In nature, even the smallest creatures can play vital roles in keeping ecosystems healthy. We often see busy bees working to help plants reproduce and grow food. And many of us have watched as industrious ants transform landscapes. You may not be as familiar with one of the small but mighty members of freshwater ecosystems: mussels!
These unassuming creatures aren’t the most noticeable or charismatic members of an aquatic ecosystem, but they play an outsized role in keeping things clean and healthy. Their presence in streams, lakes, and rivers can lead to improved water quality and increased biodiversityBiodiversity The variety of species present..
Unfortunately, freshwater mussels are some of the most imperiled species in the world. Habitat loss and water pollution have caused major population declines. Recently, scientists from the Xerces Society, with support from a Tualatin SWCD grant, conducted research to understand where mussel populations exist in the Tualatin River watershed. This information helps raise the community’s awareness about the presence and importance of mussels and helps restoration planners make careful decisions about how to protect them.
What is a freshwater mussel?
Freshwater mussels are spineless, soft-bodied creatures covered with a two-part shell. They live fully submerged in water. Mussels burrow into the bottoms of streams, lakes, and rivers, digging a “foot” in between rocks and other substrates. They are often found in groups, called “beds,” which can number anywhere from 2 to 10,000+ individual mussels. Mussels are some of the longer-lived inhabitants of our waterways. If habitat conditions are good, they can live for decades.
There are hundreds of species of freshwater mussels found across North America, but only three kinds are found in Oregon:
- floater mussels (Anodonta sp).
- western pearlshell mussel (Margaritifera falcata)
- western ridged mussel (Gonidea angulata)
Fun fact: western pearlshell mussels can live to be over 100 years old!
Freshwater mussels rely on fish to complete their lifecycle. When a mussel is ready to reproduce, it releases tiny larvae into the water. The larvae attach to the gills of fish and are transported up and downstream. After several weeks, the juvenile mussels drop off the fish and sink to the bottom of the stream to burrow in.
Freshwater mussels provide important benefits to aquatic ecosystems.
- They act like nature’s own water purifiers.
They filter algae, bacteria, and other tiny particles from the water. They remove pollutantsPollutants A substance that has negative effects on the environment. and capture nutrients. A single mussel can filter gallons of water a day.
- They are a nutrient-rich food source for predators.
Mussels are a tasty snack for wildlife including river otters, raccoons, and herons. Their presence supports the local food web.
- They improve habitat for fish and macroinvertebrates.
Mussel beds provide excellent habitat for macroinvertebrates and fish by creating spaces to hide, rest, and gather food.
Water pollution and habitat loss threaten their populations.
Over 75% of freshwater mussel species in North America are listed as endangeredEndangered A species or group at serious risk of no longer existing. It is also a legal term under the U.S. Endangered Species Act., threatened, or of special concern. Their populations have been harmed by water pollution, construction that disrupts streams, and invasive species competing for space and resources.
They are particularly sensitive to changes in water quality. As they filter water, their bodies accumulate contaminants, including heavy metals and pharmaceuticals, which can be harmful to their health. They are an indicator species, meaning that changes in the health of their populations often indicate changes in the health of the environment.
The reduction or disappearance of mussels from an ecosystem can have cascading effects. Other animals lose an important food source, streambeds are altered by the loss of mussel beds, and water quality worsens. These changes can destabilize the aquatic ecosystem and cause a decrease in biodiversity and resiliency.
Two types of native freshwater mussels were found in the Tualatin River watershed.
With funding from a Tualatin SWCD TREE Grant, researchers from the Xerces Society conducted surveys to better understand where mussels are living in the Tualatin River watershed. They searched fifteen sites, spanning urban streams, creeks running through natural areas and agricultural lands, and the mainstem Tualatin River. Researchers waded or snorkeled through the streams searching for mussel beds and shell fragments.
They found live mussels at eight locations. Western pearlshell mussels were present in Baker Creek, Chicken Creek, and Gales Creek. Floater mussels were present in Carpenter Creek, Cedar Mill Creek, Chicken Creek, Fanno Creek, Johnson Creek, and the Tualatin River. Although they did not find live western ridged mussels (an especially at-risk species), by collaborating with the Tualatin River Watershed Council, they were able to detect the species’ DNA in water samples. This means that it is present somewhere in the river.
Both wildlife and humans benefit when freshwater mussels are thriving in our waterways.
By continuing to research and raise awareness about the importance of freshwater mussels, The Xerces Society and its partners are helping protect the populations that exist in our watershed. The more we know about these incredible creatures, the better poised our community will be to take meaningful steps toward protecting the habitats they rely on.
Interested in learning more about mussels?
Check out the Fascinating Freshwater Mussels video created by the Xerces Society.
 Mazzacano, C. S., M. Blackburn. 2015. Native Freshwater Mussels in the Pacific Northwest. 16 pp. Portland, OR: The Xerces Society for Invertebrate Conservation.