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"Exotic" conjures up many mental images. Few of them would relate very closely to the environmental nightmares brought about by some unwelcome guests to Ninth District lakes, rivers and prairies.
Exotic, or nonindigenous, species refer to animals or plants that are not native to a particular region. While some nonnative species pose no threat to the native ecosystem, others pose a major threat by interfering with power and water filtration plants, fishing and tourism industries, and entire ecosystems.
The first highly publicized and troublesome exotic species event happened in the Great Lakes with the sea lamprey. They arrived via the Erie Canal in the 1920s and nearly eradicated the entire fishing industry in the '50s before being brought under control.
More recently, invasions of zebra mussels have caused headaches for environmental and industry groups. Thanks to media attention, the zebra mussel is the most recognizable, but just one of a host of exotic species doing ecological and economic damage in the Ninth District.
The battle against invasive species is a top priority for the U.S. Fish and Wildlife Service and many other groups. The scientific community and the public are only beginning to understand the full environmental effects of exotic species on native water and land resources, and their effects on local and regional economies.
Estimates differ on the number of exotic species in the five Great Lakes, but most agree it's over 100. Doug Jensen, University of Minnesota exotic species information center coordinator, said 160 new species have come to the Great Lakes since 1910. Jensen estimated there are about three dozen in Lake Superior, but added "the hard number is being reviewed."
Without a concrete head count of exotic species, information on the ecological and economic impact of exotic species is even more limited, according to experts. "It's difficult to assess" specific economic damage, according to Steve Fisher of the American Great Lakes Ports, a trade association. "More research is desperately needed."
This much is sure: Exotic species come in many different forms, and each has a unique effect on its surroundings. Weeds cause a great deal of problems both in water and on shore. The worst aquatic weed in the United States is Eurasian Watermilfoil, native to Europe, Asia and North Africa, according to research cited by the U.S. Geological Survey.
Nowhere is the watermilfoil problem worse than in Wisconsin. The weed appeared in the 1960s, and is now present in 319 bodies of water and three-fourths of all counties. In Minnesota, it arrived in 1987 and is now in 75 lakes and four streams. In efforts to deter its spread, the state has made it illegal to transport any aquatic vegetation. There is also an abundance of watermilfoil in the Great Lakes.
South Dakota also has its share of problems with watermilfoil, especially in the center of the state, along the Missouri River. "It hasn't been here long enough for us to know the economic effects, but it does interfere with recreational activities," said Doug Becklund, a resource biologist with the South Dakota Department of Game, Fish and Parks. "Our biggest worry is how to keep it from spreading. It's a matter of slowing it down rather than stopping it."
Recently added to the state's list of nuisance species is curly pondweed, said Dave Ode, a state botanist and ecologist. "Curly pondweed has occurred in a couple of isolated locations in eastern and western South Dakota for many years. But this [past] summer it caused a problem on the Missouri River in central South Dakota where it clogged two marinas and at least one public boat ramp in Pierre. ... You could almost walk on top of it," said Ode.
Among the top terrestrial annoyances in South Dakota are Canada thistle and leafy spurge, which are problematic throughout the state, said Ode. "They're not everywhere, but where they are, they're a big problem, especially for ranchers." These weeds crowd out native plants, reducing grazing and overall land quality for ranchers because cattle cannot feed off of it. "It's very difficult to sell land infested with theses weeds," said Ode.
The most recent report on the economic effects of leafy spurge in South Dakota is almost a decade old. It found ranchers and landowners in the state were losing $1.4 million per year, and spurge infestation cost Great Plains states $100 million annually.
Montana also has an extensive list of noxious weeds to battle. Jay Cole, Montana Department of Agriculture weed specialist, said there are 23 nonnative noxious weeds in the state. "Category one" weeds, which are the most widespread, reduce vegetation for livestock and wildlife. "This is a big worry for ranchers and other land managers," said Cole. These weeds not only change the aesthetics of the land, but also compete with native vegetation and displace other plants.
One example is St. Johnswort. Although known for its medicinal purposes, light-skinned cattle that graze on the plant lose weight and develop skin irritations when exposed to sunlight, Cole said. He estimated the state has approximately 60,000 acres of St. Johnswort. "It's significant."
Since it invaded Montana in the 1920s, spotted knapweed has infiltrated every county, costing livestock producers an estimated $11 million per year in lost forage production, according to Roger Sheley, Montana State University weed specialist, in a Montana weed publication. Experts around the West estimated it would take $50 million a year to wage an effective battle against the region's weeds, said Sheley. The state is also concerned about knapweed spreading into areas deforested by last year's devastating fires.
