Relationships between Demographic Features of a Pill Clam (Pisidium casertanum) and Environmental Variables

Seventeen populations of Pisidium casertanum (Poli 1795) from six rivers and eleven lakes were studied to determine how population demographics were related to environmental conditions. Univariate and multivariate analyses of the data suggest that natural variation in environmental conditions accounts for a significant amount of variation in the demography of this clam. Correlations among principal components of environmental variables and of population demographics were used to assess the relationships between environmental variables and population features. Abundance, production, and biomass were higher in habitats with warmer ice-free temperatures, but the length at which adults first developed shelled larvae, and maximum adult length and weight, were less in such habitats. Productivity, biomass, and the proportion of adults brooding shelled larvae were higher in habitats that had higher calcium hardness, conductivity, pH, alkalinity, and sulphate levels. These factors should be considered in studies that attempt to relate variation in population statistics of sphaeriid clams to environmental degradation.