Automated and quantitative characterization of benthic habitat and associated biological communities of an unknown southeast Pacific seamount.

Seamounts are prominent seafloor features that strongly influence geological processes, ocean circulation, and benthic biodiversity. Despite their importance, most seamounts remain unmapped and poorly characterized, particularly in the southeast Pacific Ocean, a region recognized for high marine endemism and ecological isolation. In this study, we present a quantitative habitat characterization of a previously undocumented seamount, informally named Solito Seamount, located between the Nazca-Desventuradas Marine Park and the Juan Fernández Archipelago, within Chile's Exclusive Economic Zone. The seamount is a conical volcanic edifice approximately 37 km wide, rising >3,500 m above the surrounding abyssal plain. High-resolution multibeam bathymetry and backscatter intensity data were integrated with in situ observations from two remotely operated vehicle (ROV) dives (S0643 and S0645) to quantitatively investigate how seamount morphology and substrate distribution influence benthic community patterns. An automated abiotic habitat mapping framework incorporating objective terrain analysis and multivariate statistical techniques, including principal component analysis and clustering, was applied to delineate five distinct mesohabitat types: flat, basal slope, valley, ridge slope, and ridge crest. ROV video transects traversing these habitats revealed five associated substrate types, forming macrohabitats: bedrock, bedrock with sediment veneer, sediment-rock transition, sediment, and biogenic rubble. Outputs were used to examine how environmental heterogeneity structures megafaunal assemblages of Solito Seamount. Multivariate analysis revealed a combined effect of habitat and substrate types on benthic megafaunal assemblages across the depth gradient. These compositional dissimilarities were primarily driven by habitat-forming taxa. In the deeper dive (S0643), dissimilarities were distributed across multiple habitats, with ridge crest characterised by reef-building scleractinian community, whereas the ridge slope hosted mixed antipatharian, gorgonian and actiniarian assemblages. In contrast, the shallower dive (S0645) exhibited simpler patterns with fewer taxa driving variation, with substrate effects more evident in biogenic rubble field dominated by sponges (Stelletta sp.). Pronounced biological differences between dives may also represent depth-dependent structuring resulting from differences in oxygen regimes associated with water masses, underscoring the role of oceanographic forcing. This study provides the first quantitative habitat map of this previously undocumented seamount, delivering essential baseline information for this largely unexplored region of the southeast Pacific. The integrated multi-scale geophysical and biological approach presented here offers a robust framework for advancing seamount ecosystem understanding and supporting future biodiversity assessments and conservation planning.