From quagga mussels to European frog-bit, these are Wisconsin’s most destructive invasive aquatic species

Eurasian watermilfoil impedes boats and native plant growth

Eurasian watermilfoil is a feather-like aquatic plant with reddish stems and leaves. It has been documented in over 800 Wisconsin waterbodies. Its effects vary across waterbodies and can be economic, social and ecological, Kretlow said.

Milfoil populations can form large, floating vegetation mats that prevent boaters from traveling through infested waters. These same mats can block sunlight from reaching native plants, reducing their vitality. This allows the milfoil to outcompete native species and decreases biodiversity.

Cold-resistant curly-leaf pondweed blocks waters from recreational enjoyment

Curly-leaf pondweed is a submersed aquatic plant with wavy leaves that look like lasagna noodles. Like Eurasian watermilfoil, curly-leaf pondweed can “form extensive mats and impede recreational activities like fishing, boating and swimming,” Kretlow said.

When compared to most native aquatic plants, this species starts growing earlier in the spring and withstands colder temperatures. Kretlow said some studies show curly-leaf pondweed can outcompete native plants “since its tolerance with cold temperatures allows it to start growing earlier in the year,” while other research indicates that, because it grows earlier, it doesn’t always directly compete with native species.

What is known is that the species has “midsummer die-offs,” which remove some of the competition for native plants but also release phosphorus into the ecosystem.

“The midsummer die-off (releases) phosphorous into the water column as it decomposes, which can potentially cause algae blooms in some of the lakes,” Kretlow explained. “And then, when the algae blooms, the algae will decompose and use a lot of oxygen, which could lead to a dissolved oxygen crash.”

European frog-bit is prohibited in Wisconsin

European frog-bit is a free-floating aquatic plant native to Europe and northeast Asia. This species especially likes to inhabit calm or slow-moving waterbodies and looks like “small lily pads” with little, light-colored flowers, Kretlow said. Like the two species above, populations can form large mats that impede navigation and negatively impact native species.

However, while Eurasian watermilfoil and curly-leaf pondweed are restricted species in Wisconsin, European frog-bit is a prohibited species, meaning it is further regulated by the DNR. The DNR defines prohibited species as species that are either not currently found in Wisconsin but could pose a significant threat if introduced or “small pioneer stands of … species that are isolated to a specific watershed in the state or the Great Lakes.” European frog-bit falls into this second category.

The species was first introduced to North America in the 1930s as an ornamental plant and spread to the Great Lakes in the 1970s, Kretlow said. The first population found in Wisconsin was discovered in 2021 along the Green Bay coastal areas of Marinette and Oconto counties. Conservations in the Green Bay area have undertaken extensive efforts to prevent the species’ spread.

Last year, Kretlow said, a population was found in Brown County, but a DNR hand-pulling event seems to have vanquished it. She said if you encounter what you believe to be an invasive species, especially a prohibited species like European frog-bit, it’s best to contact one of the DNR’s five regional aquatic invasive species biologists.

‘Very aggressive’ red swamp crayfish outcompete native species

Also a prohibited species, red swamp crayfish are “dark red with raised bright red spots covering the body and claws and a black wedge-shaped stripe on the top of the abdomen,” the DNR states. They are two to five inches long.

These crayfish are omnivorous and feed on aquatic plants, snails, insects, fish, amphibian eggs and other young organisms, Kretlow said. They are also “very, very aggressive” and chase off native species, she continued. In some ecosystems, they’ve been known to “decimate amphibian life” by eating amphibian eggs.

Red swamp crayfish are native to the coastal Gulf plain region from the Florida panhandle to Mexico and can now be found “in Southern Mississippi River drainage areas all the way up to into Illinois,” Kretlow said.

Purchases from pet stores and for crayfish boils are major avenues by which red swamp crayfish reach Wisconsin. It is illegal to transport red swamp crayfish to Wisconsin for crayfish boils unless they are dead and frozen because crayfish can escape into our ecosystems during transportation, Kretlow said.

The financial burden of removing released or escaped invasive crayfish is too great to allow for live importation, Kretlow wrote in a follow-up email. In 2009, red swamp crayfish were found at two sites in southeastern Wisconsin. It took the DNR over $750,000 and “years of work” to clean up the site, Kretlow wrote.

Faucet snails carry parasites that kill off waterfowl

Pale brown faucet snails only grow up to a half-inch long according to Wisconsin Sea Grant, but they host parasites that cause large-scale die-offs of birds and waterfowl species. This hurts ecosystems, as well as the economy because it greatly diminishes hunting opportunities for waterfowl hunters.

The snails can also “clog water intake pipes, infest municipal water supplies and compete with native snails for resources,” Wisconsin Sea Grant states.

Native to Europe, the snails were likely first released into the Great Lakes through boats’ ballast water and spread through hitchhiking on people’s clothing and equipment, Kretlow said. The species is now commonly found in major fishing spots like freshwater ponds, shallow lakes and canals.

“So that’s why we’re really, really stressing to fishermen to be cleaning their boots and their equipment, because (the snails) can last for a really long time outside of the water and be transferred on soles of boots and stuff to another area,” Kretlow said.

Quagga mussels have outcompeted zebra mussels in Lake Michigan

Tan, black-striped quagga mussels ― no bigger than “an adult’s thumbnail” according to the DNR ― are a relatively recent arrival in Wisconsin, but have already substantially altered the ecosystem, especially in Lake Michigan, Great Lakes specialist Kari Fenske said.

Lake Michigan historically had good nutrient levels and food webs, but the introduction of quagga mussels about a decade ago changed that because they are really good filter feeders. Fenske said people have noticed that Lake Michigan is “a lot clearer than it used to be.” because quagga mussels filter out things like still plankton and phytoplankton,

SDGs, Targets, and Indicators

SDG 14: Life Below Water

• Target 14.1: By 2025, prevent and significantly reduce marine pollution of all kinds, particularly from land-based activities, including marine debris and nutrient pollution.
• Target 14.2: By 2020, sustainably manage and protect marine and coastal ecosystems to avoid significant adverse impacts, including by strengthening their resilience, and take action for their restoration in order to achieve healthy and productive oceans.
• Target 14.4: By 2020, effectively regulate harvesting and end overfishing, illegal, unreported and unregulated (IUU) fishing and destructive fishing practices and implement science-based management plans, in order to restore fish stocks in the shortest time feasible, at least to levels that can produce maximum sustainable yield as determined by their biological characteristics.

SDG 15: Life on Land

• Target 15.8: By 2020, introduce measures to prevent the introduction and significantly reduce the impact of invasive alien species on land and water ecosystems and control or eradicate the priority species.

SDG 6: Clean Water and Sanitation

• Target 6.3: By 2030, improve water quality by reducing pollution, eliminating dumping and minimizing release of hazardous chemicals and materials, halving the proportion of untreated wastewater and substantially increasing recycling and safe reuse globally.

SDG 12: Responsible Consumption and Production

• Target 12.4: By 2020, achieve the environmentally sound management of chemicals and all wastes throughout their life cycle, in accordance with agreed international frameworks, and significantly reduce their release to air, water and soil in order to minimize their adverse impacts on human health and the environment.

Table: SDGs, Targets, and Indicators

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Source: jsonline.com

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