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The Effect of Introduced Euglandina Snails on Endemic Snails of Moorea, French Polynesia


Critics sometimes point out correctly that conservation biologists have little direct, unambiguous scientific evidence implicating invasive nonindigenous species in the extinction of native species. Indeed, long-term intensive studies of native island species are rare, and most damage done by invasive nonindigenous species is observed sporadically, providing only anecdotal evidence. The extinction of land snails of the genus Partula in French Polynesia provides a sad but noteworthy exception to this circumstance. Partula snails on the island of Moorea had been studied intensively by biologists in the 1920's through 1930's, and again in the 1960's through 1970's to examine patterns of genetic variation and formation of new species (Johnson et al. 1977). The Euglandina snail (Fig. 1), a predatory species native to Florida and Central America, was introduced purposely by two government agencies in 1977 to one location on the island of Moorea. The species was intended to act as a biological control (for which it proved ineffective) for the giant African snail, which became established on Moorea about 1970. Moorea is a small island with a diameter of about 12 kilometers and a maximum elevation of 1,207 meters. After 1980 the invading snail was advancing its distribution 1.2 kilometers per year. Clarke et al. (1984) provided precise status and trends information and predicted the extinction of all 14 taxa of Partula snails on Moorea by 1986-1987 (Fig. 2); populations of these snails were removed from the wild for captive breeding. The last wild population of Partula snails was seen in November 1986. An expedition to the highest ridgetops in June-July 1987 failed to find a single individual Partula snail (Murray et al. 1988).

Fig. 1. Euglandina rosea.
Courtesy R. Hue, Hawaii Department of Agriculture
  Author
Lloyd L. Loope
U.S. Geological Survey
Biological Resources Division
Haleakala National Park Field Station
P. O. Box 369
Makawao, Hawaii 96768

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