With its WALL-E look, the Bathybot robot will be exploring the seabed for 10 years at a depth of 2,400 metres off the coast of Toulon. Between bioluminescence and underwater snow, it will be helping the international scientific community to unravel the many mysteries of this little-known world.
A robot equipped with tracks, cameras and sensors, 1.2 metres long and 1 metre wide, its appearance is reminiscent of its star counterpart, the Perseverance rover on Mars. Bathybot's mission is much closer, on our planet, but concerns an equally distant universe in terms of scientific and human exploration: the ocean abysses.
The Abyss? "We're not talking about the abyssopelagic zone, which lies at a depth of 4,000 to 6,000 metres," explains Christian Tamburini, one of the fathers of the project. The researcher at the Mediterranean Institute of Oceanology (MIO) in Marseilles points out that, "as its name suggests, Bathybot studies the zone above, known as the bathyal or bathypelagic zone".
At 2,400 metres below the surface, in an environment that combines extreme conditions: total absence of light, extreme cold and high pressure. A place where human missions are extremely difficult and only last a few hours in a submarine. Nothing to frighten this WALL-E-like concentrate of technology, which has been submerged since 3 February 40 kilometres off the coast of Toulon. It will carry out its scientific mission for almost 10 years. "It will collect data never before available in this environment, 24 hours a day, seven days a week", the researcher is delighted to say.
An underwater scientific base off the coast of Toulon
Off the Côte d'Azur, the continental slope is at a much steeper angle than elsewhere, making it possible to reach these depths quickly. This short distance means that the little yellow robot can be connected to the ground by cable, so that it can be controlled remotely and supplied with energy.
All the more so as the site has already been connected to the surface for many years via the Provence Méditerranée submarine laboratory (LSMP). In particular, it is home to the giant Antares underwater telescope, a "neutrino detector" initially dedicated to high-energy astronomy and the search for dark matter.
Bathybot has set up shop nearby. "We're using a 'node' on this site to connect. We're going to put in a 2.5 km extension cable, and the whole thing will be connected in a few weeks' time. We'll then be able to control the robot directly from our computer", Christian Tamburini is delighted to say.
Shedding light on bioluminescence
This will open up a window onto a little-known world of scientific interest that is "fascinating in more ways than one", says the researcher. Firstly, bioluminescence. This is the ability of organisms, microscopic or larger, to produce light in an environment that lacks any.
"Three quarters of species are bioluminescent at these depths. We know that it is used for intra-species communication, to recognise each other and for sexuality. For others, it's a way of attracting prey. Or vice versa, like these shrimps that emit light to divert predators". But for Christian Tamburini, this phenomenon is still largely "unknown in its scope and functions".
As with bacteria, "for which the role of bioluminescence is more ambiguous. We don't know why they do it, it makes no ecological sense. Perhaps they attract species to be ingested and end up in the body". That's what Bathybot will help to find out.
Marine snow and global warming
The researchers will also be attempting to link bioluminescence with another major oceanic phenomenon, the "biological carbon pump". The robot will be able to continuously observe and film a central element in this process: "marine snow". These 'flakes' of sediment and organic matter (including phytoplankton) form at the surface where they capture CO2 and fall into the water column to trap it in the abyss.
According to the researcher, "50 % of carbon is absorbed by the oceans thanks to this phenomenon". At a time of climate crisis, he hopes to gain a better understanding of this mechanism. In particular, how much of this carbon "is permanently sequestered in the seabed, and how much is released, for example when organisms consume phytoplankton".
Bathybot's high-precision cameras will make it possible to "take images of marine snow, which is thought to be potentially bioluminescent. Perhaps at 70 %. But we have no direct proof of that".
The BathyReef and BathyBot duo
As the new star of the deep, Bathybot even has the right to a podium. Not to be seen, but to see better. Because on the abyssal plain, visibility can be poor. Particularly near the bottom, where sediment can be lifted up".
A ramp resembling a coral reef has been specially designed to enable it to rise to a height of 1.2 metres: Bathyreef. This inert concrete module resembling a coral reef was designed by Rougerie + Tangram, a laboratory based in Marseille whose architects and engineers specialise in biomimetics. Or the art of drawing inspiration from living things.
It will also attract organisms, as the structure is designed as an artificial reef. "Bathybot will be able to observe and analyse colonisation in this environment. This module is also designed to stimulate bioluminescent organisms that will pass through it thanks to the current, creating turbulence and friction. The robot will be able to observe this phenomenon at close quarters.
"ISS underwater
Bathybot and the associated instruments form a unique underwater scientific base for observing the deep environment: the dynamics of the physico-chemical characteristics of the sedimentary bed, acidification, temperature, oxygenation of the Mediterranean...
The Mediterranean Institute of Oceanology (MIO) in Marseille is at the forefront of this project, with Christian Tamburini and his colleague Séverine Martini. But a broad scientific community is also involved. From Paris to La Seyne-sur-Mer, with institutions such as CNRS, INRAE, IRD, Ifremer, Aix-Marseille University...
And scientific cooperation is soon to become international. "Scientists from Germany, Spain and Italy are interested," explains Christian Tamburini. He talks of an "ISS (International Space Station) underwater". Although the cost of the equipment is "around 600,000 euros", not including the cost of the operation, "it's still well below the cost of space campaigns".