CONICET | Buscador de Institutos y Recursos Humanos

We investigated the effects of ocean warming and glacial melting on phytoplankton assemblage composition and physiology in coastal Antarctica by exposing assemblages to a 4ºC increase in seawater temperature (T) and a 4 psu decrease in salinity (S) with respect to ambient values in a 6-day microcosm experiment. Seawater samples from Potter Cove in King George Island (Antarctica) were placed in 100-L outdoor microcosms and exposed to four treatments in triplicate: ambient S-ambient T (S0T0, control), low S-ambient T (S-T0), ambient S-high T (S0T+), and low S-high T (S-T+). The relative abundance of unsaturated fatty acids (FAs) 20:5ω3, 18:4ω3 and 16:1ω7 in relation to saturated FAs (14:0 and 16:0) significantly increased in all treatments after 24 h, compared to the control. A simultaneous increase in the production of Thiobarbituric Acid Reactive Substances (TBARS), used as a proxy for lipid damage from oxidative stress, was detected in the S-T0 and the S0T+ treatments most likely due to the high abundance of unsaturated FAs during the first 24 h. In contrast, in S-T+, concentrations of TBARS remained significantly lower than in the control until day 4 of the experiment. Although phytoplankton species composition did not change during the experiment, an increase in the relative abundance of diatoms (>20 µm) was found in all treatments compared to the control at 24 h, with no further changes for the rest of the experiment. Furthermore, the relative abundance of small diatoms (10-20 µm) increased only in S0T+, and small prasinophytes decreased at S-T+ at the end of the incubations. Therefore, the variations observed in FAs composition from 24 to 48 h were most likely due to changes in cellular metabolism and were not caused by changes in species composition.Overall, under a combined high temperature and lower salinity condition, the maintenance of a stable unsaturated to saturated FA ratio protect the cell from further lipid damage in comparison with phytoplankton exposed to high temperature or low salinity separately. Separate incubations for both conditions, modify the FA composition after 48 h with an increased proportion of unsaturated FAs and the consequent increment in lipid damage. It could be avoided with an antioxidant responses or suggested changes in survival mechanisms, such as osmoregulation proteins and FA synthesis by the activation or inactivation of desaturase enzymes. Changes in plankton quality as a food source can have critical implications for the entire food web under changing environmental conditions.

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