First published September 19, 2018.
Photo: JC Photo/Shutterstock
In September 2018 the Reef & Rainforest Research Centre (RRRC), a non-profit research organisation working for the Queensland government, reported that many coral sites around Cairns were recovering well from the severe bleaching of 2016 and 2017. It was genuine good news, but it came with a clear warning from the scientists themselves: the recovery depended on a kind summer, and the next marine heatwave could undo it.
That warning turned out to be accurate. This article explains what the 2018 report found, why corals can bounce back, and what has happened to the reef since.
What the 2018 report found
The RRRC had surveyed bleaching at important dive sites around Cairns in 2016, working with the Association of Marine Park Tourism Operators. Many of those sites escaped the 2016 event but were hit hard in 2017. By mid-2018, photographs and surveys showed strong recovery at places such as Fitzroy Island, Moore Reef and Saxon Reef, and the Quicksilver pontoon site at Agincourt Reef was also described as recovering.
Saxon Reef was a useful example. In 2016 some degree of bleaching affected 47.1% of its live coral cover, yet much of that coral regained its colour rather than dying. Sheriden Morris, the RRRC's managing director, stressed that bleaching happens in stages and that a bleached coral is not automatically a dead one, a detail often lost in news coverage.
The centre credited two things. The first was a milder 2017–18 summer, which gave stressed corals time to recover. The second was cooperation between scientists, tourism operators and government agencies. Doug Baird of the Quicksilver Group said every one of the company's regular sites that had survived the mass bleaching was showing strong signs of recovery.
Morris was equally clear about the limits: she said recovery would always be contingent on environmental conditions, and that the reef remained under pressure from continued warming.
Why bleached coral can recover
Reef-building corals live in partnership with microscopic algae, the zooxanthellae, that sit inside their tissues. The coral offers shelter and a place in the sunlight; the algae photosynthesise and pass on sugars that can supply up to about 90% of the coral's energy. The algae also give corals much of their colour.
When water stays too warm for too long, or when corals face other stresses such as strong light, pollution or disease, the partnership breaks down and the algae are expelled. The coral turns pale or white, which is what "bleaching" describes. It is still alive at this point, but it is starving and more vulnerable to disease.
If temperatures fall back quickly enough, the coral can take up algae again and recover, as many corals near Cairns did. If the heat lasts, the coral dies and is soon covered by seaweed. Restoring a badly damaged reef can take a decade or more, because new corals need years to grow and reach breeding age.
Bleached coral, pale where its algae have been expelled. Photo: Richard Whitcombe/Shutterstock
Why the Great Barrier Reef matters
The Great Barrier Reef stretches more than 2,300 km (about 1,430 miles) along the coast of Queensland and is made up of over 3,000 individual reefs and coral cays. It is the largest coral reef system on Earth and is visible from space.
Coral reefs cover a tiny fraction of the ocean floor but hold an outsized share of marine life; one widely cited estimate puts it at roughly a third of known marine species. On the Great Barrier Reef that includes turtles, sharks, dugongs, seahorses and thousands of fish species. Reefs also protect coastlines from waves and support fisheries.
For Queensland the reef is an economic engine too. Tourism operators depend on healthy dive and snorkel sites, which is one reason companies such as Quicksilver were involved in monitoring, and visitor fees help fund the Great Barrier Reef Marine Park Authority.
Restoration efforts in 2018
The 2018 report also highlighted early restoration work. In December 2017 the Reef Restoration Foundation set up the first ocean-based coral nursery on the reef, at Fitzroy Island. Its first crop grew about 2.5 times in six months, nine of ten corals thrived, and 24 original pieces produced 222 new fragments, about 100 of which were planned for attachment to damaged areas.
In July 2018 more than 300 people from 14 countries gathered in Cairns for the Great Barrier Reef Restoration Symposium. Nurseries like this are valuable for research and for repairing small, high-value sites such as tourist reefs, but scientists are clear that they cannot replace natural recovery across a reef system this large.
What happened after 2018
For several years the optimism looked justified. Parts of the reef went on to reach the highest coral cover recorded since monitoring began in the 1980s. Much of that growth came from fast-growing Acropora corals, the branching and table corals that spread quickly in good years.
The same corals are also the first to suffer. They are sensitive to heat and storms and are a favourite food of the coral-eating crown-of-thorns starfish. When a mass bleaching struck in 2024, during the fourth global bleaching event that began in 2023, followed by cyclones, the gains were reversed quickly.
In August 2025 the Australian Institute of Marine Science (AIMS) published the results of its long-term monitoring survey of 124 reefs:
- Northern region (Cape York to Cooktown): coral cover fell from 39.8% to 30%, a drop of about a quarter.
- Central region (Cooktown to Proserpine): down from 33.2% to 28.6%, a fall of 13.9%.
- Southern region (Proserpine to Gladstone): down from 38.9% to 26.9%, almost a third lower.
For the northern and southern regions, no bigger one-year fall had ever been recorded. AIMS named heat stress from the 2024 bleaching as the main cause, with cyclones and crown-of-thorns outbreaks adding to the damage. AIMS chief executive Selina Stead said mass bleaching events were becoming more intense and more frequent, pointing to back-to-back events in 2024 and 2025.
Reading reef news sensibly
The story of 2018 and 2025 shows why single headlines about the reef can mislead in both directions. A few points help:
- Location matters. The reef is huge, and one region can recover while another is badly damaged.
- Bleached is not the same as dead. Surveys months later show how much coral actually died.
- High cover can be fragile. A reef dominated by fast-growing corals can gain quickly and lose quickly.
- Gaps between heatwaves are shrinking. Corals need years of calm conditions to rebuild, and those windows are getting shorter as oceans warm.
The 2018 recovery was real and showed how resilient corals can be when given the chance. The losses since then show that resilience alone is not enough if marine heatwaves keep returning. Cutting greenhouse gas emissions, improving water quality and controlling starfish outbreaks remain the measures scientists say give the reef its best odds.
Sources: Tourism and Events Queensland / RRRC press release, September 2018; Australian Institute of Marine Science, 6 August 2025: Great Barrier Reef more volatile, with sharp declines in coral cover; Wikipedia: Coral bleaching; ARC Centre of Excellence for Coral Reef Studies: 2016 bleaching taskforce; Current Biology: estimate of reef biodiversity; originally reported by IFLScience.
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