Zinc effect on the sea urchin Paracentrotus lividus immunological competence

► We evaluated the effect of zinc on P. lividus immune system defence. ► Zinc affected both cellular and acellular components of the sea urchin. ► Amebocytes changed in shape and the red spherula cells increased in number. ► Antibacterial activity decreased after zinc treatment. ► Modifications in defence mechanism might represent biological pollution indicators.