Exploration
How research on little-known “marine animal forests” could shine a light on ocean hope spots — and why they need protecting
The sky is a hot, cloudless blue as a boat belonging to underwater science and exploration program Under the Pole speeds down the western coast of Basse-Terre, Guadeloupe. Clad in navy wetsuits, leaning into the wind and spray, the scientists and technical divers on board look like superheroes racing to save the ocean — and in a way, they are.
Driver Nicolas Mollon cuts the engine at a faded orange buoy off the island’s southwestern tip and divers Ghislain Bardout and Erwan Marivint shrug on harnesses heavy with scuba gear. They are about to descend into another world, 120 metres below the surface, where the strong Caribbean sun is diffused into a permanent dusk. Just as the steep slopes of this volcanic island are covered with lush forests, so too is the surrounding seafloor home to a forest-like ecosystem, where corals and sponges stand in for trees and shrubs. Bardout and Marivint will spend about 20 minutes gathering as much information as possible about this alien place, capturing images, recording sound, taking coral samples and measuring the light, temperature, current and sediment content of the water. They will do this again at each decompression stop on their slow ascent, taking about three hours in total to return to the surface.
While I wait, I snorkel in a shallow cove close to shore. To my untrained eye on the surface, the reef looks busy and vibrant. Sea fans and plumes wave lazily in the current while iridescent fish dart in and out of huge vase-like sponges. At one point I find myself surrounded by a cloud of brown damselfish, unbothered by the giant interloper in their midst. The scientists working with Under the Pole later shatter this illusion of health: since the 1980s, surface reefs throughout the Caribbean — indeed, the world — have been badly degraded by heat stress, pollution, disease, overfishing and invasive species. In the French Antilles, including Guadeloupe, a massive bleaching event in 2005 resulted in the loss of about 40 per cent of the region’s coral cover.
But below 30 metres, it’s a different story. Recent research in other parts of the world has shown that coral reefs in the mesophotic (“middle light”) zone — the twilight world between the brighter-lit shallows above 30 metres and the darker deeps below 150 metres — are healthier and more biodiverse than reefs at the surface because they are buffered from the natural and anthropogenic stressors affecting the surface. This could make them important refugia for wildlife that can move between the surface and the mesophotic zone. They may be “hope spots” in a global ocean in peril.
While the ecosystems within this zone have long been recognized by the scientific community, they’ve been given relatively little attention compared with both their shallower and deeper counterparts, largely due to how difficult and expensive it is to observe them. Scientific literature on the importance of these ecosystems has exponentially increased in the past few decades, but more research and exploration are needed to understand how these deep reefs function — and to make a compelling case for their conservation.
Enter Under the Pole. Led by French husband-and-wife team Ghislain Bardout and Emmanuelle Périé-Bardout, they are a team of skilled and passionate divers who have made it their life’s mission to advance ocean science through exploration. They live at sea for months at a time aboard an ice-capable schooner, the WHY, going wherever researchers need data — and pushing the limits of self-contained diving to obtain it. Searching, as Ghislain puts it, “for answers to an open question.”
Neither of the Bardouts grew up near the ocean, but they did grow up watching the films of Jacques Cousteau, which sparked a shared fascination with underwater exploration. Ghislain started scuba diving at the age of 15, and by the time he finished his studies in mechanical engineering, was an accomplished diver. Emmanuelle initially pursued her passion on the waves rather than beneath them, moving to Brittany after school to become a sailing teacher. It was there that she met Ghislain; he was her diving instructor.
In the mid-aughts, both were tapped to help coordinate logistics for the French polar explorer Jean-Louis Étienne, who was planning an expedition to the geographic North Pole. For Ghislain, diving under the Arctic sea ice for the first time was both the fulfillment of a childhood dream and a call to action: he would leverage his skills as a technical diver to study the ice shelf from under the water and “testify about a world that is disappearing.”
