I want to introduce you to the Western Pearlshell mussel (Margaritifera falcata). It is a bivalved, freshwater mollusk that can be found in the Willamette River.
Besides being a beautiful creature, they are important part of the ecology of a stream. They are filter feeders which helps improve water quality and clarity. Their shells store nitrogen, calcium, and phosphorus that are slowly released back into the ecosystem when they die. Beds of mussels provide habitat for invertebrates, and the empty shells are safe havens for developing fish.
The breeding cycle of the western pearlshell mussel is fascinating. For fertilization to occur, the male will release sperm and the female will filter it out of the water. The embryos develop into larvae called glochidia and are released into the water where they must encounter and attach to the gill filaments of a host fish. The glochidia are parasites on the fish and remain on them for several weeks or months as they develop into tiny juvenile mussels. When they are ready, they release and fall back to the stream bottom where they to continue to grow and mature. Most freshwater mussels need a host fish to complete their lifecycle. The known host fish for the western pearlshell are salmonids, such as Chinook salmon, coho salmon, cutthroat trout, redband trout, and steelhead. Not only are these fish part of the lifecycle, they are important for distributing the mussels as they move and migrate through the river system.
Amazingly, these mussels have been recorded to live to over a hundred years old, so they are important indicators of the health of the ecosystem. Alarmingly, over seventy percent of North America’s species of freshwater mussels are listed as endangered, threatened or of special concern. This is due to factors like pollution, habitat loss, and decline in host fish populations.
This is another reminder of the crisis we are facing on this planet with the continual degradation of biodiversity and vitality of our ecosystems in nature. We know that we need to be better stewards of the earth. I hope there is a local place in nature that you visit often, have become connected to, and are inspired to help make it a better place.
Nature is an inexhaustible source of wonder. I look forward to seeing you out there.
Sources
“Native Freshwater Mussels in the Pacific Northwest | Xerces Society.” Xerces.org, 2025, xerces.org/publications/guidelines/native-freshwater-mussels-in-pacific-northwest. Accessed 28 July 2025.
Western Pearlshell (Margaritifera Falcata) | U.S. Fish & Wildlife Service. https://www.fws.gov/species/western-pearlshell-margaritifera-falcata. Accessed 28 Jul. 2025.
Western Pearlshell Mussel | Washington Department of Fish & Wildlife. https://wdfw.wa.gov/species-habitats/species/margaritifera-falcata. Accessed 28 Jul. 2025.
Williams, James D., et al. “Conservation Status of Freshwater Mussels of the United States and Canada.” Fisheries, vol. 18, no. 9, Sep. 1993, pp. 6–22. DOI.org (Crossref), https://doi.org/10.1577/1548-8446(1993)018<0006:CSOFMO>2.0.CO;2.
