Published: Mon Jan 24, 2005They’re often referred to as “living rocks,” but freshwater mussels are more than just that to the international cultured pearl industry and to one Tennessee Tech University biologist who’s devoted 17 years to studying them.
Jim Layzer is a Ph.D.-level research scientist with the U.S. Geological Survey who is stationed at TTU’s Center for the Management, Utilization and Protection of Water Resources, and his latest project will help protect the mussels in Kentucky’s dam-regulated Green River.
Although mussels can live for decades, they make no sound, can’t see and seldom move from their secure spots, usually burrowed to the bottom of rivers — but in spite of their humble characteristics, they have incredible adaptations for reproducing and serve an important function in the cultured pearl industry of Japan and other nations.
“Small pieces of mussel shell are used as implant beads in oysters to start the growth of cultured pearls in Japan and other nations, and Tennessee commercially harvests — primarily from Kentucky Lake — more freshwater mussels than any other place worldwide,” Layzer said.
“No other country in the world equals the variety of freshwater mussels found in the United States. Europe has only 12 different species, but there are about 300 different species here, most of which are native to the Mississippi River watershed,” he continued.
Of those 300 species, however, as many as 70 percent are endangered, threatened or extinct and in need of special protection, according to statistics from the U.S. Fish and Wildlife Service.
To help protect the varieties of freshwater mussel living in Kentucky’s Green River, Layzer has been working with The Nature Conservancy since 2000 on a research project to develop and test a conservation regime that can be used by the U.S. Army Corps of Engineers to regulate water flow through the river’s dams.
“The basis of my research is monitoring how the mussels respond to this new discharge regime,” he said.
“During times of unusually heavy rains, those dams hold the excess water in reservoirs. Then it’s released over an extended number of days, creating a river flow that’s somewhat abnormally high for the season — and while that’s great for flood control, we’ve found that practice seems to harm mussel populations more than an actual flood would,” Layzer continued.
That’s because mussels generally reproduce the same way they “eat” — by siphoning microorganisms like plankton and sperm from the male species into their shells, thus fertilizing the female’s eggs. Far from looking like their parents, however, infant mussels are born as larvae that must live on the body of a “host” fish for several weeks until it reaches maturity and drops to the river bottom.
“But the high flows in the Green River prevent the juveniles from dropping off their fish hosts as they should, and many wind up in unsuitable habitats, where they die,” Layzer said.
Certain species of mussel depend on certain species of fish to serve as hosts too, so the vitality of the host fish populations have a direct impact on mussel populations.
“In fact, my ongoing research seems to indicate that no single factor is responsible for declining mussel populations in regulated rivers,” he said.
Other factors threatening freshwater mussels, he concluded, are pollution, sedimentation, habitat loss and dams that discharge cold water. Although the dams on the Green River don’t discharge cold water, Layzer has said his research at other locations indicates that the number of juvenile mussels are much lower below the discharge.