Geomorphology and bait-attending hadal fauna of the Sui-shin hole (Philippine Basin, NW Pacific; 5616–6410 m)

The Sui-shin Hole, formerly referred to as the ‘Black Hole’, is a structurally complex area of the Philippine tectonic plate (NW Pacific Ocean) that attains a maximum water depth of 6410 m and is topographically isolated from all adjacent basins. Here we present new high-resolution bathymetry and geomorphological characterisation of the feature, and baited camera and trap lander data to examine patterns in bait-attending fauna, and other incidental fauna, across the abyssal-hadal transition zone in a non-subduction setting less typical of hadal ecological studies. The occurrence, depth ranges and maximum numbers of species between 5589 and 6405 m water depth are presented, along with an analysis of drivers of community composition. The dominant taxa of fish, Decapoda, and Amphipoda were mostly abyssal and cosmopolitan that are known to inhabit the upper depths of larger trenches elsewhere. Seafloor morphology itself is therefore unlikely to be a factor in controlling presence/absence or depth ranges in these species, nor was an effect of the complex and somewhat unique geomorphology of the Sui-shin Hole observed on the bait-attending faunal community. The presence of some hadal amphipod families suggests that these populations will emerge where the minimum depth they require is available, despite otherwise occupying very large depth ranges in other features. Contrastingly, snailfish (Liparidae) are entirely absent despite the availability of a compatible minimal depth, suggesting that this group requires a far deeper hadal feature with suitable inhabitable depth ranges for a population to emerge. • Sui-shin Hole is an isolated hadal environment within the Parece Vela Basin. • The feature is 6415 m deep and hosts dome-like putative oceanic core complexes. • Diversity and depth ranges of bait-attending fauna are reported using video data and traps. • Dominant bait-attending taxa are mostly abyssal and cosmopolitan. • Minimum depth for species endemic to hadal depths are evaluated. • Seafloor geomorphology does not control Amphipoda presence/absence or maximum depth. • Snailfish are entirely absent from the Sui-shin Hole despite availability of inhabitable depths.