Evaluation of seasonal variations in energy sources and trophic positions of Calanus sinicus and Euphausia pacifica in the central-eastern Yellow Sea using bulk and compound-specific stable isotope analyses

초록

A comprehensive understanding of energy pathways sustaining zooplankton that support abundant fishery resources of the Yellow Sea is essential for elucidating ecosystem functioning and informing management strategies. However, knowledge of the trophic dynamics of major zooplankton species in the Yellow Sea remains limited. To investigate the energy sources and trophic positions (TPs) of the copepod Calanus sinicus and the krill Euphausia pacifica , two dominant species in the central-eastern Yellow Sea, we analyzed stable carbon and nitrogen isotope ratios in bulk tissue as well as compound-specific nitrogen isotope analysis of amino acids (CSIA-AA). Samples were collected in August 2020, May and November 2021, and March 2022 to assess seasonal variability. Bulk stable isotope analysis revealed that the TPs of the two species were generally similar, with no apparent differences observed across sampling periods, although some differences in energy sources were observed during spring and at coastal stations. In contrast, the TPs estimated from a CSIA-AA revealed relatively lower values for E. pacifica . Both species exhibited relatively low TPs in spring (∼2), increasing to nearly 3 in winter. Furthermore, the proportion of energy transferred through the microbial food web was lower in E. pacifica than in C. sinicus . In addition, a markedly depleted nitrogen isotopic composition in primary producers was observed during the winter when nitrate concentrations were sufficiently high. These findings demonstrate that CSIA-AA is a powerful tool for detecting subtle seasonal and interspecific differences in the trophic dynamics of zooplankton—key intermediaries linking lower trophic levels to fishery resources. © 2026 Elsevier Ltd.

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