Status of Tree Snails ( Gastropoda : Partulidae ) on Guam , with a Resurvey of Sites Studied by H . E . Crampton in 1920

Tree snails of the family Partulidae have declined on Guam since World War II. One species, indigenous to the western Pacific, Partu/a radio/ata, is still locally common along stream courses in southern areas of the island. The Mariana Island endemic Samoanajragilis is present but not found in abundance anywhere on Guam. Partu/a gibba, another Mariana endemic, is currently known only from one isolated coastal valley along the northwestern coast, and appears to be in a state of decline. The Guam endemic Partu/a sa/ifana was not found in areas where it had been previously collected by earlier researchers, and is thus believed to be extinct. The decline and extinction of these snails are related to human activities. The single most important factor is likely predation by snails that were introduced as biological control agents for the giant African snail, Achatina ju/ica. The current, most serious threat is probably the introduced flatworm P/atydemus manokwari. This flatworm is also the likely cause of extinctions of other native and introduced gastropods on Guam and may be the most important threat to the Mariana Partulidae. 1970). With the exception of the partulids of the Society Islands, all are lacking study. The most extensive studies that addressed the endemic and native snails of the Mariana Islands were conducted by early explorers, such as those of the French Freycinet expedition of 1817-1820. More recent collections made by Abbott in 1945 and Langford in 1946 are housed in the U.S. National Museum of Natural History. Kondo (1970) and Easley (1970) provided further information about the biology of the Mariana partulids, based on specimens collected during the Pacific Science Board's survey for the giant African snail, Achatinaju/ica, in 1949. The most comprehensive study of the partulids of the Marianas was conducted in 1920 by H. E. Crampton. In 2 months of study, Crampton was able to collect specimens of Partulidae on the island of Guam and, to a lesser extent, on Saipan to the north. Crampton's findings were published in a monograph of the Partulidae of the Mariana Islands (Crampton 1925). Both Guam and Saipan have undergone extensive environmental disturbance since World War II. Recent economic development 77 1 Contribution No. 306, University of Guam Marine Laboratory. Manuscript accepted 8 April 1991. 2 Marine Laboratory, University of Guam, UOG Station, Mangilao, Guam 96923. TREE SNAILS OF TROPICAL PACIFIC islands have been of interest since early exploration of Oceania and have proven to be useful subjects to organismal and evolutionary biologists (Crampton 1916, 1925, 1932, Clarke and Murray 1969, Johnson et al. 1977, 1986, Hadfield and Mountain 1980, Murray and Clarke 1980, 1984, Hadfield 1986, Hadfield and Miller 1988). Recent work has focused largely on the conservation of these snails (Clarke, pers. comm.) as they disappear from their former ranges for a variety of reasons (Hart 1978; Kondo, pers. comm, 1980; Tillier and Clarke 1983, Clarke et al. 1984, Hadfield 1986, Murray et al. 1988, Meadows 1989). Most of this work has been concentrated on the Hawaiian achatinelline snails and the Partulidae of French Polynesia. However, tree snails of the family Partulidae are widely distributed in Oceania, with five species reported from the Mariana Islands in the western Pacific (Crampton 1925, Kondo 1968,