Conservation Status of Tree Snail Species in the Genus Partulina (Achatinellinae) on the Island of Hawai'i: A Modern and Historical Perspective

Abstract

The Hawaiian tree snail genus Partulina, from Maui, Moloka'i, Uina'i, O'ahu, and the island of Hawai'i, is the sister-genus of the endangered Achatinella, found only on the island of O'ahu. Life histories of species in the two genera are similar, and undoubtedly the Partulina species have been as severely impacted by the collective effects of habitat destruction and introduced predators as have those of the genus Achatinella. Three species of Partulina have been described from the island of Hawai'i: Partulina physa, P. confusa, and P. horneri. Until 1992, there were no recorded sightings of these species for more than 46 yr. Historically, Partulina spp. were recorded at various locations in almost all districts of the island of Hawai'i, including North and South Kona, North and South Kohala, Hamakua, North and South Hilo, and Puna. Partulina physa was found nearly islandwide, whereas P. confusa and P. horneri were mostly located in the Hamakua and Kohala Districts. Partulina confusa and P. horneri were not found in the current surveys. Extensive field surveys on the island of Hawai'i between May 1995 and December 1997 resulted in the location of only one population of Partulina physa, inhabiting a narrow range in the Kohala Mountains. The shell length and reproductive state were recorded for 82 individuals of P. physa from that population. Mean adult shell length was 15.08 mm. Habitat loss, much of which occurred between 200 and 100 yr ago, has likely been the greatest factor contributing to the decline of the Partulina spp. of the island of Hawai'i. Predation and shell collecting, and possibly climatic changes and pathogens, have also contributed to the decline of the Partulina species on Hawai'i Island. A small captive population of P. physa at the University of Hawai'i at Manoa has suffered high juvenile mortality (78%).