Acute effects of a prolonged high-intensity marine heatwave on coral communities of Ningaloo lagoon

Updated: 2026-10-30

Increasingly severe marine heatwaves are expected to continue under current greenhouse gas emissions, with direct consequences for ongoing Global Coral Bleaching Events (GCBEs). We used in situ sea temperatures and ecological surveys to assess how coral communities responded to a severe marine heatwave along the Ningaloo coast during the Fourth GCBE. Sustained warming in the Ningaloo lagoon during 2024/25 caused Degree Heat Weeks (DHW) to exceed the coral bleaching threshold (4 ºC-weeks) for 23 weeks (January-June 2025), peaking at 18–19 ºC-weeks in April 2025 based on a 12-week sliding window; a wider 20-week window indicated 24 ºC-weeks occurred in May 2025. Heat stress was apparent in most coral families and growth forms at all ten survey sites from February to October 2025. However, the highest frequencies of heat stress (23–48% of colonies) and recent mortality (25–46%) were observed in May across the northern sites with the most bleaching-susceptible coral types. Accordingly, live coral cover in the north declined 75% from February (23 ± 2% cover) to October (6 ± 1%), while southern sites remained relatively stable (10–12% cover). Wider effects were apparent in the loss of juvenile corallivorous fishes and a three-fold increase in corallivorous Drupella densities at northern sites. Successive heatwaves have reduced live coral cover to a historical low in many sections of northern and southern Ningaloo lagoon.