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The Largest Coral Atoll In The World Lost 80 Percent Of Its Coral To Bleaching

A reef in Kiritimati after the bleaching event. CREDIT: KRISTINA TIETJEN, UNIVERSITY OF VICTORIA
A reef in Kiritimati after the bleaching event. CREDIT: KRISTINA TIETJEN, UNIVERSITY OF VICTORIA

As global ocean temperatures begin to recover from the record-breaking El Niño, the tremendous impact on the world’s coral reefs is still being calculated.

Coral reefs are more important than many people realize: Taking up just 0.2 percent of the ocean, they support about a quarter of all marine species, and provide support to livelihoods of 500 million people. But beyond that, a healthy reef is stunningly beautiful. They’re part of what makes life on Earth so special.

During an El Niño event, corals can “bleach” — abnormally hot water makes their symbiotic bacteria emit toxins, and the coral polyps, which are tiny animals, expel them reflexively. Since healthy bacteria provide food to the corals, without them, the corals can starve to death.

When that happens, reefs that have grown up over centuries can die in a matter of weeks.

White areas indicate bleaching. CREDIT: Julia Baum, University of Victoria
White areas indicate bleaching. CREDIT: Julia Baum, University of Victoria

“This is a huge, looming planetary crisis, and we are sticking our heads in the sand about it,” Justin Marshall, a coral researcher at the University of Queensland, recently told the New York Times. Since coral reefs are often out of sight, their destruction can also — unfortunately — be out of mind.

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Take Kiritimati (pronounced “Christmas”) Atoll, for example, about 1,300 miles south of Hawaii. If you look at a map of this El Niño, Kiritimati Atoll is right smack dab in the middle. Kiritimati is the largest coral atoll in the world, and up until about 10 months ago, one of the most pristine marine ecosystems on Earth.

Over the past two weeks, a team of researchers led by Julia Baum, a biologist at the University of Victoria and Kim Cobb, a climate scientist at Georgia Tech, has been stationed at Kiritimati, and via hundreds of dives they have taken comprehensive measurements of the reef’s health, or lack thereof in this case.

As corals die from bleaching, the reef as a whole suffers CREDIT: Danielle Claar, University of Victoria
As corals die from bleaching, the reef as a whole suffers CREDIT: Danielle Claar, University of Victoria

Their estimate is, as of early April, about 80 percent of the coral colonies at Kiritimati are now dead, and another 15 percent are severely bleached and likely to die. It’s as if someone decided to cut down 90 percent of the Redwood Forest. Overnight, an entire ecosystem has essentially blinked out of existence.

I spoke with the team by satellite phone on one of their last days of dives, and the shock in their voices was palpable.

“There’s a good chance that this reef will never be the same,” said Cobb. “It’s a wake-up call.”

From cores that Cobb’s team has analyzed, she estimated there’s been nothing like the current die-off in Kiritimati in the 7,000 years of ancient coral history there. About 10 months ago, this reef was still mostly healthy, as it has been for thousands of years. Global warming will make the pressure on global corals even worse in the coming decades, and many of the world’s reefs can expect future bleaching events to occur more frequently. For some, like those in Kiritimati, the last few months — the worst global coral bleaching episode in history — may be a point of no return.

The reef, pre-bleaching event, bustles with life and color. CREDIT: Kieran Cox, University of Victoria
The reef, pre-bleaching event, bustles with life and color. CREDIT: Kieran Cox, University of Victoria

“The Great Barrier Reef has only been under bleaching alert two for a matter of weeks, whereas here it’s been continuous for 10 months now,” says Baum. That means, as far as bleaching goes, “[Kiritimati is] the worst location in the world.”

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And, in fact, that’s part of the reason why Baum and Cobb are focusing their efforts in Kiritimati, and at the epicenter of this El Niño. The records they’ve collected from corals in Kiritimati provide evidence that El Niño events have become more intense there over the last several decades, perhaps as a result of climate change. So far, during this El Niño, severe coral bleaching has been recorded in every ocean basin on the planet.

The temperature surge from El Niño was the driving force behind the widespread bleaching and coral mortality in Kiritimati, but the devastation wouldn’t have been as total without a boost from global warming. Since 1998, when the last big El Niño event peaked, global ocean temperatures have warmed by 0.3 degrees Celsius, enough to push some corals past their survivability threshold. In the hardest-hit regions, like Kiritimati, local water temperatures were as much as 4 degrees Celsius warmer than normal — a death sentence for a coral ecosystem.

Bleached, dying reefs, murky waters. CREDIT: Danielle Claar, University of Victoria
Bleached, dying reefs, murky waters. CREDIT: Danielle Claar, University of Victoria

The National Oceanic and Atmospheric Administration warns that abnormally warm water may linger into 2017, locking in an unprecedented third consecutive year of bleaching on a global scale.

“This is a story that the rest of the world should hear,” Cobb said. She says that the death of the corals at Kiritimati is proof that “climate change isn’t just a steady linear progression to some different kind of planetary state. … Climate change will occur through these kinds of extremes. It’s like a staircase to a different kind of system.”

That we now live with a climate system that can blink out entire ecosystems in a matter of weeks or months should be frightening. This is a changed planet, and Kiritimati Atoll is one of the first tragedies as Earth continues to climb the climate staircase.

Eric Holthaus, self-described “weather nerd,” is a weather and climate journalist and meteorologist for Slate.