Hidden behind the huge chimpanzee ‘Budongo Trail’ building at Edinburgh Zoo is a small shed in which a little-known conservation project is growing. Zookeeper Ross Poulter introduced me to the tiny, shy inhabitants of the glass tank in the warm, red-lit room, picking out a pearly grey shell with two dark bands across it and leaving it on his palm. Slowly a wrinkled, slimy creature began to unfold itself from its spiral home, gradually morphing into a familiar shape as its delicate eye stalks extended towards me and it slides forward, leaving a shining trail behind. Some may have been repulsed, but for me there was nothing repellent about this intricate invertebrate, and they definitely won my sympathy after Ross told me the little-known tale of a familiar story; how human ignorance and mistakes had caused their population collapse in their native tropical islands in French Polynesia.
“The issues with the Partula are that back in 1967 the Polynesian government introduced African land snails as a food source for the islanders and they soon went out of control because they lay hundreds of eggs and they started eating the farmer’s crops. So the government decided to introduce a carnivorous snail called Euglandinea rosea to kill the African land snails but without any trials being done the carnivorous snail (which is actually about a third of the size of the African land snail) was always only going to eat the young African land snails so it turned its attention to the native snails, the Partula, which is why they have become so rare.”
In times past, before human interference, Polynesian tree snails had evolved an array of species to utilise the many niches within their island ecosystem, not unlike Darwin’s famous finches. However, from boasting a diverse 125 species in 3 genera (including Partula), 50 species are now extinct in the wild and 24 only exist in captivity. However, Poulter is involved in a collaborative project between several British zoos to amend the mistakes of previous generations and bring these little molluscs back home.
“We’re going to go with three types of snails, the hyalina, the affinis and the nodosa. Affinis is the only one we have in this zoo, and we’re taking back 93 adults which we’ve bred over the last year. We’re only taking back the adults because the juveniles are too small and won’t survive the journey, as they become hardier as they grow up. The reason why we’re going to take these three from different collections around Europe and America is because where the reserve is in Tahiti is historically the natural site for these three snails. Affinis is still there, hyalina is still there on Tahiti but not in the valley where the reserve is and nodosa is extinct in the wild.
“There’s also some work being done on the Euglandina because we want to get rid of the Euglandina from Polynesia, of course it’s pretty difficult to get rid of a snail that has taken complete control of the island so some people are looking into different types of toxins that are poisonous to that kind of snail, and they’re also looking at recreating the slime trails so we can encourage them into a physical trap and kill them that way.”
This is not the first project of its kind. In 1996 a reserve was built on the island Moorea, and three Partula species were introduced, but it failed through human error.
“The barriers of the reserve are basically a salt bath that runs along the ground and two electric wires along the top to stop Euglandina from getting in. One of the human errors was the salt bath not being topped up and the electric fence was touching foliage from outside the reserve and it was shorting out. So it was breached by Euglandina which got in and ate most of the snails so it had to be restocked and similar problems happened again so the decision was made to remove all the remaining snails and send them back to captivity.”
The Partula reserve is the world’s smallest nature reserve, at 12m by 9m, but the history of these diminutive creatures shows that little animals do not mean little problems, and our species is just as responsible for them as we are for the bigger beasts that we visit the Zoo to see.
Originally published in the Student, October 2013.