Oysters’ Return Sought in Bid to Save California Bay

To the casual observer, Tomales Bay appears almost untouched. No large structure mars the shoreline and, as pelicans dive for their dinner, herds of deer graze in the surrounding green hills.

The human footprint may be hard to spot here, but underneath the cold gray-green surface, one of the bay’s most important species -- the native oyster -- had disappeared. Overfishing and a silty bay floor blamed in part on upstream development are partly to blame.

“They were really extremely abundant, and they were a big part of the ecology,” said Tom Moore, California Department of Fish and Game marine biologist.

Known as Olympia oysters, Olys or native oysters, this keystone species once provided habitat for birds, fish and other animals, not only in Tomales but also San Francisco Bay to the south. Acting as tiny filters, the purple-brown mollusks also purified 30 quarts of water a day through their gills.

Today, only small pockets of the slow-growing creatures remain.

A group of scientists is working to bring them back -- to learn more about the diminutive oyster and to address larger questions about maintaining the quality of an important California estuary.

Tomales Bay is 12 miles long, with a narrow mouth that opens northward to Bodega Bay and the Pacific Ocean. Its 6,800 acres form the shallow, seaward end of a long valley created by the San Andreas fault.

The bay is famous for its commercially grown oysters -- none of which are native -- that are sold from roadside stands along Highway 1 and fetch top dollar in seafood restaurants.

Surrounded by Point Reyes National Seashore, a state park and thousands of acres of forest and grassland, the area seems farther than 40 miles north of San Francisco.

Still, development and population pressures are increasing even here, and while the bay still provides a well-functioning ecosystem, it needs protection, said marine scientist Paul Olin, one of project’s leaders.

The bay is officially considered an impaired body of water by the San Francisco Bay Regional Water Quality Control Board. It doesn’t always meet certain water quality standards for silt, fecal coliform levels and mercury, said Dale Hopkins, staff environmental scientist.

“One component of this project is to try to restore a natural resource in the bay and protect it against further degradation,” Olin said.

There is surprisingly little concrete information about Tomales’ native oysters. The researchers believe that a robust wild oyster population would improve water quality and provide crucial habitat. If they succeed in rebuilding their numbers, they might try to set up a cottage native oyster fishery.

First, says Ted Grosholz, another scientist on the project, they have to make sure that their efforts will work. They hope that they’ll know that next year.

“We want to see what happens if we give the oysters a boost by providing hard substrate for them to settle on and grow,” Olin said.

Oyster arrays -- 18 four-foot-long polypropylene bags strung together and filled with oyster shells, kept in place by small boat anchors -- were placed at four different sites.

Since 1999, researchers have provided this “hard substrate” -- the oyster shells -- hoping to catch natural-born larval oysters as they drift over the silty floor in search of places to settle and grow.

The oyster’s role in maintaining a healthy ecosystem might not be obvious. But Olin, Grosholz and Mike McGowan, another partner in the project, are quick to detail its ecological perks.

“Having oysters improves the environment for all,” said McGowan, who is studying the oyster’s effect on vertebrates. “More oysters would provide more habitat diversity as well as more species diversity.”

Native oysters produce habitat for others like the tiny goby fish, which lays its eggs inside their shell. Other species like the striped bass, California halibut, angel shark and bat ray also benefit from the presence of oysters.

And they keep the water clean. More than 100 years ago, oysters filtered the Chesapeake Bay’s entire volume in 3.3 days. By 1988, the oyster population had changed so dramatically that it took them 325 days.

Take out this filtration system and “everything else starts to fall apart,” said Roger Mann, a professor at the Virginia Institute of Marine Studies, who has led larger-scale oyster-restoration efforts in the Chesapeake Bay.

Drew Alden, co-owner of the Tomales Bay Oyster Co. since 1988, says native oysters are too small and slow-growing to be sold commercially.

“Their value is in forming foundations for everything else,” Alden said. “The most important thing is to try to increase filtration capacity so we don’t fall by the wayside like Chesapeake Bay.”