Freshwater mussels: Oregon floater (Anodonta oregonensis)

(Bivalvia: Unionoida: Unionidae)

Profile prepared by Lisa Schonberg, the Xerces Society for Invertebrate Conservation

The Oregon floater is distributed across western North America, including Oregon, Washington, Nevada, California and British Columbia. It prefers low gradient and low elevation rivers, lakes and reservoirs, and often shares habitat with the California floater. The coho salmon serves as a host for immature Oregon floaters.

The genus Anodonta, commonly known as “floaters,” includes six of the eight currently recognized freshwater mussel species native to the western United States. The Anodonta are fast-growing generalists, and are more tolerant of lower dissolved oxygen levels than other native mussel species. They prefer the softer substrates, such as sand and silt, that are characteristic of permanently flooded wetlands, lakes, and reservoirs. The shells of Anodonta species are thinner and usually lighter colored than those of other Northwest genera. They also have a light colored interior, are generally rounded, and lack a prominent ridge on their shell. Much of the information on this page was adapted from the guide: Freshwater Mussels of the Pacific Northwest.

conservation status
Anodonta oregonensis is thought to be more tolerant of poor water quality than many of the other species of freshwater mussel native to the Pacific Northwest. Anodonta oregonensis currently receives no state or federal protection. More research is needed on the taxonomic status and distribution of Anodonta species in order to evaluate the conservation status of this species. The Xerces Society, in collaboration with members of the Pacific Northwest Native Freshwater Mussel Workgroup, is currently investigating the conservation status of this species.
description and taxonomic status

The Oregon floater can be up to 7.25 inches long.  It is elliptical, with a compressed dorsal posterior margin, and is formed into a slight wing.  Its valves are laterally inflated, thin and fragile.

The taxonomic status of Anodonta oregonensis (Lea 1838) is currently under review. Chong et al. (2008) found that A. oregonensis and A. kennerlyi belong to a single clade, which is highly divergent from the clade that A. californiensis and A. nuttalliana belong to. The genetic work also suggests that the A. oregonensis/A. kennerlyi clade is highly divergent from the clade that A. beringiana belongs to.

photograph

Please contact The Xerces Society for information on how to obtain permission to use this image.

life history

The Oregon floater prefers low gradient and low elevation rivers, lakes and reservoirs, and often shares habitat with the California floater. The coho salmon serves as a host for immature Oregon floaters.

distribution

Mussels identified as A. oregonensis have been found across western North America, including Oregon, Washington, Nevada, California and British Columbia.

threats

Freshwater mussels are vulnerable to water level fluctuation and are thus threatened by the diversion of water for irrigation, water supply and power generation. Freshwater mussels rely on native fish as hosts during their immature, or glochidial, life stage. The replacement of native fish by introduced fish species may be the greatest threat to the reproduction of mussel populations. Because freshwater mussels are filter-feeders, they can be adversely impacted by sedimentation and the accumulation of pollutants in sediments.

references

Chong, J.P., J.C. Brim-Box, J.K. Howard, D. Wolf, T.L. Myers, and K.E. Mock. 2008. Three deeply divided lineages of the freshwater mussel genus Anodonta in western North America. Conservation Genetics.

Nedeau, E., A.K. Smith, and J. Stone. 2005. Freshwater Mussels of the Pacific Northwest. Pacific Northwest Native Freshwater Mussel Workgroup, Vancouver, Washington. 45 pp.

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