NC scientists find that oyster reefs can grow faster than sea-level rise

Climate scientists predict that by 2100 sea level will be 2 to 3 feet higher than it is today, but it appears oyster reefs may adapt to the change.

New research at the UNC Marine Science Institute finds oyster reefs grow fast enough to keep pace with rising seas. Unprecedented climate warming and sea-ice loss is causing sea levels to rise, threatening to bury coastal ecosystems in the process.

A long history of overfishing and habitat degradation has led to the loss of approximately 95 percent of oyster reefs on the East Coast, making them particularly sensitive to any additional habitat loss from rising seas. Biologists Tony Rodriguez and Joel Fodrie at the UNC Marine Science Institute are studying how oyster reefs respond to sea-level rise and how shoreline restoration improves their chance of survival.

The project began in 1997 when a graduate student planted artificial oyster reefs in the sand flats near Morehead City. With time, planted reefs transform into large dense structures of oysters, shell and sand. More than 10 years passed before UNC biologists at the institute surveyed the reefs again.

“They had grown really high,” Rodriguez said. “We thought that just can’t be right... So, we decided to try and measure their growth, and that is how it all started.”

Rodriguez and Fodrie set out to take the first direct measurements of oyster reef expansion. They created 11 additional artificial reefs and measured their growth over the following two years.

Using laser scanning technology, Rodriguez and Fodrie generated topographic maps of the oyster reefs. The laser works by shooting at a rotating mirror, which scatters light onto the reef and measures the return. These maps allow scientists to calculate precise rates of reef accumulation by comparing depths to original GPS coordinates.

They discovered oyster reefs can grow up to 10 times faster than previous estimates and fast enough to outpace even the most extreme predictions of sea-level rise.

Future oyster restoration projects will benefit from their findings, which were published in the April issue of Nature Climate Change. Their work gives guidelines on where to construct new reefs and how much material to put out to get the biggest and healthiest reef.

Rodriguez purchased oyster shells from a cannery for $128, which he used to create an oyster bed the size of four queen-size mattresses. Over time, his reefs accumulated sediment, organic material and juvenile oysters. Now, more than 10 years later, the oyster beds are teeming with life and have more than doubled in size.

Rodriguez hopes coastal residents will consider protecting their homes by building oyster reefs instead of bulkheads.

“That oyster reef will grow up and give them some protection from erosion,” he said.

Annamaria Frankic, a research professor at the University of Massachusetts Boston and director of the Green Harbor Project, agrees. A living shoreline with protected oyster reefs offers several benefits, including storm protection, improved water quality, increased biodiversity and carbon storage. Oyster reefs do not need maintenance like bulkheads because they are resilient and expand with rising seas. Bulkheads have a maximum lifespan of 50 years while oyster reefs are self-sustaining.

UNC Chapel Hill recognizes these benefits and has pledged to reach carbon neutrality by cutting net carbon emissions to zero by mid century. Earlier this month, students and faculty at the Marine Science Institute added about a half a million oyster shells to the sand flats bordering their lab, in a project that could store up to a ton of carbon dioxide per year and accrue $3,190 per year in benefits to water quality, shoreline protection and fisheries, according to Rodriguez.

Frankic makes another case for oyster reef restoration: the survival of oysters themselves. Restoration and protection will give oysters a chance to establish large, genetically diverse reefs, qualities that reduce sensitivity to disease and climate warming, she said.

“If we don’t restore oysters, I don’t think they will be able to sustain more stress exacerbated with climate change,” she said.