When Emilie Blevins was an undergraduate studying biology and wildlife in Kentucky, she was hired her freshman summer by a researcher interested in parasites in aquatic mollusks. “It was the first time I ever climbed into a creek and looked down and saw freshwater mussels,” she recounts. Over the course of the season, the research team collected mussels and ran experiments on them back in their lab.
That time in the field stuck with Blevins: “[it] was really exciting to learn about this creature I didn’t know anything about, and then to find out that my home watershed was home to this huge diversity of these species, and I didn’t know anything about them. That was a really cool opportunity as a student to learn about this wildlife in my backyard.”
Blevins would work with a variety of wildlife species, get a master’s degree in biology, and eventually move out to Oregon, where she’s circled back to freshwater mussels in her role as a Senior Conservation Biologist for the Xerces Society for Invertebrate Conservation in the non-profit organization’s Endangered Species and Aquatics Program. Beyond the enduring excitement of finding backyard wildlife, Blevins has good reason to commit her career to these mollusks. Freshwater mussel species can live between a decade to over 100 years, and during this time “they filter feed and really become part of the streambed, they essentially are improving ecosystems for species like native fish…just by how they live and breathe,” she says.
This water filtration role is important at any time, and is especially so during times of stressful conditions. When adult freshwater mussels are present in the remaining pools of a stream that is experiencing drying, “we see higher survival of fish…because the mussels feed on bacteria and algae—things that could potentially cause harm to a fish in warm, tight spaces,” Blevins says. “We also know they remove things like pharmaceuticals and other pollutants from the water.” This is a benefit to both native fish and humans sourcing water for drinking and irrigation.
In addition to the benefits freshwater mussels provide by removing potential harms, they also positively impact the places in which they’re found through additions: their excretions contribute to the aquatic food web. “We know that they can help increase the biomass of certain aquatic insects or other invertebrates during the summer months and that’s fish food,” says Blevins.
Even more, “freshwater mussels have been used since time immemorial for a food resource…for trade and pottery. There’s examples of jewelry and tools that have used mussel shells. We know that they’ve played an important role just by finding these archaeological sites and through traditional ecological knowledge.”
That indigenous peoples of this continent incorporated freshwater mussels into their cultures isn’t so surprising when you learn that all of North America is considered a global hotspot for the organisms, with the present-day U.S. containing about 300 species, or about a third of the species found globally. While much of this richness—or number of species—is concentrated in the eastern and southeastern parts of the country, the West’s five freshwater mussel species are unique for their comparably large distributions. And within the extremely varied geographies of the West, differences in freshwater mussel populations can be stark as well.
We have “really dry areas that don’t have rivers that necessarily flow year-round — so there are large portions of the West that don’t have any mussels, and other areas where you can find a combination of two of the species or maybe three of them,” Blevins explains. “It’s pretty variable and changing rapidly as mussel populations decline.”
Threats to Freshwater Mussels
Because freshwater mussels live the majority of their long lives in a sedentary lifestyle, it is not surprising that they are highly susceptible to changes in the stream habitat. Unlike marine mussel and oyster relatives on rocks, freshwater mussel species are not directly connected to the streambed, but rather “burrow into the bottom with their foot, it’s a pseudofoot, so they kind of dig down in and just try to hang on, especially during high flows,” Blevins explains.
High flow events can be intensified when human activities straighten stream channels. Channel dredging for navigation can destroy mussel beds. Changes to the landscape that cause more sediment to run into waterways—such as clearcutting forests or human development—can bury mussel beds. If water temperatures get too hot, they may not survive. And, if mussels find themselves on the dry side of a drying stream, they can desiccate. They do not have the ability that their marine cousins do to survive regular periods of drying during low tides.
These kinds of impacts likely contributed to the extinctions of freshwater mussel species in the Southeast. All combined, it is thought that 30-35 of North America’s freshwater mussel species have been lost. That amounts to 10% of the species.
Meanwhile, Blevins says that “we are seeing really worrisome trends in parts of western U.S. where…an entire mussel bed of thousands of mussels will be killed outright over the course of one season, one summer, or over several years. When that happens, those populations take long to rebuild.”
Mussel bed die offs are an active area of research for the Xerces Society. In Oregon and Washington, the organization has partnered with the Washington Department of Fish and Wildlife, the USFWS, and University of Wisconsin Madison to determine what variables may be correlated to healthy versus sick mussels at various sites, and what’s different between sites where die off events have and have not occurred.
Early results show that some viruses and bacteria appear to be associated with sick mussels, but analysis is difficult because “a mussel is open to the river, and they’re little ecosystems of their own as they harbor unique species inside of them. So, it’s hard to tease apart whether, for example, a virus is killing the mussel or the virus was already present and the mussel just becomes stressed from something like hot water or pollutants and then succumbs to an illness.”
Petition to List the Western Ridged Mussel
In 2020, the Xerces Society filed a petition to list the Western ridged mussel (Gonideaangulate) as endangered under the ESA. Among the West’s already few freshwater mussel species, the Western ridged mussel is unique in that it seems to have a smaller distribution than its compatriots, mostly on the dry side of the Cascades – though it can also be found in streams of the Oregon Coast. It is also the only member of its genus, and generally lives over 60 years with a slow reproduction cycle.
The species is experiencing the kinds of die offs Blevins previously described, saying this was “a mussel bed that I visited in 2016 and had plenty of younger and older Western ridged mussels. When I returned in 2019, 2020 — they’re gone. It happens very quickly, and again since we don’t really understand why it’s occurring and that it’s occurring in different watersheds across different states, there’s a real fear that without protection that that issue could spread.”
In the meantime, the petition for listing is currently undergoing a “twelve-month” review in which the species’ status is being thoroughly assessed to inform the final decision of whether the species will be warranted a listing as endangered or threatened, warranted with preclusions, or not warranted or listed at all. Because the USFWS currently has such a large number of species to consider for ESA-listing, the determination is not expected to be completed until 2024.
After learning from Blevins about this unique organism and its role in making environments more livable, it is hard to hear about the slowness of bureaucracy.
“I will admit it’s hard to work on species that you see facing all these challenges,” she says. Adding, “I’m really encouraged by all the people I work with and that I meet to talk about mussels because I think people get it. We have so many things that are taking our attention and we are responding to so many crises right now, so something that keeps me going is that there are people who — in spite of all that, in spite of all the challenges — they care and they also want to live in a world that has mussels.”
Resources & Ways to Help
- Knowledge is power: https://xerces.org/endangered-species/freshwater-mussels
- Take delight: https://www.wired.com/2015/10/absurd-creature-of-the-week-lampsilis/
- Educate the next generation: https://xerces.org/xkids
One last thing Blevins wants everyone to know is to share what you see. If you wade in streams frequently “submit photos of freshwater mussel shells observed to iNaturalist,” she says, “that’s information that we are able to use to help clear up the distribution picture, so I definitely encourage that.”
As a Solstice gift, these stories are completely free until Sunday, June 26, we hope you enjoy them.
By Ari Blatt
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