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Bleached coral. (Photo Credit: Creative Commons)

Bleached coral. (Photo Credit: Creative Commons)

Coral reefs throughout the Pacific Ocean are turning ghostly white, and scientists say this is probably just the beginning.

On Thursday, the National Oceanic and Atmospheric Administration (NOAA) officially declared a global “coral bleaching event” for the planet. By the end of this year, the NOAA estimates that the bleaching could spread to over one-third of the world’s coral reefs, affecting some 12,000 square kilometers.

“We’re in shock and awe of what’s happening,” Ove Hoegh-Guldberg, a marine scientist at the University of Queensland in Brisbane, Australia, told Nature News. “It’s a doozy of an event.”

What Is Coral Bleaching?

Coral bleaching is a process that occurs when coral – which is a living organism – expels the symbiotic algae that keeps it healthy and alive. These algae (zooxanthellae) live inside the coral, feed off the sun and feed the coral in the process. Sudden changes in water temperature – both increases and decreases – can distress coral to the point that they expel their algae. A coral that has expelled its algae will become paler over time, weakening and possibly dying.

Sometimes bleaching occurs due to a regional change in temperature or some sort of atmospheric stress. As the ocean warms across the planet, these events will likely become more frequent and widespread. Worse still, the more frequent bleaching becomes, the less time corals will have to recover.

Image Credit: NOAA

Click to embiggen. (Image Credit: NOAA)

As NOAAA explains, “In 2005, 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.”

Thus far, NOAA has recognized three major bleaching events. The largest occurred in 1998 (previously considered the hottest year on record) when 16 percent of the world’s coral reefs were destroyed.

We Knew This Was Coming

Since 2014, NOAA has been sharing alarming reports of coral bleaching around Hawaii and the Florida Keys and warning that 2015’s El Niño may cause an unprecedented destruction of coral. That could in turn cause an unprecedented loss of marine life.

Though coral reefs cover less than one percent of the ocean floor, they support a quarter of all underwater life, including more than 4,000 species of fish.

Great Barrier Reef at the Whitsunday Islands, Australia. (Photo Credit: Sarah Ackerman / Flickr)

Great Barrier Reef at the Whitsunday Islands, Australia. (Photo Credit: Sarah Ackerman / Flickr)

Now that El Niño has finally arrived, NOAA officials are bracing for a very bad year. “We came into 2015 with very warm oceans, and now we have a full-formed El Niño coming,” said Mark Eakin, coordinator of NOAA’s Coral Reef Watch program. Currently, Hawaii, Papua New Guinea and the Maldives have all been hit, and one of the agency’s models suggests that bleaching will spread throughout the Indian Ocean and South Pacific.

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