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Researchers have discovered animal life beneath the seafloor at hydrothermal vents in the eastern Pacific, near the Galápagos Islands. Scientists found enormous tubeworms and other vent animals thriving, challenging the previous belief that only microbes and viruses can inhibit inhospitable subseafloor crust.
The East Pacific Rise is a volcanically active region boasting numerous hydrothermal vent fields. Recent eruptions have uncovered megafauna colonization patterns at new vent sites, mainly tubeworms and bathymodiolin mussels. Hydrothermal vents in volcanically active regions erupt as boiling mineral-rich fluid, attracting animal life.
While the scientists knew that life existed in and around the hydrothermal vents, they are unclear about how these larvae arrive to settle at a vent.
As larvae cannot swim against the currents, their efficient dispersal by the ocean current seems more likely. Therefore, researchers hypothesized that larvae get entrained with seawater into the ocean crust. Since the shallow Earth’s crust is a porous volcanic rock, these creatures finally settle at vents.
Study reproduces origins of life on ocean floor
Cross-section of lobate lava that is built up by layers of lava shelves with cavities in between. The ceiling of cavities can have lava drips (D). Cracks occur in different localities in the lava shelves. In the recharge zone, cold seawater enters the shallow crustal subseafloor via cracks in the lava shelves and mixes in the subseafloor with upwelling warm hydrothermal vent fluid to be later discharged through cracks in the lava shelves. Seafloor surface vent tubeworms Riftia pachyptila (R) and Oasisia alvinae (O) release fertilized eggs to develop in the water column into trochophore larvae which get entrained into the crustal subseafloor cavity system in the recharge zone. They settle in the crustal subseafloor, in the cracks, or at the seafloor surface in the discharge zone to grow into adults. Mobile animals, e.g. Paralvinella (P) and Lepetodrilus (L) either also transit through the circulation system as larvae or migrate in and out of the cracks of the lobate lava. Some animals, e.g. Bathymodiolus thermophilus (B) mussels colonize the seafloor surface vents but have not been visually detected in the crustal subseafloor. Scale: lava shelf thickness is ~10 cm, cavities are ~5 to ~15 cm in height, with animals depicted to relative scale (larvae not to scale). The three-dimensional extent of cavities likely reaches several lava shelfs down to lower floors of subsurface.
“Rapid colonization by these animals suggests efficient larval dispersal, with larvae assumed to be transported through the bottom, ridge, and ocean currents before they settle at vents through downwards swimming or sinking,” says the study.
To test their hypothesis, the group utilized the Remotely Operated Vehicle (ROV) SuBastian to a vent site 8,250 feet (2,515 meters) beneath the ocean surface. ROV drilled smaller holes at the sampling site (nicknamed Fava Flow Suburbs) and uplifted the lava slab.
Tubeworms in a shallow subsurface cavity beneath deep-sea hydrothermal vents. (Image via: Schmidt Ocean Institute)
ROV discovered caves of approximately 10 cm height below a 10-15 cm thick lava shelf, revealing hydrothermal fluid-filled pockets. They studied six caves inhabited by macroscopically visible animals, and the results showcased the shallow subseafloor as a suitable habitat for vent animals.
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“Here we report, to our knowledge for the first time, the discovery of animals excavated from fluid-filled, shallow cavities in the subseafloor of deep-sea hydrothermal vents,” says the study.
These small vents appeared to be populated with tubeworms. One of the caves even demonstrated males’ testes filled with sperm and female species with egg-filled gonads. This hinted at the reproduction occurring in the subseafloor cavities.
“We note that even when mussels were present at the seafloor surface above four of these cavities, they were not visible in the subseafloor cavities. The most abundant tubeworm species, growing from the roof of all five caves and often wrapped around lava drips, was O. alvinae with record sizes of 20 cm tube length, exceeding the ones described from the surface, indicating that these large specimens were adult,” describes the study.
The study pointed out that the subseafloor could be a transient or a permanent habitat, depending on the location. A few larvae could disperse in cavities to potentially colonize other lava cracks or settle at the existing site as permanent fauna.
Ancient seafloor vents supplied life-giving minerals into Earth’s early oceans
Journal Reference
- Bright, M., Gollner, S., De Oliveira, A. L., Fulford, A., Hughes, I. V., Hourdez, S., Karthäuser, C., Kolar, I., Krause, N., Le Layec, V., Makovec, T., Messora, A., Mitchell, J., Pröts, P., Sieler, F., Sievert, S. M., Steger, J., Tinta, T., Winter, T. R., . . . Paris, A. (2024). Animal life in the shallow subseafloor crust at deep-sea hydrothermal vents. Nature Communications, 15(1), 1-9. DOI: 10.1038/s41467-024-52631-9
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