Freshwater Mussels Pacific Northwest - The Xerces Society

that live in flowing water may inhabit a variety of substrate types, but require
flow velocities adequate to keep the water and sediment well oxygenated, and
depths that are not prone to dewatering during dry periods.
Some species can be found in lake and pond habitats that have muddy
substrates, lower levels of dissolved oxygen, and warmer water temperatures.
Mussels also can be found in freshwater tidal habitats such as the lower Columbia
River and Kalama River. Brief exposure during low tides does not
seem to affect their populations 122 . Although many mussel species are sensitive
to pollution and habitat disturbance, some appear to be able to tolerate
moderate human disturbance and persist near the densely populated areas of
Seattle and Portland.
Role in Ecosystems
Mussels are important to food webs, water quality, nutrient cycling, and habitat
quality in freshwater ecosystems 52,108 . Mussels greatly influence food webs
by filtering tiny suspended materials such as algae, bacteria, zooplankton,
and sediment from the water column. Some of the material they ingest is
bound and released as larger particles that sink to the bottom and become important
food for other benthic (bottom-dwelling) animals, especially aquatic
macroinvertebrates 108 . Mussels can filter a substantial volume of water each
year and may help reduce turbidity and control nutrient levels 55,70,98 . Mussels
sometimes comprise the greatest proportion of animal biomass (the sum total
of living tissue and shells) in a waterbody 71 . Because mussels are so long-lived,
they retain nutrients and minerals for a very long time.
Mussels that sense receding water levels will often move to avoid exposure, but they
are vulnerable to predators during these events (line drawn for emphasis). photos: Allan Smith
Freshwater Mussels of the Pacific Northwest 7