Tahiti

In support of efforts being made by the Zoological Society of London we are acting now to protect seven of Tahiti’s unique tree snails (Partula affinis, P. clara, P. hyaline, P. otaheitana, Samoana attenuata, Trochomorpha cressida and T. pallens). Found nowhere else on earth they are in a very precarious situation and without our assistance it has been predicted that they will go extinct during the year 2002.

All of the islands native snails are threatened with imminent extinction resulting directly from predation by the introduced rosy wolf snail (Euglandina rosea), a species occurring naturally in the south-eastern part of the United States. On several other islands in the Pacific region 100% of the native snails are now extinct as a direct consequence of the predatory behaviour of Euglandina rosea. On the nearby island of Raiatea, for example, 30 out of 35 species have vanished and Hawaii has lost about 50% of its endemic snails.

The endangered Tahitian endemic snail, (Partula otaheitana) - Image courtesy ZSL

The introduced predatory snail, (Euglandina rosea)

From the date of introduction of the predator to the final extinction of the native species takes approximately 10 years on the larger islands but it can occur much more quickly if conditions are ideal and if there was more than a single release point. There were three on Tahiti! Fortunately captive populations exist for some, but not all, of the endemics whose unique genetic diversity is being maintained by carefully managed breeding programmes at some of the more renowned scientific research institutions in the world. According to IUCN Partulid, Samoanid and Trochomorphid snails are the most endangered invertebrates on earth.

Partula hebe bella, a species endemic to the island of Raiatea - Image courtesy ZSL

Endangered Partulid snails are protected within the protective barriers - Image courtesy ZSL

Island species are particularly vulnerable to extinction. They lack behavioural avoidance strategies against introduced predators. They do not have the option of escaping the danger and are, therefore, particularly vulnerable to the slightest change in their circumstances. One stronghold is left for the seven species along the Faaroa Valley on Tahiti where they can still be found but this site is under direct threat as the carnivorous species is spreading rapidly along this isolated valley. The area also has the distinction of containing the best surviving example of Pacific island montane rainforest so our efforts will help to protect these as well. Recent field reports are encouraging and we have every hope of success.

Our funds are being used to create two new ‘exclosures’ within which the last surviving wild populations will be protected. This method has always proven to be successful wherever it has been attempted. Until the introduced predatory snail is eliminated there will always be a threat to the Partulid snails continued existence. When a successful method of controlling Euglandina rosea has been developed the captively reared populations can be re-introduced into their natural habitats once the issue of continued habitat degredation has been resolved!

Partulid snails are regularly monitored by scientists - Image courtesy ZSL

A Partulid snail in close-up - Image courtesy ZSL

Partula otaheitana, a polymorphic species - Image courtesy ZSL

Partula clara - Image courtesy ZSL