A snail from New Zealand that reproduces itself by cloning found in Lake Superior
Friday, May 16, 2003
A tiny snail from New Zealand that reproduces by cloning itself found in Lake Superior
Duluth News Tribune
May 16, 2003
John Myers, staff writer
Five new exotic aquatic species have been discovered in Lake Superior -- including a tiny mudsnail from New Zealand that clones itself and is already wreaking havoc in some Rocky Mountain trout streams.
The five new species also include an amphipod, or freshwater "side swimmer" shrimp, and three new fingernail clams.
The findings were made by a team of Canadian researchers including Igor Grigorovich of the University of Windsor. Their discoveries will be published in the scientific journal Hydrobiologia.
Grigorovich isn't sure if the lake's low calcium levels and cold water will allow the mudsnail to thrive. Local experts aren't expecting the best.
"A Thunder Bay infestation could mean not only is it an issue for Lake Superior, but it's a jumping-off point for inland waters," said Doug Jensen, exotic species information coordinator for Minnesota Sea Grant at the University of Minnesota Duluth.
The tiny mudsnail first came to the United States in 1987, infesting the Snake River in Idaho, apparently after being imported with New Zealand trout. It has spread widely across the mountain West, apparently by trout anglers. It was first seen in the Great Lakes in Lake Ontario in 1991.
The snail has no natural enemies in North America. They reproduce without mating by producing fully formed clones of themselves. One snail can produce hundreds of thousands of clones of itself in a year.
The snails have adapted so well in mountain rivers that they have virtually pushed out native snails, in some cases 95 percent of the invertebrates in some waters. In some rivers, such as the Madison near Yellowstone National Park, mudsnails have colonized in numbers as high as 300,000 per square meter.
David Richards, a research ecologist at Montana State University in Bozeman, said limited research shows the exotic may also be displacing native species like caddis flies and mayflies, which form the backbone of a trout stream's ecosystem.
"The mudsnails are actually changing the food base in streams in the west," Richards said. But the impact on overall trout populations remains unclear, he said.
Unlike some other foreign species that have colonized in Lake Superior -- such as the zebra mussel, goby and ruffe -- the mudsnail appears to favor colder water.
With shipping between Thunder Bay and other ports, it's likely the snail could be moved to other ports and then to inland waters by recreational boaters. So far, Sea Grant educational efforts have helped stall such inland invasions of other exotic species.
If swallowed by fish, the mudsnails can close trapdoors in their shells that prevent fish from digesting them -- so the fish expend energy eating the snails, but get no nutritional value from them.
The trapdoor also allows the snails to survive out of the water for up to a week, Richards said, and makes other disinfection efforts, such as bleach, ineffective.
"Fishermen need to make sure they clean off their equipment, or hose it down to knock them off. They (anglers) can be moving these around and not know it," Richards said. "Once you get them into a watershed, you'll never get them out. You have to try to keep them out if you can."
Research shows mudsnails disperse quickly and easily in rivers, although their numbers are higher in calmer waters. The sections of the study area with the fewest mudsnails held the highest numbers of a threatened native snail, suggesting a competitive relationship between the two.
A parasitic fluke seems to control mudsnail numbers in its native New Zealand, but the fluke apparently didn't accompany the mudsnails to North America.
Researchers are considering using the fluke, but it may first take years of testing to determine if the fluke can harm native snails.
So far, only water warmer than 113 degrees killed the mudsnails in large numbers.
Among the other species found by Grigorovich and his team were a freshwater amphipod shrimp from Europe known as a sideswimmer. Little is known about this species and how it might affect Great Lakes or inland ecosystems, Jensen said.
The additional discovery of the new clams isn't as jolting because they are free-swimming and don't colonize or attach themselves to hard surfaces as do zebra mussels, Jensen said.
There is some good news in Grigorovich's report. Lake Superior, the paper notes, actually has fewer invasive species than might be expected considering the high number of ships that visit the lake's ports each year. That's probably because of the lake's cold, infertile waters, experts said.
The bad news is that the Twin Port's St. Louis River estuary is a hot spot for invasive species because of its warmer, more fertile waters.
Grigorovich said he hopes to return to western Lake Superior this summer or next for more research.