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SAN FRANCISCO BAY / SHELL GAME FOR OYSTERS / Scientists building reefs to allow the return of the natives,
Carl T. Hall, Chronicle Science Writer
Published 4:00 am, Monday, August 14, 2006
Biologists dumped a dozen boatloads of oyster shells into the shallow waters off Point San Quentin over the weekend, hoping the castoffs will seed the comeback of native oysters that once flourished in San Francisco Bay.
Twenty volunteers did much of the heavy lifting near the wooden pier of the Marin Rod and Gun Club, which provided a convenient jumping-off point for what sponsors say is the largest native-oyster restoration effort in California.
Oysters that once blanketed the bay largely disappeared after the Gold Rush and urban settlement brought overharvesting, pollution and habitat loss. Now that bay restoration has helped restore water quality, ecologists want to expand the few oyster populations that managed to hold on.
Drake's Bay Oyster Co. donated 24 pallet-loads, about 55 cubic yards, of oyster shells for the project. About 30 cubic yards were dumped Saturday and Sunday, the rest being saved for next spring.
Forming 2-foot piles on the bay floor, the shells make just enough of a solid, calcium-rich foundation to anchor living shellfish reefs in the bay's otherwise unholy muck.
Oyster larvae typically die in a couple of weeks if they can't find suitable bottom substrate, or cultch, upon which to attach and form their own shell. Other oyster shells are an ideal surface -- even though the donated shells in the restoration project are from a different variety, the Pacific oyster, or Crassostrea gigas, not the West Coast's native Olympia variety, Ostrea conchaphila. There aren't enough native shells available for the project.
Even if the restoration plan works, the tiny bay oysters will be too few to harvest. And because of copper and other heavy-metal contaminants in the estuary, the oysters that grow will be metallic-tasting and potentially unhealthy for humans.
Still, biologists financed by the National Oceanic and Atmospheric Administration, which contributed a $50,000 grant for the current phase of the work, say oysters are vital for the health of the bay.
"The goal is to build up these remaining populations to the point where they can sustain themselves," said Summer Morlock, a marine specialist with the agency. "It would be wonderful to imagine the day when we can have an oyster harvest. But that isn't really the goal."
The project is still very much in the small-scale, experimental phase. Biologists at the conservation group Save the Bay are also working on oyster-restoration projects at different sites around the bay. Restoration spots were picked based on where native oysters can still be found -- and where landowners are willing to allow access from shore.
On Sunday, Bill Craig, a Marin Rod and Gun Club volunteer, used his small motorboat to ferry out the last few sacks of oyster shells, along with scientists Rena Obernolte and Larry Floyd, both employees of MACTEC Engineering and Consulting Inc., a Petaluma company under contract to the National Oceanic and Atmospheric Administration.
The donated shells had undergone a long drying-out period at the Point Reyes oyster farm to keep any oceangoing invasive species from being imported into the bay. Volunteers bagged the shells in black mesh and stacked them like hay bales on wood pallets.
They were loaded by hand into the boat and hauled out under the pier. Wearing wetsuits, the scientists jumped into the chest-deep water to guide the shells to their resting place.
A few early-morning anglers watched from the pier, along with project manager Robert "Bud" Abbott, a MACTEC senior principal biologist. Abbott said he hopes to eventually build oyster beds over wide expanses of the bay floor.
"What we want to do is acres," he said. "But we need to be sure we are doing it right. Before we can do acres, we have to do the research. There's no textbook for how to go about this kind of thing."
Each 2- or 3-inch oyster can filter several liters of water an hour. As their shells pile up, the growing reefs become habitat for other bay creatures, such as fish seeking shelter from predators or a spot to lay eggs.
The oysters' filtration helps keep the water clear of phytoplankton and sediments, which may help sunlight make it through for the benefit of vegetation -- such as native eelgrass, the focus of a separate restoration project under way nearby the half-mile-long Marin fishing pier.
Over time, the featureless mudflats could become thriving oyster meadows, the reefs forming a series of water breaks that retard sediment buildup and support a complex ecosystem -- lunch stops, perhaps, for migrating juvenile salmon on their way to the sea.
"Oysters really can help build the food chain," Morlock said.
The project faces many unknowns, including such threats as water pollution and invasive water snails, which have a rasplike tongue that can bore through oyster shells. Scientists plan to return to the experiment monthly to check how many oysters are taking up residence.