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It’s official: the Great Barrier Reef is suffering its Fourth mass bleaching eventSince 2016. We dived into a reef yesterday to see the unfolding crisis.
We were immediately drawn to John Brewer Reef’s iridescent whites and blues. They are among the deeper browns, reds, and greens of the healthier colonies.
It’s a depressing, but all-too-familiar feeling. A sense of: “here we go again”
This is the first instance of the reef bleaching under the natural cooling conditions. La Niña weather patternThis illustrates how strong the long term warming trend of climate changes is. Despite the cooling temperatures, 2021 was one The hottest years ever recorded.
When coral bleaches, it is not dead – yet. Coral reefs that suffer widespread bleaching can still recover if conditions improve, but it’s estimated to take Maximum 12 years. That is, if there’s no new disturbance in the meantime, such as a cyclone or another bleaching event.
What conditions are necessary for coral recovery? What conditions are necessary for coral recovery?
Harriet Spark/Grumpy Turtle, Author provided
How coral can die
The length of time that conditions remain stressful and at what level determines whether corals can survive bleaching. What’s more, some Sensitive species are more vulnerable than others, such as branching acropora corals, especially if they’ve bleached previously.
Corals will eventually die if water is left too warm for too much time. However, corals may survive if they are exposed to less ultraviolet light and their water temperature drops.
While the average sea temperatures in the reef currently remain above average, they’ve shown signs of cooling to a more amenable average for coral survival.
Nathan Cook, Author provided
Sea temperatures in Cleveland Bay, near Townsville, were above 31℃ in early March, but thankfully have now reduced to below 29℃. Similar in the Whitsundays, Hardy Reef experienced temperatures as high as 30℃ but has receded to nearer 26℃ in the past few weeks.
Even if coral survives a bleaching event it is still affected physiologically. Bleaching can slow down. Growth ratesReduce Capacity to reproduce. Surviving colonies are also more susceptible to other challenges like disease.
Signs of stress
Survival also depends on each individual coral’s own resilience: its ability to cope with higher temperatures and increased ultraviolet stress.
For example, branching corals that are fast growing are most susceptible to bleaching. They are also the first to die. Porites and long-lived corals such as porites may be less prone to bleaching, have a lower rate of bleaching, and are more likely to recover quickly.
Harriet Spark/Grumpy Turtle, Author provided
Corals can use fluorescent pigments to shield themselves from excessive ultraviolet radiation – a bit like sunscreen that lets coral manage, filter and attempt to regulate the incoming light.
Fluorescent corals can be seen as brightly colored, such as yellow, pink, blue, and purple. For reef scientists, fluorescence signals that corals have lost their internal balance and are stressed. As we’ve seen, white and fluorescent corals are currently a common sight on many reefs.
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Adapt, move, and die: Coral bleaching repeatedly leaves wildlife on the Great Barrier Reef without many options
Many coral species have fluorescent pigments within their tissue. Some are visible to humans all the time, especially branching corals with brightly colored or pink hues at the tips of their branches.
Others are invisible and are only visible during heat stress, when coral colonies increase the fluorescent pigments to combat the rising ultraviolet intensity in warmer waters.
Harriet Spark/Grumpy Turtle, Author provided
Coral can’t adapt fast enough
Scientists measure heat stress on corals using a metric called “Heating weeks in the degree”.
One degree heating week is when the temperature at a given location is more than 1℃ over the historical maximum temperature. If the water is 2℃ above the historical maximum for one week, this would be considered two degree heating weeks.
Scientists expect to see signs and symptoms of stress and coral bleaching at four degrees heating weeks. Coral can usually die after eight weeks of heating.
Bureau of Meteorology DataMany parts of the Great Barrier Reef (off Cairns, Port Douglas) are still in the four to eight degree heating week window. However, some areas near Townsville and Whitsundays are experiencing severe bleaching stress above eight degree heating week.
While we hope coral reefs recover from this round bleaching, the long-term consequences cannot be underestimated.
When corals bleach, they eject their zooxanthellae – single-celled algae that gives coral colour and energy. Some corals will regain their Zooxanthellae when the bleaching process is over. This usually takes between three to six months.
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No, sunscreen chemicals do not bleach the Great Barrier Reef
To make matters worse: Full reef recovery requires no new bleaching or other disturbances in any of the years following. The reef has been bleached six times in the last decade, and the global climate trajectories make this seem an implausible situation. unlikely scenario.
Although some corals might adapt to these new conditions by acquiring more heat-tolerant Zooxanthellae, it is not likely that corals will be able to adapt to the changes in their environment.
The severity of bleaching in the past years may make future events less severe. This is because most corals are heat sensitive. already diedThis could potentially reduce the likelihood of severe bleaching spreading.
Harriet Spark/Grumpy Turtle, Author provided
We need stronger climate actions and policies
Australia has the world’s best marine scientists and marine park managers. And yet, our policies are rated “Highly insufficient”, according to the latest Climate Action Tracker.
Australia may heat up if the global emissions are not reduced. by 4℃ or moreThis century. This scenario would lead to coral bleaching on the Great Barrier Reef every single year. From 2044 onward.
In recent years, there have been some glimmers for hope in federal policy. Statements recognisingCoral reefs are at grave risk from climate change. Despite this recognition of the danger, little is being done to take action.
If the federal government and reef businesses, as well as individuals, are to lead and maintain healthy reefs we must all work together and take swift, drastic action to reduce carbon emission.
A stronger 2030 emissions target and a carbon neutral footprint would be a big step in demonstrating the change needed if coral reefs are to survive in their current form.
Continue reading:
Australia is already being affected by climate change. IPCC warns that unless we act now, Australia will be more hot, dry, and dangerous in the future.
