Daily Metabolic Carbon Balance in Spring and Summer and Vertical Distribution of Two Macroalgal Key Species In Potter Cove, South Shetland Islands, Antarctica

DOLORES DEREGIBUS; KATHARINA ZACHER; GABRIELA LAURA CAMPANA; CHRISTIAN WIENCKE; MARIA LILIANA QUARTINO

Rio Grande

Workshop; II WORKSHOP APECS-BRASIL; 2012

Universidad Federal do Rio Grande (FURG)

INTRODUCTION The Western Antarctic Peninsula is one of the most rapidly warming regions on Earth (Turner et al. 2010). Glacial systems have shown a direct response to the higher temperatures with a marked retreat (Cook et al., 2005). As a consequence of glacier retreat "newly ice-free areas" have become available for colonization and biological succession (Rϋckamp et al., 2011). Simuntaneously, continental ice melting produces alterations in the water column by increasing the sediment input and causing salinity variations (Schloss et al., 2008). Major changes in coastal and shelf pelagic systems have already become apparent (Ducklow et al. 2007). Light availability for photosynthesis is a major factor determining the distribution limits of sublittoral macrolgae (Luning & Dring, 1979, Gómez et al., 1997). Increased sediment loads have been proposed to be an important factor involved in the decreases in macroalgal depth distributions (Eriksson & Johansson, 2004). A decrease in light penetration constitutes a constraint limitating light for photosynthesis (Gómez et al., 1997). At Potter Cove (25 de Mayo/ King George Island), a visible melting of Fourcade glacier has exposed several newly ice-free areas (Rϋckamp et al, 2011). Therefore, the aim of the present study constitutes an initial effort to explain the algal zonation from a physiological point of view at Potter Cove (Isla 25 de Mayo/ King George Island) in three selected newly ice-free areas. MATERIAL AND METHODS The study was carried out at Potter Cove (62º 14? S, 58º 38? W). Three different newly ice-free areas with different degree of glacial influence (different degree of sedimentation/underwater light penetration) were selected to study. Each area is exposed to a different degree of glacial influence (low: area 1, intermediate: area 2, and high: area 3), and thus a different degree of sedimentation/underwater light penetration.In summer 2010 (January and February) and spring 2011 (November), two key macroalgal 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, 400-700 nm) was logged continuously over seven 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. RESULTS AND DISCUSSION In areas with high glacial influence the maximal vertical distribution limit of both 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 (1-way ANOVA, p < 0.05). In addition, both species DMCB values decreased significantly with increasing depth (1-way ANOVA, p < 0.05), and were significantly higher in areas 1 and 2 (low and intermediate glacial influence) compared to area 3 (high glacial effect) (1-way ANOVA, p < 0.05).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 or even negative for both species to explain their survival. 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