[drums playing] Narrator: They are constructed from the building blocks of life.

Islands created by the forces of nature.

Geological in structure, yet inextricably linked to their biological past.

Some were assisted along the way by volcanic and tectonic upheaval, others by symbiotic relationships... But all owe their existence to a unique marine creature.

Alone, tiny in stature, but collectively, the most prolific builder the world has ever known.

These are the world's greatest coral islands.

A local legend says that a family of dragons created these fantastical islets along the coast of Northern Vietnam, spitting them out to form a protective wall to ward off seafaring invaders.

But, as romantic as this notion sounds, modern science suggests a different origin story.

Rising spectacularly from the ocean, the monolithic karsts in ha long bay have been 500 million years in the making.

Of the 2,000 islets within this 1,500-square-kilometer area, the vast majority are made of limestone, a sedimentary rock composed of the skeletal remains of marine animals, like coral.

These limestone formations began life deep beneath the sea.

Formed, layer by layer, on the seafloor by the compression of sediment under the enormous weight of the water above.

Over time, tectonic forces pushed the seafloor above the water's surface to form high mountains, which have since been eroded by the relentless whims of the wind and sea, ultimately shaping the impressive karsts we see today.

The hot and wet climate that helped sculpt the islets of ha long bay now supports the lush tropical vegetation that crowns them, including several species of flora that can only be found here.

The region experiences around two meters of annual rainfall, which has done more than nurture the endemic plant life.

Over the millennia, rain water has mixed with the nutrients provided by plants before penetrating the surface, dissolving the limestone below to carve out an intricate system of caves within the interior of many of the karsts.

The process continues today.

Each drop of water contains tiny deposits of calcite crystal, which continues to slowly shape the caverns.

But rain isn't the only architect here.

Other karsts exhibit a different group of caves.

Marine notch caves are formed by the relentless pounding of waves along the fringes of the islets, where the land meets the sea.

Many of these crevices extend through the limestone islets, serving as entrances to unexpected inland lakes which have their own creation myths associated with ancient kings, holy swords, and giant sea monsters.

In 2012, this bay area was named as one of the new 7 natural wonders of the world, and has proven extremely popular with tourists over the years.

Houseboats and kayaks are common sights in these waters, as the tourist dollar has become the mainstay for the ever-increasing number of residents.

While impromptu tourist markets frequently pop up along the shoreline, many local hawkers here opt for a more proactive approach to selling their wares.

Spanning 260 square kilometers, cat ba is the biggest island in the bay, and home to the largest population of Ha Long's residents.

Archeological evidence suggests that people have been living here for thousands of years, cultivating the rich terra rosa soils of the karst fields, as they continue to do today.

Roughly 1/3 of the island has been set aside as national park to protect its staggering biodiversity, which includes more than 1,500 species of plant, almost half of which have medicinal purposes.

In an effort to preserve its natural attributes, eco-tourism on the island supports the use of non-motorized transport.

But the island's delicate ecology hangs in the balance, as development of the southern coast threatens to greatly impact upon the region.

Commercial fishing is another major contributor to ha long bay's economy.

A number of fishing communities live in floating villages, as their forebears have done for generations, plying the surrounding waters for the almost 200 species of fish and 400 types of mollusks that reside within the bay.

But in recent years, overfishing has threatened a number of the marine species here, prompting local authorities to take steps to better preserve ha long's natural heritage.

One of the bay's stranger residents lives a largely secretive life amongst the coral reefs.

The peacock mantis shrimp is just as exotic in appearance as the monoliths above the surface.

Although it's only about 15 centimeters long, the mantis shrimp is a formidable hunter.

Its eyes are the most complex of all the world's creatures, allowing it to accurately pinpoint prey.

When a target is selected, the mantis shrimp lies in wait before unleashing a devastating blow.

With the velocity of a .22 caliber bullet, its strike is the fastest in the animal kingdom.

The crab didn't stand a chance.

Ha long bay has certainly earned its place amongst the world's natural wonders.

It's easy to see why it's historically been associated with dragons and continues to be shrouded in myth and legend today.

Forged from ancient corals, and shaped by the forces of nature over millions of years, these unique limestone islands command respect and awe.

