VERTICAL MIGRATION AND HABITAT PARTITIONING OF 6 EUPHAUSIID SPECIES IN THE NORTHERN BENGUELA UPWELLING SYSTEM

The vertical distribution of the adults of six species of euphausiids, Thysanöessa gregaria, Nematoscelis megalops, Euphausia Americana, E.gibboides, E.hanseni, Stylocheiron longicorne, as well as the larval stages of E.hanseni, were studied during a 48 h cycle at a fixed station in the northern Benguela upwelling system. All the species, except T.gregaria and S.longicorne, proved to perform diel vertical migration, but both migratory and non-migratory species appeared to be segregated in space during night-time hours, regardless of potential prey (phytoplankton and copepods). It is suggested that water column structure and hydrographic discontinuities caused by a warm, depth-localized intrusion, as well as the reproductive strategies of particular species, are responsible for this pattern. Eggs and larval stages of E.hanseni were concentrated near the surface, and the effect of the short-term pulses of the intrusion on their abundance is discussed. © 1990 Oxford University Press.