The midnight zone begins half a mile below the surface of Monterey Bay, where sunlight can no longer reach. These dark depths are home to a menagerie of deep sea creatures, from bright red bloody-belly comb jellies (Lampocteis cruentiventer), with their strobing bioluminescence, to pale grapefruit-size pearl octopuses (Muusoctopus robustus) brooding over their eggs along warm cracks in the ocean floor.
Until recently, the deep sea was too distant, cold, and high pressure for humans to explore, and much of it remains unknown. Yet it encompasses more space than all of earth’s continents combined, making it the largest habitat on the planet and likely home to more animals than all other ecosystems.
“These beautiful, potentially very sensitive ecosystems in the deep sea are right in our backyard,” says James Barry, a seafloor ecologist at the Monterey Bay Aquarium Research Institute (MBARI). “They enrich our lives in ways that most people are not really aware of.”
The seafloor captures most of the planet’s carbon dioxide, supporting a stable climate by keeping the greenhouse gas out of the atmosphere. Cold, nutrient-rich water is churned up from these frigid depths toward shore, where it fuels the California coast’s iconic biodiversity. But while scientists plumb the deep sea’s wonders and begin to grasp its planetary importance, the ocean is also being transformed by climate change and threatened by deep sea mining. Understanding human impacts and conserving deep sea ecosystems requires documenting them in the first place. However, the same underwater robots and other advanced technology that drive documentation and conservation also enable exploitation of deep sea resources.
“We’re already seeing huge changes in ecosystems, or communities, in the ocean because of climate change,” says MBARI engineer Kakani Katija. And yet “a lot of proposed solutions to combat climate change—like deep sea mining or offshore wind—are activities that are going to impact biological communities in the ocean.”
Fathoming the depths
Off the coast of California, shelves of shale and sandstone are occasionally interrupted by seamounts and plunging underwater chasms, including Monterey Bay’s canyon, which reaches over two miles deep and begins zigzagging within a mile of the shore. For most of human history, these depths were unfathomable. Scientists gradually caught glimpses of deep sea wildlife as new technologies such as submarines, net trawling, and eventually remotely operated underwater vehicles (ROVs) became more advanced, especially in Monterey Bay’s uniquely accessible canyon. ROVs revolutionized deep sea research by allowing scientists to observe deep sea creatures in their natural habitat, without shredding delicate gelatinous critters in trawl nets or having them implode under surface pressure.
The glaring beam of ROV headlights shines through the sunless depths like an aquatic UFO. ROVs traverse the midnight zone, collecting data on temperature, location, salinity, and more while filming hundreds of thousands of hours of footage. These beams illuminate passing deep sea squid (Bathyteuthis berryi), stinging strands of goo called siphonophores, and many creatures yet to be named. By surveying the same areas regularly, researchers can identify, map, and monitor deep sea ecosystems and their inhabitants. Until recently, analyzing ROV footage required MBARI researchers to comb through thousands of hours of material, painstakingly labeling animals and geological features.
As scientific ROV surveys became more frequent, the sheer amount of footage quickly outpaced the scientists’ availability to analyze it. In the United States, deep sea exploration organizations have collected 300,000 hours of visual data, but only 15 percent of it has been analyzed or labeled, according to a survey done by the Ocean Discovery League. In recent years, the number of ROVs roaming the deep sea and hours of footage gathered have increased, a trend that seems likely to continue.
“We’re anticipating an exponential increase of data collection,” says Katija. “There’s a massive opportunity for understanding and more information if we were actually able to fully process that information.”
To address this processing gap, Katija compiled an archive called FathomNet, which contains almost 100,000 images collected and labeled by MBARI researchers since the 1990s. Machine learning programs trained on FathomNet’s data partially automate the process of identifying and labeling creatures captured in ROV footage. So far, FathomNet has improved the speed of identifying creatures by an order of magnitude, Katija says. Over time, Katija hopes to share resources like FathomNet technology with island nations to foster more inclusive ocean exploration. Ultimately, Katija says she hopes that FathomNet can become a global repository for information on ocean life.
