Masked by stinking anaerobic mud, fuggy heat, clouds of mosquitoes, and acre upon acre of flooded forest, mangroves are as mysterious as they are vital to our coasts.
Paddling south from highway 41 along the Turner River, the South Florida scenery quickly turns positively prehistoric. Schools of mullet and yard-long gar glide below my kayak, while black willows and pond-apple trees lean out from the banks of the thin, tea-colored waterway. Around a bend in the river, a dark, scaly sentinel lies warily at the water's edge; luckily my guide, David Harraden, who has been paddling these waterways for more than 30 years, and I ease past the 12-foot alligator without incident.
A few further turns and the meandering river reveals a different forest than our launch site's freshwater cypress swamp. A crazily arching latticework--the distinctive aerial prop roots of red mangrove trees--sprouts from the muck and weaves a near-impenetrable buttress comprised of boughs and branches. Harraden, an avid outdoorsman who owns an eco-hotel in nearby Everglades City, ducks into a tiny tunnel boring through the thicket, a passage that's also used by gators and river otters and serves as a flyway for belted kingfishers and egrets.
[gallery:8106|align:left|caption:GALLERY Explore more mangrove photos.]
The corridor is too narrow to paddle, so we pole and pull our way along, scattering water striders and shaking dew-covered spider webs. In the rising heat of a late spring morning, the shade provided by the mangrove forest makes things perceptibly cooler than out on the open water. This labyrinth lasts a quarter-mile, maybe longer; on such a swampy slalom course, it's impossible to know. The songs of unseen birds--the shrill whistling of ospreys, the big buzz of tiny palm warblers--fill the still air. Only shards of sunlight penetrate the ancient canopy's tangle of limbs and roots. I half-expect to see dinosaurs. Wait, that gator does count.
"It's a mystical place,'' says Harraden, in the hushed, reverential voice of someone speaking inside a cathedral. "The more you immerse yourself, the longer you stay, the more beautiful it becomes.''
Admittedly, the beauty to be found here amid the stinking anaerobic mud and fuggy heat and clouds of mosquitoes is subtle. This landscape has none of the undeniable drama seen at many other nature destinations, from the splendor of a soaring California sequoia grove to the Crayola colors of Belize's barrier reef. Yet these humble mangroves are freakishly resilient, with an ability to survive, and even thrive, in a harsh tidewater environment that would kill any other tree. A closer look at this landscape, with its flocks of wading birds and brigades of scuttling crabs, its schools of juvenile fish and gantlets of lurking alligators, only hints at their vital value as nursing, feeding, spawning, and sheltering grounds. Mangroves also stabilize coastlines, filter sediments, and mitigate storm damage.
The three different types of Florida mangroves--red, black, and white--have each developed a magic alchemy for surviving in salty, oxygen-depleted soils created from a soggy mix of sand, silt, clay, and detritus. Closest to shore--and sometimes even erupting in the midst of shallow bays--red mangroves (Rhizophora mangle) are distinguished by stiltlike prop roots that provide stability in the face of wind and tide. The roots are also pocked with small openings called lenticels through which oxygen moves into and out of the plant. Salt is expelled at the roots as well as by the leaves, which are then dropped. Black mangroves (Avicennia germinans), which typically grow on slightly higher ground than Rhizophora, feature clusters of pencil-sized aerial roots called pneumatophores that function like snorkels to supply oxygen to the plant during high tides. These trees also excrete salt in visible crystals on their leaves. White mangroves (Laguncularia racemosa), which grow above the high-tide line and usually have no need for specialized prop or air roots, have a gland at the base of each leaf that expels salt and sugar.
These adaptations are why mangroves flourish along tropical and subtropical shorelines and tidal estuaries. They grow in more than 120 countries and territories, from Indonesia, which has one-fifth of the planet's estimated 37 million remaining mangrove acres, to the tiny South Pacific island nation of Nauru, which holds just five acres. The Bengal tiger's last stronghold is also the biggest mangrove forest in the world, the Sundarbans of India and Bangladesh.
