The top 10 Caribbean snorkeling parks

Coral 101
Every coral reef that snorkelers and divers enjoy — including the Caribbean’s gigantic Mesoamerican Barrier Reef, which stands as a gigantic bulwark running from the top of Mexico’s Yucatán Peninsula south through Belize, Guatemala and Honduras — has been constructed by squishy little critters called hermatypic polyps. These transparent, pencil-eraser-size Gummi Bears are born as plankton and then sink and settle onto the sea bottom, where they build a stony skeleton and begin to clone themselves. Eventually, if conditions are favorable, a single polyp can create an entire colony. But that’s far from a sure thing. Corals are the Goldilocks of the sea, in that everything has to be just right for them to flourish: not too hot, not too cold; not too shallow, not too deep; with just the right amount of sunlight, nutrients, seaweeds and other reef inhabitants.

The Caribbean Sea is so clear because it has relatively few nutrients and little plankton. Growing a complex coral reef in this setting is akin to a rainforest sprouting from a parking lot. But that’s the magic of corals, which use alchemy and a special relationship with another tiny organism to create the world’s most biodiverse ecosystem in essentially barren waters. The alchemy is the polyp’s ability to extract calcium and carbonate from the ocean and combine them into aragonite — literally changing water into stone — and using it to make a castle. The vast reefs are built from generation after generation of corals constructing layer upon layer of these minute domiciles. Corals are given invaluable help in these ambitious building projects by photosynthetic dinoflagellates called zooxan-thellae (zoh-ZAN-thell-ee), which live inside the polyps’ tissues and act as power plant, personal chef and cleanup crew all in one. The zoox use the sun’s energy and the polyps’ own wastes (as fertilizer) to provide 80 to 90 percent of the coral’s energy needs. Thus the coral is free to concentrate on laying down more stone.

In the right conditions, corals build fantastical structures that support a dizzying array of plants and animals, literally thousands of species, many of which we know nothing about. We’ve already discovered powerful painkillers, antivirals and cancer killers in reef compounds, and it’s much more likely that the reef, not the forest, is where we’ll find the next great medicines.

Coral reefs feed and support millions of people in the Caribbean region (41 million live within 5 miles of a Caribbean coastline) and provide millions more with tourism and recreation opportunities. The World Resources Institute estimates that tourism and related businesses contribute about $105 billion per year to the Caribbean economy.

When you consider that coral reefs are major contributors to the superlative white-sand beaches that are the region’s number-one draw, and that healthy reefs and their attendant fish are the sole attraction for all those who snorkel and dive, you begin to see their value. Add artisanal fishing, which employs more than 120,000 local fishermen, and the ability of the reefs to protect the shoreline (a service that’s valued at up to $2.2 billion per year), and it’s obvious that coral reefs are the Caribbean’s premier natural resource. Which is why a series of natural and man-made threats are such a grave concern: They are causing what John Ogden, director of the Florida Institute of Oceanography, calls the reefs’ “death by 1,000 cuts.”

Calling Dr. Reef
“The health of the Caribbean’s reefs was gradually declining until the early ’80s,” says John McManus, professor of marine biology and fisheries at the University of Miami’s National Center for Coral Reef Research. “Then we saw the abrupt loss of elkhorn and staghorn coral, and the diadema sea urchins began to die off.” As much as 90 percent of the spectacular branching corals — recently listed as threatened under the Endangered Species Act — died from a plague of white band disease. And beyond losing the spectacular forest quality of the underwater world, the death of these corals reduced the intricacy of the reefs. “Elkhorn is very important,” says McManus. “It forms very steep spur-and-groove formations filled with holes, and it’s that three-dimensional space that keeps the fish population alive by giving them places to hide.”

The diademas suffered their own plague and disappeared almost overnight. “These urchins are so important,” says McManus, “because they eat the algae that can overgrow corals and can out-compete young corals for space.”

The good news: The epidemics appear to be over. “In the last five years, we’re beginning to see some recovery,” reports McManus. “Populations of diademas are coming back, and we’re seeing nice regrowth of elkhorn — which is the world’s fastest-growing coral - in Belize, northern Antigua, Buck Island [USVI], Puerto Rico and Cuba.”

Gone (over)fishing
“Overfishing is a major problem common to the Caribbean, threatening 60 percent of the reefs,” says Allisandra Khorai-Vanzella, marine biologist and program officer for the United Nations Environmental Program based in Kingston, Jamaica. Populations of prized food fish like grouper and snapper have been devastated in many areas, but it’s the loss of herbivores like parrotfish and surgeonfish that more directly affect the reefs. “Think of removing the [bad] algae as cutting off a beard,” says Professor McManus. “The sea urchins are like a razor, which doesn’t work on long hair — first you need scissors to crop the hair short. The herbivores are the scissors.”

The good news: Marine Protected Areas (MPAs). “It’s getting easier to work with local communities and fishermen to create MPAs,” says Khorai-Vanzella, “because they see the results — how controlling the fishing in one place quickly leads to an increase in fish populations which then spreads outside the protected area.” Good examples of MPAs can be found in St. Lucia, Belize and the Bahamas. Unfortunately, of the Caribbean’s nearly 300 MPAs (covering some 20 percent of the total reef), only 17 are being managed effectively. “It’s still very hard to get governments to pay due attention and support the enforcement of protected areas,” says Khorai-Vanzella.