Problems with nonnative species can go very deep—even underground. Believe it or not, earthworms are not a part of the nation's native ecosystem, having come from Europe, according to Lee Frelich, director of the University of Minnesota's Center for Hardwood Ecology. Earthworms have been in the Twin Cities metro area for over a century, and have gradually spread to remote areas through transport by fishermen.
"They are changing our entire nutrient ecosystem," he said. Forests floors used to have leaf layers which release stored nutrients slowly. But worms eat the leaf layers and cause the floor to release all the nutrients at once. This process causes erosion, since the rain goes straight to the soil, not through the leaves, and undermines the growth of wildflowers and tree seedlings. Frelich said some areas that used to have 30 to 50 kinds of wildflowers now have only one or two. The lack of vegetation has a ripple effect, as insects and small rodents that depend on the floor forage go elsewhere, and birds follow.
"This is a big issue that took us by surprise," Frelich said. In northern Minnesota's Chippewa National Forest, native sugar maple forests are vanishing. On the outer edge of the Minneapolis metro region, "there is massive erosion and no native species in Long Lake and Orono," said Frelich. "We are trying to get the message out to people not to spread worms because you can't get rid of them. Erosion leads to a loss of productivity in forests, affecting the timber industry, and the quality of water. ... The fishing industry suffers and tourism suffers."
The king of exotic
Probably the most familiar exotic species is the zebra mussel. These tiny, clamlike creatures range from one-quarter inch to one inch in size and are believed to have come to United States in the 1980s in ballast water from Eastern Europe. (Ballast water is carried in tanks below a ship's deck for stability.)
Natives of the Black, Caspian and Aral seas, zebra mussels were first identified in Lake St. Clair near Detroit in 1988. By 1990 they were in all the Great Lakes and have spread to the Mississippi, Missouri and St. Croix rivers and a few inland lakes in Minnesota.
All told, the zebra mussel infests water bodies in 20 states, according to the U.S. Fish and Wildlife Service, exacting over $3.1 billion in damages over 10 years to intake pipes, water filtration equipment and power plants. The cost to large ships in the Great Lakes averages $360,000 per year for each ship.
Adult zebra mussels feed primarily on free-floating algae and can filter about one liter of water per day. This process removes plankton and gives water much more clarity than normal, making small fish—such as yellow perch—easy prey for larger fish, and completely disrupts the ecosystem. Zebra mussels also kill native mussels by encrusting their shells so solidly that the native species cannot open to feed or breathe. One environmentalist estimated that 140 native mussels in the Mississippi River alone face extinction as zebra mussels spread.
Pesky zebra mussels don't discriminate. They've affected golf courses, marinas, hospitals, colleges, fish hatcheries, navigation locks, shipping, drinking water treatment facilities and electric power generation facilities. Zebra mussel densities were as high as 700,000 per square meter at one power plant in Michigan; water treatment facilities have seen the diameters of intake pipes reduced by two-thirds, and found the critters in their filtration systems.
They cause problems in other ways as well. The zebra mussel's voracious appetite has pushed growth of a second type of algae, which attaches to rocks, closer to shore where it had not previously grown until the mussels' arrival. The mussels feed on free-floating microscopic algae, increasing water clarity and sunlight, which encourages growth of the attached algae, especially in shallow water, said David Michaud, principal environmental scientist for Wisconsin Electric Power Co. When algae detaches from rocks in the fall, it gets caught in the filtration system and can cause outages. This problem is more common in lakes than in rivers, said Michaud.
"Anytime you lose a major unit, you can lose hundreds of thousands [of dollars] per day. It is a serious issue we watch closely," said Michaud. "We have debris removal equipment and do what we can do, but we're at the mercy of the lake."
In 1993, the company, which operates six power plants that use Great Lakes water, one of which is in Michigan's Upper Peninsula, spent $1 million on maintenance alone from zebra mussels, Michaud said. Sub-sequent research has discovered more effective means of dealing with the creatures, but Wisconsin power plants still spend between $250,000 and $500,000 treating zebra mussels each year. "Water utilities are in the same ballpark, or less," he said.
Other power plants on the Mississippi River have similar problems. Environmental biologist John Theil of Dairyland Power Cooperative in La Crosse, Wis., said zebra mussels can "become lodged in the heat exchanges, and mostly dead shells collect in places we don't want them, such as equipment that depends on water for cooling."
Each of the four plants he oversees on the Mississippi in the Ninth District spends about $250,000 annually, but this varies from plant to plant, Theil said. "We were spending twice that before realizing how to cut costs."
