Self-maintaining or continuously refreshed? The genetic structure of Euphausia lucens populations in the Benguela upwelling ecosystem

Abstract

Populations of Euphausia lucens over the shelf of the southern Benguela upwelling region could be self-maintaining. Alternatively, they could be continually refreshed by expatriates from the SWAtlantic that enter the system via South Atlantic Central Water in the south, before developing and then being lost through advection off Namibia. These two hypotheses are investigated here by examining geographic heterogeneity and molecular variation (cox1 and ND1) of the species across its distributional range in the Southern Hemisphere. Comparisons are made with E. vallentini, which is assumed to show panmixia associated with its circumglobal distribution between 50 and 608S. Phylogenetic analysis with mitochondrial 16S ribosomal RNA and cytochrome oxidase 1 (cox1) confirmed that E. lucens and E. vallentini represent sister taxa. Strong geographic structuring of cox1 and ND1 mtDNA genetic variation by ocean basin was recorded in E. lucens, indicating that neritic populations off South Africa are likely self-maintaining.