In the middle of the Atlantic, somewhere over a section of seafloor that no human eye has ever directly seen, a certain kind of silence descends upon a ship deck at four in the morning. For years, the NOAA Ship Okeanos Explorer has lowered Deep Discoverer, its remotely operated vehicle, into that silence while a live feed beams images of creatures that resemble rejected concept art rather than biology. However, something changed on that ship beginning in 2021. Scientists started sketching water, which is far less dramatic to look at, alongside the cameras.
It turns out that the footage might not be as important as that water. The first environmental DNA, or eDNA, data from Okeanos Explorer expeditions conducted between 2021 and 2023 and sampled at depths greater than 200 meters throughout the Atlantic and Pacific was made public earlier this year by NOAA Ocean Exploration. The dataset isn’t particularly eye-catching. It doesn’t have any viral videos of jellyfish or animals acting strangely on camera. Sequences, taxonomic IDs, and spreadsheets are all involved. However, marine biologists continue to characterize it using language typically associated with much more dramatic discoveries.
What the data actually revealed is partly to blame. Genetic traces of barreleye fish, Pacific viperfish, a bioluminescent organism known as the “green bomber worm,” and, more startlingly, blue whales and orcas—species that the ROV cameras were unable to record on camera during those same dives—were buried in those water samples. There were animals. They went unnoticed. However, they had left behind scales, mucus, waste, and skin cells that floated in the water column like a biological exhaust trail.
It’s difficult not to find that somewhat unsettling, but in a good way. Deep-sea biology has been predicated for decades on the idea that you couldn’t truly claim something was there if you couldn’t see it on camera or catch it in a net. That assumption is subtly challenged by eDNA. Luke Thompson, a researcher with NOAA’s Atlantic Oceanographic and Meteorological Laboratory who contributed to the development of the analytical pipeline behind the release, described the work’s eventual application on actual deep-sea data as “deeply gratifying”—a modest term for what amounts to demonstrating that ocean exploration has been overlooking a layer of life all along.
The process has an almost forensic quality, and NOAA Fisheries scientists have drawn comparisons to crime-show DNA analysis. In order to identify a suspect from a single hair, a lab filters a sample, copies a target region of DNA millions of times, and then compares the results against a reference library. However, in this case, the “suspect” could be a whale that passed by three days ago and only left behind a chemical rumor.
The practical implications of this are not entirely clear to everyone. In her online response to the announcement, Dr. Antonella Preti made it clear that she finds it annoying when people think eDNA can take the place of stomach-content analysis, and she has every right to object. As of yet, eDNA cannot determine an animal’s size, age, or meal. It conveys presence rather than biography. This distinction is important, and it should not be overlooked in the rush.
However, what seems to be most exciting to people is the scale of what is being constructed here. The organism identifications can be searched using OBIS, the world’s largest marine biodiversity database, and the raw sequences are currently stored in the NCBI’s public repository. Anyone can access this data and pose their own queries to it, whether they are a policy assistant in Brussels or a graduate student in Manila. In oceanography, where physical samples have traditionally resided in a small number of institutional freezers, such open access is uncommon.
A gradual change in the definition of what constitutes ocean exploration appears to be taking place. These days, it’s more than just cameras, nets, and the occasional fortunate encounter. Additionally, it’s genetic residue that was filtered out of seawater without anyone’s knowledge, exposing a much more crowded ocean than the video ever hinted. To be honest, it’s a bold claim to say that this specific dataset will prove to be the most significant of the decade; these things are typically evaluated in retrospect rather than in press releases. However, there’s a good chance it will be remembered as the time when deep-sea biology ceased to require visual evidence for its existence.
