ALBERT

Description: According to diverse model predictions Arctic seaweed systems are proposed to alter structure and composition due to global change in future. Two major factors that will influence these systems are (1) ocean warming and (2) increased glacier melting leading to a reduction in ice cover and ice-scouring and changing light quantity and quality as well as substrate characteristics. In 2012 / 13 we investigated a polar kelp system along a depth transect off Hansneset, Kongfjorden (Svalbard) and compared these data with a baseline study performed at the same site in 1996/98. Probably as a consequence of continuously ice-free winters since 2006, biomass and biodiversity changes were observed. Concurrent laboratory studies revealed the susceptibility of kelp recruitment towards a combination of increased sedimentation, warming and grazing. Furthermore we will report on ecotypic differentiation and first calculations of carbon budgets for the kelp system

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: 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.

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.

Description: The aim of this study is to understand the macroalgal vertical zonation at Potter Cove (Isla 25 de Mayo/ King George Island) in three selected newly ice-free areas with different degree of glacial influence (low: area 1, intermediate: area 2, and high: area 3), and thus a different degree of sedimentation, from a physiological point of view. In summer 2010 and spring 2011, two macroalgal key species (Himantothallus grandifolius and Palmaria decipiens) were sampled at 5, 10, 20 and 30 m depth. After collection, photosynthesis – irradiance curves were performed and photosynthetic parameters were calculated. Photosynthetically Active Radiation (PAR) was logged continuously over 7 days during spring 2011 and summer 2012 at 0, 5, 10, 20 and 30 meters depth in each area. Subsequently, the daily metabolic carbon balance (DMCB) was determined using the obtained photosynthetic parameters and the underwater PAR data. 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 glacial impact, it was 20 and 30 m depth, respectively. PAR values were higher in spring than in summer. For both species, DMCB values were significantly higher in spring compared to summer. In addition, both species DMCB values decreased significantly with increasing depth, and were significantly higher in areas 1 and 2 (low and intermediate glacial influence) compared to area 3 (high glacial influence). The observed vertical distribution in all the studied areas seem to be determined mainly by the spring PAR conditions, as in summer the DMCB values are too low for both species to explain their survival. Furthermore, 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.