The distribution of benthic Ostreopsis species is poorly known in the Moroccan coasts. The current study is aiming to investigate: i) the distribution of Ostreopsis spp. cells on macroalgae and in the seawater column of the Cape Ghir area (North-West of Agadir) during the summer season of Ostreopsis from July 15 to November 17, 2020; ii) the toxic profile at the level of the three matrices (benthic Ostreopsis attached to macroalgae, Ostreopsis in the water column and mussels) via chemical analysis using mass spectrometry. A taxonomic study of Ostreopsis spp. was carried out using the light and inverted optical microscopes. Chemical analysis showed the presence of ovatoxins (OvTX-A and OvTX-B) in Ostreopsis samples in low quantities, in the order of fg.cell −1 and at levels below the limit of quantification (0.04 g.mL −1) in mussels. Morphological observations showed that the cells were ovoid and flattened, large, and ventrally pointed with a dorsoventral diameter (DV) and width (W) of 57- and 33-, respectively, and a dorsoventral/anteroposterior diameter (DV/AP) of about 3.23.