Which coral reef system is the largest in the world, stretching for more than 2,300 kilometres?

The Great Barrier Reef is the largest coral reef system in the world, stretching for more than 2,300 kilometres.

It lies off the northeastern coast of Australia in the Coral Sea and includes thousands of individual reefs and hundreds of islands. The system is so extensive that it can be seen from space in suitable conditions, although individual corals and reef structures are not visible as a single solid wall.

The reef supports extraordinary biodiversity, including hard corals, sea turtles, dugongs, reef fish, seabirds, and many invertebrates. Its living structures are built chiefly by tiny coral polyps, which form calcium-carbonate skeletons over generations.

The Great Barrier Reef is not immune to environmental change. Marine heatwaves have caused repeated coral bleaching, while storms, crown-of-thorns starfish, pollution, and coastal development add further pressure. A reef system is different from a single reef, an important distinction in this record.