Shell dissolution and mortality in the freshwater snailViviparus ater

Populations of the prosobranch snailViviparus ater (Christ. and Jan) in Lake Zürich and Lake Maggiore (Switzerland) were compared in order to evaluate how soft water in Lake Maggiore affects shell morphology and population dynamics. A low calcium concentration of the water (3.5 mg CaCO₃l⁻¹) was the main reason for shell dissolution in Lake Maggiore. At some places shell damage was augmented by a stony ground and wave action. In Lake Zürich (11.5 mg CaCO₃l⁻¹) the shells were not damaged. The snails in Lake Maggiore were smaller, suffered higher mortality and had a shorter life span than those in Lake Zürich.