The Summer One Third of the Great Barrier Reef Died

By Christie Wilcox | May 29, 2016 11:25 pm
Researchers survey bleached corals in the shallow water in Cygnet Bay, Western Australia, during current bleaching event. Photo Credit: Chris Cornwall

Researchers survey bleached corals in the shallow water in Cygnet Bay, Western Australia, during current bleaching event. Photo Credit: Chris Cornwall

April marked the twelfth consecutive month of record-breaking temperatures. That’s an entire year of our planet, on land and in the sea, being hotter-than-ever-recorded since record keeping began in 1880. Such extraordinary warmth is affecting ecosystems globally, but perhaps the hardest hit are coral reefs, whose fundamental organisms are incredibly sensitive to the heat.

Earlier this year, authorities in Australia reported that the Great Barrier Reef was in the midst of its worst bleaching event ever. Surveys above and below the water estimated that over 90% of the reefs were affected by bleaching. Now, as the summer wanes down under, scientists are finally able to begin to assess the lasting damage caused by this event. Their findings are heartbreaking.

“This year is the third time in 18 years that the Great Barrier Reef has experienced mass bleaching due to global warming, and the current event is much more extreme than we’ve measured before,” said Professor Terry Hughes, Director of the ARC Centre of Excellence for Coral Reef Studies at James Cook University, in a press release. “These three events have all occurred while global temperatures have risen by just one degree Centigrade above the pre-industrial period.”

When corals bleach, it indicates that they are stressed, but there is still hope for recovery. Bleaching indicates the loss of the corals’ symbiotic algae, called zooxanthellae, which are essential to the survival and health of the coral. While the color change is dramatic, corals are able to recover from a bleached state, granted that the stress which caused them to bleach in the first place is removed expediently. But if the coral stays too long without its algal aids, it dies, and is often overtaken by much less cooperative algae species. When that happens to too many corals in one area, entire tracts of reef can shift from being coral-dominated to algae-dominated—an often irreversible change of habitat known as a phase shift.

A graphic explaining coral bleaching versus death, from The Great Barrier Reef Marine Park Authority

A graphic explaining coral bleaching versus death, from The Great Barrier Reef Marine Park Authority

The hope was that, although the percentage of reefs with bleached corals noted in April was gut-wrenching, most of them would weather the storm. But after surveys of more than 100,000 corals on 84 different reefs, the results are grim.

The corals of the Great Barrier Reef have been struggling for some time. Scientists estimated that between 1985 and 2012, the Great Barrier Reef lost over 50% of its corals. Some fell victim to crown-of-thorns starfish outbreaks fueled by agricultural runoff, while others were smashed by cyclones or stressed to death by warmer waters. Per year, just under 3.5% of the reef’s corals vanished.

But the reef has never been hit as hard by anything as it was by this most recent bleaching event. Scientists now estimate that 35% of the corals in the north and central sections of the reef, from Townsville, Queensland to Papua New Guinea, are dead.

That’s a decade’s worth of damage in just one summer.

A map of the estimated death of corals on reefs along the Great Barrier Reef. Provided by the ARC Centre of Excellence for Coral Reef Studies

A map of the estimated death of corals on reefs along the Great Barrier Reef. Provided by the ARC Centre of Excellence for Coral Reef Studies

In some areas, particularly south of Cairns, the carnage has been minimal. Scientists say that weather events early in the season kept the southernmost portions of the barrier reef cooler than normal, so that when temperatures spiked in the summer aided by El Niño, the temperatures in the south never reached the extreme highs that areas northward did. Between Cairns and Townsville, surveyors found only 5-20% mortality. But north of Cairns, particularly in the central area off the coast of Cooktown, more than 50% mortality was found. Many of those corals were decades to hundreds of years old.


May A mature field of staghorn coral from Lizard Island in February (top), when surveyors found extensive bleaching, and in April (bottom), with algae grown over the now-dead coral. Photo Credits: ARC Centre of Excellence for Coral Reef Studies

Back in 2012, scientists said that recovery was still possible—that if the stressors caused by climate change and nutrient runoff were relieved, the reef could increase in coral cover by nearly 3% per year. And even if all we did was keep crown of thorns sea stars in check (and there are now highly funded efforts seeking to do just that), the reef could still recover by nearly 1% per year. So before this past year’s bleaching, it was already going to take an estimated half a century to get back to pre-1985 levels. We can now tack on another one to three more decades after this. And that’s even assuming decisive action is taken now to curb our bad habits that have led to this mess in the first place.

I’m thirty years old. I was born in 1985. For much of my life, scientists touted the Great Barrier Reef as one of the great untouched natural wonders of this world—a pristine ocean habitat, safe from the horrors that had wiped out corals in the Atlantic and Caribbean. Now, the world’s largest coral reef ecosystem is dying. Much of it is dead already. And the sobering truth is, even if we righted the ship today, I will not live to see the day that the reef looks how it did when I was born. I can only hope that the Great Barrier Reef of legend isn’t gone forever.

  • OWilson

    Relax, don’t make the common mistake of projecting a 35% loss in one area of the GBR to the whole.

    According to the Scientific American, and even WIKI, the greatest stress factor are the natural cycles of El Nono, particularly damaging in 1998, 2010 and 2015.

