The thought that millions of years of animal life have been developing on the ocean floor—whole migrations, entire generations, evolutionary journeys of astounding distance—and we have virtually no knowledge of it is almost unsettling. Not because researchers weren’t searching. However, searching the deep ocean is actually one of the most difficult tasks that people have ever attempted.
Few people outside of the marine science community seem to have noticed that this is starting to change.
For the past two years, researchers working in isolated areas of the U.S. Pacific have been gathering seawater and extracting species from it—a task that would have seemed nearly impossible ten years ago. Only the DNA that the animals leave behind, not the animals themselves. A coral sheds a few cells as it moves through a current. In complete darkness, a brittle star crawls across a seamount ridge. That genetic trail is still floating hours later. After being filtered, preserved, and transported to a research vessel, those traces are now providing scientists with information that years of conventional deep-sea expeditions were unable to provide.
Environmental DNA, or eDNA, is the technology behind this, and it functions similarly to forensics at a crime scene. The body is not necessary. All you need is what it left behind. Researchers from the Ocean Exploration Trust and related organizations have been using their remotely operated vehicle Hercules to gather water samples over coral gardens in remote Pacific coral communities at depths that most people would never consider visiting. The video from one such dive shows a robotic arm drawing in seawater above a living, unnamed world while hovering over a coral garden in what was then known as the Pacific Remote Islands Marine National Monument. This is truly bizarre.
Some of these species may have never been recorded at all. That’s just the truth about how little the deep ocean has been cataloged; it’s not a dramatic statement for effect. In these settings, taxonomy lags behind what is physically present by years or even decades.
Meanwhile, a different but closely related study by the Museums Victoria Research Institute that was published in Nature has completely changed the way scientists view the deep sea. Under the direction of Dr. Tim O’Hara, the study used DNA from approximately 2,700 brittle star specimens that were gathered over 332 research expeditions and kept in 48 natural history museums worldwide. What it discovered casts doubt on a long-held belief that the deep ocean is made up of disparate, isolated ecosystems. It isn’t. It resembles a slow-motion highway more.
Animals on the other side of the world, in the North Atlantic, have close evolutionary ties to species found off the coast of southern Australia. For more than 480 million years, brittle stars have been crawling across the ocean floor. Their patience, rather than their speed, has allowed them to colonize great distances. Their larvae cover ground that would astound any reasonable expectation as they drift for long periods of time on cold, deep currents.
The specimens that made this discovery possible were gathered decades ago by researchers who had no idea what they would be used for in the future, which is somewhat ironic. One of the world’s most important genomic datasets has been secretly stored in museums, which are sometimes written off as dusty remnants of a bygone scientific era. All that was needed was for Dr. O’Hara’s team to open the drawers.
All of this suggests that ocean management needs to be rethought; perhaps the word “urgence” is appropriate. Proposals and licenses for deep-sea mining operations are already underway. Water temperatures at previously thought-to-be stable depths are changing due to climate change. Damage to one area of the Pacific doesn’t only impact that area if species are more interconnected throughout the seafloor than previously thought. Although the precise fragility of that connectivity in practice is still unknown, the fact that researchers are asking the question now, before the damage is done, is at least something.
In the future, the eDNA data gathered from the Pacific expeditions will provide baseline data for tracking coral communities in these isolated regions and guiding the administration of marine national monuments. That’s careful, useful science. Unlike a new megafauna discovery, it won’t make headlines. However, there’s a sense that the long arc of humanity’s relationship with the ocean is actually altered by this kind of quiet, methodical groundwork—not the dramatic moments, but the gradual accumulation of knowledge about what’s down there, waiting to be discovered.
