Diatom development depends on several environmental factors, including the availability in metals. When micronutrients are present of adequate amount, cells exhibit a strong fitness and develop at their maximum growth rate. In many circumstances, the optimal metal amount in the cell environment is disrupted and cells experience starvation or excess for one or more elements. The metals in excess interfere with biochemical and cellular processes triggering a dysfunctioning that reduces growth and may ultimately lead to cell death. The ability of diatoms to adapt/resist to environmental changes has ecological consequences in term of biodiversity. To survive, diatoms activate defence mechanisms, such as the production of antioxidants or/and metal chelators. In this contribution, the diatom requirements for cadmium, copper, zinc and sodium are briefly reviewed. Then the impacts of an excess or a deprivation in one of these elements on diatom physiology is discussed from the molecular and biochemical point of views. The defence mechanisms enabling diatoms to overcome the metal stress are presented. At the end of this contribution, an assay on the integration of the defence mechanisms is presented.