weight is related to decreasing calcium bicarbonate alkalinity relative to total hardness for Physella gyrina but to increases in these buffer variables for Cincinnatia cincinnatiensis. All species except E. complanata showed more than one significant canonical variate suggesting that acidic deposition would not be a factor in the disappearance of any species from water with pH > 5.50.