p. 189 - 203 IMPACT OF HEAVY METALS ON THE PRIMARY PRODUCTION A. N. Khalil 1), A. M. Ibrahim 2) 1) Oceanography Department, Faculty of Sciences, Alexandria, University, Alexandria, Egypt 2) Institute of Oceanography and Fisheries, Alexandria, Egypt Abstract Effect of different concentrations of some heavy metals on the preliminary production was studied at two locali- ties near Jeddah (Red Sea), by estimating chlorophill-a. Metal toxicity of the phytoplankton, and can be arranged in the following order: Pb> Zn> Ni> Cd. More depress on the phytoplankton productivity took place, when Zn accom- panied another/other metal (s) in the media. Impact of heavy metals on the primary production at the sheltered area (inside Obhur Creek), was relatively higher than that observed at the exposed area (Open Sea).