Interactive effects of UV radiation and temperature on microstages of Laminariales (Phaeophyceae) from the Arctic and North Sea

Spores and gametophytes are considered to be those life-history stages of kelps most susceptible to environmental perturbations and, in particular, to temperature and UV radiation. Microstages of Arctic (Saccharina latissima, Laminaria digitata, Alaria esculenta from Spitsbergen) and temperate kelp species (S. latissima, L. digitata, L. hyperborea from the North Sea) were exposed in 2-factorial experiments to different temperatures (2 to 18°C) and radiation conditions (photosynthetic active radiation, UV-A radiation, UV-B radiation). Our results reveal ecotypic differentiations in the stress responses of zoospores of L. digitata and S. latissima from the Arctic and North Sea. UVA radiation either enhanced the formation of gametes at elevated temperatures in L. digitata or impaired egg release and subsequent sporophyte formation in L. hyperborea. Microstages exposed to additional UV-B radiation were strongly inhibited to a population-, speciesand life phase-specific degree at suboptimal and optimal temperatures. Only gametogenesis of Laminaria spp. was shown to be tolerant to UV-B exposure. Conclusively, in respect to a future scenario of elevated UV radiation regimes and higher summer temperatures in Arctic and North Sea waters, summer-recruiting Arctic species and L. digitata from the North Sea might become endangered by a frequent disturbance of their microstages.