Over the eons, many of the world's great coral islands have been formed by the perpetual growth and decay of reef systems.

But not all began life so long ago.

Redang, like all the islands off the east coast of peninsular Malaysia, was once part of the mainland, before rising sea levels set it adrift in the South China sea.

It wasn't until the last few thousand years that coral began to leave its indelible mark upon the island's fringes.

Today, coral reefs cover more than 70% of Redang's shoreline, transforming it into a gateway between the land and sea.

Situated just 45 kilometers off Malaysia's eastern coast, redang island is the largest of 9 islands that form the Redang Archipelago.

Its modest landmass, 1/10 the size of Honolulu, belies its immense value as a sanctuary for life, both in and out of the water.

Redang's lush center is dominated by tropical forests, which play host to a rather unusual resident.

Colugos spend much of the day resting high in the canopy.

Their large, bulbous eyes are better suited to seeing in the dark.

Colugos are nocturnal herbivores, feeding on fruit, leaves, and sap under the cover of darkness.

It's not just their looks that are unusual.

For a species that dwells in trees, they're not very good at climbing.

But when danger approaches, they're more than equipped to beat a hasty retreat.

Capable of gliding up to 70 meters, colugos are the most proficient of all gliding mammals, a trait that's earned it the nickname "flying lemur."

but colugos aren't the only special inhabitant of these forests.

The local people have long looked to the island's tropical interior to remedy their ailments.

The forests here are known to house several plant species with medicinal properties which can be used to relieve pain and even lower fever, helping this once-isolated community to remain self-sufficient.

Of course, the jungle can provide more than medicine.

Historically, many of the animals here were hunted for bush meat.

But today, strict laws protect not just the wildlife, but all of the region's natural resources.

Redang's earliest settlers are believed to have been mariners and traders who plied the waters between Malaysia and Thailand, often relying on this archipelago to shelter from storms.

But as the dutch established alternative trade routes in the region during the 17th century, the local people resorted to fishing as a means of livelihood.

Today, the island is populated by around 250 families, and while fishing remains an important part of life here, the island's idyllic location has shifted the mainstay of its economy towards tourism.

While it was spearfishing that drew the first travelers to the region in the 1970s, today, the rich diversity of sea life is protected within a marine sanctuary that spans the archipelago, and visitors are more likely to take aim with cameras.

Redang has become famous for its easily accessible coral gardens.

Fringing reefs line almost every inch of the island's shoreline, instantly bridging the terrestrial realm with a stunning underwater reality.

Redang is situated in a geographical region known as the coral triangle.

Spanning the western Pacific Ocean between the waters of Indonesia, Malaysia, the Solomon Islands, and the Philippines... The coral triangle is an area of immense ecological and social importance.

Otherwise known as the amazon of the seas, it's recognized as the global center of marine biodiversity... An ecosystem that's home to a greater range of marine life than anywhere else on Earth.

While covering an area of less than 2% of the planet's oceanic surface, the coral triangle supports over 75% of the world's coral species, and more than 1/3 of all reef fish species, an invaluable source of food for the global community.

It's estimated that the biological resources contained within these waters sustain the lives of over 100 million people.

The waters surrounding Redang alone are home to over 500 species of coral... Which, in turn, support and nurture over 3,000 species of fish and a huge spectrum of other marine life.

Sea cucumbers and cone shells were once valuable commodities to be exploited here, but are now safe within the sanctuary of the marine park, and since the collection of sea turtle eggs was recently banned, numbers of these majestic marine creatures are once again on the rise.

Snorkeling in these waters opens a window to another world, but those that choose to dive a little deeper are generously rewarded.

Redang is a scuba diver's paradise, a submerged playground populated by both hard and soft corals, and the wealth of marine creatures that have made them home.

Deeper waters also offer the occasional surprise, though some are larger than others.

Redang is a living, breathing island.

Built layer upon layer of previous generations, the coral reefs here not only support the myriad of life that calls them home, but the ever-expanding nature of the island itself.

The warm tropical water of the gulf of Thailand is brimming with life.

Many of the marine species found here are reliant on the region's abundant coral reefs for food, shelter, and the life-giving nutrients they provide.

