Limpet thought extinct for 60 years is rediscovered

June 2011: A freshwater limpet that has not been seen for more than 60 years, has been discovered in a river in Alabama's Mobile River Basin.

REDISCOVERED: The limpet has been found in a tributary of Coosa River in Alabama

The limpet was thought to be one of the 47 species of mollusc wiped out during the first half of the 20th century when a watershed in which they lived was dammed.

But now Rhodacmea filosa's has reappeared in a tributary of the heavily dammed Coosa River. The Mobile River Basin, a global hotspot of temperate freshwater biodiversity, was extensively industrialised throughout the 20th century, and 36 major dams and locks were built. ‘The dams were seen as signs of progress,' explained Diarmaid Ó Foighil, professor of ecology and evolutionary and a curator at the U-M Museum of Zoology.

'All in the name of progress'
Molluscs were found nowhere else in tBut progress came at the expense of molluscs that were found only in that area and nowhere else in the world. Limpets are snails with shells shaped like caps rather than coils. They 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.

‘Their habitat was destroyed in huge chunks,' Ó Foighil said. The result: 47 of 139 endemic mollusk species were lost, representing a full one-third of all known freshwater mollusc extinctions worldwide.

Then, about 20 years ago, thanks to increased interest in and funding for conservation projects, biologists began searching patches of the drainage that weren't affected by damming, trying to find remnants of the original, rich fauna.

Captive breeding facility now set up
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.

‘This is very good news,' Ó Foighil said. ‘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 a few of the limpets have been found, does that mean the species can continue to survive?
‘I think they can, because of two things,' Ó Foighil said. ‘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.'

Should serve as a warning to Mekong dam-builders
However, although the news about this particular limpet is welcomed, similar extinctions could well still be happening worldwid, said Ó Foighil. ‘The industrialisation of freshwater watersheds that happened across America 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 the negative downsides when it comes to issues of economic development, freshwater biodiversity almost always loses.'