UV radiation and grazing impacts on an intertidal macroalgal assemblage in Antarctica

While most research on ultraviolet radiation (UVR) was focused on the effect of UVR on the physiology of individual organisms, little is known about the impact of UVR on assemblages in combination with other ecologically relevant factors. In particular, field-experiments on macrophytobenthos are scarce, even more in the Antarctic region. As macroalgae may be affected by enhanced UVR due to stratospheric ozone depletion, we studied the effects of UVR and consumers on early successional stages of a hard bottom macroalgal community on King George Island, Antarctica. In a two-factorial design 32 experimental units (PAR+UVA+UVB=280-700 nm; PAR+UVA=320-700 nm; PAR=400-700 nm vs. grazerno grazer) were installed for 106 days. In general, biomass and growth rates were very low. Both UVAR and UVBR showed negative effects during succession. The UV depleted treatment exhibited a significantly higher diversity after 106 days of exposure. Species richness was significantly depressed by UVAR at the end of the experiment. UVB radiation led to a significant difference in species composition between the UV depleted treatment and the one with the total solar spectrum. Small developmental stages of macroalgae were particularly sensitive to UVR but spores from intertidal macroalgae were better adapted to UVR than species occurring in the subtidal as shown in laboratory experiments. Both, UV radiation and herbivory exhibit a significant impact on macroalgal succession in the Antarctic intertidal. UVR may therefore change the community structure and alter trophic interactions in this system