Description: Ultraviolet B radiation (UVBR, 280-315 nm) is known to be a stress factor for Antarctic benthic algae and invertebrates. However, there is almost no available information regarding these effects at the community level. A two-factorial colonization experiment (UVR, three levels and grazing, two levels) was performed at an intertidal and a subtidal site on King George Island/I. 25 de Mayo. Structural parameters of the community were followed for fifteen and ten weeks, respectively. The effects on the intertidal community are presented in detail in Zacher et al. Subtidal communities were dominated macroscopically by colonial diatoms and green algal filaments. Ultraviolet radiation (UVR, 280-400nm) did not affect diatoms but exerted a group-specific effect on the macroalgal assemblage. Overall, red algal cover was negatively impacted by UVR whereas for green algal filaments a significant interaction between grazing and UVR was detected. Grazers introduced a shift in both micro- and macroalgal species composition and reduced the community biomass, with stronger effects when UVBR was absent. When comparing intertidal and subtidal experiments, community architecture and biomass production was markedly different at both sites, with higher biomass and more complex diatom composition at the subtidal spot. However, UVR and grazing affected both sites in a similar pattern. Our findings suggest that UVR and grazing play a key role in shaping the subtidal and intertidal benthic algal communities in Antarctica. UVR impact on subtidal communities seemed to be more complex than in the intertidal, exerting both direct and indirect effects on the community structure.

Description: The aim of this study is to understand the macroalgal vertical zonation at Potter Cove (Isla 25 de Mayo/ King George Island) in five selected areas with different degree of glacial influence, and thus a different degree of sedimentation, from a physiological point of view. From December 2009 to March 2010, five macroalgal species (Desmarestia anceps, Himantothallus grandifolius, Ascoseira mirabilis, Iridaea cordata and Palmaria decipiens) were sampled at 5, 10, 20 and 30 m depth. After collection, photosynthetic parameters and chlorophyll a content were determined. In areas with high glacial influence the maximal vertical distribution limit of all species was 10 m depth, while in areas with intermediate and low/none glacial impact, it was 20 and 30 m depth, respectively. Areas with high glacial influence presented limiting light conditions below 20 m depth coinciding with the absence of macroalgae. In intermediate and low disturbed areas, light intensities were not limiting. Palmaria decipiens was the only studied species showing lower light saturation points at deeper depths. Chl a content did not show significant differences with increasing depth. Our first results show that the vertical zonation of the studied species is positively correlated to the light penetration which decreases as the glacial influence (as production of sediment input) increases. A further increase of sedimentation due to global warming will undoubtedly lead to an elevation of the lower distribution limit of the studied species and will probably have a great effect on macroalgal primary productivity in Potter Cove.

Description: Local climate warming recorded at maritime Antarctica since 50 years dramatically affects small ice caps such as on King George Island (KGI) at the Northern tip of the Antarctic Peninsula. DGPS measurements revealed surface lowering in elevations up to 270 m above ellipsoid with a maximum of 14 m over 11 years. Glacial area loss at KGI amounted to 20 sqkm between 2000 and 2008. Newly ice free areas opened and succession of diatoms, ostracods and foraminifers can be read in sediments cores. Input of glacial melt water and mineral suspension into coastal areas reach highest monthly yields in January. Timing of the annual discharge wave and volume have increased during the past 5 years. Coastal biota are severely affected by melt water, shading, sedimentation and increased intensity of iceberg scour. 20 years of coastal monitoring indicate that sediment discharge in summer combines with slowly rising water temperatures and freshening in coastal surface waters fronting melting glaciers. Shifts in pelagic communities from larger diatoms to smaller phytoflagellates in the highly stratified summer scenario correlate with large quantities of beaching dead krill. Shifts in the lower distribution limit of macroalgae have cascading effects on grazers and change community structure. Elevated rates of sediment deposition on the seafloor distinctly affect different groups of benthic macrofauna and shifts in benthic community and population age structure can be well explained with species specific sensitivity to sediment and iceberg impact. Most Antarctic macrofauna are highly vulnerable to change, but in some cases we observe unexpected adaptability.

Description: Palmaria decipiens (Reinsch) R.W. Ricker (1987) represents one of the dominant rhodophyte species in Antarctic coastal ecosystems. Due to its high abundance in the intertidal and upper subtidal it plays a key role in ecosystem structure and function, providing habitat, food and shelter for a multitude of associated organisms. The physiology, reproductive strategy and life cycle of P. decipiens is considered as being well adapted to the Antarctic environment, which is characterized by permanent low water temperatures and a strong seasonality in light climate. With its obvious ecological significance and adaptive strategies P. decipiens was frequently studied as a typical representative of an endemic Antarctic macroalga. Here we provide an overview of the recent literature, summarizing the knowledge gained about the alga during the last 25 years. This review focuses on the species life cycle and physiological responses, such as temperature requirements,photosynthetic characteristics, pigment content and protective mechanisms with regard to enhanced ultraviolet radiation (UV-B radiation, 280–315 nm and UV-A radiation, 315–400nm). The ecology of P. decipiens is reviewed focussing on grazing activity and abundance patterns. Since most studies on P. decipiens have been conducted at King George Island off the western Antarctic Peninsula this overview serves as a summary of baseline data from an ecosystem particularly prone to environmental change.

Description: How are benthic Antarctic communities affected by changing environmental conditions such as UV radiation (UVR)? UVR is known to affect many biological processes but almost no information exists whether these effects, visible on the molecular and cellular level, impair polar ecosystem structure. In order to obtain more information we studied the colonization of benthic primary producers in the Antarctic rocky intertidal and subtidal over a period of 106 and 70 days, respectively. 32 experimental units were installed at each site in a two-factorial design (UVR, three levels and grazers, two levels). Intertidal communities were dominated by single cell diatoms and green algal propagules. Limpet grazing reduced the algal biomass and macroalgal recruit density and further introduced a shift in both macro- and microalgal species composition. There were no negative UVR effects on the diatom assemblage. In contrast, significant UVR effects on the macroalgal assemblage were detected. UVAR (315-400nm) negatively impacted density and richness of recruits, whereas additional UVBR (280-315nm) caused a shift in species composition and led to a lower diversity of the macroalgal community by the end of the intertidal experiment. Effects were species-specific and showed that particularly young propagules were sensitive to UVR. No interactive effects of UVR and grazing were found. It is postulated that UVR has the power to change ecosystem structure in intertidal Antarctic macroalgal communities, which might have consequences for higher trophic levels. The effects of UVR and grazers on the subtidal community and a comparison of both field experiments are presented by Campana et al.