There are 297 known species of freshwater mussels in the United States and Canada, 213 of which are listed as endangered, threatened, or species of special concern. Mussels are the backbone of our aquatic ecosystems, serving as water filtration systems. Constantly sieving through our lakes, rivers, and streams hunting for a meal, they are also absorbing any chemicals and pollutants that may be present. Mussels are also called bivalves due to the two shells, or valves, that protect and encase their soft inner body parts. Oysters, scallops, and clams also belong to the bivalve class.
Absorbing and removing some of the worst toxins in our waterways, mussels are particularly hardy creatures by nature. However, scientists are now finding which chemicals freshwater mussel species are most sensitive to and how that is impacting their overall population numbers. One of these fatal chemicals is ammonia, which is oftentimes a result of sewage or agricultural runoff. As filter feeders they are the first to feed on small organisms and bacteria in the water, but this also means they are the first victims to excess nutrient loading and increased silt sedimentation. What makes them so important as a species is also what is making them so endangered.
Aside from the increased pollution in our water, mussels are also losing something that they depend on for reproduction: fish. Most mussel species depend on fish to be their reproductive hosts. In this parasitic relationship mussels will lure in nearby fish and inject them with their larvae (glochidia), which the fish will then carry around until they are mature enough to fall off and survive on their own. With dams, pollution, invasive species and habitat loss these fish species are dwindling, making it more difficult for the next generation of mussels to transpire. Another difficulty is that not just any fish will do, mussels depend on only a handful of species and some only one.
Preventing runoff and cleaning up our lakes, rivers, and streams is one way to help our mussel friends, but many places are turning to the preservation of these host fish in hopes it will carry out many more generations of freshwater mussels. In 2016, the city of Lyons, Michigan removed a 160-year-old dam structure from the Grand River. The dam was not only in a deteriorated state but also preventing natural river functions. The endangered Snuffbox Mussel (Epioblasma triquetra) is present in the Grand River ecosystem and many individuals were manually collected and relocated prior to the dam removal in order to reduce the project’s impact. Now three years after the project’s completion, fish species, including the snuffbox’s host fish, logperch, can move more freely and naturally through the system.
As with any environmental project, monitoring and continued surveys are needed to know the true impacts. This September I was able to go along with U.S. Fish & Wildlife and Central Michigan University Staff to help survey for the threatened snuffbox. Kayaking along the Grand River, we could see most of the river bottom below, as it was a calm and very clear day. However, little did I know that the beautiful cobblestone bottom was actually a mussel bed, filled with multiple species of freshwater mussels. Mussel beds can range in size from as small as a square foot, to acres in size. Mussels are hard to find just by looking, as they often completely bury themselves in the substrate below. They are sedentary creatures, so even the exposed parts of a mussel are usually covered in algal growth making them hard to see with the naked eye. Therefore, we had to dig!
Adorned with snorkeling gear and mussel bags, the survey crew set out to collect mussels of any size and shape. We would then meet on the river bank and sort the found mussels by sex and species. Among the mussels found were elktoe, mucket, threeridge, wabash pigtoe, mapleleaf, and pocketbooks. It wasn’t until our last stop of the day that we found the snuffbox. This small-medium sized mussel is yellowish brown in color with subtle green rays running along its exterior. Males are larger and can grow to be almost 3 inches in length, while the females grow to be about 1.8 inches. We found three snuffbox mussels in our one day of surveying, which is a hopeful outcome for this species that was once in such peril. When a snuffbox was found it was adorned with a unique water proof identification number and PIT tag, or passive integrated transponder. These are both glued onto the shell of the mussel and are discreetly colored so as not to draw any extra attention from predators. This method of tagging will aid researchers in future surveys and studies to check the snuffbox population status. They will be able to tell if they are dying, or if they are still okay and recovering well after the dam removal.
Some mussel species can live up to 50 years old and just one adult mussel can filter up to 15 gallons of water per day. Sustaining their population is critical in the health of our freshwater systems. It was an honor to work alongside some of the wildlife experts that so carefully monitor even the smallest organisms on our planet. And while they may be small, they are undoubtedly one of our greatest ecosystem engineers.
What has your community done to protect the small but very important creatures of an ecosystem near you?
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