Freshwater mussels of Michigan
Native clams live long and fascinating lives in our lakes and rivers.
Mention “mussels” to a Michigander, and they’ll likely think of troublesome invasive zebra mussels - or a delicious seafood dinner! However, the word “mussel” (as well as “clam” and “bivalve”) describes a wide variety of native, two-shelled creatures.
Native mussels live their lives quietly and mostly unnoticed in the bottom sediments of lakes and streams throughout Michigan. While the troublesome invasive zebra mussels and their relatives, quagga mussels (family Dreissenidae), grab most of the headlines due to their environmental, recreational, and economic impacts, there are three other families of mussels in Michigan. Asian clams (Corbiculidae) are small, thick-shelled non-native mussels that have invaded many river systems in Michigan. The native pea or fingernail clams (Sphaeriidae) are common, relatively tiny, thin-shelled clams about which little is known. The most diverse and well-understood group of Michigan mussels are the unionid mussels (Unionidae). Around 45 native species of unionid mussels are found in Michigan – and that’s the group we’re focusing on here.
We’re most likely to notice native mussels when the pearly interior of an empty shell, lying below the water, glints in the sun and catches our eye. The exterior of a live mussel, by contrast, is typically well-camouflaged in shades of brown or green. They spend most of their time partly buried in the lake bottom or riverbed, filter-feeding on bits of suspended food, like algae and bacteria. Many mussels live for 20-30 years, with some living longer than 50 years. Mussels seem to prefer sand and gravel habitat and are most frequently found in shallow water (less than two feet deep). Far more Michigan species are found in streams and rivers than in lakes. However, impoundments, which are sections of rivers that have been slowed and enlarged behind dams, typically host an intermediate number of species.
The reproductive cycle of unionid mussels is fascinating and highly specialized. Male mussels broadcast sperm into the water, where it can be taken up by females. Females then grow embryonic young on specialized portions of their gills until they become larval mussels, known as glochidia. This is where things get weird. Unionid mussels require a fish host to continue their life cycle. Female mussels lure fish by presenting a specialized structure that looks like a wiggling worm, small fish, insect, or even a crayfish. Her goal is to trick a fish looking for its next meal to come close enough for her to deliver the glochidia to the gills, fins or skin of the fish. If a fish attempts to eat the lure, the female mussel releases her glochidia into the water, facilitating their attachment to the fish. Some other unionids that live in lakes broadcast their glochidia into the water in webs of tangled mucous. The glochidia then attaches to fish that become entangled in these nets. In the case of the endangered snuffbox mussel, the female mussel will snap her shell closed onto the snout of the fish to hold it captive until the glochidia can be released. After attaching to a fish, the glochidia then ride for several weeks as they develop into juveniles and then fall off into a stream or lakebed where they mature into adults.
While some of our mussel species can reproduce with the aid of a broad range of fish host species, some are very specific. For example, the widespread giant floater can use almost any fish as its host, while the snuffbox, mentioned above, can only use logperch. One mussel species, the salamander mussel, uses an aquatic salamander, the mudpuppy, as its host.
Unfortunately, many of our native mussel species are in peril. Remarkably, the United States is home to more species of mussels than any other country. Nearly 300 species of unionid mussels can be found in eastern North America, and about 45 in Michigan. However, of those in Michigan, 32 are considered at risk – classified as endangered, threatened, or special concern. Some of the threats to our native mussels are probably easy to guess – dams, erosion, channelization, and stormwater pollution. Mussels need good water quality and high-quality sediment conditions and are unable to easily move to better habitat if their current home becomes degraded. As we just learned, they also need host fish, so if the host fish species disappears, the mussels will be unable to reproduce. Non-native mussels may outcompete native species for food and habitat. What’s more, zebra mussels, which require a solid surface for attachment, are regularly seen encrusting native mussels, often to the point that the native mussel cannot successfully feed or reproduce, and eventually dies. Our management activities can also directly harm native mussels. For example, drawing down water levels in impoundments or lakes can leave mussels stranded because they cannot move fast enough with the receding water. Nearshore construction (such as seawall installation and shoreline stabilization) and dredging and fill projects can also destroy mussels and their habitat.
Here are some things you can do to protect mussels:
- Support projects that protect high-quality lake and river habitats.
- Minimize polluted runoff from your activities and property.
- Clean, drain, and dry your boat or other recreational equipment before moving from one waterbody to the next to avoid spreading invasive species.
- Learn about mussels present in the lakes or rivers that you visit.
- If you own or manage waterfront property, avoid harming them or their habitat with your activities.
Michigan State University (MSU) Extension and our partners offer excellent resources for anyone who wants to learn more about our Michigan’s freshwater mussels and their habitat. The Michigan Natural Features Inventory, a program of MSU Extension, recently updated their full-color poster and detailed brochure featuring Freshwater Mussels of Michigan. You can access these resources and detailed information about Michigan’s threatened and endangered native mussels on their Michigan Mussels page.
Michigan State University Extension provides resources and support to lakefront property owners and managers. Contact your county MSU Extension office for more information and visit the MSU Extension website (extension.msu.edu) to explore our natural resources programming and sign up for electronic newsletters on the topics of your choice.
A version of this article originally appeared in the March 2022 issue of the Lakefront Lifestyles Magazine.