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MADDIE SOFIA, HOST:
You're listening to SHORT WAVE from NPR.
Hey, everybody. Maddie Sofia here with national desk correspondent Nate Rott. Hey, Nate.
NATHAN ROTT, BYLINE: Hello, Maddie.
SOFIA: So what have you brought us today?
ROTT: So I have an unsolved mystery involving nature's Brita filter, everyone's favorite bivalve...
ROTT: ...Freshwater mussels.
SOFIA: Wow. I'm here for it. Let's do it.
ROTT: (Laughter) So back in 2016, biologists and fishermen in a few different parts of the country started to notice that something was wrong in some of the rivers that they were frequenting. They kept seeing these huge die-offs of freshwater mussels. They were washing up on shores or were half buried in river bottoms, dead or rotting. And nobody could figure out why. Other critters were just fine; it just seemed to be affecting mussels.
SOFIA: So are we talking, like, a mass die-off situation here?
ROTT: That's what biologists are calling it. They've confirmed mass die-offs in the Pacific Northwest, the Midwest, the Southeast. They've even been documented in Spain and Sweden. And to make it worse, freshwater mussels are already one of the most imperiled groups of species on the planet, which is a really big deal because these mussels play a critical role in keeping freshwater clean.
SOFIA: So today on the show, freshwater mussels - the mystery surrounding their die-off, the team racing to figure it out and what it means for the health of our streams and rivers.
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SOFIA: So Nate, we're talking freshwater mussels and the fact that they're dying off. Where should we start?
ROTT: So I actually want to take you to southwest Virginia, right near the border with Tennessee. Maddie, put on your waders.
ROTT: OK (laughter). Because we're about to get into the waters of the Clinch River.
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ROTT: So the Clinch River flows at the feet of the southern Appalachian Mountains. The water is cold, very clear, and that is good news because freshwater mussels live on the bottom of rivers. They're kind of like - I like to think of them as sort of like the less edible version of their saltwater cousin; you know, they don't get the same love.
SOFIA: Yeah (laughter).
ROTT: But they bury themselves in the sediment and among the rocks on the bottoms of rivers. And I went out to find some of these mussels with Jordan Richard, a biologist with the U.S. Fish and Wildlife Service, who is obsessed with freshwater mussels. And it did not take him long, wading out into the water, for him to find what he did not want to see.
JORDAN RICHARD: So we start walking along, and it's just a matter of, like, how long does it take till we see something that died very recently? You see that one? So that's a pheasantshell that's just laying there. You can see it's not buried.
RICHARD: And that's - its...
ROTT: So Jordan there, he had reached into the water and pulled out that mussel, a pheasantshell. That's the species.
RICHARD: It should be buried in by, like, a foot.
ROTT: But it's not. That's dead.
ROTT: And the shell is about the size of his palm. It's this beautiful goldish brown color. But the mussel inside, which is usually, you know, a smooth pink, is turning a grayish brown and frayed around its edges; basically, it's rotting in place.
RICHARD: I saw that one, and then I took a few steps down. And by the time I stopped, right there I found, like, five. This is not what I was expecting.
ROTT: Not in a good way.
RICHARD: No. Which I'm pretty used to. I'm pretty used to, like, coming out here thinking I know what I'm going to see and just getting completely, like, bombed with dead mussels. But it sucks. I mean...
SOFIA: Wow. So you guys were just out there finding, like, dead mussel after dead mussel?
ROTT: Yeah. I mean, they were everywhere. And you heard Jordan say it, but this was really not what he was expecting. It was not the time of year that they typically see a bunch of mortality. You know, he was just being nice and taking a reporter out.
ROTT: But biologists have been going to different sections of the Clinch River since the die-off was first noticed in 2016. And in just one section of that river, the U.S. Fish and Wildlife Service estimates that the number of pheasantshell mussels that have died is in the hundreds of thousands.
SOFIA: And Nate, it sounded like, I don't know, just hearing his voice on the tape, that he was super upset.
ROTT: Yeah. I mean, he was on the verge of tears when we were talking, and then he tried to apologize about it later, which I didn't think was - (laughter) you know, obviously not necessary. But he was so upset because he's so frustrated by what's happening. They don't know what's causing this, and they're this kind of feeling of helplessness. This guy is so passionate about freshwater ecosystems. You know, it's his entire life. I mean, he actually said that he had three fish tanks in his house - one by his bed, one by the foot of his bed and one in the living room.
SOFIA: Wow. Wow. Wow.
ROTT: So yeah, very understanding wife.
SOFIA: (Laughter) OK. But let's talk a little bit more about why people are trying so hard to save these mussels. They play a really important role in freshwater ecosystems, right?
ROTT: Totally. So they don't often get the attention they deserve.
ROTT: Here's someone who knows that all too well.
EMILIE BLEVINS: Yeah, people don't tend to get quite as excited about things that lack backbones, unfortunately.
ROTT: That was Emilie Blevins. She's a conservation biologist with the Xerces Society for Invertebrate Conservation, which, you know, besides having a really cool name (laughter) is a nonprofit that focuses on some of the world's more underloved critters.
