Know Your Neighbours: Hidden Charms of Mangroves

October-November 2002

This is an article from WaveLength Magazine, available in print in North America and globally on the web.
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by Bryan Nichols

Shallow and sunlit red mangrove roots can be completely encrusted with animals and plants. Bryan Nichols photo

What does tropical paddling mean to you? "Brochures invariably show white sandy beaches, shallow coral reefs and drooping coconut trees - our somewhat cliched northern version of paradise. At an all-inclusive resort, that may well be all the tropical ecology you see. But if you do any real paddling down south, you'll most likely find yourself in the forest.

I'm not talking about river paddling mind you - I'm talking about mangroves, the only trees capable of living in salt water. Though they rarely make the brochures, mangrove forests make up a huge portion of many tropical shorelines,particularly in the shallow areas behind coral reefs that are popular with paddlers. Believe it or not, coconut palms are not even native to the Caribbean - the groves you find everywhere were originally planted, often after the native mangrove trees had been cleared and burnt.

Do people love coconuts that much? Yes mon! And as you'll quickly discover when you paddle up close, mangroves don't have the same charm as swaying coconuts with white sand underneath. To put it mildly.

Some first impressions? Instead of white sand, picture an impenetrable tangle of roots. How about some dark, sticky muck, or maybe even no visible land at all - just roots. Don't forget bugs! Mosquitoes and biting midges might swarm you if there's no breeze. And what's that nasty, rotten eggs smell? Would you like to go "ashore" honey? Are you nuts? If the muck doesn't swallow us whole, the crocodiles lurking in all those dark nooks and crannies might.

But wait a minute. We're paddlers, not cruise shippers. We're captains of our own small, highly maneuverable boats, not grumpy passengers being ferried about by obsequious men in sailor suits. We know that some places, just like some people, need to be understood a bit better to be appreciated.

So let's talk about mangroves. To know them might not be to love them (unless you're a geeky marine botanist), but you'll find them far more interesting and appealing when you understand what makes them special.

WHAT ARE THEY

Mangroves are trees that can deal with a combination of two things that would be deadly to every other tree - salt water and flooded roots. There are essentially only three species in most of the Caribbean, but there are many more in the (much older) Pacific. Mangroves aren't necessarily closely related, and different species have different ways of dealing with salt and suffocation. We'll use the Caribbean species as examples - they likely arrived around the time of the dinosaur's demise, when Panama was open water and Pacific species could float through the gap.

The most oceanic tree is the red mangrove ( Rhizophora mangle). It can grow up from shallow salt water, blurring the line between land and sea. What looks like a forest from the air is actually more of a salt water swamp, a maze of channels and roots and short, scrubby trees. While that may not be appealing to Homo sapiens, these swamps are hugely important to a lot of other animals.

WHY SO SPECIAL?

First of all, they can be very productive. Though not too many things eat them directly, mangroves shed leaves and bark and other debris which drives an entire ecosystem of critters below. Besides just providing nutrients, this rich, convoluted region of roots becomes an ideal nursery for numerous species of fish and invertebrates, critters that grow up to become favorites on the reef - and in the restaurant.

But mangrove forests aren't just productive - they are protective as well. That maze of roots makes for the best line of defense against potential destruction from both directions. From the sea, hurricanes and cyclones would wreak far more havoc upon shorelines if much of their fury wasn't buffered by mangroves. This becomes painfully (and expensively) obvious to resorts and cities that clear all their mangroves and then get hit by one of those increasingly frequent storms.

And it works both ways - floods of freshwater, silt and pollution from land could inundate sensitive coral reefs if there weren't mangroves in between to filter the water and trap the sediment. Clearing mangroves has often resulted in rapid deterioration to invaluable offshore reefs.

UH OH

So what happens to an ecosystem that is hugely important but not well known or liked? Though the majority of tropical coastland was dominated by mangroves once, today they are probably one of the most threatened ecosystems in the world. Careless development and the recent boom in shrimp farming (which starts with a mangrove clearcut) has contributed to the loss of more than half of the world's mangrove forest, a loss which continues without celebrities complaining much.

Mangroves might be an "interesting place to visit, sure wouldn't want to live there" sort of spot, but they are essential to the healthy ecosystems that support a good tropical vacation. Check out the Mangrove Action Project (www.earthisland.org/map/index.htm) to learn more and help out. In the meantime, here are some tips for a successful visit on your next trip south.

WELCOME TO THE SWAMP

There are three ways to experience mangrove islands and swamps - land, sea and sub-aqua. Personally, I hate walking in mangroves. Speaking biologically, they can be muddy, smelly and buggy, as well as dark and full of icky things. There are occasional exceptions though, including boardwalk trails, so don't rule it out completely.

Paddling is a different story. When it seems like the wind is blowing too hard to be on the water, you can venture into the protection of a mangrove swamp and have a grand old time. Warning! Bring a compass and be careful not to get lost. Nobody charts these areas well, if at all, so you won't have a map. The islands look the same and channels through the trees can be a navigational mesh. I always feel like an explorer, winding my way through narrowing gaps hoping to find a route to the "other side". Paddling mangroves is great fun.

Finally, bring along your mask and snorkel and check out the edges. Red mangrove roots form impressive walls along channels that can be a couple meters deep - enough to swim along and explore. If there's current and clear water, there will likely be loads of life - colorful sponges and tunicates, schools of juvenile fish and all sorts of things on and in between the tangle of roots. On days when it's far too windy to dive or snorkel the reef, venture back to the mangroves to meet a different but equally fascinating cast of critters.

