Mussel Mass

With a healthy population of western pearlshells, Schoolhouse Creek is going strong.

In stories of conservation and habitat loss, charismatic megafauna often grab the headlines—bivalves not so much. But freshwater mussels deserve our attention. Nearly 70 percent of North America’s 297 freshwater mussel species are extinct, imperiled or vulnerable to extinction according to the Xerces Society. Thirty-five have gone extinct in the last 100 years. “Native mussels are a critical component of a healthy stream,” says Stewardship Lead Jennifer Zarnoch, who has created detailed maps of mussels’ distribution in the Pacific Northwest. “And because mussels are sensitive to changes in water quality, they can be excellent indicators of stream health.”

That’s one reason why caring for our 16-acre Schoolhouse Creek property, located in Skamania County near the Washougal River, is so important. In 2004, Columbia Land Trust created a channel there that allowed salmon to access the creek and wetlands more easily. That’s when mussel surveyors found an abundance of western pearlshells (Margaritifera falcata) in the creek. That discovery was significant.

In Washington State, the status of M. falcata, as with many freshwater fish species, is changing for the worse. Western pearlshells once were common in the Columbia River, but a 118-kilometer survey of the river conducted a few years ago found none. In several Washington waterways, large-scale die-offs of mussels have been reported. Some streams have no juveniles, suggesting the mussel populations there have stopped reproducing altogether.

This August, Zarnoch and volunteers conducted formal surveys of mussels in Schoolhouse Creek, so that we can track this particular population over time. “You have to develop mussel vision,” says Zarnoch of the survey. “Mussels can look like rocks at first glance, so you have to zero in on edges and a particular shape.” That baseline data will be used for future surveys.

The presence of the mussels—and especially the presence of juvenile mussels—is an indicator of Schoolhouse Creek’s relative health. Freshwater mussels like cold, clear creeks that support salmon or trout. In fact, mussels’ survival relies on the fish. After fertilization, female mussels release larvae called glochidia into the water. When a trout or salmon swims by, the glochidia attach themselves to its gills, where the larvae commence to grow. As the fish swims upstream, it disperses mussel populations.

“Mussels fulfill an important role in freshwater ecosystems,” says Zarnoch. “They provide food for wildlife, stabilize streambed sediments and filter water for fish and aquatic macroinvertebrates.” Freshwater mussels, in other words, are made to work. —Jill Davis