Michigan’s rivers and streams face new threats in the form of two invasive species: a snail never seen here before and an algae that used to be found in small, sporadic concentrations.
In west Michigan, scientists have found a tiny mud snail that can crowd out native species and
lead to reduced insect and fish populations. Farther north in the Upper Peninsula, the “didymo” algae’s presence is growing and can form nasty-looking masses of muck that blanket the beds of waterways, foul fishing activities and hurt ecosystems.
Both present a threat to outdoor activities in a state known for world-class freshwater fishing.
“These two species have each had significant impact on native ecosystems,” said Michigan Department of Environmental Quality Director Dan Wyant. “They degrade and in some cases ruin popular fisheries, and they can significantly alter the foundation of an entire waterway.”
In response to the new arrivals, Michigan’s Natural Resources, Environmental Quality and Agriculture departments are putting a new emphasis on guidelines designed to stop the spread of invasive species. They call most heavily on state anglers to ensure they don’t unwittingly transport unwanted algae or snails into new areas.
The two species add to Michigan’s headaches with scores of other invasives — from sea lampreys and zebra and quagga mussels, to a host of fish and plants that are altering traditional ecosystems.
Didymosphenia geminata is the scientific name for the algae that has been found in more than a dozen states and causes problems wherever it blooms. Researchers in affected states use the shorthand “didymo,” while anglers often opt for the descriptive “rock snot.”
In Michigan, it has sporadically appeared in small trace amounts during the last century. But large masses were recently discovered in a stretch of the St. Mary’s River near Sault Ste. Marie.
“This is a full-on algae bloom,” said Sarah LeSage, aquatic invasive species program coordinator for Michigan’s DEQ. “It’s a totally different scale from anything that we’ve seen before.”
Algae ‘can blanket a river’
Jeremy Hunt knows about the troubles the didymo algae presents. The 39-year-old lived near Pontiac for many years before winding up near the Arkansas/Missouri border, where he is a fishing guide dealing with the didymo along the area’s White River.
Didymo also has had a presence on the White River in west Michigan for a decade.
“It can blanket a river,” said Hunt, who every year returns to fish in Michigan. “It can kill the food sources.”
Once established in a body of water, didymo’s presence can rise and fall based on conditions.
“The jury is still out” on the algae’s long-term impact, said Bob Morgan, a lead aquatic ecologist for the Fish and Boat Commission in Pennsylvania, another state where the invasive didymo has been a problem.
“We thought the Delaware River was a goner when it first showed up, with big blooms appearing all over the place. But we haven’t seen any major blooms in the last two years.”
Snails operate as ‘grazers’
The other addition to the state’s growing list of invasive species is the New Zealand mud snail, or Potamopyrgus antipodarum. A native of the island nation, it first turned up in the United States 30 years ago.
State officials discovered the tiny snails in a section of the Pere Marquette River west of Baldwin in Lake County. It’s the first time they’ve been documented in Michigan. They’ve previously been found in large numbers in a dozen other states, particularly in the West.
The snails can disrupt the food chain of prized fish like trout and salmon by operating as “grazers,” removing algae from rocks in and near waterways that normally feed insects such as mayflies and stoneflies. Removing that food source reduces the insect population, a dietary staple of fish and salmon.
Once the algae is absorbed, the snail itself offers nothing beneficial to the ecosystem.
“They displace the original food source, but they are not nutritionally valuable to the fish,” said Seth Herbst, aquatic invasive species coordinator for the Michigan DNR.
Drinking water at risk
The didymo and New Zealand mud snails could eventually cause problems for drinking water supplies.
Last year, large algal blooms — different from didymo — fouled western Lake Erie and led to contamination of drinking water in Southeastern Michigan and Toledo. More than 400,000 households were without potable water for several days.
Didymo does not pose a significant threat to human health. But Pennsylvania ecologist Morgan said residents there have reported irritated eyes and throats after exposure. The algae’s cell walls include silica, which can be abrasive.
Snails offer a more intrusive threat to drinking water. A U.S. Federal Aquatic Nuisance Species Task Force web page notes that “In Australia, New Zealand mud snails actually emerged from domestic water taps.”
State officials urge anglers and others who use the state’s rivers, streams and lakes to take precautions to help prevent the spread of didymo and the mud snails. Boaters and anglers are asked to:
■Clean, drain and dry equipment after use in a body of water.
■Remove aquatic plants from watercraft before launching.
■Drain live wells, bilges and water from watercraft before leaving their access points at the end of the day.
■Clean equipment such as waders with hot water or a diluted bleach solution and allow them to dry for five days before re-use.
People also should report sightings of anything that looks like the two invasive species at www.michigan.gov/invasivespecies.
In Pennsylvania, Morgan has developed a keen eye for didymo and offered a short primer.
“People will see big mats of the material that are not green,” he said. “It’s tan, sometimes almost white or yellow. ... It can look more or less like wet toilet paper under water.”
And it has a different texture from what most people would assume algae would have. “Didymo is almost scratchy, like a wet cotton ball between your fingers,” Morgan said.