(CNN) — It's been said that we know more about the moon than we know about our own oceans.
That's probably total rubbish. In any case the moon is about as interesting as a cold, hard ball of rock floating around empty space.
The oceans on the other hand can captivate even the most cynical of aesthetes. But they are fragile things.
Human activities such as overfishing and pollution threaten an estimated 95% of Southeast Asia's coral reefs, says the World Resources Institute.
Climate change is also affecting them. Thailand's authorities have even been closing popular dive sites to allow them to recover from coral bleaching.
Here's a tour of 10 of Asia's most spectacular underwater dive sites, home to sharks, whales, sunfish and more -- and a glimpse at some of the threats they face.
1. Pulau Sipadan, Malaysia
Green sea turtle -- on earth for 120 million years, and counting.
Pulau Sipadan is the only oceanic island in Malaysia, and before 2002 was the subject of an intense territorial dispute between Malaysia and Indonesia. It's rated by many dive journals as one of the top dive destinations in the world.
Recently, the Malaysian government has had to clamp down on coral thieves operating around the country's coastline.
Pulau Sipadan has also fallen victim to coral bleaching in the past, a process most commonly caused by a change in sea temperature that kills the coral on reefs leaving them looking white and "bleached."
One of the island's unique features is a turtle tomb, an underwater limestone cave that features many narrow tunnels and chambers containing the remains of green sea turtles that have become trapped and drowned.
2. Similan Islands, Thailand
Clownfish -- unaffected by anemone poison, but climate change is a different matter.
A clown fish, no stranger around the Similan Islands, is familiar to younger divers as "Nemo."
The white sandy beaches, dramatic boulders and sparkling waters of the Similan Islands in the Andaman Sea are perfect for relaxing. Their remote location and marine life -- including manta rays, whale sharks, turtles and a myriad of other fish species -- also makes them a world-class diving destination.
The 11 islands of the archipelago became a protected National Park of Thailand in 1982 and are protected by strict laws.
The islands are closed from mid-May to mid-October every year during the Monsoon season as weather conditions make it dangerous to visit.
Despite the protections, the government says that local fishermen illegally fish during the monsoon season damaging the fragile coral reefs.
3. Derawan Islands, East Kalimantan, Indonesia
Stingless jellyfish -- very pretty, not at all painful.
Stingless jellyfish are some of the more unusual creatures to be found in the seas around the Derawan Islands, which consist of four inhabited islands and two uninhabited islands off the east coast of Borneo.
The jellyfish pictured here are foraging for food in Kakaban Lake on Kakaban Island.
Free from natural predators, the jellyfish lost their defense systems over thousands of years of evolution.
Being an enclosed environment however, life within Kakaban Lake is at risk from excessive human activity, such as outboard motor use.
4. Mergui Archipelago, Myanmar
Red lionfish -- sometimes considered a pest, but what a beautiful pest.
Consisting of some 800 islands, the Mergui Archipelago is a largely desolate area, tucked away from the rest of the world. Popular with exploratory divers, it offers huge boulders, caverns, tunnels and drop-offs.
As well as sharks and manta rays, a diver might encounter red lionfish (pictured). Their spectacular frills conceal venomous spines on their backs. The spines are used for defense only.
When predating, lionfish rely on their quick reflexes to swallow prey whole.
Though the Andaman Sea has escaped much of the over-development, bleaching and nutrient loading that has affected other sites around the world, trawling, longline and blast fishing have impacted fish populations here.
5. Raja Ampat Islands, Indonesia
Fusilier fish -- great baitfish, if you can catch them.
Off the northwestern tip of Indonesia's West Papua province, the Raja Ampat Islands have the highest recorded diversity of fish and coral on earth -- an amazing 537 coral species and 1,074 fish species can be found here, according to The Nature Conservancy.
To date, the islands have been relatively resistant to coral bleaching and disease. They are credited with replenishing other reefs with coral larvae.
But overfishing, pollution and urbanization of coastlines threaten the reefs. The local government is working with agencies to protect the marine ecology while also supporting local livelihoods.
Pictured are fusilier fish, a common sight around Raja Ampat. These slick fish move sweepingly in a zig-zag pattern at high speeds and apparently in perfect unison, making them a truly remarkable thing to encounter.
6. Andaman Islands, India
Ribboned sweetlips -- its coloring and pattern changes throughout its life.
The elusive ribboned sweetlips is one of the colorful inhabitants of the Andaman Islands. These fish can grow up to 50 centimeters in length. They live alone in deep water and feed on crabs, shrimps and sea snails.
Feeding is facilitated by their bright colors, which camouflages them against the corals.
To protect marine life that includes big game fish such as black marlin and sailfish, the Indian government has banned commercial fishing around the 572 islands that make up the Andaman Islands.
7. Komodo Island, Indonesia
Komodo -- with strong currents and 40-meter depths, it's best for advanced divers.
The variety of marine life around Komodo Island ranges from sunfish, mantas, dolphins and eagle rays to the fascinating pygmy seahorses, ornate ghost pipefish and blue-ringed octopus, making this one of the most diverse and vibrant dive spots on the planet.
In past years dynamite fishing and a crown of thorns infestation severely traumatized the reef system, and artificial electric reefs were introduced to help rebuild the coral.
8. Tulamben, Bali, Indonesia
A moray is among the thousands of marine species at Tulamben.
The small fishing village of Tulamben hosts one of the most popular dive sites on Bali. During World War II, a Japanese torpedo sank the USAT Liberty, a U.S. Army transport ship.
The 120-meter-long wreck is now home to a variety of fish species, such as batfish, angelfish, puffer fish and hawkfish.
Fishing is banned in the area around Tulamben and some resorts have undertaken voluntary eco-initiatives, but the number of visitors to the site -- up to 100 divers per day during peak periods -- is a potential threat.
For more information about the Tulamben Island, visit Sea Focus.
9. Kerama Islands, Okinawa, Japan
Cuttlefish -- chameleons of the sea.
The Kerama Islands are host to 76 dive sites, and are relatively well protected thanks to a local community that has embraced both its natural oceanic ecosystems and tourism.
The Akajma Marine Science Laboratory on Akajima Island (population 300) was founded in 1988 and has provided data and guidance for the whole of Japan on the conditions and best protective practices for its reef systems.
Cuttlefish (pictured) are one of the many sea species that can be seen around the islands, along with larger creatures such as humpback whales and manta rays. Despite their name, cuttlefish are not fish but molluscs, and can change color rapidly to camouflage themselves when danger is near.
10. Tubbataha Reef National Marine Park, Philippines
Hawksbill sea turtle -- better in the sea than on your arm, don't you think?
Declared a world heritage site by UNESCO in 1993, the Philippines' Tubbataha Reef National Marine Park is crawling with marine life. Sharks, turtles and reef fish can often be found congregating around the atoll.
The U.N. describes the area as "a pristine coral reef with a spectacular 100-meter perpendicular wall, extensive lagoons and two coral islands."
With shipping, marine pollution and oil exploration efforts disrupting the natural habitats, many species here are endangered.
It is hoped that a "buffer zone" around the most sensitive parts of the reef, as well as more effective enforcement of anti-littering marine laws, will enhance the longevity of many of these threatened species.
Editor's note: This article was previously published in 2011. It was reformatted and republished in 2017.