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A mussel sitting on rocky substrate with rays like growth rings on a tree and dark vertical stiping.
Information icon Cumberland combshell. Photo by Dick Biggins, USFWS.

Cumberland combshell

Epioblasma brevidens

The Cumberlandian combshell has a yellow to tawny brown shell with narrow, green, broken rays. It inhabits medium-sized streams to large rivers with shoals and riffles in coarse sand, gravel, cobble, and boulders; it is not associated with small streams.

The Cumberlandian combshell originally was described from the Cumberland River in Tennessee. This species was once widely distributed, historically occurring in fAlabama, Kentucky, Mississippi, Virginia, and Tennessee. Individuals of this species were eliminated from much of their historical ranges by human-made factors, such as impoundments, channelization, pollution, sedimentation, and other significant factors. By the 1980’s, the species was considered “extremely rare” throughout its range.

In 1997, the Cumberlandian combshell was listed as an endangered species. U.S. Fish and Wildlife Service, along with state governments and other partners, is working to restore populations among its historic range.

Appearance

The Cumberlandian combshell has a thick solid shell with a smooth to clothlike periostracum (thin, skin-like coating), which is yellow to tawny brown in color with narrow green broken rays. The nacre (mother of pearl) is white. The shells of females are inflated, with serrated teeth-like structures along a portion of the shell margin. Most mature Cumberlandian combshell are approximately 2 inches long , but may reach more than 3 inches.

A dark brown mussel with dark, vertical lines
Cumberland combshell teaching sample. Photo by Matthew Patterson, USFWS.

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. It prefers depths less than three feet, but appears to persist in the deep-water areas of the Old Hickory Reservoir on the Cumberland River, where there is still fairly strong flow from the Cordell Hull and Center Hill Reservoirs.

Diet

Adult freshwater mussels are filter feeders, orienting themselves in the substrate to facilitate the siphoning of the water column for oxygen and food. Mussels are known to consume bacteria, detritus, assimilated organic material, diatoms, phytoplankton, zooplankton, phagotrophic protozoans, and other microorganisms. Although algae forms a conspicuous component of adult mussel gut contents and contributes key nutrients such as vitamins A and D and phytosterols, algal carbons do not dominate soft-tissue stores.

Juvenile mussels employ foot (pedal) feeding and are thus suspension/deposit feeders . The juvenile diet (up to 2 weeks of age) includes bacteria, algae, and diatoms, with some detrital and inorganic colloidal particles. Contrary to its importance for adults, bacteria in riverine sediments were not deemed essential to juvenile growth and survival.

Historic range

Alabama, Kentucky, Mississippi, Tennessee, Virginia

Historically, the Cumberlandian combshell appears to have been widespread and common in its range throughout the Cumberlandian Region, occurring in three physiographic provinces (Interior Low Plateau, Cumberland Plateau, Ridge and Valley) and five states ( Alabama, Kentucky, Mississippi, Tennessee, Virginia).

In the Cumberland River, it occurred from the base of Cumberland Falls, McCreary and Whitley counties, Kentucky, downstream to Stewart County, Tennessee. In the Tennessee River, it occurred throughout the main stem, downstream to Benton and Humphreys counties, Tennessee. The Cumberlandian combshell also occurred in numerous tributaries in the Cumberland and Tennessee River systems. The most downstream records in both rivers are from archeological sites, indicating that at least in premodern times this species occurred further downstream from the area strictly defined as the Cumberlandian Region.

The Cumberlandian combshell was considered “extremely rare” throughout its range by the 1980s, and its numbers were declining in the upper Tennessee River system, particularly in Virginia. They have undergone significant reductions in total range and population density. Having once existed in thousands of river miles, they now survive in only a few generally small, isolated populations, most of which are of questionable long-term viability.