Reefs are amongst the oldest ecosystems on the planet, and today continue to support more plant and animal species than any other habitat.

But what exactly are they?

With their vibrant colors, corals can often be rigid and rock-like, but they can also be soft and flowing, like a plant dancing in the current.

While corals are often mistakenly thought of as a mineral or vegetable, in reality, they are colonies of tiny animals known as polyps.

Although closely related to free-roaming jellyfish, coral polyps are sedentary creatures that can measure anywhere between a millimeter and 25 centimeters in diameter.

As they need sunlight to live, they only proliferate in shallow waters.

A reef is formed when the harder of coral species secrete a calcium carbonate outer shell as they grow, providing a skeleton upon which to expand.

When they die, their skeletons remain, leaving a platform for other corals to carry on their endless work.

This process can continue for millennia, forming vast reef systems that underpin sprawling sub-aquatic realms.

But it's not just marine life that benefits from these remarkable living structures.

Over time, as geological forces sculpt them and push them upwards, they occasionally form coral islands, giving rise to entirely new land-based ecosystems and ways of life.

The island of Ko Samui, off the eastern coast of Thailand, was born in such a fashion.

With a surface area of just under 230 square kilometers, it's Thailand's second largest island, about half the size of phuket.

The island belongs to the Chumphon Archipelago, which is comprised of over 80 other, largely uninhabited, islands in the Ang Thong National Marine Park.

It's thought that the name Ko Samui is derived from the Malay word for safe haven, as the island was first settled by fishermen from the Malaysian peninsula around 1,500 years ago.

Settlements here have changed little over time, remaining isolated, self-sufficient communities well into the 20th century... By which time its pristine natural charms began to draw a crowd.

Tourism started here with a trickle of intrepid backpackers and surfers in the 1970s.

But with the establishment of an international airport in the following decades, it wasn't long before the floodgates were opened.

Today, the tourism industry is the bedrock of Ko Samui's economy, catering to around 800,000 visitors a year.

Resorts and hotels are largely focused around the island's tropical fringes.

While the main beaches can be quite chaotic... Ko Samui is large enough to discover more secluded slices of paradise.

The waters here are calm and clear, affording privileged glimpses into the secret lives of the coral reefs that once gave rise to the island.

Composed of calcified coral sediment, the towering limestone cliffs that dominate ko samui's rugged coastline also speak to its previous life beneath the sea... Although local legends suggest some geological features here have a different origin.

Affectionately known as the grandmother and grandfather rocks, these stone formations have become somewhat of an icon of the islands' southern shore.

They are reputedly the remains of an elderly couple who, many generations ago, drowned here when their boat sank during a storm, symbolically turning into stone to promote their son's true intentions towards a would-be bride.

Whatever their story, they're unquestionably eye-catching.

Ko Samui's lush center is dominated by steamy highland jungles... Cascading waterfalls... And traditional villages.

But the most imposing feature of the north of the island is this one, rising 12 meters high and visible from several kilometers away.

The golden Buddha statue of Wat Phra Yai sits above a Buddhist monastery on its own islet.

The stairway on the approach is flanked by mythological serpents known as naga, reputedly protecting the Buddha from devils that tried to tempt him from his quest for enlightenment.

The statue's meditative pose a symbol of purity and steadfastness.

Frequented by local devotees and tourists alike, the shrine watches over Ko Samui and the surrounding islands.

To the west, the islands of Ang Thong National Marine Park are wild and rugged.

Formed beneath the water by coral debris over millions of years, their steep limestone cliffs now reach up to 400 meters above sea level and support a wealth of terrestrial life.

Most are uninhabited, covered with dense jungle, and fringed by tropical white-sand beaches.

The island of Ko Mae Ko, or mother island, conceals a secret within her interior.

Emerald Lake is so named for the striking color of its water, which is provided by a combination of fine limestone sediment within its shallow depths.

It was the hidden treasures of these islands that inspired Alex Garland's cult classic novel, "The Beach," and the hollywood blockbuster film that followed.

Ang Thong Marine Park covers over 100 square kilometers, and is recognized as an internationally significant wetland region.

The scenery above water is truly breathtaking.

But to get a real sense of the natural beauty here requires taking a deep breath and holding onto it.

