Modeling investigation of the nutrients and phytoplankton dynamics in the Moroccan Atlantic coast: A case study of Agadir coast

Abstract Although the environmental status of the Moroccan Atlantic coastal waters has been researched in previous studies, there is still a lack of knowledge about its biogeochemical functioning. Especially for the Agadir coast where measurements are quite scarce, realistic ecological models can help identifying the key mechanisms driving fluctuations in such coastal areas. Here we implemented a three-dimensional (3D) coupled hydrodynamic-biogeochemical model in order investigate the time-space distribution of inorganic nutrients (NO₃, PO₄ and SiO₄), and their control on phytoplankton (diatoms, flagellates) biomass on the Agadir coast. Model performance was evaluated against satellite observations and climatology data. The model achieved satisfactory representation of the sea surface temperature, chlorophyll-a, and a reasonable agreement in the seasonal pattern of inorganic nutrients. Based on nutrient concentrations and their stoichiometric ratio; the study points to nitrate as the key factor controlling phytoplankton distribution (largely dominated by flagellates). Nitrate depletion occurs faster than phosphate and silicate, thus driving the area towards nitrogen limitation.