Satellites and genomics to support coral reef conservation in the warming Indian Ocean
Tropical coral reefs are hotspots of biodiversity, but they are suffering severe degradation due to anomalous heatwaves. A recent study combined satellite observation of ocean conditions with genomic analyses of reef-building corals in the Western Indian Ocean region. This analysis pinpointed reefs likely to host heat-tolerant corals, and mapped their natural larval dispersal via sea currents across more than 1,000 km of open ocean.
The study was coordinated by the United Nations Development Programme and is now published in Evolutionary Applications. It is the result of a collaboration among researchers and conservation stakeholders from Switzerland, France, Mauritius, Rodrigues, and Seychelles. Its findings can inform marine conservation strategies aimed at restoring damaged reefs in the region. However, these strategies cannot shield the entire reef system from the extreme heatwaves projected under current emission scenarios. Ultimately, the long-term survival of healthy coral reefs depends on drastic cuts in carbon emissions.
Coral reefs: biodiversity hotspots under threat
Coral reefs are the ocean’s most biodiverse ecosystems, supporting up to one-third of all marine species despite covering less than 1% of the ocean floor. This extraordinary diversity provides vital ecosystem services, such as sustaining fisheries for coastal communities in the tropics.
At the heart of coral reef ecosystems are hard corals—colonies of polyps that build calcium carbonate skeletons, forming the three-dimensional framework of the reef. Like trees in a forest, these structures create habitats for a wide range of species, including fish, crustaceans, sea turtles, and marine mammals.
Coral reefs have faced severe decline over recent decades. Between 2009-2018, global coral cover dropped by about 14%, primarily due to coral bleaching—a stress response triggered by heatwaves. Bleaching often leads to coral death, allowing seaweed and macroalgae to overrun the reef, destroying critical marine habitats. With rising ocean temperatures, the future of coral reefs remains uncertain.
Looking for heat-adapted corals in the Western Indian Ocean
However, there are reefs that have been repeatedly exposed to heatwaves, and where corals show an increased heat tolerance. Evolution is likely shaping the genomes of these heat-adapted corals, offering a potential lifeline for survival of these reefs.
Identifying reefs hosting heat-resilient corals is now crucial. On the one hand, marine protected areas could safeguard these reefs from controllable stressors—such as destructive fishing activities and boat traffic. On the other hand, these corals could be propagated in coral nurseries, with the ultimate aim to promote their dispersal toward isolated reefs via transplantation.
The Western Indian Ocean exemplifies this challenge. The reefs of Mauritius, Rodrigues and Seychelles are separated by vast stretches of open ocean and have already suffered significant coral losses.
Our study, published in Evolutionary Applications, aimed to pinpoint where heat-adapted corals are located and how they spread across the region.
Satellites and genomics to understand coral evolution in warming oceans
Using satellite earth observation, we reconstructed seascape conditions and climate trajectories for every reef in the Western Indian Ocean over recent decades. This enabled us to classify reefs based on their exposure to severe heatwaves.
Guided by this classification, we conducted an underwater field campaign to collect coral DNA samples from reefs with contrasting thermal histories. We then analyzed the genomes of these coral populations to identify genetic traits linked to heat adaptation, and to determine which thermal trajectories are most likely to select for heat-resistant corals.
Our analysis revealed reefs with strong potential for heat adaptation in Mauritius, Rodrigues, and some of the western islands of the Seychelles Archipelago. We then used earth observation data to model sea surface current circulation patterns in the region. Since coral larvae disperse passively via these currents, this analysis helped us identify which reefs are less likely to receive heat-adapted larvae via natural dispersal.
A collaborative effort across more than 1000 km of open ocean
This research is the result of a collaborative effort coordinated by the United Nations Development Programme in Mauritius, led by a team of consultants from Switzerland (Oliver Selmoni from UZH, Annie Guillaume and Stéphane Joost from EPFL) and France (Véronique Berteaux-Lecellier from CNRS and Gaël Lecellier from University of New Caledonia).
The consulting team partnered with local marine research centers, including the Mauritius Oceanographic Institute, and NGOs dedicated to coral reef conservation in Mauritius, Rodrigues, and Seychelles.
Together, project partners assessed reef conditions, designed a sampling strategy, conducted fieldwork, and processed samples. Throughout the project, the consultants provided training in field sampling, laboratory techniques, and computational analyses—using Earth observation data to characterize seascape climates and linking genomic data to climate variation.
The findings were presented at a symposium in Mauritius in June 2024, where stakeholders from across the region discussed conservation strategies. In Mauritius, the results will inform the creation of a land-based coral nursery, focusing on propagating heat-tolerant corals to support future restoration efforts.
Literature
Guillaume, A. S., Joost, S., Curpen, S., Dumur Neelayya, D., Harree-Somah, L., Sadasing, O., Saponari, L., Dale, C., Barret, L., Andrews, N., Leckraz, S. K., François, R., Seetapah, V., Munusami, V., Bacha Gian, S., Jhangeer-Khan, R., Mahoune, T., Chumun, P. K., Poretti, M., Berteaux-Lecellier, V., Lecellier, G., Selmoni, O. (2026). Coral genetic structure in the Western Indian Ocean mirrors ocean circulation and thermal stress history. Evolutionary Applications, 19(2), e70206. https://doi.org/10.1111/eva.70206
Title image: Sampling corals for DNA analysis in Seychelles (credit: Véronique Berteaux-Lecellier)
Oliver Selmoni