The reef life here is amongst the most stunning in the world, and is best viewed by snorkeling.

It may be a tropical paradise, but for how long?

In recent years, it's been reported that this fragile ecosystem has suffered extensive coral bleaching, due to the process of global warming, and that the surrounding waters have come under increasing pressure from pollution, mainly plastic.

These islands may have been millions of years in the making, but it's only taken mankind a relatively short period to threaten life on and around them.

Once a quiet enclave, now a thriving hive of activity, the challenges facing Ko Samui and its surrounding coral islands are plentiful.

Only history will tell if this island paradise will stand the tests of time.

Lying to the southwest of Sri Lanka in the Indian Ocean is a chain of remote coral atolls... Which are as unique as they are isolated.

Although separated by great stretches of open water, 26 of these atolls share a common bond.

Collectively they form the Republic of Maldives, or simply, the Maldives, a sovereign nation with a territory spanning nearly twice the area of Washington, DC, only 1% of which is land.

With less than half a million citizens spread across its many islands, the Maldives is not only one of the world's most geographically dispersed countries, but amongst its least populous.

That fact, however, may have more to do with another of the nation's claims to fame.

The highest natural point in the Maldives is a mere 2.4 meters above sea level, which also makes it the world's lowest lying nation, and vulnerable to the whims of mother nature.

In 2004, following an earthquake in the Indian Ocean, a tsunami swept the region, laying devastating waste to many of the islands here, indiscriminately claiming life and land in its wake.

A stark reminder for the people of this tropical paradise that their idyllic home is delicately balanced between heaven and hell.

The island nation has since moved beyond the aftermath, defiantly rebuilding much of which was lost.

The atolls that make up the Maldives contain within them over 1,000 islands.

They're not like older sedimentary coral islands, which are established over eons by the compression of the calcified remains of deceased marine creatures into solid rock, before being thrust above the surface by tectonic forces.

The Maldives have been brought to life by living coral, continuously adding to the legacy of their forebears.

Of course, they have had a little help from geological processes along the way.

The Maldives sit atop an enormous underwater mountain range, which stretches for nearly 1,000 kilometers beneath the surface of the Indian Ocean.

Atolls are formed when underwater peaks, or extinct volcanoes, begin to erode and subside towards the seafloor.

As the volcano sinks, the reefs that fringe its crater are forced to grow upwards towards the sunlight they depend on for survival.

Those that grow faster than the rate of subsidence below occasionally breach the surface, often capturing a lagoon within the crater rim.

The Maldives are such prime examples of this process that the word "atoll" itself is derived from the local language here.

While some of the atolls in the chain are divided by vast distances and deep oceanic rifts, daily life in the Maldives remains quite similar across its scattered islands.

The ancestral roots of the Maldives are as far-flung as the islands themselves, with historical influences coming from Sri Lanka, India, Malaysia, and North Africa, creating a vibrant melting pot of traditions and cultures.

Maldivians have inherited a wealth of ancient folklores passed down by word of mouth from generation to generation, telling stories of great demons and spirits that inhabit the sea that surrounds them, causing mischief and mayhem.

But the most profound influence on the local belief systems came with Arabic traders in the mid-12th century, who brought with them the Islamic faith, to which the nation adheres today.

Outside the capital city, Male, the average number of residents amongst the 200 populated islands is around 300.

Fishing remains the primary industry, but tourism is increasingly becoming an important source of income for the island nation, and it's easy to see why.

Visitors arrive to this exotic location in suitable fashion, by air and sea.

But boat captains must be wary of the ever-changing conditions that define these often-unpredictable waters, in which reefs and sand bars appear and disappear with the tides.

Once safely ashore, visitors quickly discover that the long trip was worth it, as the trappings here are designed to wash away the worries of the outside world.

Many of the resorts make the most of their tropical surroundings, with some going to extreme lengths to show off the archipelago's natural treasures.

Diving amongst the many coral gardens here is big business, as this region of the Indian Ocean is particularly blessed with an abundance of marine life.

Despite suffering significant coral bleaching in recent years, the reef systems here are beginning to make a comeback, with a little help from ecologically minded communities.

