In September 2019, photographer Alexis Rosenfeld joined a joint Greenpeace-CNRS mission to the recently discovered Great Amazon Reef: a deep-sea dive into an astonishing underwater world, the remnant of a former coral reef, now the kingdom of brittle stars and crinoids.

It's 7 p.m., and the tropical night has already been falling for some time. Aboard theEsperanza, the 70-metre Greenpeace vessel supporting the expedition, the team is preparing for the next day. Based on the day's sonar readings, they must choose the most suitable area for the next dive. " The reef is discontinuous and there can be several kilometers between interesting zones, so we have to be precise," explains Serge Planes, the expedition's scientific manager. Roughly speaking," continues François Chartier, Ocean Campaigner for Greenpeace, " the patches are 100 to 200 meters by 100 to 300 meters, which is quite small. We're working at the edge of the continental shelf, around 80 nautical miles from the coast."

And, given the depth involved (over 100 meters at most sites), there's no room for approximation. In view of the difficult conditions, the Préfecture Maritime only authorizes them to dive in the morning. In the event of a search, the launch time is set for 8.30 a.m. at the latest each day.

DIVING TOWARDS THE BLACK STAR

The currents in the area are particularly violent, forcing the surface teams to calculate the drift of the divers according to their estimated descent time, so as not to miss the target! We knew we were going to find currents," explains Olivier Bianchimani, director of Septentrion-Environnement, who was assisting the photographer on the mission, " and we were well served, as they usually reached 3 knots. On the ascent to the landing, we really had to endure it: it sometimes felt like we were abseiling! But what we hadn't imagined," he continues, "was complete darkness. In the photos we'd brought back from Brazil, there was a lot more light and we were hoping to find the same thing. Here, it was very lunar! And all the sites are extremely deep (between 100 and 120 metres), whereas before leaving, the team had imagined that some were no deeper than 80 metres.

Between 0 and 30 metres," explains Alexis Rosenfeld, " everything is green, loaded with particles; and you can clearly see the mixture of fresh and salt water that blurs everything ". Yet they are over 100 kilometers from the coast and over 300 km from the mouth of the Amazon itself. But the flow of the world's largest river is so great (on the order of 200,000 cubic metres per second) that its influence is felt all the way to here. The water is full of jellyfish, salps and suspended particles. The photographer is equipped with a scooter to save time and effort on the descent. And when he turns on the two lights fixed to his shoulders, he has " the impression of being in Star Wars ", so numerous are the suspended particles. Barely three minutes later, they're at the bottom, more than 100 meters down, in a perfectly untouched world. The almost fluorescent green gives way to half-light. You arrive, you try to understand what you're seeing," says Alexis, " the configuration of the place; you discover this crowd of species entangled in each other..." A biologist and scuba diver, Olivier is no stranger to the deep waters of the Mediterranean. I had the impression," he notes, "of finding things that visually resembled our deep coralligenous, even if - of course - the species are different.

The world of brittle stars and crinoids

At the bottom, they enter the world of brittle stars. They can be found in impressive numbers, their long arms intertwined in the gorgonians or in the black coral bushes. There are an incredible number of them ," explains Serge Planes. And, perhaps among them, some new species. But in the end, that's not what interests us most. What's important, and what makes the site so interesting, is the extraordinary combination of all these species. But , as the researcher points out, this is not a coral reef in the usual sense of the word. What we now assume is that it was indeed a coastal reef, but at a time when sea level was around 100 metres lower. " And it is on the remains of this reef that a new ecosystem has managed to establish itself. For example, there are many tube worms that continue to build on this base. "They are slow builders, but they create calcified structures on which many species - sponges, various filter-feeding organisms - settle, creating a rather remarkable centre of biodiversity in a place where we didn't think there would be this kind of development. And what's interesting ," continues Serge Planes, "is precisely this unusual assemblage of species. 

Quelques poissons, même s’ils sont peu nombreux, complètent la liste des espèces : par exemple, des poissons-anges que l’on ne s’attendrait pas, a priori, à trouver dans un environnement aussi sombre et à de telles profondeurs ; également, une petite demoiselle, de la famille des Pomacanthidés, supposée jusque là ne pas dépasser les 30 mètres de profondeur et qu’ils découvrent à 110 m.

