Last summer, I began working working with marine biologist Christopher Lim, then Living Shorelines Program Manager at The Watershed Project, on design for two potential artificial oyster reefs at Point Emery in Emeryville and Point Molate in Richmond (both are in the San Francisco Bay Area in California). With the help of community volunteers, Christopher built a 100-unit artificial reef at Point Pinole in 2013. He has since moved on to work on salmonid (anadromous fish) conservation on the Central Coast, and I am looking forward to working with another marine biologist on this project.
The impetus for these kinds of habitat restoration projects is that oysters are a cornerstone species in the bay ecosystem. They improve water quality through filtration, and they provide habitat and food for other species. The native Olympia Oyster was once much more numerous in the bay, but its habitat was undermined by sedimentation from agricultural and industrial development. Mud gradually covered up much of the hard substrate oysters require for attachment. The goal of artificial oyster reefs is to replace that lost hard substrate. Oyster reef restoration also helps to mitigate tidal surges in our bay caused by climate change.
Christopher and I did low tide site visits to get a handle on the conditions. Both sites have tremendous potential for oyster recruitment, and both sites have their challenges.
Point Emery
Point Emery’s north side is open to the fetch of wind waves on the bay. It is also a launch site for local kite boarders. This factor that will have to be taken into account when designing an artificial oyster reef, so as to facilitate safe and sustainable egress.
Perhaps more challenging is the significant erosion on this side of the point, which is threatening the trail, and the very integrity of the point.
Despite these challenges, there is a diverse local ecosystem and good potential for oyster recruitment, especially on the relatively sheltered south side of the point.
Even the ecosystem has its challenges. We see some oyster recruitment, but lots of sediment covers much of the hard substrate.
There are some competing organisms, including barnacles, limpets, and some oyster predators (oyster drills).
Point Molate
Point Molate is an open beach on the north side of the Richmond Bridge, with a rock reef that has excellent potential for greater oyster recruitment. As you can see from this photo, there is robust oyster recruitment despite the muddy conditions outside the reef.
There is a lot of eel grass in the mud flats outside of the rock reef. Eel grass is a great habitat for crustaceans and bait fish. It is suspected that the water filtration oysters provide has a clarifying effect on water that allows a greater degree of photosynthesis in eel grass and other marine plants. This is yet another reason oysters are considered to be a cornerstone species in the bay ecosystem. Here we see a large clump of eel grass washed up in the wrack line:
Again, erosion is a challenging factor at Point Molate, which is also exposed to the fetch of wind waves. We observed cliff erosion, a fallen tree, and another tree threatened.
Despite these challenges, oyster recruitment is robust a Point Molate. We think that it’s a good site for habitat restoration.
The Latest Design
Above and below are a 3D modeled digital version and 3D printed 1″=1′ scale model of my latest design for artificial oyster reef units made with these site conditions in mind. The latest iteration is designed in hemispheres to make the casting process easier. Interlocking half spheres will also be lighter to facilitate transportation and installation. The full-size, 3′ diameter, units will be cast in an oyster shell/concrete mixture called Baycrete from a single composite shell mold. The units are designed as hollow spheres with holes to maximize surface area for oyster attachment while minimizing footprint, and to allow water flow while discouraging predation. The 3′ diameter and stack-ability is intended to ameliorate erosion and corresponds to a six foot tidal range.
You can see more detail of the design and process in my recent posts: Casting Hollow Spheres in a Mold for an Artificial Reef and How to really Print Sphere Molds.
ADVERTISEMENT
