A Blue View: Floating Forests

Published April 07, 2015

by John Racanelli, Chief Executive Officer

Elegantly tangled at the ocean’s edge, mangroves provide a protective home for a variety of animals. These floating forests use bacteria to break down organic matter and energy from fallen leaves and branches, releasing important nutrients into the water.

Mangrove forests are rich hubs of biodiversity, supporting a unique ecosystem of bacteria, plants, mammals, amphibians, invertebrates and birds! The largest mangrove forest on Earth—the Sundarbans of India and Bangladesh—is home to at least 250 species of birds, endangered estuarine crocodiles and even the occasional Bengal tiger.

In North America, mangroves are found throughout the Gulf Coast, from Florida to Texas. One typical resident of these mangroves is the beautiful scarlet ibis. Its long, curved bill allows the ibis to easily pluck a meal out of the knobby network of forest roots.

Scarlet Ibis

The scarlet ibis is just one of many animals threatened in some areas due to habitat destruction—more than half of the world’s mangrove forests have been destroyed in the past 30 to 40 years for commercial purposes, such as shrimp farming, agriculture and coastal development.

Conservationists are struggling to find ways to protect these environments by restoring damaged mangrove forests and establishing more marine reserves in mangrove-lined coastlines.

Interested in supporting mangrove conservation worldwide? Click Here.

Episode Transcript

Gardeners in Maryland know that most trees in our temperate climate don't like having wet feet. And water that's salty? Forget about it. Around here, having tree roots submerged in saltwater is guaranteed to kill off your landscaping. But far south of the Chesapeake, fringing tropical and subtropical coastlines, there exist floating forests of mangroves, whose roots grow in a luxuriant tangle at the ocean’s edge. And there, they thrive.

Botanists call the 50 species of mangroves halophylic, or "salt loving." Mangroves have adapted to putting down roots where other plants can't: in areas inundated daily by the tide; in thin, nutrient-poor, low-oxygen soils; and in water that varies from fresh to brackish to salty.

Just how much salt can mangroves tolerate? Well, typical seawater has a salinity of 35 parts per thousand; in other words, about 35 grams of salt for every liter of sea water. Some species of mangroves can survive in salinities of more than 90 parts per thousand!

To thrive in this salty abundance, these plants need strategies to clear the excess salt. Some species excrete it through glands in their leaves. Others use their roots. Another adaptation of some mangroves is the ability to live in anoxic soil by "breathing" through pneumatophores, specialized roots that grow up instead of down, rising from the muddy substrate above the water like thick fingers. The weird, knobby roots of mangroves actually make traveling to paradise for a tropical vacation possible—tough, woody evergreen mangroves stabilize the soil and prevent many islands from simply washing away.

Thank the mangroves, too, for the colorful diversity of fish and invertebrates you see on your next coral reef dive. Many oceanic and coral reef fish—including snapper, tarpon and lobster—spawn in the nursery provided by the mangrove’s submerged tangle of roots.

A mangrove forest is a rich hub of biodiversity, supporting a unique ecosystem of bacteria, plants, mammals, amphibians, invertebrates and birds—some found nowhere else.

Earth’s largest mangrove forest—the Sunderbans of India and Bangladesh—is a UNESCO World Heritage Site, home to at least 250 species of birds, endangered estuarine crocodiles and even Bengal tigers.

In North America, mangrove swamps are found throughout the Gulf Coast, from Florida to Texas. The largest mangrove forest in the United States is in Florida’s aptly named Ten Thousand Islands National Wildlife Refuge. This special place is home to many endangered species, including West Indian Manatees, and clouds of scarlet ibis and white pelicans.

Although mangrove forests host so-called “charismatic megafauna” like manatees and tigers, truly their greatest treasure may be the thick mud of mangrove leaf litter—fertile with bacteria and fungi—that accumulates in the water below the trees. There, detritivores, like crabs and other animals, feed on decaying leaf litter and contribute to a complex food web that begins, literally, in the mud.

Other microfauna encrust the mangrove's submerged roots, including a profusion of filter feeding mussels and barnacles. Like Chesapeake’s oysters, mangrove barnacles efficiently filter pollutants from the water.

These crustaceans and mollusks in turn support populations of shrimp and fish that are economically important to Gulf of Mexico fisheries. So, the next time you’re dining on sustainably caught shrimp, take a moment to thank a mangrove for your meal.

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John Racanelli

Chief Executive Officer

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