The rise of an atoll

Of the many intricate and incredible forms that coral reefs take, atolls are possibly the most majestic. Rising straight out of the deep ocean, these relatively tiny specs of coral attract huge amounts of marine life and make for a spectacular sight, both above and below the water.

But how did these oases in the middle of the ocean appear? What forces created them and why do they attract so much life?

While not known as his most famous discovery, it was actually Darwin who uncovered the secrets of the atolls.

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Darwin's atoll

He was puzzled by their odd formation, rising so abruptly out of the seemingly featureless ocean and always protecting a shallow lagoon. Darwin suggested that coral atolls were once part of ancient volcanoes, which are now long submerged below the waves.

His theory proposed that these old volcanoes once rose above the surface of the sea and the coral reefs that we now see were once fringing reefs on its slopes. In time, as with many old mountain chains, the volcano began to sink below the waves. This sinking process, just a few centimetres per year, was slow enough to allow the coral reef to build upon its foundations and stay in touch with the warm, shallow waters near the surface.

As the volcano continued to sink, so the coral continued growing upwards, always remaining just below the surface, but plunging down to ever deeper depths as its foundations sunk with the volcano.

Eventually, the entire volcano sunk below the waves, leaving behind a ring of coral reef surrounding a central, shallow lagoon - the crater of the volcano - and creating the coral atolls we know and love today.

While Darwin's theory has always been widely accepted, more recently scientists have looked to back the theory up with hard evidence. They drilled down in atolls in the Pacific in search of evidence of submerged volcanoes. They found exactly the evidence they were looking for, confirming Darwin's theory to be an almost word perfect account of a coral atolls' history.

Atol diagram

The gift of life

The wonderful atolls that dot the seas and oceans of Asia have some of the best diving in the world. They have exceptional visibility, coral growth is often incredible and the wealth & diversity of life they support is bewildering.

So what makes these atolls such an ideal place for marine life to flourish?

Their remote locations, well away from land, mean that the water is usually clean & clear, which results in fantastic conditions for coral growth. Plenty of coral, means plenty of places to live & hide for smaller reef life and juvenile species, which result in enormous fish populations.

Added to this, regular up-wellings of colder, nutrient-rich waters from the surrounding depths bring plenty of food, feeding corals - especially soft corals, reef life and large, plankton eating pelagics such Manta Rays & Whale Sharks. The atolls act as a refuge for Turtles on their long journeys across the seas and the healthy populations of marine life also attracts predators in great numbers- Tuna, Trevally, Rainbow Runner, Wahoo, Barracuda & often many species of Shark. The remote, difficult to reach nature of atolls have also protected them, to a certain extent at least, from over-fishing, which has helped to keep reefs pristine and marine life plentiful.

Much of South-east Asia sits on the Pacific Ring of Fire, a geologically active ring around the Pacific where tectonic plates converge. As a result, there has always been a lot of volcanic activity and there are many stunning atolls that have truly outstanding diving. Layang Layang in Malaysia is an atoll, as are Apo Reef & Tubbataha in the Philippines. You can find atolls in Wakatobi & the Togians Islands in Indonesia and also south of Papua New Guinea in the Eastern Fields.

They are truly the jewels of Asia's oceans, offering almost everything a diver could wish for - great visibility, stunning coral formations, diversity, huge numbers of fish, predators and even gentle giants. A trip to a coral atoll is a trip that will be remembered for a lifetime.