Researchers working to restore population of Olympia oysters along California coast
Genevieve Bookwalter
Oakland Tribune
08/01/2010
After the Gold Rush, diners' tastes led fishermen to harvest almost the entire population of native oysters from the San Francisco Bay. Then they headed south to Elkhorn Slough, seeking the clean-tasting, tangy delicacy.
The Central Coast oyster population never fully recovered from the overfishing, nor from the effects of water pollution and invasive species.
Now, a researcher at Elkhorn Slough National Estuarine Research Reserve has visions of creating artificial oyster reefs along the tide line in an effort to restore the West Coast's only native oyster species: Ostreola conchaphila, commonly known the Olympia oyster.
Efforts have been under way to bring them back to San Francisco Bay for years.
But "the fact that no one had paid attention to them in Elkhorn was a gap that needed to be filled," said research coordinator and Santa Cruz resident Kerstin Wasson, 41, who works both at the reserve about five miles south of Watsonville and with graduate students at UC Santa Cruz.
On a recent day, Wasson and her team ventured out at low tide to place the last six of 24 artificial oyster reefs that are set in four different locations in the slough. Some reefs are 1 foot by 2 foot trays of concrete, about an inch deep. Others are wooden boxes of the same size with metal mesh bottoms. A 4-foot bat ray circled nearby under a gray, foggy sky.
Although the historic population of Olympia oysters in Elkhorn Slough is unknown, geological records show the ridged shells with gold, brown and black streaks have accumulated off the Central Coast for 10,000 years. A couple inches across, the shells also have been found in middens — piles of oyster, clam and mussel shells around the slough — left by early Native Americans.
The species is not endangered, but populations have dwindled so much that it is considered a "conservation target" by West Coast scientists, Wasson said. She believes the original oyster population was much greater than it is now.
The oyster's native range stretches from Baja California to Alaska. Elkhorn Slough is a vital home for them, Wasson said, as larvae drift in from the open sea, finding their way into inlets and estuaries and cementing themselves to hard surfaces along the low-tide line. The slough is a crucial part of the cycle, as it allows oysters a place to settle down, grow and produce more larvae that will drift out and continue the population moving along the coast, she said.
"This is an important steppingstone between Southern California and Northern California," Wasson said.
Along with post-Gold Rush oyster harvesting, invasive sponges and other creatures threaten the oyster by colonizing the tide-line level preferred by the native mollusks, said Rikke Preisler, oyster research scientist at the reserve.
Farmland runoff and other pollutants have compounded the oysters' shrinking-population problem, researchers said, and crabs, bat rays and other creatures consider them a tasty treat.
Most of the invasive species, Preisler said, "get in with ballast water on ships" that is dropped in San Francisco Bay. Then the problem creatures slowly make their way south, she said.
Ideally, Wasson said, oyster larvae will find the reefs a suitable place to secure themselves, grow and produce offspring. She hopes to increase the estuary's 5,000-member oyster population by 10 percent this year, with a long-term goal of doubling the number of oysters in Elkhorn Slough. Wasson's recent paper on the effort was published in June in Wetlands, the Journal of the Society of Wetland Scientists.
If all goes well, the new reefs could remain for a decade, providing a welcome spot for the oysters to colonize, researchers said.
