Mussels on the move!

By Wildlife Biologist Sarah Boyden

While surveying for geese the other day, I launched my canoe at the Muddy Brook boat launch on the Sandy River, in New Sharon and noticed scrawling lines along the bottom of the river.  Some were short paths, some were long, winding trails.  At the end of each was a chubby fresh water mussel, partially buried and waiting for its food to float by.  Most of us probably don’t look at mussels and think of them as a mobile species, but their intricate trails through the sandy substrate tell a different story. 

Freshwater mussels occur throughout Maine’s inland waterways, in ponds and lakes, stream and rivers.  Maine has ten species of mussel and the where each mussels occur is likely a result of migrating fish.  Mussel larvae look like microscopic mussels and are expelled into the water by females during a time that corresponds with migrating fish.  The hitchhiking larvae attach themselves to passing fish and form a small parasitic cyst on the gills or fins that allows them receive nutrients and grow for up to 160 days.  At the end of the parasitic phase, mussel larvae metamorphize into juvenile mussels and drop off the host fish, spending the rest of their lives in that location. 

Mussels have adaptations to survive yearly water fluctuations and avoid being stranded during low water conditions.  They can make short movements by extending their foot, which looks like a tongue sticking out.  By repeatedly sticking out and retracting their foot, they slowly position themselves into better feeding areas, or make a move to escape a receding water line during low water conditions.  These movements result in the winding trails seen along the bottom of some waterways. 

Although some species of mussel look like they would be delicious, steamed and drenched in butter, eating a freshwater mussel is a bit like chewing on a muddy rubber band and is not recommended.  Wildlife apparently don’t mind the flavor, as mussels are an important food source for river otter, muskrat and racoons.   

Mussels are filter feeders, sucking in water and consuming suspended particles including phytoplankton, and detritus.  While filter feeding, mussels also filter out bacteria, algae, pollutants and suspended particles from the water column.  Depending on the species, mussels can filter up to 10 gallons of water per day.  Healthy mussel populations can filter a significant portion of some lakes and streams, helping maintain water quality in the systems.  Abundant mussel populations can also be used as an indicator of overall health of a waterbody.  Polluted systems typically have fewer species and a less abundant mussel population.  Of the ten species of mussels found in Maine, conservation concerns lead to the listing of three species as state Threatened and one as special concern. 

Next time you’re up to camp, bring along your snorkel and take a look at the diversity of mussels in your area.  If you pick them up to investigate, be sure to place them back the same way you found them.  Mussels position themselves so their breathing and feeding apertures (essentially their mouths) face up into the water column, so try not to replace them “face down” in the mud when you return them to the water.  Once you notice mussels in the water, you will start to see them nearly everywhere you look.   They are quietly filtering your favorite swimming hole, or fishing spot, and providing a food source for other wildlife species.