Inter-species comparison of the copepodite stage morphology, vertical distribution, and seasonal population structure of five sympatric mesopelagic aetideid copepods in the western Arctic Ocean

Aetideidae is a calanoid copepod family dominant in the mesopelagic layer of Arctic Ocean for which little ecological information available because species identification, especially early copepodite stages, difficult. In this study, we developed identification flow whole stages five sympatric aetideid copepods ( Chiridius obtusifrons , Gaetanus tenuispinus G. brevispinus Aetideopsis minor and A. rostrata ). Vertical distributions seasonal population structures these were evaluated using year-round sample time-series collected at drifting ice station (SHEBA) western Ocean. Combinations morphological characteristics (prosome length, cephalosome, prosome widths) used to identify species. was distributed deep waters (1,032–1,065 m) throughout year. The other all found 600–700 m during midnight sun. However, polar night, vertical each distinct, resulting from ascent, descent, or depth maintenance, indicating migration may function reduce inter-specific competition night when food resources are scarce. Reproduction timing varied among four copepods: C.obtusifrons showed ascent reproduction end whereas descent maintenance beginning night. There not sufficient data examine . Common species, δ 15 N values adult females indicate more carnivorous feeding modes than those Such distribution variation