Mangroves already on the move in Southwest Florida

The spidery-looking mangroves stretch about 60 feet from the seawall guarding Centennial Park in downtown Fort Myers.

The plants separate the park from the Caloosahatchee River and provide welcome greenery. But they have nowhere to move, which means they're doomed to drown in the next hundred years due to sea level rise.

"They can't move away from the water, which means they probably won't survive," said Jim Beever, principal planner for the Southwest Florida Regional Planning Council.

Mangroves are trees that are tolerant of salt water, but only to a certain extent. They will drown when seawater rises.

In the past, mangroves have dealt with sea level rise and fall through their ability to migrate and "build land" around them. However, as the rate of sea level rise accelerated during the 20th century, mangroves became less effective at building land, said Kevin Cunniff, research coordinator for Rookery Bay National Estuarine Research Reserve in an emailed response to The News-Press.

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How is everyone else dealing with sea level rise?

Mangrove wetlands provide a host of ecological benefits to Southwest Florida.

They're the primary nursery habitat for most important commercial and recreational fish species, including tarpon and grouper. In addition to serving as a food source, most of the fallen leaves from mangroves pile up beneath the roots and enable the trees to essentially create land, Cunniff said.

Mangrove loss also severely impacts estuarine food webs, reduces species diversity, and results in an overall decline in coastal/estuarine ecosystem health.

The created land serves as a barrier for coast structure, mitigating the effects of storm surge and erosion. Intact mangrove forests also capture sediments transported inland during storms, enhancing their ability to serve as land builder, he said.

The issue for many of Southwest Florida's mangroves is a lack of space. Coastal development and erosion control structures like the seawall at Centennial Park prevent the trees from migrating away from the rising seas, Beever said.

Also at issue is the rate at which sea levels rise. Mangroves and salt marshes can move when the Gulf gets higher. It's already happening across the region.

Salt marshes near Matlacha Pass, San Carlos Bay and Little Pine Island moved more than a football field inland between 1953 and 2010 due to sea level rise, according to research from the regional planning council.

Scientists have also recorded a phenomena in Pine Island Sound called "doughnut islands." These are mangrove islands with a forested interior. As sea levels have risen, the less salt-tolerant plants in the center of the island drown, leaving only the mangroves around the exterior.

"It's all a matter of time for the mangroves," Beever said. "If given the time and space these plants will adapt. If not, they'll die."

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