MPR News Primer: Invasive species

Eurasian water milfoil, zebra mussels
Eurasian watermilfoil and zebra mussels are two invasive species that threaten Minnesota and other U.S. waterways.
Images courtesy of Army Corps of Engineers and Wikimedia under GNU license

Minnesota is knee-deep in a growing mess of pests and plants that should not be here. The state is pressing the fight against invasive species. Is it possible to stop their spread?

What is an invasive species?

Invasive species are those "not native to Minnesota and cause economic or environmental harm or harm to human health," the Minnesota Department of Natural Resources says.

Eurasian watermilfoil, infesting scores of lakes with a green slop, may be the best known of local invaders. And battles against zebra mussels are grabbing more headlines. Then there's the growing threat of bighead and silver carp -- yes, the fish that eat everything and then jump out of the water to club you in the head.

Invasive species are more than just a nuisance. They can be incredibly destructive.

Nationally, some 50,000 "invading alien species" cause environmental damage and losses totaling nearly $120 billion a year. Cornell University researchers believe invaders are responsible for more than 40 percent of threatened or endangered species.

The National Park Service estimates about 5 percent of park lands are dominated by invasive plants.

What invaders have been found in Minnesota's waters?

Infested lakes and waterways can be found across Minnesota. More than a dozen critters who shouldn't be here live and breed in Minnesota's waters, including zebra mussels, carp and the sea lamprey.

The zebra mussel, a native of Eastern Europe brought to the Great Lakes in the ballast of freighters, has been here for more than 20 years. They have become increasingly worrisome as they have infected more Minnesota lakes. Their presence causes more algae and weed growth and kills native clams.

As zebra mussels spread across the state, there has been growing tension between lake property owners and the state Department of Natural Resources over how to deal with them.

The carp present a huge potential threat to the state's fisheries. They are voracious eaters with the ability to muscle out native fish. Imported from China in the 1970s to control plankton in aquaculture ponds, they escaped from Southern states into open waters, the DNR says.

Asian carp
From left to right: Commercial fishermen George Richtman, Tim Adams and Bob Davis hold Asian carp caught March 1, 2012 in the Mississippi River. Richtman is holding a grass carp, Adams is holding a silver carp and Davis is holding a bighead carp.
Photo courtesy Nicholas Schlesser, MN DNR

They have been moving steadily into Minnesota. Several southwestern Minnesota lakes are considered infested. In March, Winona area fisherman caught a silver carp and bighead carp in the Mississippi.

Eurasian watermilfoil and purple loosestrife are some of the most common invasive aquatic plants. Loosestrife invades marshes and lakeshores, supplanting cattails and creating conditions that make it hard for ducks, frogs, turtles and other creatures to nest and feed. Eurasian watermilfoil, notorious for its ability to choke a lake starting with a plant fragment stuck to the side of a boat, can turn waterways into green matted messes.

What about the non-native plants and animals on land that have become a problem?

Damage from ash borer
Emerald ash borers create "galleries" under the bark of ash trees, and the damage can eventually kill the tree.
Photo courtesy of Michigan Department of Agriculture

There are plenty of threats off the water. The best-known menace these days is the emerald ash borer, a killer of ash trees that has devastated swaths of the Midwest and has become a serious problem in the Twin Cities.

Consider the common earthworm a public enemy, too. It is not native to Minnesota and its presence can cause havoc in state forests. The worms eat the leaves that create the cover for seedlings. "In areas heavily infested by earthworms, soil erosion and leaching of nutrients may reduce the productivity of forests and ultimately degrade fish habitat," the DNR says.

There are some 50 ground plants on the DNR's invasive species list. Much of it looks like it belongs here but doesn't. Take, for instance, buckthorn, which the DNR says was first brought to Minnesota in the mid-1800s to make hedges. It's probably the best known and it's likely in your backyard right now. It's fast-growing, crowds out native plants and lacks any natural check on its growth.

The Norway Maple sounds like a vital part of Minnesota's heritage. Instead, it's an ecological troublemaker, out-muscling sugar maples and damaging native wildflowers with its dense canopy that's stingy with the light.

What steps have regulators and citizens taken to prevent their spread?

Prevention, enforcement and education are the DNR's main weapons in the invasive species fight.

DNR data show it's upped the battle. Agency data at the end of 2011 showed a jump in enforcement activities and citations issued.

A DNR prevention grant program channeled tens of thousands of dollars in grants to lake and associations and other groups. In 2011, state regulators could point to the fact that there were no new aquatic invading species discovered in the state's waters.

The state has also recently experimented with a poison that regulators believe can kill the pernicious zebra mussel without hurting plants, wildlife or people; and lawmakers found money to open an invasive species center at the University of Minnesota.

In Detroit Lakes and other towns, citizens and local governments are joining the effort to slow the spread of the unwanted plants and animals.

Over the summer, fines doubled for boaters caught not draining or cleaning boats after pulling them from a lake. The DNR also doubled its annual invasive species spending, to $8.6 million, using money from surcharges on boat and fishing licenses and one-time funding from the lottery.

Local communities have also become more aggressive. In the west metro, local leaders this summer made it a misdemeanor to put a boat into Christmas Lake without it first being inspected for aquatic invaders.

For all the effort, though, there's still a sense among many Minnesotans that the battle is moving at a snail's pace. Tensions boiled over in June during a meeting in St. Paul between DNR Commissioner Tom Landwehr and a half dozen people representing lake property groups across the state.

What does the future hold?

"Mission accomplished" is a phrase rarely heard in the battle against invasive species. Unlimited funds could make a huge difference. But funds are not unlimited.

"Requiring every boat in Minnesota to be inspected for invasive species before watercraft are launched into a lake or river would cost about $600 million yearly -- or about half the cost of a new Vikings stadium," the Star Tribune writes. "If boaters alone were required to pay for that, the current $5-per-boat surcharge would have to be increased to $2,300."

Climate change will complicate the future -- stuff that historically couldn't survive in Minnesota weather may find conditions more favorable to invasion.

And there's more to come. As officials plan for the silver carp, a battle looms with the northern snakehead, a predatory fish introduced to the U.S. from Asia that some experts worry will find its way here. It has been found in Arkansas and Mississippi and may follow the Mississippi River north, just like the carp.

Even when officials do catch invasive species early, Mother Nature seems to find a way.

When water hyacinth and water lettuce were found growing in a Mississippi backwater near Winona last year, state and federal workers removed about 1,500 plants by hand, believing that and the winter would end it. But the exotic plants not only survived the winter, the population exploded this summer to about 10,000 plants in the same area.

The lesson: Whether they arrive by bird or the wind or the mistakes of well-intentioned humans, it's nearly impossible to eject an invasive species completely. Perhaps the best proof comes from England, where the Canada goose remains on Great Britain's invasive species list -- 400 years after arriving.

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