It’s the biggest conservation crisis that no one talks about. — Paul Johnson, Director, Alabama Aquatic Biodiversity Center
What group of species is more common in North America than anywhere else in the world? The answer: freshwater mussels. But this unique group of organisms rarely reaches the headlines or even becomes the center of discussion in school biology classes.
Even more amazing is the fact that, of the 297 species found on our continent, two-thirds are concentrated in the southeastern United States, allegedly due to the region’s unique geology and relatively stable environment over the past 60 million years.
Mussels have three claims to fame: They provided an important food source for Native Americans, fostered the button industry in the 1800s, and comprise an essential part of freshwater food chains. Many middens (archaeological remains from Native Americans) contain remnant mussel shells, indicating their historical importance for human diet.
Mussels operate as filter-feeders, removing bacteria and algae from water and ultimately contributing to water quality. One square meter of stream-bottom houses from 10 to 700 mussels, and each one filters approximately one liter of water per hour, essentially providing a free water filtration system for our freshwater streams!
With this extraordinary function, mussels provide a critical ecosystem service, meaning they volunteer an important benefit to the health of our environment. As we sleep and without any extra taxes imposed, these small creatures filter water, keeping our streams and lakes healthy.
Currently, mussels are in great danger. Twenty-five species are already extinct, and about 75 percent of mussel species are at some level of imperilment. The biggest threat to mussels was the widespread construction of dams in the early 1900s, and more recently, deforestation and mining that create muddy waterways.
Although mussels are cleaning agents for the water column, they cannot survive in overly polluted, silt-laden waters; and many species have suffered a rapid population crash.
In a sense, mussels serve as a “canary in the coal mine” for water quality. Their population decrease is causing water quality decline that ultimately will affect humans and agriculture; so, monitoring mussels serves as a key indicator of stream health.
Mussels are also unique among all bivalves because of their relationship with fish. They have a parasitic larval stage on the gills or fins of fish; and if their fish hosts are affected by pollution, the reproduction of mussels is jeopardized. In this sense, mussels and fish have a mutualistic relationship, where both the fish and the mussels are essential for the success of our free water-filtration ecosystem service.
Some biologists have developed programs to repopulate mussels by rearing them in hatcheries and releasing them into the wild. Although still under trial, these mussel farms could aid in the restoration of water quality in many streams and reverse the ominous decline of mussels throughout America.
Malacologists are scientists who study soft-tissue organisms that include fresh-water mussels. In their tool kit for fieldwork, mussel biologists carry scuba gear, rubber waders, dip nets, water-proof collection boxes, and a thermos of coffee. These scientists are aquatic detectives, finding and classifying the mussel species. In the southeastern United States, they also seek to figure out why this region is a global biodiversity hot spot for these unique critters.
Like their subject matter, the number of professionally trained mussel experts in North America is also declining. Are any readers interested in scuba-diving in local streams, with a chance to find new species never seen before by human eyes? Well, perhaps a career as a malacologist is waiting for you!
Meg Lowman, a longtime Sarasota-based scientist and educator, is chief of science and sustainability at the California Academy of Sciences.
Originally posted in the Sarasota Herald-Tribune.