In 2008, he and Emmanuelle founded Under the Pole, and they have since undertaken several expeditions, collaborating with scientists from around the world to gather data on everything from snow depth and ice quality on the northern polar ice cap to bioluminescent organisms in the depths of the Northwest Passage. For their third exploration program, which began in 2017, Under the Pole shifted their focus from the warming Arctic to the biodiversity of the little-studied mesophotic zone. After transiting the Northwest Passage east to west, the Bardouts — now with two young sons along for the adventure — sailed the WHY to French Polynesia, where scientists at the Centre for Island Research and Environmental Observatory (CRIOBE) were studying the mesophotic reef system.
That mission saw the Under the Pole team collect more than 6,000 coral samples, including the deepest sample ever retrieved, at 172 metres. Finding living coral at that depth “proved we had a very limited view of coral,” says Laetitia Hedouin, a CRIOBE researcher and one of two scientific directors for DEEPLIFE, Under the Pole’s current exploration program. Corals live in symbiosis with microalgae that photosynthesize energy from the sun, so Hedouin wondered how they were able to survive at the outer limits of light penetration. She doesn’t dive, so teamed up with Under the Pole to study deep reefs across 11 islands. The team found biodiversity hotspots, particularly between 40 and 60 metres, where corals appear to be thriving. The reasons why are not fully understood, but what’s clear to Hedouin and her DEEPLIFE scientific co-director Lorenzo Bramanti is that conservation decisions must take deep reefs into account as well as shallow ones, with protections applied throughout the water column.
Bramanti, a researcher with the French National Centre for Scientific Research (CNRS), is one of a growing number of marine biologists advocating for a shift in how we view reef ecosystems. When they grow together in great enough numbers, corals, gorgonians, sponges, bivalves and other sessile marine animals function much like terrestrial forests: they form a canopy, moderate light, currents, and water temperature, cycle nutrients, and provide food and habitat for a wide range of species. Viewing these systems as “marine animal forests,” a term that was first used by Alfred Russel Wallace in 1869, is essential for their conservation, Bramanti says, because it moves the conversation from the protection of individual species to the protection of the whole. “[On land], we protect the forest, not the trees. If the forest is functioning well, it can support the health of the surrounding environment.”
DEEPLIFE is Under the Pole’s most ambitious exploration program yet — a 10-year program supported by Rolex’s Perpetual Planet Initiative, and endorsed by the United Nations Decade of Ocean Science for Sustainable Development, to dive on and study mesophotic marine animal forests in polar, tropical and temperate regions of the ocean. In 2022, the team completed their first DEEPLIFE missions. In Svalbard, Norway, they documented and sampled what they believe to be the first marine animal forest ever identified in the Arctic, made up of hydroids: animals related to jellyfish and corals that resemble terrestrial flowers and ferns. In the Canary Islands, they discovered a new genus of amphipod and achieved their deepest dive yet, to a crushing 200 metres. Now they’ve come to Guadeloupe to sample and study the gorgonians and black corals that make up the mesophotic marine animal forest here. The goals of DEEPLIFE are four-fold: discover new types of marine animal forests, advance the depth limits of known forests, evaluate their health, and begin to develop a framework for their protection, including minimum conservation units — or as Bramanti puts it, how many trees you need for the forest to function.
“We’re buying time,” he says. “It’s not too late to protect these deep reefs, but we need exploration, we need data, and this data will inform conservation efforts.”
Scuba diving below 60 metres is outrageously risky. Divers must breathe a special mixture of gases, as oxygen becomes toxic at higher pressures. Because of the risk of carbon dioxide retention, divers can only spend a few minutes at maximum depth, and must make several decompression stops, precisely timed with a dive computer, to prevent decompression sickness, also known as the bends. If something goes wrong, a fast ascent to the surface is impossible without serious complications. (Guadeloupe was chosen as a study site partly because the local teaching hospital has a hyperbaric chamber to treat divers suffering from the bends.)
