What is a Mangrove?
Mangroves are trees that grow in tropical and subtropical intertidal zones. These areas are tough places for plants to grow. During low tides intertidal zones are exposed to air. During high tides they’re covered by salt water. They flood frequently. The soil is poor. But mangrove trees survive and even thrive in these harsh conditions. Big groups of mangroves and other plants that live here are called mangrove swamps, mangrove forests, and sometimes simply mangal.
All Over the World
Mangroves live in more than two-thirds of the saltwater coast areas of tropical and subtropical Africa, Asia, Australia, and North and South America. They’re found only in a thin fringe right along the coast. Altogether, mangal covers 172,000 km2. That’s an area slightly larger than the state of Florida, USA.
Survival of the Few
At high tide many different animals can move in and out of the mangrove easily. Food sources also move in and out with the tide.©G.Ellis.GLOBIO.org
Not many plants can make it in the mangal. Only about one hundred plant species are found in most mangrove swamps. Some swamps are home to only one or two species! (The rain forest, on the other hand, has many thousands.) Ferns live in mangrove swamps, as well as some kinds of pine and palm trees.
Please Pass the Salt
White mangroves survive in the very salty mangrove waters because they can get rid of the salt through the glands in their leaves.©K.Campbell/GLOBIO.org
The plants that do survive have “tricks” up their sleeves called adaptations to deal with the special challenges. One of the biggest challenges is the salinity, or the amount of salt in the water. The water in a mangrove swamp is so salty it would kill most plants. But the roots of red mangroves contain a waxy substance that helps keep salt out. The salt that does get through this barrier is sent to old leaves that the trees then shed. It’s like taking the trash to the curb so the garbage truck can haul it away.
White mangrove trees have glands in their leaves that let salt pass from the inside of the tree to the outside. The leaves become speckled with white salt crystals, which is how they got their name.
Rain, Rain, DON’T Go Away!
Red mangroves are one of four mangrove species in the world. The other three mangrove species are white, black and buttonwood.©G.Ellis/GLOBIO.org
Just as mangroves can keep salt out, they have other adaptations to keep freshwater in. They can close up the pores in their leaves. They can also turn their leaves away from the sun to keep from drying out.
All of the plants found only in mangroves are woody and tree-like. They tend to be short with tough, evergreen leaves – another adaptation that keeps the moisture in.
Take a Deep Breath. Well, Try.
Lack of oxygen is a huge challenge in mangrove forests. The soil is covered with salt water every time the tide comes in. Salt water’s low oxygen level means bacteria can thrive. These bacteria free up chemicals and substances harmful to plants, like phosphates, sulfides, and methane.
So mangrove trees grow fancy systems of roots that make the trees look as if they’re growing on a bunch of stilts. The roots “breathe” through knobby holes called lenticels (LEN-tuh-sels). They take in carbon dioxide directly from the air, instead of from the soil like other plants.
Let’s Root for the Roots
Mangrove roots provide shelter for animals and supports the ground around the roots.©M.Campbell/GLOBIO.org
The tangle of mangrove roots offers safe habitats for fish, shrimp, and oysters. The roots help stop erosion by anchoring the ground and also lessening the effects of the waves. They prevent silt from damaging reefs and sea grass beds. They trapsediments that can contain dangerous heavy metals, keeping them away from inland waters and fragile animal (and human) populations.
Manatees, Monkeys and a Fishing Cat
Many different birds depend on the mangrove forest. The birds build nests on the mangrove branches every year and their chicks will do the same when they are older.©K.Campbell/GLOBIO.org
Mangrove forests are nesting grounds for hundreds of species of birds. They’re home to manatees, monkeys, turtles, fish, monitor lizards, and, in parts of Asia, the fishing cat. In Florida, mangroves shelter endangeredspecies such as hawksbill turtles, bald eagles, and American crocodiles.
Mangroves for Many Uses
Millions of people in developing parts of the world where mangroves flourish rely on the mangal for a huge portion of their daily needs. They use mangrove wood for fuel and to build boats and furniture. They use the bark for dye and medicine. They use leaves for tea and animal feed and the fruit for food. These coastal swamps protect property and lives during storms and hurricanes by acting as a buffer against the winds and waves.
Harshest Threat: Humans
Mangrove trees survive harsh natural conditions, but threats frompollution and industry are an even bigger problem. The land where mangroves live has often been sold cheaply to businesses, which cut down many of the trees. Sewage, weed-killers, and spilled oil are extremely unhealthy for the mangroves.
Red mangrove cleared to make way for human development. Many animals and plants depend on mangroves and cannot survive without them.©G.Ellis/GLOBIO.org
Human destruction of an environment can come in many forms: cutting forests, air pollution and littering. Candy wrappers and other garbage thrown into the mangrove pollute water and harm animals.©M.Campbell/GLOBIO.org
As human activity around mangroves increases, more and more mangrove forestland is lost.Dredgingcoastal areas and filling them in to make them suitable for building also leads to destruction of mangroves. Artificial dikes cause long-term flooding that the mangroves simply cannot handle. Thousands of acres have been cut down to make room for the artificial ponds required by the shrimp industry.
Even the beauty of mangrove swamps threatens them. More tourists are coming to see them, and with more tourism comes more garbage, along with air and water pollution.
A Global Rescue Mission
Mangroves do not recover quickly from severe damage. This mangrove forest in Honduras never recovered from the destruction caused by the development of a shrimp farm.©Francesco Cabras /Greenpeace
According to some experts, half of the world’s mangrove swamps have already been lost. So is all hope lost? Not at all. Environmental activists are raising awareness of mangrove swamps’ unique features and benefits around the world. They are trying to pass laws to protect mangroves, and to encourage people to stop buying shrimp grown in areas where mangroves once used to thrive.
The Mangrove Replenishment Initiative (MRI)could make a difference around the world. One of MRI’s goals is to research and develop effective ways of replanting mangrove forests. Growing these trees from seeds, from the ground up, is difficult. It’s not enough to drop seeds and hope for the best.
The Forestry and Agriculture Organization of the United Nations is also involved in studying ways to preserve mangroves. In Belize, where increased population and the construction of homes threatened mangrove swamps, an educational workshop helped to raise the residents’ awareness of the true value of the mangroves. A similar program might be introduced in Malaysia.
A local Ecuadorian woman plants red mangrove seedlings to restore the forest that had been cut down to develop an area for shrimp farming.©Clive Shirley/Greenpeace
In Florida, the Mangrove Trimming and Preservation Act makes it illegal to use poisonous chemicals in mangroves. People need a permit from the government before they can disturb mangroves in any way.
What Can You Do?
How can you do your part to save the mangroves and the rich variety of life that depends on them?
- Find out more at your local library, or go online.
- Get people interested in mangroves. (Weird trees, endangered animals, native populations in trouble—shouldn’t be too hard!)
- Don’t buy shrimp raised on former mangrove land. Be an all-around friend to the environment.
- Donate money to the Mangrove Action Project Web site TK.