Enlisting One of Nature’s Ecosystem Engineers to Assist with Coastal Defense

By Kathleen Saal

Oyster habitat restoration could make a lasting difference in the protection of the vulnerable Gulf Coast shoreline.

Oysters receive a lot of attention along the United States Gulf Coast, a region that produces a majority of the country’s commercially harvested bivalve mollusk. 

But oysters are highly regarded for much more than their economic value. The key role they play in creating and maintaining healthy coastal and estuarine environments makes them an essential part of this important ecosystem. 

A current study, funded by the Defense Advanced Research Projects Agency (DARPA), is taking a deeper dive into innovative methods that would enable oysters to better protect coastal shorelines. 

The project, “Reefense: A Mosaic Oyster Habitat for Coastal Defense,” is exploring the development of self-healing, hybrid biological, and ecologically engineered reef-mimicking structures to achieve two main goals — increasing wave attenuation to reduce damaging coastal impacts and erosion, and promoting the development and growth of healthy, self-sustaining oyster populations. 

Rutgers University is leading the 18-month project during its first phase, with options that could extend out to a total of five years. The three main areas of study include:

• design of the macro structure itself, 
• selectively breeding oysters that grow faster and are more disease resistant, and 
• protecting oysters from being eaten by predators.

The development of novel materials and reef design is aimed at enabling the use of low-cost, interlocking reef modules that are adaptable to different conditions and can be arranged to minimize any wave energy reaching the shoreline. In locations where wave attenuation is less important, the modular design would protect against erosion from daily currents, while also providing additional habitat value.

“We don’t have a module in the water yet, but, from the perspective of progress towards overall project goals, the work has been moving — either on target or earlier than expected,” said Nigel Temple, a coastal restoration specialist with WSP USA and professor at the University of South Alabama. “We are doing wave flume testing and we’ve coalesced around a general design for the modules.” 

Temple is serving as the firm’s main liaison with the project and research team. “Our engineers will need to sign off on these designs before they are put in the water and, for them to do that, they have to be convinced that these structures are stable and will hold up in this environment,” he said.

The selective breeding of native oysters that are shown to grow faster and be more resistant to disease is another key and ongoing focus for the research teams. Researchers at Auburn University and Louisiana State University are working in collaboration with Rutgers to breed oysters, through phenotypic and genomic selection, for faster growth and tolerance to dermo disease (Perkinsus marinus), which can easily spread among oysters and is associated with extensive oyster mortalities. This part of the project involves maintaining broodstock, managing the spawning and rearing of oysters, and field testing the resulting offspring. 

After that, researchers are challenged with preventing dermo disease, as part of the selection process led by Rutgers. Oyster lines that make it through this phase are then field tested at three locations in the Gulf of Mexico: St. Andrews Bay, Florida; Grand Bay, Alabama; and Grand Isle, Louisiana. 

Why Oysters?

As a popular seafood, oysters have a tremendous economic impact on the Gulf region. But perhaps lesser known is the outsized and beneficial role they play within their own habitats and natural environment — not least of which are the many benefits they provide other species within the same ecosystem. 

Oysters are regarded as both “Keystone Species” and “Ecosystem Engineers.” The reefs where they live are made of hard substrate and the ecosystem they create accommodates microhabitats for other species that would not otherwise exist. 

Conversely, without oysters, ecological communities in brackish and salty waters would be dramatically different. Oyster reefs protect marsh habitat that benefit from wave attenuation and support several other coastal species including fishes and other invertebrates which forage and take shelter from larger predators among these habitats. On top of that, oysters also feed on phytoplankton (tiny plants floating in the water), acting as a natural filter to clean the waters. This enables light to reach the bottom, where seagrasses grow, and help to remove an overabundance of nutrients that would otherwise pollute the waters.

The oyster population in the region took a serious hit in 2010 following the Deepwater Horizon oil spill, which is estimated to have killed more than eight billion oysters in the Gulf of Mexico. A long-term goal of the Reefense project is to create methods and technology that will help restore that population so it can protect shorelines.

The overall mission of the Reefense project is to create a mosaic of habitats that work together to provide resilience as they support multiple species, while simultaneously promoting self-sustaining oyster populations and helping diminish wave intensity. The magnitude of wave attenuation would be governed by physical characteristics, like water depth, reef crest elevation and overall structure width and depth, which are typically used to design non-living wave-breaking structures.

Work began in May 2022 and will be completed in three phases. WSP will manage the eventual reef construction and is currently working in bay waters off the Florida panhandle to characterize the site and monitor seasonal changes. The firm is also monitoring selectively bred native oysters to evaluate performance and collecting native oysters (under Florida Fish and Wildlife Conservation Commission special activity license number SAL-22-2391-SR), which are shipped to Rutgers for disease testing. 

Other tasks include deploying and retrieving wave gauges and other sensors, which collect data that will be used to compare before-and-after measurements, following installation of the engineered reefs.

WSP is also collaborating on predator exclusion experiments aimed at finding an effective microstructural design to reduce the threat of gastropod predators such as oyster drills and crown conchs. 

“Gastropods are snails and they have various mechanisms for eating oysters,” Temple said. “For example, the oyster drill, as its name implies, drills a hole in the oyster shell while crown conchs get to the oyster by prying the shell open. They are one of the biggest influences on the decline of oysters in a lot of ecosystems.” 

This Gulf study is one of three DARPA-funded projects currently being conducted independently of each other. The other two are coral reef studies — one in Florida and the other in Hawaii. Although the teams are not collaborating directly, they are connected through federal permitting. While the individual state permits are proceeding independently, the federal permits are being grouped together and led by the US Navy. 

In addition to WSP and Rutgers University, the full research team for the Reefense project includes Auburn University, Louisiana State University, Mississippi State University, the University of Arizona, the University of Central Florida, the University of Melbourne, the University of Western Australia, Reef Design Lab and the Partnership for Delaware Estuary. 

WSP has been involved in a variety of coastal restoration projects using engineered oyster reefs, including the Franklin-98 Living Shoreline, where 20 acres of oyster reefs and 30 acres of salt marshes are being created to protect routinely eroded areas of the Apalachicola Bay shoreline along Highway 98 in Franklin County, Florida. 

WSP also is monitoring the development of oyster reefs in Pensacola Bay, Florida, and is supporting the Living Breakwaters project off the coast of Staten Island, New York.