Great Barrier Reef - National Geographic

Great Barrier Reef

Photograph by David Doubilet, National Geographic

Coral reefs are found throughout the world’s tropical oceans, often in relatively shallow waters where algae use photosynthesis to covert the sun’s energy into vital nutrients. Australia’s incomparable Great Barrier Reef, pictured here, traces a graceful 1,250-mile-long (2,000-kilometer-long) arc off the nation’s northeast coast. This largest of all coral habitats—it covers an area larger than Poland—is actually made up of some 2,800 separate reefs.