South Pacific coral hit by warmer waters

Expert says return of El Niño conditions means global die-off increasingly likely, though it may not be as severe as in 1998 and 2010
Karl Mathiesen The Guardian 1 Apr 15;

The corals of the South Pacific have been ravaged by bleaching, according to US government scientists.

The National Oceanic and Atmospheric Administration (Noaa) said a global die-off was increasingly likely with the return of El Niño conditions.

The warmth that caused an unprecedented die-off in the North Pacific in the second half of 2014 shifted southwards in the southern summer. Noaa said reefs off the Solomon Islands, Vanuatu, Tuvalu, Fiji and the Samoas had been hit hard by warm waters in the first months of 2015.

High temperatures are now returning in the north, where reefs off the Marshall Islands and Kiribati are still in recovery.

In March the US National Weather Service announced a new El Niño, the first since 2010. An El Niño involves a warming of a certain patch of the central Pacific that changes weather patterns worldwide. Higher sea temperatures cause coral bleaching.

“The models are looking like El Niño conditions may be around through much of 2015. If so, that will just keep hammering corals in the Pacific,” said Dr Mark Eakin, the coordinator of Noaa’s Coral Reef Watch.

“With the change of seasons we continue to see signs of this developing into a full-fledged global event with warming in the eastern Indian Ocean and starting in the extreme south-western Caribbean.”

Almost all Indian Ocean reefs below the equator are now on alert for bleaching. As the northern summer gets going, the coasts of India, Sri Lanka, Oman, the Maldives and Thailand will also be under threat.

Eakin said the event may not be as bad as previous global die-offs in 1998 and 2010. “At this point I expect 2015 bleaching to not be as severe as 2010 globally. However, it could be worse in some locations, just as we saw record thermal stress in the northernmost Mariana Islands and the north-western Hawaiian islands in 2014.”

Australia’s Great Barrier Reef had so far avoided the worst impacts of the warming, but the prognosis was that the hot patch could hit the site during 2016. “My big concern for the GBR has always been next year,” Eakin said.

Coral reefs are vulnerable to small but persistent increases in water temperature. A 1C rise that lasts a week or more can be enough to cause long-term breakdown of reef ecosystems. Whether or not reefs bounce back from bleaching depends on the health of the reef, particularly its herbivorous fish populations that clean the corals from algae. Overfishing means reefs are now far less likely to recover after bleaching.