Mesozooplankton distribution in the Guinea Current Large Marine Ecosystem (GCLME) during the west African monsoon: a...

The Guinea Current Large Marine Ecosystem (GCLME), located in the Eastern Equatorial Atlantic, is highly productive and supports important coastal livelihoods and fisheries across West Africa. Mesozooplankton and hydrographic sampling were conducted across an extended area of the GCLME, from Guinea-Bissau to Ghana, during two consecutive surveys between July and September 2017. The sampling coincided with the West African Monsoon and the major upwelling period in the central GCLME (C-GCLME: Côte d'Ivoire, Ghana), while the western GCLME (W-GCLME: Guinea-Bissau to Liberia) experienced its main rainy season. Contrasting hydrographic regimes between the two subsystems were reflected in the zooplankton community structure and distribution patterns. The cooler upwelled waters of the C-GCLME supported significantly higher mesozooplankton stock and a copepod assemblage characterized by opportunistic, or upwelling-associated species (i.e. Calanoides natalis, Centropages chierchiae), most prominently along the Ivorian and eastern Ghanaian coasts. In contrast, the W-GCLME was characterized by thermally stratified, low-salinity waters influenced by riverine inputs, supporting thermophilic, as well as opportunistic species, particularly along the Guinea-Sierra Leone Plateau. These results highlight clear ecological differences between the two subsystems and provide baseline information on zooplankton biomass and biodiversity, relevant to local food web dynamics and ecosystem-based management efforts.