BRINGING BACK A CALIFORNIA NATIVE:
THE OLYMPIA OYSTER
At sites around the San Francisco Bay, including in Belvedere and Strawberry Cove, researchers are working to restore the miniature filters, which promote healthy habitats
By LIDIA WASOWICZ-PRINGLE
lpringle@thearknewspaper.com
Meeting the fate of many native species, the Olympia oyster populations in waters off Tiburon, Belvedere and other parts of San Francisco Bay sank after miners and other settlers poured into the region during the California Gold Rush.
More than a century and a half later, it’s taking a village to raise them from near extinction.
Researchers from federal, state and local agencies, conservationists, community leaders, educators, students and volunteers have combined forces to restore waters and wetlands once teeming with Ostrea lurida, California’s only indigenous oyster species, which serve as natural filters that promote healthy habitats.
As part of a multipronged effort that began more than a decade ago, they are mining for clues to the marine mollusk’s past existence, collecting scientific data on its current condition and testing ways to lure it back home.
“Olympia oysters are a part of the natural and human history of San Francisco Bay,” says Chela Zabin, a research biologist at the Smithsonian Environmental Research Center lab housed at the Romberg Tiburon Center for Environmental Studies, San Francisco State University’s marine research and teaching facility. “If we lose them, we lose a part of the uniqueness of this place.”
Key to a healthy bay
An essential component of a thriving ecosystem, the 2½- to 3-inch oysters lay the foundation for a complex food web, shelter sea life, protect shorelines, provide a gauge to watershed health and clean their home turf by filtering up to 12 gallons of sea water per day per adult.
“The improved water quality supports healthy eelgrass beds, where salmon, herring and other foraging animals lay eggs,” says Rachel Spadafore, restoration ecologist at the Richardson Bay Audubon Center and Sanctuary in Tiburon.
Suspecting a link between withering eelgrass and drooping bird and herring numbers in their front yard, investigators from the center, along with a team from San Francisco State, have begun a pilot planting project to determine the most effective revival methods for the perennial flowering plant.
The role of oysters in the circle of sea life stands uncontested.
“Oysters are a keystone species that create habitat for small organisms, including worms, crabs and other macroinvertebrates,” says Helen Dickson, manager of The Watershed Project’s Living Shoreline Initiative, the University of California’s Richmond-based project that focuses specifically on monitoring and rebuilding the bay’s oyster communities.
These habitats, in turn, nourish larger critters, including fish such as salmon, white sturgeon and striped bass, and seabirds such as oystercatchers and diving ducks, Dickson says.
Her team is working to restore the oyster community decimated in part by overharvesting and hydraulic mining in the Sierra foothills, which flushed smothering sediment into the bay, forcing the scrappy tenants to seek shelter in less hospitable habitats.
“I’ve seen (the native oysters) growing in all kinds of nasty, polluted locations in San Francisco Bay, attached to old submerged tires, shopping carts, you name it,” says Zabin, the Romberg researcher, who is also a biologist at the University of California at Davis and lead researcher for the Living Shoreline Initiative. “They are hanging in there.”
Just how many are hanging in and how well in comparison to the past are questions under study.
“We have a lot of anecdotal evidence oysters were plentiful in Richardson Bay and San Francisco Bay, but we have no hard data, no historical numbers, no definitive answers regarding any details,” says Marilyn Latta, project manager for the California Coastal Conservancy.
Lacking documented records of the oysters’ falling fortunes, scientists can only theorize about the causes and conditions surrounding their near-demise.
“The exact nature and extent of Olympia oyster populations in San Francisco Bay, and Richardson Bay in particular, appear to be lost to time, as the earliest scientific investigations of San Francisco Bay biota didn’t occur until the late 19th century, by which time much change to the bay’s physical and biological environment had already occurred,” says ecologist Andy Chang, the program leader for the Romberg-based Smithsonian center.
Wanting to get up to date, he began an intensive investigation in 2009, in collaboration with the San Francisco Bay National Estuarine Research Reserve. To date, the study has shown a slow increase in oyster numbers in Richardson Bay off Strawberry’s shores.
“It’s still too soon to say whether this might really reflect a longer-term trend,” Chang says.
What’s already apparent is the neighborhood’s affinity for the finicky shellfish.
Hope in Strawberry Cove
In an examination of livability conducted between 2011 and 2013 at 12 sites by several agencies, Strawberry Cove — bordered by De Silva Island and Seminary Drive — excelled on all measures tested in the bimonthly surveys.
