Coral bleaching: Barriers for the reef
Another mass bleaching, possibly the second worst of five episodes since 1998, has scientists worried about the future.
The bushfires that torched Australia’s east coast in January were still raging across the mainland when the alarm first went up that conditions offshore pointed to another round of bleaching for the Great Barrier Reef.
The GBR Marine Park Authority had become concerned that a slight rise in water temperatures could be a sign of a serious bleaching event, so the organisation was on high alert for the first six weeks of the year.
By the end of summer, it seemed that the initial fears could have been unfounded, as weather conditions again changed and water temperatures appeared to trend back to more normal levels.
However, the results of recent aerial surveys now suggest that it was no false alarm.
The Great Barrier Reef has experienced its third mass bleaching in less than five years and possibly the second worst in the five episodes since 1998.
Bleaching occurs when corals expel algae that lives inside them when the water gets too hot (or too cold). Most corals that bleach will fully recover, as they can better adapt to deal with temperature changes than virtually any other organism.
But bleaching can cause lasting damage in other corals.
A call for help
The latest survey suggests the recent bleaching stretches the length of the GBR from north to south, but the severity of the bleaching and its long-term impact will take more time to assess.
The fresh bleaching event builds on the 2019 narrative of cascading environmental crises arising from climate change, and has attracted international headlines in recent days, despite the deafening roar of COVID-19.
Teenage celebrity environmentalist Greta Thunberg tweeted that “people need to see these (bleaching) events not as depressing bits of news that adds to other depressing bits of news. They are clear signals the GBR is calling for urgent help and for us to do everything we can.”
Experienced reef watchers like marine scientist and university professor Peter Ridd are less alarmed.
“This is not a bleaching event, it is a media event for the Australia Research Council’s Centre of Excellence for Coral Reef Studies,” Dr Ridd said.
“The survey is done rapidly from a fast moving aeroplane.
“We don’t have any idea how much coral is going to die and mortality, ultimately, is the only thing that matters.”
However, with the management of the World Heritage-listed asset again up for review by the World Heritage Committee, the federal government is on the front foot to ensure one of Australia’s most prized tourist attractions avoids being put on an “endangered” list. If that were to happen, its status as an international drawcard would be irreparably harmed.
Federal Environment Minister Sussan Ley will join reef scientists on Thursday to announce progress on an ambitious program to find novel ways to build resilience on the reef. The federal government has already put in $100m, and that will soon be matched by $50m from research institutions.
Australian Institute of Marine Science chief executive Paul Hardisty says a menu of 160 potential solutions had been culled back to 43 for further investigation.
Proposals include “cloud whitening”, which involves spraying fine seawater into the air to reflect back heat and reduce water temperatures; raising and dispersing corals that are more resistant to heat; and examining ways to collect and freeze coral larvae for use in year-round coral seeding.
“We need to do more research to ensure these things are done safely, cost-effectively and in a way that is acceptable to the public and regulators,” Dr Hardisty tells Inquirer.
Shading and cooling
Economic studies have shown the benefits for Australia could run into the tens of billions of dollars, given the flow-on environmental and social positives.
There is also untold potential to export the developing technologies to struggling reefs around the world.
Dr Hardisty said it was unlikely that any method alone was going to drive success.
“It is going to be a combination of measures applied at different scale in different areas that are going to work together to achieve success in building resilience,” he says.
“Some of our modelling shows if you can get widespread shading and cooling systems working together with some powerful reseeding and deployment of hybridised heat-tolerant corals, and got really good crown-of-thorns starfish control and put it all together — and you met the Paris targets — then the reef could in 30 years be better than it is now.”
A key factor is the scale of the challenge.
“There are 3000 reefs over 344,000 square kilometres, an area bigger than Victoria and Tasmania combined,” says the federal government’s reef envoy, Warren Entsch.
Building resilience
Researchers say the work to build resilience is needed now, and in addition to any wider action on climate change.
“Already we are in a world where bleaching is happening,” Dr Hardisty says.
“Emissions have to be tackled or it will overrun the efforts taken to build resilience.”
By late January, GBRMPA observed that sea surface temperatures had increased since the last update, from a month prior.
“As of 27 January, some inshore to mid-shelf areas in the far northern and southern management areas were 2C to 2.5°C above the January average,” GBRMPA said in a statement.
