Great Barrier Reef health update

Reef Health Update | 12 April 2024 © Great Barrier Reef Marine Park Authority

Heat stress continues to accumulate in the Northern Region, while slowing in the Central and Southern Region.

The completed aerial surveys covered 1080 reefs from the southern end of the Great Barrier Reef Marine Park to the Torres Strait. The aerial surveys showed prevalent bleaching (>10 per cent coral cover bleached) was present on over 60 per cent of surveyed reefs. Low to no bleaching was evident on 94 per cent of surveyed reefs in the Torres Strait. Very high to extreme bleaching prevalence was most common in reefs both inshore and offshore in the Southern Region, whilst very high bleaching prevalence was most common in inshore and mid-shelf reefs in the Central Region and Northern Region.

Coordinated in-water surveys are under way to assess how different coral species at different depths and habitats have responded to the accumulated heat stress, and whether any coral mortality has occurred.

The Reef Authority in collaboration with science partners, the Australian Institute of Marine Science and CSIRO, will release the Reef Snapshot for Summer 2023-24 next week, which will provide a summary of conditions and impacts over summer and detailed findings from the aerial surveys.

Tropical Cyclone Paul is situated in the far northern Coral Sea, tracking towards Cape York Peninsula over the weekend and expected to weaken to a tropical low by Saturday. The tropical system is predicted to cross the Marine Park and may result in elevated wind and wave action in the Central and Northern Region of the Marine Park.

Reef health

This week, a total of 68 in-water surveys were conducted across our observer network. Of these, 49 were Reef Health Impact Surveys and all reported coral bleaching of minor to moderate impact. Again, variable levels of coral mortality were found. Other impacts included minor coral damage and disease.

A persistent crown-of-thorns starfish (CoTS) outbreak continued at offshore Swain Reefs, and isolated outbreaks were found on reefs offshore Townsville and in the Whitsundays. There is also an emerging outbreak near Lizard Island and offshore Port Douglas.

Temperature

Sea surface temperatures are up to 2 degreesC above average across the Marine Park for this time of year.

Over the past three months the Northern Region has accumulated 12 degree heating weeks, the Southern Region 11 degree heating weeks and the Central Region eight degree heating weeks.

Sea surface temperatures in the central tropical Pacific are forecasted to return to ENSO-neutral later in autumn 2024.

Rainfall

The Fitzroy catchment received 150mm across the Marine Park, where Central and Northern catchments received up-to 100mm.

Salinity levels between Cairns and Cape Melville are predicted to increase from 33 to 34 PSU over the week as rainfall eases across the Marine Park.

Reef management

The Reef Authority is continuing to work with the Australian Institute of Marine Science, Queensland Parks and Wildlife Service, crown-of-thorns starfish control program, Tourism Operators, and researchers to coordinate targeted in-water surveys.

The data from these surveys, combined with the aerial surveys, will give a greater overview of the severity of coral bleaching.

For more information visit www.gbrmpa.gov.au/learn/reef-health