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Scientists have discovered communities of animals, such as tube worms and snails, living in volcanic caves beneath the seabed, revealing a previously unknown but thriving ecosystem.
Researchers made the astonishing discovery during a 30-day expedition aboard the Schmidt Ocean Institute's research vessel "Falkor (too)" to explore an undersea volcano off the coast of Central America that is part of the East Pacific Rise .
A volcanically active ridge, the extensive rise occurs where two tectonic plates meet at the bottom of the Pacific Ocean. Along the ridge are hydrothermal vents, or openings in the seafloor where seawater and hot magma from beneath the Earth's crust come together to create a kind of underwater heat source.
A variety of marine life gather around the vents, regurgitating elements that help bacteria, mussels, tube worms and other animals survive at extreme depths of the ocean. The vent ecosystem has been studied in depth, but the areas beneath the vents have remained largely out of reach.
Using the SuBastian remotely operated vehicle, researchers uncovered parts of the undersea floor and uncovered a surprise: caves connected to the vents filled with giant tube worms, some of which could grow up to 0.5 meters in length, and other animals. The revelation suggests connectivity between seafloor and subseafloor ecosystems, allowing life to thrive in unexpected places above and below the ocean floor.
While the team first observed the ecosystem beneath the seafloor in the summer of 2023, the study describing the environment and its animals was published Tuesday in the journal Nature Communications.
"We want to understand how animals travel and disperse, so we looked into the subsurface for the first time," says co-author Dr. Sabine Gollner, marine biologist and senior scientist at the Royal Netherlands Institute for Sea Research, in a video. the Schmidt Ocean Institute released. "Animals can live under hydrothermal vents, and that's mind-boggling to me."
'Underworld' of the seabed
Scientists have long been intrigued by the animal life that gathers around hydrothermal vents and have been studying these unique ecosystems for the past 50 years.
The shifting of Earth's tectonic plates leads to new hydrothermal vents over time, and basic seafloor animals such as tube worms are known to colonize these new vents in the space of a few years.
Microbial life exists beneath the seabed based on samples of fluid released by hydrothermal vents, research shows. And tubeworms were observed living several centimeters deep in the cracks of the seabed near vents, but the research team was unsure how tiny tubeworm larvae, less than 1 millimeter long, could swim against the current. current ones to settle and grow in these spaces, Gollner said. Tube worms are immobile creatures that settle in one place and grow without moving, like barnacles.
"We therefore hypothesized that tubeworm larvae may move into subsurface cracks with the warm vent fluid to colonize the surface vents from below," Gollner said in an email.
The research expedition, led by lead study author Dr. Monika Bright, professor and head of the department of limnology and biooceanography at the University of Vienna, designed an experiment in which mesh boxes were placed on the seabed at an altitude of 2,515 meters. beneath the ocean's surface to collect samples from cracks in the Earth's crust.
But it was harder than expected, Gollner said. Direct evidence of animal life beneath the seabed would require heavier lifting - literally.
"We had to be creative and adopt a new method," Gollner said. "Browsing around the rocks gave us a view of the underworld of hydrothermal vents."
The team used the SuBastian robotic explorer to drill small holes in rocks on the seabed and lift them. The ROV's arm rotated over a small section of the volcanic crust, revealing cavities beneath the hydrothermal vents filled with water at a balmy 75 degrees Fahrenheit (24 degrees Celsius) - as well as tube worms in both larval and adult forms, mobile animals such as snails and chemosynthetic bacteria.
Sunlight cannot penetrate the depths of the ocean floor to help organisms convert elements into oxygen and sugar through photosynthesis. Instead of sunlight, chemosynthetic bacteria use chemical reactions to produce sugars that other animals around the vents use to live.
"Our understanding of animal life in deep-sea hydrothermal vents has been greatly expanded by this discovery," Bright said in a statement. "Two dynamic ventilation habitats exist. Ventilation animals above and below the surface thrive together, depending on ventilation fluid from below and oxygen in the seawater from above."
Discovering life in this previously unknown subhabitat suggests there may be many more organisms than scientists have documented in the depths of the ocean or along its bottom, says Alex Rogers, marine biologist and scientific director of Ocean Census. Rogers was not involved in the new study.
It's also likely that these underground ecosystems persist once the vents become inactive over time, allowing them to provide new habitats for other species, he said.
"The paper contributes to our understanding of ventilation ecosystems, how populations of ventilation organisms are maintained and how much life exists in these systems," Rogers said.
Protecting an underground world
Next, the team wants to determine whether life exists beneath all the deep-sea hydrothermal vents and how far the caves extend horizontally and vertically, Gollner said.
"The discovery of animal life beneath the surface of the Earth's crust raises questions about the extent of these ecosystems, which are larger than what is seen on the seafloor," the authors wrote in the scientific report. "Research into the subseafloor biosphere for animal life has only just begun."
But extreme caution is needed when studying these fragile ecosystems.
For the study, the researchers lifted just six small squares of the seabed measuring about 20 by 20 inches (50 by 50 centimeters) to cause as little disturbance as possible.
The team is concerned that lifting larger pieces or any form of large drilling, such as deep-sea mining, could change the route of hydrothermal vents and push them to other locations, killing the animal life that gathers around the vents . Gollner said.
"With this insight, we also know that we must not only protect what we see on the surface, but also protect what lives beneath it, because it is an important part of this ecosystem," Bright said.
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