Comparative analysis of feeding-related behavior in three copepod species differing in body size across six prey size classes

High-speed videography advances zooplankton feeding-related behavior studies. Employing the technique, this study analyzed foraging effort in three copepod species: Calanus sinicus (2.00 mm), Centropages dorsispinatus (0.93 mm), and Paracalanus parvus (0.68 mm) using natural prey in natural seawater, by measuring beating frequency (BF) and beating time (BT) of feeding appendages. All three species exhibited feeding-current feeding, but differed significantly in BF, BT and swimming trajectory distance. Foraging effort across six prey size classes revealed distinct patterns: C. sinicus exhibited lowest BF for 0.7–10 μm size-class and highest on >250 μm size-class, indicating avoidance of prey <10 μm and active capture of prey >250 μm (including microzooplankton) via increased BF. C. dorsispinatus showed low BF for both smallest (0.7–10 μm) and largest (>250 μm) classes and its lowest BT for 100–250 μm size-class, indicating peak foraging effort for 10–100 μm prey. P. parvus showed minimal BF variation (except pronounced decrease at 20–50 μm) and consistent BT, reflecting broad feeding adaptability. These findings elucidate foraging effort and suggest potential differences in trophic niches of different copepods, highlighting strong food-adaptability of small copepods like P. parvus . This supports observations of copepod miniaturization and aids evaluation of small copepods' ecological role.