Volunteers working at Heron’s Head Park | Instagram/@thewildoysterproject Volunteers with San Francisco’s Wild Oyster Project prepared about 2,000 pounds of cured oyster shells in July 2022, that were collected from local restaurants and were placed inside 60 oyster reef balls. The work was part of a shoreline restoration project that was designed to address erosion while creating habitat in the waters around the park. According to the Wild Oyster Project, 70 volunteers spent two days preparing and bagging the recycled shells, which were then placed inside the reef structures before the balls were deployed along the southern shoreline of Heron’s Head Park.The shells came through the group’s “Save Your Shucks” program, which collects discarded restaurant oyster shells and cures them before they are reused in restoration projects. The project put the shells back into the ecosystem as a surface where young native oysters can settle, rather than sending them to a landfill.
Volunteers working at Heron’s Head Park | Instagram/@thewildoysterproject
The reef balls are more than oyster homesThe Port of San Francisco’s construction documents called for 60 oyster reef balls along with a new stabilized shoreline made from coarse sand and gravel. The reef structures were intended to provide habitat for oysters, herring larvae and other native plants and animals. Heron’s Head Park occupies an approximately 21-acre peninsula along the San Francisco waterfront, and its southern shoreline had been retreating before the restoration work because of erosion from wind-driven waves and tidal flows.Port officials estimated that without additional protection, the park could lose another two acres over 30 years. The shoreline project therefore combined several features such as a coarse-material beach that was built to reduce wave energy, rock structures that helped stabilize the shoreline, wetland vegetation that was restored and the oyster reef balls that were installed below the water. The goal was to keep the shoreline functioning as habitat while giving wetlands room to adapt as sea levels rise.Restaurant waste became reef materialYoung Olympia oysters need hard surfaces on which to settle. Loose mud does not provide the same kind of substrate as oyster shells, so the recycled shells gave the reef structures material that could support new oysters. The Wild Oyster Project says the reef balls were made from “baycrete,” which is a concrete mixture incorporating oyster shells, while the additional cured shells were placed in biodegradable bags inside the structures.The organization also added juvenile fish habitat blocks inside the reef balls, and each structure weighed more than 1,100 pounds, according to the project description. Once placed on the bay floor, the structures became part of the shoreline’s developing underwater habitat rather than simply serving as barriers against waves.The park had already been losing shorelinePort records say the shoreline had experienced a reduced supply of sediment that was capable of replenishing the marsh. The shoreline had moved as much as 50 feet inland from its 1999 position in the most affected section, and the park’s wetlands were also dealing with invasive plants and declining habitat quality.The restoration project was designed as a living shoreline, and the port incorporated sand, and subtidal reef structures into the design instead of relying entirely on a conventional hardened seawall. The reef can become habitat for other organisms while contributing to the biological complexity of the shoreline, as oysters establish themselves on the available shell.
The main path in Heron’s Head Park in April 2021 | Wikimedia Commons
Volunteers supplied part of the materialThe physical reef structures came from the larger Port-led project, but Wild Oyster volunteers supplied the recycled shell component. The group’s account of the 2022 work describes volunteers washing, weighing and transporting the shells before they were moved to the reef-ball staging area.The shells were then incorporated into the 60 structures that were installed along the park’s southern shore, and by the end of 2022, the Port reported that the Heron’s Head shoreline resilience project had been completed. The finished project included a gravel beach, rock structures and the subtidal oyster reef installations. The project was intended to protect the shoreline and wetlands while adding habitat in an area where erosion had already taken a measurable toll, and for the volunteers, the material at the center of that effort had originally been something restaurants were throwing away: oyster shells.
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