SOFIA: Nate, I will say it once; I'll say it a thousand times - invertebrates don't get enough credit.
ROTT: I know. I'm in. I think us vertebrates are a little biased.
ROTT: But these mussels do deserve a ton of credit. They're filter feeders, so that means that they filter water through them while they're down there just chilling on river bottoms.
BLEVINS: There's research that's shown they can remove pharmaceuticals from the water pesticides and flame retardants, and they remove E. coli from the water.
SOFIA: They're like our little water filters.
ROTT: Exactly. So a few of the biologists I talked to really did say, you can think of them as nature's equivalent to a Brita filter, cleaning up the water that we drink and plant. But, you know, they do all other sorts of cool stuff, like reducing the size and impacts of dead zones - those big nasty, you know, fish- and life-killing phenomena...
ROTT: ...That keep occurring in the Gulf. They do that by filtering out sediment and agricultural runoff. They sequester carbon, phosphorus, heavy metals in their shells. They reduce fecal bacteria from water. And, you know, like, what's not to love about that?
SOFIA: Somebody's got to do it. Somebody's got to do it.
ROTT: (Laughter) Thank God. A single freshwater mussel can filter more than 15 gallons of water in a day. And besides all that, they provide habitat to tons of other species. One biologist described them as, like, the freshwater equivalent to a coral reef.
SOFIA: So these mussels are clearly out here doing a lot of work. We don't have any idea what's causing these die-offs?
ROTT: So no. I mean, we have some hunches. But, you know, Jordan the biologist said it could be a million different things that is causing this. There's a bunch of folks working on this from around the country. University of Wisconsin is doing a lot of work. And they've recently identified a virus and a bacteria that they say are statistically associated with the die-off - keywords being, you know, statistically associated. So not enough to say, hey, ding-di-da-ling (ph), we found it. But they're highly suspicious of a pathogenic cause, and that is where their research is focused right now.
SOFIA: What about the stuff, like, we humans are doing? Climate change, for example - does that seem to be a contributor at all?
ROTT: Well, I mean, there's no doubt that climate change is stressing river ecosystems, as it is just about every ecosystem everywhere. But it does not seem to be the driver of what's going on here, as far as scientists can tell. But I think it's important to note that there are other human components that sort of brought us to this place. As I mentioned, freshwater mussels are already on the brink, and that is because of human activity. Fun fact - before the era of plastic, freshwater mussels were actually collected and cultivated by the millions to satisfy a commercial demand for buttons.
ROTT: Their shells were pearly white inside, right?
SOFIA: Thanks for buttons freshwater mussels.
ROTT: (Laughter) Yeah. But even more damaging was just, you know, the general destruction that was brought along by human development. So there was pollution from coal mining in the southern Appalachia, rivers dammed for power, streams diverted for agriculture, wetlands paved for housing. And all of those things have brought freshwater mussels to the point where a mysterious die-off can happen, and it becomes so crucial to find out why fast because there's so little wiggle room left in the system.
SOFIA: All right, Nate. You're bumming me out. What's the plan?
ROTT: (Laughter) So there is a contingency plan, all right? And there always needs to be a contingency plan.
ROTT: But like most contingency plans, it's one that nobody wants to use. In this case, it's a hatchery - or a nursery, more or less - for freshwater mussels.
TIM LANE: This is one of our living streams. So pheasantshell is in here. That's the one that's been going through the die-off.
SOFIA: So basically, this place is like a last line of defense for some of these species. They're going to breed them in captivity so at least they're not totally gone from planet Earth.
ROTT: Exactly. So Tim and the other biologists are reproducing mussels here, keeping them safe until they're mature enough to be brought back into the wild. They're basically stock. And when the recent die-off started on the Clinch River, they brought a bunch of mussels here from a part of the river that wasn't affected. And those mussels could not just be used to stock but they could also be used as a baseline, you know, a healthy sample to use as they search for the die-off's cause. Worst case scenario - they have to take some of those muscles and try to repopulate parts of the Clinch River where the muscles have died off.
LANE: We're not going to stand idly by and just watch them wither away. We're going to do the best we can to help them produce progeny so the species isn't going forever.
ROTT: Jordan Richard, the biologist we met at the beginning, also is helping with this effort. And he says that, you know, he knows that mussels aren't as photogenic as a rhinoceros or polar bears, but freshwater mussels are crucial to the health of other species. So if they go, we're going to have a lot of problems.
RICHARD: It's not sexy to care about the foundation of your house when you could renovate your kitchen.
ROTT: But he says if that foundation is crumbling and you ignore it...
RICHARD: By the time you notice the problem because you fall through the floor, it's too late to do anything about it.
ROTT: And then everything else, including your fancy new kitchen, is going to fall through, too.
SOFIA: All right. Nate Rott, thank you so much for bringing us this story.
ROTT: My pleasure, Maddie.
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SOFIA: This episode was produced by Brit Hanson and edited by Viet Le. The facts were checked by Emily Vaughn. I'm Maddie Sofia. Thanks for listening to SHORT WAVE from NPR.
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