Sign In
Australia; NSW; VIC; QLD; SA; TAS; ACT
Media release
From:
Recent marine heatwave transformed Great Barrier Reef coral assemblages
Corals on the Great Barrier Reef experienced a catastrophic die-off following the extended marine heatwave of 2016, transforming the ecological functioning of almost one-third of the 3,863 reefs that comprise the world’s largest reef system. These findings, reported online in Nature this week, reinforce the need for risk assessment for reef ecosystem collapse, especially if global action on climate change fails to limit warming to 1.5‒2 °C above pre-industrial levels.
Terry Hughes and colleagues map the geographical pattern of heat exposure and resultant coral death along the 2,300-km length of the Great Barrier Reef following the extreme marine heatwave of 2016. They find that although many corals died immediately from the heat stress, others died more slowly following the depletion of their zooxanthellae — the yellowish brown symbiotic algae that live within most reef-building corals. Coral death was highly correlated with the amount of bleaching and level of heat exposure, with the northern third of the Great Barrier Reef most affected. The coral die-off also led to radical changes in the composition and functional traits of coral assemblages on hundreds of individual reefs, with mature and diverse assemblages transformed into more degraded systems.
The authors note that a full recovery to the pre-bleaching assemblages is unlikely to occur, because many surviving coral colonies continue to die slowly, and the replacement of dead corals will take at least a decade even for fast-growing species. Moreover, the Great Barrier Reef experienced severe bleaching again in 2017, causing further extensive damage. As such, coral reefs throughout the tropics are likely to continue to degrade until climate change stabilizes, allowing remnant populations to reorganize into heat-tolerant reef assemblages, the authors conclude.
Expert Reaction
These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.
Professor Sarah Perkins-Kirkpatrick is a professor at the ANU Fenner School of Environment and Society, and Deputy Director (communications) for the ARC Centre of Excellence for the Weather of the 21st Century
The results of this study confirm our worst fears of the detrimental impact man-made climate change is having on the Great Barrier Reef, and our natural ecosystems as a whole.
As human influence on the climate increases, so too will the intensity, frequency and duration of marine heatwaves that cause this sort of devastation.
Globally, we have already seen a 34 per cent increase in the frequency of marine heatwaves, and 17 per cent increase in their duration. Unfortunately these increases in marine heatwaves are much faster than the recovery time of coral reefs themselves.
The future is looking bleak for coral reef ecosystems, as well as the services and economies that rely on them.
Ian Lowe is Emeritus professor of science, technology and society at Griffith University, Qld and former President of the Australian Conservation Foundation.
This is yet another concrete example of the costs of climate change. The science is clear. We are doing massive damage to the Great Barrier Reef, and there is justifiable concern that some of the damage might be irreversible. A unique, global feature is being destroyed on our watch.
This is not just an environmental disaster, but also a serious economic issue. Reef tourism employs far more people and generates far more revenue than the coal industry.
A government that was looking ahead would be managing a rapid transition to clean energy. This would allow Australia to play a leading role in the global move to a low-carbon future, the only hope of saving the Great Barrier Reef.
Instead, the proposed National Energy Guarantee would effectively end large-scale wind and solar construction in 2020.
Professor John Cole is the Executive Director for the Institute for Resilient Regions at the University of Southern Queensland
In contrast to Australia’s political inertia on energy and climate, global warming relentlessly degrades our greatest marine asset, the Great Barrier Reef.
In just a few years, close to half the shallow corals of the reef have been lost and with them a vast, vital platform for Queensland’s coastal regional economy.
Ignoring the science endangers further the reef’s resilience, and with it the enormous ecological, economic and social contributions it makes to our world.
In regional development terms, the death of the GBR remains the greatest threat to realising sustainably the potential of northern Australia.
Professor Pete Strutton is from the Institute for Marine and Antarctic Studies at the University of Tasmania and the ARC Centre of Excellence for Climate Extremes
This paper thoroughly documents the impact of marine heatwaves on coral reef ecosystems.
When considering these conclusions, we should keep in mind that the conditions experienced in 2016 and 2017 are likely to become the new normal within decades.
Associate Professor Jochen Kaempf is an oceanographer in the College of Science and Engineering at Flinders University
Heatwaves are transient features that are linked to anomalous weather events or, if prolonged, to climate variability, such as the El-Nino Southern Oscillation. The most pronounced heat waves in the ocean are associated with variations of the dynamics of western boundary currents, such as the East Australian Current.
As such, an individual heatwave triggering coral bleaching cannot be linked to global warming as the process triggering an individual heatwave is fundamentally different from that triggering global warming. The claimed link between the 2016 heat wave and global warming has no scientific basis.
The claim that the GBR will not recover in the future cannot be tested yet. Unfortunately, the scientific method insists that we have wait several decades before we can scientifically conclude that the GBR has or has not recovered from the 2016 heat wave. Speculation should not be the highlight of a research study.
Indeed, the above argumentation cannot be turned upside down to argue that there is no global warming. Such a statement would not be supported by the overwhelming scientific evidence that exists.
I don't dispute the scientific findings of the study. Instead I call for more scientific rigour and caution in the formulation of conclusions.
UPDATED: We know for some time that the reef is under threat – on short timescales (weeks to months) from marine heat waves, on medium time scales (seasons) from eutrophication, and on longer times scales (decades) from ocean acidification (global warming).
On the other hand, climate variability (such as El Nino events) sets the background temperature level on periods of several years (and may lower the short-term effect of a heat wave).
While an individual heat wave cannot be attributed to global warming, and this is really irrelevant, it is sad to see that a marine heat wave can cause such widespread damage.
Dr Michael Dunlop is from the Climate Risks and Resilience Group at CSIRO
These results highlight the potential for climate change to transform ecosystems.
Increasing levels of climate change are likely to see such ecosystem transformations around the world in the oceans, at the coast right through to the tops of mountains.
The challenge this presents to managers, scientists, policy makers, and society more broadly is, what does it mean to conserve ecosystems while the species and processes within them change dramatically?
The societal expectations, policy and knowledge bases that underpin the way we currently conserve nature are derived from an assumption that while species and ecosystem may fluctuate, they should not change dramatically.
Observations of current climate change, exemplified by this study, and innumerable explorations of future impacts to species and ecosystems, show ecological transformation is occurring and has the potential to become widespread.
To cope with this we need new expectations, knowledge and conservation programs that focus on those aspects of nature that can persist through change and are valued by society.
In 2003, a collaboration between CSIRO and the Australian Institute of Marine Science developed a reef bleaching model, ReefClim, that simulated five stages of bleaching from heat stress through to catastrophic bleaching, where recovery from the latter was projected to take decades.
It used total degree days over a bleaching threshold to measure the severity of bleaching. The critical bleaching level for sea surface temperatures was reached when the risk of future bleaching showed the next event was likely to occur before recovery from the last event. This paper measures heat stress the same way.
The level of damage the authors describe show that some areas of the northern reef will take decades to recover.
Sea surface temperatures from October 2015 over the whole of the Great Barrier Reef are 0.55°C higher than they were from summer 1998 to winter 2015. If the reef has moved into a new temperature regime compared to the one that existed between 1997 and 2015, parts of the reef will now be subject to critical levels of bleaching, if they were not already.
This suggests the authors have been conservative in their conclusions, as devastating as they are.
Multimedia
Attachments
Note: Not all attachments are visible to the general public. Research URLs will go live after the embargo ends.
