Can glacial melting cause interannual variations in the productivity of Antarctic seaweeds (Potter Cove, Antarctica)?.

DOLORES DEREGIBUS; KATHARINA ZACHER; GABRIELA LAURA CAMPANA; EDUARDO RUIZ BARLETT; MARTA EUGENIA SIERRA; GABRIELA V TOSONOTTO ; CHRISTIAN WIENCKE; MARIA LILIANA QUARTINO

Barcelona

Simposio; XIth SCAR Biology Symposium; 2013

XIth SCAR Biology Symposium

The aim of this study is to investigate interannual changes of the macroalgal daily metabolic carbon balance (DMCB). In two years (spring/summer 2011/2012 vs. spring/summer 2012/2013) the Antarctic endemic Himantothallus grandifolius (Phaeophyceae) and Palmaria decipiens (Rhodophyta) were sampled at three different newly ice-free areas in Potter Cove (Isla 25 de Mayo/ King George Island, Antarctica) at 5, 10, 20 and 30 m depth. After collection, photosynthesis ? irradiance (P-I) curves were obtained and used to calculate photosynthetic parameters. At each area, CTD profiles were performed. Photosynthetically active radiation (PAR, 400-700 nm) was logged continuously over seven days at each area. Subsequently, the DMCB was calculated using the obtained photosynthetic parameters and the underwater PAR data. During the first study year air temperatures were higher than in the second, resulting in a higher inflow of meltwater from the glacier into the cove, a higher turbidity of the seawater and a lower penetration of light into the water column. The study areas are exposed to a different level of sedimentation (low: area1, intermediate: area 2, and high: area 3), and the seaweeds are thus exposed to different light regimes. At area 1 with low sedimentation rates the lower vertical distribution limit of both species was 30 m depth, while in areas with intermediate and high sedimentation, it was 20 and 10 m depth, respectively. For both species, DMCB values were higher in the second study year compared to the first year and significantly higher in areas 1 and 2 compared to area 3. In 2011/2012 the DMCB values were too low or even negative for both species to explain their survival, while in 2012/2013 DMCB values were higher. Therefore, interannual physical variations need to be considered to better understand the observed macroalgal depth distribution in Potter Cove. The vertical zonation of the studied species is positively correlated to the light penetration which decreases as the glacial influence (as a result of the sediment inflow) increases. Multiple factors interacting in this changing scenario make predictions challenging and more information is needed in order to assess the potential changes of benthic algal communities due to global change in the long term.