This article originally appeared in 2018 in the Ground Below blog.
A century ago, miners famously kept canaries in coal mines to warn of deadly fumes. Today, the bellwethers of different toxins live quiet lives tucked in the mud of rivers and lakes: freshwater mussels. These modern “canaries” have a special spokesperson in the form of Abbie Gascho Landis, a veterinarian, mother to a young family and perhaps one of the best emerging science writers of the 2010s, whose 2017 book Immersion tells the plight of these fascinating organisms.
Freshwater mussels are part of the same phylum as snails, slugs and octopus and are believed to have existed for 500 million years. Globally, they play a key role in water purification. Mussels constantly ingest water through their foot muscle and are permanently immersed. An egg-size mussel can filter up to 24 liters of water a day and mussels in large numbers filter all the water in creeks, helping to make surface water safe for humans and our neighbors in the environment. Out of 890 mussel species around the world, 302 live in the US—and the southeastern US has the most biodiversity anywhere in the world. Every year, America’s population shifts further south, bringing new building, agriculture and quarrying that damages rivers, beginning with mussels. As filter feeders, they concentrate pollutants and because they rely on fish to host parasitic larvae mussels (harmless to the fish and to other species) they are especially vulnerable to overfishing.
Historically, few people consumed freshwater mussels, because of high concentrations of putrescine. Choctaws were among the few that ate them regularly, crafting them into jewelry and crushing them to strengthen clay. Mussels secrete shells, adding rings like trees. Mussels first came under threat in the late 19th century, as they were fished not for food but for decoration. There was a brief craze in New Jersey, Arkansas, Wisconsin, Texas and Louisiana for mussel pearls, depleting many species and soon their shells were widely used as buttons. A German immigrant, Johann Boepple, launched a business in Muscatine, Iowa, punching buttons out of mussel shells, but met his fate along with the industry in the 1910s, when he cut his foot on a mussel shell and died from an infection.
In the 20th century, major dam building projects for drinking water, irrigation and hydropower began in the South. Mussels don’t do well with dam building. Deep lake water has fewer nutrients, tends to be colder and has a different profile of dissolved oxygen than a river. Because most water released from artificial lakes comes from the base of dams, where the water is deepest, darkest and coldest it is low in oxygen and can cause lethal temperature shocks downstream. Mussels clump together in beds and don’t distribute evenly in rivers. They need a goldilocks zone of temperature. Islands and winding rivers slow water, making it easier for mussels to survive, but many of these twist and turns are eliminated by dam projects. The damming of the Coosa River caused the largest mass extinction of species in modern US history, claiming six mussel species and 34 different types of snails. The Tennessee-Tombigbee project from 1972 to 1985 proved to be a federal boondoggle that killed the river, leaving only a few remnant mussels in the detached East Fork of the Tombigbee River.
Although dam building has mostly halted in the US, new threats have emerged for mussels. Zebra mussels arrived in the early 1980s and spread from the Great Lakes southward through America’s rivers. Unlike American mussels, they don’t need to parasitize fish and have nearly microscopic larvae with small tentacles for swimming, eating and latching on. So far, higher temperatures in the South have made it harder for them to thrive. Fluoxetine, the antidepressant better known as Prozac, causes deadly inflammation in mussels even at low concentrations in river water.
Landis first discovered the plight of vanishing mussels through her husband, an aquatic biologist. As he researched for a PhD, the two naturalists relocated to Auburn University in Alabama, the center of mussel research. Spanning from the Appalachians to Floridian swamps, Alabama may be the state most overlooked for its biodiversity and it is now on the front-lines of the fight to keep rivers whole.
Chewakla Creek begins by the Georgia line and flows past Martin Marietta Materials’ quarry, where alkaline effluent damages the water quality. Water disappears into sinkholes and becomes further eutrophied and useless near Auburn, Alabama from cattle, wastewater and golf course runoff. A local attorney, hired by residents troubled by the drying out of the creek in 2000—and frustrated with a new road for quarrying, limiting access to their properties—filed suit under the Endangered Species Act. Landowners ended up getting a Safe Harbor Agreement instead of a court settlement that required monitoring and active measures to prevent toxic material getting into the creek. The Chewakla Creek Safe Harbor Agreement, in 2003, was the first legal action taken to protect freshwater mussels.
To save mussels and the rivers they keep clean, scientists first need to understand them. Landis and her husband dissected a giant floater mussel on their kitchen table, peering at the crystalline style—a clear, solid secretion in the stomach used to grind food—and took out the heart which pumps translucent hemolymph. In spite of having only three paired neurons, mussels can react to light, changes in temperature, chemicals and exposure to air. As a result, the American Veterinary Medical Association has actually created guidelines on euthanizing mussels. Like larger animals, mussels can have infections or cancers. Since the 1990s, scientists have discovered how to draw blood from mussels without killing them, piercing a vein in the muscle that holds the shell closed and some researchers at North Carolina State have used MRIs to explore mussel anatomy. Tiny cilia pump constantly, even for a time after a mussel’s death, drawing water through its gills. In addition to filtering water through their foot, they can also use it to eat. Using their sole foot, mussels move along creeks throughout the year and burrow into the mud for winter.
Getting mussels to reproduce is key to their long term survival, but as Landis explains, mussel reproduction is complicated. “My mussel reproduction knowledge was a summary akin to CliffsNotes of Shakespeare’s plays,” she quipped. Many mussel species release sperm into creeks. Individual cells join together in common plumes, until they get sucked up along with food into the female mussel’s gills. Until 1988, no one had any idea how glochidia—mussel larvae—got into fish. Bob Butler, a biologist working in the Choctawhatchee River noticed a fish-like lure on a southern sandshell mussel. It turns out glochidia are packaged to look like bugs, worms and small fish. Mussels are some of the most amazing imitators in nature, crafting organic lures far more convincing than anything a human angler has access to. Some species are generalists, while others rely on a single species. Threatened bankclimber mussels rely on equally endangered Gulf sturgeon.
Getting out into rivers to study mussels poses its own challenges. Aquatic biologists have received plenty of quizzical looks wandering streams in wetsuits, but they face real hazards from water moccasins, alligators and the ever present risk of arrest (or getting shot) if they stray onto unmarked private property. According to Landis, aquatic biologists find a surprising number of baby doll heads stuck in the river mud, which they’ve come to regard as a sign of good luck.
While the situation for mussels in some rivers looks dire, new hope is emerging. The Alabama Aquatic Biodiversity Center, near Marion, is the deeded over remains of a shuttered federal research station closed in 1995. But since the State of Alabama reopened it in 1999, it has led the largest non-game animal species reintroduction for threatened snails and mussels. Today, Alabama and its neighbors Louisiana, Tennessee and Georgia are the epicenter of efforts to understand and protect mussels.
The Upper Mississippi River once had over 40 species of mussels, extinguished by water pollution around 1900. But today, thanks to a cleaner environment, 20 species have returned. However, some like the Higgins eye pearlymussel are still endangered—threatened by the introduction of zebra mussels riding up-river on the hulls of boats.
Through her literary science writing in Immersion, Abbie Gascho Landis makes a strong case for the need to preserve America’s bizarre and beautiful mussels—and by extension the many threatened mollusks worldwide. The future of our rivers, our water and our environment may depend on it. For federal, state, and local policymakers, Landis' book is a reminder of the many often overlooked environmental issues that can have a big impact on the overall health of ecosystems.
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