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Victims of an experiment in biological control that went disastrously
wrong may soon get their revenge. Last week, an expedition set off for the
tiny South Pacific island of Moorea, part of French Polynesia, to find out
if it is safe to reintroduce the island’s native Partula snails. The snails
were wiped out by a voraciously carnivorous mollusc introduced to rid the
island of another exotic species, the giant African land snail, which had
become a serious pest.

In 1977, the Rural Economy Service of Moorea had introduced ‘killer’
Euglandina snails to control the African snail. But Euglandina preferred
to eat the native Partula, and by 1987 the native snails had disappeared
(see ‘Snails going extinct at speed’, New Å®ÉúСÊÓƵ, 11 February 1988).

But since 1986 biologists have been breeding six species of Moorean
Partula snails in captivity; a seventh species became extinct. The first
colonies were established for genetic research at universities in Nottingham,
Perth in Western Australia, and Virginia, but the damage caused by Euglandina
prompted a wider effort to build up a captive population. There are now
17 institutions in the breeding programme, and 3000 captive snails. The
largest colonies are at Nottingham and Jersey and London zoos.

But not all the species are thriving in captivity. Before the researchers
can release captive snails into the wild, they must ensure they are healthy.
So, as well as making a detailed study of the snails’ natural surroundings,
the expedition will spend part of their three weeks on Moorea collecting
information on native plants that could improve the snails’ diet.

Partula has been the subject of intense study for more than a century.
The genus provides biologists with an elegant model for the mechanisms of
evolution. Researchers think the seven species of Moorean Partula probably
evolved from a common ancestor. The deep-sided valleys on the island provided
ideal conditions for speciation. ‘It’s one of the most beautiful, clear
instances of evolution in action,’ says Paul Pearce-Kelly, head keeper of
the Invertebrate Conservation Centre at London Zoo, who is coordinating
the expedition.

The researchers hope to find that the killer snails have died out on
Moorea. ‘If Euglandina are still around, it might be possible to create
safe areas and buffer zones for Partula on the island,’ says Pearce-Kelly.
On Mahe, in the Seychelles, cinnamon plants seem to have stopped the spread
of Euglandina. If planted on Moorea, they might do the same.