The secrets of the world’s coral reefs are slowly being uncovered thanks to the ambitious TARA Pacific Expedition, co-led by the Centre Scientifique de Monaco’s Denis Allemand.  

The project began in 2016, when the research schooner Tara left France on a voyage that would see it sail some 100,000 kilometres, visit 30 countries and study 32 different sites, from the isolated coral reefs of the Pitcairn Islands, Samoa, Tuvalu, Kiribati, Wallis and Futun to locations much closer to urban centres.  

70 scientists from eight countries and representing 23 institutions and research laboratories spent time onboard, while hundreds more backed them up on land.

One of the leading figures was the Centre Scientifique de Monaco’s (CSM) Denis Allemand, who is continuing to unpick the fascinating findings of a project that is unique in its scale and objectives: to study biodiversity of coral reefs and their evolution in response to climate change across the entire Pacific Ocean.  

“This was a highly ambitious project,” says Allemand. “Two and a half years of sailing that crossed the Pacific Ocean, 58,000 samples taken… Almost the whole Centre Scientifique de Monaco team was involved… A brand new technique had to be developed to achieve the project.”

Coral reefs cover less than 0.2% of the surface of the oceans, but are home to 30% of known marine biodiversity. The Pacific Ocean alone contains around 60% of the world’s coral reefs, from far-flung atolls to the barrier reefs beloved of the tourism industry, which made it the obvious choice for a project that seeks to better understand the nature and workings of coral reefs.  

Five years of intense analysis

During the expedition, scientists systematically sampled the same three coral morphotypes, two fish species and planktonic communities in various locations to assess reef microbiome composition and biogeography. The results – the product of five years of intense analysis – were astounding.  

“We found almost 20% of all known microbes on these species alone,” says Allemand. “If we amplify that across all the coral species of the Pacific then the total microbe diversity amongst corals is in line with the numbers for all known microorganisms on our planet. That tells us that our knowledge of terrestrial microbes is vastly underestimated.”

Essentially, life on coral reefs could well be as rich and diverse as the entire known world. 

This is but the first major finding of the TARA Pacific Expedition. Thus far, only one report of eight has been published in the journal Nature, and the others will soon come its heels. Among them will be the results of studies into the effects of climate change on coral reefs.

Climate change and coral reefs

Corals across the Pacific are already struggling with climate change. The biggest threats facing them today are rising temperatures and ocean acidification, along with pollution, overfishing, coastal development and subsequent sedimentation. A rise of 1°C over just a few weeks can cause coral bleaching while a change in pH can significantly limit the growth of corals as well as impact the ability of the animals that live in and around them to grow their skeletons and, ultimately, survive.  

“The coral ecosystem could be the first to disappear, from the face of the Earth, because of humans,” says Allemand, “so it was important to us to study the capacity of coral reefs to adapt. We were able to identify some elements of adaptation amongst these organisms thanks to the breadth of the samples and data collected. There are those who have suffered from the phenomenon of rising temperatures, but have changed part of their microbiome and have been able to adapt, some more easily than others, which we must take as a positive. This adaptation could prevent the total destruction of coral reefs in the future.”

How that will play out remains to be seen. Figures already released by the project show that 20% of reefs have been destroyed and show no signs of possible reconstruction, 15% of reefs will be in great danger in the next 10 to 20 years, and a further 20% of reefs will be threatened in the next 20 to 40 years. Just 25% of those observed appear to be in good health. 

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Featured photo credit: Pete West / BioQuest Studios