Many people don’t realize that we have native freshwater mussels in our rivers in the Pacific Northwest. In fact, even though they are pretty hidden at the bottom of streams, mussels are important. Mussels are filter feeders that help keep water clear, and in doing so keep nutrients fish and other organisms need from washing downstream.They live for as many as 100 years, and are a sensitive indicators of pollution. During those long lives mussels record important information in their shells. 

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Mussel shells record information a lot like a tree holds information in its rings. In the Current Archives lab we recover these patterns from mussel shells to learn about how mussels grow and how their environment has changed. We also go out in the field to survey native freshwater mussels in the Northwest, figuring out where they live and how many there are. As sessile animals that are not part of a European diet, mussels have been largely overlooked and their populations are not well surveyed in the West. We’re trying to change that. 

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We’ve surveyed mussels in multiple watersheds, finding new populations in the Palouse, North Fork Coeur d’Alene, and Little Spokane Rivers. We’ve also found a small population of western ridged mussels (a population that may be listed under the Endangered Species act soon), in Chatcolet Lake during surveys with the Coeur d’Alene Tribal Fisheries department. 

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Our work with records stored in mussel shells has shown that the western ridged mussel and western pearlshells mussel record average air temperature in the width of their growth increments. When it’s cold they grow less, when it’s warm they grow more. Other researchers have found that mussels can also record the ups and downs of river flow in their shells. This is similar to how a tree grows a thicker ring in years when water is abundant, but will have a thin ring when water is scarce. Mussels will have thicker bands when water temperature and flow-rate are optimal, and thinner rings when water temperature or flow rate is suboptima.

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We hope to use those records of temperature and river flow to reconstruct what was going on in their environment. Ideally, by examining how temperature and flow-rate records from mussel shells, we can understand what conditions were like in the first few years of a mussel’s life…and how that has changed over the ensuing 100 years. This kind of hyper-local information would be invaluable for watershed restoration and for understanding the ecology of specific rivers. 

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We are also coupling our efforts to analyze growth rings with the geochemical and stable isotopes stored in the calcium carbonate of their shells. The chemistry inside their shells has not been very well researched, but potentially it could add even more layers to our understanding of the information mussels store in their shells as they clean our streamwater and provide nutrients to the base of the food chain.