The susceptibility of spores of the red alga Iridaea cordata and the brown algae Adenocystis utricularis and Himantothallus grandifolius to UV (UVR) and photosynthetically active radiation (PAR) was tested in field-experiments on King George Island. Spores were exposed to i) natural radiation, ii) radiation depleted of UVBR and iii) radiation depleted of UVAR and UVBR, in different water depths (1, 2, 4 and 8m). Concomitantly, spores were exposed in the laboratory for different times to artificial radiation (1, 2, 4 and 8h). Germination rates were determined after laboratory post-culture under dim white light. Germination of the intertidal species A. utricularis was not affected by depth, exposure time or radiation treatment, while germination of the other two subtidal species showed significant differences between different depth and/or radiation regimes. Spores from I. cordata and H. grandifolius were inhibited by high PAR at 1 m and 1-2 m water depth, respectively, but not in deeper waters. Spores of the two subtidal species were, in contrast to A. utricularis spores from the intertidal, affected not only by UVR but also by high PAR. In the laboratory approach under low PAR, the subtidal species were only affected by UVR under short term exposure (1-2h). Our results show that already algal spores, being the most sensitive part in the life-cycle of macroalgae, show species-specific adaptations. Not only UVR but also the high PAR fluxes penetrating into the water column in the field are important factors determining the upper distribution limit of Antarctic macroalgae.