Reef Life

Researchers discover natural oyster reefs grow fast enough to keep up with the projected rise in sea levels, suggesting oyster reefs could be used for storm protection and erosion control, all the while doing what oyster reefs naturally do, which is filter the water and provide a habitat for fish.

BEAUFORT — By early July in 2014, North Carolina’s coastline had already felt the brunt of one hurricane. 

Granted, Hurricane Arthur was a Category 2 storm when it hit; not super powerful but still strong enough to knock out power, flood and damage roads, and cause some minor property damage. What is really scary is that we aren’t into the really active part of the hurricane season yet and the state already experienced a major storm.

It’s not surprising then that there is renewed talk about how best to protect coastal communities. And while beach nourishment, the restoration of coastal wetlands, and even sea walls are currently used, North Carolina scientists say they may have found a new way. 

Oysters. Or more specifically, oyster reefs.

You have to journey out to Middle Marsh to really see and appreciate the idea. It’s a section of the Rachel Carson Estuarine Research Reserve near Beaufort.

“The way we construct an oyster reef is by putting out oyster shells along the sandy bottom and letting the oyster larvae that is floating in the water settle on the shells,” Dr. Antonio Rodriguez, a professor of Coastal Geology at the University of North Carolina Institute of Marine Sciences, explains while standing in knee-deep water. “It’s really pretty simple; the larvae settle on the shells and grow up and grow on top of each other.”

The shells are set out in regular dimensions: three meters by five meters by 15 centimeters high. But what’s amazing about these reefs is how fast they grew. From 1997 through 2011, the 11 reefs started in the estuary grew in size at a pace that would match any predicted sea-level rise through at least the year 2100.

That’s right, the reefs grew faster than projected sea-level rise.

“The reef just keeps building on itself,” explains Dr. Rodriguez, as he points out the levels of oysters in the reef. “So this guy's alive and he’s at the bottom, then this one, then this one. So if each one of these oysters is growing at five centimeters, and they are growing on top of one another, that means the reef is adding height. And so that’s why the reef, as a structure, grows up much faster than the individual oysters grow."

The discovery is the first to suggest oyster reefs could provide better protection from storms and erosion than a traditional sea wall because the oyster reefs keep growing faster than the seas are rising. It also suggests oyster reef restoration projects could be used to help rebuild declining oyster populations at the same time the reefs are stabilizing shorelines and protecting coastal communities.

Just think of the possibilities... A community could build a series of reefs along the shoreline, creating a kind of oyster wall, for storm protection.

To make this work however, Dr. Rodriguez and his team found the reefs needed to benefit from what he termed “The Goldilocks Effect.” The reef had to be located in just the right spot. It had to be exposed to air only 40% of the time. The reefs built too high or too low didn’t do as well. In addition, the reefs needed to be located in inter-tidal areas, where the water wasn’t too salty.

However, if all those conditions were met, researchers found the reefs continue to add about six inches per year until the height was reached where the reefs were uncovered more than 40 percent of the time.  Once it was past the “Goldilocks” point, the reef hit a plateau. It wasn’t growing any higher, but it still continued to widen.

“This is a discovery that can benefit much of the state because in North Carolina we don’t have rocky cliffs for a shoreline, we have a gently sloping shoreline with vegetation and oysters,” says John Fear, Deputy Director of North Carolina Sea Grant and the Water Resources Research Institute. “If we can mimic that shoreline and get protection, we’re working with nature and not against it."

North Carolina Sea Grant helps to fund oyster restoration projects and Fear believes the work on oyster reefs is a win for people, oysters and nature.

“Oysters provide many services to humans besides being tasty things to eat,” adds Fear. “Oysters clean the water because they are filter feeders and the reefs provide habitat for recreational fisheries as well as protect shoreline from wave erosion. It’s another sign of how efficient nature is.”

To confirm the findings, Dr. Rodriguez and his team measured the reefs with laser scanners, creating 3D models of the reefs. The models will also help in the next part of the study, which will further refine the exact conditions in which the oyster reefs will grow best.

“The 3D model is very precise, within two centimeters to be exact,” explains Dr. Rodriguez. “So if we do this today, and we come back a year from now, we can see how the reef has grown. So we take those two maps, and we subtract from each other, and that highlights where we saw erosion and where we saw growth.”

The discovery has leaders and residents of coastal communities intrigued. Rodriguez is pleased he’s offering a new option for protecting coastal communities as well as helping the environment.

“Oyster reefs are incredibly important for the coastal environment, not only for cleaning the water and habitat but also as protection from storms and erosion,” adds Dr. Rodriguez. “Because if they exist next to a shoreline, they provide better protection because the reef is so much harder than the normal shoreline.  And now with our findings, these types of reefs should keep up with sea-level rise."

Related Resources: