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FIn an unmanned submersible, protected by a stainless steel case about one inch thick and a super-resistant sapphire crystal window, we can observe the life that develops in the deepest and darkest depths of our planet. Thanks to the technology and the strength of the materials, we can temporarily enter this high-pressure environment. However, unlike the robust offshore imaging equipment we rely on, the creatures recorded by our camera appear extremely fragile.
Four and a half kilometers below our research vessel, which floated on the surface of the Pacific Ocean, we captured images of several species of hadal gastropods not yet discovered. With delicate fins and transparent, gelatinous bodies, they are among the most enigmatic inhabitants of this environment, fish that at first sight seem to be unable to survive under such pressures. And yet, it seems that they thrive in this strange world.
In the spring, a team of 40 scientists from 17 different countries conducted an expedition to the Atacama Trough, which runs along the west coast of South America. We were there to find a particular snail.
During a previous expedition, our lead investigator (Alan Jamieson) had photographed a snail with long wing-shaped fins at 7,000 feet deep. One species, Notoliparis antonbruuni was known to inhabit this area to such depth. It has been described from a single specimen, so badly damaged that we can not use it to identify our images of live animals. We wanted to find this elusive winged snail to learn more and observe it in its natural habitat.
These snails tend to live between 7,000 and 8,200 meters ("hadal" simply means less than 6,000 meters), but their apparent rarity may be poorly understood. Because of their extreme habitat (at least for humans), they are difficult to observe rather than actually "rare" as we know it. And with the right equipment and the right opportunities, we were convinced, after ten years of study, that we knew where and how to find them.
The Atacama pit is part of the Peru-Chile subduction zone, a vast area of 590,000 square kilometers where one tectonic plate is forced under another and the seafloor dives rapidly to more than 8,000 meters. Its volume is almost the same as that of the neighboring Andes mountain range, which the tectonic subduction zone also creates, and exploring it is not a trivial matter.
A trio of snails
We deployed our free-fall cameras 27 times, starting from relative shallow at 2500 meters to the deepest point of the trench, Richard's Deep, at a little over 8000 meters. This allowed us to take more than 100 hours of video and 11,000 photographs at the bottom of the sea – and the results did not disappoint. The snails we were looking for appeared – and they were not. Two other previously unknown species of hadal snail fish were present in the sequence. In fact, all three species appeared in the same shot at once. By necessity, they were given fast and alternate names: we called them Atacama snails "purple", "pink" and "blue".
The "blue" seemed to be the "winged" species that Jamieson had previously recorded. Its long trailing fins and prominent snout resembled the Ethereal cod that we recorded during another expedition to the Marianas Trench, far away on the other side of the Pacific.
The "pink" species, on the other hand, was more robust and looked more like the Marianas snail (Pseudoliparis swirei) that we described in 2017 and who also lives in the Mariana Trench. To see these two species – with so different body shots – to share a trench again made us think: they have to do something different from each other to carve out a niche.
The third species, a small purple fish, looked more like a snail than we expected to see on the shallower abyssal plains – at about 3500 meters deep. But one of these purple molluscs, only 9 cm long, followed its prey of invertebrates in one of our traps. This fragile little fish is currently the only physical specimen of the new species and should ultimately allow us to give it a formal scientific name. And although we much prefer our video of the living animal, only a physical specimen can be deposited in a museum and used to formally describe a new species.
Preservation
Once on the surface, we photographed this specimen while it was suspended in chilled seawater – its body is just too fragile to stay in the air and we did not want not that he undergoes the same fate as poor blobfish. , are not really sad (their jelly-like bodies collapse when they are exposed to the surface).
In the following months, we then proceeded to several sample conservation steps to avoid shrinking his largely gelatinous body. In order for scientists (and the interested public) not to struggle to access a unique and fragile specimen, it was also scanned at the Natural History Museum in London, creating a detailed 3D digital model inside and out. outside. Such digital backups are gaining ground in science – take for example the Scan All Fishes project. Disasters such as the recent fire at the National Museum of Brazil, which will have destroyed many unique specimens, also show why they are so important.
But what did we discover about these mysterious creatures? First, as fish approach absolute extremes of the environmental conditions they may face, they not only survive but thrive. It also appears that some trenches support not only a single specialized species, but also several species whose bodily plans suggest different ways of life in the trench.
Second, the crayfish family (Liparidés) is not only the absolute winner of the highest price of fish (found in many other trenches), but the species live in trenches sometimes more than 10,000 km apart and completely isolated from each other. Incredibly, snails exist at these extreme depths, wherever these extreme depths are, and in numbers never thought possible.
And the snail fish is just a story that has emerged from our expedition. Over the next few months, we will continue to process the huge amount of data we have collected, the most we have ever collected in one trip. Our assessment of the large moving animals we filmed will contribute to the project's broader goal of understanding the biological and chemical processes within the trench as a whole.
Thomas Linley is an associate researcher in marine ecology and Alan Jamieson is a senior lecturer in marine ecology at Newcastle University. This article was originally featured on The Conversation.
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