Zooplankton species composition and distributional characteristics in the high seas of the Northwest Pacific Ocean in 2021-2022.

Zooplankton is an important link between primary producers and lower trophic level organisms in the marine food web, and is an important biological basis for the formation of fishing grounds. Based on the Zooplankton samples collected by the fishery resources survey vessel "Songhang" of Shanghai Ocean University during the comprehensive scientific survey of fishery resources in the high seas of the Northwest Pacific Ocean from June to August in 2021 and 2022, the Zooplankton samples were analyzed in terms of their species composition, distributional characteristics, and their relationship with the environment. The results showed that a total of 174 Zooplankton species were collected in the surveyed area over the two years, belonging to 10 groups. Copepoda and planktonic larvae were the most abundant Zooplankton, with 95 and 22 species identified respectively, accounting for 54.6% and 12.6% of the total number of species, followed by ScyphoZoa, with 18 species identified, and Ostracoda, Tunicata, Chaetognatha, Euphausiacea, and Gastropoda with 11, 9, 6, 4 and 3 species respectively. Additionally, two species each of Polychaeta, Amphipoda, and Cladocera were identified. The dominant genes (species) included seven categories: Clausocalanus sp., Oncaea sp., Paracalanus sp., Calocalanus sp., Oithona plumifera, Oithona decipiens and Metridinidae larvae. The species diversity and dominant genes (species) composition were similar in both years. The mean Zooplankton abundance in 2021 was 732.89 ind./m³, lower than that in 2022 (1 418.88 ind./m³). The Shannon-Wiener index in 2021 was 1.57-3.16, the Evenness index was 0.54-0.91, and the abundance index was 0.84-3.36. All three indices were higher than those in 2022, which ranged from 0.66 to 2.92, 0.26 to 0.94, and 0.77 to 3.11, respectively. GAM analyses showed that Zooplankton abundance was significantly and negatively correlated with the sea-surface salinity and the water temperature in the 200 m layer, and the analyses suggested that the Kuroshio current and the Oyashio also had a certain effect on the temporal and spatial distributions of the abundance. The results of this study will provide basic information for the study of Zooplankton in the high seas of the Northwest Pacific Ocean. [ABSTRACT FROM AUTHOR]