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The effects of stratospheric ozone depletion and of global warming on the marine biosphere are still underexplored, especially in the Arctic. Seaweeds are very important primary producers but are strongly susceptible to enhanced UV radiation and elevated temperatures, especially their spores. The UV susceptibility of spores has previously been invoked to determine the depth distribution of seaweeds. Therefore, we will investigate the effect of different radiation and temperature conditions on the ultra-structure, physiology and biochemistry of spores from various brown and green algae growing in different water depths. Moreover, we will study competition between zoospores of various species of brown macroalgae in order to get an insight about biotic factors structuring seaweed communities and also to explain more clearly the present seaweed zonation pattern.
The succession of macro- and microalgal communities in the Antarctic will be investigated in field experiments under various UV radiation (UVR) conditions and in the absence or presence of grazers. The observed differences in the succession process will be correlated to physiological traits of single species, especially in spores and germlings, which are the most vulnerable stages in their life histories. Photosynthetic activity of the different developmental stages will be measured routinely. Additionally we plan the determination of pigment composition, C:N ratios, content of UV protective pigments and of possible DNA damage. The experiments will start in spring, concomitant to the time of highest UVBR, due to the seasonal depletion of the ozone layer in the Antarctic region. Supplemental laboratory experiments will be conducted to determine the effects of UVR on spores and germlings of individual species. In addition to the above analyses, we plan to examine of UVR induced damage of cell fine structure and of the cytoskeleton. The results of both the field and laboratory experiments will allow us to predict the consequences of enhanced UVR for the diversity and stability of the algal community.