The Chesapeake Bay is home to the world’s largest oyster restoration project, which will restore more than 1,800 acres of habitat. Work is taking place in 10 rivers around the Bay. The Chesapeake is the largest estuary in the United States. Spanning roughly 200 miles from its head at Havre de Grace, Maryland, to its mouth at Virginia Beach, Virginia, the Bay encompasses a range of habitats and water conditions.
That means the ways that oyster restoration partners work must vary from one part of the Bay to another. In Virginia, saltier waters support higher levels of natural oyster reproduction. Oyster reef restoration work there is generally limited to constructing reefs made of hard material that oyster larvae can settle on, like oyster shell, other kinds of shell, or rock.
In Maryland waters, salinity levels are lower. In addition to constructing reefs, oyster reef restorers also need to plant spat-on-shell (juvenile oysters) on top of those reefs in order to jump start populations.
Restoration Is a Complex Process
These restoration efforts can be expensive and time consuming. Experts working in oyster hatcheries keep oysters in special tanks. They can collect larvae when the oysters spawn. Then the larvae go through the grow-out process. They are moved to tanks where they settle on oyster shells that have been collected specially for this purpose. The hatchery feeds and takes care of these juvenile oysters until they have grown large enough to be planted on constructed reefs.
NOAA Fisheries joined a group of researchers, including scientists from the NOAA National Ocean Service and the U.S. Naval Academy. They wondered if it would work to skip the grow-out process and to simply let oyster larvae settle on a constructed reef area. This process is called “direct setting” because the oyster larvae are set directly on the restoration reef without being set onto hard substrate first. If this works, it could potentially save time and money.
Is There a Better Way?
The researchers had another question: How can you tell the difference between the oysters that are there because of the experiment and oysters that are there because of natural reproduction from nearby reefs?
They decided to stain the oyster larvae with calcein, which is a kind of dye that “glows” when it is viewed under blue light. These marked larvae were placed in the water so that they could settle on a reef. The project used scuba divers to precisely release larvae at predetermined locations. In the experiment, 1.6 million larvae were released at each of three reefs in Maryland’s Tred Avon River in July 2019, and again in September 2019.
Researchers went back after roughly 1 week to see if they could find oysters, stained from the experiment, attached and growing on the reef. They did! That means that, in certain situations, oyster larvae can be set directly onto reefs.
More remains to be learned about how such efforts could be scaled up to set oyster larvae directly onto larger reefs.
To document their results, the researchers developed a scientific paper that was recently published in Estuaries and Coasts.