A coral reef is like an oasis in a vast, endless desert. The tropical sea is low in nutrients and has little shelter from the ravages of the seas and unrelenting predators, not to mention the endless miles of driftnets. On the contrary, the coral reef is teeming with life. It is a formidable fortress that resists the constant pounding of the waves and currents to provide shelter filled with nooks and crannies for its motley of inhabitants to hide from their predators. Records from fossil findings and carbon dating show that the reef system dates back at least 2 billion years ago and is deemed the oldest ecosystem in the world with complex animal and plant relationships that only the tropical rainforest can rival. With such long history, it's amazing the reefs could have survived so many catastrophes that the world has known. Considering the coral reefs are the oceans' barometers and are extremely sensitive to - weather pattern changes (the optimum temperature for
these reefs to survive and flourish is between 25 and 29 degrees), - pollution washed into the sea from the land, - heavy sedimentation from flooding that flows down from the lands covering the corals or changing the salinity levels of the waters. Large areas of coral reefs can perish from such changes to their environment.
But each time, the reefs bounced back from their states of disrepair to form new colonies and a more diverse collection of species. But remember all this happened over hundreds of millions of years and not just in our lifetime. Changes are slow and the evolutionary process is as much trial and error as persistence -help conserve what nature has already taken 2 billion years to perfect and imagine, in our short time revelling in the (mis)fortunes of the industrial revolution and the new markets etc…we are successfully breaking up the equilibrium of the Earth's momentum and relinquishing our children's' future.
How does a coral reef form?
So then, how does it all happen? How does the first seed of life grow in this great, piece of desert under the sea? It all starts with a relationship and a simple, multicellular animal called the coral polyp. The coral polyp produces a stony skeleton from calcium particles extracted from the water. As they reproduce, they form colonies that link together to form a skeleton coral base that weigh many tonnes and can sometimes stretch for miles. The older generation dies and the new generations grow over the old layers of skeletons and so on, building and creating vast coral reefs. But the polyps grow very slowly and if on its own, they cannot build large coral reefs. Polyps are, after all animals and they do not create food but rather consume it. To be productive reef builders, the polyps sets up a symbiotic relationship with tiny, yellow-brown plants known as zooxanthellae. These plants are algae and they live inside the polyps giving the corals that familiar dull yellow, green and brown tint. These zooxanthellae pick up carbon and phosphates dissolved in the water and convert them, via photosynthesis into oxygen and various organic compounds like sugars and amino acids. The polyps then convert these into proteins, fats and carbohydrates. The zooxanthellae also consume the polyps' waste products like carbon dioxide and ammonia and recycles them, creating fresh oxygen and food from them. The algae may provide as much as 98% of the polyp's nutrients.
As plants, zooxanthellae need sunlight for photosynthesis. This is why most corals are located in shallow, clear tropical or semitropical waters. which means that the most exuberant reef corals are found in the shallow areas not more than 75feet. The zooxanthellae also enhance skeleton growth, which therefore increases the growth rate of the coral reef. The algae convert the calcium particles extracted from the surrounding water into calcium carbonate (similar to limestone). This calcification process with the aid of the algae has a growth rate of 14 times faster in sunlight than during the night. Such symbiotic relationship is important to the growth of the coral reef… of which without, the coral reefs we see now would not even exist in such wonderful variations. This is the basis of the food structure in the coral reefs and this is now the seed is sown.
However, not all corals are reliant on these algae for food and growth. The ones that are have dull greenish or brownish corals, adopting the colour of the algae itself whilst those that do not rely on zooxanthellae are vibrantly coloured like the Dendronephthya.
There are approximately 500 species of corals to be found in the Indo-Pacific regions and about 70% of the total species live on coral reefs in Southeast Asia and Australia.
Hard Corals
Hard corals are the reef builders. Many of these have created symbiotic relationships with tiny yellow brown plants called zooxanthellae. As discussed earlier the algae processes almost all the nutrients that the coral polyps need in return for a home and also by-products received from the polyps are taken in by the algae for photosynthesis. Most hard corals depend on the sunlight for optimal growth and that's why we find the greatest variety of hard corals closer to the surface. Corals found in deeper waters do not rely on the zooxanthellae for food. Instead they 'fish' for their food, utilising their stinging cells to capture planktonic prey.
These corals are made up of colonies consisting of many individual polyps. These polyps secrete calcerous skeletons around them they retreat into, leaving only a ring of six or a multiple of 6 tentacles flagellating around the mouth opening. Each tentacle is equipped with a toxin filled, hair-like stinging cell called nematocyst. As the zooplankton touches the tentacles, it triggers a series of poisonous explosions, stunning the prey before it is whipped into the mouth. Some polyps also produce sticky threads of mucus to entrap the zooplankton. These threads of mucus are extruded from the linings of its stomach or from the edges of its mouth, used to entangle the hapless prey as it floats pass.
