Researchers in La Crosse and around the state are asking the public to help them spot dying freshwater mussels in local waterways, looking for more clues why the animal has been dying off in mass numbers in recent years.
The phenomenon has been happening for a number of years, people calling from all over the continent to report cases. More than 70% of freshwater mussels are threatened, endangered or vulnerable.
In Wisconsin, there are more than 50 species of freshwater mussels, and 39 species found along the Wisconsin portion of the Mississippi River alone. And recently, researchers discovered a novel virus in a mussel near La Crosse, indicating the phenomenon is happening in our own backyard, too.
But locating the mussel deaths are harder than expected.
"It isn't like fish, where when there's a fish mortality event, the fish die and they tend to float at the surface. Mussels, that doesn't really happen, so it's really difficult to spot them," said Eric Leis, a fish biologist with the La Crosse Fish Health Center.
Researchers most recently have been studying a massive die-off in the Clinch River in Virginia and Tennessee, where they discovered that about 80% of the pheasant shell mussel population had died off.
Leis called the event "alarming," because they couldn't figure out exactly what had caused the deaths.
"There wasn't really an explanation as to why the mussels were dying, and dying in such large numbers," he said.
The group of researchers — the University of Wisconsin-Madison, Upper Midwest Environmental Sciences Center, National Wildlife Health Center and the La Crosse Fish Health Center — were able to identify bacteria and 17 novel viruses in the morbid mussels.
But it's still not the whole picture.
"We're still trying to sort out what that really means. The bacteria, it doesn't appear to be a pathogen as far as the actual cause to the mortality events," Leis said. Instead, the bacteria might be an indicator of a pollutant.
"The viruses may explain," some of it, Leis said, "but there's just likely other stressors that are present too, so the mussels might be stressed and eventually the virus is what gets them in the end."
To better understand, the groups of researchers are asking for the public's help in locating mussel mortality events while out on local waterways.
The fall is the best time to spot the events, Leis said, and mussels often hang out in shallow water near sandbars or shores of rivers.
"Mussels are incredibly diverse. North America is one of the most biodiverse locations for mussels in the world, so the mussels live in a wide variety of habitats. And really, it just amounts to people being in the right place at the right time," Leis said.
A mussel that is lying on its side, with a gaping, wide-open shell, or is unresponsive or does not react when you grab it, it's sick. Healthy mussels will typically be half buried in the sand and will close up tight when grabbed.
The mass deaths of the freshwater mussels serves as a reminder of just how critical they are to the entire ecosystem, Leis said.
Mussels are "nature's Brita Filter," and serve as a filtering system for the waterways, cleaning out bacteria, viruses and pollutants.
"I think anytime an animal that filters water is dying, I think everyone should be concerned," Leis said.
"There's implications in both directions," he continued. "If there is something in the water that's stressing them, obviously that should be a reason for concern. But then if those mussels aren't there to filter things out of the water, like bacteria, viruses and pollutants, if they're not there, that also impacts the ecosystem."
For example, fish and mussels often depend on each other in the environment, Leis saying "fish and mussels go hand-in-hand," noting that typically where there's a fishery, there is also a healthy mussel population.
"It's sad to see, you know? There's mussels dying, you don't really know why, and there's not really a good explanation," Leis said.
If you spot a mussel mortality event, you should contact researchers by emailing email@example.com or calling 608-783-8440.
"It isn't like fish, where when there's a fish mortality event, the fish die and they tend to float at the surface. Mussels, that doesn't really happen, so it's really difficult to spot them."
Eric Leis, a fish biologist with the La Crosse Fish Health Center.