Scientists are searching the ocean floor for strange and undiscovered deep-sea forests, hoping to safeguard them before it’s too late
The Twilight Zone, known scientifically as the mesophotic zone, is an area of ocean between the shallows and the deepest, darkest depths. Here in the dimly lit waters, some 30–200 metres below the surface, researchers have found areas of ‘forest’ that stretch across the sea floor. Unlike the kelp beds and seagrass meadows that grow close to coasts, these deep-sea reefs are devoid of plant life, and are instead made up entirely of carnivorous and plankton-eating animals.
These mesophotic ecosystems, which Ghislain Bardout calls ‘marine animal forests’, can be found in all of the world’s oceans. However, despite their global distribution, little is known about them, and most remain undiscovered. Bardout is on a mission to find them. He’s just returned from Guadeloupe, where the conditions on the seabeds surrounding the Caribbean island are ideal for their development, concluding another successful research expedition.
Bardout is a mechanical engineer and, more importantly (he stresses), a passionate deep-sea diver. In 2008, alongside his wife and fellow ocean-lover Emmanuelle Périé-Bardout, he founded the Under the Pole exploration programme, which has been supported by Rolex since 2010 as part of its Perpetual Planet initiative. Its goal is to facilitate the research and preservation of the oceans. One area of focus is the DeepLife programme, a collaboration between divers and scientists to search for marine animal forests around Svalbard, the Canary Islands and in the Caribbean.
Finding marine animal forests can be a challenge. Each expedition begins with what Bardout describes as a huge exploration phase. ‘At this point, we are just searching, diving down to depths of 100, 120, 140 metres or deeper, and we’re looking for environments that have the characteristics of a forest.’ It took weeks for Bardout and his team to find their first Arctic forest – the first, he believes, to have ever been studied.
Until recently, studies of marine animal forests have been severely limited by a lack of technology. The lower regions of the mesophotic zone are too deep for conventional scuba diving, but too shallow to justify the costs of remote operated vehicles (ROVs) and submersibles. Even as new submersibles and so-called soft robots are developed, Bardout says there’s no question of them replacing human divers. ‘Submarines and ROVs are excellent tools, particularly for use in places where humans cannot go – for example, you’ll never get a diver 1,000 metres deep. But they can’t achieve the same level of performance that we can with our hands and our eyes, tools that are much more efficient than those of a robot.’
Bardout says that science has always been a part of the Under the Pole missions. It was natural, he says, that they chose to focus their work where it could add the most value – and the team’s skills were perfectly suited to searching for life in the Twilight Zone. ‘We specialise in technical deep-sea diving, down to depths of 200 metres. That requires a lot of knowledge and experience, and there aren’t a lot of teams around the world that have the expertise to do this.’
Marine animal forests are all formed from communities of filter-feeding animals, such as corals and algae, but the Under the Pole expeditions have highlighted that these islands of biodiversity come in all shapes and sizes. The Arctic forest near Svalbard is the smallest found so far, at just 25–30 centimetres tall, and is composed of hydroids (small predatory animals similar to sea anemones), while the forests around the Canary Islands are a mass of black corals, and in Guadaloupe they were found to contain a mix of different corals, gorgonians and sponges.
These different species create a canopy on the ocean floor, similar to trees in a terrestrial forest, that provides a raft of ecosystem services – such as food, shelter and nursing grounds for other species – and act as carbon sinks. What we don’t quite understand is how they interact with other, more studied, ocean ecosystems.
‘In addition to creating an inventory of the different species, we are also working to establish the different functions of these ecosystems,’ says Bardout. ‘It’s starting to become evident that marine animal forests are connected to both the ecosystems in shallow ocean waters and in the deep.What we are trying to demonstrate is that, if all these ecosystems are interconnected, then the destruction of one of them could also have dramatic consequences for the others.’
Currently, marine animal forests are largely omitted from conservation plans and are threatened by various human activities, including trawling and deep-sea mining. Bardout says that this comes down to a lack of understanding, both in terms of their importance and their locations. This urgently needs to change, he says. ‘These ecosystems can be centuries old, but activities like trawling can destroy them just like that.’
