Green-blossom Pearlymussel

Epioblasma torulosa gubernaculum

Description

The green-blossom pearlymussel, Epioblasma torulosa gubernaculum, is a medium-sized Cumberlandian mussel with an irregularly elliptical shell, which is smooth and shiny, tawny or straw-colored, and patterned with numerous fine green rays. The shell surface is marked with distinct growth lines. The nacre (inner shell) color varies from white to salmon-red. The species is sexually dimorphic—i.e., the anatomies of males and females differ noticeably. The female's shell is generally larger than the male's and the posterior margin is more broadly rounded. The female possesses a large, flattened marsupial swelling, usually green in color and marked with radial furrows.

The green-blossom pearlymussel (previously classified as Dysnomia torulosa gubernaculum ) is smaller, has a more compressed shell, and less developed knobs than its downstream relative, the tubercled-blossom pearly mussel (E. t. torulosa ). Also federally listed as endangered, the tubercled-blossom may well be extinct.

Behavior

See the Upland Combshell (Epioblasma metastriata ) entry.

Habitat

This mussel is found in clean, fast-flowing streams that contain firm rubble, gravel, and sand substrates, swept free of silt by the current.

Distribution

Cumberlandian mussels are endemic to the southern Appalachian Mountains and the Cumberland Plateau region. Of 90 species of freshwater mussels found in the Tennessee River, 37 are considered Cumberlandian. Twenty-seven of 78 species found in the Cumberland River are Cumberlandian. Records indicate that the green-blossom pearly mussel has always been restricted to the headwaters of the Tennessee River above Knoxville, Tennessee.

The green-blossom pearlymussel is now found only in the free-flowing reaches of the upper Clinch River above Norris Reservoir. One of the larger tributaries of the Tennessee River, the Clinch River arises in Tazewell County, Virginia, and flows southwest through the Cumberland Gap region into Tennessee. Biologists from the Tennessee Valley Authority (TVA) have conducted extensive surveys along the Clinch River from Cedar Bluff, Virginia, to the Norris Reservoir. A single live specimen was found in 1982, the first green-blossom collected since 1965.

Threats

The green-blossom pearlymussel has always been rare but is now on the verge of extinction. The genus Epioblasma has generally suffered because its members are typically found only in shallow portions of major rivers with rapid currents. Water control projects have greatly diminished this type of habitat. Although the green-blossom is found in a river that supports the most abundant and diverse freshwater mussel community in the United States, it is being eliminated by factors that are not yet affecting other mussels. Dam construction, siltation, and pollution are likely causes.

The TVA has built nine major dams on the main channel of the Tennessee River and 27 smaller dams on tributary streams. The Norris Dam created one of the largest reservoirs in the state and probably flooded a crucial portion of the green-blossom's historic range. Silt runoff from strip mining and agriculture has buried many of the gravel and sand bottoms in which the pearlymussel lives. It is estimated that more than 67% of coal production in the Appalachian region is extracted by strip mining. Because mussels siphon gallons of water each day while feeding, the effects of water pollutants, such as herbicides and pesticides, are intensified. Silt clogs the mussels' feeding siphons.

Conservation and Recovery

Sections of the Clinch River appear eligible for "scenic river" status under the National Wild and Scenic Rivers Act. Such a designation would provide additional protection for this and other freshwater mussels. The State of Tennessee has designated all of the Clinch River in Tennessee as a mussel sanctuary, but the headwaters for the Clinch originate in Virginia, where coal mining is extensive.

Contacts

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
http://southeast.fws.gov/

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
300 Westgate Center Dr.
Hadley, Massachusetts 01035-9589
Telephone: (413) 253-8200
Fax: (413) 253-8308
http://northeast.fws.gov/

References

Bates, J. M., and S. D. Dennis. 1978. "The Mussel Fauna of the Clinch River, Tennessee and Virginia." Sterkiana 69/70: 3-23.

Neel, J. K., and W. Allen. 1964. "The Mussel Fauna of the Upper Cumberland Basin before Its Impoundment." Malacologia 1 (3): 427-459.

U. S. Fish and Wildlife Service. 1983. "Green-Blossom Pearly Mussel Recovery Plan." U. S. Fish and Wildlife Service, Atlanta.