Coral 2mn

Record survival rate for Mauritius coral, raised to restore reefs

Breeding techniques enable the reproduction of corals selected for their resistance to marine heatwaves.

Nestled in the heart of the Indian Ocean, Mauritius is home to more than 250 species of corals and hydrozoans. They form reefs that shelter a quarter of the island's marine life and provide food for fish and human populations.

Unfortunately, this cornucopia is threatened by successive waves of bleaching, which have occurred four times since the first in 1998. During the last one, in the summer of 2025, the water temperature reached over 31°C. Thermal stress causes the coral to expel its host algae, zooxanthellae. The latter provides nutrients to the coral, and without it, the coral dies and bleaches.

Until now, bleached reefs have been restored by cloning cuttings from robust coral colonies. However, previous bleaching episodes have shown that this technique has its limitations. With financial support from the government and the UN, scientists from the Mauritius Institute of Oceanography, the University of Mauritius and the Odysseo Oceanarium have collected coral eggs and sperm, thanks to improved forecasting of spawning periods, before raising and selecting the most heat-resistant corals in protected nurseries.

Record survival rates

After three years, the survival rate reached 98% for the four species of branching corals placed at the Pointe aux Feuilles site, which is enriched in nutrients and has little impact from tourism, compared to 88% in the Flic-en-Flac lagoon, which is affected by severe soil erosion and tourist pressure.

The record survival rate is held by the hydrozoan Millepora with 99.8%, compared to 88% for all corals and only 10% for corals grown using the old method.

These results are extremely encouraging for the preservation of coral reefs, but we must not forget that the best way to combat marine heatwaves is still to drastically reduce our greenhouse gas emissions.