http://www.coris.noaa.gov/ about/what_are/ http://www.coris.noaa.gov/about/what_are/ What Are Corals and Coral Reefs? NOAA very picky about their habitats "What are coral reefs?" What Are Corals and Coral Reefs? coral reef http://www.coris.noaa.gov/about/what_are/ reef crest http://www.coris.noaa.gov/about/what_are/ Learn more about Coral Reefs http://www.coris.noaa.gov/about/what_are/ O2 400 million years colonies NOAA Coral Information Program healthy coral reefs Coral reefs coral reefs coral reef What are coral reefs? corals healthy coral reefs NOAA Coral Information Program 400 million years coral reef coral reef What are Coral Reefs reef-building corals NOAA: CORIS--What Are Coral Reefs? Coral reefs What are Corals and Coral Reefs? Coral reefs healthy coral reefs 6000 known coral species https://www.coris.noaa.gov/about/what_are/#Anchor-From-63388 coral reef Coral reefs coral reef Coral reefs hardened coral structure coral reef coral reef Source: NOAA coral reefs http://www.coris.noaa.gov/about/what_are/ O2 coral reef development.