Mangroves took a wallop from Hurricane Irma

Hurricane Irma devastated mangroves already living on the edge, according to a new study from FIU and East Carolina University.

Even the most salt-tolerant species of mangroves in the Everglades couldn’t overcome the loss of their canopy and the ponding of saltwater storm surge pushed into the bowl like areas they can live in.

Losing these mangrove forests is particularly problematic. Not only do they protect shorelines and serve as a barrier to keep storm surge from pounding too far inland, but they provide homes and breeding grounds for fish and crustaceans of important economic value to the state of Florida. And as these forests begin to break apart and die becoming ghost forests, they can no longer keep soil together so seas will more easily creep in and storm surge will move farther inland when the next storm strikes.

Irma, a monster storm that at one point threatened the entire Florida peninsula in 2017, weakened to a category 3 hurricane with winds of 120 mph and shifted its track at the last moment to spare the east coast from the worst of its winds.

That shift, while beneficial for the state’s largest population centers, proved catastrophic for certain mangroves in the southwestern Everglades.

“Black mangroves can live on the edge but once they’re physically damaged by the wind and then permanently flooded, they’re just not able to recover,” said David Lagomasino, an FIU alumnus and East Carolina University assistant professor who led the study. “In those spots where they’re living on the edge, they are the only species that can tolerate the harsh conditions, but that doesn’t mean that they’re thriving.”

Researchers tracked the devastation using a combination of data from the FIU-led Florida Coastal Everglades Long-Term Ecological Research program, East Carolina University and NASA.

“This study is important because it’s the first landscape-level assessment of mangrove die-back and recovery as a result of hurricane disturbance in Southwest Florida using state-of-the-art airborne and satellite remote sensing data,” said the study’s co-author, Edward Castañeda, a research assistant professor in FIU’s Institute of Environment.

This broad look at the storm’s effect on mangroves showed the news wasn’t all bad. Mangroves growing in Shark River estuary and other southwestern estuaries were able to recover in about a year because the flow of water in the Everglades helped them from becoming overwhelmed with stagnant saltwater.

"This pivotal study demonstrates both the value and vulnerability of coastal mangrove wetlands exposed to hurricane disturbance,” said Everglades Foundation Chief Science Officer Steve Davis. “This paper also underscores the need to advance restoration of freshwater flow through the Everglades to build resilience in our nation’s largest mangrove forest."

The study was published in the journal Nature Communications.