Influence of the Benguela Upwelling System on the genetic connectivity of blacktail seabream Diplodus capensis across southern Africa

Oceanographic features such as upwelling cells and currents contribute to shaping the evolutionary history of marine fishes, including species that may be important socio-economic resources. However, the impacts of these barriers are often cryptic and may change, particularly in a rapidly changing climate. Hence, sustainable fisheries management strategies need to take into consideration the influence of oceanographic barriers to the genetic structure of populations. Here, we evaluated the influence of the Benguela Upwelling System, a known barrier for warm-temperate fishes, on the evolutionary history of the blacktail seabream Diplodus capensis (family Sparidae), using eight microsatellite loci in conjunction with DNA barcoding of the cytochrome c oxidase 1 gene. Diplodus capensis is an important recreational and small-scale fishery species, distributed across southern Africa. Overall, there was significant genetic differentiation across the region, but the level of divergence varied with the genetic marker. Our results identified two isolated populations—in the northern and southern subsystems of the Benguela Upwelling System—with limited contemporary gene flow, and no sub-structuring detected within the subsystems. Because the species is vulnerable to exploitation, with declines in South Africa, our results suggest that management policies should aim at regional levels for the northern population (off Angola and Namibia), whereas the southern population (off South Africa) was identified as an isolated and highly connected population.