The Cumberlandian combshell has disappeared from a large percentage of its former range (Table 3). Main-stem populations in both the Cumberland and Tennessee Rivers are now considered gone. This species has apparently also been eliminated from numerous tributaries in the Cumberland River system (e.g., Rockcastle River, Beaver Creek, Obey River, Caney Fork, Stones River, Red River) and the Tennessee River system (e.g., Station Creek, Wallen Creek, Holston River, Nolichucky River, West Prong Little Pigeon River, Little Tennessee River, Paint Rock River, Elk River, Little Bear Creek, Cedar Creek, Duck River) (Table 3). The Cumberlandian combshell has also gone from large portions of additional tributaries in the Cumberlandian Region (e.g., Clinch River, Powell River, North Fork Holston River, Bear Creek).

Current range

The Cumberlandian combshell is found in two streams of the Cumberland River system in Kentucky and Tennessee, and three streams of the Tennessee River in Alabama, Mississippi, Tennessee, and Virginia.

Cumberland River system populations occur in Buck Creek, Pulaski County, Kentucky; Big South Fork, Scott County, Tennessee; and McCreary County, Kentucky. In the Tennessee River system, populations are thought to remain in the Clinch River, Scott County, Virginia; Hancock County, Tennessee; Powell River, Lee County, Virginia; and Claiborne and Hancock counties, Tennessee; Bear Creek, Colbert County, Alabama; and Tishimingo County, Mississippi.

Currently, the largest population of the Cumberlandian combshell occurs in the Clinch River in Tennessee. Biologists have recently documented the presence of significant numbers of adults and verified recent recruitment with the presence of juvenile specimens from muskrat middens in the Clinch River. The Big South Fork population is sizable and recruiting. Recent evidence of recruitment has also been detected in the Powell River, but populations in other stream reaches are small and of questionable long-term viability (e.g., Buck Creek, Bear Creek).

Conservation challenges

The fate of freshwater mussel populations is influenced by a number of complex biological and ecological factors that are, in turn, ultimately affected by human-made forces. Current threats to surviving populations of these mussels include continued habitat loss and fragmentation, cumulative effects of land use activities on aquatic environments, population isolation and associated deleterious genetic effects such as inbreeding depression, and competition with invasive exotic mussel species.

Females brood eggs in modified sections of the gills, called marsupia, where they develop into bivalved larvae, called glochidia. This species appears to be a long-termed brooder with spawning occurring in late summer and embryoinc stages/glochidia held in the marsupia until late spring. The glochidium is parasitic and must attach to the gills or fins of a fish to complete its development. Female mussels produce large numbers of glochidia but few find a fish host and even fewer survive to maturity. Glochidia of the Cumberlandian combshell have been identified on several native host fish species, including the wounded darter, redline darter, bluebreast darter, snubnose darter, greenside darter , logperch, banded sculpin, black sculpin, and mottled sculpin . Glochidia transform to juvenile mussels after 16 - 45 days of encystment of these fish. This inter-dependence between mussels and fish means that the wellbeing of mussel communities is closely linked to the health of the resident fish community.

These mussels, like many other Cumberlandian Region mussels, have undergone significant reductions in total range and population density, primarily resulting from human-induced changes in stream and river channels, including channel modifications (e.g., dams, dredging, mining) and historic or episodic water pollution events.

Populations are extremely vulnerable to a number of threats, including habitat loss/fragmentation; chemical and organic pollution; barriers to fish migration.

The entire length of the main stems of the Tennessee and Cumberland rivers and many of their largest tributaries are now impounded or greatly modified by the discharge of tailwaters. For example, more than 3,700 river km (2,300 river mi) (about 20 percent) of the Tennessee River and its tributaries were impounded by the Tennessee Valley Authority by 1971. Dams permanently alter the free-flowing aquatic habitat required by many mussels and their host fish.

These mussels are not known to survive in impounded waters. Riverine mussels are killed during construction of dams; they may be suffocated by sediments that accumulate behind the dams and the reduced water flow behind dams limits food and oxygen available to mussels. Mussel populations in free-flowing river sections below dams can be adversely affected or extirpated from reduced dissolved oxygen levels, unnatural flow regimes, and colder temperatures, or greatly modified by the dams or their tailwater releases. Many fish species that serve as hosts to mussel larvae are also eliminated by dams and impounded waters.