One day, " recounts Olivier, " in this complete darkness, we also came across a huge shoal of trevally some twenty meters off the bottom, attracted by our powerful lights. It was a wonderful encounter! Another time, on the way up, five great hammerhead sharks, appearing out of nowhere, came to visit us on the landing. Very peaceful and curious, they continued on their way. And it's true that, given the non-existent visibility, you kind of wonder what might come ashore! "

20 minutes to collect precious samples

At the bottom, the five divers have only 15 to 20 minutes to work. Alexis and Olivier work on the images, while the other three collect the precious samples. At a depth of 100 or 120 meters, they are the researchers' workers, waiting for the harvest on the surface. They collect both water samples and living species. They work practically in the dark, dimly lit, " and some days," says Olivier, " they'll decide to dive with ropes. Patrick Plantard, head diver, is joined by Gilles Siu from Criobe, Camille Loisil and Julien Marais, whose job it is to sonar the most promising patches. After a maximum of 20 minutes, all the samples are parachuted to the surface, to minimize the interval between sampling and study, and to avoid being encumbered during the long decompression stops. In the 15 days of their mission, they collected almost 2,500 samples! Then, as they go along, they have to photograph them, list them, measure them, condition them so that they can be repatriated and identified. This painstaking daily task takes the research team 3 to 4 hours every day. At the end of the day, they draw up a list of the most interesting samples to collect the following day, based on what they already have and the species that appear on the images brought back from the bottom. Pour différencier les espèces, les chercheurs ont plusieurs armes : le séquençage ADN, qui sera fait dans la première moitié de l’année 2020, et l’ADN environnemental* qui, grâce aux prélèvements d’eau, permettra de détecter la présence d’autres espèces, « et de compléter ainsi, précise Serge Planes, la caractérisation de la biodiversité de cet écosystème ».

The expedition members will have been the first to dive on the immense Amazon reef, where the term exploration really comes into its own. This is also the message they want to convey: "In 2020," concludes Alexis, " we can still venture into unexplored underwater regions and discover unknown worlds. 

* Each species leaves a detectable DNA trace in the water, several hours after its passage. By comparing the DNA present with "catalogs" compiled by teams of researchers around the world, this innovative technique makes it possible to confirm the presence of rare or hard-to-observe species.

Dives prepared in Marseille

All the gases used for the rebreathers were prepared in Marseille and transported by container, along with the rest of the equipment. A rescue procedure was developed with the team led by Dr Coulange, head of the hyperbaric department at Sainte-Marguerite hospital. We decided," explains Alexis Rosenfeld, " to start the deep stops at 57 metres, to ensure the most effective desaturation possible. On site, Hervé le Coq Saint-Gilles, hyperbaric doctor, systematically waits aboard one of the two zodiacs parked on the surface; on board, they have a decompression chamber. To spare their bodies a little, the team worked in shifts: three days of diving, followed by a day of rest, before starting again. 

And before setting off, given the depth and conditions forecast, they made several dives to test their equipment, decompression procedures and gas mixes, as well as the heavy lighting that would enable them to take images.

A reef discovered only a few years ago

The existence of the Amazon reef off the coast of Brazil was only revealed in 2016, and its presence in Guiana's waters in 2018. This very special ecosystem, which developed at the edge of the twilight zone, known as mesophotic, is one of the largest reefs known to date: scientists estimate that it is over 1,000 kilometers long, covering 9,300 km². Barely discovered, it is threatened by oil exploration projects in nearby Brazilian waters, and by trawling; and, although the Guianese part seems to be out of danger, it is in fact the whole area that needs protecting.

Part of a long Greenpeace expedition

For one year, the ship Esperanza will cross the Atlantic Ocean, from the Arctic to the Antarctic, to highlight the richness of marine ecosystems and denounce the threats facing the oceans. When Greenpeace management decided to mount this expedition," says François Chartier, " we immediately wanted to include the Amazon reef. In French Guiana, another team also worked on cetaceans, in conjunction with the PELAGIS observatory in La Rochelle.

We have a political aim , of course," he explains. But in the broadest sense of the term: to bring the voice of the oceans to the forefront of the international stage and highlight their role in the planet's resilience in the face of climate change. " The aim is to achieve a target of 30% Marine Protected Areas by 2030, but also real protection for the High Seas: " Negotiations are still underway at the UN, but there is still no satisfactory legal framework. Ce que nous voulons, c’est apporter notre pierre à l’édifice en montrant que des menaces directes existent. »Et, pour la première fois, sur le volet « récif », l’ONG s’est associée au CNRS : « En travaillant sur le récif de l’Amazone, nous voulions montrer qu’il y a encore des écosystèmes inconnus à découvrir et à protéger, notamment face à l’exploitation pétrolière. We had already worked on Brazil in 2017 and 2018, first by submarine, then by ROV, which had only brought back a few images, but no samples. In 2018, we began discussing the project with Serge Planes. Very quickly, the CNRS management showed an interest in the project, and we came to the conclusion that this time we had to send men ". It was up to Serge to put together a team. For our part," admits François, " this was the first time we'd involved deep divers. We had to put in place very precise safety protocols and familiarize ourselves with ways of working with which we were unfamiliar. We're used to big operations on the high seas, which is very different. But we really succeeded in combining our different ways of working, and the mayonnaise really took off between the teams!