Great Barrier Reef - Coral reefs

The Great Barrier Reef has a story millions of years in the making. In ancient times the Reef was a coastal plain attached to the Australian mainland covered in eucalyptus and paperbark forests. Mainland animals roamed the area, and the Traditional Owners hunted for food. The plains had many large limestone hills, part of older reefs that had died out through previous mass extinction events.

Around 20,000 years ago, the earth's climate started to heat up, and the ice around the poles began to melt. Over time, the sea levels rose and eventually flooded this low-lying coast, shifting the mainland coastline to its current position. Coral reefs grew on the continental shelf's rocky edge, creating a natural barrier. The hills covered most of the way by water formed the numerous islands found today. Around the islands' coasts, fringing reefs developed. Shallow lagoons separate the fringing reefs from the islands. Fringing reefs are not limited to islands as they also grow along continental coasts. One such example is the Ningaloo Reef in Western Australia, which at 160mi (260km), is the longest fringing reef in the world.

The large body of water between the mainland and the continental shelf is a lagoon that varies widely in size, depth, and types of coral that live there. There are different zones of coral reefs depending on their location. The zone nearest to the mainland is a reef flat, where corals may be exposed due to shifting tides. Exposure to air for too long stresses the corals, impeding their ability to grow properly. However, marine life is abundant, with clams, oysters, crabs, and lobsters dominating. The next zone slopes upwards, called the reef crest. It is the highest point of the reef. When exposed at low tide, the reef receives the full brunt of the waves. Only robust corals can survive here, such as the coralline algae. This pinkish-encrusting seaweed grows in thin layers over stones and coral rubble. They act like a binding agent, stabilising the reef structure, reducing erosion, and providing shelter for reef dwellers. Past the reef crest is the last zone, the fore reef or outer reef. Warmed by ocean currents and sheltered from winds and wave actions, the fore reef is where most corals and the widest variety of them grow. Divers have a high chance of swimming with sharks and barracuda in this area.

The Great Barrier Reef is an incredibly complex ecosystem, and the above description of its composition barely scratches the surface. Still, I hope it provides an insight into this magnificent natural feature.



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