australia DIVE SITES

The Great Barrier Reef is the largest structure on the earth built by living organisms, and the only one of such to be visible from space.

When we look at a coral reef and experience the wonderful display of shape and colour, what we see is the top living layer of coral. The layers underneath are made up of the dead skeletons of a range of minute marine plants and animals, bonded together by the encrusting coralline algae.

There are approximately 350 species of hard corals, and these are the primary reef-building animals. They have a symbiotic relationship with single-celled plants called zooxanthellae, which provide the coral with energy from sugars via photosynthesis. This energy enables the corals to remove dissolved limestone from the water and use it to build a hard exoskeleton around themselves. As the reef is built up, the coral animals in the lower layers die off, leaving their hard limestone skeleton, and creating the recognisable coral structures.

The exact shape of the structures on the reef are dependent upon the conditions which prevail as the individual coral polyps form their skeletons, and how these polyps reproduce (bud). The pigments contained within the polyps determine which colours are displayed, and size is primarily controlled by the energy from the zooxanthellae.