| Summary: | Abstract Background Early life stages of macroalgae, especially from polar species, can be highly vulnerable to physical stressors, leading to important consequences for the fate of the whole population in scenarios of changing environmental variability. In the present study, tolerance to UV and temperature stress, as measured by rapid adjustment of photochemistry, F v /F m , and photosynthetic characteristics based on P-E curves (ETR max , α and E k ), was assessed in the early life stages of six Antarctic macroalgal species from eulittoral ( Pyropia endiviifolia , Iridaea cordata , Adenocystis utricularis and Monostroma hariotii ) and sublittoral ( Ascoseira mirabilis and Gigartina skottsbergii ). Results Reproductive cells of eulittoral species showed the highest light demands (E k >45 μmol photon m −2 s −1 ) when compared to those from sublittoral species (E k < 30 μmol photon m −2 s −1 ). Short-term experiments of 1 h revealed that reproductive cells of P. endiviifolia , A. utricularis and M. hariotii had the highest temperature tolerance with a decrease of F v /F m observed only at 30 °C, while carpospores of G. skottsbergii exhibited the highest sensitivity to temperature increase with a decrease of F v /F m , which could be observed at 5 °C. UV tolerance was observed in reproductive cells of the eulittoral species with < 20 % inhibition in F v /F m from UV after four hours of exposure, while sublittoral species were more sensitive with >30 % inhibition in F v /F m in the same condition. Enhanced temperature (7 and 12 °C) improved the tolerance of I. cordata compared to 2 °C, but exacerbated the detrimental effects of UV on A. mirabilis . Conclusion Results showed that photosynthetic characteristics varied among reproductive cells of different species, reflecting the vertical zonation of parental thalli. Otherwise, these differences appear to underlie biogeographical .
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