Photo by Alexandria Living Magazine
Potomac River at sunrise.
The closest many people come to a mussel is eyeing their bulging dark shells crammed in mesh bags awaiting sale next to bags of clams at the supermarket seafood counter.
Mussels are aquatic mollusks, invertebrate animals with soft bodies usually enclosed in a hinged shell. Some have intriguing names like the shiny pigtoe, Cumberland monkeyface and birdwing pearlymussel. “Cousins” of marine clams and oysters, they live from 20 to 100 years.
Their shells are usually, but not always, blackish in color on the outside and pearly on the inside. Mussels grow in both freshwater and saltwater. They spend much of their lives partially buried in sediment.
Freshwater bivalves, meaning “two shells, they can range from thumbnail to pie plate size. While not charismatic to most humans and seemingly sedentary, they are important. Often called nature’s “cleanup crew,” one adult mussel can clean up between 10 to 20 gallons of water per day. They draw in water with their incurrent siphon and discharge it through their excurrent siphon, filtering bacteria, algae and other small particles. As filter feeders, they obtain food by filtering water for nutritious particles.
At Risk
“When the first English settlers arrived on these shores, they were astonished to discover rivers practically paved in freshwater mussels,” according to the Virginia Department of Wildlife Resources. Seventy percent of mussel species in this country are extinct or at risk of extinction. Of Virginia’s 82 species, only 30 percent are stable.
Dams, invasive species and pollution from stormwater flowing off roofs, parking lots, roads and other hard surfaces and from lawns and agricultural sites imperil them. Destroying trees along riverbanks can unleash sediments and heat up waters to unsustainable temperatures by letting in too much light.
Too many sediments can smother mussel beds and create turbidity which blocks sunlight needed for underwater plants that invertebrates, fish, ducks and other aquatic organisms need for food and protection. Climate change is bringing more frequent and more intense rain events that can exacerbate streambank erosion and increase pollutants flowing into waterways.
The absence of freshwater mussels usually indicates chronic water pollution problems, say experts.
Enter the Potomac Riverkeeper Network
In 2019, the Potomac Riverkeeper Network (PRKN) launched the 50 Million Mussel Project to restore freshwater mussel populations in the Potomac and Shenandoah Rivers. For the Potomac, the goal is to have 50 million by 2030. The Potomac River and its tributaries are home to 16 species of mussels.
While the river’s condition is improving and the Potomac Conservancy gave the river an overall grade of "B" in 2023, the “report card” warned that pollution remains a problem. “Polluted urban runoff is the only growing source of pollution to the Potomac River. Polluted runoff occurs when excess rainwater flows across paved and hardened surfaces and carries street oils, lawn fertilizers, trash and even diluted sewage directly into local streams,” the report said.
Mussels can help clean up the Potomac, argues Dean Naujoks, the Potomac Riverkeeper.
More Mussels Near Oronoco Park
In November 2023, PRKN and the Virginia Department of Wildlife Resources Virginia Tech scientists seeded mussels in the river just off Alexandria’s Oronoco Bay Park. They plan to introduce more than 14,000 mussels into the Alexandria waters of the river between 2024 and 2026.
The project is part of the $300,000 settlement with the city to remediate decades of coal tar residue pollution containing toxic chemicals from the Alexandria Town Gas Plant, in operation from 1851 to 1946. Coal tar is a dark liquid byproduct of coal processing and contains some carcinogenic chemicals like benzene.
On Feb. 23, in a talk to the Friends of Dyke Marsh, Naujoks explained that under the settlement, the city is now capturing the coal tar, has relined the pipeline and will dredge the soil to remove the pollutants.
“We commend the city for agreeing to take the necessary corrective action to halt and clean up this pollution, which has been harming the Potomac River for decades,” Nancy Stoner, the group’s president, said at the time. “This is a win for the Potomac River, the residents of Alexandria and for everyone who relies on the river for drinking water and recreation.”
Growing Mussels at National Harbor
Across the river at Maryland’s National Harbor, the riverkeepers have been propagating native mussels in Smoot’s Cove. Project managers hope that that eventually the seeded mussels will grow into a self-sustaining population.
They started with floating cages suspending above the river bottom designed to catch baby mussels, a technique successfully used to restore oysters. They pull up the cages, brush them off and resubmerge them into the water column, to prevent sediment buildup that can suffocate the mussels.
Some of the forces working against them are waves and currents that can move the baby mussels out of the cages. Some cages get damaged by hungry otters or birds that have torn into them. One of their goals is to help develop the most effective type of cage and identify other suitable sites for mussel nurseries.
“2024 was our most most successful year,” Naujoks reported. “We put 4,000 mussels in the river and there are more to come.” He explained “the country has done a good job” addressing big sources of pollution like discharges from industrial plants. “Mussels are vital to augment those efforts,” he said.
When owners tore down the former fish market in southwest Washington, they donated a barge to the Potomac Riverkeepers who are now raising funds to convert it into a science lab. They hope to install an upweller system that will function like a mussel incubator with compartments that circulate food and fresh water.
Naujoks hopes that one day, people along the Potomac will raise mussels off their docks like oyster growers down river.
The network’s partners are Peterson Companies/National Harbor, the Joseph Manning Hatchery in Charles County, Maryland, Oasis Marinas, Underwater Adventure Seekers, the Maryland Department of Natural Resources and the Virginia Department of Wildlife Resources. PRKN hopes to expand their partnerships to other organizations.
Freshwater mussel restoration projects are also underway on the Anacostia River in Washington, D.C., on Virginia’s James Rivers and in southwest Virginia.
From May to September, PRKN volunteers conduct water testing at 30 public access points along the Potomac, including one at Belle Haven Marina. “PRKN wants to make the river swimmable again,” Naujoks told the February 23 gathering, not just for mussels but for people too. “The river will be a lot cleaner than it is today by 2030,” he predicted.
Complex Reproduction Strategy
Freshwater mussels have one of the most complex reproductive processes in nature, linked with fish populations, which makes restoration complicated and challenging.
Males release sperm which the water’s current carries to a downstream female who draws it in through her siphon. A fertilized egg develops within her gills into the microscopic larval stage called a glochidium.
Once mature, the glochidia enter the water column and attach to gills, fins or scales of freshwater fish, their host, so the fish serves as a host or “taxi” for the mussel’s eggs. Still microscopic, the juvenile mussel drops off the fish and continues to develop to maturity on the stream bottom.
