Ocean warming and freshening effects on lipid metabolism in coastal Antarctic phytoplankton assemblages dominated by sub-Antarctic species

Abstract

Marine phytoplankton can utilize different strategies to cope with ocean warming and freshening from glacialmelting in polar regions, which are disproportionally impacted by global warming. In the present study, we investigatedthe individual and combined effects of a 4 °C increase in seawater temperature (T+) and a 4 psu decreasein salinity (S−) from ambient values on biomass, nutrient use, fatty acid composition and lipid damagebiochemistry of natural phytoplankton assemblages from Potter Cove (25 de Mayo/King George Island,Antarctica). Experiments were conducted by exposing the assemblages to four treatments during a 7-day incubationperiod using microcosm located along shore from January 23 to 31, 2016. The N:P ratio decreased in alltreatments from day 4 onwards, but especially under high temperature (T+). Lipid damage was mainly detected under S0T+ and S−T+ conditions, and it decreased when the production of the antioxidant α-tocopherol increased.This antioxidant protection resulted in a build-up of phytoplankton biomass, especially at T+. Underthe combined effect of both stressors (S−T+), the concentration of ω3 fatty acids increased, potentially leadingto higher-quality FA composition. These results, which were related to the dominance of sub-Antarctic speciesin phytoplankton assemblages, contribute to the understanding of the potential consequences of oceanwarmingand increase seawater freshening on the trophic webs of the Southern Ocean.