Studying deep corals
Since July 2018, the Under The Pole III expedition led by Emmanuelle Périé-Bardout and Ghislain Bardout has been working on the DeepHope research program, a study on deep corals, called mesophotic corals. In partnership with the Criobe - Centre de Recherches Insulaires and Observatoire de l'Environnement - the diving team collects corals located between 30 and 150 m deep in French Polynesia. Today, nearly 4000 samples have been collected, forming the largest collection of mesophotic corals in the world.
An unexpected discovery
On April 4, 2019, when Ghislain and two crew members surveyed the depths of the Gambiers archipelago they ascend the Hawaiian Leptoseris, the deepest coral ever collected, to a depth of 172 m.
This discovery proves that surface corals - impacted by global warming - migrate to the depths of the oceans to find refuge and develop.
Aldo Ferrucci / Under The Pole
"They now represent a real hope for restoring reefs through a supply of larvae that can recolonize the surface. Without these deep reefs, the chances of survival of reefs are very low in the face of unprecedented changes to the planet.
By highlighting a largely unknown part of coral reefs, we hope to contribute to the establishment of appropriate management and protection measures to safeguard these reefs. These discoveries reveal a completely new vision of how they work. They are a continuum from the surface to mesophobic areas where coral communities follow one another. Our knowledge suggested that 25% of corals could descend from the surface to the depths and today, after more than 4000 samples collected, the trend is completely reversed, with more than 60% of the surface species capable of colonizing the depths.
This discovery is fundamental and helps to support the hypothesis of a refuge for corals in the depths, where the environment is less impacted than on the surface. The harvesting of a mesophotic coral at a depth of 172 m raises new intriguing questions about the capacité? corals to live in these hostile environments. The expedition will continue for another three months, and the results of this program will be international in scope and will form the basis of our in-depth knowledge of mesophobic reefs explains Laetitia Hédouin, a CNRS researcher at the Centre de recherche insulaire et observatoire de l'environnement and an expert in coral biology.
A new challenge
In August 2019, the crew of Under The Pole will submerge the "Capsule", allowing expedition divers to stay underwater for several days. Located on the outer slope of Moorea Reef, the team will be able to continue coral studies and especially its reproduction.
"A few nights a year the coral releases sexual cells into the water column which will fertilize in the water to give a coral larva. This process is vital for the renewal of coral populations, as it allows the arrival of new individuals on the reef. However, today, the exact date and time of this moment clé? of the coral life cycle are only known for a few species in French Polynesia and have never been observed in situ at été?" explains the people in charge of the expedition.
