Land Snail Extinctions at Kalaeloa, O'ahu

Abstract

A decline over time in the proportion of native land snail taxa believed to be extinct today at Kalae10a has been interpreted and widely cited as an example of Polynesian influence on the Hawaiian environment. This interpretation is shown to be based on an inappropriate measure of decline and nonstandard calibrations of 14C dates. An analysis of change over time in the diversity of land snail taxa from Kalaeloa sinkholes and recalibration of 14C dates using Bayesian techniques reveals a different pattern, which is interpreted as having two components. There is a long-term, gradual decline in the diversity of native, extinct land snail taxa, explained as the result of desiccation of the sinkhole environment due to a drop in the water table when sea level fell from its mid-Holocene high stand. There is also an abrupt disruption of the land snail fauna late in the stratigraphic sequence. It is argued that this disruption dates to the historic period, when the environment of the 'Ewa plain was drastically altered for sugarcane production and when the vegetation that now dominates the region was introduced. Aside from the appearance of the snail Lamellaxis gracilis, which was introduced to the Islands by Polynesians, the land snail assemblages from the Kalaeloa sinkholes yield no evidence for Polynesian influence on the environment.