“Extinct” Snail Found Alive—But for How Long?

Scientists are, well, tickled pink to rediscover a rosy-colored snail once deemed extinct in the Seychelles

A little over a century ago, it was easy to spot the colorful shells of the Aldabra banded snail (Rhachistia aldabrae). The mollusk was the most common snail species on Aldabra Atoll, a coral island in the Indian Ocean that’s part of the Seychelles but is located closer to Madagascar.

One of the newly rediscovered Aldabra banded snails on Malabar Island, part of the Aldabra Atoll in the Seychelles. Photograph by SIF/C Onezia

As recently as 2005, it seemed shells were the only remnant of the banded snail population. No one had seen one alive since 1997, and experts believed that reduced rainfall as a result of climate change had triggered the snail’s demise. (Also see “Pictures: ‘Extinct’ Monkeys With Sideburns Found in Borneo.”)

In 2007, the journal Biology Letters published a report that declared that, for all intents and purposes, the Aldabra banded snail had joined the ranks of the dodo.

However, in late August, a research team from the Seychelles Islands Foundation (SIF) ventured into a particularly inaccessible area of the atoll and found some suspicious snails. After consulting with several mollusk experts, they announced the snails’ rediscovery to the world.

Bush Bashing

The SIF team had many action items on their three-day expedition to the atoll, but searching for the extinct snails wasn’t one of them. Instead, the team planned to document the habitat of another recently extinct species, the Aldabra warbler, and look for signs of the giant tortoises for which the atoll is famous.

If it hadn’t been for the island’s thick scrub forest, the expedition may have missed the snails altogether. Thick thorn bushes make it difficult to go anywhere quickly, so the crew was taking turns beating back the foliage, or “bush bashing.”

That’s when Shane Brice, the team’s first skipper, noticed a flamboyant little snail on a native tree. Once Brice showed his prize to Catherina Onezia, the senior ranger; Heather Richards, the Aldabra scientific coordinator; and Giovanni Rose, the team’s cook, the team was able to find half a dozen more specimens. (Also see “Photos: Hot-Pink Slug and 5 Other Rosy Animals.”)

Perhaps most notably of all, some of the Aldabra banded snails they found were juveniles.

“So I Was Wrong”

Justin Gerlach, the scientific coordinator for the Nature Protection Trust of Seychelles and the sole author of the 2007 Biology Letters paper, had written that increasingly arid conditions on the island dried out the snails—especially the juveniles, since baby snails require high humidity to survive—and led to their demise.

Gerlach also pieced together rainfall data that showed Aldabra’s dry season had gotten longer, and there were more years with low rates of rainfall.

Gerlach’s hypothesis also fit well with the fact that the last young Aldabra banded snails had been collected in 1976. (See “Pictures: Extinct Species That Could Be Brought Back.”)

“Although the population of the snail around the atoll crashed after the 1970s, it seems that a small number did survive and continued to breed successfully,” Gerlach, who’s also facilitator of the International Union for Conservation of Nature’s Climate Change Working Group on amphibians, told National Geographic.

“So I was wrong—it is not quite extinct; it is extremely close but fortunately still around.”

Not Out of the Woods

For the record, the snail’s comeback isn’t a total shock to the scientists who made the discovery.

Richards, who was part of the discovery team, and colleague Nancy Bunbury said that the general feeling was always that Gerlach’s declaration was a bit premature. (Also see “‘Extinct’ Bird Seen, Eaten.”)

“Aldabra is a very big place, and the fact that a [well-hidden] species like this snail has not been seen for 17 years is not very surprising,” Richards and Bunbury wrote in an email.

“However, the long-term future of this species is of concern in light of its rapid decline.”

Richards and Bunbury said that climate change and sea-level rise remain a long-term threat for the snail, just as they do many other species on the atoll and in coastal areas around the world. Gerlach echoed the same concerns.

“I am delighted that it isn’t actually extinct,” said Gerlach, “but seven survivors is hardly proof that there is nothing to worry about.”

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