by Caroline Grass
July 27, 2022
Oysters are an important species in the Chesapeake as they help improve water quality and support one of the most valuable commercial fisheries in the Bay, but populations are only at 1-2% of historic levels due to pollution and unsustainable harvesting.
One way to help get oysters back to sustainable levels in the Chesapeake Bay is to restore the reefs they use for habitat. Oyster reefs are colonies of oysters that attach themselves to hard structures, typically older shells, rocks or piers. While these reefs can form naturally, teams in Maryland and Virginia working through the Bay Program have been restoring and creating reefs in 10 key tributaries of the Bay.
Want to know all that goes into creating oyster habitat? Follow along to learn more about our four-step process.
1. Choosing a location
The first step to restoring oyster habitat was choosing what tributaries to focus on. We looked for locations where oysters had historically been and had healthy water quality to sustain reefs. We also did not want to interfere with harvest areas as much as possible since the constructed reefs are considered sanctuaries and oysters living on them cannot be harvested. Maryland and Virginia have maps detailing which areas are protected and which are approved shellfish harvesting locations.
In the end, 10 tributaries were selected (five in Maryland and five in Virginia) for restoration. The five chosen in Maryland were Harris Creek, Little Choptank River, Tred Avon River, Upper St. Mary’s River and Manokin River. In Virginia, the five chosen were the Piankatank River, Lynnhaven River, Lower York and Great Wicomico. In 2020, the eastern branch of the Elizabeth River was added as a sixth “bonus” tributary to be restored in Virginia.
2. Creating a restoration blueprint
For each selected tributary we then created a restoration blueprint. These plans outline how the reefs at each tributary should be built, including their size, how many there should be and where to place them.
One main factor is looking at what type of river bottom an area has. A reef has to be built on a surface that is hard enough so it does not sink from its own weight. Sonar is used to see what the river bottom looks like in areas where restoration is planned. Reefs are also planned so they stay outside of commercial harvest areas and navigation channels so that boats can still move through waterways safely.
3. Reef construction and seeding
Once a location has been chosen and a plan is in place, there are three ways reef restoration occurs. If the area already has an existing reef, but does not have any living oysters on it, spat-on-shell juvenile oysters will be placed on the reef.
The University of Maryland Center for Environmental Science’s Horn Point Laboratory Oyster Hatchery produces most of the juvenile oysters used in restoration. They create optimal conditions so oysters can spawn and then the free-swimming larvae attach to a shell. This creates the spat-on-shell that is used to seed reefs.
If an area does not have an existing reef but does have a natural population of oysters, substrate will be placed and existing oysters will populate the reef. Substrate can be broken oyster shells, stone or crushed concrete. In Virginia, most areas only need substrate since they have higher oyster reproduction rates than Maryland.
If an area does not have a reef and has a low oyster reproduction rate, substrate and spat-on-shell juvenile oysters will be used. The reef is created first and then spat-on-shell is added. Boats will take millions of spat-on-shell at a time and spray them onto the area with a reef to populate. As of 2021, 5.43 billion shells have been planted in the selected tributaries.
4. Monitoring and Evaluation
Once the seeding is complete, reefs are monitored at the three-year and six-year marks to track if they meet the standards for a “restored reef.” A restored reef must meet a set of criteria that includes having a proper oyster density and reef size and height among other standards.
To monitor reefs, we use sonar, divers and patent tongs, which are hydraulic claws attached to boats that pick up oyster samples. To help lower costs of monitoring, a new approach is being developed called the Rapid Assessment Protocol which uses underwater cameras to monitor reefs.
The final product
The Chesapeake Bay Program has successfully restored oyster habitat in six tributaries, plus Virginia’s bonus tributary. At the three-year mark, 98% of reefs met restoration standards and 1,740 acres of reef have been restored since the project started.
While oyster restoration is not new, creating reefs and re–seeding areas at this scale has never been done before. As of 2022, we are on course to meet our 2025 goal of restoring habitat in all ten tributaries.
Want to contribute to oyster restoration yourself? Consider recycling oyster shells through programs such as the Oyster Recovery Partnership’s Shell Recycling Alliance and the Chesapeake Bay Foundation’s Save Oyster Shells program so that they can be used at restoration sites.
Oysters can also be grown off docks and individuals in waterfront property or have access to docks can participate in initiatives such as the Maryland Grows Oysters program.