Coral

Coral are the most ubiquitous creatures you will see when recreational diving, but they are often overlooked. The coral reef is at the centre of a rich marine ecosystem which is why its conservation is of paramount importance. It's eminently worthy of our attention.

Our aim here is to tell you about the main coral types you will find around Koh Tao, and to help you identify them. As the Marinapedia gows, we'll tell you about how other marine life interacts with the coral, so when you see something happening while your diving, you'll understand what's actually happening. It makes your diving experience much more interesting when you know something about the things you see around you.

The Basics

The class Anthozoa is a group of species which contains the marine corals. Numerous corals can be found in waters surrounding Koh Tao. The many reef building species found excrete a hard exoskeleton formed of calcium carbonate (otherwise known as chalk) by colonies of coral polyps; polyps divide and grow and the reef therefore expands. Reef growth is very important for the ecology of the area.

Table Coral (Acropora hyacinthus)

Table corals are flat and like their name suggests tabular in form. They can grow up to an impressive 3 metres in diameter, but this can take decades to achieve. Their flat structure allows the coral to have a large surface area to enable maximum light exposure. Light exposure is important for the reef building corals as energy is needed for construction.

A single celled alga (zooxanthellae) lives within the cells of the coral polyps of reef building corals; this alga photosynthesizes producing organic matter, which is used by the coral for growth. This relationship between the zooxanthellae and the coral is a classic example of mutual symbiosis (a close association between two organisms); the coral benefits from the zooxanthellae by receiving extra nutrients and the zooxanthellae benefits from the coral by having a safe place to live.

The coral does however actively feed; this is achieved by the coral polyps’ stretching out tentacles in order to filter feed plankton from the water, this method usually occurs at night.

Hump Coral (Porites lobata)

Hump coral resemble a large lumpy rock, and they can grow to an imposing 6 metres in diameter, making them an extremly important reef building coral. The coral has rows of dome shaped nodules in which the coral polyps inhabit, the methods of feeding and nutrient attainment are the same as the table coral as they are both reef building corals.

Brain coral (Diploria sp.)

As the name suggests, brain coral resembles a large brain, with winding ridges and valleys and they can grow up to 1.8m in height. The polyp mouths are located in the valleys of the coral and can be extended to feed during the day, and wrapped over surface grooves for protection at night. Brain coral grows particularly slowly, but it's particularly strong, withstanding wild storms that pound other more delicate coral (such as staghorn and table varieties) to fine rubble. Their are several species of Brain coral, but all are reef builders. Brain coral can reach 200 years of age.

Mushroom Coral (Fungia scruposa)

Mushroom corals are different to those above, in that it is a single individual rather than a colony. Juvenile coral attaches itself to dead rock or coral, and in later life they become detached. The coral uses its tentacles to feed during the night, however they can also be used to turn itself the right way up if it becomes over-turned by turbulent waters.

Where will I see them?

All of the coral species above (and many more besides) can be seen at multiple sites around Koh Tao, but the best place to see all these together is between Nang Yuan Pinnacle and Japanese Gardens. We recommend taking the Nang Yuan drop-off, exploring the swim-through, then moving on to Japanese Gardens. On the way you will see large expanses of these coral, many mature and full grown, forming an eerily beautiful view that could easily be an alien landscape.

This route is suitable for all competent Open Water Divers.

Environmental Issues:

Coral Bleaching: The pure white colour of the coral results from the loss of symbiotic zooxantheallae, and can be caused by a number of natural causes including changes in sea temperature and sedimentation, but it has been increasing in both frequency and extent for the last twenty years.

'Global warming' is frequently blamed as a major contributor to this problem.

Ecosystem Imbalance: Another contributor is thought to be the removal of protective landscape features, such as mangroves, which allows a greater quantity of sediment to be washed into the sea, choking the polyps. As mangroves are often replaced by farmland, this can result in high levels of nitrates being washed into the ocean as well, cuasing an imbalance in the aquatic life that usually favours those creatures that feed on coral.

This is precisely what happened near the Great Barrier Reef, threatening the complete eradication of the largest coral reef in the world if it hadn't been addressed quickly. An explosion in the population of 'Crown of Thorns Starfish' which eat living coral tissue, resulted in coral being destroyed faster than it could grow. This is known as an 'outbreak'. Initially divers were sent down to cut the starfish into pieces, but this only resulted in the realization that these creatures have incredible regenerative capabilities, and even quite small pieces of the creature would grow to become a complete new starfish, a clone of the original. The problem became even more serious. Then one day, a diver noticed that a conch shell moved up on top of one of the starfish, and soon afterwards, the starfish broke apart. Studies went on to show that this is how the conch feeds - it injects a substance into the starfish, breaking it down into a soup that the conch consumes. Divers operators provided divers with a non-polluting chemical solution injection to kill these starfish individually: this strategy is successful, but Crown of Thorns Starfish outbreaks continue. Over 77,000 Crown of Thorns Starfish have been killed in this manner.

Ongoing conservation projects around the world are investigating means of protecting these fragile reef environments.

Tourism: Unfortunately, many tourists who dive, snorkel, or even just swim around coral reefs are unaware how their actions can affect it. Standing on it, carelessly kicking it - these thoughtless actions can break off large pieces of the coral. It can take decades for a coral to recover from just one such occurrence. But even less obviously violent actions can also be detrimental, such as touching it lightly with your fingers. The pressure might be enough to kill some species, and the proteins and bacteria (found naturally on our skin, but which are alien to this environment) can also cause massive damage.

Always follow the golden rule - don't touch! Some important new reefs that have been discovered within the last few years are being protected by keeping their locations secret and halting public access, in the belief that education is not doing enough to halt this kind of damage. Whether we ever get to see these newly discovered, pristine reefs is up to us.