Geosight #4: The Great Barrier Reef

Its Australian publicists term the Great Barrier Reef “the largest natural feature on Earth” which it is not. There are plenty of mountain ranges that beat it for size. But their enthusiasm is understandable. The reef is undoubtedly the largest living thing on Earth, running for 2300km off the north-east coast of Australia. Its northward boundary seems to be the point at which the water gets too hot for the corals that build it to survive.

Its physical foundation is the work of 359 species of hard corals that manufacture limestone and give the reef its solid structure. They are accompanied by soft corals. These are far more hazardous to humans than hard ones, because they have developed toxins to deter predators. Indeed, the whole reef is a chemical warfare zone. The jellyfish have vicious stings, and one called the Box Jellyfish is said to be the most hazardous animal in the world to humans. Even the fish are not to be messed with. The stonefish gets its name from its rocky camouflage but also has deadly venomous spines.

However, none of these defences are effective against the challenges that humanity offers the reef. The sheer number of people that go there means they are a pollution hazard, even if all they do is perform normal human bodily functions during their visit. They tend to arrive in boats, whose anchors can damage the coral.

The reef now has management who aim to minimize such local hazards. But in the longer term, bigger environmental changes could be harder to avoid. If sea level rises, can coral grow fast enough to keep up? In the past, the answer has been yes, but it might not stay that way. Or might hotter seas reduce the range of the reef? Hot water can kill by “coral bleaching'in which the heat kills the algae that sustain it.

For more information see: Great Barrier Reef Marine Park Authority www.gbrmpa.gov.au