Fatty acid contents and its compositions of mesozooplankton community in the Kuroshio Current and neighboring waters

• Metazoan LC-PUFA contents were comparable between the Kuroshio and its neighboring waters. • Positive correlation was found for contents of haptophyte biomarker FA to metazoan LC-PUFA. • LC-PUFA contents were higher for larval beaked sandfish than Anguilliformes leptocephali. • FA compositions were similar between beaked sandfish larvae and omnivorous crustaceans. • Omnivorous crustaceans in the Kuroshio provide nutritionally sufficient prey for fish larvae. The Kuroshio Current and its neighboring waters are nursery grounds for the early life stages of migratory fish, despite poor food availability under oligotrophic conditions. Although recent findings suggest that standing stocks of mesozooplankton are not low and provide good prey availability for fish larvae, no information is available at their prey quality. Here, we investigated the spatial and temporal variations in the fatty acid content of mesozooplankton communities from transect lines across the Kuroshio to evaluate the nutritional quality of mesozooplankton as prey for fish larvae. We identified 5 saturated fatty acids (SFAs), 4 mono-unsaturated fatty acids (MUFAs), and 13 poly-unsaturated fatty acids (PUFAs) in the mesozooplankton community. Multivariate analysis demonstrated that fatty acid contents in mesozooplankton dry mass were more variable between the seasons than at the sites, with increasing SFA in summer. Long-chain PUFA (LC-PUFA) content, represented by arachidonic, eicosapentaenoic, and docosahexaenoic acids, was comparable between the Kuroshio and its neighboring waters. These LC-PUFA contents exhibited significant positive correlations with the relative abundance of Eucalanidae copepods and molluscans determined with metabarcoding analysis. These contents were also positively correlated with the fatty acid content of the haptophyte biomarker. Beaked sandfish larvae had higher LC-PUFA contents than those of Anguilliformes leptocephali. Multivariate analysis demonstrated that the fatty acid composition of omnivorous crustaceans, such as decapods and Eucalanidae copepods, was synchronized with that of beaked sandfish larvae. These findings suggest that the LC-PUFA contents of mesozooplankton communities accumulate in omnivorous crustaceans feeding on nano- to micro-sized phytoplankton and are transferred to planktivorous fish larvae.