Moorean snails were on a fast pace to extinction

Plants and animals on islands are particularly prone to extinction. Mostly, these island species consist of very small populations, and if something happens to their small island habitat, they basically have nowhere else to go. One of the largest threats to animal species on islands is the introduction of foreign species. May these be predators or competitors to the natives, usually the struggle for survival goes in favor of the introduced species. Mostly, introduced species stem from widespread populations on the continents, and they have evolved under enormous pressure from predators, competitors, and parasites. Island species, on the other hand, experienced less pressure from other organims in their past. Therefore, they might end up being the weaker opponent in a fight for resources in their limited island habitat. In this context, the story of the Partula snails on the French Polynesian island of Moorea is particularly drastic. Snails of the genus Partula once were the most common land snails on the Pacific islands. According to the IUCN, there might have been around 100 species of Partula at one time. On the island of Moorea, seven species of Partula have been found until the early 1980's. They used a diversity of different microhabitats, some of them living on tree trunks or leaves, others on the ground. Only seven years later, in 1987, an extensive survey revealed that none of these Partula species existed in the wild any more. One of the seven species was definitively lost, the other six were saved by captive breeding programs. What has happened? Obviously, Partula became rare on Moorea when a carnivorous snail, Euglandina rosea, was introduced to the area in 1978, in order to control the Giant African Snail (Achatina fulica). Giant African Snails have been introduced in the 1960's to be farmed for food, and soon developed into a major agricultural pest. However, instead of controlling Achatina, the carnivorous Euglandina preferred to feed on the smaller Partula species, and managed to eradicate all species of Partula which were native on Moorea.

Luckily, scientists reacted early enough to establish a number of captive Partula populations, which are now bred in different zoos in America and Europe. Rather than in their native habitat, you might see Partula in a number of zoos which participate in the breeding program (for example, there is a large colony at Jersey Zoo). There are still hopes that the pest snail Achatina and the carnivorous Euglandina can be eradicated on Moorea, and give way to the land's native Partula. In certain areas deep in the island's forest, cleared of their fierce predator and protected by Euglandina-proof barriers, Partula from captive breeding programs have been reintroduced.

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