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The ongoing coral bleaching event that has killed or severely injured reefs from the Great Barrier Reef to Hawaii and the Indian Ocean has set its sights on the U.S. during the rest of 2016 and into next year, according to the National Oceanic and Atmospheric Administration (NOAA). 

The agency's Coral Reef Watch computer model outlooks show that the bleaching event will continue worldwide "with no signs of stopping," the agency said in a press release and media conference call Monday. 

Satellite observations show that this has been the most widespread coral bleaching event on record, with more than half of the reefs worldwide already hit twice by this event.

The major U.S. targets look to be two "freely associated states:" Palau and the Federated States of Micronesia.

In addition, NOAA says the Commonwealth of the Northern Mariana Islands, Hawaii, Guam, the U.S. Virgin Islands, the Florida Keys and Puerto Rico all stand a significant chance of seeing damaging coral bleaching through the end of this year. 

Thermal stress outlook from NOAA's Coral Reef Watch, showing areas with a 90 percent probability of experiencing heat stress that could cause coral bleaching.Credit: NOAA

The Coral Reef Watch outlook shows a 90 percent chance of widespread coral bleaching in the Pacific island nations of Palau and the Federated States of Micronesia during a probable La Niña event in the tropical Pacific Ocean. 

While La Niña conditions tend to be known for bringing cooler than average ocean temperatures to the tropical Pacific Ocean, such events can also cause warmer than average ocean waters to develop and persist in the western Pacific. 

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Prior to the ongoing coral bleaching event, there had only been two observed global coral bleaching episodes, and both of them were tied to an El Niño. 

This one, however, started before the onset of an El Niño event, and is continuing for long after it has concluded. This points to the role being played by human-caused global warming, which is elevating ocean temperatures and making such bleaching events more likely to occur. 

“All Northern Hemisphere U.S. coral reefs are on alert for coral bleaching this year,” said Mark Eakin, coordinator of Coral Reef Watch at NOAA, during the press call. “If we see bleaching in Florida or Hawaii this year, it will be three years in a row.”

Such repeated bleaching episodes can eventually kill these delicate marine ecosystems.

Potential thermal stress level during the June through September period in the western Pacific and Indian Oceans.Credit: NOAA

Coral bleaching occurs when coral expels the algae that lives in its tissue, giving it color and nutrients. This action, caused by stresses such as increased water temperatures and pollution, leaves the coral skeleton exposed, making it more susceptible to heat stress, disease and pollution.

Bleached coral can recover if it is not exposed to further amounts of stress, but scientists are finding that some reefs are more resilient than others. 

"Many reefs, especially in the Pacific have seen more severe bleaching and coral death than ever before," Eakin said in an email to reporters. 

Since the onset of this bleaching event in mid-2014, all U.S. coral reefs have seen above normal temperatures, and more than 70 percent of them have been exposed to the prolonged high temperatures that can cause bleaching, NOAA said in a statement. 

“It’s time to shift this conversation to what can be done to conserve these amazing organisms in the face of this unprecedented global bleaching event,” said Jennifer Koss, NOAA’s Coral Reef Conservation Program director, in a press release. 

“We have boots on the ground and fins in the water to reduce local stressors. Local conservation buys us time, but it isn’t enough. Globally, we need to better understand what actions we all can take to combat the effects of climate change."

(责任编辑：時尚)