The reproductive cells of seaweeds are the developmental stages of seaweeds most susceptible to environmental stress, including UV radiation. In our study, exposed zoospores of the brown algae Saccorhiza dermatodea, Alaria esculenta and Laminaria digitata occuring in this sequence from the upper to the mid sublittoral on Spitsbergen were exposed to photosynthetically active radiation (P, 400-700 nm), P + UVA radiation (PA, 320-700 nm) and PA + UVB (280-700 nm) in the laboratory. Photoinhibition and recovery of photosynthesis, the presence of UV-absorbing compounds as well as DNA damage and repair was investigated. In parallel, germination rates were determined and the germination process was documented by light microscopy. Photosynthesis was strongly reduced after exposure in all species, especially after PAB exposure. Recovery was faster in S. dermatodea under all treatments compared to the other species. Zoospore suspensions, zoospores and the external medium showed a strong absorbance below 350 nm, probably due to the presence of phlorotannins. A great part of the radiation was absorbed by the spores themselves, the rest was absorbed by the medium. Phlorotannin containing physodes were observed in the cytoplasm and, in A. esculenta and L. digitata also outside the cells suggesting exocytosis especially after UV exposure. We hypothesise that this process is related to the UV absorbing capacity in the external medium. DNA damage was lowest in S. dermatodea, the repair rate was higher in A. esculenta and lowest in L. digitata. As a result of these processes, germination was inhibited after PAB exposure, especially in L. digitata. We conclude that UV tolerance is one of the most important factors determining the upper distribution limit of the studied species. The results cast light on the potential impact of enhanced UVB radiation on dominant components of the seaweed community on Spitsbergen.
Helmholtz Research Programs > MARCOPOLI (2004-2008) > POL4-Response of higher marine life to change