CONICET | Buscador de Institutos y Recursos Humanos

We investigated the effects of ocean warming and glacial melting on phytoplankton assemblage composition andphysiology in coastal Antarctica by exposing assemblages to a 4 °C increase in seawater temperature (T) and a4 psu decrease in salinity (S) with respect to ambient values in a 6-day microcosm experiment. Seawater samplesfrom Potter Cove in King George Island (Antarctica) were placed in outdoor microcosms and exposed to fourtreatments: ambient S-ambient T (S0T0, control), low S-ambient T (S-T0), ambient S-high T (S0T+), and low ShighT (S-T+). The relative abundance of unsaturated fatty acids (UFAs) 20:5ω3, 18:4ω3 and 16:1ω7 in relationto saturated FAs (14:0 and 16:0) significantly increased in all treatments at 24 h, compared to the control. At thesame time, we detected a significant increase in the production of Thiobarbituric Acid Reactive Substances(TBARS), used as a proxy for lipid damage, in the S-T0 and the S0T+ treatments. In contrast, in S-T+, concentrationsof TBARS remained significantly lower than in the control throughout the experiment. Althoughphytoplankton species composition did not change during the experiment, an increase in the relative abundanceof diatoms (> 20 μm) was found in all treatments compared to the control at 24 h, with no further changesduring the rest of the experiment. Furthermore, the relative abundance of small diatoms (10?20 μm) increasedonly in S0T+, and small prasinophytes decreased at S-T+ at the end of the incubation period.Our results show a stable unsaturated to saturated FA ratio under the synergistic effects of high temperatureand lower salinity, which may help protect phytoplankton cells from lipid damage. When phytoplankton assemblageswere exposed to high temperature or low salinity, separately, the proportion of unsaturated FAsincreased after 48 h. This increase in FAs resulted in greater lipid damage, which could be potentially avoided, asshown by previous studies, by antioxidant responses or changes in osmoregulatory proteins and FA synthesis bythe activation or inactivation of desaturase enzymes. Variations in FA content due to changing environmentalconditions can alter the quality of phytoplankton as a food source with potentially critical implications for themarine food web.