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Scientists Collect Floating Bits of DNA to Study Deep Sea Creatures

Analyzing seawater samples reveals what critters lurk there—without having to see them

Of the deep-water samples collected by this team, they identified 11 fish families, 11 genera and eight species. This fish, from the genus Leptochilichthys, was discovered at nearly 3,000 feet deep. (NOAA Office of Ocean Exploration and Research, Gulf of Mexico 2017)
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The deep sea is one of the greatest enigmas of all. Despite the harsh, pitch-black, frigid conditions of the abyss, an abundance of sea critters still manage to thrive there, leaving scientists curious about what exactly lurks below the surface.

A new paper published last week in the journal PLOS One describes how scientists can track deep sea creatures using the DNA they leave behind in the seawater, reports Kat Eschner for Popular Science.

Every organism has a unique genome, and many animals ditch bits of DNA when they shed skin cells or poop. Scientists can study this discarded genetic material using an approach called environmental DNA (eDNA) metabarcoding. (You may recognize the word "barcode" in this scientific term, and in fact, the process is sort of like a cashier scanning a barcode to find out how much something costs, reports Fabienne Lang for Interesting Engineering.)

To test how effective eDNA metabarcoding is in identifying species, lead author Beverly McClenaghan, an ecologist for the Centre for Biodiversity Genomics Applications at the University of Guelph in Canada, and her team collected seawater samples from various depths of the Labrador Sea, reaching up to 8,200 feet, according to a press release. Of the deep-water samples, they identified 11 fish families, 11 genera and eight species, which is more than they would've identified using traditional methods.

Scientists often use tools like baited cameras and acoustic monitoring instruments to take a glimpse of the deep sea. But since they only detect whatever critters are floating around at the moment, they only offer brief "snapshots" of data, Elizabeth Allan, a scientist at Woods Hole Oceanic Institute tells Popular Science. DNA, however, can persist in the environment for more than a day, so eDNA samples can reveal which critters have been hanging around the area, providing a more comprehensive look at the ecosystem.

"It's just a real game-changer for ocean science," Mark Stoekle, a researcher at the Rockefeller University’s Program for the Human Environment, tells Popular Science.

Plus, collecting water samples is logistically easier and less costly than dropping high-tech equipment into the depths of the ocean, making the deep sea more accessible.

Environmental DNA is already being used to study other zones of the ocean, but this study "is a perfect entry paper for filling in some of the gaps about what we really don’t know" about how eDNA metabarcoding can be used to study the deep sea, Allan tells Popular Science. And when eDNA can be coupled with other cutting-edge technology, like acoustic monitoring or underwater cameras, scientists will be able to maximize its potential and uncover the mysteries hidden deep in the ocean's abyss.

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