Oysters Help Filter Eagle Harbor’s Pollutants
By Tad Sooter | May 14, 2008

Leaning over the gunwale of a skiff at Winslow Wharf on Monday, Cara Cruickshank guided a black buoy alongside and grasped a line dangling beneath it. The rope held suspended a sturdy cage just below the surface; but both line and cage were nearly invisible under a layer of harbor organisms including sponges, worms, algae, even sea urchins.

“Each of these lines becomes a reef full of life,” Cruickshank said, stripping away a clump of mussels that clung stubbornly to the rope. “It’s just incredible.”

Inside the cage is another bounty of life, a lumpy, thriving pile of Pacific oysters.

They are a few dozen of the 100,000 “Oysters for Salmon” that have been cultivated in baskets beneath harbor marinas for the last two years as part of a Natural Landscapes project, led by Cruickshank, and supported by the Puget Sound Restoration Fund and the city.

The oysters are being grown not for food, but rather for what they eat.

Oysters are voracious filter feeders that glean over-abundant algae, plankton and nutrients from the harbor’s water. Cruickshank and her partners believe the oysters can play a role in counteracting the sewage, fertilizers and other nutrients that are washed into the bay, feeding excessive growth, which robs oxygen from eelgrass and other organisms.

Each oyster is capable of filtering 55 gallons of water per day. Put together, the more than 500 baskets of oysters in the harbor are cycling through an estimated 5 million gallons of water daily. Oysters absorb nutrients into their bodies, depositing some waste onto the seafloor, where it can be used by aquatic plants, and outgassing some to the surface.