Diversity and current conservation status of Melanesian–New Zealand placostyline land snails (Gastropoda : Bothriembryontidae), with discussion of conservation imperatives, priorities and methodology issues

Abstract

We review the diversity and conservation status of Placostylinae, land snails endemic to the western Pacific. Their narrow-range endemism, large size and associated vulnerability, consumptive exploitation by people, and habitat loss and degradation (inclusive of invasive predators) threaten their survival. There has been considerable attention from conservation biologists in New Caledonia, Lord Howe Island and New Zealand aimed at species recovery. Nonetheless, only on uninhabited, pest-free islands do these native snails persist in high numbers, and these remaining ‘sanctuaries’ are dependent on biosecurity vigilance. For other populations in New Caledonia, Lord Howe Island and New Zealand, the benefits of control of invasive mesopredators have been demonstrated, but it remains unclear if long-term persistence of Placostylinae can be achieved in degraded landscapes that continue to be subject to anthropogenic pressures. For species in Fiji, Vanuatu, and the Solomon Islands – the centre of Placostylinae diversity – their conservation status is not known with any certainty due to lack of basic data on range and population trends. Recent IUCN Red List assessments indicate a high level of extinction risk among Fijian species due to narrow geographic range coupled with decline in habitat extent and quality. Further inventory and ecological work is urgently needed in the Solomon Islands and Vanuatu to enable assessment of extinction risk and identify threatening processes. We identify four priority areas for advancing the conservation of Placostylinae, especially in Melanesia, and discuss the most pressing methodological issues. Molecular phylogenetic analyses are needed to provide an evolutionary framework for taxonomic revision and to underpin development of both conservation policy and species recovery plans.