Lakes and rivers often seem like huge, majestic parts of the landscape, made up of powerful forces of water and wind and home to charming animals like fish, birds, and mammals. What is often unknown is that something small and secretive plays an important role in these wonderful places: freshwater mussels. These animals might not be the charismatic rockstars of the aquatic ecosystem, but they provide support that is crucial in keeping lakes and rivers running smoothly.
You may have seen or even eaten marine mussels or other bivalves such as scallops and oysters before, but when was the last time you saw a freshwater mussel? For many people, the answer is never, and that’s not surprising when you look further into a mussel’s lifestyle. Freshwater mussels live along the bottom of rivers and lakes. A muscular appendage called a foot helps mussels anchor themselves in the mud or sand, out of sight from all but the most inquisitive humans.
Mussels are filter feeders and provide vital ecosystem services. As they filter feed, they draw in water from their environment and pump it back out to trap tiny bits of food. In doing so, they also end up filtering out pollutants, excessive nutrients, heavy metals, and even some bacteria and pharmaceuticals. The more mussels there are in a body of water, the more they can remove these harmful substances from our waterways, which is beneficial for everything that lives there.
(Photo: Roger Tabor / USFWS.) https://www.xerces.org/blog/merit-of-mussels
Freshwater mussels fill other roles that support the living things around them, too. Animals such as otters, muskrats, and various birds love eating mussels. Perhaps you have seen their leftover shells on the banks of your favorite creek, after a hungry raccoon’s meal (these piles are known as middens). Groups of mussels can clump together into beds that provide a habitat for other invertebrates too, which in turn serve as food for fish and other animals. Freshwater mussels even help the environment when they die, because their decaying shells slowly release nutrients into the water, without overwhelming the ecosystem.
They are also important indicators of how an ecosystem is doing. Freshwater mussels live a long time (sometimes up to 100 years!) with their age indicated by the number of rings on their shells, but during their life, they move very little. Because of that, scientists can investigate the health of the mussels in a section of a lake or river and use information from the populations to understand how healthy that environment is or has been over time. With increasing pollution, mussels are starting to reach their threshold for the amount of toxins and chemicals they can withstand, causing population declines. Their absence can indicate an unhealthy, contaminated environment.
The PWA started assessing freshwater mussel populations throughout the Petitcodiac watershed in 2018. Habitat changes, degraded water quality, and altered food webs have been driving population declines for over 50 years. One species monitored by the PWA, the Brook Floater, is around 5 cm long and can look brown, yellow, or greenish. In Canada, Brook Floaters are only found in a handful of rivers, including the Petitcodiac River. Our local population of Brook Floaters is important to the species’ survival because the Brook Floater is an at-risk species, classified as being of Special Concern.
You can help freshwater mussels too, by reducing your use of fertilizer and pesticides, emptying septic tanks frequently (vs. all at once), and leaving a buffer zone of at least 30 meters of uncut grass, bushes, and trees around bodies of water. It’s also helpful to simply appreciate the benefits that freshwater mussels bring to our watershed and to share this appreciation with others. So next time you find yourself at the edge of a river or lake, take a moment to think about the humble freshwater mussel and all it does to keep the water clean, keep aquatic animals fed and sheltered, and keep us informed of the health of the environment.
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Belvins, E. (2021). The Merit of Mussels. Xerces Society. Retrieved November 28, 2023, from https://www.xerces.org/blog/merit-of-mussels
Canada, E. and C. C. (2010). Brook floater (Alasmidonta varicosa): COSEWIC assessment and status report 2009 [Assessments;research]. https://www.canada.ca/en/environment-climate-change/services/species-risk-public-registry/cosewic-assessments-status-reports/brook-floater-2009.html
Fisheries and Oceans Canada. (2016). Management Plan for the Brook Floater (Alasmidonta varicosa) in Canada [Proposed]. Species at Risk Act Management Plan Series. Department of Fisheries and Oceans Canada, Ottawa. iv + 41 pp. https://www.sararegistry.gc.ca/virtual_sara/files/plans/Mp-BrookFloater-v00-2016Oct18-Eng.pdf
Xerces Society. (n.d.). About Freshwater Mussels. Retrieved November 28, 2023, from https://xerces.org/endangered-species/freshwater-mussels/about