How do two key seaweed species respond to glacier retreat in Potter Cove, South Shetland Islands, Antarctica

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

Portland

Congreso; XXXII SCAR Open Science Conference; 2012

Scientific committee of antarctic research

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. 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. 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. 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 effect). 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. 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 lead to an elevation of the lower distribution limit of the studied species, probably affecting macroalgal primary productivity in Potter Cove.