Coastal lagoons are ecosystems highly vulnerable to human impacts because of their situation between terrestrial and marine environment. Mar Menor coastal lagoon is one of the largest lagoons of the Mediterranean Sea, placed in SE Spain and subjected to major human impacts, in particular the mining of metal sulphides. As a consequence, metal concentration in water column and sediments of this ecosystem is usually higher than in other areas. For monitoring ecosystem health, the present study has assessed the ability of Cotylorhiza tuberculata for bioaccumulating metals from sea water. Up to 65 individuals were sampled at 8 different sampling stations during the summer of 2012. Although the concentration values for different elements considered were moderate (Pb: 0.04-29.50 ppm, Zn: 2.27-93.44 ppm, Cd: 0-0.67 ppm, As: 0.56-130.31 ppm) by dry weight of the jellyfish tissues (bell and oral arms combined), bioconcentration levels in relation to seawater metal concentration were extremely high. In any case, the use or disposal of these organisms should consider their metal content because of their potential environmental and health implications.