Inter-population differences in inherited copper tolerance involve photosynthetic adaptation and exclusion mechanisms...

•  A comparative study of copper (Cu) toxicity and tolerance in three populations of Fucus serratus was conducted by examining Cu²⁺ effects on various physiological parameters. •  Chlorophyll fluorescence, oxygen evolution, copper content, and relative growth rate of embryos and adults were measured on Cu²⁺ -exposed material. •  Algae naturally exposed to elevated total Cu concentration (Cu_T ), were more Cu²⁺ resistant than those from clean sites, as indicated by higher embryo and adult growth rates and lower copper contents. The Cu²⁺ tolerance of F. serratus is at least partly inherited and relies partly on metal exclusion. •  There were inhibitory effects of Cu²⁺ on oxygen exchange rates in both tolerant and non-tolerant algae. By contrast to sensitive algae, the maximum efficiency of photosystem II (F_v /F_m ), maximum fluorescence (F_m ) and zero fluorescence (F_o ) of resistant algae were unaffected by Cu²⁺ , whereas decreased quantum yield (ΦPSII) and increased nonphotochemical quenching (NPQ) were most pronounced in resistant algae. Inhibitory effects of Cu²⁺ on ΦPSII may result in the excitation energy being dissipated through xanthophyll-dependent quenching mechanisms in tolerant algae. In nontolerant algae, lower energy dissipation may result in chlorophyll degradation.