Purple Snail May Be Climate Change Casualty

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The Aldabra banded snail. i

The Aldabra banded snail lived on the Seychelles Islands in the Indian Ocean. John Nielsen/NPR hide caption

toggle caption John Nielsen/NPR
The Aldabra banded snail.

The Aldabra banded snail lived on the Seychelles Islands in the Indian Ocean.

John Nielsen/NPR

A snail you've probably never heard of on the far side of the world was declared extinct this week. Normally, that wouldn't be worth mentioning. But this was not your typical extinction; it may be the first tied directly to global warming.

The Aldabra banded snail lived on the Seychelles Islands in the Indian Ocean. Biologist Justin Gerlach of Oxford University says it had very pretty shell: dark, purplish blue with an orange band around.

"It's quite a conspicuous species," Gerlach says.

Or at least it was 30 years ago, when scientists plucked them off of fresh leaves all over the islands.

"Since then, it has been impossible to find. The last one was found in 1997 and it was collected simply because the person who collected it thought it was strange and didn't know what it was," Gerlach says.

It's hard to prove conclusively that a species is extinct, but Gerlach says he's all but certain that in the late 1990s, the last Aldabra banded snail curled up inside its purplish shell and died. In a paper in the journal Biology Letters, Gerlach lays the blame on an unusual series of summers so long and hot that they killed off all the younger snails.

"So the juveniles just weren't surviving, and the adults gradually died off," Gerlach says. "Now we don't have juveniles or adults."

Gerlach says he found the proof he needed in shells gathered up by collectors. Smaller shells, once common, disappeared with the frequent long, hot summers. He suspects — but cannot prove — that these bad summers are a side effect of global warming. If he's right, then this snail has earned itself a grim distinction: It would be the first species in the modern era to become extinct as a direct result of climate change.

It probably won't be last, says biologist Diane Debinski of Iowa State University.

"I think what we are seeing is the tip of the iceberg in terms of extinction events. I expect that we're going to be seeing more stories like this," Debinski says.

Debinski studies the links between extinctions and climate changes. She says the paper doesn't prove that this snail was done in by global warming, but she wouldn't be surprised if it turned out to be true. That's partly because ecologists have been saying for years that the species most vulnerable to climate change are the ones trapped in isolated habitats, like small islands, mountain tops, or wild lands surrounded by people.

In those situations, says Debinski, "organisms can't move as easily, and so if the world changes, they are pretty much stranded in these patches of habitat. Maybe they can't go across an interstate highway, maybe they can't go through an urban area, and so the climate they like to move into is not accessible."

In other words, if the globe continues to get warmer, what happened to that snail you never heard of could soon be happening all over the world.



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