Description: Radiation damage can inter alia result in lipid peroxidation of macroalgal cell membranes. To prevent photo-oxidation within the cells, photoprotective substances such as phlorotannins are synthesized. In the present study, changes in total fatty acids (FA), FA composition and intra ⁄ extracellular phlorotannin contents were determined by gas chromatography and the Folin-Ciocalteu method to investigate the photoprotective potential of phlorotannins to prevent lipid peroxidation. Alaria esculenta juveniles (Phaeophyceae) were exposed over 20 days to high ⁄ low photosynthetically active radiation (PAR) in combination with UV radiation (UVR) in the treatments: PAB (low ⁄ high PAR + UV-B + UV-A), PA (low ⁄ high PAR + UV-A) or low ⁄ high PAR only. While extracellular phlorotannins increased after 10 days, intracellular phlorotannins increased with exposure time and PA and decreased under PAB. Interactive effects of time:radiation wavebands, time:PAR dose as well as radiation wavebands:PAR dose were observed. Low FA contents were detected in the PA and PAB treatments; interactive effects were observed between time:high PAR and PAB:high PAR. Total FA contents were correlated to extra ⁄ intracellular phlorotannin contents. Our results suggest that phlorotannins might play a role in intra ⁄ extracellular protection by absorption and oxidation processes. Changes in FA content ⁄ composition upon UVR and high PAR might be considered as an adaptive mechanism of the A. esculenta juveniles subjected to variations in solar irradiance.

Description: Enhanced UV-radiation (UVR) through stratospheric ozone depletion and global warming are crucial stressors to marine macroalgae. Damages may arise through formation of reactive oxygen species (ROS) in gametophytes of ecologically important kelps, brown algae of the order Laminariales, Such stress-induced damages may have a negative impact on their fitness and further impact their following life stages. In our study, gametophytes of three kelp species Alaria esculenta (L.) Grev., Laminaria digitata (Huds.) Lamour., Saccharina latissima (L.) Lane, Mayes, Druehl, Saunders from the Arctic, and of L. hyperborea (Gunnerus) Foslie from the North Sea were exposed to photosynthetically active radiation, UV-A, and UV-B radiation and four temperatures (2–18°C). ROS are formed predominantly in the peripheral cytoplasm and in chloroplasts especially after exposure to UVR. Superoxide (O2*-) is additionally formed in small, globular cytoplasmic structures, possibly mitochondria. In the surrounding medium O2*--concentration increased markedly at elevated temperatures and under UV stress in some cases. Ultrastructural damage was negligible pointing to a high stress tolerance of this developmental stage. Our data indicate that stress tolerant gametophytes of three Arctic kelp species should sustain their crucial function as seed bank for kelp populations even under prospective rising environmental perturbations.