NETWORK that spans across 2,600km and is made up of corals, SEAGRASS, islands, and cays that is make up the Great Barrier Reef Marine Park.THE FORMATION OF THE REEF:All reefs, including the Great Barrier Reef, begin to form with a single organism.A drifting coral polyp, expelled into the open sea by its parents, will come to rest on a stationary object, such as a rock or shell, where it will permanently attach itself to live its life. Here is where we see the humble beginnings of a reef. After they settle, polyps will begin to SECRETE a calcium carbonate, which hardens to form the BONY white structure, or skeleton, that forms the shape of the coral itself. The polyp lives on the outside of this bony structure, where more of the same species will join it, BECOMING one organism. The polyps develop a relationship with algae, which is its source of food, and its color, which gives the coral its look.The healthy coral will continue to grow at a rate of about 5mm - 20cm per year, depending on the species, and grow best in temperatures between 21C and 29C.Hence, Barrier reefs are formed when some marine organisms secrete calcium carbonate.