Some coral more resilient to global warming than previously thought, scientists find

Coral reefs and negative human impact tend to be inextricably linked in news headlines, ever since French ocean explorer Jacques Cousteau first expressed alarm back in 1974.

However, an international team of researchers involving a University of Galway scientist has discovered that some coral is proving to be more resilient to climate change than previously thought.

“Yes, it is good to be able to report something positive,” agrees Prof Olivier Thomas, University of Galway professor of marine biodiscovery.

Thomas was invited to take part in parts of a two-year expedition on the French research schooner Tara, partly funded by the Tara Ocean Foundation, to study the health of coral reef biodiversity in the Pacific Ocean.

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As he and fellow scientists document, contemporary warm-water coral reefs have dominated shallow-water marine environments on Earth for more than 500,000 years.

They describe the “biodiversity hotspots” as “some of the most productive ecosystems in the world, providing essential goods and services and high socio-economic returns to coastal nations”.

The Tara Pacific expedition which Thomas participated in took place between 2016 and 2018. The scientists sampled sea areas extending from Colombia to Japan, documenting the health of coral reefs around 32 islands in the Pacific Ocean.

[ Most severe effects of the climate crisis have been hidden in the ocean’s depths ]

The large number of samples taken – a total of more than 58,000 – means that results have only recently been published. The project has been described as the first of its kind at this scale and the largest investigation of the diversity of coral reef microbiome or community of micro-organisms to date.

Thomas was invited to participate due to his extensive experience as a scientific diver in tropical waters.

He also has expertise in “metabolomics” analysis of marine organisms – “metabolomics” being the study of small molecules, commonly known as metabolites, within cells, biofluids, tissues or organisms.

“Diving across the 32 islands was a privilege to discover the coral reefs, but also to meet the local populations most affected by climate change and its impact on local coral ecosystems,” he adds.

“While some coral species may be extinct in the near future together with the diverse ecosystems they support, some species are more resilient.

The geography of the individual Pacific islands we visited for sampling was a factor, with some of the islands experiencing long periods of heat stress, where water temperatures were high for a long time

—  Prof Olivier Thomas, University of Galway

“Our research suggests that mesophotic coral ecosystems – as in deeper than 30 metres – are less affected by temperature changes, and may serve as a repository of biological diversity for our future oceans,” Thomas notes.

As he explains, coral reefs are “among the most diverse ecosystems on Earth and support 25 per cent of marine diversity, including multicellular organisms and associated microorganisms”.

The advantage of being on a research schooner such as Tara is its flexibility in working in shallower waters. The 36-metre vessel, based in Lorient, France, is underpinned by a mixture of private and public funds, and French designer Agnes B is one of its main sponsors.

The 58,000 samples collected over the duration of the two-year cruise ranged from fish to sediment to water. Some 2,500 of them were of coral, and Thomas and colleague Dr Maggie Reddy were involved in their analysis.

They have concluded that the diversity in the microbiome – or community of organisms – present in coral reefs is “largely underestimated, and matches the diversity present on land”.

[ Rampant heatwaves threaten food security of entire planet, scientists warn ]

They have also noted how corals tend to try to adapt under an acute thermal stress event. They describe how telomeres, a structure at the end of the coral chromosomes, were found to be influenced by the environment, and especially by heatwaves.

“The geography of the individual Pacific islands we visited for sampling was a factor, with some of the islands experiencing long periods of heat stress, where water temperatures were high for a long time,” Thomas says.

“Other islands had shorter peaks, which allowed the coral to recover after periods of bleaching,” he says. “In theory, this means that we could transfer more fragile species of coral to less affected islands.”

The three main studied species of coral use different strategies to adapt and fight the impacts of climate change, Thomas notes.

“Some reefs are more sensitive to climate change and are now endangered, leading to the risk of the whole ecosystem in that area disappearing, while the more robust ecosystems will survive the current changes happening to the planet,” he says.

“While the first part of the project was more to develop methods to study such a large number of samples, the next phase is now to build working groups where all the data generated will address key questions,” Thomas notes.

These questions range from coral health to the capacity of adaptation or resilience of different species of corals, the biocomplexity of the coral reef and its ecosystem, and the study of the metabolism of the different components of the coral in interaction with its microbiome or community of organisms.

[ Ireland is experiencing one of the most extreme marine heatwaves on earth, so why aren’t we more alarmed? ]

“University of Galway will lead the last question, and discussions are ongoing to prepare for a following expedition,” he says. He expects to be involved in more trips to monitor any changes.

Fellow coral scientist and University of Galway adjunct professor Peter Vine is heartened by the project’s findings. He considers himself fortunate to have experienced “almost pristine underwater habitats” when he began studying them half a century ago.

“My own first encounter with corals was around the Micronesian atoll reef of Tarawa in what was then the Gilbert Islands, but is now Kiribati,” recounts Vine, who is author of a new book on coral reefs.

“It was 1964 and I was there as a teacher on Voluntary Service Overseas. After arriving at my new island home, on completing the final leg of a memorable Pacific odyssey... I was presented with a thatch-roofed house about as close to the atoll’s rhythmic pounding breakers as one could get,” Vine says.

“There was no escaping the vivid mottled tapestry of blues, greens, reds and browns of the near-by reef-top and it was not long before I was snorkelling over the shallows, imagining I was Jacques Cousteau or [Austrian biologist and underwater explorer] Hans Hass. I was well and truly hooked.”

After taking a degree at Swansea University, which included a field course studying sponges in the Galway Gaeltacht at Carna, Vine participated in “countless underwater adventures” in Australia (Great Barrier Reef), Sudan, Seychelles, New Zealand, New Guinea, New Ireland, New Hebrides, Hawaii and the Caribbean.

During that time, he was involved in observing several “coral killers”, not all man-made. The crown-of-thorns starfish and toxic thin film sponges were, and still are, among serious predators.

[ AI offers new approach to help cold-water corals ]

However, he recalls that 1998 was “annus horribilis”, when bleaching caused by heat stress resulted in up to 90 per cent mortality of coral in some areas.

The devastation extended right across the Caribbean and Indo-Pacific, with “notable damage” to Australia’s Great Barrier Reef. However, there was some indication then that some corals were proving to be more tolerant than others, he recalls.

The Tara team had a unique opportunity to apply the latest biological and analytical cutting-edge technologies to develop new ways to assess the health of the reefs over a wide area of the Pacific

—  Peter Vine, University of Galway adjunct professor

Vine cites a University of Lausanne study from the Gulf of Aqaba, which reported that a wide range of coral species growing there had tolerated temperature increases of up to seven degrees in summer. By contrast, a jump of only two to three degrees was enough to trigger bleaching on Australia’s Great Barrier Reef.

He also observed two kinds of coral bleaching – one associated with mass events, and another which is more seasonal, where colonies in the northern Red Sea experienced it during the summer months but began to recover their symbiotic algae and colour in October.

Vine regards coral reefs as the “rainforests of the oceans”. Recent studies might also regard them as “canaries in the mine” when it comes to climate change, he says – amid concerns they may not last this century.

“The Tara team had a unique opportunity to apply the latest biological and analytical cutting-edge technologies to develop new ways to assess the health of the reefs over a wide area of the Pacific. We need such studies to recognise where areas of special interest might occur,” he points out.

Peter Vine’s book Growth and Decay of Coral Reefs, 50 Years of Learning, is published by CRC Press – a global academic imprint of the Taylor and Francis Group. The research findings from the Tara Ocean Foundation expedition have been published in Nature journals