Restoring and Protecting Georgia’s Coast — With Oysters

Sarah Roney studies oysters —and coastline restoration, wave energy, erosion, blue crabs, and predator chemical cues. A Ph.D. candidate in Georgia Tech’s Ocean Science and Engineering program and a Brook Byers Graduate Fellow, Roney has spent the past four years studying how strategically placing oyster reefs along Georgia’s coast could yield significant benefits.

Georgia’s coastal ecology is being degraded by several threats. Erosion caused by a combination of traffic from water vessels, sea-level rise, increased storm intensity and frequency, and property development, are negatively impacting both coastal living systems and the state’s economy. Tourism, agriculture, recreation, fisheries, property development, and trade (through the Port of Savannah) all rely on healthy coastlines.

Roney’s interest in coastal ecology and oysters drew her to focus her doctoral thesis on this problem. She divided her project into two parts. The first involved understanding how much oyster reefs reduce the erosion caused by wave energy (ship wake) from water traffic. The second part demonstrated a method for making young oysters resistant to predation — increasing their survival rates and that of the reef colonies they call home. Roney focused her research on two major waterways in the Savannah area. The Intracoastal Waterway and the South Channel of the Savannah River, which leads to the Port of Savannah, are both subject to heavy ship and boat traffic. According to Roney’s collaborators at Georgia Tech, 65% of the wave energy lashing the South Channel’s shores is generated by cargo vessels navigating to and from the Port of Savannah. Because traffic along the Intracoastal Waterway is subject to very few speed restrictions, there is plenty of erosive wave energy there also, even though the vessels are almost exclusively small.

Roney chose one site in each waterway to place her reef structures. Mesh bags of oyster shells were seeded with young oysters by personnel working at a University of Georgia Shellfish Research Lab. Roney created her reef structures by placing these bags in a row 15 to 20 meters long and a meter wide. Once established, Roney found that constructed reefs dissipate 40% of the wave energy before it reaches the marsh edge. “This is an experimental pilot study, so the reefs are on the smaller side,” Roney explained. “Reefs as large as 100 meters long may be necessary to protect certain areas — which sounds like a big investment. But because these are living shorelines, they are self-sustaining, and will keep growing and building on themselves.”

Establishing oyster reefs can be challenging, however, because predators feast on young oysters. Blue crabs are among the most voracious. The second part of Roney’s research was to develop a method that improves adolescent oysters’ chances of surviving to adulthood — when they infrequently succumb to predation. Roney and her collaborators at Georgia Tech identified two compounds found in blue crab urine, called trigonelline and homarine, that induce young oysters to devote more energy toward growing their shells, which become 25-60% stronger than normal. Roney found that after four to eight weeks of exposure to these compounds in hatchery conditions, their overall survival rate improved by 30% once placed in a reef. Her method not only helps constructed reefs to become established, but can also help existing oyster reefs become more resilient by slowing, or reversing, their decline.

While coastal restoration projects are not new in Georgia, the techniques Roney developed are relatively novel. Conventional shoreline restoration projects involve excavation, placing gravel beds, and extensive plantings, mostly with sea grasses. Roney has shown that using living shoreline strategies are less intensive and less expensive to establish and are also effective in reducing wave energy in waterways vulnerable to erosion. Perhaps most significantly, these techniques also restore the foundational functions of the ecosystems in which they are placed. The reefs become nurseries, incubating fish, bird, plant, and crustacean species.

Roney engaged several partners over the four years of her project, many in the communities along Georgia’s coast. Over 35 coastal residents, business owners, citizen scientists, and students volunteered their time and resources to help Roney’s project succeed. Roney said, “I think the most rewarding part of the project has been seeing how many people are truly invested in our coastal resources and want oyster reefs to thrive.”

This project isn’t likely to end once Roney earns her PhD. For living shoreline restoration practices to catch on, several other problems require investigation. Roney wants to devise a way to slowly release predator cue compounds into the water near oyster reefs, so baby oysters won’t need to spend as much time in a hatchery before being placed in the wild. Perfecting such a time-release mechanism could also help rejuvenate naturally occurring oyster reefs under threat from erosion and predation.

Roney also wants to try combining constructed oyster reefs with oyster farms, integrating one of the most sustainable ways that protein can be raised with living shoreline restoration. “As the mariculture industry in Georgia grows, there will be lots of opportunities to investigate the possible intersections between the ecological benefits, engineering benefits, and cultural benefits of oyster farming,” Roney said. “Food might be a continuous byproduct of shoreline restoration projects.”

Roney’s research shows that economic development and preserving, or even regenerating, diverse and productive coastal habitats for future generations don’t have to be mutually exclusive propositions.

Roney’s thesis advisor is Marc Weissburg, Brook Byers Professor in the School of Biological Sciences. Kevin Haas, professor in the School of Civil and Environmental Engineering, helped Roney map and measure the hydrodynamic forces in her study zones. The Coastal Resources Division of the Georgia Department of Natural Resources, the National Parks Service, and the University of Georgia Marine Extension and Georgia Sea Grant program provided access, permitting, funding, and resources.