Plants and animals that have been introduced by human actions to areas where they do not naturally occur are designated as exotic, non-native or alien, by the Minnesota Department of Natural Resources. The department applies the term “invasive” to species that cause ecological or economic harm in their new environments.
In some cases, the invasive species out-compete natives for nutrients. In other cases, the invaders damage water bodies in ways that choke out native species. Bottom-feeding carp, for example, consume native invertebrates, uproot native plants and excrete high quantities of waste that spurs algae growth.
Here are some of the invasive plants and animals, either already established in Minnesota or perhaps poised to become established here, that the DNR considers threats:
Eurasian watermilfoil — Eurasian watermilfoil was accidentally introduced to North America from Europe, according to the Minnesota Department of Natural Resources. In nutrient-rich lakes, it forms vast mats of vegetation at the surface of lakes, and in shallow waters it can interfere with swimming, boating and fishing. Stems or leaves torn off from plants easily take root and form new colonies. That makes it easy for boaters to infect new lakes by carrying plant debris on their propellers, rudders and keels.The good news is that there is evidence the invasive milfoil has difficulty becoming well-established in lakes with healthy populations of native plants, according to the DNR.Infestations of milfoil have been found in about 210 Minnesota lakes, rivers and wetlands. Most of the infected lakes are in the Twin Cities metro area.
Curly-leaf pondweed— Curly-leaf pondweed has been observed in Minnesota since 1910, leading some people to suppose it is a native plant, according to the Minnesota Department of Natural Resources. It continues growing under ice, and is often the first plant to appear after ice-out.Like Eurasian watemilfoil, it forms dense mats of vegetation that can interfere with swimming and boating.
In mid-summer, the plants die back, often leading to an increase of phosphorus in the water and subsequent growth of undesirable algae. The plant has been found in 759 lakes in 70 of Minnesota’s 87 counties, the DNR reports. Curly-leaf pondweed easily is spread from one water body to another through the transport of the plant’s turions – hardened stem tips – on boats and trailers.
Purple loosestrife– Purple loosestrife is a wetland plant from Europe and Asia that displaces cattails and other native plants in marshes and lakeshores throughout Minnesota, according to the Minnesota Department of Natural Resources. Loosestrife infestations have been documented in 2,408 locations in Minnesota, and the state has more than 63,000 acres afflicted with the invasive plant, the DNR reports. Infestations are heaviest in the Twin Cities metro area.Since 1992, the DNR has promoted the cultivation and release of four species of insects – two beetles and two weevils – that eat loosestrife leaves, roots or flowers. The strategy has proven very successful. For a time, kits to grow the loosestrife-fighting insects were widely distributed to schools and 4-H and garden clubs. Since 2004, the DNR gas collected leaf-eating beetles from sites where they flourished and relocated new populations to areas with new loosestrife infestations. In 2008, the DNR trapped and moved more than 12,000 beetles.
Asian carp – If you ever get knocked out of your boat by a fish, the chances are it will be a silver carp that gets you. The silver carp, which grow as big as 60 pounds, are known for jumping high out of the water when they are disturbed by boats. It is not unusual for them to hit boaters and water skiers.
All carp are designated as invasives by the DNR, and the agency works to keep them from spreading to waters they do not now inhabit.
Priority also is put on removing carp from high-quality waterfowl areas, such as shallow lakes and wetlands. Carp can carry a disease, spring viremia of carp, that can afflict northern pike.
But the DNR is especially concerned about four non-native carp species – the silver, the bighead, the grass and the black – that are not believed to have established populations in Minnesota. Those four types of carp imported from China in the 1970s to control plankton in commercial fish farms in the southern U.S. But they escaped to open waters, and all but the black carp are known to have established populations in the Mississippi River, according to the DNR. In March 2012, a commercial fisherman caught a silver carp near Winona. That’s the farthest upriver the species has been caught. In November 2008, a commercial fisherman caught five Asian carp — silver, bighead and grass – in the Mississippi River near La Crosse, Wis. In 1996, a bighead was caught in the St Croix River, and another was caught there in April 2011. The DNR rates all four of the Asian carp as severe threats to Minnesota. The agency does not currently believe any of the four has an established population in the state. Learn more – read the DNR’s Asian Carp Action Plan.
All the invasive Asian carp eat huge amounts of plankton, competing with native organisms such as mussels, larval fish and some adult fish, such as paddlefish, according to the DNR.
