Confirmation of Hard-Substrate Predictions in the abyssal Vema Fracture Zone

Torben Riehl^1,2*Linus Budke¹Angelika Brandt^1,2Mats Henseler^1,2Pedro Martinez Arbizu³Farzaneh Momtazi¹Nico Augustin⁴

• ¹Marine Zoology, Senckenberg Forschungsinstitut und Naturmuseum Frankfurt am Main, Frankfurt, Germany
• ²Department of Biological Sciences, Goethe-Universitat Frankfurt am Main, Frankfurt, Germany
• ³German Centre for Marine Biodiversity Research, Senckenberg am Meer, Wilhelmshaven, Germany
• ⁴OceanQuest, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia

HydroacousƟc mapping has recently challenged the long-held view of a uniform abyssal seafloor by predicƟng substanƟal habitat heterogeneity. The RUBBLE expediƟon M205 validated these predicƟons in the Vema Fracture Zone (VFZ) with visual surveys at six locaƟons using a towed deep-sea camera system. Exposed rock outcrops and varied hard substrates were consistently confirmed in areas of high hard-rock exposure, while moderately predicted areas contained a mix of sediments, cobbles, and pebbles; low-potenƟal sites were almost enƟrely sediment-covered. Although detailed quanƟficaƟon is beyond the scope of this report, visual correspondence supports the reliability of hydroacousƟc predicƟons for abyssal habitats. Notably, this study pioneers the applicaƟon of hydroacousƟc-based seafloor characterizaƟon at abyssal depths—extending methods formerly focused on bathyal zones to the planet's largest benthic environment and enabling direct ground-truthing of habitat models below 5,000 meters. These findings highlight abyssal habitat heterogeneity, confirm the uƟlity of hydroacousƟc tools for broad-scale benthic mapping, and establish a baseline for future research on deep-sea biodiversity and ecological dynamics.