How do corals cope with global warming?
With climate change accelerating, coral reefs are among the most threatened ecosystems on the planet. However, some corals seem to be more resistant to rising temperatures. With the Tara Coral expedition, the Tara Ocean Foundation and its scientific partners are conducting an expedition to the heart of the Coral Triangle, one of the world's largest marine biodiversity hotspots, to understand the mechanisms of this thermotolerance. The results of this study will be used to feed into a freely accessible global database and to propose strategies for the conservation of corals and their ecosystems.
Understanding the coral ecosystem under pressure
Corals and their environment
Corals are living organisms made up of thousands of tiny animals called polyps, which form colonies attached to their calcareous skeletons. Their survival depends on an essential symbiosis with zooxanthellae, microalgae that provide them with energy and colour through photosynthesis. Coral reefs are among the most biodiverse ecosystems.
In order to grow, corals need very specific environmental conditions:
- clear water,
- high light levels,
- stable salinity
- and a temperature between 18°C and 30°C, depending on the species.
Coral bleaching
Global warming is disrupting this fragile balance. Even a half-degree rise in ocean temperature can break the symbiosis between coral and its zooxanthellae, causing the coral to lose its colour and its main source of energy. This is known as coral bleaching. Weakened, it becomes more vulnerable to disease and may die if conditions do not quickly become favourable.
Because of this sensitivity, coral reefs are now considered true sentinels of climate change, and these episodes of bleaching are increasing in frequency and intensity worldwide. Once rare and localised, they now affect the entire ocean, sometimes only a few years apart, leaving little time for reefs to regenerate.
More than 40% of coral species are threatened with extinction, due to both global threats (rising temperatures, ocean acidification, rising sea levels) and local threats (destructive fishing practices and overfishing,intensive coastal development, land-based pollution).
The Coral Triangle, a global biodiversity hotspot
Unlike other regions of the world where global warming has led to widespread coral bleaching, the reefs of the Coral Triangle have retained their coral cover.
The Coral Triangle is an extraordinary natural laboratory for identifying mechanisms of resilience
These observations in the Coral Triangle highlight a reality that is still poorly understood: some corals are more resistant to thermal stress than others, without us understanding why or how. It is precisely to shed light on these grey areas and better anticipate the future of the reefs that the Tara Coral expedition was conceived.
The Tara Coral expedition: studying coral resistance
Why are some corals resistant? The scientific questions at the heart of Tara Coral
Ten years after the departure of Tara Pacific, the schooner Tara is setting sail for an 18-month voyage in the Coral Triangle to understand why and how certain corals are resistant to global warming, and to inform future conservation strategies.
One of the unique features of the Tara Coral expedition is its comprehensive scientific approach, which brings together a range of scientific expertise: divers, oceanographers, marine biologists, eDNA specialists, bioinformaticians, microbiologists, photogrammetry specialists, microplastics specialists, palaeoclimatologists, biochemists and many others.
The expedition involves 67 scientists from more than 40 international partners, including 11 local institutions, and is based on an exceptional field effort:
- 26 stopovers,
- 1,440 scientific dives
- and more than 30 protocols.
Tara will remain at each of the 10 planned sampling sites for 35 days, and the scientific teams will adopt a comprehensive approach to the ecosystem, focusing on four types of coral: Acropora, Millipora, Porites and Pocillopora. A comprehensive approach is essential in order to understand which species exist, how they adapt and interact with each other and with their environment.
‘The Tara Coral expedition aims to unlock the secrets of climate change-resistant corals in the Coral Triangle. Their past exposure to thermal stress, the effect of internal waves, their genetics, their symbionts, their microbiome, their diversity and how they organise themselves: these are all avenues that the expedition will explore to understand what protects the reefs.’
Serge Planes, Scientific Director, CNRS Research Director
Why this expedition is essential today
The Tara Coral expedition is implementing innovative protocols such as photogrammetry, environmental DNA sampling and thermal stress testing to collect detailed and standardised data. This information will be made available to all via an open science database, enabling researchers to conduct studies and develop comprehensive and appropriate conservation strategies.
Understanding coral heat tolerance and reef resilience in the Coral Triangle region will help guide measures to protect reefs, which are vital for marine biodiversity and for the millions of people who depend on them.
“The Tara Coral expedition is unique because of its combination of scientific scope, methodological standardisation, geographical focus and integration between disciplines and partners. Now is the time to act to understand, preserve and strengthen the resilience of coral reefs.”
Christian Voolstra, Scientific Director, Professor at the University of Konstanz
From knowledge to action
Beyond the production of scientific knowledge, the data collected during the Tara Coral expedition will be used to drive action. Made available through open science, it will enable researchers around the world to further their study of coral thermotolerance, as well as support advocacy for ambitious conservation policies. Conservation issues will be given high priority, working alongside governments and local stakeholders to identify and protect the reefs that are most resistant to global warming.
The Tara Ocean Foundation will organise several ‘science-to-policy’ workshops during Tara Coral’s stopovers and will actively participate in international summits working to conserve coral reefs.
Each of the Tara Ocean Foundation’s expeditions provides an opportunity to engage society, create innovative tools to reach new audiences, and share the excitement of discovery. On board the schooner, correspondents, scientists, local actors, and artists in residence recount the expedition as it makes its stops. The ‘Science-Society’ sharing initiative will revolve around two key awareness-raising tools: a travelling exhibition dedicated to the Tara Coral expedition and a scientific mediation tool focused on the global importance of coral ecosystems. These will be developed in collaboration with local stakeholders to ensure their cultural relevance, inclusiveness and sustainable use.
Finally, the expedition invites everyone to follow the adventure in real time through videos, logbooks and educational content posted on social media and the Tara Ocean Foundation’s platforms, particularly YouTube. This is a way of extending the scientific mission and mobilising citizens, decision-makers and future generations around the protection of coral reefs.
Ocean, a vital ally against climate change
We all depend on the ocean, as it plays a major role in the climate.
