Invasive Potamopyrgus antipodarum (New Zealand mud snails) and native snails differ in sensitivity to specific electrical conductivity and cations

When species are introduced to novel environments, abiotic conditions must be suitable for species to become invasive. For example, water chemistry must be acceptable for aquatic non-natives to colonize and persist. In two laboratory experiments, we measured growth and survival of Potamopyrgus antipodarum, a worldwide invasive snail from New Zealand, and two co-occurring native snails [Pyrgulopsis robusta and Galba (Bakerilymnaea) bulimoides group] to contrast the relative sensitivity of the three species to aspects of water chemistry (specific conductivity and concentration of multiple cations). Low conductivity reduced growth and survival of Potamopyrgus but did not affect growth of native snails and only reduced survival of one native species, Pyrgulopsis, at extremely low conductivity. In contrast, neither specific cations nor concentration affected growth and survival of Potamopyrgus, but both affected native snails; Pyrgulopsis, grew more at higher concentrations of cations, and Galba grew nine times faster with added potassium than with added magnesium and had higher survival in concentrated than in diluted solutions. Thus, the invasive and native snails differed in their sensitivity to water chemistry: the invasive snail is more sensitive to conductivity, and the native snails are more sensitive to the concentration of specific cations. Our conclusions are consistent with previous studies and with the distribution of Potamopyrgus in the western USA, and parts of Europe, where density of the invasive snail increases with conductivity. Thus, native snails may be able to escape negative effects of the invasive snails by inhabiting areas with low conductivity, when ion concentrations are sufficient.