How is a coral reef formed in the Great Barrier Reef Marine Park?
All coral reefs are formed the same, no matter where they are in the world. The reason why the Great Barrier Reef Marine Park is special and unique is that it is the largest reef system in the world with 2,900 reefs connecting it across 2,600km.
How does it begin?
A reef starts very simple and very, very small. It all begins when one little coral planula, or coral larvae, attaches itself to a clean piece of ocean floor, a rock, or other hard surface. This one solo coral then will secrete a cup-like carbonate skeleton, which will secure it to its new surface. Now it is called polyp and is officially a resident coral in the ocean. It will again and again reproduce itself until it has a solid skeleton structure attached to its rooting place. Eventually, other animals and corals will attach and do the same, as the original coral would provide shelter and safety. Among these creatures will come the algae - the life force behind coral.
What role does algae play?
Algae have a symbiotic relationship with coral. The single-celled organisms, called zooxanthellae, live inside the coral. As plants, they have the ability to photosynthesize, creating energy for both itself and the coral. In return, the algae get nitrogen and CO2 from the coral, which is vital for their survival. Algae are responsible for 30 to 90 per cent of the coral's food requirements, meaning they play a vital role in their survival, too. They are also the reasoning behind coral's colouring! Coral itself is quite colourless, while algae can be bright and vibrant. So while the algae is busy providing food, the coral can then concentrate on building a bigger skeleton and producing more polyps as it gets larger and larger.
Then what happens?
And so, as the coral continues to get larger, even fish will seek out shelter among its branches or plates. Bigger fish will come in to eat the smaller fish, and crabs and other bottom feeders come in to clean up the mess. Then we have a full functional coral reef! This process continues on until we have large systems of individual reefs like we see in the Great Barrier Reef today.