Will coastal squeeze affect sea turtles in the Southeast?

Researchers predict that sea level rise on barrier islands in the southeastern U.S. will impact loggerhead and green sea turtle nesting, even in remote areas on barrier islands. Even low levels of beach loss could affect their populations, they found.

With support from the National Park Service, biologist Marta Lyons and her colleagues projected how green turtles (Chelonia mydas) and loggerheads (Caretta caretta) would be affected on Canaveral, Cumberland Island, Cape Lookout and Cape Hatteras national seashores by 2100. The Park Service already had records on where the turtles had been nesting as well as the locations of potential barriers to natural beach migration.

The researchers were looking at “coastal squeeze,” when a beach is sandwiched between rising sea levels that erode the beach on one side and a hard structure, like a road or seawall, that prevents the beach from expanding on the other.

“We wanted to quantify the potential for coastal squeeze on those beaches to identify where it might be a problem,” said Lyons, a postdoctoral fellow at the University of Central Florida’s department of biology and the lead author of the study published in Ecological Applications.

It was a complicated question, she found. Some beaches are wider than others and sea turtles don’t necessarily use the whole beach. But the answers her team came up with surprised them.

“We predicted beaches with the most development close to the actual shoreline would show the highest loss in percent of nesting area,” Lyons said. Cape Hatteras, in North Carolina, has roads that run along the entire extent of the beaches widely used for recreation, so her team expected higher losses there compared with areas with less coastal development, like Cape Lookout, to the south.

Instead, Cumberland Island, in Georgia, which has no infrastructure close to the beach, was projected to lose 6% of nesting area — the most of all the seashores. “It’s a pristine area,” Lyons said.

Canaveral National Seashore, in Florida, where half the beach length is backed by a road, was projected to lose less area — just 1% — but this decrease could have more impact on turtle numbers because of the higher density of nests there. “Canaveral has reasonably high density and other beaches within Florida have an even higher density,” she said. “Increasing density a little may not have a large negative impact, but it could also force nests to occur in less desirable locations.”

That could have “disproportionate impacts on the population growth of these species,” the researchers found.