Great Barrier Reef, Queensland, Australia

The largest living organism on Earth

World Reef Day returns for its second year in a bid to help focus attention on the plight of our planet's vital reef systems and to boost efforts to help them recover. Our homepage image shows the world’s largest coral reef system, Australia’s Great Barrier Reef, made up of more than 2,900 individual reefs and 900 islands. It supports a wealth of marine life from fish and coral to hundreds of bird species and is the only living thing on Earth which is visible from space.

Why should you care about the health of such ecosystems? Because reefs are an easy indicator of how healthy our oceans are. And right now, reefs aren’t doing too well. What can you do? Learn about reefs, not just the dangers that put healthy reefs at risk, but why they are such a critical part of Earth's greater ecosystems.