Background
Freshwater mussels are little recognized organisms that inhabit the Willamette River and many of its tributaries. Five native freshwater mussel species may be found in the Willamette River. These organisms reside in the substrate of our waterways, filtering their planktonic food from the water column. All of the mussel species found in the Willamette River have a larval phase that is dependent upon a fish host. The mussel larvae, known as glochidia, attach to the gills and fins of a passing fish and spend several weeks tapping their host's blood and hitching a ride. After detaching, the larvae settles to the substrate where it burrows into the sediment and resides for several years. After emerging from the substrate, mussels will remain relatively sessile for the rest of their lives. Some species such as Margaratifera falcata, a species that forms dense beds in the Willamette River, can live over a century.
Since mussels are sessile and can do little to avoid anthropogenic impacts, they are declining at an alarming rate worldwide. Altered hydrology from dams, sedimentation, pollution, invasive species and overharvesting are some of the impacts causing mussel decline. Although most people might not miss mussels themselves, they may miss the benefits mussels provide. Freshwater mussels purify water through filtration, provide substrate for the aquatic insects fish eat, are a food source for wildlife (sturgeon, otters, muskrats) and act as a long term record of water quality and stream health readily accessible to researchers.
As a result of their declining numbers, freshwater mussels have recently stepped into the spotlight of scientific research. Still these subtle creatures hold many secrets. In the Pacific Northwest, freshwater mussels have received little attention and the status of local species is largely unknown. The Pacific Northwest Native Freshwater Mussel Workgroup is changing that by promoting research and freshwater mussel education. Check their website for a field guide to freshwater mussels in our region.