Most hard corals feed during the night and on night dives, one can witness a complete transformation of the coral reef. The entire coral reef seems to be swaying with the motion of the sea like the autumn forest with leaves of various hues waving in the autumn breeze.
Those that feed day and night rely on their tentacles and their mucus strands to feed.
Polyps can reproduce by regenerating from broken pieces of sufficient size. Soft tissues begin to grow at the line of breakage, secreting calcium carbonate for the new base. This occurs a few weeks after detachment. However, polyps also reproduce sexually. The eggs and sperms develop within the stomach walls of the polyp. The sperm is released into the water through the mouth and are drawn into neighbouring polyps, using its vacuum system created by the beating cilia in the polyp. The eggs fertilise and develop internally and leave at the swimming larval stage. The release of the larvae depends largely on the species and the region but it occurs in lunar cycles and with seasonalities. The larvae will float around for a few days or weeks and those that survive will settle on hard surfaces to found their own colonies, sometimes miles from its origin.
Staghorn Coral (Agropora formosa) - 300cm wide
These corals flourish in still waters of lagoons or deeper sections of fringing reefs. They are very common in our coral reefs and unfortunately, one can find many dead, bleached staghorns strewn on the beaches and shallow waters around popular holiday destination islands. About 70-80 species of the 100 known Acropora species is found in our region.
Montipora Coral (Montipora sp) - 200cm wide
This is the second largest group of corals found on Southeast Asian reefs with habitats ranging from silty, coastal lagoons to the clear water reef fringes. This species is relatively difficult to identify with various forms such as table, branching and encrusting all in one species.
Warty Coral (Pocillopora verrucosa) - 30cm
This coral can be found in various habitats from strong wave exposed outer reef to the fringing coastal reefs. Warty because of the numerous wart-like growths covers the surface.
Creamy Coral (Stylophora pistillata) - 200cm wide
Creamy corals are found in large colonies, sometimes creating large garden patches on the upper reaches of the outer reef slopes. They are recognisable from the thick branches with smooth, creamy texture. They are also found in shades of grey, pink, green or blue.
Lobate Coral (Pories lobata) - 150cm height
This coral is common in lagoons and coastal reefs or on the outer reefs. The ones found at Pulau Lima, off Pulau Redang has impressive structures of these porites. The largest specimens found grow to heights of 6m and are estimated to be over 800 years old! The colours tend to range from cream to khaki or green but in shallower waters the porites may be bright blue or purple coloured. Massive corals such as porites, monastrea and pocillopora have flat tops with its centre bald or killed off by siltation or regular exposure to low tides
Mushroom Coral (Fungia scutaria) - 18cm
This coral is flat and oval-shaped and varies in colour but is usually green or yellowish. This coral is not attached to any hard surfaces and are often found rocking and tossing on the sandy bottom or rubble areas. they are generally solitary, different from the other corals. They look as though they have been discarded especially when knocked upside down be wave actions but they are very much alive. Fleshy tentacles can be seen protruding from the gill like skeleton. They are able to move around, using these tentacles to aid them and can even extract themselves from under sand if buried.
Table Coral (Acropora hyacinthus) - 150cm wide
This is extremely common found growing on the upper edge of reef flats and outer reefs. They extend out like a flat plate and are seen to shelter a variety of fishes underneath, especially groupers. The large colonies are usually cream coloured or greenish brown and quite often the edges seem to have been bleached. But the growing tips are coloured pink or purplish. This is a sort of pigmentation that protects the young polyps from the u-v light.
Flower Coral (Alveopora fenestrata) - 8cm wide
This looks like a soft coral but it the polyps on long, fleshy stalks, which gave it its namesake is connected to a hard coral skeleton. The polyp has 12 tentacles surrounding its mouth. This coral can withstand turbid waters, sometimes found in back reef channels and on outer reefs.
Tentacle Coral (Goniospora sp) - 30cm high
Like the Flower coral, its stalked polyps are attached at the base to a hard coral skeleton. This coral is also common in turbid waters of coastal reefs and lagoons. This can be differentiated form the Alveopora where the Goniospora has 24 tentacles ringed round the polyp's mouth instead of 12 found in the former. The Tentacle coral is extremely aggressive towards other corals and can be seen whipping its tentacles around to prevent other coral species from encroaching its territory.
Cellular Coral (Lobophyllia hemprichii) - 300cm
Found in sprawling colonies in upper reaches of reef slopes, they are usually grey, brown or green in colour. They can be distinguished from the ridged margins that separate one colony from the other.
Dome Coral(Diploastrea heliopora) - 50cm high
This coral is often mistaken for huge boulders in shallow waters where snorkellers would take their rests on. This rounded mounds have neatly arranged polyps on the surface and are densely packed. They are hardly attacked by boring worms, burrowing molluscs, even the Crown-of-thorns starfish avoids feeding on it.
