Diet and feeding of Euphausia hanseni and Nematoscelis megalops (Euphausiacea) in the northern Benguela Current: ecological significance of vertical space partitioning

Abstract

Patterns of diel migration and feeding of Euphausia hanseni and Nernatoscelis rnegalops were investigated in waters of the northern Benguela (Namibia) upwelling system. N. megalops migrated to just below the thermocline at night and fed maximally in the early evening E. hanseni migrated to above the thermocline at night and fed progressively throughout the night. Although both species were omnivorous and consumed similar size ranges of copepod prey, differential prey sizefrequency with depth resulted in E. hanseni consuming mostly small-sized copepods and N. megalops preferring m e d u m size classes. At depths of overlap the 2 species appeared to partition copepod food resources on the basis of size. Verhcal spatial partitioning is examined in light of temporal and dietary separation, and overlapping horizontal distribution patterns of the species in the northern Benguela upwelling system. It is concluded that vertical space partitioning is a reflection of the structure of shelf break zooplankton communities, which is a strategy of sharing highly productive areas and avoiding competition.