The Great Barrier Reef is not one reef. It is nearly 3,000 of them, strung along Australia’s northeast coast. It is also the largest structure on Earth built entirely by living animals.
Timeline
- 1770: Captain James Cook’s ship, the Endeavour, runs aground on the reef and is nearly lost.
- 20 June 1975: The Great Barrier Reef Marine Park Act creates the Great Barrier Reef Marine Park Authority.
- 1981: UNESCO lists the Great Barrier Reef as a World Heritage Site.
- 1998 and 2002: The reef suffers its first two recorded mass coral bleaching events.
- 2016 and 2017: Back-to-back mass bleaching strikes the reef for the first time on record.
- 2021: UNESCO recommends listing the reef as “World Heritage in Danger.” Australia lobbies against it, and the decision is delayed.
- 2024: The reef suffers its most extensive mass bleaching event yet, affecting 74% of surveyed reefs.
- 2025: A sixth mass bleaching event hits, the first time the Great Barrier Reef and Ningaloo Reef have bleached in the same year.
- 2026: The World Heritage Committee again declines to place the reef on the “in danger” list, while expressing grave concern over its outlook.
The World’s Largest Reef System Need to Know
- The Great Barrier Reef lies off the northeast coast of Queensland, Australia, in the Coral Sea.
- It stretches about 2,300 kilometres, making it the world’s largest coral reef system.
- The Great Barrier Reef Marine Park covers 344,400 square kilometres, an area larger than Italy.
- It is made up of more than 2,900 individual reefs and around 900 islands.
- It is not a single reef. It is a connected system of thousands of smaller reefs, separated by channels and lagoons.
- It can be seen clearly in satellite images, because of its enormous size.
A Structure Built by Tiny Animals Need to Know
- Coral reefs are built by tiny animals called coral polyps, not by plants or rocks.
- Each polyp secretes a hard skeleton of calcium carbonate around itself.
- Over generations, these skeletons pile up and fuse, forming the reef’s physical structure.
- The reef hosts at least 400 species of hard coral, plus about a third of the world’s soft coral species.
- It is home to more than 1,500 species of fish, along with sea turtles, sharks, and dugongs.
- Scientists consider it one of the richest and most complex ecosystems on Earth.
Test Yourself
A Warming Ocean and a Fragile Record Good to Know
- Coral bleaching happens when ocean water gets too warm for too long.
- Heat stress causes coral polyps to expel the algae living inside them. This algae normally gives coral its color and much of its food.
- Bleached coral turns white. It is not dead, but it is badly weakened and can die if the heat doesn’t ease.
- The reef has suffered six mass bleaching events since 2016: in 2016, 2017, 2020, 2022, 2024, and 2025.
- Before 2016, mass bleaching had only struck the reef twice, in 1998 and 2002.
- The 2024 event was the most extensive yet, affecting 74% of surveyed reefs across all regions.
- In 2025, the Great Barrier Reef and Western Australia’s Ningaloo Reef bleached in the same year for the first time on record.
- In 2021, UNESCO recommended listing the reef as “World Heritage in Danger.” Australia successfully lobbied to delay that decision.
- As of 2026, the reef still hasn’t been placed on that list, even after repeated bleaching. The World Heritage Committee has called its long-term outlook one of “continued deterioration due largely to climate change.”
The Wider Story Great to Know
- For India’s own coral reef systems and the threats they face, see EnvEco0025 — Coral Reefs and Marine Biodiversity Conservation in India: Four Reef Zones.
- The Great Barrier Reef’s story is a warning shared by every coral reef system on Earth: warming oceans threaten even the largest, best-protected reefs.
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