Coral is a tiny sea animal that lives in warm, shallow ocean waters and builds a hard skeleton around itself for protection. When millions of these creatures live together in colonies, their skeletons pile up over hundreds or thousands of years to create massive underwater structures called coral reefs.

Individual coral animals, called polyps, are small and soft-bodied, with tentacles that catch passing food. They live in partnership with microscopic algae that provide them with energy through photosynthesis, which is why many coral reefs need sunlight and clear water to thrive. The Great Barrier Reef off Australia's coast stretches over 1,400 miles and was built largely by countless generations of these small creatures.

Coral comes in stunning colors: brilliant oranges, purples, greens, and blues. These vibrant reefs become home to thousands of fish species and other marine life, making them some of the most diverse ecosystems on Earth. Scientists sometimes call coral reefs the “rainforests of the sea.”

The word coral also describes the pinkish-orange color of many coral species. You might see coral-colored clothing, paint, or decorations that capture that warm, tropical hue.

When coral loses its algae, it turns white (called coral bleaching). If the stress continues, the coral can die, and its skeleton eventually becomes part of the reef structure that future coral grows upon.