The effect of Mauritanian and Benguela upwelling waters on micronekton (Decapoda, Euphausiacea, and Lophogastrida) in the Southeastern Atlantic Ocean

Abstract

Eastern Boundary Upwelling Systems play a crucial role in marine productivity, supporting rich biodiversity and sustaining significant global fisheries. These dynamic regions are characterized by nutrient-rich waters that fuel complex food webs, making them vital for ecosystem functioning and fisheries management. Understanding the composition and distribution of key zooplankton groups, such as pelagic crustaceans, is essential for assessing ecosystem dynamics, particularly in the context of climate variability. In this study, we describe the community composition of pelagic crustaceans in the Mauritanian Upwelling (MU) and Benguela Upwelling System (BUS). The stations sampled in both ecosystems were grouped in relation to the water masses, with MU (10−22ºN) stations associated to high temperature and salinity, and southern BUS (30−34ºS) to rich oxygen waters. A total of 43 species were identified in MU and 48 in BUS, with the same number for Decapoda and Lophogastrida, but more euphausiid species in the BUS (14 and 19 species, respectively). Sergestidae was the most diverse family from Decapoda, with 13 and 14 species in MU and BUS, respectively. We found the highest abundance and biomass of pelagic crustaceans in the permanent upwelling area of the MU. Considering organisms body size, the largest individuals (surface area > 100 mm2) showed the highest frequency of occurrence in the MU. However, the smallest organisms (surface area 0–20 mm2) predominated in the BUS, probably due to a high intensity of the upwelling. Additionally, in the BUS, we identified the tropical euphausiid Thysanopoda tricuspidata, likely transported from the Indian Ocean by the Agulhas Current. Our results highlight the influence of large-scale oceanographic processes on pelagic crustacean distribution.