Invertebrate Invasions on Pacific Islands and the Replacement of Unique Native Faunas: A Synthesis of the Land and Freshwater Snails*Contribution no. 2001-001 of Bishop Museum's Pacific Biological Survey.

Abstract

The once immense diversity of native Pacific island land snail species, with high single island or archipelago endemism, is declining dramatically. The native/endemic species are being replaced by a much smaller number of widespread tropical ‘tramps’, that is, those species that are most readily transported by humans. The 82 introduced (including 14 ‘cryptogenic’) land snail species recorded include some that were distributed accidentally by Pacific islanders before European exploration of the Pacific and that are now widespread. However, the majority are modern introductions, with many recent accidental introductions often associated with the horticultural trade. Native freshwater faunas were less diverse than the terrestrial faunas and exhibited much lower endemism. Among the 59 alien freshwater species recorded (including 38 ‘cryptogenic’ species), the most diverse and widespread are the thiarids. Predation by and competition with these aliens (as well as habitat loss) are probably important mechanisms underlying the loss of native taxa, but almost no quantitative or experimental work has been done to demonstrate such ecological interactions. Prevention of further spread and of new introductions should be the main approach. Increased public education and development of public trust is essential to the success of these efforts.