Explainer: How has the Great Barrier Reef fared?

Summer can be tough on the Great Barrier Reef with high temperatures, extreme storms and flooding, so we asked the reef’s top scientists the $6 billion question, how did it cope?

Recent downpours have sent plumes of sediment 100's of kilometres across the Queensland coast. Snapshots of Tully river on February 6, extracted from the Copernicus Browser and analysed by TropWATER James Cook University.

The Great Barrier Reef has survived floods, heatwaves and cyclones in recent years and is faring well considering the extreme stress it has been under, experts say.

In 2017, 2022 and early 2024 the reef experienced mass bleaching that decimated parts of it.

This summer it managed to avoid high water temperatures but faced unprecedented flooding.

In just 14 days the Burdekin River alone discharged 15.6 million litres of water, sending sediment plumes 100km offshore and 700km along the coast.

Principal research scientist at James Cook University’s TropWater Doctor, Stephen Lewis, said the muddied water could stick around for up to six months, restricting light and allowing algae to bloom.

The rare volume of water in recent floods meant plumes of sediment have even reached parts of the outer reef. Snapshot from February 6, extracted from the Copernicus Browser and analysed by TropWATER James Cook University.

“A short pulse of nutrients can really stimulate the growth of macroalgae on the coral reefs and the macro algae can tend to out compete the corals,” Mr Lewis said.

“This material can also be quite sticky and takes a lot of energy for the coral to clean itself … it can make the coral a little bit more stressed and prone to disease.”

In the coming months the Australian Institute of Marine Science will release a more detailed picture about the overall health of the reef but since Cyclone Jasper, the Far North has fared relatively well with no major bleaching events and some increases in coral cover.

Great Barrier Reef Marine Park Authority Chief Scientist Roger Beeden is optimistic about the reefs resilience but warned reef dynamics were more complex than annual timescales. Picture: Reef Resilience Symposium

Great Barrier Reef Marine Park Authority chief scientist doctor Roger Beeden said during disturbances faster growing and less hardy corals rapidly expand leaving slower species by the wayside.

“The evidence we’ve seen … really sophisticated ecosystem models all of them are saying we are already seeing change in the kind of species composition that we have in our coral reefs,” Mr Beeden said.

“I think it can be very confusing … when we can be saying that the reef’s in significant trouble when we’ve got this unprecedented coral cover … what is actually a consequence of this more frequent disturbance is you’re opening up space for these fast growing corals to dominate.

Lady Elliot Island located on Australia’s Southern Great Barrier Reef was recently voted the number one place to snorkel in the world. Picture: Ross Long

“There’s 450 species maybe of hard coral s … the ones that build the reef but there’s maybe a thousand species of soft corals … so your potentially losing some of the other diversity of species.”

Floods, heatwaves and cyclones don’t necessarily kill reefs but they do weaken their overall condition, Mr Beeden said.

He said decades of data showed that more frequent and severe disturbances had placed greater pressure on reefs but remained optimistic of its overall resilience.

“Because of the number of species, the size the fact that there’s usually variability within the stresses that occur, it (the reef) is actually as well placed as any coral reef system anywhere.”

Originally published as Explainer: How has the Great Barrier Reef fared?