The Freshwater Mussels of the Pacific Northwest
Freshwater Mussels can be found all over pacific northwest Region. Freshwater Mussels are quite sedentary and do not move very far during their adult lives. But these humble creatures can ascend waterfalls when they are newborn. The young attach to unwitting fish that carry them to new places in a watershed, over waterfalls, across lakes and up and down rivers. They can live for more than 100 years.
Freshwater mussels are quite common on the coast, but in the rest of North America we are losing many species before we know much about them. Normally, freshwater mussels can outlive most animal species on Earth, one species on Vancouver Island can live longer than a century. But their longevity depends on stability in the environment where they live and with which fish species they share their home waters. Mussels are very sensitive to environmental changes and may indicate long term problems in their ecosystems.
Nearly three quarters of all 297 native freshwater mussel species in North America are imperiled with 35 of them going extinct in the last century. They are one of the most endangered groups of animals on Earth, yet surprisingly little is known about their life history, habitat needs, or even how to distinguish different species, especially in the Pacific Northwest.
Freshwater mussels are mollusks that produce a bivalve shell. The two halves of the shell are connected by an elastic-like ligament along the dorsal hinge. The outside of the valves is covered with material that gives the shell its color, and the inside is lined with a smooth mother of pearl material called nacre.
The raised rounded area along the dorsal margin is called the beak, the shells grow outward from the beak in a concentric pattern. Mussels may possess teeth on the hinge that create a strong and sturdy connection between the valves.
The living mussel occupies the cavity between the two valves. The only body parts that are visible outside of the shell are the foot that is used for locomotion and feeding, and the mantle edges that are modified into inhalant and exhalant apertures.