A fourth global coral bleaching event was recorded between February 2023 and April 2024 by the U.S. National Oceanic and Atmospheric Administration (NOAA). This phenomenon, the second in a decade, is causing concern among scientists. Indeed, exacerbated by the increasing frequency of marine heatwaves, the degradation of reef ecosystems triggers cascading impacts across all levels of life, both in the sea and on land.
What is a Coral?
Corals are bioconstructive animals belonging to the class Cnidaria, which also includes jellyfish. Tropical corals live in symbiosis with algae called zooxanthellae, which supply the coral with essential nutrients through photosynthesis. This partnership allows them to build impressively large reefs, some even visible from space, such as the Great Barrier Reef in Australia.
Most tropical corals live in colonies, growing between one and ten centimetres per year, depending on the species. These reefs play a unique role in marine biodiversity. “Corals are the habitat of numerous species. Acting as a refuge, nursery, and food source, coral reefs provide invaluable services to their ecosystem“, highlights Pascale Joannot, oceanographer and member of the National Committee of the French Initiative for Coral Reefs (IFRECOR).
What is the importance of Coral Reefs Worldwide?
Coral reefs, true treasures of biodiversity, are home to approximately 25% of the world’s marine species despite covering only 0.1% of the ocean floor. They also play a crucial role in coastal protection, with some reefs capable of absorbing up to 97% of wave energy. In doing so, reefs not only shield shorelines from erosion but also serve as a vital barrier against extreme weather events, which are becoming more frequent and intense due to climate change.
Beyond their natural barrier function, coral reefs are essential to human societies. “One billion people worldwide depend on reefs for their livelihood“, explains Victor Brun, former doctoral researcher at CRIOBE and scientific coordinator for the Ocean & Climate Platform. The abundance and diversity of species inhabiting coral ecosystems make them prime areas for fishing and tourism, directly supporting food security for nearby populations and providing significant employment and income opportunities.
Additionally, these ecosystems represent a rich cultural and natural heritage, around which millennia-old traditions have developed. Coral reefs are not only crucial for biodiversity and environmental stability but also for sustaining human communities and preserving cultural identities.
What threats do coral reefs face?
The twin crises of climate change and biodiversity loss pose severe threats to the health of coral reefs. The current state of these ecosystems is especially alarming. According to Pascale Joannot, “climate change is a major stressor for corals.” This stress triggers a difficult-to-reverse process: coral bleaching. During this process, corals expel the symbiotic algae they rely on for survival, rendering them unable to feed and stripping them of their vibrant colours. If bleaching persists, corals eventually die.
Marine heatwaves exacerbate coral health issues, as observed by NOAA between February 2023 and April 2024. A direct consequence of climate change, these heatwaves are becoming longer and more frequent, intensifying bleaching events globally. According to the IPCC’s RCP 8.5 scenario, if global temperatures rise by more than 2°C above pre-industrial levels, up to 90% of coral reefs could vanish by 2100. Another impact of climate change, ocean acidification, impairs coral skeletal formation by limiting calcium carbonate availability, hindering coral growth and resilience. This threat has been identified as the seventh planetary boundary nearing breach. Together, these climate-related factors significantly reduce the ability of corals to grow and regenerate.
In addition to climate threats, coral reefs face multiple pressures linked to human activities, such as destructive fishing practices, coastal artificialisation, and marine pollution. “Even if you throw something into the Seine, it will eventually reach the sea and likely end up in submarine canyons. Even at great depths, corals are impacted!” explains Julie Tourolle, a research engineer in benthic ecology at the French Research Institute for Exploitation of the Sea (Ifremer). At such depths, a different type of coral inhabits the seabed: cold-water corals. Found in all ocean basins, these corals can thrive at depths ranging from 40 meters (notably in the Norwegian Sea) to over 6,000 meters for some alcyonarians and antipatharians. In the Atlantic and Mediterranean, colonial scleractinian corals, which have a calcium carbonate skeleton, form spectacular reefs in submarine canyons between 600 and 1,700 meters deep.
Unlike tropical corals, cold-water corals do not live in symbiosis with algae but remain extremely vulnerable to both climatic and human-induced disturbances. Thus, all types of corals are susceptible to these multiple stresses, requiring special attention to ensure they are protected in line with their crucial importance to our societies and biodiversity.
How can we protect coral reefs and support their regeneration?
