Not Your Ordinary Culverts: Bringing Native Oysters Back to the Presidio

Olympia oysters (Ostrea lurida) just beginning to grow on a test substrate in Crissy Marsh.

Presidio Trust

June 2020 - This year the Presidio is expanding the wetlands along its northern waterfront at a site known as Quartermaster Reach. The project will allow water to flow through new culverts, or underground water tunnels, beneath Mason Street. This will create seven acres of new habitat for birds, plants, and other native species.

But the culverts for this project will not be your usual culverts. They’ll also be fitted with specially formed fiberglass panels designed to create habitat for San Francisco’s native Olympia oysters. These oysters were once unbelievably prevalent in the San Francisco Bay. But due to overharvesting and sedimentation during the Gold Rush era, by the 1860s they had all but disappeared. Their tiny larvae have remained out in the Bay. Still, they’ve had difficulty finding the right habitat to latch onto and grow. They need the right combination of substrate, water flow and depth, light, and salinity to succeed.

To figure out how to create new oyster habitat, Presidio Trust natural resources and landscape architecture staff teamed up with designers, materials engineers, and biologists, including teachers and students from the Architectural Ecologies Lab at the California College of the Arts, and biologists from the Moss Landing Marine Laboratory. After two years of prototype development and testing, they had a solution: textured fiberglass panels coated with a sandy surface that could be fixed to the culvert walls. The panels will also be moveable so ecologists can pull them out of the water and study them.

After lots of testing, the team found that textured fiberglass panels coated with a sandy surface made for the best juvenile oyster habitat. The shapes are digitally fabricated by Kreysler & Associates, the company who created the façade of the new SFMOMA.

Presidio Trust

The team is excited about the project’s multiple possibilities. These range from expanding the use of architecture to aid nature where wholly natural restoration isn’t possible, to improved water quality and biodiversity in the Presidio’s wetlands due to the oysters’ water filtering abilities. It could even provide critical insights for scientists studying the use of sea walls to combat rising sea levels.

The Quartermaster Reach marsh project, which will also include a trail so visitors can get up close with nature, will be complete in late fall 2020.

For more information

• Check out the original Presidio blog article: “Discovery: Bringing Native Oysters Back to the Presidio”

• Contact Presidio Ecologist Lew Stringer

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