In a new study researchers sequenced DNA from deep-sea sediments around the world and found that there is at least three times more life on the seafloor than there is higher up in the ocean. And nearly two-thirds of that life has not been formally identified yet.
“It’s been known since the 1960s that species diversity is very high in the deep sea,” co-author Andrew Gooday, a deep-sea biologist and emeritus fellow at the National Oceanography Centre in England, told Live Science. “What was new about this study was that there was a lot of novel diversity at the higher taxonomic level.”
In other words, there are a lot of unknown evolutionary lineages — whole families of species — waiting to be discovered.
The deep-ocean floor covers more than half of Earth’s surface but is home to some of the least-studied ecosystems, according to the study. Previous research analyzed DNA collected through the water column, from above the ocean floor up to the surface, so this latest study sought to complete the picture and give a global view of biodiversity in the ocean by looking at seafloor DNA within deep-sea sediments.
Rather than trying to identify individual species from the DNA, the team looked at what they called sequence variants, or different versions of DNA sequences, to discriminate between major groups of species, like families or orders.
Most of the seafloor DNA could not be assigned to a known group on the tree of life, meaning it belonged to an undiscovered family, order, or other taxonomic group. The team focused on eukaryotic DNA from small organisms. “We’re talking about small animals, less than a millimeter [0.04 inches] in size, and probably a lot of protozoans, a lot of single-celled organisms,” Dr. Gooday said.
The researchers also learned more about the role the deep ocean plays in the so-called biological pump, the process by which ocean organisms such as phytoplankton absorb carbon from the atmosphere near the surface and sink to the deep sea, where the carbon is sequestered in the sediments.
The team could predict the strength of the pump based on the composition of DNA in the sediments, so the researchers now know some plankton communities play a greater role than others in absorbing carbon dioxide and regulating the climate.
The findings were published February 4th in the journal Science Advances. Originally published on Live Science.
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