Cumberland Monkeyface

Quadrula intermedia

Description

The shell of the Cumberland monkeyface pearly-mussel (Quadrula intermedia ) is medium in size (2.8 in [7.1 cm]), triangular to quadrangular in outline, and marked with numerous tubercles or knobs. The valves are flat and display a deep beak cavity. The outer shell surface is greenish-yellow with green spots, chevrons, zigzags, and sometimes broken green rays. The inner shell surface is white, straw-colored, or salmon.

Behavior

The life of mussels is complex, and reproduction often depends upon a stable habitat—unaltered stream conditions, clean water, and an undisturbed stream bottom. The cycle also depends upon the abundance of suitable fish hosts to complete the mussel's larval development.

To reproduce, males discharge sperm, which are dispersed by stream currents. In the process of feeding, females nearby or downstream take in sperm, which fertilizes eggs stored in their gills. The gills serve as brood pouches (marsupia), where the glochidia hatch and begin to develop. After a time, these glochidia are released into the stream. A few mussels have inner parts that resemble a tiny minnow and can be manipulated to lure host fish. When a fish gets close to the shell, the mussel expels its glochidia. The fish hosts for this particular pearly-mussel are unknown.

Glochidia have tiny bean-or spoon-shaped valves that attach to the gill filaments of host fish. Glochidia can only progress to the juvenile stage while attached to the fish's gills. Those that do not fortuitously encounter a host fish do not survive when released by the female mussel. They sink to the bottom and die.

When the juvenile has developed a shell and is large enough to survive on its own, it detaches from the host fish and falls to the stream bottom, beginning a long association with a single stretch of stream. Maturing mussels bury themselves in riffles and shoals with only the shell margins and feeding siphons exposed to the water. Some mussels live as long as 50 years or more.

A short-term (or tachytictic) breeder, this mussel produces glochidia in the spring and releases them by mid-to late summer of the same year.

Freshwater mussels feed by siphoning phytoplankton and other plant matter from the water. Indigestible particles are expelled from the shell by reverse siphoning. Silt in the water can kill mussels by clogging their feeding siphons.

There are no known interspecific differences in feeding among freshwater mussels. The glochidia are obligate parasites on the gills or fins of fish. Adult mussels are filter-feeders and consume particulate matter in the water column. Identifiable stomach contents almost invariably include desmids, di-atoms, algae, protozoa, and zooplankton.

Most freshwater mussel species display seasonal variations in activity associated with water temperature and reproduction. Metabolic rate is, in part, positively correlated with temperature. Many ectothermic species have the capacity to adjust their metabolic rates in response to long-term changes in temperature. Thus, metabolic rates do not continue to rise as temperatures rise in the summer, and they do not continue to fall during the winter as temperatures decline.

Some freshwater mussels also show diurnal changes in metabolic rates that indicate a tendency toward nocturnal activity patterns. Mussels may move to the surface to feed at night and move deeper into the substrate during the day; this is one way to avoid predators that hunt by visual contact.

Freshwater mussels are nonmigratory.

Habitat

This mussel is typically found in shallow, fast-flowing water with a stable, clean substrate of sand or coarse gravel. It requires highly oxygenated water and, therefore, does not survive in still pools.

Distribution

The monkeyface pearlymussel was historically restricted to the headwaters of the Tennessee River and probably the upper Cumberland River. It is a Cumberlandian species—endemic to the southern Appalachian Mountains and the Cumberland Plateau. Of the 90 species of freshwater mussels found in the Tennessee River, 37 are Cumberlandian; of 78 species found in the Cumberland River, 27 are considered Cumberlandian. Together, these mussels represent the largest number of freshwater mussel species found in any of the world's rivers.

Threats

This pearlymussel was apparently never abundant, and the reasons for its decline are not fully understood. Impoundments, siltation, and pollution are presumed to be the major causes. The Tennessee Valley Authority (TVA) has constructed 36 dams in the Tennessee River basin. These dams and reservoirs have inundated mussel shoals upstream, disrupted stream flow, and altered downstream habitat with sporadic cold-water discharges. Siltation caused by strip-mining and poor agricultural practices often covers the substrates of gravel and sand and smothers mussel beds. Because mussels must siphon gallons of water each day to feed, the effects of water pollutants such as herbicides and pesticides are intensified.

Conservation and Recovery

Surveys conducted by the TVA in 1988 and 1989 revealed that mussel populations in the Duck River (which flows into the Tennessee River) had stabilized. The status of mussel populations in the Elk and Powell Rivers (which flow into the Tennessee and Clinch Rivers, respectively) has not yet been determined. Sections of the Powell River appear eligible for "scenic river" status under the National Wild and Scenic Rivers Act. Such a designation would provide additional protection for the Cumberland monkeyface and its habitat.

If the Columbia Dam was completed, most of the Cumberland monkeyface's habitat in the Duck River would have been lost. The dam project was stalled by controversy. Whenever the TVA has expressed an opinion that the Columbia Dam should be abandoned, powerful local interests have continued to push for its completion. The dam was never completed. Demolition started in June 1999.

Contacts

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

Dennis, S.D. 1981. "Mussel Fauna of the Powell River, Tennessee and Virginia." Sterkiana 71: 1-7.

Isom, B.G., and P. Yokley, Jr. 1968. "The Mussel Fauna of Duck River in Tennessee, 1965." American Midland Naturalist 80 (1): 34-42.

"Protest Won't Stop Columbia Dam's Demise." InThe Tennessean, 3 June 1999.

U.S. Fish and Wildlife Service. 1982. "Cumberland Monkeyface Pearly Mussel Recovery Plan." U.S. Fish and Wildlife Service, Atlanta.