This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The mangroves of Biscayne Bay have been getting help from an unlikely neighbor—the seagrass meadows just offshore. Dead seagrass blades and seaweed drift loose until the tide carries them into the mangroves, where they pile up, rot slowly and then become part of the ground.
In a paper published in Estuaries and Coasts, researchers from FIU and the National Park Service found the natural buildup of soil in Biscayne Bay's mangrove forest isn't fast enough to keep pace with rising seas. But seagrass washing in from nearby meadows is helping in two ways—adding material to the forest floor and slowing decomposition, allowing more of that material to accumulate over time. The soil beneath the mangroves is rising 2 to 4 millimeters (0.08 to 0.16 inches) a year while the sea level is rising by 8.5 millimeters (0.33 inches) a year.
Seagrass alone will not close the gap, but the study shows that it makes up a much larger part of the mangroves' defense. To track this challenge, biology Ph.D. student Kevin Montenegro loaded a 16-foot (4.9-meter) canoe onto a truck before sunrise every month for two years. He would paddle an hour into Biscayne National Park and wade into the mangroves to see what washed in.
"I see mangroves and seagrass ecosystems as part of our city and community, just like streetlights, schools and businesses," Montenegro said. "They're puzzle pieces that make our community whole. If we lose mangroves, we lose a huge piece of our community and identity—but also a major part of our infrastructure." Wrack is usually studied on beaches, where researchers can walk up to it or measure it from satellite images.
But mangrove canopies are difficult to see through in satellite imagery, and mangrove forests are difficult to access on foot. For this reason, he and a field partner worked at two sites in the park, recording where wrack landed and how deep it piled at set points moving inland from the shoreline. Every few months, they collected soil samples for chemical analysis and checked mesh bags of mangrove leaves and seagrass left on the swamp floor to see how fast each broke down.
They combined this with elevation measurements the National Park Service has taken at the same sites since 2011. South Florida's mangroves are generally thought to build their soil from their own leaves, wood and roots. Chemical analysis found between 36% and 53% of the carbon near the surface came from seagrass.
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