Coral reefs cover less than 1% of the ocean floor yet support 25% of all marine species. These "rainforests of the sea" are among Earth's most productive and biodiverse ecosystems.
Corals are animals, not plants, though they depend on photosynthetic algae living within their tissues. This symbiosis—coral provides shelter and nutrients, algae provide food through photosynthesis—forms the foundation of reef ecosystems.
Reef structures build over thousands of years as coral colonies deposit calcium carbonate skeletons. The Great Barrier Reef, visible from space, comprises nearly 3,000 individual reef systems stretching over 1,400 miles along Australia's coast.