 | The paperbark tree (Melaleuca quinquenervia) disposes of salt by shedding its bark. © David Nance / USDA |
Mangroves dominate tropical shorelines for one simple reason: no other tree can live in seawater so successfully. Seawater contains enough salt to kill most flowering plants-yet mangroves appear to wade right into the sea. And daily flooding by the tides would drown most trees, which take up oxygen through their roots.
So how do mangroves survive?
Mangroves remove the salt from seawater, creating their own supply of nearly salt-free water.
Many mangroves filter salt out of seawater as it enters their roots. Some mangrove species remove over 90 percent of the salt in seawater this way.
Some mangrove species excrete salt through glands in their leaves. These leaves become covered with dried salt crystals and taste salty if you lick them.
A third defense used by some mangrove species is to concentrate salt in older leaves or bark. When these leaves drop to the ground, they take the salt with them.
 | Salt crystals form on the kacang-kacang (Aegiceras corniculatum), one of many mangroves that exudes salt through its leaves—an adaptation that helps it survive in saltwater. © Jan Taylor / Bruce Coleman Inc. |
Using adaptations similar to those of desert plants, mangroves store the freshwater they create in thick, succulent leaves.
A waxy surface coats the leaves of some mangrove species to seal in water. This is why many mangrove leaves look shiny.
Small hairs on the leaves of other mangrove species deflect wind and sunlight, reducing water loss through the tiny openings where gases enter and exit during photosynthesis.
On some mangroves, these tiny openings, or stoma, are sunken below the leaf's surface, which keeps them out of the drying wind and sun.
 | Many mangroves breathe oxygen through specialized root extensions called pneumatophores that rise up out of the water. © J. H. Carmichael, Jr. / Bruce Coleman Inc. |
Many mangroves breathe oxygen from the air through specialized roots that rise up out of the mud. Oxygen enters through tiny holes called lenticels. The lenticels close tightly when tides rise over them, keeping water out.
The roots of some mangrove species arch high above the water, enabling them to absorb oxygen from the air. These aerial roots give mangroves their distinctive appearance, creating a maze of spidery roots.
Other mangroves grow pencil-like roots that stick up out of the ground like snorkels. These breathing tubes, called pneumatophores, can handle daily flooding by the tides. But if they are submerged for too long-or clogged by pollution such as an oil spill-the tree will drown.
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