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Coral Reefs on Koh Tao

Explore Koh Tao’s coral reefs with us!

When we go snorkeling or fun diving, we are often fully focused on seeing fish, and corals tend to get a raw deal in terms of appreciation of their very existence, let alone their beauty and the role they serve in the marine ecosystem. Yet the waters that surround Koh Tao are full of corals. In fact shallow coral reefs stretch all the way around our beautiful island, and although coral reefs are estimated to comprise only 0.5% of the world’s oceans, they are home to over 25% of all the world’s marine life. So we thought it was about time to give some appreciation to our amazing corals, the unsung heroes of our reefs!


What is Coral?

Many people think corals are plants, mainly due to the way they affix themselves to the ocean floor, rocky pinnacles, and in many instances, other corals too. This is not the case however, as in order to be classified as a plant they would need to produce their own food, which they do not. So corals are in fact classed as animals, and use tiny – often imperceptible to the eye – tentacles that to trap food to feed themselves. It’s often difficult for new divers to wrap their head around coral being an animal, as we are so used to the animals we are familiar with on land having very distinct features – such as limbs and faces, and more specifically mouths, eyes etc. And while they do have some of these features – let’s take mouths for example, they can be very difficult to identify. Join us on a UV Night Diving trip and it’s easier to watch coral feeding in action.


Corals live in a state of symbiosis within the marine environment, as they rely on a mutualistic relationship with a plant based algae called zooxanthellae. Coral itself is colourless, and it is the colour of the zooxanthellae living within its calcium carbonate (limestone) skeleton that provides the colours that we see. This is why in periods of high water temperatures much of the coral appears white/bleached. It’s not a case of the coral changing colour, just that the zooxanthellae can no longer survive in such a hot conditions, so has left the coral to find a cooler place to call home.


What Does Coral Do?

Well, for starters they provide food and shelter for a wide variety of marine life. None of the marine life you see on your dives with us would be there is it was not for the coral reefs, and its widely regarded that coral reefs are home to the most diverse ecosystem on the planet. Even some fish species that normally inhabit deeper areas of the open ocean use reef areas to spawn and raise their young.

Corals also offer protection for the shorelines and atolls from winds, storms and strong currents (hence the term barrier reef). Corals are so good at building structures, that it’s often hard to see where one coral ends and another begins. In fact most coral structures are comprised of several hundred thousand individual creatures, commonly known as polyps. But to us, they look as one. Corals structures form some of the largest biological masses on the planet. For example the Great Barrier Reef on the East coast of Australia can be seen from outer space.

soft-coral-koh-tao colal-polyp-koh-tao

Another role of coral is the regulation of carbon dioxide levels, something of great importance for us land lubbers, as well as to marine creatures! Corals play their role in the carbon cycle by taking calcium ions and dissolved carbon dioxide, and metabolising it into calcium carbonate to grow their hard skeletons. In layman’s terms, this essentially enables our oceans to act as a sinkhole for excess carbon dioxide in the atmosphere, as well as in the water in general, to the benefit of sea and land dwellers alike.


How Many Types of Coral are there?

There are over 2,500 different species of coral, all of which fall under 2 general classifications – hard corals and soft corals. Just under half of these are hard corals, and the others are soft corals. Unlike hard corals, soft corals have no stony skeleton, are more flexible and can bend/move in the water. However they still have calcium carbonate elements in the form of tiny skeletal parts known as sclerites.




Here on Koh Tao we have a variation of both hard and soft corals, which come in a multitude of different shapes, sizes and textures. Some are more colourful and intricate than others, making them more interesting for divers. But all play their role in the balance of the marine ecosystem. So let’s hear it for our coral reefs!

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