By Carrie Schuman, Ph.D., SCCF Coastal Resilience Manager
The following is part of a regularly occurring series that explores how building coastal resilience is interwoven with a variety of local issues and topics.
Mangrove forests that fringe and dot our local island shorelines are vibrant threads in the fabric of our ecological identity in the southern reaches of Florida. Though there are many different species of mangroves across the globe, our state is home to just three – red, black, and white mangroves (Rhizophora mangle, Avicennia germinans, and Laguncularia racemosa respectively). Besides differences in appearance, all three have contrasting environmental sweet spots, with each species tending to occur in a particular location or “zone” relative to the influence of brackish estuarine waters.
Red mangroves, with expansive tangles of arched roots, grow closest to tidal waters and are the most tolerant of dynamic wind and water conditions. Surrounded by characteristic short, slender, jutting root projections called pnuematophores, black mangroves tend to occur farther from the water’s edge. This species uses these specialized structures to access more oxygen than is often found in the mucky oxygen-poor sediments they grow in. Lastly, white mangroves have a slimmer range of tolerance for varying salinities and temperature compared to the other two and are often found furthest inland.
The mangroves common along south Florida shorelines, along with other associated species like buttonwood (Conocarpus erectus), represent an important source of coastal protection. SCCF Marine Laboratory Director Eric Milbrandt, Ph.D., recalls when Hurricane Charley came through the islands and mangroves demonstrated their ability to take a bite out of gusting winds: “SCCF has a ground-level marine laboratory behind mangroves…we didn’t lose a single roof shingle. We didn’t have any problem because we had mangroves all around us protecting us from the wind.” He also notes that research has illustrated that waves can be significantly reduced even if you only have fringing mangrove forest. For example, during the 2004 Indonesian Tsunami, Milbrandt says, “the fringe – the edge – was particularly important as far as decreasing the wave energy.” Because studies show that the majority of wave energy is reduced by the first 300 feet of mangroves that come in contact with incoming water, he says “in a lot of ways, it’s hyper-protection from waves. You really don’t need massive swaths of mangrove forests, but you do need to protect that edge to the extent you can.”
Like other nature-based resilience options, mangrove forests provide lots of additional function and value beyond guarding coastlines. Red mangrove roots support a tiny universe of colorful anemones, sponges, corals, and tunicates. Fish—including the critically endangered and federally protected smalltooth sawfish and a large percentage of Florida’s commercially important species during their earliest life stages—lurk within submerged portions of mangrove forest, stealthily hiding from predators or searching for prey. Many coastal birds nest among mangrove canopy.
Mangroves ecosystems are extraordinary at sopping up extra nutrients. However, most of these are not locked up in the biomass of the trees or shrubs themselves, but rather the sediments below that build up from the breakdown of leaf litter or the trapping of sediment introduced with the ebb and flow of tides. This translates into better nearby water quality. It also means that mangroves are a great mitigation mechanism—pulling carbon dioxide from the atmospheric pool of greenhouse gases that contribute to climate change and locking it into a more persistent reservoir.
While mangroves are invaluable to building coastal resilience and providing many socially and environmentally important co-benefits, these services are contingent upon their qualities and health. Researchers continue to hone in on characteristics like density and tree height that improve the protective capacity of mangrove forest in balance with their environmental benefits. Mangroves are also at risk from sea level rise and climate change and have limited adaptation options. These include building up underlying sediment or shifting more inland, which may be challenging in places where people have built their homes or other types of infrastructure. To foster the advantages of this integral resource, including sheltering our coastlines from wind and waves, local mangrove forests will need our consistent assistance and maintenance into the future. SCCF, along with our supporters and volunteers, have and will continue to lend that helping hand through our robust research and restoration efforts.