Reef health update | 5 April 2024

Reef health update – 5 April 2024

Aerial surveys conducted over the Great Barrier Reef have been completed and confirm widespread bleaching across all three regions of the Marine Park.

The surveys conducted by the Reef Authority and the Australian Institute of Marine Science assessed more than 1000 individual reefs, including 836 reefs in the Marine Park and 244 reefs in the Torres Strait region.

Reef health

Of the reefs surveyed by air in the Great Barrier Reef Marine Park:

A quarter of individual reefs surveyed recorded no to low levels of bleaching. This included reefs in the far north, along the outer shelf north of Port Douglas and north of Lockhart River where less bleaching was observed.

Half recorded high or very high levels of coral bleaching. Very high bleaching was found on many of the inshore reefs in the central region of the Marine Park. Several mid-shelf reefs from Innisfail to Cape Melville, including the Lizard Island region, were also affected by very high and extreme levels of bleaching.

Less than 10 per cent had extreme levels of coral bleaching. High to extreme levels of bleaching were common in both offshore and inshore reefs in the southern region of the Marine Park.

This week, 63 in-water surveys were conducted across our observer network. Of these, 52 Reef Health Impacts Surveys were carried out and most reported coral bleaching of moderate to severe impact. Variable levels of mortality have been found.

A persistent crown-of-thorns starfish (CoTS) outbreak continued at some reefs in the offshore Swain Reefs, and isolated outbreaks were found on reefs offshore Townsville and in the Whitsundays. There was also a continued build-up of crown-of-thorns starfish in the northern region with increasing densities near Lizard Island and offshore Port Douglas.

The Reef Authority in collaboration with science partners, the Australian Institute of Marine Science and CSIRO, will soon release the Reef Snapshot for Summer 2023-24, which will provide a summary of conditions over the Great Barrier Reef during the past summer, including impacts from elevated sea surface temperatures, cyclones and flooding.

Temperature

Sea surface temperatures remain 0.5-1.5 degrees above average for this time of year.

A build-up of heat stress is again starting to accumulate in the northern and offshore central region but continues to plateau in the southern region.

Rainfall

Above average March rainfall was recorded for Far North Queensland, resulting in very high streamflow in catchments that drain into the Marine Park. 

This has reduced salinity levels in areas between Cairns and Cape Melville, and north of Princess Charlotte Bay. Flood plumes may result in additional stress on reefs already experiencing prolonged heat exposure.

Reef management

The Reef Authority is continuing to work with the Australian Institute of Marine Science, crown-of-thorns starfish control program, Tourism Operators, and researchers on further in-water surveys.

The data from these surveys, combined with the aerial surveys, will give a greater overview of the severity of bleaching among different coral types, habitats, and depths. In-water surveys are critical to quantify coral mortality due to bleaching and heat stress over the coming months.

Over the current holiday period, Marine Park compliance patrols are out in force, particularly at known illegal fishing hotspots, to ensure Marine Park users are doing the right thing to minimise additional stress to the Great Barrier Reef.


Everyone who visits the Great Barrier Reef can do their bit to help protect it. When anchoring boats:

Use public moorings where available and do not anchor within no-anchoring areas – they are there to protect the coral.

Where possible, anchor in sand or mud away from corals and other fragile marine environments. Suitable areas often show up as flat and smooth on your sounder.

Never wrap anchor rope or chain around bommies or large coral heads.

If anchoring overnight, anchor before nightfall and double-check the swing room.

Use your sand anchor and reef pick appropriately to minimise damage.

Motor towards the anchor when hauling it in and retrieve the anchor when the line is vertical.

If the anchor is caught on a reef, free it by hand wherever possible.

Do not force the anchor free by motoring forward.

Keep watch to make sure the anchor isn’t dragging.  

For more information, visit https://www2.gbrmpa.gov.au/learn/reef...

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