June 2025

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June 2025 | Oceanography

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FIGURE 5. A sample of habitat heterogeneity and biological diversity of vent-associated and vent periphery fauna at Endeavour. (a,b) Black smoker

chimneys colonized by dense assemblages of R. piscesae tubeworms. (c,d) Typical assemblages that occur near diffusive hydrothermal flow, includ­

ing alvinelid polychaetes (Paralvinella sulfincola, Paralvinella palmiiformis), polynoid scale worms (Branchinotogluma tunnicliffae), limpets (Lepetodrilus

fucensis), and snails (Buccinum thermophilum). (e) Field of view of the Mothra vent field observatory camera showing the seafloor partially covered

by white bacterial mats, Ridgeia piscesae tubeworms, Buccinum thermophilum gastropods, and the deep-sea spider crab, Macroregonia macrochira.

(f) Vent periphery sulfide and (g,h) basalt structured seafloor that provide habitat for corals, sponges, and mobile macro- and megafauna. Image credits:

ONC and CSSF–ROPOS

over vent species community composition and biorhythms. At

Main Endeavour Field, a video camera platform (TEMPO-Mini;

Auffret et al., 2009), installed in collaboration with the French

national institute for ocean science and technology (IFREMER),

provided nearly 10 years of continuous data. The length of the

video time series enabled analyses that, for the first time, estab­

lished astronomical (tidal) and atmospheric (storm passages)

forcing as a control on vent macrofauna behavior (Cuvelier et al.,

2014, 2017; Lelièvre et al., 2017). The data revealed that mobile

macrofauna, such as sea spiders (pycnogonids) and polychaete

scale worms (polynoids), responded to the passage of win­

ter storms 2.2 km above by regulating their biorhythms to the

storm-​triggered cyclical oscillations in the diffusive vent flow

dynamics (Lelièvre et al., 2017). Video observations of picno­

gonids and scale worms living in association with R. piscesae

tubeworm bushes that are supported by low-temperature dif­

fuse venting also indicated that the animals respond to the cur­

rents generated by these storms. At the latitude of Endeavour,

storm-induced currents have a four-day cycle due to the pas­

sage of the storms and a 16-hour cycle resulting from the iner­

tial oscillations generated by the storm winds that can propa­

gate to the seafloor as inertial internal waves. As the currents

cyclically increase, they dilute the warm, low-oxygen vent fluids,

and the animals can be observed moving deeper into the bush,

disappearing from camera view. A study performed in waters

1,688 m deep at the EMSO-Azores Mid-Atlantic Ridge obser­

vatory (EMSO = European Multidisciplinary Seafloor and water

column Observatory) corroborates these findings, as biologi­

cal rhythms and circadian clock gene expression of the hydro­

thermal vent mussel Bathymodiolus azoricus were found to be

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