Phytoplankton occupies a primordial trophic position in the marine ecosystem and therefore constitutes a key element in its functioning. Its proliferation depends on several biotic, abiotic and environmental factors. Our study consists in determining the seasonal temporal evolution and the search for physico-chemical parameters determining the presence of taxa in Cape 7 (Aftissat).

The results obtained made it possible to identify 6 most abundant species throughout the year: Alexandrium sp, Dinophisis sp., Gymnodinum sp Pseudo-Nitschia sp Lingulodium sp. and Prorocentrium sp. These species are endowed with a poisonous power. However, the density is maximum during the warm months and correlated positively with the variation in temperature and negatively with the variation in nitrate and phosphate. A clear increase in density was observed between 2019 and 2020.

Key words: Phytoplankton – physicochemical parameters – density – toxic power – Aftissat