HONOLULU (AP) -– Corals at remote atolls northwest of the main Hawaiian islands suffered some bleaching this summer as ocean temperatures rose to higher-than-normal levels for a couple of weeks, but they were spared the large-scale mass bleaching observed this year in Indonesia and other parts of Southeast Asia, scientists said Wednesday.

Corals appear white or “bleached” when the ocean becomes too hot and they expel the algae they rely on to survive. Corals may recover if the algae returns, but they're still significantly weaker and more vulnerable to disease.
Thirty percent of the Kure atoll reef and one-fifth of the Pearl and Hermes atoll reef bleached, according to scientists who spent the past month on a research cruise in the Papahanaumokuakea Marine National Monument. Corals at other atolls inside the monument were unaffected.
“There were certain areas where the bleaching was kind of severe, where it was just a white carpet essentially,” said Peter Vroom, chief scientist of the cruise, which returned to Oahu on Wednesday.
“Other areas you would see a coral head that's had a lot of color, but maybe a quarter of it would be white,” Vroom said.
Scientists say it's unclear what the long-term effect of this summer's bleaching will be. Corals in the monument — which account for 69 percent of all coral under U.S. jurisdiction — were exposed to only two weeks of slightly above normal temperatures.
Rusty Brainard, chief of the NOAA Pacific Islands Fisheries Science Center's coral reef ecosystem division, said coral starts dying after about two months of being exposed to higher-than-normal temperatures.