Though their work is free of fanfare, McMurray and Roberts believe the project could do much more than boost populations of endangered mussels that are no longer reproducing on their own. It could ultimately result in a new way of detecting toxic water pollution and lead to cleaner water.
“Water quality standards are set by the average of the most sensitive species,” said Chris Barnhart, professor of biology at Missouri State University. “Freshwater mussels are pushing that average lower. What we are finding out about mussels could lead to more stringent water standards” for certain pollutants.
Over the years, populations of freshwater mussels have dramatically dropped because of pollution, loss of habitat and competition for food with non-native species, such as the invasive zebra mussel. Mussels are ecologically important aquatic creatures because they feed by filtering the water, removing bacteria, algae and silt.
They also play an important economic role. Their iridescent shells, once the source of material for making buttons, are now used to support a worldwide cultured pearl industry.
State and federal scientists have been propagating freshwater mussels since the late 1990s, but the young mussels were so small — no bigger than a grain of rice — they were impossible to track.
This summer, scientists from the Missouri Department of Conservation, U.S. Fish and Wildlife Service and Missouri State University developed a new system for growing four types of freshwater mussels, including a federally endangered species. Using a contraption called the “flupsy” — floating upweller system — the scientists were able to simulate a natural stream flow in research ponds at the Kansas City Zoo and Little Dixie Lake Conservation Area in Callaway County.
The result was juvenile mussels so big — some up to 4 inches long — scientists could tag each one with a number glued to its shell. The mussels were released in streams across the state, including Silver Fork Creek, Sack Creek and the Meramec River.
If all goes as planned, biologists such as McMurray and Roberts will return to the creeks next year and chart their progress.
“I hope the glue holds,” Roberts quipped as he and McMurray released about 100 mussels into Silver Fork Creek. In addition to the offspring, the female mussels were returned to the stream as well.
Of the 300 species of freshwater mussels indigenous to North America, 38 are extinct, and 70 are listed as threatened or endangered. Nearly half of the 65 species found in Missouri are of conservation concern. Ten are considered endangered, either on the state or federal level, Barnhart said.
Mussels always have been a food source for animals such as otters, minks, raccoons and some water fowl. American Indians used them for tools and jewelry and relied on the chewy meat as a source of protein during the winter.
Populations of freshwater mussels took their first hit in the early 1900s, when they were used to make fashionable buttons. The button industry sprung up in the Midwest because there seemed to be an endless supply of the long-lived, thick-shelled creatures in the Mississippi River. Every day, barge loads of mussels were taken from the rivers and creeks.
But the mussels couldn’t reproduce fast enough to keep up with the harvest, and their populations rapidly declined. The introduction of plastics in the 1940s saved the mussel population and put an end to the shell button industry.
Today, mussels are plucked from rivers and creeks to be used by the cultured pearl industry, Roberts said. The pearly-white insides of the mussel are removed, formed into beads, shipped to Japan and slipped into oysters as nuclei for forming a cultured pearl.
“The bead is seen as an irritant by the oyster,” said Roberts, a biologist with the U.S. Fish and Wildlife Service. The oyster responds by producing a thick coating of secretions, and in two to four years, the bead becomes a pearl. According to the wildlife service, freshwater mussels support a pearl industry valued at about $50 million annually.
That’s a heavy load for an animal that doesn’t even have a head, not to mention arms or legs. A freshwater mussel basically is a large moving foot that contracts and withdraws into its shell when it’s pulled from the stream bottom, where it spends most of its time. There are gills on either side of the foot for breathing and twin siphons on top that are used for drawing in water and food and blowing out waste, which becomes food for other aquatic animals.
Barnhart said freshwater mussels have a complex life cycle because they depend on a host, typically a fish. After the female’s eggs are fertilized, her modified gills become a brooding chamber for embryos that mature into larvae. The tricky part comes next — fooling a host fish into carrying the larvae.
Barnhart said each mussel species uses a unique lure to attract its particular host. Some display what appear to be small fish or crawdads, which move and dance across the stream floor. When the host fish tries to eat the lure, it gets a mouthful of mussel larvae, which adhere to the fish’s gills and fins. After a few days or weeks, the juvenile mussels fall off and drop to the stream bottom. If they’re lucky and land in suitable habit, they will grow; if not, they will die.
Volunteering their services, McMurray and Roberts built the experimental device to help grow the mussels in Roberts’ shop at his home. The device cost about $300 to construct and measures only 4 feet square. A bigger version is planned, but it will still float in a single fish hatchery pond.
Perhaps most important is the discovery that freshwater mussels can be used as biological indicators of water quality. They are an ideal sentinel for environmental hazards because they are long-living and relatively immobile. As nature’s “vacuum cleaners,” mussels accumulate contaminants from the water and sediments that can be scientifically analyzed.
“They are the canary in the coal mine for rivers and streams” because they can sense the presence of some toxins long before they reach levels dangerous for people, Barnhart said.
Roberts said that most of the juvenile mussels produced from females taken from Silver Fork Creek were used in toxicity testing at the U.S. Geological Survey’s Environmental Center in Columbia. Scientists were trying to determine the toxicity of ammonia, chlorine, copper, lead, zinc and cadmium.
In October, the journal “Environmental Toxicology and Chemistry” devoted a special section to the “pollutant sensitivity of freshwater mussels.” The findings discovered mussels are sensitive to some pollutants, particularly copper, ammonia, a fungicide called “chlorothalonil” and some components used in pesticide mixtures.
The study found that “mussels are more sensitive than other animals used to develop water quality criteria and standards for some pollutants,” such as ammonia.
Barnhart said he expects that freshwater mussels’ sensitivity will lead to more stringent water quality guidelines for some pollutants set by the Environmental Protection Agency.
“Your water will be cleaner eventually because it was found to be harmful to mussels,” he said. “They are improving water quality directly because they clean the water, and they are improving water quality indirectly through more rigorous water standards.”
Roberts said there are about 20 species of freshwater mussels in Boone County, none of which are listed as endangered. Most of the troubled populations of mussels are in the Meramec, Bourbeuse, Gasconade and lower Osage rivers, where loss of habitat often is to blame for the decline.
Development also can play havoc on mussels, which cannot tolerate shifting, unstable stream bottoms. Excessive silt and gravel often follow excessive land disturbances and can smother young mussels and interfere with the filtering and feeding of adults. Roberts said mussels can close their shell for awhile, but eventually they must breathe and feed. Long-term pollutants or silt in the water will kill them.
Habitat restoration will be the key to restoring the freshwater mussel population, but that takes time.
For now, scientists will continue propagating species and using juvenile mussels as biological indicators for water quality. In the summer, biologists hope to double the number of juvenile mussels grown in captivity. Old river channels, such as Silver Fork Creek, will play an important role in the science of saving freshwater mussels.
“These mussels will probably stay in this pool for the rest of their lives,” McMurray said.
Reach Sara Agnew at (573) 815-1723 or sjagnew@tribmail.com.
Parker Eshelman photo Andy Roberts of the U.S. Fish and Wildlife Service carefully inserts mussels into the bottom of Silver Fork Creek. 
Parker Eshelman photo Missouri Conservation Department biologist Steve McMurray holds a group of artificially grown and tagged juvenile mussels before releasing them in Silver Fork Creek north of Columbia.
