Antarctica is experiencing one of the fastest warming rates globally, profoundly impacting seawater temperature and salinity, with direct consequences for marine life. The present study examined the combined effects of salinity fluctuations at 20, 33 (control salinity), and 41 psu, and temperatures of 2 °C (control temperature) and 8 °C (thermal stress) for 3 days, on the health and physiology of the Antarctic intertidal macroalga Adenocystis utricularis. Photosynthetic activity, photoinhibition, and photoprotective processes were assessed alongside biomarkers of oxidative stress/damage (total ROS, lipid peroxidation, and protein carbonylation) and antioxidant/osmotic response (ascorbate, free amino acids, and proline). The results showed that maximum quantum yield (Fv/Fm) remained stable under both salinity and thermal stress. However, productivity (ETRmax), the photoprotection index (NPQmax), and irradiance saturation (EkETR) were significantly decreased at 8 °C, remaining constant under salinity fluctuations. At 2 °C, oxidative stress and damage were significantly higher under hypo- and hypersalinity conditions. However, at 8 °C, oxidative stress indicators decreased, accompanied by increased ascorbate levels in both hypo- (20 psu) and hypersalinity (41 psu) treatments compared to the control salinity. While warming temperatures negatively altered the oxidative response of A. utricularis at a 33 psu, we report here an interactive effect between salinity and temperature, leading to an altered stress response to salinity fluctuations under thermal stress. This study provides key information to better understand the adaptation of Antarctic intertidal macroalgae to multifactor climate change consequences.

Microorganisms play a crucial role in maintaining ecosystem functions by transforming matter and energy. The impact of environmental perturbations on the cycling and loss of aquatic microbial communities remains poorly characterized, particularly in the Southern Hemisphere. Here, we present the shifts in active microbial community and the maintenance of glacier-derived microbial core along the Aconcagua Basin, Central Chile. Through metabarcoding of the 16S rRNA transcripts and genes in water samples from 13 sites along the river continuum—including glacier-influenced headwaters, mining-proximal zones, agro-industrial reaches, and estuarine environments—distinct shifts in microbial community composition were observed. Glacier-fed waters harbored rich, cold-adapted microbial communities with elevated viral pressure, while mining and/or natural acid drainage promoted the dominance (up to 52% relative abundance) of sulfur-oxidizing bacteria (SOB) and reduced overall diversity. Among the SOB taxa, Thiovirga, Sulfuricurvum, and Thiobacillus-affiliated ASVs dominated together with minor taxa such as Thiomonas, Longilinea, Alishewenella, and Acidithiobacillus. Downstream, runoff and wastewater inputs from agricultural and urban areas altered microbial assemblages, introducing new taxa (e.g., C39 and Cellvibrio) and further diminishing glacier-derived core members. Estuarine sites exhibited pronounced eutrophication and significant loss of upstream microbial diversity. Along the basin, the virus-to-prokaryotes ratio gradually decreased (i.e., 95 to 5) from the glacier-fed lagoon with low prokaryotic biomass to the estuarine wetland with high virus and prokaryotic abundances. This study underscores the importance of integrating microbial diversity into water resource management and conservation policy to ensure ecosystem resilience amid climate change and intensifying human impacts.

In the central region of Chile, the Mega-Drought together with the demographic increase near the coast threatens groundwater availability and the hydrogeological functioning of coastal wetlands. To understand the hydric relationship between an aquifer and a wetland in a semi-arid coastal region of Central Chile (Valparaíso, Chile), as well as its geoenvironmental effects, four data collection campaigns were conducted in the wetland–estuary hydric system and surroundings, between 2021 and 2022, including physical, hydrochemical, and isotopic analyses in groundwater (n = 16 sites) and surface water (n = 8 sites). The results generated a conceptual model that indicates a hydraulic connection between the wetland and the aquifer, where the water use in one affects the availability in the other. With an average precipitation of 400 mm per year, the main recharge for both systems is rainwater. Three specific sources of pollution were identified from anthropic discharges that affect the water quality of the wetland and the estuary (flow from sanitary landfill, agricultural and livestock industry, and septic tank discharges in populated areas), exacerbated by the infiltration of seawater laterally and superficially through sandy sediments and the estuary, increasing salinity and electrical conductivity in the coastal zone (i.e., 3694 µS/cm). The Del Sauce subbasin faces strong hydric stress triggered by the poor conservation state of the riparian–coastal wetland and groundwater in the same area. This study provides a detailed understanding of hydrological interactions and serves as a model for understanding the possible effects on similar ecosystems, highlighting the need for integrated and appropriate environmental management.

Although Quintero-Puchuncaví Bay, Chile, is a coastal area historically known to be subject to multiple industrial pressures, few studies have focused on the associated risks to marine ecosystems and, through edible species, to human health. We studied concentrations of Cd, Cr, Cu, Mn, Pb, V, Zn, and Hg in marine species and sediments from Quintero-Puchuncaví Bay and a reference site. Results were compared with seafood safety guidelines, and target hazard quotients (THQs) were evaluated. Sediments and biota from the impacted area generally exhibited higher metal concentrations. Zinc (Zn) and copper (Cu) levels were the highest across all species, particularly in crustaceans, reflecting both physiological requirements and anthropogenic inputs. Cadmium (Cd) concentrations were higher in pelagic species from the impacted bay, but no differences were found in sediments or benthic species, suggesting the influence of upwelling conditions. Comparison with seafood safety guidelines revealed that Cd and Pb concentrations exceeded permissible limits in crabs, fish, and mussel species, and THQ ≥ 1 values were found for Cd concentrations in benthic species from the impacted bay, highlighting potential risks to consumers. The absence of permissible thresholds for certain environmentally relevant metals in Chilean regulations underscores the need to align with international standards, certainly to protect coastal ecosystems and human health.

The Antarctic intertidal zone hosts ecologically pivotal holobionts such as the brown macroalga Adenocystis utricularis, whose response to climate-driven stressors remains poorly understood. Here, we applied an integrative holobiont framework combining microbial community profiling, host physiological assays, and phycosphere metabolomics to assess how thermal stress (2°C vs. 8°C) influences microbiome dynamics, host stress responses, and algal surface chemistry after 5 days under experimental conditions. Results showed that warming induced a transient reduction in microbial diversity, with Shannon diversity decreasing at Day 3 under 8°C and returning to levels comparable to the control by Day 5, accompanied by marked community structural reorganization. Elevated temperature enriched Campylobacteria and Gammaproteobacteria, while Bacteroidia and Verrucomicrobia decreased. Functional predictions revealed a shift from nutrient cycling and carbon turnover at 2°C toward heterotrophy, fermentation, and bacterivory-related pathways at 8°C. Microbiome disruption was associated with impaired photosynthetic performance, increased oxidative damage, reduced antioxidant defenses, and altered osmolyte accumulation, under warming conditions. Untargeted metabolomics uncovered pronounced thermal reprogramming of the algal surface metabolome, with >98% of detected features remaining chemically uncharacterized. Detected key metabolites included ceramides, N-acyl amino acids, and amphipathic compounds with putative cytotoxic or antioxidant activities, many of which increased under 8°C. Together, these findings demonstrate that A. utricularis response to thermal stress emerges from dynamic host–microbiome–metabolome interactions. By linking microbial restructuring, host physiology, and metabolomic plasticity, our study highlights the holobiont as the operative unit of adaptation in Antarctic coastal ecosystems facing climate change.