The ocean’s deepest point, the Mariana Trench, is 11 km below the surface—so deep that it could swallow all of Mount Everest, and still leave over 2,000 m of water above the mountain’s submerged peak. Down there, the weight of overhead water creates a pressure comparable to “having an African elephant stand on your big toenail,” says Bruce Shillito of the Université Pierre et Marie Curie in Paris. But somehow, creatures manage to survive and even thrive.
Over 80 per cent of life on our planet lives deep in the ocean, in conditions that are unimaginable to us (the world record for free-diving, without fins or a scuba suit, is 101 m). Starting April 6, the public will get a look at some of these creatures. Shillito has designed a pressurized aquarium, called the AbyssBox, and two of them will be on display at the Océanopolis in Brest, France. Inside will be shrimp and crabs from hydrothermal vents—animals from 2,000 m below the surface—recovered by Ifremer, a French research institute. “The public will see deep sea animals at their natural pressure,” Shillito says. “This has never been done before.” He and Sven Thatje of the University of Southampton were in Vancouver recently for the annual meeting of the American Association for the Advancement of Science, presenting their work.
“Imagine a great big washing machine,” Shilling says: that’s what the AbyssBox looks like, with a porthole in front to see through. “We can change the water without depressurizing it,” because water constantly flows in and out, Shilling says. The feeding process is something like the docking of the space shuttle with the Space Station. Food is placed in a compartment attached to the aquarium, which is brought to the same pressure, before it drops in. “It is rocket science,” Thatje says, “but it’s not impossible.”
We’re only beginning to understand the deep ocean. “What we once called the ‘dull abyssal plain’ is in fact a patchwork of very different zones,” Shillito says. Scientists have discovered sea mounts—underwater volcanoes—that are teeming with life, and sunken woods at the mouths of great rivers, like the Amazon, where wood-boring creatures thrive. Dead carcasses of whales and tuna support myriad life forms, too. The deep sea is “the largest environment on Earth, by far, and I’m not sure there are a dozen scientific deep-sea submersibles to explore it,” Shillito says. “We know about a certain number of species that live there,” Thatje adds, “but we know so very little about how they live.” Simple questions about lifespan and how they reproduce have yet to be answered.
Pressure has played an important role in the evolution of deep ocean life. In one study, Shillito and Thatje looked at the ditch shrimp, which lives in surface waters. In Thatje’s lab, they increased pressure to see how the shrimp would respond, and surprisingly, saw it behaving normally even at simulated depths of 1,000 m. But when the temperature changed, its behaviour did, too. “The first thing you see is a loss of equilibrium,” Thatje says. “The subject can’t stand up anymore. It falls on its side, but it’s not dying.” Warmer water seemed to increase the shrimp’s pressure tolerance, suggesting that changing temperatures might lead to unexpected migrations deeper into the ocean.
Some creatures, like fish, are much more fragile, and capturing these animals is a challenge. In 2008, Shillito caught a live fish at 2,300 m, a record depth, but it didn’t survive long after that. To retrieve an animal so deep, a suction device (controlled remotely from a submersible) is used to grab the fish; with the help of a robotic arm, the fish is then put inside a pressurized recovery cell. This cell is brought over to the “shuttle,” a separate device moored near the submersible, that carries heavy equipment to and fro. Once the fish is caught, the shuttle launches back up to the surface, and a ship recovers it.
As the temperature warms, scientists have observed marine species migrating toward the poles. “We propose that an equally important dimension to watch over is migrations in depth,” Thatje says. “If the surface is warm, you might go deeper.” By studying these animals, it will become clear which ones can go deeper, and what impact they could have.
In the meantime, peering into the AbyssBox, the public will see some of the creatures we share our planet with—and they might as well be aliens from another planet. “We know much better the surface of the moon than we know the surface of the sea floor,” Schilling says. Deep under the ocean, a vast portion of Earth’s biosphere remains a mystery.