ANNAPOLIS, Md. – Freshwater mussels, unassuming filter feeders that help keep rivers and streams clean, are among the nation’s most endangered organisms. So, the Maryland Department of Natural Resources is trying to give them a “lift.”
DNR has set up a mobile mussel propagation laboratory in a large trailer originally designed to haul race cars. With it, state biologists aim to boost the natural reproduction of freshwater bivalves wherever needed, enhancing water quality and aquatic habitat in the process.
“We’re trying to essentially just increase mussel biomass and filtering capacity in the wild,” explained DNR biologist Matt Ashton, who specializes in freshwater mussels.
Oysters are the better-known filter feeders in the Chesapeake Bay watershed, but freshwater mussels are no slouches, with some able to process about 20 gallons a day under ideal circumstances.
They have a complex reproductive cycle, which requires them to implant their larvae, or glochidia, in the gills of an eel or other fish until the young grow large enough to sustain themselves. Then, they drop off. That hitchhiking phase may be a factor in their shrinking populations and range, especially in rivers that have dams or other blockages to fish passage.
There are 16 species of freshwater mussels native to Maryland, and all but two are in peril because of habitat loss and poor water quality. Maryland classifies six as threatened or endangered, and two are federally endangered.
DNR has tried restoring freshwater mussels by transplanting some from Deer Creek in Harford County to the Patapsco River west of Baltimore. The agency also cultures mussels at its Brandywine fish hatchery in Charles County.
This spring, the new mobile mussel trailer is parked at Susquehanna State Park along Deer Creek, a tributary of the Bay’s largest river.
On one sunny March morning, Ashton and natural resources technician Megan Kubala worked to “inoculate” some bluegill sunfish with the larvae of an eastern floater mussel.
The oval-shaped eastern floater, collected from the Susquehanna Flats off Perryville, is one of the few mussel species not in trouble in Maryland or most of the Bay watershed.
“We want to focus on this species because it’s easy to culture,” explained Zach Taylor, DNR’s freshwater mussel hatchery manager, “and frankly it produces a lot of juveniles.”
But a mussel known as the tidewater mucket, another species that the DNR pair had on hand, is comparatively rare. Its range is limited to the tidal freshwater areas. Although the mucket hasn’t declined enough to warrant listing as a threatened or endangered species, it is a prime candidate for the lab’s help, Ashton said.
“It’ll cost us a lot less to improve their populations now,” he said, “than in 10 to 15 years if things are dire.”
First, the scientists must persuade the mussels to give up their tiny offspring, harbored inside their shells since spawning last fall. They normally do so on their own when the water climbs above 50 degrees Fahrenheit. But on this day, Ashton pried open an eastern floater’s shell and inserted a syringe filled with water to flush the larvae out. Thousands dribbled into a petri dish, looking like orangish grains of sand.
Peering at them through a microscope, Ashton said, “they look like little Pac-mans” as they open and shut their translucent shells.
“You see them moving?” he asked. “These are great. These are ready to go.”
Next, he poured larvae into water-filled buckets holding four or five sunfish and stirred the water every so often. After about 20 minutes, Ashton examined the fish to confirm that speck-sized larvae were clinging to their gills. The fish would then stay in tanks lining the trailer wall until the larvae develop enough to drop off and go it alone, which can take one to three weeks.
At that point, they will sift the still-tiny juveniles from the tank and take them to the Brandywine hatchery to grow larger. After they reach about the size of a quarter, they’ll be released in the Susquehanna River.
It’s an involved, labor-intensive process developed in part through trial and error, Ashton said.
“This is a field that has as much artistry, maybe, as science,” he said. Eastern floaters need less than nine months to reach releasable size, while tidewater muckets take twice as long.
But by transforming the larvae by hand and rearing them at the predator-free hatchery until larger, their odds of surviving in the wild are better.
The mobile lab is a byproduct of an agreement reached in 2019 between Maryland and the owner of Conowingo Dam to relicense the hydropower facility on the lower Susquehanna. Under the deal, the dam’s owner, now Constellation Energy, pledged to underwrite efforts to restore freshwater mussels in the river.
That deal has since been revoked by a federal court, after environmental groups filed a lawsuit challenging it for other reasons. But before that happened, Constellation had paid the first installment of $2 million.
DNR had planned to use the promised funding to build a new mussel hatchery. Design work is ongoing, though further funding is in limbo while the parties negotiate the dam’s relicensing. So DNR opted to start with a mobile lab.
Ashton said he knew that race car trailers are roomy because he has an uncle in motor sports. This new one cost the state $95,000 and another $75,000 to outfit it with fish tanks, piping, refrigerators and other equipment.
“It makes our efforts efficient and places mussels where they are of most need,” Taylor said.
The trailer’s mobility also enables DNR to take it on the road to help educate the public about the importance of freshwater mussels. The trailer has large flaps on the side that can be opened to display the fish tanks and show biologists at work inside.
“It’s providing some level of production,” Taylor added, “but it’s also forward facing.”