Saving snails

It's not just the big mammals that need saving - snails do too!
14 November 2017

Interview with 

Dave Clarke, ZSL London Zoo


Partula snails


When we think about conserving wildlife, you probably think of the big stuff - pandas, tigers, elephants and other endangered mammals. But, as Dave Clarke - head of invertebrates at ZSL London Zoo - told Kat Arney, the truly endangered animals are at the other end of the scale.

Dave - We’re in our Polynesian tree snail breeding room at the moment. So we’re surrounded by tanks with loads of little snails in them. They're one of our rarest animals that we keep here and one of the rarest in the world.

Kat - When you think of a zoo, you probably think of the big things like tigers and elephants. It seems strange to me that these small snails are incredibly rare. What is their story?

Dave - Well, there's probably far more invertebrate animals that are rare than the big animals, because the big animals are easy to see. There's a lot of invertebrates which go extinct all the time because of loss of habitat. Many of that haven't even been described yet. The other thing about that is that the invertebrates are fundamental to ecosystems so can be as important, if not more important in recycling and pollination, and things like that.

So, they have a great importance which is much greater than their size. So these little guys here feed on decaying plant material which is an important job in ecosystems. They're just as worthy of conservation as a big beautiful elephant.

Kat - These are Polynesian snails. What was their journey to Polynesia to here and why have you got them?

Dave - Well, they were studied actually over a hundred years ago by someone called Crampton who was looking at the speciation of the snails. You get different types of snails in different valleys on each individual island throughout South Pacific.

That work was picked up in the 1980s and ‘90s by a group of professors. They realised that at that time, the animals are also becoming extinct in the wild and this was a slightly complicated story of biological control gone wrong because the giant African land snail was introduced into Polynesia as a potential food crop.

They became a pest and what they did to try and control their numbers was introduce a predatory snail from America called the rosy wolf snail. But the rosy wolf snail liked bite-size Partula snails and not the big giant land snails and set about the extinction of them on the islands. On one island, most of the species have become extinct within just 10 years.

Kat - Wow! And how did you manage to salvage these snails and bring them here and what have you been doing with them?

Dave - Because people were studying them, they had quite a few in captivity. We then got involved and started mounting rescue expeditions for the ones that were going extinct in the wild. Some, we were lucky with; some, we were too late. In some cases, the animals went down to tiny numbers.

There's a species over there called Partula tohiveana and they went down 23 individuals at one time. But we have the opportunity to get them going in captivity but that species is over 2,000 now and we’re have been able now to release some back to the wild.

Kat - That species, if it went down to three individuals and now, you’ve grown it back up to 2,000, and you're putting them back into the wild. Surely, that is now quite an inbred population. How have you been studying them at a genetic level to make sure that they're OK?

Dave - What probably happened with these snails was that they had a relatively small gene pool anyway because they popped up on these Pacific islands as they were coming up, volcanic activity from the ground.

So, they're less than a million or two years old in many cases. But they probably arrived just on a bird’s foot or a log or something like that so it would’ve been a small genetic base anyway. So, loss of diversity in these may not that be significant and there is perfect example there. Others, we do try to maintain as much diversity as possible.

Where we’ve been able to, we’ve collected larger numbers from the wild, and we we’ve tried to manage them on a group basis. So, unlike individuals where you might know who Derek the Gorilla is, with the Partulas, we have them in tanks and you can see these are populations of snails usually, between maybe 20 and 100 snails.

They are our base level group and we might out cross some of them to other groups of the same species. But in most cases, we keep them as direct lines and they do very well.

Kat - So you're effectively treating each tank of snails as kind of one thing, one genetic organism.

Dave - That’s right. We’ve had a stud book for snails for 20 years now. We keep records of all the different species, how many each year, who’s keeping them because it’s a worldwide programme. There are 15 institutions worldwide that keep them and we help maintain the numbers here at London Zoo.

Kat - Now, I see quite a lot these tanks are empty and you mentioned you’ve been reintroducing these snails back to the wild. Presumably, they’ve gone back where they came from. What did you do with them?

Dave - That’s right. A little earlier this year we did some reintroductions to the wild. We’re doing it for a few years now and 1,300 of the snails in this room went out to the wild alongside animals from Edinburgh Zoo and a few other zoos in the UK. That’s a global programme in trying to reintroduce the species back into the wild.

That’s obviously the main aim of any conservation breeding programme. And it isn’t always easy to get to that point but we have done so after what's over 30 years of working with these snails in captivity. It’s great to be actually putting them back in the wild where they belong.

Kat - But what about the predator that was introduced? Is it now safer for them to be there or are we just going to see them being wiped out again by these predatory snails?

Dave - Well, it’s still a complicated dynamic in the wild. So the predator snail is still there but what happened, which happens with a lot of biological controls, is there was kind of boom and bust where when they first got to the island, they went, “Yippee! Loads of food!” and spread across the island within 10 years. But now that their populations have dropped right back, there's a good chance of our Partula snails surviving even with some predation.

So, that’s what we’re looking at. It gets more and more complicated. Life is never easy. There's a little flatworm which has been introduced as well which can predate the snails, but what we’ve got is ongoing situation working with the Tahitian government, people on the ground studying the snails, looking how well they're doing, and we also know that animals that were released a year or two ago are still persisting in the wild. So everything is looking good.


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