Environmental predictors of benthic meiofaunal densities in the abyssal and hadal zones of the North Pacific: a combined Gradient Forest and GLMM approach

The northern North Pacific forms a heterogeneous deep-sea environment with dynamic currents, distinct water masses, and complex bathymetry, including the Kuril–Kamchatka (KKT) and Aleutian Trenches (AT). As a climate-sensitive region, warming and sea-ice loss alter surface productivity and organic matter flux, potentially affecting deep-sea benthic communities. We quantified metazoan meiofaunal densities across abyssal and hadal zones of the KKT and AT, integrating samples from the 2022 AleutBio (SO293) expedition with legacy datasets. Gradient-Forest modeling captured broad productivity patterns across higher taxonomic levels, while generalized linear mixed effects models (GLMMs) quantified taxon-specific responses to environmental factors. Meiofaunal densities varied substantially, peaking on the abyssal KKT plain and reaching minima in the hadal AT. Gradient-Forest analysis identified surface chlorophyll a, bottom-water temperature, and monthly primary production as primary drivers of regional density patterns. However, taxon-specific GLMMs revealed that once spatial effects and overdispersion were controlled, bottom-water chemistry and hydrography exerted the most consistent control on local abundances. These results demonstrate a two-tier ecological control: surface-derived food availability governs meiofaunal densities at regional scales, whereas bottom-water chemistry, hydrographic regimes, and grain size fine-tune local distributions. This study provides critical baseline data for understudied deep-sea regions and informs predictions of meiofaunal responses to climate-driven changes.