Little mussels offer big flex for Chesapeake Bay watershed

ASHLAND, Va. (CN) — Volunteers splashed and waded while planting 750 mussels as part of a larger project to revive a Chesapeake Bay tributary after it was dammed for a century.

They worked Friday alongside the Chesapeake Bay Foundation, the Virginia Department of Wildlife Resources and the U.S. Fish and Wildlife Service to plant the shellfish in the South Anna River, around 15 miles north of Richmond, in hopes of increasing filtration and decreasing excess nitrogen.

The event marked the return of the alewife floater species to the river two years after the demolition of a dam opened up more than 100 miles of streams and rivers to migratory fish.

“Alewife floaters were functionally extinct in this system,” Joe Wood, senior scientist with the Chesapeake Bay Foundation, said at the planting. “We are really excited today to start the process of recolonizing this river.”

The freshwater mussels, which have oval shells, live in the mud on the floor of the river. They can filter up to 15 gallons of water a day, improving clarity and removing nitrogen in the process. They also serve as homes for aquatic bugs called macroinvertebrates that fish eat.

When nitrogen combines with phosphorus, it can create dead zones where oxygen levels are too low for aquatic life to survive. Too much nitrogen — which enters the river from farms’ fertilizer runoff, among other sources— and phosphorus can spur harmful levels of algal blooms. According to the Chesapeake Bay Foundation, the bay’s dead zone covers about 1.2 cubic miles during the summer months.

A private company that operates as a mitigation bank, selling environmental credits to developers to offset the environmental impacts of real estate projects, paid to demolish the dam that local environmentalists have long sought to remove.

Charles Gowan, the recently retired director of the environmental studies program at nearby Randolph-Macon College, said the dam was on the radar of those working in the Chesapeake Bay watershed for decades. Gowan said all seven target species, including eels, returned upstream from the dam in the first year after it was torn down.

Alan Weaver, fish passage coordinator for the Department of Wildlife Resources, said he and Gowan have been working to help fish pass the dam site since the early 1990s.

“It took my whole career practically to get to the point where the dam came out,” Weaver said.

The removal has prompted the return of fish such as river herrings and American and hickory shad. The alewife floater uses the fish as a sort of taxi, where the mussels’ offspring clings to a fish’s gills while they hitchhike upstream.

Weaver said he has seen fish as far as 9 miles beyond the dam site.

“The fish are moving upstream, they are spawning, the larvae are hatching, they are finding food resources to grow,” Weaver said. “It’s just been really exciting."

The U.S. Fish and Wildlife Service raised the 750 mussels at Harrison Lake National Fish Hatchery in Charles City, Virginia. Zachary Taylor, the assistant state malacologist for the Department of Wildlife Resources, said his team has marked the mussels and is hoping to see at least 70% survive in the coming years.

Taylor said one concern is kayakers and canoers accidentally crushing the mussels, which live under the mud.  Around two-thirds of freshwater species are vulnerable to extinction.

Funding to reintroduce the species comes from the federal grant program Chesapeake Watershed Investments for Landscape Defense. The South Anna River flows into the Pamunkey River, named for the Pamunkey Indian Tribe. The Pamunkey hosts at least 18 different species of freshwater mussels. The Pamunkey Freshwater Alliance works to teach landowners in mussel hot spots, identify threatened and endangered mussels, and raise mussels at the Pamunkey Tribe hatchery.

The push mirrors similar efforts to expand oyster populations and their reefs in the bay, which provide food, cover and a home for small and juvenile fish, crabs and shrimp. The bay’s oyster population is tiny compared to the number European settlers would have encountered; it has been overfished as one of the world’s largest oyster-harvesting regions.

With restoration efforts, the oyster population in Maryland has tripled in the last 20 years.