Scientists have chronicled the “mass mortality” of corals on the Great Barrier Reef, in a new report that says 30% of the reef’s corals died in a catastrophic nine-month marine heatwave. The study, published in Nature and led by Prof Terry Hughes, the director of the ARC Centre of Excellence for Coral Reef Studies, examined the link between the level of heat exposure, subsequent coral bleaching and ultimately coral death. The extent and severity of the coral die-off recorded in the Great Barrier Reef surprised even the researchers. Hughes told Guardian Australia the 2016 marine heatwave had been far more harmful than historical bleaching events, where an estimated 5% to 10% of corals died.

“When corals bleach from a heatwave, they can either survive and regain their colour slowly as the temperature drops, or they can die,” Hughes said. “Averaged across the whole Great Barrier Reef, we lost 30% of the corals in the nine-month period between March and November 2016.” The scientists set out to map the impact of the 2016 marine heatwave on coral along the 2,300km length of the Great Barrier Reef. They established a close link between the coral die-off and areas where heat exposure was most extreme. The northern third of the reef was the most severely affected.(theguardian)…[+]