The Savannah River swapped bare marsh edge for oyster reefs in 2023; wave energy fell by up to 40%, giving Georgia coasts a tougher storm shield

In May 2023, a team of scientists built two oyster reefs in Georgia’s Savannah River. They used bags of oyster shells covered in baby oysters, only one to two meters from the edge of the marsh. These reefs reduced wave energy hitting the shoreline by as much as 40 percent compared to nearby areas without a reef, according to a study published in the journal Ecological Engineering by researcher Mariah Kachmar and her colleagues.

Why oysters matter for more than dinner

Oysters are mostly seen as a delicacy and not infrastructure, but oyster reefs have dual purposes. Oysters lie in shallow waters and weaken any approaching waves before these waves get to the landmass behind them. This results in minimal wave energy and, therefore, less erosion. With minimal erosion, the marshes and soils in the back of the oyster reefs remain intact for a long time. The Savannah River is a difficult place to test. It is one of the busiest cargo shipping lanes on the US East Coast. Boat wakes and tides are constantly hitting the shoreline. Kachmar's team pointed out that previous research has looked at other parts of the East Coast, but no one had measured oyster reef wave attenuation in Georgia until now.

How the study actually worked

The technique used in this experiment was the "spat-on-shell" approach. This involves collecting old oyster shells with spat on them and using them to build a reef. This approach is one of the oldest and least expensive ways of creating a reef and requires no large equipment or concrete. Over 18 months, the team measured the wave energy in the reef areas and compared it to control areas without a reef present. The team also monitored the percentage of each reef that remained covered by living oysters. At the end of the experiment, living oyster cover ranged from 17% to 40%. That suggests the reefs were doing more than dissipating waves; they were alive and growing and adding new shell over time.

The trade-off nobody talks about

While this paper talks about successful wave attenuation, some studies show that oyster reefs cannot attenuate waves the same way everywhere. A 2021 study in the journal Ecological Applications, ‘Large-scale variation in wave attenuation of oyster reef living shorelines and the influence of inundation duration’ by Rebecca Morris and an international team of coastal scientists, found that the wave attenuation effect of oyster reef living shorelines differs from location to location. There is a paradox here: the study found that reefs submerged less than half the time provided little oyster habitat but reduced wave height by 68 percent. Reefs submerged more than half the time can provide better oyster habitat but reduce wave height by only 5 percent. This means that an oyster reef living shoreline's ability to attenuate waves and its ability to support oyster habitat tend to trade off depending on how long the reef stays submerged; the two goals don't always peak in the same design. The Savannah River reefs were built at mean tidal height, roughly the midpoint of the local tidal cycle, a position that straddles the threshold Morris and colleagues identified, rather than falling clearly into either the high-attenuation or high-habitat category. The published study doesn't report an exact inundation percentage, so it's not possible to say from the data alone which side of the trade-off the Savannah reefs land on. Design engineers must choose between the two goals or find a workable middle ground.

The bigger monitoring effort behind all this

Georgia is not the only region that has been following up on this. A project funded by NOAA's National Centers for Coastal Ocean Science identified 17 oyster reefs and their paired control sites in New Jersey, Virginia, Florida, Alabama, Mississippi, and Louisiana. From July to November 2020, the team deployed a network of low-cost wave gauges, about $160 each, to record wave conditions before, during, and after storms. The goal was the same as the Savannah River project: to find out whether these reefs can survive and still function under real storm stress, not just in calm weather.

Why this should matter to you

Coastal change can feel immediate for communities that have seen shorelines shift over time. This study suggests a lower-cost approach that may require only a stretch of shoreline, oyster shells, and patience. It’s also part of a larger shift in how engineers think about coastal defense. Instead of just building walls to fight the water, some engineers are now working with living systems that grow, repair themselves, and support marine life at the same time.

The catch worth remembering

This is not a universal fix. The Savannah River study involved testing of just two reef locations over 18 months in a single river system. The Ecological Applications research shows that outcomes vary significantly depending on the period for which the reef remains submerged. Each shoreline is unique; thus, what works in Savannah might require some tweaking elsewhere. However, a 40 percent reduction in wave energy in one of America's busiest rivers is a notable result.