Did you know that Michigan has 43 species of freshwater mussels? Mussels are unique animals
that have an essential role in aquatic ecosystems.
Freshwater mussels are one of the most critically imperiled groups of organisms in the world.
In North America, 65% of the remaining 300 species are vulnerable to extinction.
Mussels are bivalves. They consist of two hard outer shells, soft tissue, mantles, open circulatory system
and a digestive system. Mussels use their foot to move around in the substrate.
Freshwater mussels have unique lifecycles. Male mussels release sperm in the water and the egg is
fertilized once it reaches a female. Female mussels brood the eggs in a specialized area in the gills called, marsupia.
Then, larvae mussels called glochidia, are released into the water until they attach to the gills of host fish.
The Glochidia grow on gills for a few weeks and then drop off and continue to grow in the substrate.
Glochidia are parasitic but they do not harm the host fish.
To attract a host fish, an adult mussel can use different luring techniques. Some do this by using mantles that resemble prey.
This is an example of a freshwater mussel displaying their mantle.
Mussels provide ecosystem services and are considered “ecosystem engineers”. Mussels filter nutrients in the
water, and since they are highly sensitive to pollutions, they are indicators of water quality. They help stabilize
substrate of rivers and are food for other organisms such as raccoons and muskrats.
Their shells can provide habitat for other organisms such as macroinvertebrates.
Michigan has 4 federally endangered mussels: clubshell, snuffbox, northern riffleshell and rayed bean.
These are all under protection by the Endangered Species Act and are regulated by the U.S. Fish and Wildlife Service.
The clubshell is a small to medium sized mussel that can grow up to 3 inches long. Their exterior is yellow to
brown with bright green blotchy rays. Their habitat is loose sand and gravel in medium to small rivers and streams.
The snuffbox mussel is a small to medium sized mussel that can grow up to 2.8 inches. They have a yellow, green
or brown shell interrupted with green rays, blotches or chevron-shaped lines. They are found in small to medium sized creeks with a swift current.
Northern riffleshell is a small to medium sized mussel that can grow to 3 inches long. Its shell exterior is brownish yellow to yellowish green with fine green rays.
Rayed bean are small sized mussels. They are less than 1.5 inches long and their shell is smooth textured.
The shell is green, yellow-green or brown with numerous dark-green wavy lines. They prefer to live in small, headwater creeks.
There are many threats to freshwater mussels. Dams affect both upstream and downstream mussel populations
by disrupting natural river flow patterns, scouring river bottoms and changing water temperatures.
Because mussels tend to stay in one place, they are easily harmed by toxins
and poor water quality caused by pollution.
Pollution can come from accidental spills, factory discharges, and more.
Poor land use practices, dredging, impoundments, intensive timber harvesting and heavy recreational use
can accelerate erosion and increase sedimentation. Sediment that can blanket a river bottom can suffocate mussels.
Non-native species such as zebra mussels and round goby are serious threats to freshwater mussels.
Zebra mussels use up food resources and attach to native mussels in such large numbers, the native mussel cannot eat or breathe.
Round goby's can displace native host fish, reducing the ability of mussels to reproduce.
Michigan’s four federally endangered mussels are protected under the Endangered Species Act.
The Endangered Species Act provides protection against practices that kill or harm the species
and requires planning for recovery and conservation actions.
You can help freshwater mussels by learning more about how the destruction of habitat leads to loss of endangered and threatened species.
You can help improve water quality locally in streams by minimizing use of lawn-care chemicals
and properly disposing of or recycling hazardous materials found in your home, such as batteries paint, car oil and pesticides.
When boating, please follow any rules established to prevent the spread of exotic pests like the zebra mussels.
And lastly, join a conservation group or volunteer at a local nature center, zoo, or wildlife refuge.
Thank you for watching. We hope that you’ll think about these amazing animals next time you visit a river or stream.