U. MICHIGAN (US) — Using century-old reference specimens, scientists have discovered a freshwater limpet not seen for more than 60 years in a tributary in the heavily dammed Coosa River in Alabama.
The story of Rhodacmea filosa’s disappearance and reappearance is both a conservation success story and a cautionary tale for other parts of the world where rivers are being dammed, says Diarmaid Ó Foighil, professor of ecology and evolutionary biology at the University of Michigan.
Limpets are snails with shells shaped like caps rather than coils that make their homes in the riffles and shoals of fast-flowing rivers and streams, where they graze on microscopic algae. When rivers are dammed, shoals and riffles are replaced with reservoirs, and the swiftly-moving water the limpets require is stilled.
During the first half of the 20th century, 36 major dams and locks were built in the Mobile River Basin, known to be a “global hotspot of temperate freshwater biodiversity.” At the time, the prevailing attitude was, “What’s not to like about getting electricity from a natural source—especially in impoverished, rural areas—and using that to drive industrialization?” Ó Foighil says. “The dams were seen as signs of progress.”
But progress came at the expense of mollusks that were found only in that area and nowhere else in the world. “Their habitat was destroyed in huge chunks,” Ó Foighil says. The result: 47 of 139 endemic mollusk species were lost, representing a full one-third of all known freshwater mollusk extinctions worldwide.
The study is reported online in the journal PLos One.
About 20 years ago, biologists began searching patches of the drainage that weren’t affected by damming, to find remnants of the original, rich fauna and save whatever still could be saved. At the Alabama Aquatic Biodiversity Center (AABC), a former catfish experimental research station has been converted into a captive breeding facility, with the aim of breeding survivors of the mass extinction and reintroducing them into unaffected parts of the watershed.
It was through those efforts that AABC director Paul Johnson discovered the surviving population of what he thought might be Rhodacmea filosa. But with no living members, how to definitively identify a species that hasn’t been seen in decades?
One hundred years ago, biologists collected multitudes of mollusks from the Mobile River Basin—never envisioning the habitat destruction and resulting extinctions that were to come—specimens that ended up in the U-M collection and used by Ó Foighil, professor emeritus John Burch, graduate student Jingchun Li and collection coordinator Taehwan Lee, along withdetailed morphometric and DNA analyses.
“This is very good news,” Ó Foighil says. “With conservation biology, usually it’s all gloom and doom, but this is one of those rare events where we have something positive to say.”
But just because survivors have been found, does that mean the species can continue to survive?
“I think they can, because of two things. We have a persistent population in this little tributary, but we also now have in place the infrastructure for their captive breeding and reintroduction to other tributaries.”
This snail tale might well serve as an object lesson, Ó Foighil says.
“The industrialization of freshwater watersheds that happened across the U.S. in the last century is now happening all over the world. For instance, right now one of the most egregious examples is the ongoing damming of the Mekong, and there are likely thousands of endemic species there.
“Even though we’re now more aware of this—of the negative downsides—when it comes to issues of economic development, freshwater biodiversity almost always loses.”
Funding was provided by the State Wildlife Grant Program, the U.S. Fish and Wildlife Service, and the National Science Foundation.
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