ABSTRACT. – The present study investigated the abundance and distribution of dinoflagellate species between seasons and the different tidal periods (flood, slack and ebb) in Kerkennah Islands (southern coast of Tunisia) from February to October 2007. Nutrients varied significantly during seasons, increased in spring and decreased dramatically in autumn and winter. Sixtyfour dinoflagellates were identified with a remarkable increase in spring and summer. Dinoflagellate abundance between tidal periods was variable and the highest abundance was detected in the slack period (T2), whereas abundance was low on flood (T1) and ebb (T3) periods, due mainly to the high amount of suspended particulate matter which reduced the penetration of irradiance into the water column and the dinoflagellate motility by affecting cell trajectories. We found significant relationships between dinoflagellate abundance and temperature, NO2-, Si(OH)4, and PO43-. We found evidence that abiotic variables are not the only factors governing the dynamics of dinoflagellates and food availability may be the most important factor regulating seasonal and tidal dynamics of dinoflagellate species.