Mornings aboard the WHY are mostly dedicated to organizing, checking, and re-checking equipment, which now is arrayed over almost every inch of the schooner’s decks. Each Under the Pole diver is saddled with around 80 to 90 kilograms of gear, including gas and decompression cylinders, a rebreather, a dive computer, a scooter, a camera and tools for sampling and measuring. The gear is checked again on the tender before the divers enter the water. Even after this rigorous attention to detail, things can go wrong: on our second day on the reef, divers Luiz Rocha and Mauritius Bell have to cut their descent short due to a problem with the carbon dioxide scrubber in Bell’s rebreather.
Given the risks and hassles of diving, why not just use a submersible?
On this point, Rocha is emphatic: “Trying to study fish in a coral reef with a submarine is like trying to study birds in the rainforest with a helicopter. Technical diving is the best way to do science at those depths.”
Luiz Rocha“It happens on almost every dive: we find new species, and we find plastic in a reef that no one has ever seen.”
Rocha is the curator of ichthyology at the California Academy of Sciences in San Francisco and a technical diver who shares Under the Pole’s desire to advance deep exploration. He was selected as a laureate of the 2021 Rolex Awards for Enterprise for a multi-year project to study mesophotic reefs in the Maldives. During his first expedition, Rocha and his Maldivian collaborators discovered eight species of fish that were new to science and passed critical data to the Maldivian government to inform conservation work. Given Rocha’s extensive diving experience — which includes more than 6,000 hours underwater on some 70 scientific expeditions — and the overlap between his research interests and and the goals of DEEPLIFE, Rolex connected him with Under the Pole for the Guadeloupe DEEPLIFE mission. Rocha will conduct fish counts on the reef, assessing species diversity at different depths to figure out how fish communities are structured and whether shallow reef species ever visit deeper reefs. So far, studies have found very little species overlap between the different zones of the ocean, but when it comes to deep reefs, Rocha says, “there are more questions than answers.” Because the mesophotic zone has historically been so difficult to study, new species of fish are discovered on practically every dive.
For Rocha, like Under the Pole, the end goal of this research is meaningful conservation that maximizes impact instead of achieving arbitrary targets. Mesophotic animal forests may be healthier than their surface counterparts for now, but they are still vulnerable to threats like plastic pollution and destruction from bottom trawling. In many areas of the Pacific and Indian oceans, Rocha has found more plastic trash in the depths than at the surface, mostly discarded fishing gear.
“It happens on almost every dive,” he says. “We find new species, and we find plastic in a reef that no one has ever seen.”
On my final night in Guadeloupe, over a round of local beer, I ask the Bardouts and Rocha what gives them hope for the future of the ocean. Emmanuelle thinks for a moment, then confesses that a few years ago, when the Intergovernmental Panel on Climate Change warned that 1.5 C of climate warming would result in the loss of up to 90 per cent of the world’s coral reefs by the middle of this century, she and Ghislain almost lost hope. But that was before they made their remarkable discoveries on the mesophotic reefs in French Polynesia.
“We have two kids, and I don’t want to lose hope for them,” she says. “I think there is hope in science, but only if we take the emergency seriously.”
Rocha takes a slightly different tack: “I think nature is more resilient than people think it is. I do expeditions all over the place and I see that reefs are not dying, they’re changing. But I don’t want to be the species or the generation that causes them to change in a big way.”
For now, the work to uncover the secrets of mesophotic reefs continues. After Guadeloupe, Under the Pole will sail home to France to dive in the Mediterranean and try to raise the capital for the WHY NOT, a bigger, state-of-the-art schooner with room for a hyperbaric chamber on board, which will facilitate truly remote exploration. Rocha will head to French Polynesia to collect live fish samples for an exhibit at the California Academy of Sciences, then back to the Maldives to continue his work on the reefs there. Laetitia Hedouin, Lorenzo Bramanti and Under the Pole’s other scientific collaborators will analyze the samples and data they collected in Guadeloupe to determine the health of this marine animal forest. They plan to return to the Caribbean in 2025.
Beneath the waves, the twilight zone beckons, an open question waiting to be answered.
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