The distribution of freshwater gastropods on four Vanuatuislands : Espiritu Santo, Pentecost, Éfate and Tanna(South Pacific)

Abstract

Streams and rivers on the Vanuatu islands of Espiritu Santo, Pentecost, Éfate and Tanna were sampled for gastropods and thephysical and chemical characteristics of the water were investigated between 25/11/95 and 13/12/95. Twenty three species of neritidand forteen of thiarid prosobranch gastropods were found, together with the pulmonate Physastra nasuta and an opisthobranchspecies Strubellia. Six thiarid, two Clithon and one Neritina species, which are present in the Solomon Islands and SouthEast Asia, but which are absent further south on New Caledonia and the Fiji islands, were found on the Vanuatu islands. Onthe other hand, Septaria bougainvillei and Clithon pritchardi, which are present on the Fiji islands and New Caledonia, werefound no further north than the southern Vanuatu island of Tanna. This suggests that Vanuatu is a transition zone for both northernand southern freshwater snails. Éfate had many more species (26) than the other islands (16-19-. This was partly explainedby its central geographical position and the higher ion content of its streams.