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Oceans and Coasts

Coral Bleaching: What You Need to Know

"Corals have a limited temperature range within which they can live. When it gets too hot, they get stressed out."
— Stephanie Wear, Conservancy director of coral reef conservation

If coral bleaching isn’t on your radar yet, it will be soon. According to Stephanie Wear, The Nature Conservancy’s director of coral reef conservation, recent steamy temperatures indicate a rough year ahead for the world’s coral reefs.

“When you have really hot summers, you can expect that corals will get stressed, and bleaching is likely,” says Wear.

But what does coral bleaching mean for us and our seas? Read on to get the skinny on this phenomenon—and what can be done to lessen the impacts. Then, visit our Adopt a Coral Reef page to find out what you can do to help us help coral reefs.

What is coral bleaching? Why is it such a bad thing?

On the surface, coral bleaching looks exactly like what you’re envisioning right now: white, bleached-out coral reefs, which is quite a departure from the colorful structures we all know and love.

“The first thing to understand is that corals get their brilliant colors from tiny algae that live in their tissues. These tiny organisms live in harmony with coral animals, and they basically share resources,” Wear explains. “For example, the most important thing that the algae do is provide food to the corals through carbohydrates they produce during photosynthesis.”

“The next thing to understand is that corals have a limited temperature range within which they can live,” Wear continues. “When it gets too hot, they get stressed out—and this relationship with the algae goes sour. The tiny algae are ejected from the corals, turning them white, thus the term ‘bleached.’”

And what happens then? “If these algae aren’t reabsorbed in the near term, the coral will die,” says Wear. “They just can’t survive long-term without them.”

But could we survive without corals? Reefs make up less than 1 percent of Earth’s undersea ecosystems, but don’t underestimate their importance:

  • They shelter 25 percent of marine species,
  • protect shorelines,
  • support fishing industries,
  • provide tourist dollars—and
  • could be home to the next big, undiscovered medical breakthrough.


A decline in healthy reefs is a huge blow to us all.

Why does coral bleaching happen?

Elevated sea temperatures — often "thanks" to climate change — are the biggest culprits when it comes to coral bleaching. El Niño also plays a role in heating up ocean waters. “The bleaching activity this year was actually predicted last year because of the El Niño cycle that began in mid-2009,” says Wear.

But it can be a perfect storm of stress factors, like the ones listed below, that lead to significant bleaching events:

    * Extra-bright sunlight, especially when combined with the aforementioned extra-warm seawater
      
    * Disease
      
    * Pollution from urban or agricultural run-off
      
    * Changes in the salinity, or saltiness, of seawater
      
    * Sedimentation from undersea activities like dredging

Lots of living things (including humans) under serious stress may be more susceptible to problems with their health, and corals are no exception. Coral reefs—they’re just like us!

What’s The Nature Conservancy doing about coral bleaching?

Bleaching doesn’t have to be a death sentence. Not every reef that experiences a stressful event is destroyed — some healthy reefs, called “resilient reefs,” are capable of bouncing back. The Conservancy’s work is focused on increasing the likelihood that reefs can recover when faced with a major disturbance, like a climate-related event.

The Nature Conservancy is a pioneer in reef resilience, and we’re sharing our science-based strategies and years of on-the-ground experience with our partners and local reef practitioners. Reef resilience workshops teach participants how they can keep their reefs healthy, and get their communities on board with reef protection.

“On the ground, we are working with countries to establish resilient marine protected area networks by incorporating what we know about reef resilience into the design and management of marine parks,” says Wear. “We are also developing and implementing other management strategies to better respond to bleaching events, such as developing comprehensive bleaching response plans.”

Is there anything I can do?

Even those who live far from the coasts can help protect coral reefs.

The things you do to reduce your carbon footprint not only save energy — they keep greenhouse gases out of the atmosphere, which helps combat climate change and maintain appropriately cool ocean temperatures.

  • Try walking, biking or taking public transportation instead of driving.
  • Plant a tree and support forest conservation! Trees store carbon and reduce agricultural run-off, which may ultimately end up in the ocean.
  • Contact your local legislators, and tell them you support comprehensive climate legislation.


You can also support the Conservancy’s work to protect corals by adopting a coral reef in honor of family members and friends (or yourself!).

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