The high-stakes scramble to save the Appalachian monkeyface mussel

Mussels bred in the lab are once again beginning their unsung work of filtering rivers, 50 years after the U.S. Clean Water Act became law.

By Carrie Arnold
Published 19 Oct 2022, 14:42 BST
NationalGeographic_2796942
The Appalachian monkeyface mussel is critically endangered. Scientists hoping to save the species by breeding the mussels in the Aquatic Wildlife Conservation Center in Marion, Virginia, found this one in the Powell River in Tennessee.
Photograph by Joël Sartore, National Geographic Photo Ark

Tim Lane thought he knew all 195 miles of the Powell River. Much of his time was spent in waders and wet suits, tromping through its swift, cold waters and those of the neighbouring Clinch River. As the Southwest Virginia Freshwater Mussel Recovery Coordinator for the Virginia Department of Wildlife Resources, Lane was searching for the Appalachian monkeyface mussel—a small, brown bivalve found nowhere else on Earth and only an oil spill or drought away from oblivion.

A group of juvenile Appalachian monkeyface mussel, Theliderma sparsa, from the Powell River, Tennessee photographed at the Aquatic Wildlife Conservation Center in Marion, Virginia. This species is listed as Critically Endangered by the IUCN.
Photograph by Joël Sartore, National Geographic Photo Ark
Streamline chub, Erimystax dissimilis, collected from Big Darby Creek near Circleville, Ohio.
Photograph by Joël Sartore, National Geographic Photo Ark

The Powell and the Clinch have cut deep gashes into Appalachia’s ancient sandstone and shale over tens of millions of years, creating two of North America’s most biodiverse rivers. The Clinch alone is home to a hundred species of fish (including smallmouth bass, walleye, and a variety of minnows and darters), as well as 50 species of freshwater mussel, more than any other river in the world.

The sheer variety of colours, sizes, and shapes of the mussels in these waters inspired such creative names as three-horned wartyback, Carolina heelsplitter, rough pigtoe, wavy-rayed lampmussel.

To the gilt darter, larvae of the federally endangered fanshell mussel resemble a worm. When the darter moves in to eat the larvae, they attach to the fish’s gills. Larvae can stay there for weeks, even months, stealing nutrients from the darter to fuel their growth. The gilt darter is common in the southeastern U.S. but has largely been extirpated from northern and western parts of its range.
Photograph by Joël Sartore, National Geographic Photo Ark
Although the relationship between a freshwater mussel and its fish is parasitic, the fish does benefit from the pairing. The critically endangered rough pigtoe filters and cleans the water of the Clinch River of Tennessee and Virginia, which improves water quality for its partner, the striped shiner, and other fish species that live in the river.
Photograph by Joël Sartore, National Geographic Photo Ark

Yet these Edenic rivers of the southeastern United States, once chock-full of mussels, have been stripped of their shelled residents, which can live for upwards of a century. During the past hundred years, industrial and mining pollution combined with a dam-building spree have degraded rivers, threatening the mussels and other natural wonders.

Thanks to the Clean Water Act, passed 50 years ago today, the region’s riparian life is starting to thrive again. “Decades-long efforts to improve water quality in particular reaches are proving capable of harbouring even the rarest species left in each stream. This gives us hope that our efforts have not and will not be in vain,” Lane says.

Picture of the critically endangered (IUCN) and federally endangered Cumberlandian Combshell, Epioblasma brevidens. It has lures that look like fish eggs on top that are used to attract fish. When a fish strikes at the lures, the mussels then eject their larvae into the fish’s gills and are able to increase their distribution, even upstream. The Clinch River near Sneedville.
Photograph by Joël Sartore, National Geographic Photo Ark
Picture of a male Tangerine Darter, Percina aurantiaca, Conservation Fisheries a native stream fish breeding center.
Photograph by Joël Sartore, National Geographic Photo Ark

But the situation for Appalachian monkeyface mussels remains dire. According to Lane, they’re limited to a few dozen individuals in the Powell’s riffles just north of the invisible border where Virginia becomes Tennessee. “These aren’t just one of the rarest mussels,” he says. “We’re talking about one of the rarest creatures left in the world.”

