Vertical migration, dispersal and transport of Euphausia lucens in the southern Benguela Current

Abstract

Diurnal vertical distributions and ontogenetic migration of Euphausia lucens (Hansen) were investigated off the west coast of South Africa. Eggs and nauphi remained in the near-surface layer and did not migrate. Older larvae (calyptopes and furciliae) migrated to deeper depths during the day but were generally restricted to the upper layers of the water column. Juveniles had similar vertical distribution to adults and were capable of migrating to the bottom layers of the water column. As a result of layering and migration, different stages of E. lucens have different probabilities of cross-shelf and longshore transport in the southern Benguela upwelling system. Initially, wind-driven Ekman transport advects the early reproductive stages offshore where the thermal front may present a potential barrier to further offshore transport. By migrating below the near-surface layer the older stages would be more subject to longshore transport via the northward-flowing jet current. Southward transport is facilitated by the deep under-current, but penetration to the east coast of South Africa would be constrained by the influence of the Agulhas Current.