Heat Stress And Rare Black Band Disease Devastate Great Barrier Reef Corals

A severe combination of extreme ocean temperatures and a rare coral disease has caused catastrophic losses among Goniopora corals at One Tree Reef on the Great Barrier Reef. Scientists report that three-quarters of colonies at the study site have died, marking one of the most alarming climate-linked mortality events recorded in recent years.

Mass Bleaching Followed By Aggressive Infection

Researchers observed that prolonged heat stress triggered widespread bleaching across 112 monitored colonies. Weakened by temperature-induced stress, the corals then succumbed to black band disease, a virulent bacterial infection that rapidly destroys living tissue. The study notes that Goniopora, usually regarded as thermally tolerant, experienced unprecedented mortality, underscoring the severity of conditions.

Record-Breaking Temperatures And Disease Dynamics

Between late 2023 and early 2025, water temperatures exceeded bleaching thresholds for extended periods, with readings above 28°C for 74 consecutive days and peaks reaching 34–35°C. The disease appeared in early 2024 and spread rapidly, affecting more than 60 per cent of bleached colonies within weeks. Surveys of over 700 colonies reflected the same pattern: bleaching, rapid onset of disease and major population decline.

Why The Outbreak Is Unusual

Black band disease is typically associated with nearshore pollution, yet One Tree Reef’s offshore location limits such stressors. While the lagoon experiences moderate nutrient inputs, this factor alone could not explain the outbreak. The disease affected only bleached Goniopora colonies and did not occur in other coral genera that bleached during the same event, highlighting a unique vulnerability within this species.

Exam Oriented Facts

• About 75% of Goniopora colonies at One Tree Reef died following bleaching and disease.
• Black band disease affected over 60% of bleached colonies within weeks.
• Water temperatures exceeded 28°C for 74 consecutive days, with peaks of 34–35°C.
• The study was published in December 2025 in Proceedings of the Royal Society B.

Global Implications For Coral Reef Survival

Scientists warn that this event forms part of the fourth global mass bleaching episode, affecting nearly 84 per cent of reefs worldwide. The collapse of large, structure-forming corals threatens biodiversity, fisheries and coastal protection. Experts stress that coral resilience is diminishing rapidly and that only urgent global emissions reductions can curb the accelerating decline of reef ecosystems.