Cumberland bean (Villosa trabalis)
Federal Status: Endangered, Listed June 14, 1976
Description: The Cumberland bean is a small to medium sized freshwater mussel with relatively thick, elongated, oval shells. The shells of the females are somewhat more rounded and slightly larger (maximum about 55 millimeters or 2.2 inches long). The periostracum (outer shell surface) is smooth (no ridges or bumps) and somewhat shinny; it is olive green, yellowish brown, or blackish with fine wavy dark green or blackish rays. However, these rays are often difficult to see unless the shell surface is cleaned. The nacre (inside shell surface) is bluish white or white with a bluish iridescence towards posterior end of the shell. Males release sperm into the water column, which are taken in by females through their siphons during feeding and respiration. The eggs are fertilized and retained in specialized portion of the gills (marsupium) until the larvae (glochidia) fully develop. After the glochidia are released into the water, they attach and encyst on the gills and/or fins of a host fish. When metamorphosis (change to a young mussel) is complete, they drop to the streambed as juvenile mussels. Spawning likely occur in late summer through early fall; the glochidia are likely released in late spring and early summer. Two fish have been identified as host--fantail darter (Etheostoma flabellare) and striped darter (Etheostoma virgatum).
Habitat: The Cumberland bean pearlymussel inhabits small rivers and streams in fast riffles with gravel or sand and gravel substrate. Individuals have been found in riffle and run habitat areas with shallow water depths (less than one meter) and clean, stable substrate. Individuals can often be found in transitional zones between sand and gravel substrates.
Distribution: The Cumberland bean was historically known from ten river systems in the Cumberland and Tennessee river basins in Alabama, Georgia, Kentucky, Tennessee, and Virginia. Currently, the species survives in only a few streams in the upper Cumberland River system, Kentucky and Tennessee and in the upper Tennessee River system, Tennessee. A relatively strong population still exists in a short reach of the Hiwassee River downstream of the North Carolina/Tennessee State line in Polk County, Tennessee. Although no specimens have been collected in North Carolina, the habitat appears suitable, and we believe the species likely also occurs in small numbers in the North Carolina portion of the Hiwassee River below Appalachia Dam, Cherokee County (J. Fridell, USFWS, pers. Comm. 2000).
Threats: The Cumberland bean, like most mussels in the Ohio River basin, has been directly impacted by impoundments, siltation, channelization, and water pollution. Reservoir construction is the most obvious cause of the loss of mussel diversity in the basin's larger rivers. Most of the main stem of both the Tennessee and Cumberland River and many of their tributaries are impounded. For example: over 2,300 river miles or about 20 percent of the Tennessee River and its tributaries with drainage areas of 25 square miles or greater are impounded (Tennessee Valley Authority 1971). In addition to the loss of riverine habitat within impoundments, most impoundments also seriously alter downstream aquatic habitat; and mussel populations upstream of reservoirs may be adversely affected by changes in the fish fauna essential to a mussel's reproductive cycle.
Coal mining related siltation and associated toxic runoff have adversely impacted many stream reaches. Numerous streams have experienced mussel and fish kills from toxic chemical spills, and poor land use practices have fouled many waters with silt. Runoff from urban areas has degraded water and substrate quality. Because of the extent of habitat destruction, the overall aquatic faunal diversity in many of the basins' rivers has declined significantly (USFWS 1984).
U.S. Fish and Wildlife Service. 1984. Cumberland Bean Pearly Mussel Recovery Plan. Atlanta, GA. 58 pp.
Bob Butler, Fish and Wildlife Biologist, 828-258-3939 ext. 235
Species profile revised on October 4, 2011.