Mangrove near Aldabra Atoll

The Amazing Mangrove

Zegrahm Contributor|April 19, 2006|Blog Post

What plant appears to walk out and over water, grows its roots upward to "breathe," has seeds that germinate before they fall, eliminates salt from its pores, and serves as a nursery for baby tropical fish?

Why, the incredible, inter-tidal, flowering mangrove, of course! This tropical and sub-tropical tree boasts a unique adaptability that allows it to make a happy home in the harshest of conditions--a twice-daily immersion in salt water, and heavy, stinky mud without oxygen to nurture its roots.

How does the mighty mangrove do it? Among its scintillating secrets of evolutionary success:

Salt water adaptation and survival is perhaps the most amazing attribute of the mangrove. To cope, the trees either exclude or excrete salt. The exclusionary species produce a waterproof, wet-suit-like casing of thick, waxy cuticle over the leaves that sheds the salty water as it washes over them. To allow for the necessary process of photosynthesis, each leaf is equipped with a built-in breathing pore on its underside. The excretionary species have special glands under the surface of each leaf that release a concentrated brine to be rinsed away by either rain or rising tides. And other mangrove species use a leaf-shedding technique by isolating and dropping about 60 percent of their old, salt-saturated leaves every year.

Since mangrove roots cannot dig deep into the tightly-packed estuary silt in which they grow because there is no air, the tree compensates by sending thousands of "snorkels" upward along each root to reach above the mud. These pneumatophores, or "breath-carriers," bring air down to the roots in the soil during high tide. When the tide is out, small lenticles, or "port holes," in the outer surface give air to the root.

As with other flowering plants and trees, insects fertilize mangrove flowers, lured by their blended scent of tropical fruit and sweet sherry. But, mangroves do not produce a normal, standard issue tree seed at this point. Instead, young mangroves, called propagules, develop in protective, torpedo-shaped casings on the mother tree. When it is time for them to fall, they are equipped to unfold and take root quickly, in-between tides, if they find the right soil. And in case they don't fall in just the right spot, each propagule has its own three-day portable food supply and a "life-jacket" to float to some place better on the next tide.

Throughout the regions where it grows, the mangrove has long been thought of as a tangled, mosquito-infested nuisance, and tragically, more than half of the world's mangrove forests have been devastated. But its amazing ecological functions are finally being recognized and increasingly, mangroves are being protected and encouraged to grow. Currently, more than 50 species of this adaptable, life-sustaining plant rim about one fourth of the world's tropical and sub-tropical coast- line, providing soil stabilization, and breeding, spawning, hatching, and nursery grounds for many marine creatures.

Zegrahm cofounder, marine biologist, and naturalist, Jack Grove is also a resident of the Florida Keys with a special respect for mangroves: "I live surrounded by mangrove forests (mangal) and locally it is a well-known fact that during hurricanes, the tenacious roots of these plants are what keep us safe--they may even prevent our home from being sucked off its coral foundation. My real infatuation with mangroves, though, stems from my love of fishes that utilize the mangrove estuaries as nurseries. Without them, entire marine ecosystems would collapse, and shorelines could even wash away. This sad fact became obvious in the wake of the 2004 tsunami which destroyed vast portions of coastline that had been denuded of mangroves. Those areas left intact were the regions where residents and local governments had protected their mangroves."

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