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Mussels and freshwater clams are to a river what canaries are to coal mines – a sort of alarm system for hazardous conditions.

This week biologists are taking a mussel census, gauging the health of one of the world’s most diverse ecosystems flowing through southern Middle Tennessee – the Duck River.

These census takers are squeezed into wet suits and scuba masks. The counting is done on their bellies in less than a foot of water.

“In the gravel, here’s an endangered mussel right here, says biologist Steve Ahlstedt as he spits out his snorkel. “It’s called a birdwing pearly mussel…This is the best population in the world of that species.”

There are 55 mussel species in the Duck River. The most common has a much cooler name – the purple warty back, not to be confused with the pimple back. Both look like they have acne problems. Then there’s the pocketbook mussel. You get the picture.

“Because it looks like a woman’s pocketbook,” Ahlstedt says. He’s been tracking mussel populations in the Duck River for more than three decades, first with the Tennessee Valley Authority, then the U.S. Geological Survey. Some of the mussels have been around longer than that, with lifespans of 50 and 60 years.

“As they go, eventually we will go.”

Longevity and immobility are what mussels such good indicators. They sit in the same section of river for a lifetime.

Leslie Colley with the Tennessee Nature Conservancy counts out the mussels as biologists bring their finds to shore in mesh bags. One cracks itself open to figure out what’s going on.

“It’s trying to escape and get back to the water,” Colley says. “Eww, and it’s sticky.”

The mussels will be returned, but only after they’re measured and cataloged. Don Hubbs is the state’s mussel expert with the Tennessee Wildlife Resources Agency and he’s the one scribbling down the data in his field book.

“Mussels, they depend on the water to bring them their food. They depend on the fish to disperse their young, so they’re a real good indication of ecosystem completeness,” Hubbs says. “They’re exposed to all the things we insult our rivers with. And as they go, eventually we will go.”

Hubbs will compare his findings with historical figures, and he says one of the best outcomes would be finding a balanced population with old and young mussels. That indicates reproduction is occurring.

“You can tell by the diversity and the size range we’re getting of the different species, things look at least as good as they did 10 years ago,” Hubbs says.

Newly recognized species appears in census count

The team has even stumbled upon a few species that were only recently recognized.

Most mussels use the same method to disperse their young. They attract fish with a lure, similar to something people would use with a rod and reel. It’s almost like they stick out their tongue – which looks like something good to eat – and the fish can’t help but come in close. Then they get sprayed in the face with eggs.

The new Duck River Darter Snapper has modified the process.

“It attracts a darter into this area here,” says Dr. Jess Jones with U.S. Geological Survey based at Virginia Tech, pointing to where the clam shells come together. “And the darter comes in here and it snaps shut and captures it like a Venus fly trap. And it puts its glochidia – its babies – on the fish host, and after a couple of minutes it opens back up and lets it go.”

Aside from the excitement of handling one of the more interesting mussel species, Jones says there’s more good news. This she-clam is expecting.

“That means that it’s beginning to complete its reproductive cycle in this river,” Jones says.

Each mussel species a “rivet” in the Duck River

There was a time in the last 70 years that parts of the river bottom were almost cobblestoned with clams. Now you can avoid stepping on any mussels with just a little effort, still that’s an improvement. Industrial and farming pollution is largely blamed for massive mussel population declines.

Nearly a quarter million people get their drinking water from the Duck River, and that gets even those without a bent toward conservation interested. But Leslie Colley with the Nature Conservancy says every species of mussel should hold significance too.

“Imagine that you’re on an airplane, a jet, 35,000 feet in the air and that each species is a rivet in that jet,” Colley says. “Each time you lose a species, which we’ve had some real species loss in this river over time, every time a species blinks out, that’s a rivet that’s popping out of that airplane. At some point, that baby’s going down.”

The good news, Colley says, is the Duck River appears to still be in a slow climb.

(Photos – Click for larger images)
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LINK: Why the Nature Conservancy thinks the Duck River is so special

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