Reef health update | 24 May 2024

In March this year, the Reef Authority announced a mass coral bleaching event following aerial surveys which recorded varying levels of bleaching from Gladstone in the south to reefs beyond Lizard Island in the north. This was followed in April with the National Oceanic and Atmospheric Administration in the US declaring a fourth global mass coral bleaching event affecting reefs across more than 53 countries.
The Reef Snapshot: Summer 23-24 was released on 17 April 2024, detailed conditions on the Reef and confirmed the cumulative impacts experienced across the Reef the 2023-24 summer were higher than previous summers.
Temperature
Sea surface temperatures across the Marine Park are currently below the threshold that typically causes heat stress to corals; however they are still 1 degree above the average for May.
The El Niño weather pattern has ended as sea surface temperatures in the Central Pacific cooled to neutral El Niño-Southern Oscillation (ENSO) levels in April.
The month of May has seen low rainfall marking the start of northern Australia's dry season.
Reef Health
As detailed in the Reef Snapshot: Summer 23-24, the Great Barrier Reef has been subjected to cumulative impacts over summer.
Two cyclones crossed the Reef this summer: Cyclone Jasper crossed the Great Barrier Reef north of Port Douglas as a category 2 in December and Cyclone Kirrily crossed the Reef offshore from Townsville as a category 3 in January. Damage to corals by cyclonic waves was reported in the northern and central regions after these events.
Flood plumes associated with Cyclone Jasper led to freshwater coral bleaching and some mortality, particularly among inshore environments.
The level of heat stress exposure across the Reef over summer was unprecedented.
Results from aerial and in-water surveys completed to date reveal the bleaching is variable across the Reef, ranging from no bleaching detected in the least exposed areas on some reefs up to over 90 per cent coral cover bleached in the most exposed areas on other reefs.
We have recorded coral mortality and bleaching across all three regions of the Reef. Corals in the northern and southern sections of the Reef were most affected by heat stress and subsequent bleaching.
Coral mortality has been recorded mainly on the shallowest parts of reefs but extending down to 20 metres on those most affected.
Evidence of coral recovery is also being observed, mainly of partially bleached corals. In general, partially bleached corals have a greater likelihood of recovering than fully bleached corals.
Since the beginning of summer, more than 8300 in-water surveys on 273 reefs have been submitted through the Reef Authority’s Eye on the Reef Program by key contributors such as tourism operators, the Crown-of-thorns Starfish Control Program, and Queensland Parks and Wildlife Service. In addition, more than 60,000 images have been collected through the Tourism Reef Protection Initiative, providing a valuable record of coral health.
This data will help Reef managers and scientists determine the overall impact of the event, including an assessment of coral recovery vs coral mortality.
Observations to date show that the 2024 coral bleaching event is significant - but the severity of coral bleaching has been variable across the entirety of the Great Barrier Reef. We will not know the full impact this event has had on the long-term trend in coral cover until the Australian Institute of Maine Science’s Long-Term Monitoring Program Annual Summary Report of Coral Reef Condition in 2025.
What we do know is that the Great Barrier Reef, thanks in part to its sheer size and amazing biodiversity, is a resilient ecosystem.
We have seen the Reef bounce back before from severe impacts such as the consecutive bleaching events in 2016 and 2017. This was followed by widespread coral recovery between 2017 and 2022.
Management Actions
Ongoing ecosystem management actions such as enforcing compliance with the Reef’s zoning plan and controlling the coral-eating crown-of-thorns starfish are critical in supporting and building the Reef’s resilience.
However, this resilience is likely to be constrained by escalating climate change, which is driving more frequent and severe events, including mass coral bleaching.
Safeguarding the long-term future of the world’s coral reefs requires urgent global action to reduce greenhouse gas emissions.
Staff from the Australian and Queensland government are out patrolling the Marine Park as part of the Reef Joint Field Management Program, monitoring and ensuring zoning laws and Marine Park rules are being followed.
View the full Reef health update: www2.gbrmpa.gov.au/learn/reef...