Glacier melting effects on coastal Antarctic phytoplankton ecophysiology

SCHLOSS, I. R.; HERNANDO, M.; MALANGA, G.; ALMANDOZ G. O.; FERREYRA, G. A.; AGUIAR, M.B:; PUNTARULO, S.

Auckland

Conferencia; XXXIII SCAR Open Science Conference; 2014

SCAR

Glacier melting, a consequence of air temperature increase in Antarctica, adds freshwater to surface coastal marine waters. During austral summer 2010 the effects of low salinity on Antarctic phytoplankton assemblages? composition as well as on the microbial community production and response to hypo-osmotic stress were studied in situ in two coastal environments presenting a different degree of influence from glacier melting in Potter Cove (King George Island/25 de Mayo, South Shetlands). In order to experimentally test the field observations, in both 2010 and 2011 natural plankton was exposed during 8-10 days to a low salinity treatment (LST, 30 PSU) and a control, normal salinity treatment (NST, 34 PSU) in controlled microcosms. Community primary production was measured by means of the oxygen exchange method both in the experiments and in the field. An inhibition of community production was observed in both studies, and of instantaneous growth rate in the microcosms? experiments. However, in this last case growth recovered some days later, becoming significantly higher in LST than in NST at the end of the experiment. Total phytoplankton biomass was lower in LST than in NST and in the low-salinity waters in the field. These results were confirmed by the 2011 experiments. Here, two different phytoplankton assemblages developed: while in the control big centric diatoms (Odontella weissflogii, Porosira glacialis and chains of Thalassiosira antarctica, Chaetoceros tortissimus and C. socialis) were the most abundant phytoplankton species, comparable to those found in the field under similar conditions, relatively smaller pennate diatoms (Navicula glaciei, N. perminuta, Nitzschia cf. lecointei and Fragilariopsis cylindrus/nana) dominated the assemblage in LST. 2- Thiobarbituric acid reactive substances (TBARS) and dichlorofluorescein diatetate (DCF-DA) oxidation (both oxidative stress damage indices), were significantly higher in the low salinity field samples and in LST than in the experimental control on days 4 and 6 of exposure, but later these last values decreases to initial levels. This coincided with a significant increase in the concentrations of lipophilic antioxidants á-tocopherol (áT) and â carotene (âC) in LST. Our results suggest the existence of selective protection mechanisms against lipid peroxidation in some diatom species, which in turn could be the driving force to deeply alter the composition of the phytoplankton assemblage and its potential role in carbon fixation under hypo-osmotic stress conditions.