Oyster Reef Restoration

For each place where the partners are working to restore oysters, a “blueprint” is developed to precisely guide the scientifically based work. Blueprints include maps to show where reefs are to be built or oysters are to be planted. NOAA uses several different types of sonar and other validation techniques to collect information on where the Bay bottom is hard rather than soft.

Projects can’t be built on soft bottom, because they would sink into the mud under their own weight. Instead, reefs are built or rebuilt where they once were or in areas that still have shell or other hard river bottom.

NOAA scientists use sidescan sonar from on board a boat to get visual data about what the river bottom is like in each tributary where restoration work is planned. The sidescan sonar data are then used to make a map—like above, from the Piankatank River—to show where soft and hard bottom areas are located. In the image above, the light areas are softer, and the darker areas are harder. Maps like this are especially useful for identifying the location of existing natural oyster habitat, previously restored sites, and candidate areas for future restoration reefs.

Depending on what the habitat analysis reveals, areas are restored in different ways. Some locations have existing reef structure—but no living oysters. In these places, the population can be jump-started by planting spat-on-shell juvenile oysters.

Other places get “substrate only.” These areas have good natural oyster reproduction—but don’t have hard places or reef structure for oyster larvae to settle on. In these places, partners build reefs from stone, crushed concrete, or shell—and then let local oysters populate the rebuilt reef. Thanks to warmer waters and higher salinities that support higher oyster reproduction, many Virginia areas need only to have hard substrate built into reefs.

Other locations need both seed and substrate and seed. These places have no reef left, and there is low natural oyster reproduction. Here, partners build the reef—and then they seed it with juvenile oysters.

Many of those juvenile oysters are produced by the University of Maryland Center for Environmental Science’s Horn Point Oyster Hatchery, seen in the photo above. The Hatchery team grows oysters by encouraging mature oysters to spawn, nurturing free-swimming larvae, and enabling them to attach to a piece of shell to become the “spat on shell” that are used to seed reefs. NOAA and the State of Maryland have funded hatchery production for restoration use in Maryland. In Virginia, there is typically enough natural oyster production for reefs to seed naturally.

As of mid 2020, more than 800 acres have been restored around the Bay under this initiative. More than 700 acres remain toward the overall goal of restoring healthy reefs to 10 tributaries by 2025.

The scale of this work is unprecedented globally. Partners in the Chesapeake Bay Program have shared the science of large-scale oyster restoration with visitors from several other countries who are interested in similar projects around the world. 

But simply restoring the reefs is not the whole story. Because restoration comes at a hefty price tag—(the 350 acres in Harris Creek cost roughly $28 million total),—partners track the health of these areas after the restoration work has happened. At three years and again six years after restoration is completed, NOAA uses sonar to track how big and complex the physical reefs are. Images, like the one above from Harris Creek that shows data from multibeam sonar, let scientists and resource managers "see" how the reefs are doing. Watermen (local wild oyster harvesters), local divers, academics, and other partners check on the biology of the oysters.

To date, 98 percent of the reefs monitored three years after restoration meet the standards for a restored reef—an outstanding success rate.