June 2025 | Oceanography
19
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