Mystery of the Mangroves

“Walkin’ trees” provide a nursery for a multitude of local fish and wildlife. But where will they walk to next?

Mystery of the Mangroves

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“Walkin’ trees” provide a nursery for a multitude of local fish and wildlife. But where will they walk to next?

Mystery of the Mangroves written and photographed by james phillips

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n the Florida Keys where I spent my youth, exotic plants and animals were commonplace. There were deer the size of poodles and land crabs as big as dinner plates. There were great white herons, short-tailed hawks and short-eared owls. There were sunburned trees with wood as hard as nails, and about as buoyant. The rich tapestry of oddball organisms would have given Darwin pause.

If you were into nature like my school chums and I, the Keys were their own theme park, and each day was an E-ticket ride. But nothing piqued our interest more than the woods at the edge of the sea.

The conchs and oldtimers called them “walkin’ trees,” a nickname coined by the Seminoles. Since they’re often found growing just offshore, maybe “wadin’ trees” would have been more apt. To us they were just The Mangroves, and even though we were irresistibly drawn to them the minute school let out, in retrospect I think we found them kind of unsettling – maybe even a little creepy. Perched above the waves on their spindly stilt roots, they looked like they were fixing to scuttle off the minute you turned your back.

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n the sheltered backwaters of the Indian River Lagoon, wave energy is low. The shores of the Atlantic Intracoastal are garnished with grass beds, mudflats and oyster bars. Here, as on most of the world’s tropical coastlines, mangroves predominate. They are most abundant on the landward flanks of barrier islands and in the mouths of

estuaries, forming densely interwoven stands, thriving in places where few other terrestrial plants can survive.

Seen from the water, the mangrove fringe is a featureless, undifferentiated green band into which individual trees seem to disappear. Maybe this makes them easier to take for granted, something we can’t afford to do.

Mangroves are indispensable to the health of tropical coastlines.

They provide habitat for mollusks, crustaceans, reptiles and small mammals. Their roots shelter small fish from larger predators, trap and filter out chemical pollutants, and stabilize the soil, preventing it from washing away in storm surges or boat wakes. Their canopies buffer coastal uplands against high winds.

The tangled foliage of a secluded mangrove island is prime real estate for nesting seabirds, and each spring numerous tiny, uninhabited keys are transformed into crowded, noisy rookeries.

Their greatest contribution occurs when they shed their leaves.

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Sunset on the mangrove fringe.

healthy mangrove forest rains leaves at an average annual rate of 31/2 tons per acre. The leaves are shed throughout the year, accumulating around the trees and becoming trapped among the roots. Soon they sink and decompose. The sulfursmelling ooze beneath a red mangrove is a blast furnace of biotic energy, teeming with life forms feeding and fed upon. Mangrove leaf litter sustains fungi, bacteria, protozoans, marine worms, copepods,

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amphipods, shrimp, crabs, mollusks and striped mullet. About 75 percent of the Treasure Coast’s game fish and 90 percent of its commercial fish depend on the mangroves in some way at some point in their existence.

Without mangroves, Florida’s fishing industry would be dead in the water.

Worldwide, there are more than 50 mangrove species, with the most diversity occurring in Southeast Asia, where they are thought to have originated. From there, the further one travels, the more monotypic and less diverse mangrove forests tend to be. In Florida, there are only three species of mangroves, living more or less communally. Each belongs to a different taxonomic family. Red mangroves, Rhizophora mangle, are typically found growing at, or a little above, mean sea level. Their long

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Echinaster sentus, the spiny sea star, is seen here on a red mangrove root.

Marsh rabbits are one of the many mammals that rely on the root zone of mangroves.

A young white mangrove emerges from the lagoon’s murky water.

prop roots arch into the sea like the tines of an inverted antler, providing sanctuary for young game fish and anchorage for oysters and barnacles.

Black mangroves, Avicennia germinans, colonize the upper reaches of the intertidal zone. Clusters of odd “breathing tubes,” called pnuematophores, grow from their shallow, extensive root systems, projecting from the mud like thousands of cigars.

White mangroves, Laguncularia racemosa, favor slightly higher ground, thriving in soil that’s seldom flooded except during the highest tides and storm surges. They are usually accompanied by a fourth species, Buttonwood, Conocarpus erecta, considered a “mangrove associate” because it lacks some of the characteristics of the other three.

The main thing that sets mangroves

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Black mangroves are slightly more cold-tolerant than reds and whites. They are also more widespread, with minor populations found as far north as Louisiana.

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apart from other trees is the way they handle salt. Botanists refer to them as “facultative halophytes,” meaning they tolerate salinity and grow in either fresh or saltwater. They are most common in brackish estuaries and maritime swamps, where they face less competition from less salttolerant plants. Some mangroves filter salt from their roots, while others excrete it from their leaves. Black mangrove leaves, for example, often have a crust of salt on the underside exuded by a gland near the stem.