The site scored “very high” on oyster density, diversity of sizes — indicating a healthy mix of young and mature — number of larvae, survival and growth rates, Latta says.
The area meets the housing needs of the most discriminating Olympias: abundant food, just the right amount of salt, shallow water with good circulation, mild temperatures, protection from winds, waves and tides and plenty of rocks and other hard surfaces to which they can make lifetime attachments.
“One thing we do know is that Olympia oysters generally grow very well in Richardson Bay,” Chang says. “Their survival and growth rates are high relative to other regions of San Francisco Bay.”
To keep current, teams from Chang’s lab and the local Estuarine Research Reserve take a census each spring of the Strawberry oyster population and maintain a monthly log on new arrivals there and at a number of other Marin County sites.
The occasional surges and slides they have noted might result from heavy rainstorms that water down salinity — or from hungry predators.
A predator lurks in Belvedere
The Atlantic oyster drill, an invasive snail ravenous for the munchy mollusks, has been implicated in the recent decline and disappearance of Olympias in several areas.
“We have data from a site near Belvedere that had consistently low numbers of adult oysters and virtually no recruitment for three years,” Zabin says.
Tellingly, the site also registered a high number of the inch-long oyster hunters.
In a survey of the shoreline fronting the Audubon sanctuary, investigators could find no live oysters, just remnants of shells and a few corpses still attached to their top shell.
They identified the killer by the characteristic round hole it leaves on the victim’s shell as it bores in to dissolve the animal with digestive juices, then sucks up the liquefied meal.
Researchers worry the snail could threaten oyster revitalization efforts.
“Newly settled oysters are especially vulnerable to predation, which is bad news for oyster restoration projects relying on natural recruitment, which all of them do in San Francisco Bay,” Chang says.
“If those projects are near locations with large numbers of these snails, then predation may hinder our ability to restore the population before they all get eaten.”
To thwart the predator, the Smithsonian lab, estuarine reserve and the Audubon center launched a pilot project in June that has middle-school students and other volunteers exploring the invader’s locations and modes of mobility.
Local involvement in Olympia restoration dates back more than a decade.
In 2004, the community embraced an Audubon plan to lure the natives to Richardson Bay.
“The town provided a dump truck to pick up cylinders stuffed with oyster shells, and volunteers placed them in six different locations by Blackie’s Pasture and the Lyford House,” recalled Arlene Nielsen, a 12-year board member who got the Tiburon Peninsula Foundation into the act.
Initial excitement over thriving colonies waned along with the oyster numbers.
Looking ahead, scientists hope for greater public participation and individual involvement.
Residents doing their part
Latta has proposed retrieving oyster shells discarded by restaurants to build reef mounds. She envisions shell recycling centers, such as those for plastic and paper.
Sarah Ferner, education coordinator for the estuarine reserve, says she would like to get more citizen scientists on board in the next two years.
She cited a Redwood High School pilot project in which students monitor oyster recruitment in nearby Corte Madera Creek. Although after three years funding has dried up and the program must be scaled back, she retains hope for its future.
Scientists at the Smithsonian lab also want to expand collaborations with communities to boost native oyster populations in Richardson Bay and are “actively seeking funds to do so,” Zabin says.
Everyone can contribute by refraining from harvesting native oysters or spreading predators that endanger them, she says. The Atlantic oyster drill, for one, abounds around the shoreline ringing Belvedere and meandering to Blackie’s Pasture and the Audubon sanctuary, but has never been spotted at Strawberry Cove, she says.
“It would be very easy for people to accidentally pick up snails in mud stuck to boots, boats and anchors,” Zabin says. “The snail can remain alive out of water for quite a long time, so it’s important to thoroughly rinse and dry anything that moves between different locations within the bay.”
And while in the vicinity, strollers can consider reasons to care about the final fate of the forgotten native, Ferner says: “If you want to walk along a vibrant, lively bay with a big variety of animal life around, support your local oysters.”
For more information about becoming a citizen scientist, contact Ferner at daviess@sfsu.edu. Anyone with pre-Gold Rush-era photographs or other documentation related to native oysters in local waters, contact Zabin at 415–435–7128 or zabinc@si.edu.
Lidia Wasowicz Pringle of Tiburon began contributing to The Ark in 2009 after spending 30 years at United Press International.
This story originally appeared in the Aug. 12, 2015, edition of The Ark.
