Elevated concentrations of Cu2+ can have inhibitory effects on early development in plants and algae by targeting specific cellular processes. In the present study the effects of elevated Cu2+ on developmental processes in embryos of the brown algae Fucus serratus (Phaeophyceae) were investigated. Elevated Cu2+ was shown to inhibit fixation of the zygotic polar axis but not its formation. Actin localization was unaffected by elevated Cu2+ but polarized secretion, which occurs downstream, was inhibited. Significant differences in tolerance to Cu2+ were observed for polarization and rhizoid elongation of embryos derived from adults from Cu2+-contaminated and uncontaminated locations. Moderate Cu2+ exposure inhibited the generation of cytosolic Ca2+ signals in response to hypo-osmotic shocks. In contrast, cytosolic Ca2+ was elevated by treatments with high [Cu2+] and this coincided with production of reactive oxygen species. The results indicate that direct effects on signalling processes involved in polarization and growth may in part explain complex, concentration-dependent effects of Cu2+ on early development.