Alabama Heelsplitter

Potamilus inflatus

Description

The Alabama heelsplitter (Potamilus inflatus ) has a compressed to moderately inflated, thin, oval shell. The valves may gape anteriorly, the umbos are low, and there is a prominent posterior wing that may extend anteriorly to the beaks in young individuals. The shell is brown to black and may have green rays in young individuals. The umbonal cavity is very shallow and the inside of the shell is pink to purple. Shell length reaches 5.5 in (14 cm) in adults.

The heelsplitter closely resembles the pink paper-shell (P. ohioensis ), yet it is easily distinguished by shell morphology. The teeth and shell of the heel-splitter are more delicate, and the shell is darker and has a pointed posterior, while the pink papershell has a rounded posterior. The heelsplitter appears more inflated due to a more developed and rounded posterior ridge. The posterior wing of the heelsplitter is more pronounced and abruptly rounded over the dorsum. The pink papershell may lack much of a wing, and when pronounced, it may be only slightly rounded and extend scarcely above the dorsum.

Behavior

See the Upland Combshell (Epioblasma metastriata ) entry.

Habitat

The preferred habitat of this species is soft, stable substrate in slow to moderate currents. It has been found in sand, mud, silt, and sandy-gravel, but not in large gravel or armored gravel. It is usually collected on the protected side of bars and may occur in depths over 20 ft (6 m). The occurrence of this species in silt may not indicate that the life cycle can be successful in that substrate. Adult mussels may survive limited amounts of time in silt where juveniles would suffocate. The occurrence of this species in silt may be because it was established prior to deposition of the silt.

Distribution

The Alabama heelsplitter was known historically from the Amite and Tangipahoa Rivers, Louisiana; the Pearl River, Mississippi; and the Tombigbee, Black Warrior, Alabama, and Coosa Rivers, Alabama. The presently known distribution is limited to the Amite River, Louisiana, and the Tombigbee and Black Warrior Rivers, Alabama. A single specimen was collected from the Tangipahoa River, Louisiana, in 1964 but could not be found there in 1989. The species has not been reported from the Coosa or Alabama rivers since the 1970s.

This species is not abundant within any known habitat. Exact population numbers are unknown.

Threats

The species is currently known from only the Amite, Tombigbee, and Black Warrior Rivers. Other historic habitat has been affected by channel modification for navigation and flood control, impoundment (the collection and confining of water, as in a reservoir), pollution, and gravel dredging. Impoundment for navigation and sedimentation from surface mining have affected the Black Warrior River. And most of the Tombigbee River was modified by construction of the Tennessee-Tombigbee Waterway, resulting in the loss of river habitat by impoundment, channelization, and flow diversion. Habitats that otherwise would have supported mussel populations have been destroyed by heavy accumulations of sediment. Navigation dredging threatens this species by the deposition of spoil on bars along the sides of the river channel. This material washes onto mussel habitat below the bars and may suffocate mussels and make conditions unfavorable for recruitment. The major threats in the Amite River are gravel dredging and channel modification for flood control.

Thirty percent of the range of this species in the Amite River has been lost since 1976, due primarily to gravel mining. The impact of the proposed Darlington Reservoir as a flood control measure will likely be determined by the type and method of water releases incorporated. An alternative flood control measure under consideration is the widening and channelization of the Amite River. This potential action would likely eliminate the Alabama heelsplitter from the Amite River, leaving the only population in the Tombigbee and Black Warrior system.

The known populations are isolated from each other and apparently are limited in extent. This could result in low genetic variation and make these populations more susceptible to environmental disturbance due to loss of adaptability.

Conservation and Recovery

Enforcement of existing regulations will protect the known populations from channel modification. The restoration of habitat and reestablishment of this species to historic habitat may be possible.

Contacts

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
(404) 679-4000
http://southeast.fws.gov/

Jackson Ecological Services Field Office
6578 Dogwood View Parkway, Suite A
Jackson, Mississippi 39213-7856
Telephone: (601) 965-4900
Fax: (601) 965-4340

References

Hartfield, Paul. 1989. "Status Survey for the Alabama Heelsplitter Mussel Potamilus inflatus (Lea 1831)." A Report to the U. S. Fish and Wildlife Service.

U. S. Fish and Wildlife Service. 28 September 1990. "Determination of Threatened Status for the Inflated Heelsplitter, Potamilus inflatus." Federal Register 55 (189): 39868-39872.