By February 27, the authority said cloud and rain had provided cooling to some parts of the Great Barrier Reef, although it was continuing to monitor the situation because the risks of bleaching had not entirely diminished.
“Local weather conditions over the next few weeks will play a key role in determining outcomes for the reef this summer,” the GBRMPA said.
By March 31, GBRMPA said sea surface temperatures across the Great Barrier Reef were near average and well below the temperatures that had caused mass coral bleaching this summer.
Reef-wide aerial surveys to determine the extent and severity of coral bleaching across the reef had concluded on March 27.
Early results of the survey suggested there had been widespread moderate-to-severe bleaching across much of the reef.
However, major tourism areas of the reef mostly only experienced “no, negligible, or moderate” bleaching, the exception being one area in the southern part of the marine park with “severe” bleaching.
When the results of the aerial and underwater survey were analysed by James Cook University researchers Terry Hughes and Morgan Pratchett, the extent of the damage was laid bare.
The 2020 bleaching was assessed as the second-worst mass bleaching event of the five experienced by the Great Barrier Reef since 1998.
Concerns centre both on the extent of bleaching and the short time frame between bleaching episodes.
The sheer size of the Great Barrier Reef has always been one of its biggest strengths in terms of resilience, but as the area of bleaching expands and the time between bleaching events shortens, the concern is that the reef’s natural resilience will be compromised.
“For the first time, severe bleaching has struck all three regions of the Great Barrier Reef — the northern, central and now large parts of the southern sectors,” Professor Hughes said.
The north was the worst-affected region in 2016, followed by the central region in 2017.
This year bleaching has expanded to include the south.
‘Deeply concerning’
Professor Hughes said the distinctive footprint of each bleaching event closely matched the location of hotter and cooler conditions in different years.
“As summers grow hotter and hotter, we no longer need an El Nino event to trigger mass bleaching,” Professor Hughes said.
“Of the five events we have seen so far, only 1998 and 2016 occurred during El Nino conditions.”
Professor Pratchett, who led the underwater surveys, said not all corals that bleached would die.
“A pale or lightly bleached coral typically regains its colour within a few weeks or months and survives,” he said.
“We will go back underwater later this year to assess the losses of corals from this most recent event.”
Unbleached and lightly bleached reefs this year are predominantly offshore, mostly close to the edge of the continental shelf in the northern and southern Great Barrier Reef.
Coastal reefs are also badly bleached at almost all locations, stretching from the Torres Strait in the north to the southern boundary of the Great Barrier Reef Marine Park.
Ley says the latest bleaching is “deeply concerning”.
“Thankfully some of the most recognised tourism areas have been less impacted but that does not change the importance of the issue and the importance of co-ordinated global action on emissions reduction to reduce global ocean temperatures.”
Environment department analysis of the aerial surveys shows that about 40 per cent of reefs within the GBR had little or no bleaching.
About 25 per cent of reefs were severely bleached (that is, on each reef more than 60 per cent of the corals were bleached), while 35 per cent had moderate levels of bleaching.
Severe bleaching was more widespread than in past bleaching events.
On mildly or moderately bleached reefs, there was deemed to be a good chance that most bleached corals would recover and survive.
Review of strategies
The federal government is preparing a detailed report on the 2020 bleaching event for the World Heritage Committee.
The committee is conducting a scheduled review of the state of conservation of the Great Barrier Reef at its meeting scheduled in Fuzhou, China, later this year.
Ley says the federal and Queensland governments are investing $2.7bn in protecting the Great Barrier Reef under the Reef 2050 plan.
The federal government says it is confident the World Heritage review will support the strategies the government has in place to protect the reef.
But the likes of Dr Ridd still believe that concerns about the reef are overblown.
“We have been hearing similar doom scenarios about the reef since the late 1960s when scientists first studied the reef in earnest,” Dr Ridd says.
“The latest bleaching is just another cycle that has been going on for eons.
“Some strains of algae allow them to grow fast, but make them more susceptible to bleaching. Others give relative immunity to bleaching, but make the coral grow slowly.
“Just by changing the algae, the coral can deal with a different climate.
“Other organisms have to go through several generations of natural selection, which might take decades or centuries. Corals can do this in a few weeks.”
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