As the ice begins to melt, here are some invasive species to be on the lookout for

By Jenny Seifert, UWEX Aquatic Invasive Species Outreach Specialist

The weird spring tease we got this week – in February – got me thinking about what sorts of aquatic invasive species (AIS) water lovers could be on the lookout for as Wisconsin’s lakes begin to awaken from their icy slumber. So I had a quick chat with one of the state’s AIS gurus, Paul Skawinski, the Citizen Lake Monitoring Network Educator with UW-Extension Lakes and a self-proclaimed “dorky botanist.”

According to Skawinski, a few AIS are active during the winter, meaning they aren’t dead or dormant, but are still photosynthesizing (albeit slowly), eating plankton, and going about their usual ways. People can keep their eyes out for these species while seizing the day with some late-season ice fishing or just wandering about a thawing lakescape.

Eurasian water milfoil and curly leaf pondweed are typically still standing and readily visible under the ice,” says Skawinski, naming two of those hardy few that can tough it out through a Wisconsin winter.

The advantage these two invasive plants have is their tolerance of darkness and cold water. In the summer, they can grow in deep waters, where light and warmth are scarce, which means when ice and snow curtain lakes in the winter, it’s no big deal for them.

Another winter-resistant species is starry stonewort, an invasive alga that is relatively new to Wisconsin. While its green “planty” parts die off in the winter, its star-shaped bulbils, or its namesake reproduction centers, are still detectable, staying cozy in the lake sediment and ready to sprout come spring.

Starry stonewort’s bulbil, or reproduction center, can overwinter in lake sediments. Credit: Paul Skawinski

“These species can grow fast and tall, and quickly shade out other species, making it harder for some native species to grow back in the spring,” says Skawinski of why winter hardiness among invasive flora contributes to their potential dominance in a lake.

One more invasive critter to be on the lookout for as Wisconsin melts is the zebra mussel, that pipe-clogging filter feeder that can smother native mussels, promote algal growth and generally get all over everything.

A stubborn zebra mussel clings to an aquatic plant, even during winter’s deep freeze. Credit: Paul Skawinski

“I was out on a lake last weekend and pulled Eurasian water milfoil through the ice with several zebra mussels attached,” says Skawinski of a trip he made with some citizen lake monitors to Cedar Lake. For the past four or five years, he has done wintertime explorations around the state to see what he can find lurking under the ice.

So what should you do if find any of these or other invasive flora or fauna as winter turns to spring?

“Contact someone,” says Skawinski.

Specifically, you can choose among your regional AIS Coordinator at the DNR, your regional Tribal or County Coordinator or your regional Citizen Lake Monitoring Network Coordinator. Be sure to tell them what species you found, how much of it you saw, when you found it and whether you have a sample you could send them. This information helps them keep track of invasive populations and recommend appropriate management actions.

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