It was once believed that only microbes and viruses had the kind of resilience that would enable them to inhabit the subsea extremities of hydrothermal vents – openings in the seafloor that form where seawater meets the magma beneath the Earth’s crust. Yet, it would appear life – as the old adage goes – finds a way.

A team of deep sea researchers have now discovered that macrofauna – or animal life like the giant tubeworm Riftia pachyptila – can not only survive but ‘thrive’ at such subsea levels, transforming scientific understanding of ecology and the evolution of animal life as we know it.

In the summer of 2023, an international team of researchers led by #VentUnderworld’s Chief Scientist, Dr Monika Bright set out to explore a long-held hypothesis that ecosystems existed beneath the seafloor. Aboard the remotely operated vehicle SuBastian, launched from the research vessel Falkor (too), the team set out to discover, observe, and document the diversity of life living beneath deep-sea hydrothermal vents.

Their investigation was carried out at about 8,250 feet (2,515 metres) beneath the sea on a stretch of ocean floor nicknamed the Fava Flow Suburbs in the eastern Pacific Ocean.

Among their many suspicions about what they’d find among ecosystems at this depth, the team held the belief that – as water was sucked into and pumped out of cracks in the surrounding seafloor and vents – natural mechanism were being created for building new hydrothermal vents. It was thought that within these subseafloor systems of vents, the right conditions were being maintained for macrobiotic life.

Some 15 months on from that expedition to the depths, and Bright’s research has now been published in a new scientific paper with Nature Communications, revealing findings now considered by researchers and scientists as “transformative” for our understanding of life “at and beneath hydrothermal vents in the deep sea.”

Among the discoveries made, the team found that macrofauna like tubeworms had the ability to move through cavities in the subseafloor, identifying that the tubeworms R. Pachyptila and O. Alvinae, as well as the mussels B. Thermophilus alongside polychaete worms and limpets, are among the species living in these undersea habitats. 

“The discovery of animal life beneath the surface of the Earth’s crust raises questions concerning the extent of these ecosystems, which is larger than what can be seen on the seafloor surface,” the team writes in its research paper. 

Using the Schmidt Ocean Institute’s underwater robot, SuBastian, the science team overturned chunks of volcanic crust, discovering cave systems “teeming with worms, snails, and chemosynthetic bacteria” living in 75 degrees Fahrenheit water. It’s a point of revelation for scientists, who have spent the past 46 years studying hydrothermal vents and microbial life in the subsurface, but had never – until now – looked for the life that lays beneath them.

Additionally, the team found evidence of vent animals, like tubeworms, travelling underneath the seafloor through vent fluid to colonise new habitats. Tubeworms are one of the foundational hydrothermal vent animals but very few of their young have been found in the water above hydrothermal vents. This led Dr Bright’s team to suspect they travel beneath the Earth’s surface to create new hydrothermal communities.

“Our understanding of animal life at deep-sea hydrothermal vents has greatly expanded with this discovery,” said Bright. “Two dynamic vent habitats exist. Vent animals above and below the surface thrive together in unison, depending on vent fluid from below and oxygen in seawater form above.”

At the time of the discovery in summer 2023, little was known about how animal larvae found new vent fields. After months of diving into the findings, however, the team has now found evidence in strong support of initial hypotheses that larval dispersal occurs “via the crustal subseafloor”, adding “a new dimension to the known larval dispersal of oceanic, ridge-controlled, and bottom-currents.”

“On land, we have long known of animals living in cavities underground, and in the ocean of animals living in sand and mud, but for the first time, scientists have looked for animals beneath hydrothermal vents,” said Schmidt Ocean Institute’s executive director, Dr Jyotika Virmani. “This truly remarkable discovery of a new ecosystem provides fresh evidence that life exists in incredible places. Schmidt Ocean Institute is proud to have provided a platform for Dr. Bright and her team to gather new insights into these systems that may be vulnerable to deep-sea mining.”

Wendy Schmidt, president and co-founder of the non-profit, family-founded Schmidt Ocean Institute, added: “The discoveries made on each Schmidt Ocean Institute expedition reinforce the urgency of fully exploring our ocean so we know what exists in the deep sea.

“The discovery of new creatures, landscapes, and now, an entirely new ecosystem underscores just how much we have yet to discover about our Ocean and how important it is to protect what we don’t yet know or understand.”

For more from our Ocean Newsroom, click here.