Massive swaths of floor in the Bay could be dedicated to expensive native-oyster restoration projects despite an emerging consensus that the mollusks are naturally rare in the waterway.
The native Olympia oyster population was thought to have crashed during more than a century because of overharvesting, pollution, silt buildup and competition from non-native species.
Long-running efforts to revive the population by installing artificial reefs made of concrete and bagged shells could expand radically under a 50-year nonwaterfront habitat plan being prepared by multiple agencies.
The San Francisco Bay Subtidal Habitat Goals Project’s draft plan calls for restoration of hundreds of acres of habitat for native oysters, which clean the water, stabilize shorelines and provide homes for smaller organisms that live on their shells.
But, researchers and officials are realizing that little evidence exists that the species of bivalve was locally prevalent in recent millennia.
Analysis of towering shell mounds left behind by Muwekma Ohlone Indian tribes suggests the oysters were commonly eaten until 2,000 to 2,300 years ago, when they suddenly became rare, researcher Andrew Cohen said at a San Francisco Bay Conservation and Development Commission hearing Thursday.
“What we have to come to grips with is that the Bay has not been a suitable environment for abundant oyster beds for at least 2,000 years,” Cohen said.
But changing views on historical oyster populations might not affect conservation goals.
As the Bay Area’s environment changes irrevocably, restoration plans are emphasizing the importance of some species based on their ecological roles instead of historical abundance, according Marilyn Latta, who leads the habitat goals project.
Latta said more research is needed on historical oyster populations.
Commissioners called for more discussion about the matter.
“Whether they were there before is not as important as, ‘Are they beneficial?’” Commissioner Eric Carruthers said.
Other commissioners said boosting oyster populations could cause environmental harm or prove impossible.
Commissioner Charles McGlashan, a Marin County lawmaker, said water-quality standards crafted to enhance oyster populations are expensive to meet.
“I would want to explicitly discuss the working assumption that more bivalve activity is good for the Bay before we use it as a framework that costs local governments lots of money,” McGlashan said.
Richardson Bay: 80 acres
San Rafael Shoreline: 50 acres
North Cesar Chavez Park: 30 acres
Oyster Point to Sierra Point Marina: 50 acres
Cost of artificial oyster habitat: $25,000 per acre
Permitting and other costs: $10,000 per acre
Cost to seed habitat with spawn: $1,375 per acre
Source: San Francisco Bay Subtidal Habitat Goals Project