Symphyllia Coral (Symphyllia sp), Crispy Coral(Oulophyllia crispia) and Brain Coral(Platygyra sp)
These coral species are commonly found in lagoons, on the outer reefs and especially in clear waters with moderate current flow. These domed shaped species is covered with ridges and valleys. The feeding polyps are extended during the night to catch passing zooplanktons. They are generally dull coloured - brownish, creamy or greenish.
Orange Daisy Coral (Tubastraea faulkneri) - 10cm wide
This beautiful bouquet is often seen while exploring shipwrecks and caves at depths of 10-15m. They are able to live in dark areas as they are not dependent on the sunlight. instead they whip their numerous tentacles high on the stalks to pluck zooplanktons from the current. During the day, these tentacles are retracted. A certain species of Nudibranch and a species of mollusc that prey upon the vibrant orange polyps, assume similar coloration.
Flex Coral (Favites flexuosa) - 40cm high
The Acroporidae and the Faviidae are two families that are major contributors to the mass spawning scenes that have been well documented. The structure of colonies are incredibly variable from flat plates to rising columns.
Soft corals
These corals differ from the hard corals in that they do not possess hard skeletons. Instead they have a fleshy central body, in some species also strengthened by sclerites - a mesh made of silica or calcium particles. The polyps are attached to the central body by long stalks.
Soft Corals come in a spectrum of vibrant colours. Most do not rely of the helpful zooplanktons but instead they 'fish' for their food with the tentacles. Therefore they can live in deeper waters as they are less reliant of the sunlight for food.
Soft corals seldom have growths of algae, sea squirts and sponges on their surface. The tentacles do a good job of clearing these unwanteds from settling. These animals also secrete various chemicals that prevent the alien elements from attaching themselves and this substance has been of great interest to scientists in search of their anti-foreign growth properties, there may be a secret key to anti cancer drugs.
Laminar Coral (Turbinaria reniformis) - 300cm wide
This coral species is extremely difficult to identify as the form and coloration varies with the environment.
Blue Coral (Heliopora coerulea) -150cm high
The blue coral is often mistaken for a hard coral because of it looks as though it is protected by the calcareous skeleton and generally seem to be living in colonies The blue comes from the colour of the internal skeleton which is stored with iron salts. In shallower waters, its form is generally have robust vertical blades; in deeper waters, they form horizontal plates. These corals prefer clearer waters, in sheltered areas like lagoons, reef flats and sometimes they become dominant coral species spreading across these areas. The zooxanthellae live in these animals, providing them with coloration familiar in hard corals.
Wrinkled Soft Coral (Sarcophyton trocheliophorum) - 60cm wide
They are often seen in individual colonies but sometimes they form groups that can spread 10m wide and may be closely positioned to each other - giving it a sort of luxuriant carpet look. They are normally found in sheltered areas. When fully extended, they look like a furry coat and when retracted they look like the underside of a sheepskin coat.
Dendronepthya Soft Coral (Dendronepthya sp)
These corals stand out on its own. They are found in all reef habitats but they grow to impressive forms mostly at depths between 10-30m(33-100ft). dubbed the reef's wildflowers, these corals come in dazzling colours of pink, yellow, purple and red. They have stems where polyps are seen sprouting from the branches. The colonies look prickly which is the calcium shards used to support each polyp on the branch.
Flexible soft coral (Sinularia flexibilis) - 50cm
This coral has a fleshy trunk that has short vertical branches rising from it. The sclerites are densely packed into the animal's soft tissue to provide support.
These animals have strong, horny skeletons made of gorgonin. This gives the animal strength and support but at the same time flexibility is achieved. Normally found at depths of 10 - 30m, the sea fan can be seen on vertical walls, facing currents and feeding on the microscopic food from the passing flow. Sea fans are hosts to a variety of symbiotic relationships. Some even shelters colonies of tiny seahorses.
Black Coral (Antipathes sp) - 120cm high
I used to be really disappointed on dives when I never got to see the black corals that the other divers were talking about. Then I realised that black corals are not black but are in fact variations of yellow, brown, orange or white. The black comes from polishing its horn-like skeleton and is used to make coral jewellery. The larger specimens are found on steep walls below 20-30ms depth.
Harp Coral (Ctenocella pectinata) - 100cm high
This is a rare Gorgonian sea fan which is found at depths of 20-30m (65-100ft) in areas where currents are strong. They are mostly red but sometimes can be found in shades of yellow or white. It is easily distinguished by its vertical, parallel branches rising from a y-shaped base that is anchored to the surface by a stumpy trunk.
Delicate Sea Whip (Junceela fragilis) - 180cm high
The sea whip actually resembles long twigs that have been stabbed vertically into the ground. Individual stalks may grow to a length of 3-4m.
Wire Coral (Hicksonella sp) - 100cm high
The branches of this coral is covered with a soft leathery 'skin' which hides the black skeleton. This skeleton is also harvested for making black coral jewellery. As with other sea fans, this relative also thrive in areas where water currents are strong.
Illustrations provided by Dennis Ho: Underwater photography by Moti Uttam