The monkeyface mussel and “so many of these species are just hanging on by a thread,” he adds. “They’re very much a canary in the coal mine for human beings.” They’re unsung heroes that “really tell us about the health of our waters.”

It’s easy, but a mistake, to overlook mussels, says Todd Amacker, a conservation biologist with the Tennessee Valley Authority. “They’re the livers of the rivers,” he says, referring to the underrated role of bivalves in filtering sediment, toxins, and other impurities from water in their search for food.

Lane hopes intensive propagation efforts in the Aquatic Wildlife Conservation Centre, outside Marion, Virginia, will make it possible for monkeyface mussels to regain their former importance in the wild.

But before they could be fruitful and multiply, Lane and his small crew of malacologists, or freshwater mussel enthusiasts, had to find some. It took them 1,100 hours over four years to find nine individuals, which the U.S. Fish and Wildlife Service allowed them to bring back to the lab to breed.

How dams and dirty water kill mussels

“Dams, dams, dams, and more dams” are what’s killed off so many mussels across North America, says Paul Johnson, a biologist at the Alabama Department of Conservation and Natural Resources. “And pollution.”

Picture of an endangered Higgins Eye Pearly Mussel,Lampsilis higginsii, displaying a fish-like lure at the Geneo National Fish Hatchery.
Photograph by Joël Sartore, National Geographic Photo Ark
Picture of a Smallmouth Bass, Micropterus dolomieu, at the Geneo National Fish Hatchery.
Photograph by Joël Sartore, National Geographic Photo Ark

The Great Depression led to a surge in dam building throughout the Tennessee River watershed to control flooding and provide the region with hydroelectric power. But dams had a hidden cost: They prevented the free movement of fish and other aquatic creatures. That might not seem a big deal for animals that spend decades immobile in mud, but the dams have had an outsize impact because of the complicated life cycle of freshwater mussels.

Freshwater mussels depend on fish (or in a few cases, salamanders) to disperse their young. Gravid females, brimming with fertilised eggs, lure passing fish to their shells so they can inject their larvae into the fish’s gills. But not any fish will do. Most mussels have co-evolved with one or two species of fish to serve as hosts for their larvae.

What do the fish get out of it? For a relatively small investment of resources, they enjoy improved water quality provided by the mussels.

To entice the tangerine darter, the Cumberlandian combshell, for example, creates the appearance of fish eggs on its shell. The rainbow mussel waves small protrusions on its shell that dance in an imitation of crayfish legs to attract rock bass.

Picture of the endangered Rough Rabbitsfoot mussel, Quadrula cylindrica strigilatta, at Conservation Fisheries.
Photograph by Joël Sartore, National Geographic Photo Ark
Picture of a River Chub, Nocomis micropogon, at the Tennessee Aquarium.
Photograph by Joël Sartore, National Geographic Photo Ark

Safely ensconced in their fishy home, the larvae mature over several weeks, drawing nutrients from their hosts. Then they fall into the mud where they’ll spend the rest of their years.

“The Southeast U.S. is like the tropical rainforest of freshwater species,” says Traci DuBose, a postdoctoral fellow at Virginia Tech, in Blacksburg. “The diversity is absolutely astounding,” and the diversity of fish fuelled the diversity of mussels.

But dams have limited the movement of fish and hence the distribution of mussels, and some dams also may have separated female mussels from their hosts.

It’s not just dams. The Powell remains undammed, and the Clinch River has only two. For the Appalachian monkeyface mussel, the main threats are from toxic chemicals and coal ash from power plants that have fouled the rivers. In addition, noxious debris, especially from massive mountaintop mines and roadbuilding, has transformed pristine waters into sludge flows.

