The world's largest coral reef system, the Great Barrier Reef, is found off the coast of:

The Great Barrier Reef is the world's largest coral reef system. It lies in the Coral Sea, off the coast of Queensland in north-eastern Australia. It stretches for about 2,300 kilometres and covers an area of about 3,44,000 square kilometres. It is made up of more than 2,900 individual reefs and about 900 islands. It is the largest structure on Earth built by living organisms and can be seen from space.

Coral reefs are built by tiny marine animals called coral polyps, which live in colonies. Each polyp secretes a hard skeleton of calcium carbonate (limestone), and over thousands of years these skeletons build up into large reef structures. Corals live in a symbiotic relationship with microscopic algae called zooxanthellae, which live inside their tissues, provide food through photosynthesis and give corals their bright colours.

Conditions needed for coral growth:

• Warm water, between about 20°C and 29°C.
• Clear, shallow water (usually less than about 50-70 metres deep), so sunlight can reach the algae.
• Salty, clean water with low levels of sediment.
• Types of coral reefs: fringing reefs (close to the shore), barrier reefs (separated from the shore by a lagoon) and atolls (ring-shaped reefs surrounding a lagoon, such as those in the Maldives and Lakshadweep).

The Great Barrier Reef was declared a UNESCO World Heritage Site in 1981. It is home to thousands of species, including about 1,500 species of fish, 400 types of coral, turtles, dolphins, whales, sharks and dugongs.

It is under serious threat from climate change. Rising sea temperatures cause coral bleaching, in which corals expel their algae and turn white; if conditions do not improve, they die. The reef has suffered several mass bleaching events, including in 2016, 2017, 2020, 2022 and 2024. Pollution, ocean acidification, cyclones and crown-of-thorns starfish also harm it.

In India, coral reefs are found in the Gulf of Mannar and Palk Bay (Tamil Nadu), the Gulf of Kutch (Gujarat), Lakshadweep (atolls) and the Andaman and Nicobar Islands.

Why not the other options?

• ✗Western Australia has the Ningaloo Reef, a fringing reef.
• ✗Indonesia lies in the Coral Triangle, with the highest coral diversity.
• ✗The Maldives consists of coral atolls.