This work aims to study the spatio-temporal evolution of the genus Nitzschia longissima, one of the most important genera of marine plankton diatoms, from 3 sampling stations in the Nador lagoon and during 2 seasons (spring and summer 2018), Using Nitzschia longissima, as a study system, one of the most diverse and abundant genera among marine planktonic diatoms. This species counts, in addition to the form Nitzschia longissima forma parva Grunow, three varieties namely Nitzschia longissima var. closterium (W. Smith) Van Heurck, Nitzschia longissima var. longissima (Breb.) Ralfs and Nitzschia longissima var. reversa Grunow. Nitzschia Longissima genus density was high during the warm season (Summer 2018) with a value of 8000 cells/liter, and low during the cold seasons (Spring 2018), which may be caused by water temperature and zooplankton community structure; and underwater light intensity was an important factor influencing the spatial distribution of Nitzschia density.