Scientists discover creatures living beneath the bottom of the deep sea
Tubeworm larvae, sea snails, and marine worms were uncovered living in tiny caves underneath the ocean floor, revealing life is interconnected below and above it.
Animal life is flourishing underneath the seafloor according to a new study of deep-sea hydrothermal vents, suggesting this mysterious landscape has complex ecosystems.
Previous research had found microbes living underground near hydrothermal vents, but this is the first reported discovery of larger animals such as worms and snails in the underground habitat.
Hydrothermal vents are openings in the seafloor where the Earth’s tectonic plates meet, and seawater mixes with magma from below the Earth’s crust. Much of the ocean floor is thought to be nearly uninhabitable, but around hydrothermal vents there’s an explosion of life.
Communities of shrimp, crabs, tubeworms, mussels, and hundreds of unique animal species have been previously found around, but not underneath, these vents. They’re known as “extremophiles,” or life that can survive under extremely high temperature and pressure. These organisms survive not on the sun’s energy, which fuels the food web elsewhere on Earth, but on nutrients produced when seawater mixes with magma.
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Most of the seafloor remains a mystery to scientists, with only 26 percent of the global seafloor mapped, and this new research suggests it might be more populated than scientists thought.
“Every [new] study just confirms how little we understand about the seafloor,” says Rachel Lauer, geologist at University of Calgary, who was not involved in the new study.
An unexpected discovery at the bottom of the ocean
Seeking to understand how tubeworms settle in hydrothermal vents, marine biologist Sabine Gollner and her research team at the Royal Netherlands Institute for Sea Research sailed to the East Pacific Rise, a volcanically active ridge on the floor of the Pacific Ocean, in July of 2023. There, they sent a remotely operated robot on a series of dives to a hydrothermal vent site located 8,251 feet below the surface.
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Their goal was to collect rock samples to search for tubeworm larvae, but the rock was difficult to break into smaller, transportable pieces. The robot, equipped with arms and a camera, instead lifted sections of seafloor revealing tubeworm larvae underneath—and much more.
Flipping over rocky sections of the seafloor, it uncovered cavities about four inches deep filled with warm fluid —water mixed with magma—and with species previously only found on top of the seafloor: tubeworms, polychaete worms, and sea snails.
Finding tubeworm larvae and adult tubeworms living in the tiny caves could be a breakthrough in understanding this species’ life cycle. The researchers think tubeworm larvae might disperse throughout the cavities, with some settling and growing in cracks on the seafloor, and others staying in the cavities and growing to adulthood there—which would mean the seafloor and small caves underneath are an interconnected ecosystem, where cold and warm water flows mix and facilitate tubeworm growth.
“The [hydrothermal] vent ecosystem in this area is not restricted to what we see above, but it also includes life in the subsurface,” says Gollner.
To preserve these unique extremophiles, scientists say more of the seafloor needs to be legally protected. But that may be challenging because many of these ecosystems also contain rare minerals that can power new technology.
Protecting deep sea life
One of the biggest threats to deep-sea ecosystems is proposed deep-sea mining, the process of extracting mineral deposits, like cobalt and nickel, from the deep seabed, which scientists and conservation organizations oppose.
“We don’t know how extensive those connected little caves are, we don’t have a sense of how much biodiversity or biomass is actually being represented within the subsurface,” says Lauer. “There’s a whole other layer here—literally!”
Since seafloor ecosystems are likely interconnected, says Lauer, large stretches of the seafloor need to be protected.
“We need to at least understand what’s there before we potentially destroy these habitats,” says Heather Olins, biologist at Boston College, who was not involved in the new study.
Gollner says it’s unclear just how deep this subsurface habitat goes and how far it reaches horizontally, which is crucial to protecting the entire hydrothermal vent system beyond the visible vent itself.
Studying hydrothermal vents, and preserving vents for future study, can also help scientists understand conditions for life not on Earth.
“If there is life beyond Earth in our solar system, it’s not going to be solar powered,” says Olins, since nowhere else in our solar system has surface conditions conducive to life as we know it.
But there are places that could host extremophiles, like Jupiter’s moon Europa, with an ocean below an icy crust.
“We know that there’s volcanic activity, and an ocean," says Olins. "There’s no reason why there couldn’t be some sort of hydrothermal-vent-like life elsewhere in our solar system."
