Between 2020 and 2023, the Great Barrier Reef experienced multiple mass coral bleaching episodes associated with elevated sea surface temperatures. Bleaching was observed across significant portions of the reef system, with some monitored zones reporting bleaching levels above 50% during peak thermal stress.
Coral bleaching occurs when sustained temperature anomalies disrupt the symbiotic relationship between corals and their photosynthetic algae. During this period, degree heating weeks exceeded established thresholds in multiple reef sectors, and ecological consequences included partial mortality in some areas, altered species composition, and reduced structural complexity.
Within SIGNAL’s structure, the focus remains on measurable signals: sea surface temperature deviation, degree heating weeks, bleaching extent, and confirmed mortality where available. The sequence is recorded without assuming irreversible system collapse or projecting future trajectory.
Selected metrics: • SST anomalies: frequently >1.0°C above baseline in affected zones • Bleaching extent: >50% in some monitored sectors • Recurrence: multiple events within a compressed time window
