INTRA- AND INTERSPECIFIC VARIATIONS IN CALCIUM CONTENT OF FRESHWATER MOLLUSCA IN RELATION TO CALCIUM CONTENT OF THE WATER

Analyses of calcium content of molluscs collected from 53 freshwaterhabitats on a naturally occurring calcium gradient between theCanadian Shield and limestone formations in southern Ontarioshowed both intraspecific and interspecific variations in relationto pH, total alkalinity, total hardness and calcium hardnessof the water. The calcium content of individuals is relatedto the calcium concentration of the water for only about halfof the species analysed. Two species (Sphaerium rhomboideumand Sphaerium simile) showed negative correlations, while six(Cincinnatia cincinnatiensis, Pisidium casertanum, Pisidiumcompressum, Sphaerium striatinum, Anodonta grandis grandis,and Elliptio complanata showed positive correlations beteencalcium content of individuals and environmental calcium content.In general, species associated with the sediments (e.g. bivalves)showed better calcium concentrations than did species associatedwith macrophytes (e.g. gastropods). (Received 12 July 1982;