ATLAS · CORAL REEFS

The World’s Coral Reefs

They cover less than a thousandth of the ocean floor, yet they shelter about a quarter of all marine species. This overlay draws the world’s coral reefsover any Atlas map — the great reef belt of the warm tropical seas, in living radar-green. From the Great Barrier Reef and the Coral Triangle to the Red Sea, the Caribbeanand the atolls of the Pacific, the map shows where the rainforests of the sea are built — and, laid over a temperature or population map, what presses on them.

Open the Atlas map & toggle Coral Reefs on →

On the Atlas canvas, the Coral Reefs switch sits just under the overlays panel. The reefs draw over whatever metric (or the plain political map) you have up.

Where the reefs are

Reefs need warm, clear, sunlit, shallow water, so they ring the tropics — a belt roughly thirty degrees either side of the equator, hugging coastlines and crowning undersea ridges and sunken volcanoes. Four regions hold most of the world’s reefs.

THE CORAL TRIANGLEThe richest reef waters on Earth — the seas around Indonesia, the Philippines, Malaysia, Papua New Guinea, Timor-Leste and the Solomon Islands. More coral species live here than anywhere else, by a wide margin; it is the beating heart of the reef belt.

THE GREAT BARRIER REEFOff Australia’s north-east coast, the largest reef system in the world — over two thousand kilometres of reef, big enough to be seen from orbit. The single most famous reef on the planet, and the densest stretch of the map.

THE CARIBBEAN & THE ATLANTICThe reefs of the Caribbean Sea and the Mesoamerican Reef off Belize and Mexico — the second-longest barrier reef in the world — plus the banks of Florida and the Bahamas. A separate reef world from the Indo-Pacific, with its own corals and fish.

THE RED SEA & INDIAN OCEANThe hardy, heat-tolerant reefs of the Red Sea, and the great atolls of the Maldives and the Chagos Archipelago — rings of coral built on the rims of sunken volcanoes, encircling lagoons of impossibly clear water.

The rainforests of the sea — and the warming that threatens them

A reef is built by living animals: coral polyps, each a tiny relative of the sea anemone, laying down limestone skeletons over thousands of years. Inside their tissue live microscopic algae that feed them and give them their colour — a partnership that only works in a narrow band of temperature. When the water gets too warm, the coral expels the algae and turns bone-white: coral bleaching. A bleached coral is starving, and if the heat persists it dies. That makes reefs the first ecosystems to feel a warming ocean, which is why they read so powerfully when you lay this overlay over a sea-temperature map.

Coral Reefs Explained — What They Are, Where They Are, and Why a Warming Sea Threatens Them →

About this overlay & its data

The reefs are Natural Earthat 1:10 million — the cartographer’s standard world reef edges, the same public-domain source that supplies this atlas’s country outlines. It is a generalised world view: it shows where the reef belt lies at the scale of a world map, not a survey of every individual coral patch — so read it as the shape of the reef world, not a precise census. We checked its coverage against reality: the Coral Triangle and the Great Barrier Reef are richly represented, as are the Red Sea, the Caribbean, the Maldives and the Pacific atolls. There are no per-place pages, because the reef edges carry no individual names.

CANVAS · THE BLUE PLANETThe ocean the reefs live in →ATLAS · OVERLAYThe world’s rivers & lakes →ATLAS · PROFILESEvery country, profiled →