Contents lists available at ScienceDirect Journal of Experimental Marine Biology and Ecology journal homepage: www.elsevier.com/locate/jembe Effects of climate-induced changes in temperature and salinity on phytoplankton physiology and stress responses in coastal Antarctica Marcelo Hernando a, ⁎ , Diana E. Varela b , Gabriela Malanga c,d , Gastón O. Almandoz d,e , Irene R. Schloss f,g,h a Departamento Radiobiología, Comisión Nacional de Energía Atómica, Buenos Aires, Argentina b Department of Biology, School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada c IBIMOL-Fisico Química, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Argentina d CONICET, Argentina e División Ficología, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, Argentina f Instituto Antártico Argentino, Buenos Aires, Argentina g Centro Austral de Investigaciones Científicas (CONICET), Ushuaia, Tierra del Fuego, Argentina h Universidad Nacional de Tierra del Fuego, Ushuaia, Argentina ARTICLE INFO Keywords: Phytoplankton assemblages Antarctica High temperature Low salinity Antioxidant Biomass Nutrients ABSTRACT Coastal phytoplankton assemblages from Potter Cove in Antarctica were exposed to low salinity (S-) and high temperature (T+) conditions to simulate oceanic changes resulting from global warming. The treatments were: low salinity (30) and high temperature (S-T+); low salinity and ambient temperature (1–2 °C) (S-T0); ambient salinity (34) and increased temperature (4–5 °C) (S0T+) and ambient salinity with ambient temperature (control, S0T0). Experiments were conducted in 100-L microcosms and monitored for 6 days. Compared to the control treatment, micro-size diatoms (25–50 μm) dominated the phytoplankton assemblages while prasino- phyceae were less abundant at the end of the S-T+ and S0T+ treatments. Nano-size diatoms (10–20 μm) also increased significantly at the end of the experiment but only when exposed to S0T+. In S- treatments, the production of reactive oxygen/ nitrogen species (ROS/RNS) increased while phytoplankton biomass decreased. Under T+ conditions, the production of ROS/RNS was significantly lower than in T0 treatments. Throughout the experiment, α-Tocopherol (α-T) consumption may have prevented lipid damage, allowing for increases in photosynthetic rate and growth when nutrients concentrations were sufficiently high. Our results indicate that an increase in temperature can compensate for the lipid damage produced by low salinity, and stimulate carbon uptake in both conditions. This study demonstrated that the final composition of phytoplankton assemblages in all experimental treatments was strongly influenced by the original composition. Future changes in natural phytoplankton assemblages in Antarctic coastal waters will therefore depend on the planktonic species present at the time of the perturbation, which can strongly impact energy flow along food webs and the magnitude of carbon and nutrient fluxes in Antarctic waters. 1. Introduction Over the past few decades, the global greenhouse effect has been primarily responsible for the warming and freshening of Southern Ocean waters (Swart et al., 2018). The largest glacial ice mass loss in Antarctica was observed in the Western Antarctic Peninsula (WAP) (Spence et al., 2017), due to warming of subsurface continental shelf waters that melted the base of the glaciers (Schmidtko et al., 2014), contributing to greater freshwater inputs to coastal regions (Cape et al., 2019). Specifically, a significant temperature increase of seawater was recorded over the last decade at King George Island/25 de Mayo Island (South Shetland Islands) in Western Antarctic Peninsula (Falk and Sala, 2015). In view of the expected global air temperature rise of at least 1–3 °C over the next century (Bronselaer et al., 2018),coastal Antarctic eco- systems will likely be exposed to further warming and ice retreat. These changes in seasonal ice dynamics can result in increased water column stratification, which in turn affects mixing patterns, nutrient supply and light conditions (Schloss et al., 2012). Based on earlier experimental work, the composition of phytoplankton assemblages, photosynthetic https://doi.org/10.1016/j.jembe.2020.151400 Received 22 August 2019; Received in revised form 14 May 2020; Accepted 18 May 2020 ⁎ Corresponding author. E-mail address: mhernando@cnea.gov.ar (M. Hernando). Journal of Experimental Marine Biology and Ecology 530–531 (2020) 151400 0022-0981/ © 2020 Published by Elsevier B.V. T