‘On the Edge’ with mangroves
(Editor’s Note: This is part of a series of articles by members of the Sanibel Vegetation Committee dealing with vegetative matters of concern to island residents. For the other articles in the series, visit www.mysanibel.com/Departments/Natural-Resources.)
Based on the Sanibel Land Development Code, the vegetation requirements for the city of Sanibel identifies mangroves as “vital components of the estuary” providing multiple benefits to people, fish and wildlife, as well as creating a habitat for over 80 percent of the fish and shellfish species in Southwest Florida. Mangroves benefit communities through their ability to block wind and wave energy, stabilize soils and improve water quality through uptake of nutrients. Moreover, they provide roosting and nesting sites for many wading birds and seabirds.
The history of mangroves is fascinating and there are approximately 70 species of mangroves worldwide. There are three varieties of mangroves that are native to Florida, none of which are in the same botanical family.
Probably most recognized by the arching prop roots and the drop roots coming down from the upper branches is the red mangrove (Rhizophora mangle). The seedling, referred to as a propagule, develops into a complete plant while still attached to the parent tree. When the propagule breaks free, it may drift around in the water for a year or more before anchoring in the sediments. It is the tree found closest to the water and can tolerate and thrive in varying degrees of salinity. Red mangroves are salt excluders – the salt in seawater is prevented from entering the plant at the root interface, so only freshwater enters the tree. An acre of red mangroves can shed up to three tons of leaves per year. The resulting detritus is the foundation for the food web from micro-organisms to fish to wading birds.
Black mangroves (Avicennia germinans) with their dark bark and two-toned leaves, green on top and silvery undersides, are salt extruders – the trees take in saltwater and expel salt through small openings on the surface of the leaf. As the water evaporates, salt crystals are left. Pneumatophores, pencil or straw-like projections, along the horizontal roots are like breathing tubes for the tree and conduct oxygen to the underground root system. Black mangroves are the most cold tolerant of the three species and can extend much farther into the “frost zones.”
White mangroves (Laguncularia racemosa) grow furthest upland in the mangrove fringe and do not like their “feet” to be as wet as red and black mangroves. The leaves are oval in shape, rounded at both ends, and the leaf tip has a distinguishing notch. Much like the black mangrove, the white mangrove is also a salt extruder – they take in saltwater and excrete the salt through two small glands, referred to as nectaries, on the petiole just below the leaf base. White mangroves are the least cold tolerant of the three species and tend to colonize closer to the tropics.
Destruction of mangroves worldwide has increased the vulnerability of areas to coastal storms and flooding. Threats to mangroves include development and alteration of coastlines, poor water quality from runoff and invasion by exotic plants. In Collier County, nearly 70 percent of the mangroves have been destroyed to build homes around Naples Bay. Efforts are being made to protect and manage the areas through conservation, restoration and educational opportunities regarding the value of the trees.
Florida has approximately 400,000 to 600,000 acres of mangrove fringe, which are fortunately protected under the 1996 Mangrove Trimming and Preservation Act and reinforced by city’s local ordinance (Section 38-31-38-200). Mangrove trimming and alteration is governed by the Florida Department of Environmental Protection; however, authority has been delegated to the city to regulate mangrove protections on-island.
A homeowner who wishes to trim mangroves is required notify the city. Upon notification, city staff will inspect the project area before and after trimming to ensure compliance with mangrove regulations. Mangrove trimming projects should be designed to minimize environmental impacts and protect the natural resource. To view more information about mangrove and mangrove trimming, visit www.mysanibel.com/Departments/Natural-Resources/Vegetation-Information/Mangroves. You can also contact the city’s Natural Resources Department at 239-472-3700 to discuss mangrove trimming regulations or schedule an on-site meeting.
The public’s efforts to comply with the city’s mangrove laws help guarantee the preservation of the unique native vegetation and wildlife habitat that exists on the island. Mangroves are the bridge between the land and the sea.
Where can you learn more about native plants on Sanibel? The Vegetation Committee hosts free plant walks from November through April at City Hall to view and discuss the use of native plants. Everyone and their questions are welcome – go native with the right help!
For more information, visit www.mysanibel.com/Departments/Natural-Resources or contact the Natural Resources Department at 239-472-3700. Photos of the invasive exotic plants “Worst of the Worst” and the city’s “The Alien Invasion” brochure can also be found on the website.