The Great Barrier Reef is the world's largest coral reef system, stretching for over 2,300 kilometers along Australia's northeastern coast. It lies in the Coral Sea off Queensland and includes thousands of individual reefs and hundreds of islands.
The reef is built mainly by tiny colonial animals called coral polyps, whose calcium-carbonate skeletons accumulate over long periods. The system supports extraordinary biodiversity, including more than 1,500 fish species, six sea turtle species, dugongs, seabirds, and many mollusks. Indigenous Australian peoples have maintained cultural connections with the reef for thousands of years.
The Great Barrier Reef Marine Park was established in 1975, and UNESCO listed the reef as a World Heritage Site in 1981. Coral bleaching occurs when heat or other stress causes corals to expel their symbiotic algae. Bleaching does not always mean immediate death, but repeated or severe events can reduce coral cover and weaken the ecosystem.