Published by The Nautical Nerds: 19 September 2026
Originally reported: 11 August 2026
This is the source report date, not necessarily the date of the event.
The Australian Institute of Marine Science’s latest manta‑tow surveys show hard coral cover either increased or remained stable across the northern, central and southern sectors of the GBR during the 2025‑2026 field season, despite ongoing heat stress and emerging crown‑of‑thorns outbreaks.
The Australian Institute of Marine Science (AIMS) completed its annual Long‑Term Monitoring Program for the Great Barrier Reef (GBR) in June 2026, analysing data collected from 121 reefs between August 2025 and June 2026. Using standard manta tow surveys that sweep roughly 2,000 m² per tow, researchers recorded hard coral cover percentages for the northern, central and southern regions of the reef.
In the northern sector, the average hard coral cover increased from 30.0 % in 2025 to 35.1 % in 2026 – a relative rise of 16.7 %. The central region showed a similar upward trend, moving from 28.6 % to 31.6 %, a 10.2 % relative increase. The southern sector displayed a slight decline, slipping from 26.9 % to 26.4 %, a 2.0 % relative decrease. All three changes fell within the credible intervals of the monitoring programme, meaning the variations could be within the margin of error rather than representing a definitive shift.
Three reefs exceeded the 75 % hard coral cover threshold, a benchmark often associated with high‑quality reef health. These outliers provide valuable reference sites for future restoration and resilience studies. However, the broader picture remains mixed. While the overall trend suggests stability or modest gains, the data also reveal the continued presence of crown‑of‑thorns starfish (COTS). COTS were detected on 27 reefs across the GBR, with established outbreaks confirmed on five reefs. A fifth wave of COTS activity appears to be emerging in the northern region, though no severe outbreaks were recorded during the survey period.
Heat stress continued to challenge the reef. Sea‑surface temperatures were recorded 0.7‑1.2 °C above the long‑term average, generating degree heating weeks (DHWs) that surpassed the NOAA Coral Bleaching Alert Level 2 in parts of the north. Yet, monsoon cloud cover during the summer of 2025‑26 helped moderate sea‑temperature spikes, limiting bleaching impacts to a regional alert rather than a full‑scale event. In contrast, the 2024 mass bleaching event and the 2025 bleaching episode had more pronounced effects, but those impacts were largely absent from the 2026 dataset.
Cyclone activity added another layer of complexity. Cyclone Koji, a category 1 system, passed over the central GBR in early 2026, causing only minor coral loss. A far more powerful system, Cyclone Narelle (category 5), is projected to affect the northern reefs later in 2027, prompting AIMS to plan a comprehensive post‑storm assessment.
The Great Barrier Reef Marine Park Authority (GBRMPA) and the National Oceanic and Atmospheric Administration (NOAA) continue to collaborate on monitoring and alert frameworks. Their joint efforts ensure that any rapid changes in coral health, such as sudden declines near Lizard Island (up to a 5 % drop reported), are quickly identified and communicated to managers and stakeholders.
Overall, the 2026 survey underscores a nuanced narrative: while hard coral cover shows resilience in many areas, ongoing threats from warming seas, COTS, and future cyclones remain. The data reinforce the need for sustained monitoring, adaptive management, and proactive measures to curb warming trends and mitigate COTS impacts.
Looking ahead, AIMS will integrate the forthcoming Cyclone Narelle impact assessment into its 2027 monitoring cycle, while also refining predictive models that link monsoon patterns with bleaching risk. Maintaining or improving the observed hard coral cover will depend on limiting further temperature rises and managing COTS populations through targeted removal programmes.
The findings provide a crucial benchmark for the reef’s trajectory toward the 2050 restoration goals, offering both hope and a reminder that vigilance is essential for the GBR’s long‑term survival.
Why this matters
Hard coral cover is a primary indicator of reef health, influencing fish abundance, tourism value and coastal protection. Stable or rising cover suggests that management actions and natural resilience are buffering the reef against climate‑related stressors, but the persisting COTS presence and looming cyclone threats highlight the fragility of this balance.
What happens next
AIMS will conduct a detailed impact survey of Cyclone Narelle in 2027 and will expand COTS removal efforts on reefs showing early signs of outbreak, while continuing to track temperature anomalies and bleaching alerts across the GBR.
Marine science glossary
- Degree Heating Weeks (DHWs)
- A metric that accumulates heat stress over twelve‑week periods; higher values indicate greater risk of coral bleaching.
- Crown‑of‑thorns starfish (COTS)
- A coral‑eating predator that can cause rapid declines in hard coral cover when outbreaks occur.
- Manta tow survey
- A method where a manta‑frame net is towed behind a vessel to sample benthic organisms over a known area, typically 2,000 m² per tow.
- Credible interval
- A statistical range that conveys the uncertainty around an estimate, similar to a confidence interval.