Great Barrier Reef coral report cuts both ways

The northern and central parts of the Great Barrier Reef have recorded the highest coral cover in more than three decades according to an annual reef report card released today. 

The Australian Institute of Marine Science (AIMS) has published the results of 87 reef surveys undertaken between August 2021 and May 2022.

Marine heatwaves driven by climate change have led to four mass coral bleaching events on the Great Barrier Reef since 2016, with the most recent in Summer 2021-22.

Yet since that event, the lack of severe cyclones and fewer outbreaks of crown-of-thorns starfish has enabled coral in the northern and central parts (north of Gladstone) of the Reef to recover. 

Average hard coral cover in the region north of Cooktown increased to 36% (from 27% in 2021) and to 33% in the central Great Barrier Reef (from 26% in 2021).

New growth has largely involved Acropora corals, which are fast-growing but vulnerable to strong winds and cyclones.

The story in the southern Reef was a different kettle of fish. Between Proserpine and Gladstone, coral cover was 34% – a drop from 38% in 2021 – largely due to crown-of-thorns starfish outbreaks.

Dr Paul Hardisty, chief executive of AIMS says this shows how vulnerable the Reef is to the continued acute and severe disturbances that are occurring more often, and are longer-lasting.

Hardisty says the increased frequency of mass bleaching events are “uncharted territory” for the Great Barrier Reef.

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Read more: What’s going down at the Great Barrier Reef?

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“In our 36 years of monitoring the condition of the Great Barrier Reef we have not seen bleaching events so close together,” he says.

Professor Peter Mumby from the University of Queensland’s Marine Spatial Ecology Lab says while the report is encouraging and shows the Reef has resilience, “we can only be cautiously positive.” 

“Coral bleaching events are occurring more frequently and if we can reduce their impact by reducing our emissions, then the reef has the resilience to respond accordingly,” he says.

Dr Zoe Richards a senior research fellow from Curtin University’s Coral Conservation and Research Group says increased cover is good news given thousands of plants and animals rely on coral for habitat.

But she says the Acropora species tends to grow in a boom-and-bust pattern.

“This means the next thermal stress event could easily decimate coral communities once again. We are already finding evidence that each mass bleaching event leads to local extinctions of rarer species, so the short-term success of a handful of fast-growing coral species masks the full story about the largely hidden losses of biodiversity on the internationally significant Great Barrier Reef.”