Protecting coral reefs requires, on the one hand, mitigating climate change by drastically reducing greenhouse gas emissions and, on the other hand, reducing destructive pressures from human activities. Achieving this necessitates strong collective mobilisation, encompassing both political commitment and coordinated local actions.
As Caroline Donge, Vice President of France Nature Environnement, points out: “With its overseas territories, France ranks as the fourth-largest coral reef nation in the world,” hosting around 10% of the planet’s reefs within its territorial waters. This gives France a significant responsibility in their protection. At the national level, this is the role of the French Coral Reef Initiative (IFRECOR). Since its creation in 1999, IFRECOR has recorded significant progress through close collaboration between researchers, citizens, and policymakers. Among its achievements, the protection of 16 coral species in the French Antilles highlights the impact of collective mobilisation.
Other initiatives are also emerging at the international level. Launched during COP15 by the International Coral Reef Initiative, the Global Fund for Coral Reef, and the UN Climate Change High-Level Champions, the Coral Reef Breakthrough aims to protect 125,000 km² of coral reefs with $12 billion in investments by 2030. It proposes four key actions to be implemented globally to safeguard reefs: addressing the root causes of degradation, doubling the protected area coverage, accelerating restoration efforts, and securing sustainable financing.
Alongside the growing political focus on this issue, marine restoration and conservation projects are multiplying worldwide. Restoration projects often involve the creation of Marine Protected Areas (MPAs)—designated zones in the ocean aimed at protecting marine biodiversity while promoting the sustainable management of marine activities. “The goal is to establish MPAs that allow fish populations to regenerate, which also improves food security for fishers,” says Victor Brun, who participated in a marine conservation project led by the Sulubaaï Foundation in the Philippines as part of his PhD. Community involvement is crucial for ensuring the longevity of these projects. “A local and collaborative approach, including local associations and fishers, is often the key to success for coral restoration projects,” says Florina Jacob, a field project manager and scientist at Coral Guardian.
At the same time, everyone can contribute to coral preservation through various initiatives. Citizen science projects, such as OceanSpy developed by Ifremer, enable the public to directly contribute to scientific research, for instance, by annotating underwater images. Pascale Joannot also encourages participation in crowdfunding initiatives like SOS Corail, a program dedicated to restoring tropical reefs, emphasizing that “every action counts in protecting our marine ecosystems.”
A Possible Future for Coral Reefs?
The preservation of coral reefs is a critical challenge that depends on the ability of policymakers, scientists, and civil society actors to work collaboratively. Reducing our environmental impact and greenhouse gas emissions, engaging in local conservation initiatives, and raising public awareness are all vital to ensuring the survival of these ecosystems. “We all have a role to play. It is essential to be mindful of how our choices impact the world“, emphasizes Florina Jacob.
For effective coral reef protection, strong political commitment is also essential. Preserving coral reefs requires diverse measures, from classifying them among threatened species to establishing marine protected areas, reducing tourism-related impacts, and adopting ambitious climate policies. In this regard, the recent adoption of the Nature Restoration Law at the European level represents a significant step forward. As Caroline Donge explains, this legislation “requires member states to implement concrete policies to preserve biodiversity, with ambitious targets. Moreover, France has included in its National Biodiversity Strategy (SNB3) the goal of protecting 100% of its coral reefs by 2025.” To translate these commitments into tangible actions, civil society’s continued mobilisation will be indispensable in ensuring that coral reef preservation remains a priority at both national and international levels.
This article was produced as part of the Ocean & Climate Rendez-vous event “What Future for Coral Reefs?”, organised by the Ocean & Climate Platform on 25 September 2024 at the Climate Academy in Paris. With contributions from Pascale Joannot (IFRECOR), Julie Tourolle (Ifremer), Florina Jacob (Coral Guardian), Caroline Donge (France Nature Environnement), and Victor Brun (Sulubaaï Foundation), experts dedicated to coral reef preservation and members of the Ocean & Climate Platform.
Panellists at the Ocean & Climate Rendez-vous, from left to right: Caroline Donge, Julie Tourolle, Florina Jacob, Anaïs Deprez (Moderator), Pascale Joannot, Victor Brun.
Written by: Gauthier Carle, Maud Chevalier, Anaïs Deprez, Morgane Pierre, with contributions from Victor Brun, Caroline Donge, Pascale Joannot, and Julie Tourolle.
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