Global coral bleaching event might become new normal, expert warns

Bleaching may be standard by 2020s says leading reef researcher as new images show the damage to areas around Japanese islands of Okinawa
Michael Slezak The Guardian 22 Sep 16;

The worst global bleaching event on record could simply be the new normal, according to one of the foremost experts on coral reefs and their response to warming oceans.

Mark Eakin, head of the Coral Reef Watch program at the US National Oceanic and Atmospheric Administration, has told the Guardian he was hopeful the current global bleaching event would end in 2017, but said it was possible it would just roll on, alternating between the northern and southern hemispheres as the seasons changed.

Some of the most recent reefs to be hit by the unprecedented event are those around the Japanese islands of Okinawa.

Eakin said he had received preliminary reports that some reefs around the Japanese islands of Okinawa had 90% of their coral bleached, and about 10% of it had died so far.

“What I’d heard was that this is the worst since 1998,” Eakin said.

Striking new images reveal the impact unusually warm oceans are having on coral reefs around Okinawa in Japan have been shared exclusively with the Guardian.

Coral begins to bleach when comes into contact with water that is unusually warm. Unless that water returns to normal temperatures quickly, it begins to die.

Sometimes when coral is moderately stressed, it over-expresses some of its colour pigments, glowing in unusually rich colours, in what’s known as “fluorescing”. Each state – bleached, fluorescent and dead coral – was seen in striking detail around Okinawa.

“The fluorescing was spectacular, especially the corals that were glowing a brilliant shade of blue,” said Stephanie Roach the underwater photographer from XL Catlin Seaview Survey who took the images.

She said the bleaching was widespread in the shallow areas, generally under about two metres in depth. In that region almost all the branching coral, called acropora, was bleached, if not dead.

She said as she went below 4m, the bleaching was more sporadic.

As is commonly the case with severe bleaching, the rest of the ecosystem appeared to be suffering too, with Roach reporting that she saw very few fish, and those that she did see were mostly herbivores, which would be feeding on the algae beginning to grow over dead coral.

Richard Vevers from XL Catlin Seaview Survey said the bleaching appeared to be similar to what they witnessed in the Maldives in May, except for the widespread and spectacular fluorescing.

“It is certainly unusual to witness this level of fluorescing, however we did see even more of it in New Caledonia,” Vevers said.

The global coral bleaching event began in 2014 as a splurge of warm water spread across the Pacific Ocean was pushed further through 2015 and early 2016 by a strong El NiƱo weather pattern. It has continued during an unprecedented run of record warm weather.

The phenomenon of global coral bleaching was seen for the first time in recent decades, and the current event is the longest and most severe such event recorded.

Every major reef region has been hit by it, and some areas like Hawaii have been affected three years in a row.

Eakin said although there wasn’t a global coral bleaching event in 2013, every year featured bleaching somewhere in the world. That meant some of those regions had bleached four years in a row.

Eakin was speaking from Guam, where he was attending a US Coral Task Force meeting. He said some reefs around Guam had been hit for a fourth year in a row.

Eakin said the current forecasts suggested there would be bleaching next in Micronesia and the Marshall Islands and there was a good chance of bleaching in the Caribbean.

“It’s not finished yet but I’m hopeful at this point we are going to be seeing the end of it soon,” Eakin said.

But worryingly, Eakin said there was no guarantee. Forecasts as far out as 2017 were not very reliable but were already suggesting some warming in the Pacific, which could affect corals there again.

“I expect to see some bleaching every year from now on,” Eakin said. “The questions is: Does it continue to look like a global event, or is it just places here and places there?”

“At some point, we’re probably going to hit that level [of global warming] where it doesn’t go away and it’s continuous,” Eakin said. “The climate models have been saying for well over a decade that we’re looking to some time around the 2020s where global bleaching becomes the norm.”

Eakin said he was still hopeful that the models were over-predicting the bleaching risk in the future but he was also worried they could be under-predicting.

“That’s always been one of the problems – the global climate models tend to under-predict things,” Eakin said.

No comments:

Post a Comment