North America's most impressive mangrove forest is found along Florida's southwest coast, extending from Flamingo, at the very tip of the peninsula, all the way to Marco Island, roughly 100 miles to the northwest. Known as the Ten Thousand Islands, this maze of mangrove islets, tidal creeks, and shallow bays has long been a haven for wildlife, including large populations of wading birds and a viable population of American crocodiles, listed in Florida as a threatened species. Rumrunners and dope smugglers have also used its bewilderment to their advantage.
A handful of communities make a more legal go of it with sportfishing, airboat rides, and the public's appetite for stone crab. In this half-drowned world, boats are necessary. The vagaries of tide and weather dictate movement. Everyone is at the mercy of heat and bugs. It's a hard-knock life, even for scientists studying the biggest wilderness east of the Mississippi.
"It's not for everybody,'' says Terry Doyle, a biologist formerly with Ten Thousand Islands National Wildlife Refuge. "We haven't had any sea turtle interns that come back for a second year. One season's enough.''
The Minnesota native spent a decade at the 35,000-acre refuge after 14 years in Alaska. It comes as no surprise that he's an avid birder, with a life list thus far totaling more than 3,000 species. "There is a suite of birds found only in mangroves,'' says Doyle, ticking off the mangrove cuckoo, the black-whiskered vireo, and a subspecies of the prairie warbler. "And there are a lot of other species that use the mangroves for breeding, wintering, and migration. For some species, when they're crossing the Gulf of Mexico, it's the first habitat they fall into. It's important in terms of providing food and cover for those migrating birds.''
To better explore the refuge, Doyle has towed his government-issue, 19-foot Island skiff to Goodland, a small, mangrove-rimmed town five miles east of Marco Island with a boat ramp and a busy marina. Joined by Andy From, a Louisiana-based contractor whose company was hired by the U.S. Geological Survey, we slather on the SPF 30 and motor slowly down the channel to the Gulf, passing Coon Key, Tripod Key, and Neal Key. Admittedly, they look identical: flat, unremarkable islets entirely strangled by mangroves.
Yet this humble, hardy forest is the engine driving one of the world's rarest ecosystems while also ensuring the health and welfare of offshore habitats such as seagrass beds and coral reefs. An acre of red mangroves can annually shed more than three tons of leaves. That deadfall--the foundation of a complex food web--is quickly set upon by microorganisms like bacteria and fungi. The microorganisms are eaten by larger nematodes, worms, and shrimp. These invertebrates are then consumed by fish, which are in turn taken by wading birds, ospreys, and pelicans. Additionally, the tangle of tidal roots supports oysters, sessile barnacles, and crabs. All that structure also offers shelter from predators to scores of juvenile fish species, from mullet to Goliath grouper. "It's a huge amount of shoreline," Doyle says. "It's convoluted; it wraps around itself. Along all that shoreline is habitat for fish and so many other species.''
I first began to appreciate this fact when snorkeling a small mangrove forest in Lac Bay on Bonaire, an arid island in the Dutch Antilles famed for its healthy reef and scuba diving. With plenty of hiding places and ready food, Bonaire's mangroves form a teeming nursery filled with young reef fish like French grunt and rainbow parrotfish.
Few Americans besides fishermen have seen these forests or understand their environmental value. Mangroves can be remote and inaccessible, with limited access even by boat. Unlike iconic landscapes, such as the Serengeti or Yellowstone, these habitats harbor few beguiling terrestrial mammals. Sundarbans' tigers are an exception, but the big cats are fearsome maneaters known for assailing local woodcutters and honey collectors--so the forest is not exactly visitor friendly. "If you're given an option of diving with dolphins, snorkeling a coral reef, or walking in a mangrove swamp, what would you do?" asks Robin Lewis, a Salt Spring, Florida-based expert in tropical wetland restoration. "Mangroves are not colorful. They just don't have good PR. . . . Mangroves are a hard sell. We live and die on charismatic images.''
However, the little-known secret is those cute, postcard-perfect pictures of sea turtles and sculptural corals wouldn't happen without the grunt work done by this perceived wasteland. It is no coincidence that some of the world's best diving--Australia, Belize, Palau--takes place on barrier reefs adjacent to healthy mangrove forests.
