Discovery and Fine‐Scale Mapping of Hadal Xenophyophore Habitat in the Nova Canton Trough, Central Pacific Ocean

Abstract

The occurrence and heterogeneity of biogenic structures at hadal depths remain poorly mapped and quantified at ecologically relevant scales. Xenophyophores can be conspicuous biogenic components of deep‐sea sedimentary environments, but records of their abundance, spatial configuration, structural complexity and ecological role are scarce at hadal depths. Here, we describe the discovery of a dense epifaunal xenophyophore population at ~8000 m depth in the Nova Canton Trough. We integrate high‐resolution photogrammetry with semi‐automated delineation approaches to map and quantify their abundance and distribution and, relate this to the occurrence of benthic metazoan taxa. Spatial point pattern analysis and terrain metrics were used to characterise horizontal aggregation, vertical relief and surface complexity across 20 transects, with a total length of ~200 m. Xenophyophores were highly abundant with a mean density of 35 ind/m 2 and an estimated footprint of 4.1% of the seafloor. Principal Component Analysis revealed partially decoupled gradients in their horizontal aggregation and vertical structure, indicating that habitat heterogeneity reflects both variation in spatial configuration and structural complexity. Distance‐based linear models indicated that spatial patterning was significantly associated with metazoan community composition. Negative binomial generalised linear models showed taxon‐specific responses, with several taxa positively associated with elevated xenophyophore density, and xenophyophore height driving amphipod abundance. Results demonstrate that xenophyophores are prevalent on the sedimentary hadal basin floor of the Nova Canton Trough and are consistent with a role as biogenic habitat formers, generating structurally complex habitats that host associated assemblages. Methodologically, this study illustrates the value of photogrammetry to enable the use of semi‐automated mapping tools to characterise deep‐sea biogenic habitats.