Cumberlandian Combshell

Epioblasma brevidens

Description

The Cumberlandian combshell (Epioblasma brevi-dens ), described in 1831, has a thick, solid shell with a smooth to clothlike outer surface. It is yellow to tawny brown in color with narrow green broken rays. The inside of the shell is white. The shells of females are inflated with serrated teethlike structures along a portion of the shell margin.

The broad, yellowish shell with broken rays and the distinctive marsupial expansion of the female distinguish this species from most other mussels in the range except Pychobranchus fasciolaris and Epioblasma lenoir. Male E. brevidens are broader than P. fasciolaris, and the females of the latter species do not exhibit the marsupial development of the former. Raying patterns on P. fasciolaris usually are not developed. Epioblasma lenior is a considerably smaller species, has a much lighter shell, tends to be greenish, does not have as developed a marsupial expansion, and probably is extinct.

Behavior

Spawning in the bradytictic lampsiline Cumberlandian combshell probably occurs in late summer with the glochidia being held over winter and released in late spring. Gravid individuals have been observed in May and June. Gravid females were reported from early May (but probably occurred earlier) to early June at a temperature of 59.0-64.0°F (15.0-17.8°C). Estimated age of gravid females was eight to 13 years. Six host fish species have been identified: wounded darter, redline darter. Tennessee snubnose darter (E. simoterum), greenside darter (E. blennioides), logperch (Percina caprodes), and banded sculpin. Transformation took from 16-48 days, at 60.4-62.4°F (15.8-16.9°C).

Habitat

This species inhabits medium-sized streams to large rivers on shoals and riffles in coarse sand, gravel, cobble, and boulders. It is not associated with small stream habitats and tends not to extend as far upstream in tributaries. In general, it occurs in larger tributaries than does its congener the oyster mussel. The species prefers depths less than 3 ft (0.9 m), but it appears to persist in the deep-water areas of Old Hickory Reservoir on the Cumberland River, where there is still fairly strong flow from the Cordell Hull and Center Hill Reservoirs.

Distribution

The Cumberlandian combshell historically existed throughout much of the Cumberlandian portion of the Tennessee and Cumberland river systems in Alabama, Kentucky, Tennessee, and Virginia. Many of the Cumberlandian combshell's historic populations were lost when impoundments were constructed on the Tennessee and Cumberland Rivers by Tennessee Valley Authority and the U.S. Army Corps of Engineers. Other populations were lost due to various forms of pollution and siltation. There are now only five remaining populations of the Cumberlandian combshell.

This species survives in the Cumberland River basin as a very rare component of the benthic community in Buck Creek in Pulaski County, Kentucky, and in a few miles of the Big South Fork Cumberland River in McCreary County, Kentucky, and Scott County, Tennessee. A few old, nonreproducing individuals may also survive in Old Hickory Reservoir on the Cumberland River in Smith County, Tennessee. Within the Tennessee River basin, the species still survives in very low numbers in the Powell and Clinch Rivers, Lee and Scott Counties in Virginia; and Claiborne and Hancock Counties in Tennessee. The Clinch and Powell River populations are very small and in decline.

Threats

The present populations are threatened by the harmful habitat effects of coal mining, poor land use practices, and pollution, primarily from nonpoint sources. All the known populations are small and could be decimated by episodic events such as toxic chemical spills.

Conservation and Recovery

The taxon is considered endangered by the states of Kentucky and Virginia, and it is deemed a species of special concern in Tennessee.

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://www.northeast.fws.gov/

Reference

U. S. Fish and Wildlife Service. 10 January 1997. "Determination of Endangered Status for the Cumberland Elktoe, Oyster Mussel, Cumberlandian Combshell, Purple Bean, and Rough Rabbitsfoot." Federal Register 62 (7): 1647-1658.