In this study, Se(IV) was determined in seawater by flow injection hydride generation, trapping within the graphite furnace, followed by electrothermal atomic absorption spectrometry. The optimized protocol permitted a preconcentration factor of 1000 lowering the detection limit of Se(IV) in seawater to about 1.5 ng l-1 for a 25 ml sample volume. Because this technique is specific to Se(IV), various physico-chemical treatments leading to the conversion of other chemical forms into Se(IV) were investigated. Thermal and UV irradiation treatments of seawater samples in acidic or basic medium permitted the conversion of Se(-II)-selenomethionine and Se(VI) to Se(IV). Based on the different responses of selenium species towards the photochemical treatments, an operational speciation model of selenium species in seawater is proposed. According to our analytical protocol, 21 ng l-1 Se(VI), 10 ng l-1 Se(IV) and 13 ng l-1 organic Se-(II) species were determined in a coastal surface seawater collected near Brest.