Northern and Central GBR are at the highest recorded hard coral levels since monitoring began 38 years ago. The Southern GBR is the 4th highest recorded coral. Impact of bleaching still has to be determined, but the worst reductions in coral in the past have mostly come from cyclones and Crown of Thorns starfish. Bleaching has had little long term effect on the coral cover unless there's actual mortality.

https://www.aims.gov.au/monitoring-great-barrier-reef/gbr-condition-summary-2023-24

This report summarises the condition of coral reefs in the Northern, Central and Southern Great Barrier Reef (GBR) from the Long-Term Monitoring Program (LTMP) surveys of 94 reefs conducted between August 2023 and June 2024 (reported as ‘2024’).

Over the past 38 years of monitoring by the Australian Institute of Marine Science (AIMS), hard coral cover on reefs of the GBR has decreased and increased in response to cycles of disturbance and recovery.

Percent hard coral cover is one standard measure of reef condition recorded by scientists worldwide, it provides a simple and robust measure of reef health and is used in this report. Other important data, such as diversity or composition of coral assemblages, are collected and reported by LTMP in other ways.

Changes in coral cover are qualified with respect to the margin of error, defined by 95% credible intervals (CIs). Credible intervals describe the level of uncertainty in the estimates of hard coral cover.

Above-average water temperatures (i.e. sea-surface temperature anomalies of 1–2.5°C) occurred on the GBR over the austral summer, peaking in March 2024 and resulting in the fifth mass coral bleaching event since 2016.

The mass coral bleaching on the GBR was part of a global event declared by NOAA and ICRI in April 2024.

The Central GBR was impacted by two tropical cyclones: Cyclone Jasper (Category 5 – December 2023) and Cyclone Kirrily (Category 3 – January 2024). Although Cyclone Jasper was a Category 5 in the Coral Sea, it was only Category 2 when traversing the GBR.

Crown-of-thorns starfish (COTS) outbreaks have persisted on four Southern GBR reefs, while four reefs of the Northern GBR have low numbers of starfish.

In 2024, hard coral cover has increased across the GBR, but regional hard coral cover remains similar to that reported in 2022 and 2023. Importantly, most surveys were conducted prior to the mass coral bleaching event and passage of two cyclones, and the full impact of these events is yet to be determined. It's also important to note that bleached coral is still recorded as live coral during surveys, and the fate of these corals is not yet known.