Conservation status of Rhytidarex buddlei (Mollusca:Pulmonata:rhytididae) on the Three Kings Islands, northern New Zealand

Rhytidarex buddlei is a giant terrestrial landsnail endemic to South West Island in the Three Kings group. The distribution of old, empty shells indicates that this species was widespread over at least the northern half of the island in the 19th and possibly also early 20th centuries. However, at the end of the 20th century its geographic distribution was restricted to c. 0.03 ha on steep western slopes, and the estimated total population contained no more than 100 and probably fewer than 50 individuals. This decline correlated with, and probably resulted from, ecological changes associated with the widespread establishment of pukanui (Meryta sinclairii) forest on South West Island within the last 200 years. The modem snail population was confined to flax (Phormium aff. tenax) thickets and patches of mixed flax-broadleaved shrubland within an overall mosaic of shrubland and low pukanui forest. The very small size and narrow geographic-ecological distribution of the remaining population of R. buddlei place it at high risk of extinction from stochastic events, adverse ecological changes, and anthropic disturbances. Historical evidence of decline suggests that the species is unlikely to recover on its own without some form of external assistance. Potential conservation measures are discussed, and a preferred option is identified.