Depth distribution of Calanus finmarchicus and C. glacialis in relation to environmental conditions in the Barents Sea

Stage composition and vertical distribution of copepodids of Calanus finmarchicus and C. glacialis are described during spring and summer in Atlantic and Arctic waters, respectively. The two species co-occurred in the region of the Polar Front, both in moderate to high population densities. Ontogenetic migration, meaning that the migration range becomes progressively wider with advancing stage, was found in both species. The present study also revealed that C. finmarchicus had modifications in its ontogenetic vertical distribution. The standing crop of phytoplankton, predominantly Phaeocystis pouchetii , appeared to influence the degree of stage-specific segregation. Both low and high food concentrations tended to increase the vertical distribution of the instars. On the other hand, a narrow subsurface stratum of abundant phytoplankton led to an aggregation of copepodids at this depth. In the region of the Polar Front, where the two species co-occur, C. glacialis had a deeper distribution than C. finmarchicus , thus creating a bimodal vertical distribution pattern within the uppermost 200 m.