Schools of orange and purple fairy basslets pulse in and out of staghorn coral with the rhythm of the waves. Shafts of sunlight shimmer on tuna and trevally hovering farther off in the blue. A turtle cruises past, oblivious to the bubble-blowing divers. Fifteen metres down, this prolific reef in eastern Indonesia is more mesmerizing than any aquarium.
The Coral Triangle, the species-rich region bounded by the Philippines, Indonesia, Papua New Guinea and the Solomon Islands, has the highest marine biodiversity on earth: more than 3,000 species of fish, six of the world's seven marine turtles and nearly 600 species of hard coral – 10 times more than the Caribbean. Scientists have called the area a giant species factory, an underwater Amazon.
But the Coral Triangle is under threat. With heavily populated countries depending on its bounty, destructive practices such as dynamite fishing are common. The good news is that dozens of marine parks have been created throughout the triangle, so divers can still experience its splendour.
Bunaken National Park, in Indonesia's northern Sulawesi, was in dire straits in the 1990s. A strong management plan and an entrance-fee system helped support conservation efforts and revived its rich ecosystem. Today, Bunaken is known for its vibrant reefs and sheer underwater walls. On a dive there I swam amid Volkswagen-sized barrel sponges covered in orange and yellow feather stars throwing their tentacles into the current like bursts of fireworks. Inside the feather stars exists a microcosm of the larger reef: elegant squat lobsters, crinoid shrimps and clingfish, perfectly matching the colour of their hosts.
Further east, the reefs of Raja Ampat, in Indonesia's West Papua province, are even more spectacular. Many regard this to be the epicentre of the Coral Triangle. New species are still being discovered here, including a shark that walks on its fins. I saw a family of pygmy seahorses – barely the size of a grain of rice – on a gorgonian fan coral. They camouflaged so well I would never have spotted them without the dive master's help.
While most divers visit the Coral Triangle to see the reefs, the area is also known for the best "muck diving" in the world. On volcanic, black-sand bottoms live the weird and wonderfully cryptic creatures not found on coral reefs: harlequin ghost pipefish, devil scorpionfish, hairy frogfish and flying gurnards.
The unofficial capital of muck diving is the 12-kilometre long Lembeh Strait in northeast Sulawesi. Diving here is like a treasure hunt. After several minutes of poking around, I found a neon-orange frogfish. Fist-sized and cartoon-like in appearance, it clambered over clumps of sponge using its pectoral fins as feet. Also called an anglerfish because of the small lure on its head, the frogfish is a fish that fishes. Prey attracted to its bait is inhaled into its gaping mouth with a reflex action that takes only six-thousandths of a second. As I lay on the bottom, it cast its lure toward me. It definitely caught my attention.
IF YOU GO
What it is: The Coral Triangle is most species-rich marine environment in the world – and a place where tourism could be a force for good. Sustainable ecotourism projects and activities such as scuba diving will benefit local communities and help preserve these special reefs.
Where it is: It includes the waters of Indonesia, Malaysia, the Philippines, Papua New Guinea, Timor Leste and Solomon Islands.
How to get there: To get to Bunaken National Park, SilkAir offers direct flights from Singapore. To get to Raja Ampat, travellers must make flight connections through either Bali or Jakarta.
How to see it: Both live-aboard dive vessels and land-based dive operators are found in countries throughout the Coral Triangle. At Raja Ampat, try Kararu Dive Voyages. Rates from $320 a person a day, based on double occupancy.
Where to stay: At Bunaken National Park, try Murex Dive Resort in Manado. Room rates from $57 (€40) a person, based on double occupancy.