Picture of a Rainbow Mussel, Cambarunio iris. Collected on the Little River near Maryville Tennessee. This species is endangered.
Photograph by Joël Sartore, National Geographic Photo Ark
Picture of a Rock Bass, Ambloplites rupestris, at Gavins Point National Fish Hatchery and Aquarium.
Photograph by Joël Sartore, National Geographic Photo Ark

It took three decades after the Clean Water Act became law in 1972 for all its regulations to take effect, Johnson says. After Alabama began cleaning up its wastewater treatment plants in the 1990s, he adds, “we have seen the expansion of every species” of freshwater invertebrate that hadn’t been eliminated. “Every one of them expanded their range,” he says. Meanwhile, nonprofits such as the Nature Conservancy are working to remove obsolete dams across the Tennessee River Valley.

But no sooner had water quality in the Clinch, Powell, and other rivers begun to improve than numbers of many freshwater mussels nosedived. The culprit hasn’t been identified for certain, but evidence points to the combination of a virus with stresses from ongoing pollution and climate change.

The Appalachian monkeyface was in a struggle to survive long before this most recent setback, Lane says, but the current situation creates an additional hurdle for the species.

Reversing the mussel calamity

Lane—and counterparts in nearby states and at the U.S. Fish and Wildlife Service—are determined to reverse the grim trend. The Clinch and Powell has no shortage of endangered freshwater mussels that could use help, but the Appalachian monkeyface—because of its extreme precariousness—rose to the top of Lane’s breeding priorities.

Picture of a federally endangered Fine-rayed Pigtoe ,Fusconaia cuneolus, taken from the Clinch River near Sneedville. The Clinch River has more federally listed aquatic species than any river in North America, yet is threatened by pollution and habitat loss. Coal mining in the watershed now raises the threat even more.
Photograph by Joël Sartore, National Geographic Photo Ark
Picture of Whitetail Shiners, Cyprinella galactura, at Conservation Fisheries a native stream fish breeding center.
Photograph by Joël Sartore, National Geographic Photo Ark

After spending four years clad in a wet suit, stooping with their be-snorkelled faces immersed in the Powell’s swirling, icy waters, Lane’s team had scooped up just nine of the mussels, including, crucially, three females. But no one knew what host fish monkeyface larvae need.

Lane started with what he did know: Closely related mussels use small fish called chub. After trial and error, he discovered that female Appalachian monkeyface mussels could pair with the blotched chub and the streamline chub. Months of detailed observations revealed that the vibrations of staff walking by the large tanks—probably akin to the water movements created by swimming fish—caused the gravid females to release their eggs. “They were basically chumming the water,” to attract the fish, Lane says.

This spring, Lane’s team at last had bred enough juvenile monkeyface mussels to release 125 into the Clinch River (they kept several as breeding stock). The scientists attached a radio transmitter about the size of a grain of rice to each tiny shell so they can track the mussels as they mature.

Lane says he’ll repeat this process multiple times during the next decade. He hopes the rivers are clean enough now to support a growing community of the mussels.

What conservation biologists need, Johnson says, is a better understanding of how specific pollutants affect the health of freshwater mussels. Although the Clean Water Act mandated the provision of habitat for fish and wildlife, scientists have almost no toxicology data for freshwater mussels and other invertebrates. This means no one knows what chemicals they need to worry about, and which ones aren’t as problematic, Johnson says.

For Lane, his best guide is where other freshwater mussels are thriving—a major sign of good water quality. It’s what led him to choose these sites for releasing the lab-raised monkeyfaces, he says. Now, his team is breeding more mussels while continuing to monitor the released population.

“We can't do any more than this,” Lane says. “We can just try to spread them out as best we can, diversify their genes and give them a shot—a shot they wouldn't have had otherwise.”

National Geographic Explorer Joel Sartore photographed these freshwater mussels and fish as part of the National Geographic Photo Ark. Learn more at natgeophotoark.org

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