Coral:

Corals are one of the key components that are involved in the structure of the amazing wonder of the world- the Great Barrier Reef. The corals of Queensland reefs not only provide a home for all the plant and animal species but allow divers and snorkellers the opportunity to visit an array of colour, shape and movement that is replicated nowhere else in the world.

More than 400 (or one-third) of the world's coral species can be found in the Great Barrier Reef World Heritage Area. Amazingly what is seen is just a thin covering of living coral believed to be about 8000-years-old, which has built up on top of dead corals and algae over the past 500,000 years.

Many different species of coral can be found over the Great Barrier Reef. Hard corals are formed from a limestone-covered polyp organism dividing into two leaving behind its hard outer skeleton when a new one is formed. Growth is generally slow, especially in the first few years, with most hard corals growing at a rate of 1-1.5cm a year.

Exotic coral structures shaped like staghorns, tabletops, fans and brains create a habitat for a myriad of fishes, enchinoderms, molluscs and microoganisms such as algae and plankton.
 

Above: Staghorns, Plate and Brain Coral

Soft corals contribute in a lesser way to the reef's solid structure, but nevertheless make an important contribution to this delicately-balanced ecosystem. Like hard corals of the reef, most soft coral species have a symbiotic relationship with microscopic single-celled algae (zooxanthellae) that live inside their tissues, transferring food to the host coral.

This very important relationship depends on clear warm shallow waters with temperatures of above 18° C. Dramatic temperature variations can result in the coral expelling the algae, resulting coral death or coral bleaching.

Coral spawning or reproduction is a nocturnal phenomenon that happens annually in late spring or early summer. Colloquially know as "sex on the reef", egg-engorged corals simultaneously release masses of pretty pink eggs and sperm into the sea to become free-floating larvae. While its timing is thought to be related to the water temperature and phases of the moon, it is impossible to predict exactly when it will occur.

Coral's most voracious natural predator is the Crown of Thorns Starfish. Outbreaks of these starfish have been known to strip reefs of nearly all living coral. Fortunately new corals generally re-establish after an outbreak.