There isn't any coral reef to speak of here, but there are acres of seagrass beds grazed by hundreds of manatees. Motoring across shallow Gullivan Bay, we spot a pod of bottlenose dolphins and several marine turtles, though we're too far away to tell if they're greens or loggerheads. Overhead an American swallow-tailed kite circles effortlessly.
Doyle consults his wristwatch--we've got an incoming tide. He opens the throttle and we scoot drug-runner style through an unmarked channel, weave through a lacework of anonymous mangrove islets, then pass Dismal Key, where author Carl Hiaasen set much of his 2006 novel, Nature Girl. I'm totally lost, while Doyle navigates by dead reckoning.
"It takes a few years,'' he says. "It was such a contrast coming from Alaska, where everything is so big, where you have mountaintops. Here it's these subtle little changes and cues. Nothing's obvious.
"I know where the bad spots are, where I've gotten stuck before,'' he adds with a grin. "Those you tend to remember.''
A few more dips and swerves and we enter Pumpkin Bay, which sparkles in the early afternoon sun. Doyle points to a nearby cluster of mangroves, perhaps a half-acre in size. One summer evening in 2000 he made a startling discovery: This unnamed island, barely the size of a suburban house lot, was an enormous roost for wading birds. He returned every month to take a census. It was always a beautiful sight: the fading sun burnishing the island, the birds shining, he says, "like Christmas tree ornaments.'' That August he could barely put down his binoculars for an hour. "It's overwhelming,'' Doyle says. "There's so much going on.''
When Doyle did finally rest, the tally was 10,224 birds--including more than 7,000 white ibises. The count from the tiny island was enough for Doyle to nominate the refuge as an Important Bird Area.
"Nobody knew about that,'' he says, "and nobody would unless they were out in the middle of the Ten Thousand Islands at sunset.''
The flocks have since moved on. While the isle is a refuge from predators, Doyle believes Pumpkin Bay's changing hydrology prompted many of the species to seek fresher water. Owing to ill-considered engineering projects like the Highway 41 causeway, failed real estate schemes, and a grid of drainage canals, the lower Everglades has been thirsting for freshwater. Without this constant flow, formerly brackish bays have become hypersaline; some freshwater marshes have been lost altogether.
Since the Comprehensive Everglades Restoration Plan was approved in 2000, a massive rescue operation has been under way throughout south Florida; canals were dammed and filled, and culverts were installed under Highway 41 to promote a greater "sheet flow" of water. This is one of the reasons we're out here now, taking readings from water level and salinity recorders installed throughout the refuge's various habitats by the USGS to gauge what would result from extensive replumbing efforts (see "Think Pink," opposite). Somehow Doyle locates the Pumpkin River channel through a bulwark of foliage and we wind our way upriver. The red mangroves all look identical, but Doyle noses the skiff's bow into the confusion. We've nearly arrived at the Mangrove West site. Dead reckoning? Try GPS.
Limbs lash at us as we clamber from the boat and gingerly hop from prop root to prop root for 50 feet until we reach the muddy mainland. Here, on semisolid ground, the trees are primarily black mangroves; the rising tide has already covered their roots, leaving only thousands of spiky pneumatophores peeking above the murky surface. The forest has opened up as well, with numerous cylindrical breaks in the canopy caused by lightning strikes.
Doyle uses a syringe to draw out water samples from various soil depths to measure salinity levels, while From downloads data and changes AA batteries on a water-level recorder. Somewhere in the woods a red-bellied woodpecker knocks out a rat-a-tat beat on a hardwood.
We repeat the routine at three more stations, including Ecotone East, a messy, muddy, quarter-mile slog from the manmade Faka Union Canal through red and black mangroves and a chest-deep slough to a marsh being swallowed by white mangroves. On our return down the waterway, we spot several manatees and a breaching spotted eagle ray. Out in the islands again, garlands of oysters gleam like a jeweler's showcase upon the red mangrove buttresses. Above the canopy an osprey tears into a freshly caught mullet. The tableau is at once raw and beautiful, but I can't stop thinking about the Swiss cheese holes drilled in the mangrove-forest canopy by lightning strikes. I ask From about evasive action in the event of an electrical storm, a common occurrence this time of year.
