Climate change helps mangroves migrate from Florida to Georgia - Savannah Morning News

Climate change helps mangroves migrate from Florida to Georgia

'There are mangroves in Georgia!' Climate change lures tropical trees to state's coast
John Deem

Even seemingly small discoveries can illustrate the outsized impact of a warming planet.

That was the case recently when three curious nature explorers confirmed that a prominent tropical plant species had made its way to Georgia’s coast.

Ches Vervaeke, a coastal ecologist with the National Park Service, and his two companions had spent a day searching the northern Florida shoreline for mangroves, the saltwater-loving trees whose barbwire-like roots have long lined tidal banks in the southernmost reaches of that state as well as the Carribean and Central America.

Vervaeke and his companions – Candy Feller, a Smithsonian Institution ecologist who has studied mangroves for nearly a half century, along with a reporter from Scientific American magazine – began their exploration near Amelia Island, Florida, then the northernmost siting of the now-migrating plants.

"We boated up the Intercostal Waterway and we started to find more mangroves,” Vervaeke recalled in a phone interview Monday. “So, technically, every mangrove that we found ... was the new northernmost mangrove along the East Coast.”

The scene repeated itself about 15 times, he estimated.

“It actually became comical at the end of the day,” Vervaeke added.

By then, the explorers had made it to Fernandina Beach, just on the Florida side of the state line.

“Georgia was right there, and it was getting late in the day, so we said, ‘Hey, you know what? Let's just go take a quick peek up here and see if there are any up here,’” Vervaeke said.

They scoured the Florida side of the St. Marys River before crossing over to the Georgia and cruising into Cumberland Sound.

"That's when all three of us kind of at the same time found a mangrove and the reaction was just like, ‘Holy cow! I can't believe it. There are mangroves in Georgia,’” Vervaeke said. “Doing the research that I do, I have suspected for years that they were there. And sure enough, we found them.”

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'Migration is expected to steadily expand'

Climate change offers inviting conditions for plant and animal life to move north from tropical areas.

"Warming temperatures, including milder winters, are believed to be the driver of the expansion of mangrove habitat," noted Jaynie L. Gaskin, wetlands biologist with the Georgia Department of Natural Resources Coastal Resources Division. "Mangroves (also) are sensitive to cold temperatures and cannot survive in extended freezes. Their distributions are limited to areas where winter freezes are less frequent or prolonged."

In Jacksonville, just south of the newly discovered Georgia mangroves, average winter temperatures have risen 3.4 degrees over the past half-century, according to the organization Climate Central.

And at nearby Fernandina Beach, temperatures have dipped below 30 just once in the last decade, National Weather Service data shows.

Those numbers offer statistical evidence for climate change, which is caused primarily by the burning of fossil fuels for energy, heating and transportation. But powerful as they are, facts and figures aren’t enough to convince everyone.

“You know, you can talk about sea-level rise until you're blue in the face,” Vervaeke said. “And if you visit (the beach) once a year, you may not understand it. But if you point out a mangrove that's not supposed to be there, the educational value on that as far as climate change goes is just immense.”

And there is more to come, added Gaskin.

"Mangrove migration is expected to steadily expand along the East and Gulf coasts with the projections of continued warming," she said.

Dividing line shifts

The Merritt Island National Wildlife Refuge, about 115 miles south of St. Augustine, was long considered Florida's boundary between the more temperate north and the more tropical south, noted Dan Chapman, an Atlanta-based spokesman for the U.S. Fish and Wildlife Service.

Mangroves lined the shore to the south, and salt marshes dominated to the north. However, as temperatures climbed, that climatic border began shifting rapidly at around the turn of the century.

That means mangroves’ northern march is still a relatively new phenomenon, so its ultimate impact is unclear.

"Based on mangrove migration northward up the east coast of Florida and across the Gulf coast, we expect that mangroves and salt marsh grasses will coexist," Gaskin said. "It may take a century or more for mangroves to become the predominant species within what is currently a salt marsh system."

Mangroves, like salt marshes, create habitats for wildlife and fish, improve water quality, reduce storm damage and erosion, and even support economic growth through tourism.

"Scientists don’t know exactly how the transition from salt marsh to mangrove will occur," Gaskin added. "Therefore, we lack an understanding of how these ecosystem services may change."

Georgia’s geography, including 14 major barrier islands, also is expected to influence the migration.

"The Georgia coast is boarded by over 368,000 acres of tidal salt marsh that acts as a natural buffering system between the ocean and the mainland," Gaskin explained. "Mangroves expand into new habitats when seedlings drop from parent trees into the water and are transported through tides and currents. When ocean currents bring mangrove seedlings north from Florida wetlands, the outer fringe marshes are likely to be the site of first deposition and possible establishment."

That's how researchers believe Florida seeds, blown by winds from Hurricane Irma in 2017, reached Georgia's shore.

'Needs to be more research'

A study of areas in Texas where mangroves were observed for the first time found that mangroves and marshes are not naturally interchangeable and have distinct ecosystem benefits.

Researchers from Texas A&M University at Galveston, the University of Houston and Florida International University concluded that mangroves are better at preventing coastal erosion, but the carbon in mangrove leaves is not a good food source for organisms at the bottom of the food chain such as snails and fiddler crabs.

Birds that forage for food would have a difficult time in mangroves while nesting birds do better among the trees, the researchers found.

They also suggested that mangroves should not be introduced to areas where they would not naturally occur.

But Vervaeke, like Gaskin, says there's much more to learn about the potential impact on Georgia.

“There needs to be more research done to see if these mangroves are going to actually establish, start reproducing and actually compete with the marsh this far north,” he explained. "There are areas in Jacksonville where the mangroves are definitely competing with the marsh and they're starting to take them over and, you know, Jacksonville to St. Mary's, Georgia, isn't that far.”

John Deem covers climate change and the environment in coastal Georgia. He can be reached at 912-652-0213.