Deep sea creatures may strike many as distant and bizarre, but Katija wants to put them in regular people’s pockets. Inspired by community science apps like eBird and iNaturalist, Katija’s lab collaborated with a game design studio in the Netherlands to design and launch a mobile game called FathomVerse.
In one part of the game, players float in simulated currents, open ROV images of deep sea creatures, and decide if the image is the animal they’re searching for. Katija hopes playing FathomVerse will help landlubbing members of the public feel more connected to deep sea science. Eventually, players label a creature; their assigned classification may be included in the FathomNet database and help train its machine learning models.
“By tapping into our collective curiosity, FathomVerse seeks to transform ocean exploration by engaging a community of ocean enthusiasts to work alongside researchers,” Katija said in a FathomVerse press release.
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Protecting the unknown
FathomNet is part of a scientific race to understand the deep sea before human activity transforms its ecosystems for everything that lives there. In the last decade, the tension between exploration and exploitation has taken on particular urgency. Deep sea mining companies have begun prospecting the seafloor for polymetallic nodules—potato-size lumps of manganese, cobalt, and other metals key to making batteries for the booming electric vehicle industry. International governments and private corporations, working through the United Nations–backed International Seabed Authority, have already started to divide up large areas of the Pacific seafloor for mining. An election for the ISA’s leadership this summer was marred by allegations of corruption and bribery. A 2021 story heading in the New Yorker by environmental journalist Elizabeth Kolbert reads, “We’ve barely explored the darkest realm of the ocean. With rare-metal mining on the rise, we’re already destroying it.”
Proposed mining operations would pump sediment up from the ocean floor, sieve out the precious nodules, and unleash the leftover sediment back into the water. These plumes of sediment would likely disrupt deep sea creatures’ ability to swim, breathe, find marine snow to eat, and communicate through bioluminescence—not to mention directly disrupting the lives of animals sucked into mining machinery. Polymetallic nodules are found way out in the Pacific’s international waters, far from California’s coast and marine sanctuaries. But the potentially far-reaching effects of releasing sediment plumes into deep sea ecosystems remain unknown.
Climate change is also altering the depths by shifting the livable range for prey species, transforming ocean food webs. Many deep sea creatures are being displaced by warming ocean temperatures—and the shifting oxygen concentrations that come with them. Land animals migrate toward the poles or to higher elevations to escape warming. Underwater, creatures do the vertical equivalent, going deeper to chase colder, more oxygen-rich water.
MBARI researchers have found that as the ocean warms, a layer of water with low levels of oxygen is expanding closer to the surface and deeper toward the ocean floor, pushing animals out of the depth ranges they’ve evolved to live in. Giant larvaceans (Bathochordaeus),a group of tadpole-like creatures that live inside mucus blobs of their own making, have shifted their range upward in response to expanding low-oxygen zones. Moving closer to the surface means being exposed to stress from shearing forces and more light, enabling predators that rely on vision to hunt to more easily spot their next deep sea snack.
“The depths that [deep sea creatures] were evolved to occupy now don’t have enough oxygen,” says MBARI senior scientist Bruce Robison. “These animals are now being exposed to a level of predation that was not historically the case, in an evolutionary sense.”
Deep sea research is still in its exploration and discovery phase. As of 2023, only about a quarter of the ocean floor has been mapped. A study that sequenced genetic material from seafloor sediment found that two-thirds of the species identified were unknown to science. Almost every ROV survey reveals something new, from never-before-seen creatures to previously unseen behaviors and relationships. Outreach efforts like FathomVerse and tools like FathomNet offer new methods to speed up the pace of research necessary to understand and protect the deep sea from threats like climate change and deep sea mining before it’s too late.
“Deep sea exploration is really important for our future,” says Robison. “The more we know, the better we can anticipate the consequences of changes that are happening because of us.”
