Eddy‐Induced Forcing Reshapes Taxon‐Specific Copepod Gut Contents and Feeding Preference in the South China Sea

Abstract

Mesoscale eddies reshape pelagic habitats by modifying water‐column structure, primary production, and plankton distributions, yet how these changes affect zooplankton feeding across taxa and depths remains poorly understood. To address this gap, we tracked a cyclonic‐anticyclonic eddy pair and sampled zooplankton across cyclonic, frontal, anticyclonic, and outside‐eddy regions in the northwestern South China Sea. Based on abundance and vertical distribution, we selected adult females of three calanoid copepod taxa for gut‐content metabarcoding: Lucicutia flavicornis , Rhincalanus rostrifrons , and Pleuromamma spp. L. flavicornis occurred mainly at 0–200 m, whereas the other two taxa occupied broader vertical ranges and were concentrated at 200–500 m. Our results revealed clear taxon‐specific feeding traits as well as within‐taxon variation across eddy regimes and depths. L. flavicornis consistently selected Bacillariophyta, while its abundance and phytoplankton‐related gut signals were closely associated with elevated primary production in the cyclonic eddy. In R. rostrifrons , gut‐content composition varied with depth: Bacillariophyta signals were associated with primary production at 0–200 m, whereas a more mixed trophic profile occurred at 200–500 m in the anticyclonic core. Pleuromamma spp. showed the strongest heterotrophic signature, with prominent deep‐water Ciliophora signals, especially under anticyclonic conditions. These findings suggest that eddies may shape copepod feeding through changes in food supply linked to primary production and prey transport, together with copepod redistribution and possible changes in diel vertical migration. This study provides a trait‐based perspective on how mesoscale ocean dynamics shape taxon‐ and depth‐specific feeding patterns, with implications for pelagic trophic transfer and carbon cycling.