Seasonal dynamics drive zooplankton community structure and functional succession in the northwestern Pacific marginal seas

Abstract

The marginal seas of the northwestern Pacific, characterized by their unique topography and complex hydrology, are a focal area for studying marine biodiversity and ecosystem stability. Zooplankton serve as a key component of marine ecosystems; however, current understanding of the seasonal variability, influencing factors, and regional differences in their ecological functions within these marginal seas remains limited. This study used a trait–based method to examine seasonal and regional variations in zooplankton functional traits, functional groups, and trait space (a multidimensional Euclidean space where axes are ecologically relevant traits) across subtropical and temperate marginal seas of the northwestern Pacific, and applied generalized additive mixed models to identify the underlying environmental drivers. Results revealed significant seasonal shifts in zooplankton functional trait composition and functional groups across all study areas, which were strongly regulated by changes in the hydrological environment. The functional trait space of zooplankton communities contracted markedly in winter, largely due to lower temperatures and reduced chlorophyll a concentrations. Distinct patterns in seasonal variations of functional trait composition and functional groups were evident among different marginal seas. Omnivore‒detritivores were widespread in open marginal seas but relatively scarce in semienclosed shallow seas, suggesting stronger pelagic-benthic coupling in the latter. In semienclosed shallow seas, the peak relative abundance of giant-bodied, ambush‒feeding carnivores lagged behind that of current‒feeding omnivore‒herbivores, a pattern not observed in open marginal seas. The functional richness and trait space of zooplankton were higher in the subtropical Changjiang River estuary than in the temperate Yellow River estuary, whereas functional evenness was greater in the latter. These differences were attributed to variations in riverine input, adjacent marine conditions, and the influence of the Taiwan Warm Current. This study enhanced understanding of the seasonal variability and controlling mechanisms of zooplankton ecological functions in marginal seas.