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North Florida Mangroves Could Pose Threat To Coastal Ecosystem

Kevin Cavanaugh via Smithsonian Institute

Mangroves are quintessentially tropical and take root along the coast of the Everglades and the Keys where they are home to colorful fish and crabs. But these plants are not marooned in South Florida anymore. WFSU went searching for mangroves along the state’s Gulf Coast.

Historically, scientists believed mangroves didn’t live farther north than Cedar Key, in the middle of Florida’s Big Bend. But that’s not the case anymore. I went exploring with a scientist named Caitlin Snyder who’s based at the Apalachicola National Estuarine Research Reserve.

“Not many trees can really deal with this type of environment of such high salinities and changing either from storms or tides,” Snyder said.

We hiked into a place called East Hole, eighty miles south of Tallahassee. There’s a little spit of beach flowing into a winding series of shallow tide pools, edged with marsh grasses. Snyder has done some monitoring here before.

“When I come out here I’ll usually take a GPS point of the individual, and I get an estimate on the height. I’ll take note of any leaf damage, if the tips are black say from a freeze event, whether there's any insect damage, just kind of overall condition that I see,” she said.

And then we began to spot them, jutting out of the olive green blanket of salt marsh. Maybe two feet tall, these aren’t extensive forests like in South Florida, but individual trees scattered in the grass.

And even though these plants are in a strange new habitat, they’re vibrant and healthy. There are many factors that determine where a mangrove will take root. But they’re ultimately at the mercy of hard freezes, according to research ecologist Michael Osland with the U.S. Geological Survey.

Credit Caitlin Snyder via ANERR
A mangrove sprouting among marsh grasses off the coast of the Florida Panhandle.

“Be they mangroves, be they invasive plants, invasive species, any tropical organism, these freeze events play a really important role in setting the northern limit of those species," Osland said.

He’s watching the mangrove migration all across the Gulf Coast, where there haven’t been many hard freezes lately.

“So with climate change, as we get a shift in the frequency and intensity of those events, it’s gonna allow those tropical species to move northward…and small changes in air temperatures can trigger these really dramatic, what we call ecological regime shift,” Osland said.

Ecological regime shift. Sounds scary, right? Marsh grasses and mangroves are both really beneficial. And they’re both foundational species, meaning everything else in the ecosystem revolves around them. So when one of those bedrock species is replaced by another, it could spell chaos. But Osland says it’s too soon to know if the change will be good or bad.

“In other areas mangrove expansion to salt marsh could be beneficial in terms of increased carbon storage, or wave attenuation. But that said, there will be some pretty big shifts for the habitat that these systems support,” Osland said.

But Osland says as the effects of climate change intensify, mangroves will continue to force out salt marshes along the Gulf Coast.

To be clear, mangroves are not taking over the Panhandle yet. But Caitlin Snyder says they are here to stay.

“I think we’re kind of at that tipping point where freeze events can still knock them back, but I think they’re here,” Snyder said.

The question is, where will the mangroves show up next? And what will survive under the new regime?

As a Tallahassee native, Kate Payne grew up listening to WFSU. She loves being part of a station that had such an impact on her. Kate is a graduate of the Florida State University College of Motion Picture Arts. With a background in documentary and narrative filmmaking, Kate has a broad range of multimedia experience. When she’s not working, you can find her rock climbing, cooking or hanging out with her cat.