Invading Mud Snail Tiny, but a Big Headache

The New Zealand mud snails may be small, but their arrival in Southern California has environmentalists wondering if they’ll cause a gargantuan problem.

The snail, an invasive species one-third the size of a housefly, has been spotted in four streams. Regarded by some as aquatic locusts, these voracious gastropods hitchhike their way into waterways by clinging to boats and boots, animal fur and bird feathers.

Though small, they can consume large amounts of food that otherwise would have fed other wildlife and can reach concentrations of hundreds of thousands per square yard.

To make matters worse, no one has figured out how to eradicate the snails once they turn up.

“We’ve found there’s not much we can do to keep them from spreading,” said Steve Martarano, spokesman for the state Department of Fish and Game. “There’s just no way we can contain it.”

Local environmental groups learned last week that the snails had been found during routine bug surveys conducted last winter. The snails were discovered in sections of Malibu Creek, Las Virgenes Creek, Lindero Canyon Creek and Medea Creek. Their appearance in Malibu Creek alarmed environmentalists trying to protect the two endangered species that live there: the red-legged frog and Southern steelhead trout.

One environmental group, Heal the Bay, has suspended its monthly water quality testing activities in hopes of preventing the snails from spreading.

“It’s scary. We’re already really limited in the habitat we have for our endangered species and so anything that competes with other bugs -- bugs that are really important fish food and amphibian food -- is frightening,” said Mark Abramson, stream team manager for Heal the Bay.

Scientists in the U.S. first encountered the snails, Potamopyrgus antipodarum, in an Idaho river in the 1980s. The creatures have since established themselves in rivers in 10 Western states and three national parks. The snails arrived in California three years ago, invading rivers in the eastern Sierra Nevada.

The tiny gastropods have brown or black shells and range in size from a grain of sand to an eighth of an inch long. Asexual and prolific, the snails can double in number within months.

There’s some debate over how harmful they could turn out to be.

In Northern California, state wildlife officials say the snails have taken a lot of territory but haven’t caused any major problems to fish populations.

“There’s certainly a concern, but we just don’t know,” Martarano said. “They haven’t been around long enough.”

Controversy aside, predicting what effect the snails could have on Southern California’s streams is like playing “ecological roulette,” said James T. Carlton, professor of marine sciences at Williams College in Williamstown, Mass.

“Controlling invasive species is often like trying to get the toothpaste back in the tube: It’s best not to let it out in the first place,” he said. “In an area like Los Angeles, which has already lost so much of its native species, it’s very troubling to see another invasive come in.

“The size is deceptive, it’s the numbers that really matter here,” he said.

Environmentalists have no idea how the snails got to Southern California, but they’re responding quickly. One thought is to eradicate them by letting infested rivers run dry, but a number of other animals would die too.

An emergency meeting of environmentalists and government biologists on how to tackle the mud snail will take place June 20 in Los Angeles.

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Potential hazard

Although very small, New Zealand mud snails reproduce rapidly and can carpet the bottom of lakes or streams. They have no natural enemies.

Snail facts

* First detected in the U.S. in the Snake River in Idaho in 1987; arrived in California three years ago and are spreading rapidly in the state

* Can choke out native snails and insects

* Deprive fish of their main sources of food

* Damage fisheries and native habitats

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What can you do?

* Clean all fishing gear and boating equipment after each use, using hot water and bleach or heavy cleaner

* Never move live fish or plants from one body of water to another

Sources: National Park Service; city of Davis; www.protectyourwaters.net