The scientists have recently reported that 30% of the reef’s corals have died in a catastrophic nine-month marine heatwave in 2016. Extreme weather events due to anthropogenic global warming and El Nino are rapidly emerging as major threats to the ecosystems. The global warming has triggered the episodes of mass coral bleaching of Great Barrier Reef which occurs when the relationship between corals and their photosynthetic symbionts zooxanthellae breaks down, turning the coral pale.

The study newly published in Nature (Global warming transforms coral reef assemblages.) by Prof Terry Hughes, the director of the ARC Centre of Excellence for Coral Reef Studies has analysed the relationship between bleaching, heat exposure and the mortality of corals in initial and longer terms. The new patterns of bleaching did not predict the identity of the corals that ultimately died, many corals died suddenly from heat stress, and that others died slowly following the depletion of their zooxanthellae. The rapid death of corals has led to a radical shift in the composition and functional traits of corals assemblages on thousands of individual reefs, transforming large swaths of the Great Barrier Reef from mature and diverse assemblages to a highly altered, degraded system.

Prof Terry Hughes told that heatwaves had been more harmful than historical coral bleaching events, where on average 8% to 12% of corals died. As per the recent mapping by the Scientists, the geographical pattern of marine heatwave (2016) impact on coral is evident along 2,300 Km long Great Barrier Reef. They have found a close relationship between the corals’ death and areas where heat exposure was most extreme. The northern third of the reef was the most severely affected. The research has shown that 29% of the 3,863 reefs that build up the Great Barrier Reef have lost two-thirds or more of their corals.

The combined effect of these threats has weakened the Reef’s resilience, affecting the marine ecosystem and predicted to become more vulnerable in the future. That’s why we need to act quickly and strategically to fight for the conservation of the Great Barrier Reef.