    Corals are remarkably resillient, they grow, they die, the move, they are extensive and have been around longer than we have.

    Like the Antarctic ice that is “rapidly melting”, if it didn’t “refreeze” too, it would have been gone a long time ago.

    A little cooling, the next La Nina, and a little balance restored.

    You’ll have your coral reefs to explore and even marvel at their adaptability, (or you can just write them off as gone, and close the book).

    • saymwah

      And maybe you’re wrong.

      • OWilson

        Maybe, but I’m not the narcissist who believes all these doomsday scenarios are about to happen just because I happen to be alive in this brief moment in the earth’s 4,000,000,000 year history. :)

  • abulinix

    To add to OWilson’s comforting message: sure the Great Barrier Reef had already declined 50% in the preceding two decades, and there will be another double-digit decline this year, including complete die-off of some areas, and in 15 years the water temperatures we saw this year will be “normal”, all while inexorable ocean acidification literally dissolves the world’s coral reefs in proportion to rising atmospheric CO2. But Zeno proved long ago that no matter how rapidly corals die off they simply CANNOT disappear completely. So, relax. There will always be corals, however microscopic, for you to enjoy and marvel at… unless, of course, you surrender to the hype and write them off as gone and “close the book,” in which case you obviously can no longer see the pictures in the book, which would be your loss. (And that IS the only place you’ll be able to see coral reefs, soon enough–in books)

    • OWilson

      Your crystal ball must be a little cloudy today, did you get it from Radio Shack?

      Don’t forget the snow, that our grandchildren would never see.

      Make sure we keep some picture books of snowmen for them :)

  • Uncle Al

    Coral bleachings nicely correlate with their waters being contaminated with sunblock chemicals and human waste (bacterial plus excreted pharma and its metabolites re SSRIs and female hormones, contraception and hormone replacement). Exclude all people upstream for two years, including researchers. What better test of causality is there than rigorously doing nothing?

  • Lucia Malla
    • OWilson

      On the contrary, politics and conflicting interests always cloud the AGW industry. They once made a good movie about a similar theme, “JAWS”.

      It can be unintentionally humorous sometimes, like when genocidal dictator Robert Mugabe, funded by the U.N. is first in line for $billions in climate reparations.

      Or even when the U.N. IPCC are fretting about droughts and C02 emission, their greatest “World Heritage Sites”. include major deserts and the Hawaiian volcanoes that pump millions of tons of the stuff out every year :)

      • Uncle Al

        Bleached coral reefs are bellwether AGW warnings to us and our children. They must be maintained, expanded, and propagated worldwide. Consider the summed alternative in 2500 BCE.

        The United Nations must depopulate and level the Hiroshima hypocenter to a mile radius To Remember. It must next install To Remember sites in all civilized nations’ major cities, To Remember. The nuclearsecrecy commercial website has interactive blueprints for these vital World Heritage Sites within /nukemap/. Embrace them as Frank Gehryesque Social Justice constructs.

        Uncle Al offers balloon, candle, Teddy bear, flower franchises directly offsite.

        • OWilson

          For years the real AGW “Bellweather” was the Washington DC cherry blossom blooming date.

          They were blooming early for a few years and they were in panic mode.

          Now they are on average late again, so they are never mentioned, except true believers who get their info from old AGW promoting Site.

  • Lorie Franceschi

    I find it funny that we first were going to go into another ice age, then a hot age and now it is just called global climate change. Well, I ask, which is it? there has been proof for both for a long time. During the American Revolution, there was a mini ice age. Ice cores from the Antarctica show that the earth has survived ice ages and hot ages well before we were around. It will survive us

    • OWilson

      Global politicians decide what the scariest scenario is at the moment.

      We eventually got tired of “global cooling”, and “global warming”, and now folks have “climate change”, fatigue.

      Same scam, different name.

      In ye olden days, it was, “The end is nigh. Give up your worldly goods, and ye shall be saved”.

      This too, will pass!

      • Lorie Franceschi

        LOL glad you got it. Some on here probably are going what the heck?! Global cooling?

    • gryphyn

      The ice age theory was a small number of scientists in the 1970s. That was 40 years ago. Unsurprisingly, we have more and better data than we did then for climate science. Look at the difference in computers over the past 40 years. Climate science has had comparable improvements. And since this is how science works, more data means the theories are updated! At this point, for people in the field, we are at 97% in favor of human caused global warming. ( And yes, the earth will survive regardless but I assume you might enjoy humanity surviving as well?

      • Lorie Franceschi

        Just a thought, computers can be programed to show what you want. I do not disagree with you, but they can be programed. they can program them to show that everything is fine, every thing is getting colder and that every thing is getting hotter with the same data. Just a thought.

  • bwana

    Corals have thrived and died for millions of years. Nothing new with this dying. Just a continuation of nature’s march onward…


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About Christie Wilcox

Dr. Christie Wilcox is a science writer based in the greater Seattle area. Her bylines include National Geographic, Popular Science, and Quanta. Her debut book, Venomous, released August 2016 (Scientific American/FSG Books). To learn more about her life and work, check out her webpage or follow her on Twitter, Google+, or Facebook.


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