Juvenile life stages of the brown alga Fucus serratus L. are more sensitive to combined stress from high copper concentration and temperature than adults

The combined effects of exposure to copper and temperature were investigated in adult specimens and germlings of the canopy-forming brown alga Fucus serratus. A matrix of four temperatures, 6, 12, 17 and 22 °C, and three concentrations of copper, 0, 100 and 1,000 nM total copper were used. Measured endpoints were growth rate, chlorophyll fluorescence parameters and for germlings also survival. The growth rate of adult specimens of F. serratus changed with increasing temperature. Growth tended to be negatively affected by high concentrations of copper when exposed to heat (22 °C) though not significantly so. The photosynthetic performance (i.e., chlorophyll fluorescence parameters: F _v/F _m, maximum electron transport rate (ETR_max) and maximum non-photosynthetic quenching (NPQ_max) of adults was largely unaffected by both copper and temperature. Germling survival, growth rate and chlorophyll fluorescence parameters were affected by the combination of copper concentration and temperature. Increasing temperature led to reduced survival, increased rhizoid growth and higher F _v/F _m and ETR_max, whereas high copper concentration had a negative effect on the latter three endpoints. The negative effect of high copper concentration was amplified by high temperature. We conclude that juveniles of F. serratus are more susceptible to environmental stressors than adult specimens and recommend therefore including early life stages when assessing the risk of exposure to toxic compounds. Considering the response of adult specimens only may lead to false conclusions regarding the ecological impact of environmental stress.