Marine microalgae often live in a fluctuating environment including a decrease in salinity caused by global warming induced sea ice melting and freshwater inflows. Under conditions of fluctuating salinity, microalgae have evolved a variety of survival mechanisms such as lipid accumulation and remodeling. The purpose of this study was to investigated the membrane lipid remodeling of the marine green microalgaDunaliella tertiolectaas a short-term acclimation mechanism in response to hyposalinity (20 and 3 PSU) with respect to growth at optimal salinity (38 PSU). We identified 34 lipid species belonging to seven polar lipid classes.Dunaliella tertiolectaaccumulates cell lipids and remodels polar lipid classes and their fatty acids composition as response to hypoosmotic stress at 3 PSU. We found that the unsaturation of most polar lipids decreases overall, indicating decreased membrane fluidity and altered permeability, whereas shortening the length of fatty acids of polar lipids is not one of the strategies ofD. tertiolectato cope with the decrease in salinity. Increase in relative content (%) and unsaturation of monogalactosyldiacylglycerols (MGDG) and decrease in relative content (%) and unsaturation of phosphatidylglycerols (PG), suggesting changes in photosynthetic membranes of thylakoids at 20 and 3 PSU. At a very low salinity of 3 PSU, the relative content (%) of phosphatidylinositols (PI) increases, suggesting increased lipid trafficking and signaling in the cells. These changes are statistically significant and we hypothesize thatD. tertiolectais genetically adapted to withstand large salinity fluctuations through polar lipid composition.

Atmospheric bulk and wet deposition samples were collected simultaneously at the background coastal site in the Eastern Middle Adriatic region in order to assess the impact of major ions (Cl⁻, NO₃⁻, SO₄²⁻, Na⁺, K⁺, NH₄⁺, Mg²⁺, Ca²⁺) on deposition acidity and distinguish the main sources. Higher ion levels were observed during the cold period, especially for Cl⁻, Na⁺, Mg²⁺ and K⁺. Dust intrusion caused significant increases in levels of Ca²⁺, Mg²⁺ and K⁺, while open-fire events increased the levels of K⁺. Deposition acidity showed seasonal differences as well as the influence of dust intrusion. Low ionic balance ratios indicated acidic deposition properties and the presence of organic anions. The highest neutralization ability was found for Ca²⁺, Na⁺ and NH₄⁺. Several natural (marine, crustal) and anthropogenic sources were determined, as well as the formation of secondary aerosols. Wet deposition was characterized by higher contribution of sea salt fraction compared to bulk deposition and lower contribution of crustal fraction.

Nitrated monoaromatic hydrocarbons (NMAHs) are emerging air pollutants commonly found in biomass burning (BB) and anthropogenic aerosols (AA). Despite their frequent deposition into aquatic systems, their ecotoxicity is still poorly understood. This study evaluates the toxicity of BB and AA aerosol extracts and their main NMAH constituents (nitrocatechols, nitrophenols, and nitrosalicylic acids) using in vitro (cellular uptake, cytotoxicity) and in vivo (algal growth inhibition, zebrafish embryo development) bioassays. Polar aerosol extracts showed higher toxicity than nonpolar ones, with stronger interaction via zebrafish organic anion Oatp1d1 than organic cation Oct1 transporter, indicating selective uptake. NMAHs and their relevant mixtures showed similar toxicity patterns as BB water extract, so NMAHs were identified as contributors to aerosol toxicity. Nitrocatechols stand out for their toxicity, showing the highest chronic toxicity in algae (IC₅₀: 0.6–1.1 mg/L) and acute cytotoxicity in fish cells (IC₅₀: 2.0–4.1 mg/L), possibly because they dominated the NMAHs composition of aerosols (BB: 80.6%; AA: 79.8%). Sublethal NMAH concentrations caused developmental disorders and altered lipid homeostasis in zebrafish embryos, indicating early physiological stress on higher organisms. These findings reveal NMAHs as significant ecotoxic components of BB and AA emissions which may pose an increasing threat to aquatic ecosystems following atmospheric deposition.

Biochemical responses of oligotrophic Adriatic Sea surface layers to atmospheric deposition inputs Frka1, A. Miliković1, A. Penezić1, S. Bakija Alempijević1, B. Gašparović1, S. Skejić2, D. Šantić2, S. Brzaj3, V. Džaja Grgičin3, S. Vidič3, I. Šimić4, I. Bešlić4, S. Žužul4, R. Godec4, G. Pehnec41Division for marine and environmental research, Ruđer Bošković Institute, Zagreb, Croatia2Institute of Oceanography and Fisheries, Split, Croatia3Croatian Meteorological and Hydrological Service, Zagreb, Croatia4Institute for Medical Research and Occupational Health, Zagreb, Croatia The atmosphere is a significant pathway by which both natural and anthropogenic material is transported from continents to both coastal and open seas. Once deposited through atmospheric deposition (AD) processing, atmospheric particulate matter (PM) provides the aqueous ecosystems with an external source of nutrients and pollutants. This, in turn, influences the organic matter (OM) production by the phytoplankton, changes CO2 uptake and indirectly affects the climate. The input of AD is especially important in oligotrophic environments and it is expected to increase in the future scenarios of a warmer atmosphere with increased PM emissions and deposition rates. While the majority of the data related to the AD impacts generated so far in the Mediterranean have been conducted on its western and eastern regions, the effects of the AD inputs to oligotrophic surface waters of the Adriatic Sea sub-basin are unknown. This work is designed to assess the impact of AD on complex biochemical responses of Adriatic oligotrophic systems, considering the sea surface microlayer (SML) at the air-water interface.Field campaign was conducted during the period of retrieval of sea surface oligotrophic conditions (February-July 2019) at the Martinska, Central Adriatic, Croatia. On-line black carbon (BC) concentrations were measured while the PM10, wet and total deposition samples as well as the SML and underlying water (ULW; 0.5 m depth) samples were collected simultaneously. The temporal dynamics of the SML biology as well as concentrations of  inorganic and organic constituents enabled the assessment of their sources and the nature of the enrichments taking place within the SML. The first comprehensive insight into concentration levels of macro nutrients (N, P), trace metals (eg. Cu, Pb, Cd, Ni, Zn, Co) and OM (including aromatic pollutants) in atmospheric samples, their transport history, source apportionment and deposition fluxes to the oligotrophic Adriatic area will be presented. Daily and seasonal variations of PM10 composition were affected by local traffic and open-fire events as well as by local meteorological conditions and long-range transport. The BC contribution of biomass burning versus fossil fuel combustion changed seasonally. Source apportionment module of LOTOS-EUROS chemical transport model enabled identification and quantification of main source areas contributing to deposition of PM. The main PM contributor is a public power sector outside Croatia while other contributing sectors are energy production, traffic, residential combustion as well as shipping. First deposition fluxes estimates show reasonable agreement between model calculations and measured data, and could be used for more general assessments of atmospheric inputs. Acknowledgment: This work has been supported by Croatian Science Foundation under the IP-2018-01-3105 project: Biochemical responses of oligotrophic Adriatic surface ecosystems to atmospheric deposition inputs.