Multi-scale observations during the 2024 mass coral bleaching event on Heron Reef, Australia

In the Austral summer of 2023–2024, the Great Barrier Reef, Australia, experienced a significant mass coral bleaching event, driven by record-setting sea surface temperature anomalies. This occurrence was part of the fourth recorded global coral bleaching event. A collaborative effort was initiated between researchers from different disciplines on Heron Reef (23°27’S, 151°55’E), to fill critical gaps in our understanding of how marine heatwaves influence corals across varied ecological and spatial scales. Coral bleaching was quantified using environmental and ecological data captured across three spatial scales: the reef, community, and individual colony level. Data were collected using satellite imagery, in situ ecological surveys, temperature loggers and manipulative experiments, conducted across multiple reef zones and depths. Bleaching responses were quantified primarily from 15 January to 31 May 2024. At the reef scale, satellite remote sensing revealed that 65% of the live coral area on the reef slope presented some level of bleaching. Both reef and community-scale analyses, including citizen science surveys, indicated that the windward east reef slope had the greatest bleaching impacts. Colony-scale investigations revealed finer-scale bleaching responses, such as overall reductions in growth rates across all sites and taxa, higher bleaching prevalence in hard carbonate substrate as opposed to rubble habitats, higher bleaching susceptibility in juvenile plate corals compared to branching and massive morphologies, and intra-specific variation in thermal stress response within a population of Stylophora pistillata. This multi-scale, cross-disciplinary approach provides insights into the variability of coral bleaching at different spatial scales and underscores the importance of collaboration and scale-appropriate monitoring to accurately quantify impacts and effectively inform reef managers.