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The Land Snails of a Small Tropical Pacific Island, Aunu'u, American Samoa1
THE SAMOAN ARCHIPELAGO lies in the south-central Pacific Ocean and is divided politically between Samoa (formerly Western Samoa) and American Samoa. The native land snail fauna of the Islands exhibits a high level of endemism, but a number of widespread alien species are also present (Cowie 1998).
Recent survey work has documented the current status of land snail biodiversity on the American Samoan islands of Tutuila, Ofu, and Ta'u (Cowie and Cook 1999, 2001, Cowie 2001), and Olosega (Cowie et al. in press), demonstrating the precarious nature of some of the species, the decline of most native species, and the increase and continued introduction (Cowie 2001) of a relatively small number of widespread alien species. This paper focuses on the small (1.6 km2) island of Aunu'u, which lies 1.2 km off the eastern end of Tutuila, the main island of American Samoa (Figure 1).
Almost nothing has been published on the land snails of Aunu'u, despite its close prox- imity to and accessibility from Tutuila. Only two species have been reported, both by Solem (1983): the endemic charopid Sinployea aunuuana, and the widespread Pacific charopid Discocharopa aperta, both collected in 1926 and deposited in the Bishop Museum (Honolulu) mollusk collections. A number of additional species are also present in the Bishop Museum collections, but have never been reported in the literature.
In this paper we report on the land snail species collected during fieldwork on Aunu'u, provide a faunal inventory for the island, including species previously collected, and discuss the fauna of Aunu'u in the context of its close proximity to Tutuila.
MATERIALS AND METHODS
Field survey work was undertaken on Aunu'u in February 2001. Samples of snails were taken at 10 locations (Figure 2). These locations ranged from sea level to 58 m in elevation and from lowland coastal habitats to native forest at higher elevations and to cultivated midelevation habitats.
Collecting protocols followed Cowie and Cook (1999, 2001), Cowie (2001), and Cowie et al. (in press), essentially involving timed hand collecting. This study, like those other studies, was intended as a species inventory survey. Therefore, in the interests of maximizing number of species detected per unit effort, no litter/soil samples...