How the Great Barrier Reef was formed
The Great Barrier Reef is the largest living ecosystem in the world. It has been around for many millennia and is continually growing and changing. It is a network that spans across 2,600km and is made up of corals, sea grass, islands, and cays that is the Great Barrier Reef Marine Park.
It is said that the reef dates back as much as twenty million years ago, with an ever changing landscape and coastline. It has moved and morphed over the years and was first encountered by humans 40,000 years ago when Aboriginal and Torres Strait Islander peoples settled in the area. The current reef is about 6,000 to 8,000 years old and was formed after the last ice age began to recede and water levels and temperatures rapidly changed.
The Great Barrier Reef that we know today actually sits on what is the remains of the sediments of the Great Dividing Range, a huge mountain system. Corals began to form around the base of these mountains, which at the time were continental islands. Once sea levels began to rise, the growth of coral began to creep up the mountains, which were eventually completely submerged, leaving behind small islands and cays that we know and see today. The Whitsunday Islands for example, are the remains of mountain tops that once towered over the region.
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 the reef begins.
After they settle, polyps will begin 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 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 of its colour and give 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 21°C and 29°C.
Other types of corals will settle in the same area, expanding, fighting for space and resources, until you eventually have a fully developed coral reef. Hard and soft corals are formed in similar ways and will eventually form on older, dead corals, always expanding and growing, changing the shape of the reef. Other marine plants and fish will begin to move into the same area, using the corals for food, protection or mating grounds, creating an ever fluxing ecosystem.
The Great Barrier Reef is currently home to 1,500 species of fish, six species of sea turtles, 30 species of whales and dolphins and 411 species of hard coral. It is constantly changing before our eyes and is an ever growing system. As visitors to the reef, it’s important that you don’t touch or interfere with corals and marine species on the reef, so they continue their natural life cycle and allow the reef to continue to be healthy and thriving.