Coral Bleaching Crisis


Scientists are warning that devastating bleaching of colorful coral is becoming a worldwide crisis. (Christian Science Monitor)

Use our resources to learn more about coral reefs and the threats they face.

Teachers, scroll down for a quick list of key resources in our Teachers’ Toolkit.

Corals provide a rich, biodiverse habitat for fish, crustaceans, and other marine creatures. Photograph by Jim Maragos, courtesy U.S. Fish and Wildlife Service. This file is licensed under the Creative Commons Attribution 2.0 Generic license.
This gorgeous, healthy coral reef is part of the Pacific’s remote Palmyra Atoll National Wildlife Refuge.
Photograph by Jim Maragos, courtesy U.S. Fish and Wildlife Service. CC-BY-2.0
Click to enlarge! Or visit the great page here.
Graphic by NOAA
Coral bleaching is a dramatic impact of climate change. Ocean acidification and warming sea waters have killed this once-vibrant coral reef off Kanton Island in the Phoenix Islands Protected Area near the island nation of Kiribati in the South Pacific Ocean. Photograph by Brian J. Skerry, National Geographic
This once-vibrant coral reef off Kanton Island, in the South Pacific’s Phoenix Islands Protected Area, is a victim of coral bleaching.
Photograph by Brian J. Skerry, National Geographic

Discussion Ideas


  • Does coral bleaching kill corals?
    • No. Bleaching does make coral less healthy, however, for two main reasons.
      • Bleaching causes corals to lose a major source of nutrients (algae).
      • Corals are more susceptible to disease without their protective algae partners.
    • According to NOAA, corals can survive a bleaching event if water temperatures return to normal quickly.


  • What major factors contribute to coral bleaching?
    • A change in ocean temperature is the major reason for coral bleaching events.
      • Warming. Most coral bleaching is associated with warming waters. “In 2005,” for instance, “the U.S. lost half of its coral reefs in the Caribbean in one year due to a massive bleaching event. The warm waters centered around the northern Antilles near the Virgin Islands and Puerto Rico expanded southward. Comparison of satellite data from the previous 20 years confirmed that thermal stress from the 2005 event was greater than the previous 20 years combined.”
      • Cooling. Not all bleaching events are due to warm water, NOAA reminds us. “In January 2010, cold water temperatures in the Florida Keys caused a coral bleaching event that resulted in some coral death. Water temperatures dropped 12.06° Fahrenheit lower than the typical temperatures observed at this time of year. Researchers will evaluate if this cold-stress event will make corals more susceptible to disease in the same way that warmer waters impact corals.”
    • Runoff and pollution, overexposure to sunlight, and extreme low tides can also contribute to coral bleaching.


  • According to NOAA, we are experiencing the third recorded coral bleaching event. When were the previous two? Do the coral bleaching events have anything in common?
    • Previous coral bleaching events took place in 1997-1998 and 2009-2010.
    • All three major coral bleaching events took place during El Niño years. El Niño is a predictable climate pattern that causes unusually warm currents in the Pacific. (Learn more about El Niño here.)




Christian Science Monitor: Major coral bleaching crisis spreads worldwide

Nat Geo: Coral Reefs: An Ocean of Trouble

NOAA: What is coral bleaching?

NOAA: Zooxanthellae… What’s That?

(extra credit!) NOAA: NOAA declares third ever global coral bleaching event

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