Mangroves don’t reproduce like

most other trees. They’re viviparous, which means that, like us, they bear live young. Their seedlings, called propagules, germinate while still on the tree. The propagules of black and white mangroves are small and short-lived, but those of the red mangrove are remarkable. They’re bright green, pencil-shaped and up to a foot in length. Like torpedoes, they drop into the sea, drifting thousands of miles and remaining viable for up to a year. Eventually one end becomes waterlogged, causing the propagule to float vertically. If it comes to rest

on a tropical mudflat, wave action drills it into the sediment, where the seedling will take root.

The coastal regions of peninsular Florida and southern Texas are the only places in North America that accommodate all three mangrove species. Black mangroves are slightly more cold-tolerant than reds and whites, and are more widespread, with minor populations found as far north as Louisiana. Frost damage and low average temperatures generally result in more and smaller trees per acre. Even in the Florida

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How You Can Help

tart by educating yourself and staying informed.

Mangrove preservation involves complex water management issues. Projects that impact wellfields and rivers have major implications for mangrove wetlands. In Vero Beach, start by joining the Indian River Land Trust. For a global overview, log onto the Mangrove Action Project, or subscribe to the Mangrove Research Discussion List. Contact organizations like the Earth Island Institute, and add your name to their registry of concerned citizens. Make yourself heard; don’t be reluctant to write or e-mail legislators.

1. Don’t buy imported shrimp. Over the last decade, in countries like India and the Philippines, hundreds of thousands of acres of mangrove habitat have been lost to unregulated, fly-by-night commercial shrimp farms, playing havoc with local economies. The shrimp from these shady operations often end up on American markets.

2. Don’t pollute. Don’t fertilize your lawn just before it rains. Minimize your use of pesticides, or any toxic chemicals that could end up as storm-water runoff.

Our mangroves are only as healthy as the waters that sustain them.

3. To plant a seed is a noble deed. The next time you go down to the sea, take a moment to explore the mangroves. Keep an eye open for propagules; chances are you’ll find several, discarded by the tides. Choose one that’s green and seems viable, and stick it point first into the damp mud. A couple of inches will do fine. Plant it at, or just above, mean sea level, so that it’s sometimes wet, sometimes dry. Then go away, and come back in two or three years. With any luck, you’ll find a young and healthy tree.

In the narrow confines of a mangrove fringe, even a single tree can make a difference. But it’s a symbolic gesture, too. Think of it as casting a vote for the preservation of a habitat as fragile and lovely as it is unique. As we all know, every vote counts.

INTERNET RESOURCES:

www.irlt.org No organization in our community has done more for the preservation of mangroves than the Indian River Land Trust. By making the acquisition of lagoon-front property a priority, the Land Trust, which has preserved more than four miles of shoreline in Indian River County, is ensuring the survival of a vast number of local fish and wildlife.

Red mangrove propagules.

www.mangroverestoration.com One of three sites maintained by Robin Lewis, Florida’s foremost expert in the field of mangrove ecosystem restoration. Principles and methods are summarized here, with references to restoration projects in Florida, Puerto Rico, the U. S. Virgin Islands and Nigeria. www.fnai.org Florida Natural Areas Inventory. A comprehensive overview of Florida lands acquisitions, endangered plant and animal species, etc. www.mangroveactionproject.org The Mangrove Action Project (MAP) monitors mangrove destruction and restoration efforts worldwide. See what’s happening in Asia and South America. www.mangrovegarden.org The Mangrove Garden Foundation was created to provide charitable funding for preservation of wetland environments, for the support and maintenance of educational programs conducted in the Mangrove Gardens at Carwill Oaks, and development of its bilingual educational website.

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Red mangrove roots in a tidal flow.

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Keys, mangroves are seldom more than 40 feet tall, while in Central and South America the same species grow to 90 feet or more. Extreme weather events, like hurricanes, can also stress mangrove forests, even eradicate them completely, uprooting trees and washing away their land bases. Like all trees, mangroves need air; without a foundation of soil to keep them above the water, they drown.

Most of the mangroves remaining on the east coast of Florida are located in Indian River County, where several miles of mangrove shoreline are still unprotected. The Indian River Land Trust is working to change

that by acquiring properties such as the 111-acre Bee Gum Point and the 185-acre South Vero Conservation Land, purchased in 2011. These two properties encompass two miles of mangrove shoreline on the lagoon in Indian River County.

The devastation of a hurricane can be swift and substantial, but given time, the forest will recover. In the long-term, the effects are minimal compared to the damage done by man. Since the turn of the century, Florida has lost about 125,000 acres of mangrove forest to waterfront development. Lake Worth has lost 86 percent of its mangrove habitat, Biscayne Bay, over 82 percent; the

Indian River, from St. Lucie Inlet north to Satellite Beach, has lost 87 percent. About 469,000 acres survive statewide. According to Florida’s Department of Environmental Protection, the rate of loss has decreased in recent years, thanks mainly to tougher enforcement of the existing regulations.

The forecast? These roots are made for walkin’. As the earth warms and the oceans rise, Florida’s walkin’ trees will wander inland. Along the coast they’ll be squeezed against the steeper topography. Eventually they’ll migrate from Florida Bay into Big Cypress and the Everglades. Black mangroves, the most cold-tolerant, will lead the way north to the Panhandle and maybe even the Georgia coast. What all this will mean for our grandchildren’s children, and the world they stand to inherit, is anyone’s guess. `