Zebra mussel–Zebra mussels, native to the Black, Caspian and Azov seas, were first discovered in North America in 1988, according to the U.S. Geological Survey. Scientists believe they came to the Great Lakes in the ballast water of a cargo ship. The tiny – ¼- to 1 ½-inch-long — shellfish spread rapidly and attracted immense media coverage because of the threat they posed to inlet pipes for water utilities and electric power plants, where they cluster atop each other until they severely constrict the pipes. At a power plant in Michigan, the density of such a cluster was measured at 700,000 mussels per square meter, according to the USGS. Publicity zebra mussels received helped propel development of the science of Invasive Biology.
In addition to fouling water intakes, zebra mussels affix themselves to native shellfish and interfere with native food chains. They were first found in Minnesota – in the Duluth-Superior Harbor – in 1989. Since then, they have been found in 27 inland lakes and wetlands in Minnesota, plus Lake Superior and the Mississippi, Pine, Rum, St. Louis and Zumbro rivers, according to a 2008 report by the Minnesota Department of Natural Resources. In July 2010, zebra mussels were found in Lake Minnetonka. In 2011, zebra mussels were found in 8 more Minnesota lakes.
It is now unlawful to transport zebra mussels, or other prohibited invasive species, on public roads. The Minnesota DNR has published a list of tips for boaters, to reduce the likelihood of inadvertently spreading zebra mussels to new territory:
- Inspect and remove all visible aquatic plants, animals and mud from boats, trailers and equipment such as anchors before leaving a water access
- Inspect and remove all visible aquatic plants, animals or mud from docks, boat lifts and swim rafts before transporting to another body of water
- Drain all water from boats – including live wells, bilges and bait buckets – before leaving a water access
- Spray or rinse boats with high pressure and/or hot water, or let them dry thoroughly for five days before transporting to another body of water.
In 2015 a new law will go in to effect, which will require anyone who transports a watercraft (or water-related equipment with a trailer) to complete an online education course. After the course is completed, the person will be given a decal that must be placed on their trailer.
Spiny waterflea– The spiny waterflea, native to Europe and Asia, arrived in the Great Lakes with ballast water in ocean-going ships, according to the Minnesota Department of Natural Resources.They range in size from ¼ to 5/8 inches long, they prey on small native zooplankton, such as Daphnia, that are important food sources for native fish. They have been found in Lake Superior, plus a number of northern lakes and rivers, including several Boundary Waters lakes.Spiny waterfleas collect in what the DNR describes as “gelatinous blobs” on fishing lines and downrigger cables. You can help prevent their spread by cleaning fishing lines and cables, and draining water from boats, personal watercraft and bait containers before moving from one lake to another.
Ruffe– Ruffe, small perch with sharp spines, are native to Europe. They came to Lake Superior and the Duluth harbor with ballast water from ocean-going ships in about 1985, according to the Department of Natural Resources. They grow rapidly, although they seldom get bigger than about 5 inches, and they reproduce in their first year.Because of their spines, they are difficult for larger fish to eat, and they are suspected of causing declines in the populations of native forage fish, such as yellow perch.
So far, ruffe populations in Minnesota have been identified only in Lake Superior and the St. Louis River.
Earthworms– Most people probably don’t know this, but earthworms are not native to Minnesota. Or, at least, they have not been native to the area since the last glaciers receded about 11,000 years ago.But 15 non-native earthworm species have been found in the state, and evidence indicates that at least seven of those species damage hardwood forests, killing trees, wildflowers and ferns, according to the Department of Natural Resources.Worms — often dumped by anglers at boat launches and portages – damage the forests by consuming fallen leaves that, otherwise, would become organic matter that tree seedlings and plants need to sprout and grow.
The Great Lakes Worm Watch at the Natural Resources Research Institute at the University of Minnesota Duluth has this advice for preventing the spread of earthworms:
- If you use earthworms as bait, throw any unused worms in the trash, not in the water or on the land.
- If you use earthworms for composting, before you apply the compost, freeze it solid for at least a week.
- Do not transport leaves, mulch, compost or soil from one place to another unless you are confident that there are no earthworms or their cocoons present.
- Wash the mud from your all-terrain vehicles’ tire treads before transporting the vehicles.
- Tell others about the damage earthworms cause.