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

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Summary

  • 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 salt-concentrating 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.

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