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Severe coral bleaching hits Marshall Islands, north Pacific

MAJURO — Record warming of ocean water in the north Pacific has caused unprecedented coral bleaching from Hawaii to the Northern Mariana Islands, say scientists in the United States and the Marshall Islands.

“The worst coral bleaching event ever recorded for the Marshall Islands has been occurring since mid-September,” Dr. Karl Fellenius, the Marshall Islands coastal management extension agent in Majuro, said Friday.

“Major bleaching was seen in Guam and the Commonwealth of the Northern Marianas Islands, the northwestern Hawaiian Islands, the Marshall Islands, and Kiribati,” said Dr. C. Mark Eakin, the coordinator of the U.S. National Oceanic and Atmospheric Administration’s Coral Reef Watch, who is based in Maryland. “Thermal stress levels set new record highs in CNMI and the NWHI and we saw the first widespread bleaching event in the main Hawaiian Islands.”

While bleaching can occur on very hot days in pools of water with little circulation at very low tides on reef flats, it has become a global problem due to greenhouse gas emissions that are causing temperatures to rise. Corals in the Marshall Islands as deep as 40 meters have been damaged or killed by the high ocean temperatures the past several months, Fellenius said.

Contributing to this year’s widespread bleaching is a developing El Niño weather condition in the western Pacific that has caused trade winds to relax, worsening the situation, said Fellenius. During a super El Niño in 1997, global “coral reefs went from being 16 percent dead to an astounding 27 percent in one season,” said Fellenius. “It is difficult to say how bad it is in the Marshall Islands,” he said.

A large table top coral in the Marshall Islands is one of many showing extensive bleaching, a result of higher than normal ocean temperatures over recent months.  Photo by Karl FelleniusA large table top coral in the Marshall Islands is one of many showing extensive bleaching, a result of higher than normal ocean temperatures over recent months. Photo by Karl Fellenius

“But indications from a few sites in Majuro are that more than 75 percent of Acropora sp. are bleached, and likely 25 percent of massive varieties.”

A bad sign for recovery of the corals is that within a week of the bleaching all corals have been covered in algae growth.

Unless fish eat the algae, it will kill the corals by preventing new coral growth. Fellenius said the problem is acute in the urban centers, where subsistence and commercial fishing has reduced fish populations significantly.

He said there have been coral bleaching incidents in the Marshall Islands over the years. “The difference now is in scale,” Fellenius said. “Recent observations around Majuro, Arno and Kwajalein atolls show unprecedented bleaching.”

Fellenius said ocean water has begun to cool, so the worst of the bleaching in the Marshall Islands may be over.

Eakin said the recent coral bleaching is a Pacific-wide event. “We are worried that 2015 may be even worse for many areas,” he said. “We expect the bleaching to continue, moving a bit south as the sun is now heating the southern tropics most strongly.”