If you build it, oysters will come
Globally, oyster reefs are in free-fall. Disappearing faster than we can restore them, oyster reefs are one of the most threatened habitats on the planet. They are also one of the most valuable. Oysters create structure favored by many fish and invertebrates. They are also great at filtering water, capturing carbon, and breaking wave energy. For these reasons and more, oyster reefs are prominent features of several living shoreline projects we are building with the help of the community in Cedar Key.
Meet the materials
Oysters cannot move around once they settle in place. Young oysters, called spat, are fairly picky about where they land. They need to attach to a hard substrate, and their preference is to settle on adult oysters. But oysters can also settle and thrive on a range of other materials. In Cedar Key, we are using four types materials to form the base of new oyster reefs. These are reef balls, oyster castle blocks, shell bags, and reef prisms. Read on to learn more about each of these materials and the progress we are seeing on each.
In mid-June 2020, our team worked with Reef Innovations to place 384 reef balls along Airport Rd. in Cedar Key. These are arranged into sixteen reefs and each reef is composed of two rows of twelve reef balls. The reef balls are sitting along the -2 ft depth contour, specifically chosen to put the maximum amount of surface in the optimal zone for oysters. In just two short months, the oysters have definitely moved in! Our team is monitoring the progress of these young oysters using exciting 3D modelling technology. Using this, we can track the growth of oysters and increase in complexity over time.
You may remember that back in 2018 we installed reef balls at the UF/IFAS Nature Coast Biological Station. We reported promising results in 2019, and the oysters are still going strong today! Overall, oyster domes made of concrete (like reef balls) are a great choice for oyster restoration in our region if you have the capacity and the means to install them.
Shell bags can be made from a range of materials but most are made from plastic mesh or synthetic fabrics. At the Joe Rains Living Shoreline, the bags are made from a nylon fabric mesh and filled with clam shell. But many other projects, such as the Centipede Bay oyster reef in Hernando County, use hard plastic mesh bags with recycled or fossilized oyster shell as filler. Shell bags are one of the most commonly applied oyster restoration approaches. This is because they are easy and cheap to make, light enough for volunteers to carry, and generally have good success rates. Our team has even found that many types of shell are able to recruit oysters equally well. However, shell bags are increasingly problematic because they introduce harmful plastics into the marine environment.
Oyster Castle Blocks
June was a busy month for oyster enhancements in Cedar Key! We also constructed two point bar reefs using oyster castle blocks. Castle blocks are basically cinder blocks that are molded into a shape that easily interlocks. While many shapes are possible with these blocks, we stacked them in a linear pyramid configuration. Oysters and barnacles are already settling on the surfaces of the blocks!
Reef prisms are a new material developed by Dr. Mark Clark in the UF/IFAS Soil and Water Sciences Dept. In this configuration, they function very much like shell bags with the added benefit of being plastic-free! The basic materials that make up reef prisms are jute fiber erosion control mat and Cement-All rapid setting concrete. The jute mat is soaked in the concrete mixture and draped around a form. Once dry, the forms are removed and the prism is filled with shell and capped off. While there are many shapes and configurations possible, we are using the prism shape in the current project due to the ability to stack them in multiple rows.
As far as oyster growth, reef prisms and similar forms made of the same material perform quite well. A pilot test of the material at the Joe Rains Living Shoreline yielded impressive oyster growth. Last week, we deployed almost 90 reef prisms along G Street in Cedar Key. About a third of the prisms were moved to G Street from another location, where they were submerged in the water. These prisms were already coated with small oysters, showing a lot of promise for the future use of this material for oyster reefs elsewhere.
Have you used any of these materials on your local shorelines? Or have you used other materials? Tell us about it in the comments, and stay tuned for more shoreline updates.