Once-abundant West Coast oysters near extinction Marine life Near extinction of native species a problem for more than taste buds

Matt Ferner, from the San Francisco Bay National Estuarine Research Reserve, uses a GPS to record the precise location of Olympia oysters along the Berkeley Marina shoreline in Berkeley, Calif. on Friday, July 6, 2012. A study by the Nature Conservancy concludes that the California oyster reefs are declining. less Matt Ferner, from the San Francisco Bay National Estuarine Research Reserve, uses a GPS to record the precise location of Olympia oysters along the Berkeley Marina shoreline in Berkeley, Calif. on Friday, July ... more Photo: Paul Chinn, The Chronicle Photo: Paul Chinn, The Chronicle Image 1 of / 7 Caption Close Once-abundant West Coast oysters near extinction 1 / 7 Back to Gallery

A disturbing nationwide decline in oysters and the life-giving reefs that they build is particularly dramatic in California, where the once-abundant native species has been virtually wiped out, according to a recent scientific study.

The report, published in the scientific journal Proceedings of the Royal Society B, said Olympia oysters, once an integral part of the Native American diet and a staple during the San Francisco Gold Rush, are functionally extinct.

"Essentially, today, the number of oyster reefs is zero," said Rob Brumbaugh, restoration director for the Nature Conservancy and co-author of the study. "It's the complete elimination of a key species and habitat on the West Coast."

The loss of native oysters - not to be confused with the farm-raised Japanese Pacific oysters - is a serious issue, he said, because oysters clean the water by filter feeding. A single oyster can filter up to 30 gallons of water a day, removing nitrogen and other pollutants, Brumbaugh said. The oyster beds, or reefs, they create provide habitat for myriad fish, crabs and other creatures.

"What they do for us is filter water and help remove nitrogen pollution while increasing the growth and survival of other fish," Brumbaugh said. "Oysters and the reefs that they create are great pollution scrubbers."

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Important food source

The problem is widespread throughout the country. The first-of-its-kind study, funded with grants from the National Fish and Wildlife Foundation and the National Oceanic and Atmospheric Administration, found that the size of oyster reefs in the dozens of bays and estuaries across the U.S. where there is comparable data has shrunk 64 percent in 110 years. Worse, the number of living oysters dropped 88 percent nationwide, according to the study.

Olympia oysters, known scientifically as Ostrea lurida, once blanketed subtidal regions from Southern California to Southeastern Alaska. The tangy delicacy was a crucial source of food for local Indians long before Europeans arrived in California. The shells were abundant in the many Native American middens discovered around the bay, some dating back 4,000 years.

Early pioneers described the flavor of the tiny mollusks, which are about the size of a 50-cent piece, as "coppery." They were, in fact, a delicacy in San Francisco during the Gold Rush. The Hangtown Fry was created, according to one legend, by a condemned man who ordered the two most expensive items he knew of at the time - oysters and eggs - for his last meal.

Shell beds vanish

In 1893, Olympia oyster beds covered a total of 8,033 acres in Newport Bay, Elkhorn Slough, San Francisco Bay and Humboldt Bay, according to the study. Almost a half million oysters per acre were crowded together along the bay floor.

The oysters were so small - between 1,600 and 2,000 shucked Olympias filled a gallon jug - that it didn't take long for the oyster beds in San Francisco Bay to be depleted. By the early 1900s the native oyster beds in Tomales, Humboldt and Newport bays in California and most of the beds in Washington were also virtually scoured clean.

Although harvesting continued in some areas of California until the 1930s, wild oysters in the Bay Area were pretty much wiped out by 1911. The oysters people now eat along the West Coast are mainly Pacific oysters, which are native to Japan and cannot reproduce naturally in this climate.

There are still some Olympia oysters in San Francisco Bay and the other estuaries, but the shell beds no longer exist, Brumbaugh said.

"That's a lot of lost filtration," he said, "but more importantly it is 8,000 acres of habitat and food for other aquatic species that is gone."

Restoring the natives

The Nature Conservancy and NOAA have collaborated on more than 130 oyster restoration projects over the past 15 years along with aquatic biologists in California, Oregon and Washington.

Local conservation groups have been sinking shell mounds in areas of San Francisco and Tomales bays in an attempt to attract the oysters. The West Coast aquaculture industry, which has recently been combatting the effects of acidification caused by climate change, has also been working to restore native oysters, which are smaller but more adaptable than their Japanese cousins.

Invasive predators, like the whelk snail, also known as the Atlantic Oyster Drill, are making it difficult - killing as many as half the remaining Olympias on the Point Reyes National Seashore.

"Like a lot of things it is far easier to take things apart than to put them back together again," Brumbaugh said. "We used to have a lot of services provided by oyster reefs that we really do need, so we should double down on our oyster reef restoration. It's a process, a journey, that we need to keep on."