Image copyright Coral CoE/Gergely Torda Image caption Bleaching causes coral to lose the algae which give it its colourProlonged ocean warming events, known as marine heatwaves, take a significant toll on the complex ecosystem of the Great Barrier Reef. This is according to a new study on the impacts of the 2016 marine heatwave, published in Nature. In surveying the 3,863 individual reefs that make up the system off Australia's north-east coast, scientists found that 29% of communities were affected. In some cases up to 90% of coral died, in a process known as bleaching. This occurs when the stress of elevated temperatures causes a breakdown of the coral's symbiotic relationship with its algae, which provide the coral with energy to survive, and give the reef its distinctive colours. Certain coral species are more susceptible to this heat-induced stress, and the 2016 marine heatwave saw the death of many tabular and staghorn corals, which are a key part of the reef'..