Stochastic processes drive patterns of fish assemblage diversity in the northwestern Pacific: Insights from...

The northwestern Pacific (NWP), characterized with multiple ocean currents and different climate zones, is a critical region for marine biodiversity research. In this study, we employed environmental DNA (eDNA) metabarcoding to evaluate fish diversity from taxonomic, functional, and phylogenetic perspectives, aiming to uncover regional diversity and ecological drivers across five biogeographic zones in the NWP. Our findings reveal that the fish alpha diversity was notably greater in the Kuroshio Extension (KE) and Transition Zone (TZ) compared to the North Equatorial Current (NEC). Alpha diversity was significantly correlated with environmental factors, including temperature, chlorophyll-a, and pH in NEC and North Pacific Subtropical Gyre (NPSG); and with longitude, bathymetry, temperature, dissolved oxygen, and pH in KE and TZ, suggesting region-specific associations between environmental conditions and alpha diversity patterns. In terms of beta diversity, turnover was found to be the major contributor to the overall taxonomic, functional, and phylogenetic diversity, rather than nestedness. The variation in beta diversity due to species turnover was significantly associated with environmental factors such as pH, chlorophyll-a, dissolved oxygen, net primary productivity, and latitude across the NEC, NPSG, KE, TZ, and Kuroshio Current (KC). Furthermore, stochastic processes, particularly ecological drift and dispersal limitation, played a dominant role in shaping fish assemblages in most NWP regions. These findings demonstrate the effectiveness of eDNA in capturing multi-dimensional biodiversity and offer novel insights into community assembly mechanisms in NWP. The study advances our theoretical understanding of marine biogeography and provides a scientific basis for biodiversity monitoring and fisheries management in the face of ongoing environmental change.