Early results from an as-yet unpublished study indicate that half of all the coral in the Great Barrier Reef died within a year. Two separate bleaching events in the summers of 2016 and 2017 caused large swathes of the reef to die off, and while scientists began to study the phenomenon immediately, the extent of the damage is only now beginning to come to light. Terry Hughes, director of the ARC Center of Excellence for Coral Reef Studies, has been researching the effects of these events, and says the reef “has transformed into a completely new system”.
Scientists believe the recent destruction can be attributed to a rise in temperature brought on by a combination of climate change and the major El Niño event that occurred between 2014 & 2016. A study of the incident in 2016 conducted by Hughes and published in the journal Nature earlier this year revealed that roughly one-third of the reef’s coral died within a 9 month period. Hughes provided The Atlantic with the early results of his study into the 2017 crisis, which brought the number of coral that died up to half.
The coral in the Great Barrier Reef rely on a type of algae known as zooxanthella to provide oxygen and energy to them through photosynthesis. In exchange for this, the algae are given a safe place to live within the polyps of the coral. But when the water becomes too hot, the coral eject these algae, and begin to die off as they slowly starve. It is the loss of these colourful algae that gives us the term “coral bleaching”.
Perhaps most alarming is not the scale at which the coral bleached, but the rate at which they died. Usually, an increase in temperature would cause the coral to eject some algae, but if the temperature returns to normal within a few weeks, they can reaccept the algae and survive. But half of the coral from the 2016 event died soon after bleaching as a direct result of the heat, meaning they did not even have time to starve to death.
The Great Barrier Reef stretches for 2,300km off the coast of north-eastern Australia, covering an area of 348,700km². It is home to over 1,500 species of fish, 134 species of sharks & rays, and 6 species of marine turtles. It also houses almost half of the species of hard coral, as well as one-third of all the soft coral in the world. The destruction of the coral is likely to have a major impact on the entire ecosystem and place the survival of many of these species at risk. As coral reefs take decades to form, it would take at least 100 years without another event like this for the Great Barrier Reef to recover. Unfortunately, a recent UN report found that the world is only on track to meet one-third of its target for the Paris Agreement, which aims to keep global temperatures from rising by more than 2 degrees this century.
The authors of the newest study conclude that the health of reefs across the world will most likely continue to deteriorate over the next century, before the remaining colonies form into smaller "heat-tolerant reef assemblages". Hughes stresses that he believes it is still possible to preserve the Great Barrier Reef as a whole, but that our success depends on our ability to reduce greenhouse-gas emissions in the next few years.