The world's most extensive coral-reef ecosystem: more than 2,300 km of reefs, islands, channels, seagrass and mangroves along Australia's northeast coast, inscribed as World Heritage in 1981.
The Great Barrier Reef extends more than 2,300 km along northeast Australia. Official inventories describe about 2,500 to more than 2,900 reefs, depending on the boundary and how reef features are counted, plus more than 900 islands.
Raine Island can draw up to about 60,000 adult female green turtles in a peak nesting season. It was inscribed on the World Heritage List in 1981.
Between its reefs lie deep channels, seagrass meadows, mangroves and open-water habitats; currents and moving animals connect this vast mosaic, though each species uses it differently. Coral animals build with microscopic algal partners, while seagrass meadows and mangrove roots extend the Reef's living mosaic toward shore.
Many reef-building corals release eggs and sperm in synchronised seasonal windows. Rapid spring warming helps set the month; lunar and daily light help narrow the night and hour.
Timing still varies by latitude, species and year.
Dwarf minke whales gather around the northern Great Barrier Reef in winter.
A single clownfish may spend its whole life in just one anemone, never straying far.
Up to about 60,000 female green turtles can nest at Raine Island in a season.
Official inventories describe about 2,500 to more than 2,900 reefs, depending on the boundary and how reef features are counted.
Many reef-building corals spawn in synchronised seasonal windows, with lunar and daily light helping to time the night.
After heat turns corals pale, many Great Barrier Reef colonies can regain their colour if cooler water returns in time.
Field Notes
The Biggest Living Thing
The Great Barrier Reef is the world's most extensive coral-reef ecosystem. It extends more than 2,300 km.
Official inventories describe about 2,500 to more than 2,900 reefs, depending on the boundary and how reef features are counted, plus more than 900 islands. Between its reefs lie deep channels, seagrass meadows, mangroves and open-water habitats; currents and moving animals connect this vast mosaic, though each species uses it differently.
Coral animals build with microscopic algal partners, while seagrass meadows and mangrove roots extend the Reef's living mosaic toward shore. It was inscribed on the World Heritage List in 1981.
Research Report
The Great Coral Spawning
Many reef-building corals release eggs and sperm in synchronised seasonal windows. Rapid spring warming helps set the month; lunar and daily light help narrow the night and hour.
Timing still varies by latitude, species and year, and spawning is only the start—larvae must survive currents and find suitable reef surface before a new colony can begin. A protective mucus coat and careful acclimation let clownfish move among host-anemone tentacles on the same reef mosaic where those eggs settle.
Expert Dossier
A Turtle Beach Like No Other
Raine Island can draw up to about 60,000 adult female green turtles in a peak nesting season. Low beach levels left many nests vulnerable to tidal flooding, so Traditional Owners and managers reprofiled local sand to raise viable habitat.
A published assessment estimated up to 640,000 additional hatchlings over five years — an important site-level gain, not protection from every threat facing this regional population. Global status improved to Least Concern in 2025 after decades of protection; some regional populations remain under pressure, and Raine Island hatchling production is still climate-sensitive.