About 14% of the world’s coral has been lost in less than a decade, a study of the health of coral reefs has found. In the largest analysis of coral reef health ever undertaken, scientists found that between 2009 and 2018 the world lost about 11,700 sq km of coral – the equivalent of more than all the living coral in Australia. Meanwhile, the report, released by the Global Coral Reef Monitoring Network on Tuesday, found that reef algae, which grows when coral is under stress, soared by 20% between 2010 and 2019. The report features data collected by more than 300 scientists from 73 countries across 40 years, including 2m individual observations. The study, which analysed 10 regions with coral reefs, showed that coral bleaching events caused by raised sea surface temperatures were the biggest factor behind coral loss. It found that one such mass bleaching event in 1998 led to the loss of 8% of the world’s coral, or about 6,500 sq km, with the biggest impact observed in the Indian Ocean, Japan and the Caribbean. Experts said the decline of the last decade came amid continuous raised sea surface temperatures. They called for urgent action and said climate breakdown was the biggest threat to the world’s reefs. However, the report also offers signs of hope. Scientists found that despite the stresses reefs were under, many remained resilient and had the potential to recover under the right conditions, particularly if action was taken immediately to halt global heating. “The news is mixed,” said Paul Hardisty, the chief executive of the Australian Institute of Marine Science. “There are clearly unsettling trends toward coral loss, and we can expect these to continue as warming persists. Despite this, some reefs have shown a remarkable ability to bounce back, which offers hope for the future recovery of degraded reefs. “A clear message from the study is that climate change is the biggest threat to the world’s reefs, and we must all do our part by urgently curbing global greenhouse gas emissions and mitigating local pressures.” Coral reefs cover just 0.2% of the ocean floor but are home to at least a quarter of all marine species. They provide a vital habitat, as well as an important source of protein, medicines, food and jobs as well as protection from storms and erosion for millions of people. While in the last decade mass bleaching events have been so close frequent there has not been time for coral to recover, scientists noticed some revival in 2019 when reefs regained 2% of coral cover. This, they say, raises hope that if the factors putting pressure on reef ecosystems ease, there is potential to recover within a decade to pre-1998 levels. Other pressures on coral come from overfishing, unsustainable development on coasts and declining water quality. The latest findings follow a separate analysis last month that revealed the world’s coral reef cover had halved since the 1950s.