Vertical migration and habitat partitioning of six euphausiid species in the northern Benguela upwelling system

The vertical distribution of the adults of six species of euphausiids,Thysanöessa gregaria, Nematoscelis megalops, Euphausiaamericana, E.gibboides, E.hanseni, Stylocheiron longicorne,as well as the larval stages of E.hanseni, were studied duringa 48 h cycle at a fixed station in the northern Benguela upwellingsystem. All the species, except T.gregaria and S.longicorne,proved to perform diel vertical migration, but both migratoryand non-migratory species appeared to be segregated in spaceduring night-time hours, regardless of potential prey (phytoplanktonand copepods). It is suggested that water column structure andhydrographic discontinuities caused by a warm, depth-localizedintrusion, as well as the reproductive strategies of particularspecies, are responsible for this pattern. Eggs and larval stagesof E.hanseni were concentrated near the surface, and the effectof the short-term pulses of the intrusion on their abundanceis discussed.