Chinese mystery snail becoming a headache as they invade Cape Coral canals

By Eric Staats


December 6, 2009


A new exotic species could be crawling its way across Southwest Florida.

It’s the Chinese mystery snail — and the biggest mystery about them is what their spread could mean for native ecosystems.

“The impacts are largely unknown,” Lee County Hyacinth Control District deputy director John Cassani said.

The district’s mission to combat the troublesome water plant pest put it on the front line of the snail’s invasion of part of the canal system in Cape Coral in March 2007, Cassani said.

The snails were so numerous that workers stepping out of a canoe couldn’t make a move without crunching at least one of the critters.

Their abundance by 2007 indicated to Cassani that the snails probably had been there for a few years before they were spotted.

Earlier this year, a more formal search for the snails — scooping up random samples from 30 spots in the canal — estimated about 100 mystery snails per square meter, Cassani said.

The mystery snails were not alone. The search also found other non-native mollusks: Asian clam, island applesnail and Malaysian trumpet snail.

Since then, the mystery snails have been found in a new segment of the canal system, further downstream from the original find in west central Cape Coral.

Cassani and co-presenter Shawn Liston, an Audubon of Florida research manager based at Corkscrew Swamp Sanctuary in Collier County, sounded the alarm at a recent exotic species workshop at Florida Gulf Coast University.

“We didn’t want to get hysterical about it, but the population is expanding a bit,” Cassani said.

The snails, which are popular aquarium curiosities and algae eaters, probably found their way to the canal system when hobbyists emptied their tanks, Cassani said.

He theorized that the foreclosure crisis that hit Cape Coral might have exacerbated the problem.

Now that the snails are in the wild, the worry is that they could crowd out native snail species or have unforeseen effects further up the food chain, scientists say.

Besides that, the snails are known to be a host for some parasites that can infect humans.

Cassani said it’s not often that scientists can catch an exotic species early enough to control its spread.

“Unfortunately it may be beyond that point with this species,” he said.

Using fish to control the snails is problematic: one such fish, also a non-native species, already is swimming around Cape Coral, Cassani said.

A native snail-eater, a sunfish species, can’t get its mouth around the adult snails because they grow too big, he said.

A trapdoor-like mechanism allows the mystery snail to retreat into its shell and safely avoid chemical controls, Cassani said.

That leaves getting rid of the snails by plucking them out of a waterway — an option that’s only viable if you know where the snails are.

“Getting the word out to as many people as possible is a good first step,” Liston said.

The mystery snails are not newcomers to the exotic species scene.

As for the origin of its name, various sources chalk it up to pet store owners trying to drum up business or to the snail’s ability to give birth to live babies without a mate.

Scientific literature cites the earliest report of Chinese mystery snails in the 1890s in a market in San Francisco.

Today, they are found in states all over the nation, especially in the northeast and the Great Lakes states.

The first record of the Chinese mystery snail in Florida dates to a 1947 discovery in a lake in Orange County, according to a University of Florida database. The snail also has been reported in St. Petersburg, Polk County, Orlando and the state’s Big Bend region.

So far there have been no reports of the snail in Collier County’s estuaries.

That is little comfort to Jeff Carter, the resource manager at Rookery Bay National Estuarine Research Reserve between Naples and Marco Island.

Carter said the Chinese mystery snail, while slow on its own, could easily hitch a ride on fishing gear or a boat hull and pop up just about anywhere.

“I would not be surprised if at some time we don’t see them down here,” he said.

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