At a Glance: Coral Reefs

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 Atolls act as natural markers, encircling the places where now submerged volcanic islands once stood. 


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Produced by the Space Telescope Science Institute’s Office of Public Outreach in collaboration with the NASA Earth Observatory.

All images, illustrations, and videos courtesy of NASA except:
·       Great Barrier Reef underwater video footage courtesy of Andy Green at
·       Photo of reef fishers courtesy of Rebecca Weeks/Marine Photobank
·       Sea creature illustration copyright The National Library of Israel, Shapell Family Digitization Project _and The Hebrew University of Jerusalem, Department of Geography – Historic Cities Research Project
·       Photo of fish at a coral reef courtesy of Linda Wade/NOAA
·       Photo of a dead reef in American Samoa copyright Wolcott Henry 2005/Marine Photobank
·       Photo of a bleached reef courtesy of Armando Jenik 2009/Marine Photobank
·       Staghorn coral photo courtesy of William Harrigan/Florida Keys National Marine Sanctuary/NOAA
·       Photo of coral in Perhentian Islands, Malaysia, courtesy of Nazir Amin
·       Mediterranean red coral photo courtesy of Lorenzo Bramanti/Marine Photobank
·       Gorgonian coral photo courtesy of Mohammed Al Momany/NOAA
·       Acropora table coral photo copyright Pete Faulkner, Mission:awareness/Marine Photobank 
·       Sewage pipe photo courtesy of Steve Spring/Marine Photobank
·       Photo of coral with black band disease courtesy of Sven Zea, Universidad Nacional de Colombia/Marine Photobank
·       Blast-fishing photo courtesy of Benjamin De Ridder/Marine Photobank
·       Photo of coral with yellow band disease courtesy of Craig Quirolo, Reef Relief/Marine Photobank
·       Before-and-after photos of bleached coral courtesy of Craig Quirolo, Reef Relief/Marine Photobank
·       Photo of bleached coral in the Galapagos Islands courtesy of David Jacobsen-Fried/Marine Photobank
·       Photo of dead coral reef in Taiwan courtesy of Konstantin Tkachenko/Marine Photobank
·       Bleached coral video footage courtesy of National Oceanic and Atmospheric Administration (NOAA)
·       Thermometer and coral reef illustrations: Marc Lussier, STScI
Written by Vanessa Thomas
Designed by Marc Lussier 
Music courtesy of Associated Production Music


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An animation of Earth in a star-filled sky. Text, at-a-GLANCE, Coral Reefs
The globe turns.
The Pacific Ocean. A red circle around Fanning Atoll, Line Islands, Kiribati.
In the midst of a vast ocean, ringed islands of coral, called atolls, enclose shallow lagoons.
Atolls act as natural markers, encircling the places where now submerged volcanic islands once stood.
Arrows point to a Barrier Reef, an Atoll and a Fringing Reef. Society Islands of French Polynesia.
An atoll begins forming on the submerged rock just off the shores of an island, creating a fringing reef that traces the island's outline.
As the volcano subsides and the island erodes, the lagoon widens, transforming the reef into a barrier reef.
With continued subsidence and erosion, the island eventually disappears under water, leaving a ring of coral reef known as an atoll.
The whole process can take millions of years.