Geographical patterns of mesozooplankton functional diversity in the northwestern Pacific

To better understand how communities response to environmental change and how biodiversity affects ecosystem function, it is essential to quantify the functional diversity of communities. However, the current understanding of zooplankton functional traits and functional diversity in the northwestern Pacific (NWP) is inadequate. In this study, we analyzed the latitudinal changes in functional traits, diversities, and functional space of zooplankton in five biogeographic regions of the tropical and subtropical NWP. Zooplankton species richness varied unimodally over latitude, with the North Pacific Subtropical Gyre (NPSG) hosting the greatest number of species (367 taxa). The NWP was dominated by zooplankton of small and medium size (<2 mm; 72 %), current-feeding (47 %), omnivore-herbivore (71 %), and broadcast spawner (53 %). The functional trait composition of zooplankton varied significantly; for instance, omnivore-detritivores were prevalent in the Kuroshio Extension zone but few in the oligotrophic NPSG and North Equatorial Current regions. Protozoans with binary fission (primarily foraminifers) declined from the equator to high latitudes. The latitudinal variations of functional evenness, functional dispersion, and hypervolume of trait space of the zooplankton community were unimodal, with the maximum values occurring in the NPSG. This would suggest that the zooplankton community in the NPSG was more efficient in utilizing resources than in other regions, and the competition across functional groups was mild. Stochastic processes were crucial in zooplankton community assembly in tropical and subtropical NWP. This study enhanced our understanding of zooplankton community assembly and offered new insights into the functional traits of zooplankton communities in the NWP.