Straight flush
“Improperly treated sewage from both local populations and tourist hotels is
one of the greatest threats to coral across the region,” says Khorai-Vanzella. “The sewage causes algae to bloom and overgrow the reef [eutrophication], where overfishing has already removed many of the herbivores that could have helped to clean away the algae. The result is that corals suffer a one-two punch.”

The good news: Although less than 20 percent of the waste created in the Caribbean is currently treated, there is some light at the end of the sewer. There’s a Caribbean-wide treaty that addresses land-based pollution, including sewage and fertilizers. It’s not yet law, but fingers are crossed that it gets signed and, more importantly, that governments live up to their obligations.

Killing the golden goose
“Tourism is developing exponentially in many Caribbean countries,” says Khorai-Vanzella, who notes that reefs and fish populations suffer when hotel, golf course and cruise-ship-pier construction destroys mangroves and beach vegetation. “It’s unfortunate,” she adds, “because the main reason tourists come to the Caribbean is to enjoy the ‘pristine’ marine environment - but we are losing it very fast due to development.”

The good news: “All the governments in the region know how development should be done,” Khorai-Vanzella insists. “There is good information on best practices for land use, watershed protection and pollution control. The knowledge is there; it’s only lack of political will that prevents it from being used.”

Hot, hot, hot
“Coral reefs are the most temperature-sensitive ecosystems on earth,” says Dr. Thomas Goreau, president of the Global Coral Reef Alliance. “They will be the first lost to climate change.”

“Bleaching” is the term used when a coral polyp loses its zooxanthellae (which provide most of the coral’s color), leaving just the transparent jelly animal and its bone-white skeleton. In recent years, bleaching events have become more frequent and severe, and the primary culprit is a rise in sea-surface temperature. The last two decades have seen the 14 warmest years on record, and those Goldilocks corals that live within a very narrow band of conditions will bleach when the water temperature rises just 1 or 2 degrees above normal and stays that way for a month (or less time when it’s more than 2 degrees warmer). Without their zoox, coral polyps begin to starve and become much more sensitive to other stresses, such as hurricanes (which are getting more destructive because of the warmer sea-surface temperatures). In 2005’s severe bleaching event, up to 90 percent of the corals in some Caribbean countries were affected, and up to half of the colonies at study sites in the U.S. Virgin Islands died. Climate evidence suggests that this will only get worse.

The good news: Corals can recover from bleaching if they’re not further damaged by storms, overgrown by algae or hit by sediment, disease or pollution. “Some of the zooxanthellae remain in a colony, perhaps shaded or otherwise protected from warmer water,” says Professor McManus. “These can repopulate the coral, which may then tend to be more resistant to the next bleaching event.”

The acid test
“This is the one problem that has yet to hit the fan,” says McManus of ocean acidification, the lowering of the oceans’ pH. “It looks much more serious than bleaching. The oceans’ chemistry is changing because they’re absorbing so much of the fossil-fuel carbon we’ve been spewing.” The potential pH problems for the oceans, the food web and for us are immense. For corals, it comes down to their ability to build reefs. The more acidic the sea becomes, the less carbonate is available — eventually reaching a point where corals can’t construct a skeleton. “In 50 to 100 years,” estimates McManus, “very few places in the world will be able to support coral calcification rates that we have now.”

The good news: Depends on how much faith you have in the world quickly meeting goals to reduce carbon emissions.

The end game
With all the bad news, it’s hard for anyone who appreciates the beauty and value of the coral reef not to feel disheartened. But McManus has some encouraging words. “We’re not going to lose the ecosystem!” he says emphatically. “There’s an enormous difference between ‘coral reefs’ and ‘corals,’ and even if we do lose the corals in 100 years, it does not mean we lose the reefs, these enormous structures that were built 20,000 to 30,000 years ago. They will be beautiful, just not as beautiful as today, and they will still support tens of thousands of species.”

And rather than seeing a continual decline, McManus actually expects the health of Caribbean reefs to improve over the next 20 years. “We’ve got sea urchins coming back, the elkhorn and staghorn coming back,” he says. “Now if we can just do better at eliminating the damage we cause by pollution and overfishing, and if we offer the reefs better protection and make it socially unacceptable to damage a coral reef, then for the next 20 years, at least, we may see a coral reef renaissance.”

Caribbean Travel & Life is the magazine for anyone in search of the perfect tropical getaway. Each issue presents expert insider’s advice on where to find the Caribbean’s best beaches and attractions, its finest resorts and spas, liveliest beach bars and activities, and its friendliest people.

Don't miss these Travel stories from msnbc.com Great-value Caribbean islands  | Which Hawaii for you? Keep your vacation moments memorable Airplane part falls onto N.Y. home’s front lawn From Maori culture to Zorbing | Offbeat Auckland Photo of the Week | It’s A Snap! Cast your vote

MORE FROM TRAVEL

Travel Section Front

America’s favorite cities Southwest apologizes to mom kicked off flight Can’t-miss holiday gifts for the traveler in your life Couple accused of stealing tons of luggage What your travel agent isn't telling you Ex-cons guide tourists through Naples World’s largest cruise ship clears crucial obstacle Tips for traveling safely during flu season From L.A. to Auckland, love is in the air Pack smarter — pack like a professional Travel Section Front   Add Travel headlines to your news reader: