Oysters to defend San Francisco Bay from sea level rise? Marin research shows promising results

Contractors place oyster reef structures in San Pablo Bay at the Point Pinole Regional Shoreline in Richmond, Calif. on Thursday, April 18, 2019 as part of the San Francisco Bay Living Shorelines Project. (Michelle Orr/Environmental Science Associates)
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As sea levels continue to rise, Marin and state researchers are set to begin a second phase of tests on how San Francisco Bay and the wildlife within it can come to the defense.

While oysters and sea grasses may not immediately stand out as defenders against sea level rise, a five-year test run using oyster reefs and eelgrass beds in the waters off of San Rafael has shown promising results. Using the lessons from this first run, researchers with the San Francisco Bay Living Shoreline Project are set to begin an even larger test on the opposite side of San Pablo Bay, which in turn is expected to influence future projects in Marin and throughout the bay.

Project lead Marilyn Latta of the California Coastal Conservancy said sea walls and levies will still be necessary for certain areas. But using them on all shorelines could further diminish the bay’s tidal and wetland habitats, which are vital for wildlife but have dwindled by way of human development.

“Areas like this where you have some room and elevation to work with,” Latta said, standing at the project site at the Point Pinole Regional Shoreline in Contra Costa County, “we’re testing these natural, green shoreline treatments to see if they can do the same thing — slow down wave energy, help prevent flooding, shoreline erosion — but at the same time support native species and fisheries.”

Various models show that, by 2100, sea level rise in the Bay Area ranges from about 1 foot to nearly 10 feet, which could inundate certain coastal communities, according to a recent U.S. Geological Survey study. Marshlands, reefs and other natural habitats have proven to buffer shorelines from erosion and powerful waves, but human development over the past two centuries has resulted in a substantial loss of these natural defenses.

San Francisco Bay has lost 90% of its tidal wetlands, with the bay about a third smaller than its natural state before humans began to fill in wetlands for development, according to the Coastal Conservancy.

The Living Shorelines project hopes to restore these natural defenses, but on a faster time scale using human ingenuity.

This week, crews are set to finish installing the last of 350 oyster reef structures along different areas of Point Pinole Regional Shoreline. Weighing about 1,000 pounds each and made up of “baycrete” — a mix of bay sediment, oyster shells and concrete — these reef structures allow for a place for oysters to latch onto and grow. They come in different shapes as well, with some resembling a miniature castle or domes with Swiss cheese-like holes.

At the same time, professor Kathy Boyer and other researchers with the San Francisco State University’s Romberg Tiburon/Estuary & Ocean Science Center are set to begin planting beds of ecologically important eelgrass near the reefs. Past tests of this reef-eelgrass combination in San Rafael allowed researchers like Romberg Tiburon Center research technician Melissa Patten to figure out what spacing arrangements were most practical.

“We think there is benefit to the interaction of the two in increasing the amount of other species that can use it as habitat,” Patten said.

In addition, researchers are planting Pacific cordgrass and the endangered California seablite plant, which will provide stabilization and habitat to the shoreline.

In this way, these natural shoreline defenses also create a “hot spot” for the whole ecosystem, Latta said.

The multi-agency project is estimated to cost $3 million and is funded using a combination of federal, state and grant funding from the Cosco Busan oil spill settlement. Partners in the project include UC Davis, the Smithsonian Environmental Research Center in Tiburon, Olofson Environmental and Environmental Science Associates among others.

Over the next five years, researchers will monitor the reefs for wildlife recovery and how they hold up to powerful waves. As living shorelines are becoming more prevalent throughout the state, Latta said these collaborative, multi-agency partnerships are vitally important.

“We’re working hard to share that information broadly with a lot of partners so that we can encourage other cities and shorelines and entities to engage in this kind of work,” Latta said.

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