Reproduction of selected Mollusca in some low alkalinity lakes in south-central Ontario

Abstract

Growth and reproduction of several species of molluscs were examined in six low alkalinity lakes in south-central Ontario. Amnicola limosa (Gastropoda: Amnicolidae) held through the summer of 1982 in cages in acidic lakes (pH 5.78–5.89) grew slower (p < 0.01) than those held in less acidic lakes (pH 6.03–6.84). The development of eggs of A. limosa in the laboratory was impaired at and below pH 5.0 and delayed at pH 5.5 relative to pH 6.0. Hence the recruitment failure and elimination of A. limosa that has been reported in acidifying lakes may be caused by reduced summer growth and (or) impaired development of the eggs. In contrast, Pisidium spp. (Bivalvia: Pisidiidae) do not appear to be adversely affected by low pH in the lakes in this study (pH 5.78–6.84). Caged Pisidium equilaterale did not have reduced growth in the acidic lakes during the summer of 1982. Pisidium casertanum and Pisidium ferrugineum had only slightly reduced (p < 0.05) fecundity (number of extramarsupial larvae per adult) in acidic lakes relative to less acidic lakes sampled in 1980.