Very high concentrations of Vanadium (V)(up to 3 wt%) were reported for the first time in the Mediterranean homoscleromorph sponges Oscarella lobularis and Oscarella Tuberculata used as bioindicators of metallic contamination in the Marseille Bay area. This unexpected discovery raises a lot of questions regarding bioaccumulation and bioconcentration mechanisms as well as the physiological role of V in these sponges. Here we propose to investigate V speciation using X-ray absorption spectroscopy at the V K-edge to explore bioaccumulation mechanisms. In particular, redox state of V will be studied since it has been shown to control its bioaccumulation in other marine organisms such as ascidians. Finally, at longer term, the comprehension of V bioconcentration mechanisms may open unique opportunities for developing biomimetic approach for the selective extraction of V from secondary sources.