Organized groups on Cocoa Island perform regular underwater cleanups to assist in the regeneration of local reefs.

The project has been a huge success, and plans to expand the process to other islands are currently underway.

Eco tourism here also helps to keep local cultures alive, as residents have found ways to incorporate traditional ways of life into the businesses that sustain them.

But paradise can be fragile, and these island communities are increasingly threatened by their tropical surrounds.

The Maldives is the lowest-lying nation on Earth with a territory consisting of 99% water, and just 1% land, leaving it vulnerable to even the slightest changes in oceanic conditions.

As sea levels are predicted to rise by nearly 60 centimeters by the year 2100, climate change poses a real danger to this nation's unique way of life, so much so that plans have been set in motion for the eventual relocation of the entire populations of several atolls.

To cater for the displaced masses, money generated from tourism has been earmarked to purchase land in Sri Lanka, India, and Australia.

Until then, the proud people of the Maldives will continue to live on the edge of reality, surrounded by the natural treasures and abundances of a tropical paradise that may one day yet give sway to the sea demons and spirits of ancient folklore, allowing them to reclaim these coral gems scattered across the ocean, relegating them to a watery grave.

Not all coral islands were created equal.

But stature isn't always measured by square mileage.

Lady Elliot Island may only cover 45 hectares, but she sits atop one of the world's most iconic natural wonders.

The great barrier reef is the largest living structure on the planet.

Situated 85 kilometers off Australia's northeastern coastline, Lady Elliot is a coral cay perched on the southernmost tip of the reef, which stretches more than 2,000 kilometers northwards through the coral sea towards the equator.

What's particularly notable about this island is that it resides within the green zone, the most highly protected area of the Great Barrier Reef Marine Park, thanks to the global significance of its unique ecosystems above and below the water... Which include the breeding and nursery grounds of seabird and marine communities that depend upon this island for survival.

Lady Elliot Island is home to more species of seabirds than any other of the reef's islands, of which there are several hundred.

During the summer breeding season, there can be in excess of 100,000 birds here.

Terns, noddies, and frigate birds jostle for prime nesting spots along the shoreline and in the trees.

Rather than overburdening the island, Lady Elliot, at least in part, owes its very existence to the presence of these seabirds.

The island first raised its head above sea level around 3 millennia ago... Little more than a loose mound of coral fragments at the mercy of the currents.

But over the next few thousand years, the droppings of the birds that found sanctuary upon this isolated raft helped to bind the sediment together, eventually hardening to form the beachrock that underpins the island today.

Lady Elliot was exploited for its deposits of guano, a valuable fertilizer, for a brief period in the 1800s.

Although short-lived, the process scarred the land, and the results were less than favorable for the bird life that depends upon it.

The miners removed the vast majority of trees and topsoil, leaving the island barren and lifeless, remaining that way for almost 100 years.

But in the 1960s, staff from the island's landmark lighthouse undertook efforts to restore the unique ecosystem to its former glory, and today, the bird life is, once again, thriving.

The 1960s also saw the construction of an air strip and the island's first accommodation.

Today, Lady Elliot is serviced by regular flights from the mainland.

The approach by air gives a true sense of the island's humble stature, but also gives a bird's-eye view of what most people come here for.

Even from the air, the Great Barrier Reef is a sight to behold.

Glass-bottomed boats afford stunning views of the reef from the water's surface.

But to truly experience the wonder of this tropical paradise requires a little more commitment.

Once immersed, the veil on this secretive realm is instantly lifted... And the marvels of one of the world's greatest natural wonders come to life, in all their splendid glory.

The water is much clearer out here, kilometers away from the australian coastline, and much cooler, too, so, there's less coral bleaching.

The living, breathing, island-building coral is healthy and abundant, and seabirds aren't the only seasonal visitors to frequent Lady Elliot.

The island is an important breeding ground for endangered sea turtles.

Green turtles spend much of their time in the water, but every few years, between november and march, they come here to nest.

Females lay a number of clutches over the season, returning to shore every couple of weeks to deposit their eggs within the warm sands along the shoreline.

The eggs remain hidden from the eyes of hungry predators for two to 3 months before the hatchlings eventually emerge and head for the open sea... Where they'll feed on sea grass, algae, and even soft coral, an appetite they share with another of the reef's inhabitants.

