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By Associated Press

HONOLULU — Abnormally warm ocean temperatures are creating conditions that threaten to kill coral across the equatorial Pacific, north Pacific and western Atlantic oceans, the National Oceanic and Atmospheric Administration said Monday.

Coral bleaching occurs when coral is stressed by changes in its environment, causing it to release algae living in its tissue. The coral then turns pale or white and becomes more susceptible to disease. In severe cases, the coral can die, permanently changing the habitat for fish and shellfish.

"The bleaching that started in June 2014 has been really bad for corals in the western Pacific," Mark Eakin, NOAA's Coral Reef Watch coordinator, said in a news release. "We are worried that bleaching will spread to the western Atlantic and again into Hawaii."

Ocean temperatures, light and nutrient levels can cause bleaching. But NOAA says only warm temperatures can cause the widespread bleaching that scientists have been seeing since last year. In 2014, Hawaii experienced widespread bleaching for the first time in nearly two decades. If it happens again this year, it would be the first time in history the Hawaiian Islands saw consecutive years of bleaching, NOAA says.

Coral reefs are a critical part of the ecosystem, and their health is vital to the ocean environment. Coral cover just one-tenth of the ocean floor, but they are home to 25 percent of known marine species.