Record ocean temperatures are putting coral reefs at risk, causing a third-ever global coral bleaching effect, NOAA reported this week. The effects of global warming, which are heightened by the current El Nino effect, have exposed about 95 percent of U.S. coral reefs to conditions that cause coral bleaching, which can lead the coral to die off.
The effect has been visible across a wide area of the Papahānaumokuākea Marine National Monument in the Northwestern Hawaiian Islands, NOAA reported.
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"The coral bleaching and disease ... are the largest and most pervasive threats to coral reefs around the world," said Mark Eakin, NOAA's Coral Reef Watch coordinator.
"As a result, we are losing huge areas of coral across the U.S., as well as internationally. What really has us concerned is this event has been going on for more than a year and our preliminary model projections indicate it's likely to last well into 2016."
Coral bleaching happens when high temperatures cause the coral to expel symbiotic algae, which gives the coral its color. Short-term bleaching events occur naturally and the coral can recover.
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Long-term events, like the one NOAA scientists are observing, cause coral to lose its primary food source and expose it to disease.
The current event follows bleaching in 2014 that widely affected reefs in the main Hawaiian Islands.
"Last year's bleaching at Lisianski Atoll was the worst our scientists have seen," said Randy Kosaki, NOAA's deputy superintendent for the monument. "Almost one and a half square miles of reef bleached last year and are now completely dead."
Global bleaching first occurred in 1998, during a record El Nino, and a second bleaching event happend in 2010.