The Cumberlandian Combshell (Epioblasma brevidens ) is a species of freshwater mussel, an aquatic bivalve mollusk in the family Unionidae. This species is endemic to the United States, found mainly in the states of Tennessee and Virginia. This mussel resides in medium-sized streams to large rivers. The combshell is an endangered species and protected under the Endangered Species Act of 1973. The combshell is threatened by habitat modifications and pollution.
Combshells’ critical habitat consists of:
and is rarely found in small streams or tributaries. Within these waterways, the combshell is found in coarse sand, gravel, cobble, and boulders. Though it prefers to be in waters that are three feet deep or less, it is also found in some deeper waters, like Old Hickory Reservoir on the Cumberland River, where the water flow is strong.
Combshells’ critical habitat consists of:
Historically the Cumberlandian combshell was found in a multitude of places. This included Alabama, Kentucky, Mississippi, Tennessee, and Virginia. Within these states, combshells were found in three distinct areas of geography: The Interior Low Plateau, the Cumberlandian Plateau, and the Ridge and Valley. According to a study done by Neel and Allen, the combshell was “very common” in the upper Cumberland River below Cumberland Falls in the late 1940s. Yet, studies done by Ortmann reported it as prominent in the upper Tennessee River system but rare in the lower Tennessee and Cumberland River systems. By 1980, the species was considered ‘extremely rare’ in its historical environments. Current populations are only found in small numbers in Northeast Mississippi and in Southwest Virginia. The majority of the species are found in Tennessee and Kentucky in the Cumberland and Tennessee River basin.
Juvenile combshells are suspension/deposit feeders. This means that they allow water to flow through their gills, but are not actively pumping water in. They also pedal feed, where they use cilia on their feet to drag in food particles to eat. They feed on many microorganisms in streams and rivers.
The combshell females nurture their eggs for a rather long time. This usually lasts from late summer to late spring. These eggs grow modified sections of their gills called “marsupia”. The eggs then develop into bivalved parasitic larvae called “glochidia”. Glochidia then attach to different types of fish where they become juvenile mussels. This usually occurs between 16 to 45 days
The diet of mussels is fairly similar during different developmental stages. For the first two weeks of life, considered the juvenile stage, mussels like the combshell are considered suspension or deposit feeders. As they progress into adulthood, mussels become filter feeders, actively obtaining oxygen and nutrients from the water around them. Both juvenile and adult mussels consume bacteria, algae, diatoms, some detrital, and inorganic colloidal particles. Though bacteria make up an important part of the adult mussels diet, there is no evidence to suggest that it is important for the development of juvenile mussels. Additionally, adult mussels often feed on phytoplankton, zooplankton, phagotrophic protozoans, and other organic material in the water. Though algae are the most abundant food source found in the gut of mussels, and also provide key nutrients, algae do not contribute heavily to the mussels soft tissue stores.
During reproduction, the glochidium attaches to the gills or fins of a fish to complete its development. The larvae attach to several native host fish species, including several types of darter fish and sculpins. Female mussels produce large numbers of larvae but few juveniles find a fish host and even fewer survive to maturity. Glochidia transform into juvenile mussels after their attachment on these fish. This reliance between mussels and fish means that the combshell needs a healthy fish population to survive.
The small population sizes of the combshell put the species at high risk for extinction. Because the surviving populations are also physically isolated, there is less chance for genetic mixing (through reproduction) between the populations. This could threaten the population's ability to adapt to natural or man-made challenges.
According to the recovery plan for the Cumberlandian combshell, the species will be delisted when distinct and viable populations can be found in at least 9 streams, up from the five streams that the species is currently found in. In the combshells recovery plan, it is emphasized that ecosystem management, rather than individual species management, is the most effective method of protecting a wide array of species. The Freshwater Mollusk Conservation Society was created in order to address mussel conservation.
The Kentucky Department of Fish and Wildlife Resources Center for Mollusk Conservation raises combshells for release into their natural habitat.
On June 25, 2019, a permit was submitted to conduct presence/absence studies of the combshell in Big South Fork National River. On February 20, 2020, an application was submitted by another party, looking to perform presence/absence studies throughout several different states. There is not much information about Cumberlandian combshell conservation available on the internet, though the Fish and Wildlife Services highlights several ways common citizens can help, including:
