Spatiotemporal variability of mesozooplankton in the eastern South Yellow Sea in relation to anchovy CPUE and the Pacific Decadal Oscillation.

Zooplankton are a key intermediate trophic component in marine food webs, linking primary production to higher trophic levels and determining food availability for fish larvae and juveniles. This study examined spatiotemporal variability in mesozooplankton abundance, dry biomass, and copepod proportion in the eastern South Yellow Sea during 2010-2024, and evaluated their associations with nominal anchovy catch per unit effort (CPUE) and the Pacific Decadal Oscillation (PDO). Mesozooplankton indices showed pronounced seasonal and interannual variability, with divergent patterns among abundance, dry biomass, and copepod proportion. Sample-level and monthly anomaly-based analyses indicated that these patterns were strongly structured by seasonal and spatial heterogeneity. Associations with PDO and nominal anchovy CPUE were generally weak and inconsistent, although copepod proportion showed a significant nonlinear relationship with lag-1 nominal anchovy CPUE anomaly. Because nominal CPUE is a fisheries-dependent and non-standardized index, this relationship should be interpreted cautiously. These results suggest that mesozooplankton variability in the eastern South Yellow Sea is not well explained by simple climate- or CPUE-based relationships alone, highlighting the need for standardized anchovy stock indices and seasonal information on zooplankton community structure to better resolve food-web linkages in this region.