Effects of Calcium and pH on the Reproductive Success of Amnicola limosa (Gastropoda)

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Abstract
Field and laboratory experiments were designed to examine the relationship between water chemistry (especially pH and calcium) and the reproductive success of Amnicola limosa. Fecundity (no. eggs∙female−1) was positively correlated with lake buffering capacity (P = 0.002) in naturally occurring populations. We documented a 66% reduction in fecundity in lakes over a pH range of 7.6–5.8. However, fecundity was higher than expected in a highly-coloured, low-pH lake. The number of juveniles produced per egg was not related to any water chemistry variable (multiple R2 = 0.186). A laboratory experiment demonstrated that pH, and not calcium, was limiting embryonic development. All embryos held at pH 4.5 failed to hatch. Eggs held at pH 5.5 experienced reduced hatching success (P = 0.013) and delayed development (P < 0.001) compared with those held at pH 6.5. Length of newly hatched snails did not differ significantly between treatments (P = 0.891). The critical calcium concentration required for embryonic development in laboratory incubation lay between 0.14 and 1.11 mg∙L−1. This is well below the calcium concentration of acidifying lakes in south-central Ontario.

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