Mussels in Virginia

freshwater mussels reproduce by releasing glochidia, which attach to the gills or fins of a suitable host fish and get transported to new habitat
Source: US Fish and Wildlife Service, Extracting glochidia from freshwater mussel

In freshwater, mussels are the equivalent of marine clams. They are the longest lived invertebrates in Virginia, with adults living up to 100 years in some species. Of the 1,000 freshwater species in the world, about 1/3 live in North America. The largest number of freshwater mussel species are concentrated in the southeastern states, primarily in the watersheds of the Tennessee and Mobile rivers.

Like clams and oysters, mussels are filter feeders who pump water through their shells and extract food. They live in water that moves. Freshwater mussels prefer river riffles; saltwater mussels chose shorelines and shallows with wave action.

A distinctive feature is the "byssus," proteins which mussels secrete to attach to underwater surfaces.

mussels produce threads of protein which do not dissolve underwater, creating a "byssus" that glues the shell to a hard substrate
Source: Wikipedia, Ischadium

Being sessile and long-lived exposes mussels to pollutants in the water during their long lives. The decline of mussel populations is a clear indicator of the decline of water quality.¹

When rivers cease to flow in dry summer months, freshwater fish and other animals find refuge in the remaining pools. Freshwater mussels behave like the livers of rivers, keeping these refuges clean and ensuring animals can survive until the rains return. They maintain water quality by filtering and removing suspended sediments, nutrients, bacteria and algae. They also deposit nutrients on the river bottom, and their burrowing activity mixes and aerates the sediment.

survival of endangered purple bean mussels (Villosa perpurpurea) is tracked by tagging individual mussels
Source: US Fish and Wildlife Service, Purple bean mussels with tags before release in Indian Creek, Tazewell County, Virginia

Adult mussels remain in one spot on the riverbed, though they can change positions slightly by making a new attachment and releasing the old byssus. To occupy new habitat, they rely upon currents to carry larvae downstream and on fish to transport larvae to uoccupied habitats upstream. Without fish for larvae transport, mussel beds would gradually migrate downstream and eventually disappear.

The mussel reproduction process is distinctive. Female mussels lay their eggs in specialized chambers in their gills known as marsupia. Males release sperm into the water, and females pull it into the marsupia through siphons on their gills. The eggs grow into larvae known as glochidia. Those are released into the water where they can parasitize a passing fish. Some species release larvae as packages which attract fish, by resembling what they eat:²

Freshwater mussels have an unusual and complex mode of reproduction, which includes a brief, obligatory stage as a parasite on a fish... Inside the female mussel, fertilized eggs develop into microscopic larvae known as glochidia. Mussels need to "infect" a host fish with glochidia to complete the reproductive process. Once the glochidia are released from the female, they must attach to the gills or the fins of the right fish host and encyst to complete development...

Glochidia transform into microscopic juveniles and drop off. If by chance they settle into suitable habitat, a new mussel bed is created.

Source: Virginia Department of Wildlife Resources, Endangered Mussels Released into the Clinch River, Largest Release in Eastern US

Virginia has about 80 species of mussels, but that number could drop. The US Fish and Wildlife Service declared the green-blossom pearlymussel to be extinct in 2021, and:³

According to the Department of Wildlife Resources, only 30 percent of the state's freshwater mussels are considered stable. In the state's portion of the Tennessee River system, a staggering 31 mussel species are designated by Virginia or the federal government as endangered or threatened; in Virginia's portion of the Chesapeake Bay watershed, where freshwater mussels have received far less attention, six species bear those designations.

The Clinch River has more endangered species than any other river in the United States. One of the most significant kills of endangered species since passage of the Endangered Species Act in 1973 occurred when a tanker truck overturned in 1998 on U.S. Route 460. The accident in Tazewell County spilled a chemical which flowed into the Clinch River and killed tan riffleshell, purple bean, and rough rabbitsfoot mussels, which are three endangered species.⁴

Source: Virginia Museum of Natural History, Freshwater Mussel Restoration in Virginia and the South River Watershed

endangered freshwater mussels in the Clinch and Powell River watersheds (Bottom diagonal row, left to right: Cumberlandian combshell, Oyster mussel. Middle Row: Shiny pigtoe, Birdwing pearlymussel, Cumberland monkeyface. Top row: Rough rabitsfoot)
Source: US Fish and Wildlife Service, Endangered freshwater mussels

Mussel restoration projects depend upon two state and one Federal hatcheries. The Virginia Department of Wildlife Resources has a propagation facility in Marion, the Aquatic Wildlife Conservation Center (AWCC), while Virginia Tech operates a Freshwater Mussel Conservation Center (FMCC) in Blacksburg. The US Fish and Wildlife Service raises mussels for transplanting into rivers at the Harrison Lake National Fish Hatchery in Charles City County.⁵

biologists labeled endangered mussels before planting them in the Powell River, so their survival and growth could be tracked later
Source: US Fish and Wildlife Service, Endangered mussels bound for the Powell River and Team of volunteers, students, and biologists release mussels

in Prince William County, mussel restoration has been proposed to enhance completed stream restoration projects that reduced transport of sediment to the Chesapeake Bay. On behalf of the county, the Northern Virginia Regional Commission (NVRC) won a $75,000 grant from the National Wildlife Federation's Chesapeake WILD program. Mussels will be provided by the Harrison Lake National Fish Hatchery of the US Fish and Wildlife Service, and the George Mason University (GMU) Potomac Environmental Research and Education Center (PEREC) agreed to administer the program:⁶

Phase I of the project will consist of analyzing streams in Prince William County to identify which streams are best suited for mussel reintroduction.

Phase II will consist of deploying hatchery reared mussels in baskets to monitor growth and survivorship rates in different streams.

The final phase of the project involves the reintroduction of hatchery-reared mussels into the streams identified during the assessment phase. Mussels will be tagged and released into selected sites in Prince William County with continued monitoring of the mussels and water quality.

Links

• Science Direct
• Glochidium
• US Fish and Wildlife Service
• Harrison Lake National Fish Hatchery
• Virginia Department of Wildlife Resources
• Aquatic Wildlife Conservation Center (AWCC)
• Freshwater Mussel Restoration
• Virginia Freshwater Mussel Restoration Strategy: Upper Tennessee River Basin (May 2010)
• Zebra Mussels (Dreissena polymorpha)

to plan for stream restoration, a small number of hatchery reared mussels are placed in baskets to monitor growth and survivorship rates
Source: Prince William County, Power of Partnership: NVRC Secures $75k for Prince William County Stream Filtration Project

References

biologists found numerous dead pheasantshell mussels at Sycamore Island, when inspecting the Clinch River in 2019
Source: US Fish and Wildlife Service, Richard shows mussels

dead freshwater mussels collected by biologists from the Clinch River at Sycamore Island in 2019
Source: US Fish and Wildlife Service, Dead mussels