Coral reefs are marine ecosystems composed of reef-building corals, which are colonies of small, sessile animals known as polyps. These reefs are found in shallow, warm ocean waters and are vital for biodiversity, providing habitat for a vast array of marine life. Coral reefs are also important in the study of marine biology, ecology, and climate change, as they are sensitive indicators of environmental stress.
Source Spalding, M. D., Ravilious, C., & Green, E. P. (2001). World Atlas of Coral Reefs. University of California Press.