"Beach the boat and get as far into the mangroves as possible,'' he advises. "Pray it's not an all-day affair. And you do not want to be out in an airboat,'' referring to the craft's metal frame, which can function nicely as a lightning rod.
Naturally, the following morning we launch the refuge's airboat at the end of a one-mile track south of Highway 41. At least the rising sun, brass-brilliant as a freshly minted penny, portends a clear day. The distinctive Florida watercraft--basically a flat-bottomed launch powered by an aircraft engine--offers the best access to the eight recording stations arranged throughout wetlands that are too shallow for the skiff yet too mucky for any four-wheel-drive vehicle. We adjust sound-deadening earmuffs, and Doyle revs up the prop. Soon we're hurtling along an inches-deep channel flanked by red mangroves.
Everywhere there is a tidal waterway--bay, estuary, river, canal--within the refuge, chances are red mangroves have a foothold. In yet another ingenious adaptation, the species produces dagger-shaped seedlings that germinate while still attached to the trees; after dropping off, they can survive for months in saltwater before settling into an ooze of land or a drainage ditch. These new recruits are precocious, growing two feet their first year, producing prop roots within three, creating robust stands within a decade.
We flush tricolored and green herons as we skim across a mudflat and skip into another burgeoning gallery of red mangroves, dubbed "walking trees.'' There's no doubt that the salt-loving mangroves are making giant strides to colonize more of the Ten Thousand Islands in part because of rising salinity levels. Doyle estimates mangroves now comprise 70 percent of the refuge's land mass, encroaching on more of the marshy River of Grass every year.
While the mangroves here are on a growth spurt, worldwide they're under siege--enduring loss rates equal to or exceeding those of rainforests. According to Alfredo Quarto, executive director of the nonprofit Mangrove Action Project, more than one-third of the planet's mangroves have been destroyed in the past 30 years, felled and filled to build shrimp farms and rice paddies, marinas and seaside golf resorts, exclusive waterfront communities and coastal highways. Every year an estimated 250,000 acres of mangrove forest--equal in area to Hong Kong--vanish; in 2006 experts grimly predicted that the ecosystem could disappear within a century. Last year the International Union for Conservation of Nature warned that one-sixth of the planet's mangrove species were in danger of extinction.
Not only would that scenario devastate fisheries and wildlife, and ruin reefs and seagrass beds, it might also squander any hopes of environmental salvation. If impending sea-level-rise predictions due to global warming hold true, many mangroves will be lost, and with them will go their ability to sequester carbon (more than an estimated half-ton per acre annually). "If you had to pick a plant community we knew to hold carbon in large amounts, it would be mangroves,'' says USGS ecologist Thomas J. Smith III. "Mangroves are a drop-dead, 100 percent guarantee.''
After a circuitous, 40-minute airboat ride we approach a line of white mangroves that have migrated northward into the marsh due to changing salinity levels. There's not enough water to support the airboat anymore, so we walk the final 100 feet through sucking mud to Ecotone Center. The men make their measurements in the stultifying heat and pile back on the airboat for another thrill ride through clusters of red mangroves and across shallow, shimmering bays. Then Doyle suddenly throttles down, and the airboat glides to a stop in a watery pan swirling with fish fry. He can't resist the chance to see a bevy of birds, including short-billed dowitchers and black-necked stilts, American avocets and semipalmated plovers. He grabs his binoculars and notes field markings to From, an avid duck hunter. "This is one of the reasons work takes so long," From says with a laugh. "Terry's birdwatching.''
We linger for perhaps a quarter-hour, admiring the mixed flock, listening to a red-winged blackbird calling from a nearby hardwood hammock, a slightly elevated island in the marsh covered in cocoplum and red maple trees. All across the wetland, tiny young red mangrove recruits are sending up shoots in the shallows. Prop roots will soon follow, then trees, and finally forest. The long march will always continue for a tree that can't stand still.
For more information, visit Mangrove Action Project.