Freshwater Mussels Pacific Northwest - State Water Resources ...

Anodonta and Gonidea situated in the substrate. photo: CTUIR Freshwater Mussel ProjectAnodonta HabitatAnodonta are considered habitat generalists and are more tolerant of lentic(lake-like) conditions than most other freshwater mussels. Anodonta inhabitnatural lakes, reservoirs, and downstream, low-gradient reaches of riversin depositional habitats. Three Anodonta species can be found together insloughs along the lower Columbia and Willamette Rivers. In the Portlandarea, even degraded urban habitats often support one or more of these species.The common name “floater” has been given to all North Americanspecies of Anodonta. All species have thin fragile shells compared to mostother native mussels, enabling them to inhabit silt because they can “float”on semi-liquid substrates. A second origin of the descriptor “floater” is moremorbid—these species can thrive in small nutrient-rich waterbodies that aresubject to oxygen and temperature stress in the summer. Mussel die-offs canoccur during stressful periods, and the build-up of gases in the shell cavity ofdecaying animals may “float” the light shells to the water’s surface.Anodonta are more tolerant of low-oxygen than most species and canthrive in small nutrient-rich waterbodies such as permanently floodedmarshes, oxbow lakes, and farm ponds. Their thin shells and inflated shapeallows them to inhabit silt found in the deeper areas of lakes and reservoirs.Small rocky streams, favored by other western species such as western pearlshellsand western ridged mussels, are difficult environments for Anodontabecause their thin shells are prone to damage in such habitats. Sandbars nearthe mouths of tributary streams or below riffles are important habitats.22Freshwater Mussels of the Pacific Northwest