| Summary: | The in origin intertidal marine brown alga Fucus vesiculosus L. grow permanently sublittoral in the brackish Bothnian Sea, side by side with the recently discovered F. radicans L. Bergström et L. Kautsky. Environmental conditions like salinity, light and temperature are clearly different between F. vesiculosus growth sites in the Bothnian Sea (4-5 practical salinity units, psu; part of the Baltic Sea) and the tidal Norwegian Sea (34-35 psu; part of the Atlantic Ocean). The general aims of this thesis were to compare physiological aspects between the marine ecotype and the brackish ecotype of F. vesiculosus as well as between the two Bothnian Sea species F. vesiculosus and F. radicans. The result in the study indicates a higher number of water soluble organic compounds in the marine ecotype of F. vesiculosus compared to the brackish ecotype. These compounds are suggested to be compatible solutes and be due to an intertidal and sublittoral adaptation, respectively; where the intertidal ecotype needs the compounds as a protection from oxygen radicals produced during high irradiation at low tide. The sublittoral ecotype might have lost the ability to synthesize these compound/compounds due to its habitat adaptation. The mannitol content is also higher in the marine ecotype compared to the brackish ecotype of F. vesiculosus and this is suggested to be due to both higher level of irradiance and higher salinity at the growth site. 77 K fluorescence emission spectra and immunoblotting of D1 and PsaA proteins indicate that both ecotypes of F. vesiculosus as well as F. radicans have an uneven ratio of photosystem II/photosystem I (PSII/PSI) with an overweight of PSI. The fluorescence emission spectrum of the Bothnian Sea ecotype of F. vesiculosus however, indicates a larger light-harvesting antenna of PSII compared to the marine ecotype of F. vesiculosus and F. radicans. Distinct differences in 77 K fluorescence emission spectra between the Bothnian Sea ecotype of F. vesiculosus and F. radicans confirm that this is a ...
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