Tree Snails in Tahiti

The most endangered inverterbrates on earth

Tree Snails of Tahiti

Species Name – Partula affinisLocation – Tahiti

In support of efforts being made by the Zoological Society of London we support efforts 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: IUCN regards these as the world’s most endangered invertebrates.

ZSL Don McFarlane and a tiny tree snailPartula is a genus of air-breathing tropical land snails in the family Partulidae. More commonly known as the Polynesian tree snail, these and other endemic snails in Polynesia have come under extreme threat from the introduction of the Rosy Wolf Snail, which was intended as a biological control for another introduced species, the giant African land snail, but instead has driven several native snails extinct. We are supporting work to save the remaining species, being bred in captivity for reintroduction at London Zoo.

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 degradation has been resolved!

According to IUCN Partulid, Samoanid and Trochomorphid snails are the most endangered invertebrates on earth.

All of the island’s 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.

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.

The Habits of Tree Snails

Partula snails mostly live in trees, in densely forested, high altitude volcanic regions. Some are found at lower altitudes, but all species require a moist habitat. Older snails tend to live higher up in trees than do youngsters.

Partula are ovoviviparous. This means that rather than laying eggs, the young hatch inside the parent and the parent gives birth to living young snails. Like other pulmonate land snails the Pacific tree snails are also hermaphroditic.

There is some scientific literature about these snails, such as: “Moorean tree snail survival revisited: a multi-island genealogical perspective” – Taehwan Lee, John B Burch, Trevor Coote, Paul Pearce-Kelly, Carole Hickman, Jean-Yves Meyer and Diarmaid Ó Foighil.

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 degradation has been resolved!