Reunion island
-19.70675, 54.14863
November 2019

Gombessa Expeditions - La Pérouse


Seamounts are large underwater mountains, generally of volcanic origin, that rise from the ocean floor. They can arise along mid-ocean ridges, as isolated landmarks or as volcanoes in chains and clusters. Seamounts constitute hotspots of marine biodiversity, as they provide hard foundations for deep-sea life to settle on and grow. In addition, seamounts rising into the ocean create obstacles that shape ocean currents and direct deep, nutrient-rich waters up the sloping sides of seamounts to the surface. These factors combine to make seamounts fertile habitats for diverse communities of marine life, including sponges, crabs, sea anemones, commercially important fish, and deep-sea corals. Such hotspots serve as spawning sites for many species and marine mammals such as whales and dolphins. Moreover, large predators such as sharks rely on them to feed and rest during migrations.

Seamounts can be found throughout the world's oceans. Estimation of their number varies from tenths of thousands to a million of such geological formations, depending on the exact definition that is adopted. However, of all Earth's seamounts, only a few hundred have been studied. As often stated by oceanographers, humans know more about the topography of Mars and the Moon than we do about the ocean floor.

Today seamount biodiversity and ecosystems face an increasing number of threats, including deep sea bottom fishing and deep sea mining. In this context Blancpain together with Laurent Ballesta and his Gombessa team are working on an exploration program to raise the public's awareness of these crucial hotspots for ocean health, food security, medicine and other benefits that oceans provide to humans.

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From more than 5,000 meters, the depth passes abruptly to just a few dozen metres: this is Mont La Pérouse, an underwater mountain, 160 km northwest of Reunion Island, born from the entrails of the Earth and whose size is comparable to that of Mont Blanc, the highest mountain in the Alps. This geological structure is well known to Reunionese longliners who regularly carry out miraculous fishing operations there. However, for oceanographers, the area remains a real enigma. With Blancpain's support, Laurent Ballesta together with local researchers and part of his Gombessa team led an expedition in November 2019 to study, characterize and illustrate the exceptional biodiversity of the La Pérouse Seamount.

Carried out by deep diving with the use of electronically controlled closed circuit rebreathers, the exploration of this monumental site is a great first. Like all expeditions of the Gombessa team, the exploration of Mont La Pérouse was based on three key principles: the scientific component, the diving challenge and the promise of unpublished images. The scientific challenges were mainly characterized by the habitat inventory and the collection of data on the fauna and flora. Observation and photographic inventory, biological and geological sampling, and the use of cameras and sonars are all techniques used by Laurent Ballesta and his team to analyse the biodiversity of Mont La Pérouse.

In order to carry out this study, the divers had to adapt to complex diving conditions. As the site is in the open sea, it is beaten by trade winds and subject to almost permanent currents. Moreover, the dives were carried out in open water, with no possible return to a reef close to the surface. The ascents were therefore made without any visual clues or protection against the current. Bottom times approached the hour at depths of 60 meters and up to 30 minutes at 120 meters. Daily ascents and decompressions lasted between 3 and 5 hours.

The exploration of Mont La Pérouse resulted in rare and splendid images. These will illustrate a synthesis of the study, a scientific publication, and will be the subject of photographic exhibitions with the aim of raising public awareness of the richness of the underwater ecosystems.

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The movies

La Pérouse Expedition Episode 1
La Pérouse Expedition Episode 2
La Pérouse Expedition Episode 3
La Pérouse Expedition Episode 4