Science & Health

El Niño Is Killing Earth's Coral Reefs

El Niño Is Killing Earth's Coral Reefs

As if that binge-drinking Godzilla El Niño hadn’t caused enough trouble, scientists at the US National Oceanic and Atmospheric Administration say it’s exacerbating the longest coral bleaching event in history. It began in 2014 and might not end for two more years.

Last spring, marine biologists reported that we’re currently in the midst of one of the largest coral die-offs they’d ever seen, and the third global bleaching event on record. This week at the Ocean Sciences Conference in New Orleans, NOAA will offer its first big update on the situation. And it ain’t good. The strongest El Niño on record — which has led to elevated temperatures in the equatorial Pacific and in other tropical ocean basins worldwide — is prolonging the die-off. Based on ocean temperature forecasts for the coming year, NOAA predicts this bleaching event could extend well into 2017.

Coral are symbiotic organisms that are part animal, plant and mineral. They are highly temperature-sensitive, an unfortunate condition given our unrelenting global heat wave. When the water gets too toasty, coral expels its zooxanthellae, the symbiotic algae that it depends on for food. This leads to the condition marine scientists call “bleaching”. If a bleaching event goes on for too long, the coral will starve.

That’s exactly what’s been happening in extra-warm tropical waters around the world for about two years. Globally, over 70 per cent of the planet’s reefs are currently being exposed to elevated temperatures that place them at risk for bleaching.

“All of this started in 2014, during what was almost an El Niño year,” Mark Eakin, a biological oceanographer at NOAA, told Gizmodo. “On top of that, we’ve now added what is arguably the strongest El Niño on record. This has turned into the longest bleaching event we’ve ever seen, and it’s going to keep causing the same destruction we saw in the past.”

This isn’t the first time El Niño has sounded a death knell for coral reefs. The first two global bleaching events, in 1998 and 2010, also coincided with El Niño years. What worries Eakin and other marine biologists most is the uptick in the frequency and duration of these events. As global temperatures continue to rise, fuelling ever more powerful El Niño events, coral are being left with little time to recover before they get hit by another hot spell.

El Niño Is Killing Earth's Coral ReefsTop image: Maximum thermal stress measured by NOAA satellites in 2014 and 2015, along with locations of the worst coral bleaching events. Bottom image: Four month bleaching outlook for February – May 2016, based on NOAA’s Climate Forecast System. Via NOAA.

“You have reefs getting hammered time and time again, year after year,” Eakin said, pointing out that both Florida and Hawaii have seen several consecutive bleaching episodes since 2014. And if bleaching doesn’t kill a coral reef outright, it weakens it, making it more susceptible to diseases and the ravages of ocean acidification. “Recovery at this point is very limited,” he added.

In the past few years, we’ve seen several ambitious efforts to rescue our planet’s ailing reefs. These include a captive breeding program, which earlier this month announced that lab-grown coral have successfully reproduced in the wild for the first time. Efforts like this are an important way to fortify reefs against future climate change and disease. In order to preserve these biodiversity hotspots for the long term, however, much more dramatic action is needed.

“The big solution is what went on at COP21 in December,” Eakin said, referring to the climate conference at which 195 nations pledged to wean themselves off fossil fuels this century. “We’re finally planning to take serious action to address climate change — and that’s the root cause here.”

Top image via XL Catlin Seaview Survey


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