Of HOW THE REEF BEGAN A long time ago Australia was not the sort place where a reef could grow Stuck to Antarctica it was surrounded by a freezing sea far too cold for corals Then 85 million years ago when dinosaurs were still alive Australia split off and began to drift away towards the equator nearer to where it is today At this time in history the Earth was very cold Enormous ice sheets locked up masses of the ocean's water so sea levels were more than a hundred metres lower than they are now
Then as the last ice age ended around 10,000 years ago the world warmed up and the ice sheets melted causing an enormous flood As sea levels rose higher and higher great cliffs disappeared beneath the waves and hills were turned into islands Tiny young corals called larvae drifted in from other reefs and settled on this land that was suddenly underwater The sea became warm enough for corals to thrive and so the Great Barrier Reef began to grow As the seas rose higher some of the islands drowned completely but the corals kept growing upwards and outwards until they built wide flat reefs
BUILT BY CORAL More than 600 species of corals live on the Great Barrier Reef If you were to look closely at a piece of coral you'll see that it's covered in spots These are polyps each one is a tiny coral animal with a mouth a stomach and tentacles Coral polyps don't have brains much like their closest relatives jellyfish and anemones Each big coral known as a colony is made up of hundreds and thousands of polyps joined together Their bodies are soft but usually they live inside a tough exoskeleton made of calcium carbonate the same stuff as chalk and chickens eggshells
Branching coral TINY SECRETS With the help of a microscope you can discover one of the polyps hidden secrets inside their bodies are spherical cells called zooxanthellae or zoox for short Zoox use the sun's energy to make sugar just like plants do on land During the day corals eat this sugar At night they transform into deadly hunters using their tentacles to catch tiny animals and plant like organisms called plankton Some plankton grow into bigger animals like fish and crabs and some never get any bigger There are two different types of coral soft and hard Corals with a tough exoskeleton are known as hard corals Corals without a hard skeleton are called soft corals Elephant ear leather coral Sea whip Mushroom coral Brain coral