This issue's checklist includes a dozen things to look for on your winter vacation, so bring it along and ask the locals about a trip into the trees.

© Despite coming face to face with a gator the first time he ever snorkeled near a mangrove, biologist Bryan Nichols has since spent many a windy day paddling and drift snorkeling through channels in the mangroves off Belize.

FURTHER READING BOOK REVIEW Southeastern and Caribbean Seashores, A Peterson Field Guide. Eugene H. Kaplan Houghton Mifflin 1988 425p, $18US. ISBN 0-395-97516-6 Since hardly anyone does it, it's not easy to find a good guide to poking around in mangroves. Your best bet is probably Kaplan's excellent field guide for Florida and Caribbean seashores, which contains a chapter on mangroves as well as sections on beaches, rocky shores and turtle grass beds. Since we kayakers see these seashores up close and frequently, this is a great little book to pack along. Like all Peterson guides it's compact and stuffed with info including oodles of excellent drawings as well as black & white and color photos. The first half of the book covers the habitats, including tips on how to best experience them (written before kayaks became so popular). The second half covers critters, working its way through the myriad of weird life that lives at or just below the surface of warm southern waters. Definitely worth adding to your collection, and your drybag, for your next trip south. Complete review available at www.Wave LengthMagazine.com.

 

Checklist 27—Mangrove Mania

PROP ROOTS For sea kayakers especially, the most notable things about mangroves are the prop roots of the red mangrove ( Rhizophora mangle). On low, scrubby mangroves they form a tangle of wood that can withstand huge storms on taller mangroves they become "drop- roots" that come down from branches high above water. Under the surface, they are excellent habitat and fascinating to snorkel.

RED MANGROVE SEEDLINGS On the tree, they look like exotic tropical fruit. When they fall off they float, horizontally at first, so they drift away from the parent plant. After a day or three the root-end gets waterlogged and sinks, waiting to bump into bottom to attach to and grow. Remarkably, these little trees can drift for up to a year and still successfully "plant" themselves.

SNORKEL ROOTS Black mangrove ( Avicennia germinans) roots avoid smothering in dense mud by putting up distinctive, knobby looking pneumatophores. Looking like fingers reaching up from the mud, they surround the main trunk, radiating outward in patterns that follow the roots below. Squeeze one - they have a spongy feel because much of their tissue is airy, all the better to allow oxygen to diffuse downward.

TANNIC ACID Like our own red cedars, red mangroves contain tannin, which makes them unpalatable to most herbivores. Venture deep into mangrove swamps and the water will likely become a murky reddish brown, much like a slow moving stream or pond in the Northwest. It's best to do your snorkeling on the clearer fringes of the swamp, not the murky center.

SULFUR That nasty rotten egg smell you might experience in a mangrove swamp means that the flooded soil has lost all its oxygen. This would normally kill just about everything except bacteria which can use the sulfate in seawater instead, producing stinky hydrogen sulfide, which is also toxic to plants. Mangroves manage to survive (and be productive) using their prop roots or snorkel roots to bring oxygen down to the roots below ground, preventing them from smothering in the toxic muck.

FRIGATES & EGRETS Mangrove islands make great habitat for nesting and resting seabirds. The smaller the island, the less likely there'll be any predators, and certain islands and even specific trees can be completely covered in birds. Near shore, egrets will converge on specific trees, while farther offshore frigates, pelicans, boobies and other seabirds can easily be spotted drifting above or resting in the branches of mangroves. Kayaks are a great way to see these birds as many nesting islands are "no walking" zones.

CROCODILES Yes, there just might be crocodiles lurking in Caribbean mangroves. Though the alligator is restricted to Florida and fresh water (strays don't last long in the salt), the American crocodile (Crocodylus acutus) is fond of brackish and salty mangrove swamps. Though it gets big (rarely) to seven meters!), this species is remarkably shy and nocturnal, making sightings rare. A night paddle with a flashlight might reveal those reflective eyes, and juveniles like the one in the picture can occasionally be found in shallow pools near camp. Mangrove Mania

SPONGE (FIRE AND CHICKEN LIVER) Pop into the water and take a look at those red mangrove roots - they'll likely be covered in all sorts of things, including colorful sponges in blues, purples, reds and yes, even liver colors. Colonies of these simple, filter feeding animals use the roots as a base to feed in the passing currents. Don't touch the red ones - they're not called fire sponges because they're flammable.

TUNICATES Though they form colorful encrustations like sponges, a close look at colonies of bluebell and lightbulb tunicates will reveal they are tiny little animals with two siphons. An even closer (microscopic) look would reveal they are related to us - in Phylum Chordata.

ANEMONES Zoanthids and several species of anemone are common on and among mangrove roots, their tentacles stretching into the current to catch and consume passing animals. Though they're far to small to catch you or your boat, one or two species can give you a mild sting if you get too intimate.

FISH Fish, especially juvenile fish, love mangrove roots. Sport fishers cast along the roots hoping for bonefish, snook and even tarpon. As a paddler or snorkeler you'll likely see schools of silversides and snapper ducking for cover as you drift by. If you're lucky, you might even see rays and the occasional big barracuda.

MANATEES Everybody loves marine mammals, even when they're big and blubbery and likely less than brilliant. These large, elusive vegetarians are a Florida favorite, and in the wild they (and their Pacific relatives the dugongs) tend to roam the swampy coastlines created by mangroves. Shy and mild mannered, they can be difficult to spot - from your kayak look for a large, dark mass followed by a paddle shaped tail, or perhaps a whiskery snout rising for a breath out of murky shallows.