Recurrent Mass-Bleaching and the Potential for Ecosystem Collapse on Australia’s Great Barrier Reef

Coral reefs are extremely vulnerable to human-induced climate change. Most notably, increasing ocean temperatures are causing increasing incidence and severity of mass coral bleaching. There have been three major episodes of mass-bleaching on Australia’s Great Barrier Reef (GBR) in just the last 5 years, corresponding with extreme temperatures in 2016, 2017 and 2020. Recurrent episodes of mass-bleaching are compounding upon pre-existing disturbances and pressures to suppress coral cover and undermine key ecosystem processes, which may ultimately result in ecosystem collapse. The potential for ecosystem collapse on the GBR is already apparent based on transformation in coral assemblages and system-wide declines in coral recruitment in the immediate aftermath of recent mass-bleaching episodes, which are unlikely to be restored with accelerating changes in environmental conditions, and increasing incidence of large-scale and severe mass-bleaching episodes. Significant improvements in the management of anthropogenic pressures and disturbances are fundamental for conserving the GBR, but averting ecosystem collapse requires immediate and effective action to redress global climate change.