Which natural feature is the largest coral reef system on Earth?

The Great Barrier Reef is the largest coral reef system on Earth, extending along the coast of Queensland, Australia.

It stretches for about 2,300 kilometres and includes thousands of individual reefs and hundreds of islands. The system lies in the Coral Sea and is large enough to be seen from space, although individual coral colonies are not visible in the way popular images sometimes suggest.

The Great Barrier Reef is built mainly by tiny coral animals called polyps. Their calcium carbonate skeletons accumulate over long periods, creating habitats for fish, sea turtles, molluscs and many other species.

The reef faces pressures from marine heatwaves, coral bleaching, storms, pollution and crown-of-thorns starfish. It is a UNESCO World Heritage Site, listed in 1981.