Have you ever wondered why you see 'seashells' along the banks of the Buffalo River? These are the shells of various types of mollusks that live in the river and its tributaries. From their position in the stream bottom, these filter feeders pump water through hollow gills (also used for respiration) that filter out microscopic algae, sediments, and organic debris. They reduce fecal bacteria and sequester carbon, phosphorous, and heavy metals. Simply by eating and breathing, a single freshwater mussel can filter up to 15 gallons of water per day.
Life Cycle
Reproduction in freshwater mussels seems to leave much to chance. The female carries thousands of eggs in her gills, which are used as blood pouches. If a nearby male releases sperm, the eggs are fertilized internally as the as the sperm-laden water passes through the female's gills. After 2-3 weeks, the eggs hatch into larvae, called "glochidia". The female then releases the glochidia back into the water where they must attach themselves to the gills of a host fish. But not just any fish will do; each mussel species requires specific host fish species.
At the end of the parasitic stage, the juvenile mussels detach themselves from their hosts, leaving the fish unharmed, and sink to the bottom of the stream where they continue to develop - if they find suitable stream bottom habitat. Mussels can reproduce at three years old. Some of the larger species live for twenty to one hundred years.
Importance of Freshwater Mussels
Historically. . .
American Indians harvested mollusks for food, utensils, tools, and jewelry
From the late 1800s-1940s, mussels were collected for making pearl buttons.
From the 1950s to the present, mussel shells have been used for seeding cultured pearls in Japan. Export of freshwater mussels remains a multi-million dollar industry.
. . .and Today
Freshwater mussels are an integral part of aquatic ecosystems. They serve as an important food source for fish, many mammals and some birds.
Mussels are sensitive to water pollutants, their scarcity may be a gauge of poor water quality.
Biomedical researchers study the cancer resistivity of unionid tissue.
Current Status
Native mussels, one of the most rapidly declining animal groups in the U.S., are the largest group of federally listed endangered or threatened invertebrates. Of nearly 300 species of mussels in North America, more than 70 percent are considered imperiled (federally vulnerable, threatened, or endangered) and around 35 are considered extinct.
Though easily overlooked, the freshwater mussel communities found within the Buffalo National River are truly one of the park's greatest resources. In 1912, surveyors from the U.S. Department of Commerce and Labor, Bureau of Fisheries found that "Mussel beds, as compared with those of the White River, were neither large nor plentiful, and these occupied only the favorable places in the bed of the stream which appeared to be permanent." They also found that the abundance of the mussel populations had already been impacted by human activities: "Mussels are not so abundant as formerly." Remarkably, they recorded 22 species of freshwater mussels.
Then, in 1994, the river was resurveyed. It was concluded that two of the previous mussel species may have been extirpated during the 82 years between surveys. Currently, the park has plans to revisit the mussel beds, and efforts will be made to understand the dynamics of the physical habitat where the mussels reside to enhance the long-term preservation of these unique and sensitiv species of mollusks.
Why are freshwater mussel populations declining?
Damming, dredging, and channelization of streams prevent movement of host fish and destroy stream bottom habitat.
Loss of riparian habitat (stream-side vegetation) increases erosion and fills streams with silt which can smother both mussels and fish
Water pollution (agricultural and urban run-off, industrial discharges) can kill fish, mussels, and other aquatic life.
Competition from the abundant non-native Asiatic clams (Corbicula fluminea) that often carpet stream bottoms and filter out most food particles.
What can be done to protect freshwater mussels?
Support efforts to protect riparian buffers and stream bottom habitat. Leave streamside vegetation in place or restore it by fencing livestock out of streams and planting trees.