Other forms of habitat modification, such as channelization, channel clearing, woody debris removal and gravel mining, caused stream bed scour and erosion, increased turbidity, reduction of groundwater levels, and sedimentation, can cause severe impacts.

Sedimentation may also eliminate or reduce recruitment of juvenile mussels, and suspended sediments can also interfere with feeding. Water pollution from various sources such as mines, industrial plants, and municipal sewage treatment facilities also have contributed to the demise or decline of the species in certain portions of its historical range. Freshwater mussels, especially in their early life stages, are extremely sensitive to many pollutants (e.g., chlorine, ammonia, heavy metals, high concentrations of nutrients) commonly found in municipal and industrial wastewater effluents. Stream discharges from these sources could result in decreased dissolved oxygen concentration, increased acidity and conductivity, and other changes in water chemistry, which may impact mussels or their host fish.

Non-point source pollution, such as sediment and agrochemical run-off, which are known to adversely affect aquatic invertebrates also poses a continuing threat to the long-term survival of these remaining mussel populations. Other primarily localized impacts include coal mining, gravel mining, reduced water quality below dams, developmental activities, water withdrawal, impoundments, and alien species.

An additional major impact on individual populations of mussels that has resulted from historic activities (especially dam construction) was separation and isolation of populations by impoundments or large stretches of unsuitable habitat, rendering natural reproduction between those populations (and associated genetic interchange) problematic. Small populations are more vulnerable to natural random events such as droughts, as well as to changes in human activities and land use practices that impact aquatic habitats . Their restricted ranges and low population levels also increase their vulnerability to toxic chemical spills and the deleterious effects of genetic isolation. These isolated populations can also be vulnerable to outcompeting invasive species.

Recovery plan

Download the 2004 recovery plan.

Partnerships, research and projects

The Kentucky Department of Fish and Wildlife Resources Center for Mollusk Conservation culture the Cumberlandian combshell at their facility in Frankfort, Kentucky. Once they have grown for a few weeks they are brought to Wolf Creek National Fish Hatchery where they are then placed into cages built specifically for mussel propagation. These cages are placed in floating racks in Lake Cumberland where they will reside for one to two growing seasons, growing seasons last from April to October. Staff at Wolf Creek monitor cages weekly brushing off excess algae to allow optimal food flow through. Once the juveniles have been deemed big enough they will be released back to their natural habitat.

How you can help

  • Conserve energy in an effort to limit the construction of new hydroelectric power plants.
  • Limit or cease pesticide use to conserve soil and prevent runoff into nearby lakes and streams. Integrated Pest Management (IPM) strategies can replace pesticide use–find out more about it.
  • Help control soil erosion by planting trees and plants to avoid runoff of soil into freshwater areas.
  • Remove aquatic weeds from boat trailers and motors before using again to prevent the spread of things such as zebra mussels. DO NOT throw weeds back into the water. Help support watershed management programs by calling your local resource management agency.
  • Support and follow zebra mussel quarantine, inspection, and decontamination programs.

Learn more about how you can help freshwater mussels.

Designated critical habitat

Critical habitat was designated for the Duck River (0 river km occupied, 74 river km unoccupied habitat) in Tennessee, Bear Creek (40 river km occupied, 0 river km unoccupied habitat) in Alabama and Mississippi, Powell River (154 river km occupied, 0 river km unoccupied habitat) in Tennessee and Virginia, Clinch River (242 river km occupied, 0 river km unoccupied habitat) in Tennessee and Virginia, Nolichucky River (0 river km occupied, 8 river km unoccupied habitat) in Tennessee, Big South Fork (43 river km occupied, 0 river km unoccupied habitat) in Tennessee and Kentucky, and Buck Creek (58 river km occupied, 0 river km unoccupied habitat) in Kentucky.

Federal Register notices

The following Federal Register documents were automatically gathered by searching the Federal Register Official API with this species’ scientific name ordered by relevance. You can conduct your own search on the Federal Register website.

  • We're sorry but an error occurred. Visit the Federal Register to conduct your own search.

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