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Species Survivors
Minnesota works hard to keep invasive plants and animals from becoming established, but the global economy means the battle will never end.
By Dennis Lien
St. Paul Pioneer Press

For an enduring image of non-native species, it's tough to beat silver carp, a large, voracious Asian fish that's moving up the Mississippi River and can explode from the water like an out-of-control torpedo.

But in the past century, and especially the past decade or two, other alien invaders have left a lasting, if more insidious, mark on Minnesota.

From Eurasian water milfoil, which crowds out native lake plants, to zebra mussels, which foul beaches and out compete native clams, the state finds itself under attack from plants and animals that have established footholds here and are resisting eradication. Other potentially devastating threats, such as the New Zealand mud snail and the emerald ash borer, a killer of ash trees, are on the horizon.

They're getting here through the air, flying from other infested places. They're reaching us by water, from easy pathways such as the Great Lakes and the Mississippi River. They're hitching rides on cargo in cars and trucks. They're even coming through the mail.

The sheer speed of today's transportation systems and an increasingly global economy that ships material from all over the world has outpaced traditional geographical barriers, posing problems for state regulators trying to keep the state from being overrun.

"A lot of commodity is coming from underdeveloped parts of the world, where there's not the greatest infrastructure or sanitation,'' said Geir Friisoe, section manager for plant protection at the Minnesota Department of Agriculture.

Despite those onslaughts, Minnesota is better off than many other states, where even more non-native invaders have become established.

One reason is our climate, which is too cold for many species that have found new homes in places such as Florida. "There's something good to be said for hard, hard winters,'' Friisoe said. "It knocks down a lot of those kinds of pests.''

Another is our location midway between the two coasts, where invasive species often are introduced and addressed first.

Still another is the state's relatively early response to invasive threats. Before many other states committed resources to them, the Minnesota Department of Natural Resources and the Agriculture Department were already at work.

In 1991, the Minnesota Legislature established an Exotic Species Program within the DNR that's responsible for monitoring and managing harmful exotics, including animals and aquatics. The agriculture department handles other exotic insects and plants.

Earlier this year, the Legislature strengthened plant-protection standards and raised the exotic species program's budget from $1.2 million a year to $1.6 million. "I think it was a recognition that we have more problems, higher costs, and we need to do more to address this issue,'' said Jay Rendall, the DNR's exotic species coordinator.

"The states I talk to, they look to Minnesota as a leader in terms of education and changing boaters' behavior,'' said Jeff Gunderson, associate director of Minnesota Sea Grant in Duluth.


Invasive species have been with us for more than a century.

Common carp, for example, were brought here in the 19th century as a food source. Eventually, they took over many southern wetlands and lakes, damaging the habitat in such famous waterfowl lakes as Heron Lake in southwestern Minnesota.

European earthworms, another one, are eating away the floor in Minnesota forests, where native worms were eradicated by glaciers thousands of years ago. Anglers have spread them to northern lakes, only to discard some on land. Once there, the worms eat the small layer of duff - or leaf beds - on the forest floor, disrupting the forest's ability to sustain a rich and varied system of plants.

That pace, however, has quickened in recent decades, with more than half the state's exotic species arriving since 1985. Examples include zebra mussels, round gobies, and Japanese beetles.

Gypsy moths, tree defoliators that the state has battled successfully so far, may become a much bigger problem soon, according to Friisoe. Introduced into the United States in the 1800s, they have been moving westward and now infest much of Wisconsin.

"What's called the action line is moving across Wisconsin with frightening speed,'' Friisoe said. "It looks like gypsy moths will be arriving in Minnesota faster than our previous expectations. I would say within five years.''

If potential problems such as Asian carp from the south and gypsy moths from the east aren't enough, another potentially disruptive creature sits on our northern border. Earlier this year, researchers found the New Zealand mud snail in Thunder Bay, Ontario, prompting fears it could infest Lake Superior and other inland waters.

The tiny, prolific creatures were brought to the United States in 1987, apparently with New Zealand trout, and have since colonized hundreds of miles of the Snake River in Idaho and other Western rivers and streams. They have no natural enemies and can reach densities of 300,000 a square meter.

"Because they reach such high numbers, it's difficult to imagine they would have not have some sort of impact,'' said Billie Kerans, an associate professor of ecology at Montana State University.

"And the thing is, they are very easily transportable,'' she added, explaining how they leapfrogged their way east.

Still another emerging problem, Rendall said, is the commercial sale of aquatic plants and animals, particularly in the water-garden industry.

"Most of what they sell is not native,'' Rendall said. "It could be contaminated. You could buy a water lily and find hydrilla in with the roots.''

A University of Minnesota report to Minnesota Sea Grant and the DNR last year examined the problem.

The researchers ordered 681 plants from 34 aquatic plant vendors across the United States. They said 10 percent of purchases contained federal or state noxious weeds and 93 percent contained plant or animal species that weren't requested. Misidentified plants were found in 15 percent of the orders.


With so many potential problems, people might find it easy to get discouraged. But Gunderson said that would be a mistake.

"There are a number of myths, and one of them is it only takes one bad boater, one zebra mussel, one introduction, and the game's over,'' Gunderson said. "That's not the case at all. Every introduction isn't going to take hold. This is something that builds up over time. If we can change the majority of people's behavior, we feel we can make a difference in reducing the spread of a number of exotic species.''

Friisoe agreed, saying "99.9 percent'' of the insects that arrive in Minnesota can't survive here.

Gunderson said a Sea Grant survey show the DNR's education efforts have been very successful in changing behavior and limiting new introductions of zebra mussels and Eurasian water milfoil.

"I think Minnesota has been on the forefront of putting money into efforts, and it shows,'' Gunderson said.

Besides a bigger budget, the state has tighter regulations than many other places.

It's against the law, for example, to possess, sell, or import an exotic species. There's also a regulation against transporting any aquatic plant, native or not.

Rendall said there are reasons for that.

"One, you don't have to be a biologist to follow the rule,'' he said. "Just take it off. Two, there are plants that are not in the state yet. It makes it illegal to bring them here. Visitors must follow the same rule. Three, zebra mussels can attach themselves to aquatic plants.''

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