Our Magnificent Mangrove Trees

From Cedar Key, Florida south to Marco Island, into Florida Bay and north again to Indian River lagoon, the coastline is dotted with a series of very special vegetation known as mangrove trees. It is actually a forest that covers nearly 1,042 square miles of our subtropical coastal ecosystem.

Close to home the 10,000 Islands engulf 232 square miles of this fascinating habitat, giving Southwest Florida the largest mangrove forest in the western hemisphere and the third largest in the world.

Three species of mangroves comprise Florida’s vast ecosystem, being the Red, Black and White varieties. While the white mangroves are found further inland and require higher elevation, the black and red can survive directly in salt water.

The black species has thin, pencil shaped roots called pneumatophores that project upward from the soil to absorb oxygen for the remainder of the root system that is underwater or under the ground. It is less tolerant of water with a high salt content thus it is found growing just above the high tide line and/or at a bit higher

elevation where the roots have a better opportunity to take in air.

The Red Mangrove is the most common species in our area and can be easily distinguished by its root system that props the tree in place. Since they look like thin legs, they are often referred to as “walking

trees.” Multiple roots will also grow down from the branches to lend extra support to the tree and add stabilization for the soil because of the ebb and flow of tides and harsh storm conditions. Oxygen deficiency, or hypoxia, is combated by these roots and allows for direct intake of oxygen through these roots.

In addition, the Red Mangrove thrives on fresh water for nourishment.

Since our local forest lives primarily in salt water or brackish water they have a unique filter system. They are “salt excluders” which means they will absorb water through the roots but block and filter about 90% of salt right at the root system. The small amount of salt that enters the tree is directed to the oldest leaves, known as “sacrificial leaves” and they will absorb that salt and fall from the tree. They are often yellow in color on the branches.

Their seed, or propagule, is shaped like a string bean or cigar. They germinate on the tree, then fall to the water where they might take root at the base of the existing trees, or they might be carried by the tides and develop in a suitable habitat.

The root structure provides a home and/or feeding opportunity for a variety of fish, crustaceans and other marine life. The old leaves that fell from the tree now become food for the area microorganisms which in turn are eaten by shrimp, crabs and small fish. This will attract larger fish and even mammals, such as dolphins, which thrive on the buffet offered by these islands.

In spring several shark species will also use the mangrove islands. The offspring (pups) of some female sharks are not big enough to survive on the larger food sources offshore so they will patrol the mangroves for smaller morsels until they are big enough to live elsewhere.

Birds will utilize the mangroves as nesting areas as well. Usually in May of each year, you will see the white heads of baby Brown Pelicans popping up. Great Egrets and other avian species also use these islands for nesting as well.

For us humans the mangrove islands are the first line of defense against bad weather. As tropical storms and hurricanes approach our coast these trees are the first to feel their wrath, slowing down the surge and adding protection to the mainland.

In summary, these barrier mangrove islands are of utmost importance as they establish the basis for the wildlife that we enjoy here. From the crabs, fish, sharks and marine mammals of the waters to the variety of birds that call these islands home, they are critical to the habitat that we roam. Take a look at them - closely. You never know what you might see!

Bob is the Lead Naturalist for the 10,000 Island Dolphin Study Program on board the Dolphin Explorer. He is the author of two books, a two-time award-winning columnist for Coastal Breeze News and a regular speaker at area venues. Bob loves his wife very much!