Salt spray limits the inland penetration of a coastally restricted invertebrate: a field experiment using landhoppers (Crustacea: Amphipoda: Talitridae)

Abstract

1. Invertebrates from at least three major groups (crustaceans, gastropods and insects) have distributions that are restricted to within a few hundred metres of the coast, but unlike coastal plants there has been little discussion and no tests of the mechanisms that might control such distributions. 2. Coastally restricted landhoppers, Austrotroides maritimus Friend, were transported inland of their natural distribution and established in enclosures at a site in far southern Tasmania. Salt (dry and in solution) was added to these enclosures to test the hypothesis that this species is confined to the coast by a requirement for salt. 3. Over 5 months, A. maritimus persisted and reproduced in the dry salt treatment, but numbers remained low or declined in the other treatments. 4. The addition of salt in solution did not produce the increase in numbers seen in the dry salt treatment. There was no evidence that non-coastal species declined under the salt treatments. 5. The restriction of A. maritimus to the coast is explained in terms of its dependence on a supply of ions from salt spray, rather than a resistance to conditions which other more competitive species cannot tolerate. 6. This conclusion is qualified by the possibility that there may be occasional saltconcentrating events in the coastal zone which raise the salt concentration above the tolerance levels of non-coastal species. 7. Coastal landhoppers, in Tasmania at least, are not plesiomorphic members of their genera, so their distributions appear to be secondary, rather than representing an early stage in land colonization.