Changing dynamics of Great Barrier Reef hard coral cover in the Anthropocene

Abstract

Cycles of disturbance and recovery govern the temporal dynamics of living coral cover on coral reefs. Monitoring the state of the Great Barrier Reef at regional and individual reef scales has been ongoing by the Long-Term Monitoring Program at the Australian Institute of Marine Science since 1986. After a period of relative stability between 1986 and 2010, the latest decade of surveys recorded increased frequency of intense, large-scale disturbance events and coral cover has reached unprecedented lows and highs in each region. Following the consecutive bleaching events in 2016 and 2017, widespread recovery occurred on the northern and central Great Barrier Reef between 2017 and 2022, which was halted in 2023. An examination of the effects of the 2022 bleaching event revealed that the direct and indirect impacts of this event, along with ongoing crown-of-thorns starfish outbreaks, notable incidences of coral disease, and the passage of a tropical cyclone all contributed to the most recent coral cover changes across the Great Barrier Reef. The prognosis for future disturbances suggests increasing and longer-lasting marine heatwaves, continuing severe tropical cyclones and the ongoing risk of outbreaks of crown-of-thorns starfish. Although the observed capacity for recovery is a cause for cautious optimism for the overall state of the Great Barrier Reef, there is increasing concern for its ability to continue to bounce back in the face of escalating climatic pressure.