Feeding ecology of dominant copepods (Calanoida: Calanidae, Rhincalanidae) in the Southern Ocean inferred from mouthpart morphology and isotopic signatures

Abstract We evaluated the feeding behaviour and prey preferences of three dominant copepods, Calanus propinquus (Brady, 1883), Calanoides acutus (Giesbrecht, 1902), and Rhincalanus gigas (Brady, 1883), at different latitudes along 110°E in the Southern Ocean. An integrative approach combining mouthpart morphology, gut contents, and carbon and nitrogen stable isotopes (δ13C and δ15N) provided information on the functional adaptions for feeding, the in situ dietary preferences, and the trophic positions and feeding strategies of these copepods. Diatoms were the copepods’ major food source, accounting for more than 16 species out of the 23 taxa identified in their gut contents. Itoh’s edge index for the mandibles also indicated that the copepods are herbivores, but seta length/basis length (LS/LB) and basis width/basis length (WB/LB) of the maxillipedal endopod suggested carnivory. Principal coordinates analysis (PCoA) demonstrated a slight difference in dietary preference among copepods of the same order, but copepods of all three species collected near the edge of the ice had similar diets, indicating that their feeding behaviour is influenced by food availability. Our results provide a better understanding of the ecological roles of copepods in the Southern Ocean’s food web and their responses to changes in the polar ecosystem.