An official website of the United States government.								Here's how you know we're official.				

##### dot gov icon**Official websites use .gov**

A **.gov** website belongs to an official government organization in the United States.

##### https icon**Secure websites use HTTPS**

A small lock or **https://** means you’ve safely connected to a .gov website. Share sensitive information only on official, secure websites.

National Ocean ServiceNational Oceanic and Atmospheric Administration

              -  Home 
              -  Ocean Facts 
              -  TOPICS ****                  - Explore All Topics
                - Careers
                - Economy
                - Ecosystems
                - Geodesy
                - Hazards
                - Navigation
                - Observations
                - Ocean
                - Recreation
                - Sea Level Rise 
                - Story Maps
                - Tools 
              -  Education 
              -  News 
              -  Podcasts 
              -  Video 
              -  Images 
              -  About Us 

HomeEducationCoralsHow Do Coral Reefs Form?

# Coral Reef Profiles

Over time, many coral reefs develop similar biogeographic profiles. Moving seaward from the shore, the reef flat, reef crest, buttress zone and seaward slope form the major divisions common to most reefs. The reef flat is on the sheltered side of the reef. The substrate is formed of coral rock and loose sand, and large parts may be exposed during low tides. The reef crest, or algal ridge, is the highest point of the reef, and is almost always exposed at low tide. The reef crest is exposed to the full fury of incoming waves, and living corals are practically nonexistent here. Small crabs, shrimps, and other animals often live in the cavities under the reef crest, protected from waves and predators. The buttress zone is a rugged area of spurs, or buttresses, radiating out from the reef. Deep channels that slope down the reef face are interspersed between the buttresses. The buttress zone acts to dissipate the tremendous force of unabating waves and stabilizes the reef structure. The buttress zone also drains debris and sediment off the reef and into deeper water. The dropoff of a reef slope can extend hundreds of feet downward. While light intensity decreases, reduced wave action allows greater numbers of coral species to develop. Sponges, sea whips, sea fans, and non-reef-building corals become abundant and gradually replace stony corals in deeper, darker water.

### Corals Lessons

              - Welcome
              - What are Corals?
              - Zooxanthellae What's That?
              - How Do Stony Corals Grow?
              - How Do Coral Reefs Form?
              - Where Are Coral Reefs Found?
              - How Do Corals Reproduce?
              - Importance of Coral Reefs
              - Natural Threats to Coral Reefs
              - Anthropogenic Threats to Corals
              - Coral Diseases
              - Protecting Coral Reefs
              - References
              - Roadmap to Resources 
              - Subject Review (PDF)

----

National Science Teaching Association (NSTA)

###### **Search** Education

###### Get **Social**

Contact Us

            - Provide Feedback 
            -  Contact Us 
            -  Report an error 

##### Science. Service.Stewardship.

###### 						About NOS 					

            - About Us
            - NOS Program Offices
            - Media Inquiries
            - Website Acknowledgements

###### 						Resources 					

            - Site Index
            - Disclaimer
            - Freedom of Information Act
            - Accessibility

###### 						More Resources 					

            - Information Quality
            - Privacy Policy
            - NOS For Employees
            - USA.gov

          -  National Ocean Service
          -  National Oceanic and Atmospheric Administration
          -  Department of Commerce

##### 						Social 					

            - 
            - 
            - 
            - 
            -