Focus on Snails: 3 Snails—Rediscovery
Historically, the freshwater snail fauna of the Mobile River Basin (Basin) was the most diverse snail fauna in the world. It included nine families and about 118 species of snails. However, dam construction during the early twentieth century left the Basin fragmented, leaving surviving snail communities vulnerable to nonpoint runoff, acid mine drainage, siltation, de-stabilized river channels, and pollution from urban areas. These impacts have contributed to the extinction of nearly 40 species of snails, including all species of four endemic genera. This has had the unfortunate distinction of being the largest extinction event in the history of the continental United States.
However, late last year—2004—scientists saw a ray of hope when three of these presumed extinct species were rediscovered. Stephanie Clark, a post-doctoral researcher at the University of Alabama, discovered the Cahaba pebblesnail in a section of the Cahaba River in Bibb County, Alabama, and Jeff Garner, State Malacologist with Alabama’s Department of Conservation and Natural Resources, found two other snails—the teardrop elimia and the cobble elimia—in a stretch of the Coosa River between Lake Logan Martin and Neely Henry lake.
The pebblesnail genus Clappia is endemic to the Basin and includes two species of snails, both of which were presumed extinct. The Cahaba pebblesnail (Clappia cahabensis), one of those species, was formerly known from a single collection made in the Cahaba River in 1965. The site where Clark found the pebblesnails is near the original site but is currently a part of the recently dedicated Cahaba National Wildlife Refuge. Today, the shoals in the refuge support high numbers of native snails, including the endangered cylindrical lioplax, the threatened round rocksnail, and the recently reported endangered flat pebblesnail.
The teardrop elimia (Elimia lachryma) and the cobble elimia (Elimia vanuxemiana) were described during the mid-1800’s from a short reach of the middle Coosa River. Neither of the species had been seen in the Coosa for nearly 50 years, until Garner collected them late last year.
This section of the Coosa River, as well as the rest of the river, experienced extensive modifications during the early to mid 1900’s. The construction of large dams reduced the amount of riverine habitat available for snails and other aquatic species to short flowing reaches between the impoundments. Recent changes in dam operations and water quality improvements have likely contributed to the increase in snail diversity and numbers.
Since the rediscovery of these snails, things are hopefully looking up for the Basin. With the passage of two important pieces of legislation, the Clean Water Act and the Endangered Species Act, in the early 1970’s, water quality will hopefully continue to improve. Localized improvements in the way dams are operated, better water quality being discharged from industrial and urban sources, and increased understanding of the potential adverse affects certain land use practices have on water quality, have all been vital components to improving our rivers and streams.
Unfortunately, these three species have plenty of company on the Basin’s imperiled species list, including 39 other aquatic species listed as endangered or threatened under the Endangered Species Act, along with several candidates and a number of species of concern. These include mussels, fishes, snails, turtles and two aquatic plants. In order to maintain the positive momentum, we must continue to look for ways to improve water quality and protect riverine habitat, not only for the snails, but for everyone who relies upon its waters for consumption and recreation. In the old days, coal miners used canaries in the mines they were working to test the quality of the air before they entered. In a sense, snails are like those canaries. Every time a species goes extinct, it’s just another sign that something is not working properly in the ecosystem. Therefore, it’s up to the many citizens, researchers, and various interest groups in the Basin to continue working and searching for ways to improve both the quality and quantity of our water for the snails, as well as future human generations.
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