Range: Found only in two rivers in Eastern Tennessee and three in southwest Virginia. Unconfirmed populations reportedly found in the Cumberland River in Tennessee.
Conservation Status: Listed as endangered under ESA in 1977. No critical habitat has been designated.
Remaining Population: The current population is unknown. The 2001 population in Indian Creek was determined to be around 2000 adults.
Threat: Coal mining, and particularly coal ash, has polluted the rivers where the Tan Rifflsehell lives.
The tan riffleshell, might not look exciting—it is a medium-sized freshwater mussel with a brown to yellow colored shell with numerous green rays. But the decline of this mollusk is proving to have profound effects on Appalachian river habitats.
Freshwater mussels are the proverbial “canary in the coal mine” for America’s rivers and lakes. These tiny shellfish make a living by eating small particles suspended in the water, acting as a filter and producing clean water. So when these “filter feeders” are inundated with sediment and pollution and entire colonies start dying, alarm bells should be going off. Consider that, of the 300 mussel species that once existed in North America, more than 75 are currently considered at-risk of extinction, and 38 have already gone extinct. Riffleshells of the genus Epioblasma are the most endangered genus of unionids in the United States and are on the brink of extinction: 16 of the 25 recognized taxa in the genus were already presumed extinct in 1998, and all but one of the remaining species in the genus are listed as endangered as of 2001. The tan riffleshell may even be the only remaining representative of the genus subspecies E. florentina, and therefore represents an important genetic component of the freshwater mussel order Unionida. The only known reproducing population of tan riffleshells can be found on a two-kilometer reach of Indian Creek, a tributary to the Clinch River in southwest Virginia.
Threats From Fossil Fuel Development
The specific threat that led to the species’ listing in 1977 was water quality degradation. At the time of the tan riffleshell’s endangered listing, water quality from mine acid was the main threat to the species’ ongoing existence. In addition, mercury and lead contamination in the middle fork of the Holston, low dissolved oxygen levels in the west fork Stones River, and a history of spills of fly ash and sulfuric acid and heavy metal contamination in the Clinch River are documented pollution concerns for these historic populations. Fossil fuel development impacts were not its only threats. When the Tennessee Valley Authority Dam was built, it killed the remaining populations in the Duck River drainage and invasive species—the Asiatic clam (Corbicula fluminea) and the zebra mussel (Dreissena polymorpha)—are also likely contributing to its decline. At this point, these impacts still remain, yet the extent to which the species is affected by the coal industry in particular is notable. The species is being impacted by water pollution due to acid mine drainage and sedimentation from coal mining. Coal ash landfills are contaminating the mussel’s habitat with sulfuric acid and heavy metal contamination. (When coal is combusted to produce energy, it leaves behind a residue that may contain any number of toxins. This is referred to as coal ash.) In the Clinch River watershed in particular – the location of the last remaining reproducing population – both types of coal impacts have threatened the species.