The Summer One Third of the Great Barrier Reef Died

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.