Few corals can recover from bleaching during long aquatic heatwaves

Coral Reef
climate change could devastate nearly all of Earth's coral reef habitats by 2100

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Climate change is making aquatic heatwaves extensive and more frequent, which has caused several mass coral bleaching events in recent years. Now it looks that few corals can recover from bleaching even while aquatic heatwaves are unending.

During a tropical aquatic heatwave between 2015 and 2016, Julia Baum at the University of Victoria in Canada and her colleagues studied corals around Kiritimati in the central Pacific Ocean, the foremost coral island in the world.

The aquatic heatwave was the extended ever documented. “Scientists had projected that no coral reef would observe that much heat stress until mid-century,” says Baum.

Baum’s team categorized more than 100 corals of two species – Platygyra ryukyuensis and Favites pentagona – at many sites around the island. Some were in places close to populated villages, meaning they had already been troubled, and others were in areas that were primaeval before the heatwave began. The group snapped and traced individual corals over the progression of the heatwave.

The team was astonished to notice that some corals survived bleaching, improving even though the water temperature was still raised.

These corals primarily cohabited with heat-sensitive symbiotic algae, tolerated the bleaching event, and then improved by teaming up with heat-tolerant symbionts.

In regular marine temperatures, heat-sensitive algae are plentiful partners to their coral hosts, photosynthesizing and giving the corals with energy. Corals in companionships with heat-sensitive algae look fatter because they can make lipid reserves, says Baum.

“Corals are only shown this ability to recover from bleaching while still in hot water if they weren’t also exposed to strong local stressors,” says Baum.

The team identified that corals in highly troubled areas confined mainly heat-tolerant symbionts before the heatwave. Although they primarily counterattacked bleaching, F. pentagona corals that began with heat-tolerant algae had no existence advantage, and P. ryukyuensis corals with the symbionts were essentially 3.3 times less likely to live.

The results indicate that local shield of corals is helpful in the face of climate change, says Baum.

Journal reference: Nature Communications, DOI: 10.1038/s41467-020-19169-y

Read more: Some corals ‘killed’ by climate change are now returning to life

Reef-building corals can make unpredicted recoveries from climate change-induced damage. 

It turns out that some corals only look defunct when exposed to unusually warm water. Instead, the coral’s polyps shrink and flight into their hard skeleton, making the reef appear dead, before recolonizing the skeleton when conditions are better. It is an endurance method never seen before in today’s corals – but it may not help the corals as the climate endures to change.

Corals have been hard hit by warming waters. Reefs globally, including the Great Barrier Reef, are edging towards collapse. The slow-growing endangered species Cladocora caespitosa is particularly exposed to destruction with little sign so far as to whether it can regenerate.

Journal reference: Science Advances, DOI: 10.1126/sciadv.aax2950

To Read: What is the Climate Action Summit?

The Climate Action Summit is over. Some 70 Heads of Government, along with local and city leaders, and heads of major businesses, have delivered a series of new measures, policies and plans, aimed at making a big hollow in greenhouse gas emissions, and ensuring that the warming of the planet is limited to 1.5°C.

The number of states coming frontward with reinforced national climate plans (NDCs) grew remarkably today, with commitments covering some of the top emitters globally on display.

The UK, which is organizing next year’s UN Climate Conference, declared that it aims to cut emissions by 68%, compared to 1990 levels, within the next five years, and the European Union bloc committed to a 55% cut over the same time dated.

At least 24 states announced new pledges, strategies or plans to reach carbon neutrality, and several states set out how they are going even more, with resolute dates to reach net-zero: Finland by 2035, Austria by 2040 and Sweden by 2045.

Pakistan declared that its sparring plans for new coal power plants, India will soon more than double its renewable energy target, and China committed to increasing the share of non-fossil fuel in primary energy consumption to around 25% by 2030. 

About Zulker Naeen

Climate Journalist

Zulker Naeen is a South Asia Fellow at Climate Tracker. With three years of working experience, he has developed courses with the support of other Climate Tracker staff.

As a young climate advocate, his fellowship aims to share knowledge of climate change. Climate Tracker is a global media network closely works on Climate Change.

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Few corals can recover from bleaching during long aquatic heatwaves


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