Mémoire

Abstract

Eastern Boundary Upwelling Ecosystems (EBUEs) are among the most productive marine systems globally, playing a key role in carbon cycling and export. In the Canary Islands region, mesoscale features such as eddies and filaments, driven by both the instability of the upwelling boundary zone and the flow disruption caused by the islands, can significantly alter biological dynamics and biogeochemical processes. This study investigates the influence of these mesoscale phenomena on nano- and picoplankton abundance, community structure, and metabolic activity, by comparing two latitudinal transects, north and south of the archipelago, sampled during the CANARIAS 9110 cruise in October 1991. Results show that, despite the stratified conditions and weak upwelling influence at the time of sampling, the southern transect exhibited a globally higher abundance of organisms as well as higher respiratory activity, likely associated with mesoscale activity. Respiratory activity was also linked with significantly higher abundance of nanoflagellates, indicating a shift towards larger organisms in the south. The link between lateral transport of organic matter induced by mesoscale dynamics and the higher metabolic rates in the southern transect is also discussed. Overall, mesoscale variability appeared to influence both the structure of planktonic communities and metabolic activity across the region. The study emphasizes the ecological importance of island-induced mesoscale features and highlights their potential role in modulating carbon pathways within and beyond the Canary Upwelling System.