The Influence of the Antarctic Circumpolar Deep Water on Deep‐Sea Eukaryotic Biodiversity and Distribution in the Western Pacific Ocean

ABSTRACT

The Antarctic region, a centre of biodiversity origin, influences deep‐sea ecosystems by supplying species to distant regions. Understanding the influence of Antarctic Upper Circumpolar Deep Water (UCDW) on deep‐sea eukaryotic diversity is therefore essential for outlining global biodiversity patterns. Our results showed the UCDW community exhibited ~1.5‐fold higher taxonomic and phylogenetic diversity than the Caroline Basin control community and contained a substantial proportion of unique taxa across multiple eukaryotic lineages. Source tracking using the available Southern Ocean surface‐water reference detected a 4.42% Antarctic‐associated contribution to the UCDW community. Indicators and generalists of the UCDW community shared > 97% sequence identity with Southern Ocean samples. The community analyses suggested that the Yap‐Mariana Junction choke point did not constitute a strong barrier to connectivity between adjacent basins, consistent with UCDW‐mediated dispersal into the Philippine Basin. The UCDW microbial dispersal into the Philippine Basin occurs through two potential routes: directly through the YMJ at 2000–3000 m and via upwelling across seamounts at 500–750 m. Governed mainly by neutral, dispersal‐driven processes, the UCDW community showed strong genetic exchange and connectivity. These findings suggest a role for deep‐water circulation in shaping the diversity and distribution of eukaryotes detected in western Pacific deep‐water samples.