Native Mussels- One of Natures Best Kept Secrets
To send off the extended warm season of 2020, the 4H aquatic investigators and myself took a trip to the county park to search out native mussel shells. I had been hiking multiple times during the summer and come across the shells, as well as their live counter parts, and often wondered what species they may be. With the help of the students I knew we could figure it out!
The aquatic investigators pose with some of their findings
In the past decade the public has, unfortunately, become well aware of zebra mussels, we even have our own infestation in Lac qui Parle Lake. Zebra mussels, an invasive species that hitched a ride in the ballast tanks of cargo ships transporting between the US and the Caspian Sea, have been taking up residence in our states since the 1980’s. While we focus on these invaders to help prevent their spread and protect our waters, we have not done enough education on the importance of native mussels.
Native mussels like this 'threeridge' are significantly larger than invasive zebra and quagga mussels.
While native and invasive mussels share some distinguishing characteristics, native mussels are by far, way more impressive. Up until recently I did not have much knowledge on these mostly unseen creatures. This year low water levels paired with increased water clarity piqued my interest as I kayaked over them in local rivers and came across countless shells on shorelines. The heavy flows of the prior two years had kept them hidden beneath muddy waters, while hardly any shoreline was explorable.
Let’s start with some mussel basics:
Minnesota is home to over 40 species of native mussels! Named after characteristic shell shapes and patterns, you may come across a Snuffbox, Pocketbook, Spectaclecase, Hickorynut, Pigtoe, Elephantear, Pistolgrip, Monkeyface, Pimpleback, or a Mapleleaf, among others, depending where you are in the state.
While not all of them reside in this region, we are still graced with quite a few species. Paired with a field guide highlighting species in the local watershed, we were able to narrow down our search for the shells we found. *Click the poster to enlarge and view each MN species !*
Like many organisms, different mussel species will be present in different habitats, some preferring rocky versus smooth substrate, larger versus smaller rivers and most interestingly- differing mussel species are dependent on certain species of fish.
Mussels use fish to help them disperse their larvae through waterways. In its entire life an adult mussel will move only a couple hundred yards. Mussels have incredible adaptations to help with larvae dispersal. Some female mussels will use a ‘lure’ to fish for a host. These lures are an extension of the mussel, with some made to look like a small fish to attract a predator. The fish who is fooled by this will try to eat the false prey, which results in the mussel expelling its larvae, who then attach to the fish’s gills. The larvae will remain on the gills of the fish, without causing harm, until fully developed when they drop off to start their adult life.
Different species of mussels have different mechanism, some will pack hundreds of larvae in a capsule resembling a worm where they will once again attach to the fish’s gills upon consumption. These lures can be so detailed even replicating a specific species, and wiggling to imitate live bait, that it’s no wonder the fish is tricked! While some mussels are host specific and will choose a certain species to latch onto, some mussels are generalists and will take advantage of whoever swims by. For instance, if you find the black sandshell mussel, you can be confident that walleyes or saugers occupy the waterway. If you find the pink heelsplitter, freshwater drums are around. Check out the videos linked below to watch these mussels in action!
Native Mussel Life Cycle
Native Mussels 'Fishing' with their Lures
So now that we know how cool they are- what purpose do they serve?
Mussels have an active role in the food chain, providing food for mammals such as otters, raccoons, muskrats, as well as birds and of course- fish. Mussel shells even form habitat of their own, growing algae and hosting tiny aquatic organism for fish to feed on. An important aspect for water quality, mussels filter and clean our waterways. After filtering the water, they deposit unused particles and waste that are then utilized by other members of the food web. Mussels are also bioindicators. Because they are sensitive to pollution and habitat disruptions, their presence or absence can be used as an indicator of the health of a waterbody. Mussels often congregate in groups called a mussel bed. These mussel beds become hotspots for biodiversity where they feed a variety of fish, who in turn help increase and maintain mussel populations, creating a positive feedback loop. Everything considered we want them in our lakes and rivers!
The aquatic investigators worked hard flipping through the field guide to identify the variety of species we found. Some shells were as large as our hands, with the insides of the shell termed the nacre, a pearly bright pink. Our smaller specimens of about three inches had a pearly white nacre. By limiting our search to the handful of species recorded in our region we were able to get a positive ID! Field Guide to the Freshwater Mussels of Minnesota
The largest of the bunch was a pink heelsplitter. Supportive of its name, a large extension on the hinge of the shell looks like it could really do some damage if you stepped on it. One of the more numerous shell types we found was also confirmed by its name. The deertoe, with its shell held tightly together viewed from the side, looks exactly as you’d expect- like a deer track in the mud or snow. We also found a maple leaf, hard to distinguish from what we thought might be a pigtoe, but differing with the presence of bumps, called pustules, which lined the shell along its pronounced ridge.
Our group even came upon a freshly harvested specimen along the shoreline, where the ice had not yet covered the river completely. Evidence that someone had a nice snack!
Unfortunately, native mussels have faced a difficult past. The button industry almost decimated their population back in the 1970’s while the installation of dams has cut many species off from their host fish. These disruptions along with pollution to waterways has made a once plentiful animal scarce.
The introduction of the invasive zebra mussel has also impacted native mussels. Zebra mussels will not only compete with natives for food, but also attach to their shells making them immobilized and unable to feed.
So what can we do to help?
While mussel surveys have taken place across the state in the past, citizens sightings are always super useful in building a better understanding of population dynamics. Now that you’ve learned more about one of Minnesota’s best kept secrets, you can study up this winter in preparation for mussel viewing during the warm season. You can learn a lot about an ecosystem by identifying a mussel shell. If you come across a specimen- take a photo and share it! There are a bunch of great resources available online or as an app to help you catalog, identify, and discuss what you find in the field.
Spreading awareness and educating friends and family is a powerful tool for conservation that everyone can take advantage of!
A variety of native mussels from the MN zoo, where they partner with the DNR to raise mussels and restore populations *click photo for more info*
Visit our Aquatic Invasive Species (AIS) webpage to learn more about invasive species, and different resources for cataloging your findings in the field, both native and invasive. Reach out with any questions or for help with identification!