In warm, shallow tropical seas, generation after generation of corals have built underwater structures that rival the complexity of any terrestrial ecosystem. Coral reefs occupy less than one percent of the ocean floor yet support roughly a quarter of all marine species at some point in their life cycles.

The three-dimensional framework created by coral skeletons provides habitat for fishes, invertebrates, and algae. Primary production by symbiotic algae and turf algae fuels a web of herbivores, predators, and detritivores. Reefs also buffer shorelines against waves and supply food and income to millions of people.

Despite their value, reefs face cumulative threats from warming, acidification, overfishing, destructive fishing practices, and coastal pollution. Some reefs have already shifted to algae-dominated states. Conservation efforts focus on reducing local stressors, establishing protected areas, and supporting the recovery of herbivorous fish that keep algae in check. The long-term persistence of coral reefs will depend heavily on the trajectory of global climate.

• Underwater structures built by calcium-secreting corals
• Support exceptional marine biodiversity
• Provide coastal protection and resources
• Threatened by climate and local human impacts