BIBB COUNTY, Alabama -- Using the gastropod equivalent of dental records, a University of Alabama graduate student has positively identified a snail, declared extinct in 2000, as being alive in a small but thriving colony in the Cahaba River.
Researchers believe the find may be a sign that pollution reductions resulting from the Clean Water Act as well as improvements made to the river by conservationists may be paying off.
"To be able to find a species that was thought to be extinct is always encouraging," said Nathan Whelan, the 26-year-old doctoral student, "especially considering biodiversity and conservation stories are not typically positive these days."
Tracking down the oblong rocksnail involved hunches, field work and electron microscopes, a process that became its own version of CSI -- Cahaba Snail Investigation. Details of the discovery were published Wednesday in the scientific journal PLOS ONE.
Last collected more than 75 years ago, the snail was thought to have been lost due to the impact of pollution flowing downstream from Birmingham and coal mining along the Cahaba.
But Whelan, a student in UA's department of biological sciences, thought he might be able to locate one in an area where they had been most abundant. He persuaded a few of his friends to go along on a kayak trip.
Once they got to the target spot, it didn't take long to find the snail, which is about the size of a nickel with a yellow body and a black band on its head.
"Pretty early in our trip we found the species," Whelan said.
To be sure they had the right snail, though, they had to match it against an oblong rocksnail specimen collected in 1881 and stored in the Smithsonian's National Museum of Natural History.
A key factor in making a positive ID was an examination of the snail's microscopic teeth, called radulas. They are used as the snail grazes for food, scraping algae off the river rocks. The radulas are unique to the species, and those found in the modern snail matched the 19th Century specimen's.
"The structures were virtually identical," Whelan said.
The oblong rocksnail is unique to the Cahaba basin and historically was found along a 50-mile-stretch of the Cahaba from Buck Creek in Helena down to Centerville.
It now appears to be limited to approximately one-half mile of river around the Bibb and Shelby counties lines.
"We don't know how many individuals are left," Whelan said. "Locally, they seem somewhat abundant."
The Cahaba River has been identified by the Nature Conservancy as one of eight hotspots of aquatic biodiversity in the U.S. with 121 species of fish, 38 species of mussels and 32 species of snails. Of those species, 12 are listed federally as threatened or endangered, the most listed species of any single drainage basin in Alabama, the researchers said.
It is possible that the oblong rocksnail had just been overlooked in previous surveying, Whelan said. But it also is possible that a remnant population hung on, and with improvements in water quality, it was able to expand in numbers to the point it was detectable again.
Along with improvements to municipal sewage treatment and industrial discharges prompted by the Clean Water Act, conservation groups have sponsored several projects that have improved the river, including the removal of small dams.
The result has been a better habitat for these freshwater organisms and a recovery and spread of species.
While it seems to have recovered in one spot, the oblong rocksnail is susceptible to a single event -- natural or manmade -- wiping it out forever.
But efforts are underway to spread the population. The Alabama Aquatic Biodiversity Center has worked with samples provided by Whelan and have documented how the snails reproduce. The Center, part of the Alabama Department of Conservation and Natural Resources, cultivates freshwater endangered mussels and snails and reintroduces them to the wild in an effort to get them off the endangered species list and, at the same time, improve water quality.
Paul Johnson, the program supervisor at the center, and Phillip Harris, an associate professor of biological sciences at UA, who serves as Whelan's primary academic adviser, are co-authors with Whelan on the journal article.