Bumphead parrotfish may not be the most attractive of marine species to be found in these coral gardens, but they play a pivotal role in the ecosystem.

They're so named for both the appearance and function of their biology.

Bumphead parrotfish feed primarily on coral, which, at the best of times, is no easy meal.

But they're well equipped to deal with the challenge.

Their hard parrot-like beaks are able to cut through softer coral, and if the going gets tough, they'll use those pronounced flattened foreheads to ram the reef to break off bite-sized chunks.

Once their meal is digested, the waste is expelled as fine sand.

These fish are so prolific here that they produce the majority of sand along the reef, and are, at least in part, responsible for Australia's magnificent beaches.

Life along the Great Barrier Reef is incredibly complex and interwoven.

Lady Elliot Island has become a sanctuary for all manner of seabirds and marine life.

But, at the same time, without them, she would have never existed in the first place.

Straddling the equator, fringed by the Americas on one side and the Atlantic Ocean on the other... The Caribbean is home to some of the most storied and fabled of all islands.

They've been the envy of empires, old and new, the haunt of pirates, ancient and contemporary.

Their history is inextricably intertwined with folklore, littered with characters larger than life, neither real nor fictitious, but somewhere in between.

The region, which has been described as heaven on Earth, comprises more than 700 islands, islets, reefs, and cays.

Collectively governed by the nations of Britain, America, and Puerto Rico, the Virgin Islands straddle the divide between the Caribbean Sea and the Atlantic Ocean.

Most of the islands in the chain are part of a long, volcanic arc between the continent of South America and the greater Antilles... But not all.

With a land area of just over 200 square kilometers, Saint Croix is the largest of the American Virgin Islands.

It's a coral island.

While its terrain is rugged, Saint Croix's highest point rises a modest 350 meters above sea level, paling in comparison to the mountainous volcanic islands that surround it.

Like most of the Virgin Islands, Saint Croix was originally inhabited by indigenous peoples until European invaders forced them from their land in the late middle ages.

Before the United States acquired it from Denmark in 1916, Saint Croix had been ruled by a slew of European empires, cashing in on its lucrative agricultural landscape.

To help keep up with demand for tobacco, sugar, and other plantation crops, the Danish introduced West African slaves to the island in the 1700s.

Today, the descendants of these slaves make up a large part of Saint Croix's population, and their culture is celebrated in all its forms here, evident in the local food, music, and dance.

Created to pay homage to West African spirits, Moku Jumbie is a form of stilt dancing, and not for the faint-hearted.

Saint Croix's history is also exhibited in the architecture of its two main towns, Frederiksted and Christiansted.

Surviving to this day, the fort and colonial buildings were erected under Dutch rule, as was this church, which was constructed almost entirely from the coral that dominates both the land and sea here.

Although the largest, Saint Croix isn't the only coral island in the American Virgin Islands.

Neighboring Buck Island is known to locals as the garden of nature in the Caribbean, and it's easy to see why.

The surrounding waters are crystal clear, affording spectacular views of the region's many coral reef systems, which are particularly abundant in seahorse populations.

Another of the marine parks in the area has taken the extraordinary step of creating an underwater trail along the seabed... Designed to identify the various coral species and educate visitors about conservation in the region.

But sometimes, paradise wears a darker face.

In 2017, hurricanes Irma and Maria slammed the Caribbean.

The class 5 storms were most keenly felt in the Virgin Islands, destroying buildings and the island's power grid.

In the aftermath, over 3,000 Virgin Islanders chose to emigrate to the American mainland in search of better prospects and a new life.

The Virgin Islands have since recovered... And for those that weathered the storm, the kinder face of paradise once again smiles down upon them.

The world's seas and oceans abound with islands... Both great and small.

Coral islands and the intricate reef systems that support them are more than pockets of land floating in a vast expanse of blue.

For many species, they are a bastion of life, home, sanctuary, and source of food.

For us, they are a work of living art, sustaining, life-affirming, and mesmerizingly beautiful.

But they are also vulnerable, and if we take them for granted, these delicate island-building systems may be irretrievably lost to future generations.