They lie still at the bottom of the river for decades, housed inside two shells. Yet for all their lack of movement, mussels perform one of Mother Nature’s most important duties—they clean the river.
But these environmental gems and the water they call home are delicate, and they need to be protected. That’s why the Louisville District and the Kentucky Nature Conservancy hosted federal, state and non-governmental partners at Green River and Mammoth Cave to discuss on-going efforts to protect the mussels and preserve one of the most biologically diverse water systems in the country.
"The Corps is committed to being a responsible steward for the nation’s resources and helping to minimize negative environmental impacts," said Louisville District Commander Col. Keith Landry. "Two of the four principles of the good-to-great philosophy are setting standards for your organization and making a unique and positive contribution to your nation. Clearly, the Nature Conservancy and the Louisville District are doing that."
Several years ago, the Corps and the conservancy began the Sustainable Rivers Project, a pilot program that seeks to find the most environmentally friendly way to operate the Green River’s lock and dam systems that are crucial to flood control and economic development.
But locks and dams do—inescapably—disrupt the natural flow of water, and it’s these changes that can negatively affect the river’s ecosystem. Green River mussel species thrive in shallow, low-flowing sections of the water. Dams pool water, and, when water is eventually released, it’s often done so at a very high rate.
But the Corps’ lake dam operators on Green River use more controlled methods of release, and they’re doing everything they can to mimic the river’s historic, natural flow of water. Because pooled deeper water is cooler than flowing shallow water, the new methods prevent the sudden cold-water assaults that can damage mussel environments. The controlled releases have also nearly eliminated the backflow of water into nearby cave systems that can disrupt the aquatic life within the cave.
A healthy mussel population depends on several variables, and the river’s fish population might be the most critical. Once the female mussel’s eggs have been fertilized and then hatch into larvae, it’s time for the mussel to go fishing for a host, and no ordinary fish will do. Each species of mussel requires its own specific species of fish.
Somehow, the mussel can sense when her special fish is nearby. When the female senses the right fish, she attracts the fish to approach even closer. Some mussels have what resembles a worm attached to their shell. The mussel baits the fish with the "worm" and when the future host approaches, the mussel releases the larvae into the water around the fish. The larvae attach to the fish’s gills and feed on tissue for up to seven months before dropping to the ground. Immediately, the juvenile mussels begin their work.
"It’s an elaborate life cycle," said Kendall Moles, a researcher at Tennessee Tech University. "It just takes one little thing to interrupt that."
How do they keep the river clean?
The filtering is really a result of mussel diet. They use a siphon to pump in the water that is full of mussel food—organic matter and small microscopic organisms—as well as water-clouding particulates. The mussels extract their food from the water then release it back into the river.
"I’ve seen demonstrations where they had some muscles in a water tank," recalled Michael Floyd of the Fish and Wildlife office in Frankfort, Ky. "Then, they poured in turbid water and in just a short time, the water was clear again."
This feeding process is affected by the unnatural flow of water, and while the Corps and conservancy’s partnership has made progress in returning Green River closer to its natural flow, mussel populations in the immediate vicinity of the dam are still low. But the partnership is committed to finding out why, as well as to discovering other ways to sustain the diversity of the Green River.
"What I want to do in partnering with your organization is find the next big thing," Landry said. "Let’s do it. I’m committed to working with you all to figure it out."