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'Rock snot' algae found in Upper Manistee River

RockSnot
michigan.gov/invasives
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Nuisance blooms of didymo began appearing in the Western U.S. during the 1990s.

The discovery marks the first time didymo has been found in the lower peninsula.

A concerning algal bloom has been found in the Upper Manistee River, in Kalkaska County.

The Michigan Department of Natural Resources confirmed on Monday it’s the first detection of didymo in the lower peninsula.

Also known as “rock snot,” this algae thrives in cold, low-nutrient waters: the exact conditions in Michigan’s best trout streams. When the algae blooms, it forms thick mats on the riverbed, limiting habitat for aquatic insects.

In other words, more didymo means less fish food.

“A lot of insects will attach to clean substrate like gravel or cobble,” said Ashley Moerke, a freshwater ecologist at Lake Superior State University.

“A lot of those species are desirable for fish, like caddisfly or mayfly larvae,” Moerke said. “When didymo colonizes, they basically get pushed out and can no longer use that habitat.”

There’s a lot of mystery around recent didymo blooms. The species has been present in North America since at least the late 1800s, but it didn’t start causing problems until the 1990s. Then, big blooms started covering riverbeds—especially in the Rocky Mountain West.

It was first seen in Michigan in 2015, in the St Mary’s River. That’s where Ashley Moerke is studying the algae.

But these nuisance blooms are happening all over the world, and no one knows why they’re getting worse. Something is making this algae more productive, and more of a problem.

Moerke wants to figure out what’s causing these blooms, using experimental streams.

“They essentially will be almost like a household rain gutter, and they’re elevated so they have a gradient or a flow,” Moerke said.

“Then we just pump river water through them consistently and add whatever variable it is that we’re testing, like phosphorus or nitrogen or a combination of those two. We can manipulate it in a header tank to create the conditions we’re trying to mimic in the environment.”

While scientists don’t know how to get rid of didymo, they do know how it spreads. There’s a reason it shows up in popular recreational rivers, like the St. Mary’s or the Manistee.

In a press release on Monday, the Michigan Department of Natural Resources encouraged anglers and boaters to thoroughly clean their gear to prevent the further spread of didymo.