The dense foliage, maze of prop roots, and rich sediments of mangroves form an important habitat for a diverse wildlife community. The animals you may find there range from microscopic invertebrates to bull gators, and from the common fiddler crab to the endangered Florida panther.
Prop roots that extend below low tide provide food, shelter and attachment surfaces for small marine creatures with out backbones (invertebrates). Some invertebrates that inhabit the submerged prop root “forest” are barnacles, sponges, oysters, snails, conches, shrimp, spiny lobsters, and crabs. Larvae of spiny lobsters may hide and feed among the prop roots for most of their juvenile life. The adults of course are a highly sought after delicacy. Other invertebrates, like the tree snails, live in the above water parts of mangroves.
Crabs are sometimes referred to as the “keystone” species of mangroves. They perform key functions that support the over all ecosystem. Two of the most important functions are stimulating the transfer of mangroves leaves to the rest of the food web and aeration of the flooded soils. While shredding and eating the mangrove leaf litter, they break it into smaller particles which are more readily colonized by bacteria and fungi. Some crabs like the mangrove tree crab reside in the canopy feeding primarily on red mangrove leaves while others live in the mud flats eating dead leaves. Crabs burrowing in the mud flats allow oxygenated water to reach deeper sediments. This helps the flooded soils to “breath” and reduces the build of toxic chemical like hydrogen sulfide and ammonium.
Fish
Many fish young fish, like tarpon and snook, are spawned offshore but spend their nursery years among the mangrove roots. Mangroves are also important nursery areas for other commercially important fish like the gray snapper, spotted sea trout, and red drum. The submerged roots of mangroves provide protection and habitat diversity and their leaves start the food web. Mangroves leaves that fall into the water feed fungi, bacteria, and protozoa that in turn feed invertebrates, and they in turn feed juvenile fish. Of course the small fish attract larger picivourous (fish eating) fish like barracuda.
Different types of mangroves support different types of fish. For example riverine mangroves may contain freshwater bass and gar, especially during the rainy season when salinities are low. Fringe mangroves have higher salinities and attract marine visitors like drum and snapper. The stagnant pools of basin mangrove are low in oxygen and support fish like the mosquito fish that can breath from surface air.
Reptiles and Amphibians
The largest reptile in North America, the American crocodile, is making its last stand in the mangroves of south Florida. There are only about 500 remaining. Hunting in the past reduced their numbers and now loss of habitat threatens to eliminate them altogether. They may live over 70 years and reach lengths over 20 feet. Fortunately, they are shy of man and mostly eat crabs, turtles, fish, raccoons, and water birds. Interestingly, red mangrove seedlings have been found in their stomachs. Crocodiles can be distinguished from alligators by their more pointed snouts, raised tail scales, long exposed teeth and they can be found in salty water. Alligators lack the salt-extracting glands of crocodiles and are unable to survive in salt water for extended periods of time.
Alligators are found in the less salty inland riverine mangroves. There they play an important part in keeping the mangrove creeks open. Where alligators have declined, the mangrove roots have grown together allowing the accumulation of debris, and many former mangrove creeks are now buttonwood stands.
Other reptiles that inhabit mangroves are the mangrove water snake, several species of anole lizards, diamondback terrapin, Atlantic ridley’s and hawksbill turtles. The hawksbill gets its name from its sharp beaklike mouth (Figure?). Because its shell is extremely valuable, the hawksbill has been hunted to the brink of extinction. The marbled plastic-like scutes, which cover its shell are the source of "tortoise shell” used in the making of jewelry, carved figurines and decorative ornaments. In the United States the hawksbill is protected under the endangered species act. But worldwide demand for the shell, meat, leather and oil contributes to its continued decline.
Few amphibians can tolerate the salty conditions of mangroves. Their porous skin allows osmosis of body fluids into the salty water and limits their ability to survive in salty environments. Osmosis occurs if two aqueous solutions of different salinity are separated by a semi-permeable membrane, like the porous skin of amphibians. Osmosis will cause water to pass through the membrane in the direction of the more concentrated solution. In other words, the salty water will suck the fresh water out of most amphibians.
Mammals
In addition to North America’s largest reptile, mangroves provide food and habitat for the Key Deer, the smallest race of North American deer. Key deer are a miniature variety of the white tailed deer and are only found on a few islands of the Florida Keys. They generally weigh less than 50 pounds and are about 2 feet tall. During the last ice age (about 15,000 years ago) many animals migrated to Florida to escape the advancing glaciers. As more of the earth’s water was frozen into glaciers sea levels dropped more than 100 feet lower than they are today. At that time the Keys were hills and Florida Bay a flat forest. When the glaciers melted and sea levels rose, the deer that remained on the Keys had to adapt to the limited resources of the small islands.
Red mangrove is an important food source for the Key deer. They can drink some brackish water but most of the population is limited to the few Keys with significant permanent fresh water sources. In 1955 there were less than 50 Key deer left. Today they are protected under the endangered species act, but there are still less than 800 key deer left in the world. Habitat loss and motor vehicles continue to threaten the remaining population.
Habitat protection is the critical for the protection of endangered species and the Key Deer National Wildlife Refuge (NWR link) was established in 1957. Most of the Refuge uplands are located on Big Pine and No Name Keys. Unfortunately, much of the refuge is interfaced with suburban and urban land uses and deer must frequently cross roads. In order to reduce their attraction to roads, feeding Key Deer is prohibited. Also a slower night time speed limit is strictly enforced.
Another endangered mammal that isn’t seen very often, but is most frequently observed near mangroves in the everglades, is the Florida panther. More common inhabitants are the bobcat, skunk, raccoon and river otter (Figures????). Two marine mammals that frequent mangroves are the bottlenose porpoise and manatee.
Birds
Mangroves provide the most elevated natural structure along much of the south Florida coast and attract over 200 species of birds. The list includes wadding birds like the herons, diving birds like the pelicans, probing birds like the stilts, ibis and birds of prey like the eagle. The elevated trunk, limbs and foliage are used for resting, roosting, and nesting. In addition, the mangrove ecosystem support and attracts many fish, snails, crabs, shrimp, crayfish, and insects that birds feed on.
Mangroves are critical nesting grounds for the brown pelican, roseate spoonbill, great blue heron, reddish heron, double crested cormorant, and Louisiana heron (tricolored heron). During drought years many of the other birds that nest in the interior wetlands of south Florida find refuge and nesting in the coastal mangroves. The opportunistic mangrove cuckoo is known to take advantage of this abundant egg supply when the parents are away from the nest.
Environmental factors and adaptations
