The objective of this study was to optimize the land-based cultivation of Ulva rigida by evaluating the effects of stocking density and nutrient management on biomass yield and physiological responses, with a particular focus on the availability of nitrogen and phosphorus. The influence of nutrient concentrations and algal stocking densities on growth rates, photosynthetic efficiency, and carbohydrate content was assessed through the implementation of nine distinct treatment conditions. The findings indicated that elevated nutrient/biomass ratios notably enhanced growth rates, biomass productivity, and ulvan content. Furthermore, the enhancement of photosynthetic parameters, including maximum electron transport rates (ETR) and non-photochemical quenching (NPQmax), was observed under nutrient-rich conditions, indicating the capacity of Ulva rigida to optimize its photoprotective mechanisms. Furthermore, the resilience of Ulva to abiotic fluctuations, including pH, salinity, and temperature, demonstrates its capacity to adapt to environmental variability. These findings highlight the potential of integrating nutrient management strategies to enhance the commercial viability of Ulva cultivation, which could facilitate its role in sustainable aquaculture and blue farming systems.

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.

The use of germling clusters derived from spontaneous sporulation offers a promising strategy to stabilize Ulva cultivation, particularly during reproductive events that compromise biomass yield. This study assessed the growth, photophysiological responses, and biochemical composition of unattached Ulva sp. germling clusters cultivated in flat-bag photobioreactors under two different nutrient supplement rates: nitrate additions of 50 or 500 µmol L⁻1 every 2 days, with phosphate supplied to maintain an N:P molar ratio of 10:1, over a 14-day period. Biomass density remained stable across treatments, suggesting limited growth. Higher nitrogen availability enhanced photosynthetic performance, as indicated by increased Fv/Fm, and promoted greater accumulation of chlorophyll a, b, and lutein. In contrast, nutrient-limited conditions stimulated the accumulation of phenolic compounds and ulvan, potentially as part of a stress-induced metabolic shift. Total protein content, estimated from total nitrogen, was higher under nitrogen-enriched conditions. These results demonstrate that photobioreactors can support the early-stage cultivation of Ulva germling clusters and enable modulation of biomass composition through nutrient management. This approach may contribute to improved flexibility and efficiency in land-based macroalgae production systems.

The toxic effects of copper (Cu) excess in brown macroalgae have been well characterized. However, the interactive effects of increased temperatures, associated with climate change, and Cu stress on these macrophytes remain almost unexplored. In this study, we exposed the model brown seaweed Ectocarpus to different Cu concentrations (0, 0.8, 1.6, and 3.2 μM) at two different temperatures (15 and 25 °C). Relative growth rates decreased at 25 °C for the two highest Cu concentrations after 8 days of exposure, but a contrasting pattern was observed in the photosynthetic maximum quantum yield (Fv/Fm) and photosynthetic efficiency (α), where reductions were observed at 15 °C for the same Cu concentrations. Although no differences among treatments were observed for chlorophyll a (Chla) and chlorophyll c (Chlc), a reduction in concentration of the accessory pigment fucoxanthin (Fx) was only observed at 15 °C in all Cu treatments. Interestingly, at 25 °C, 20.1% less total Cu (intracellular + extracellularly bound) accumulated compared to 15 °C upon exposure to 3.2 μM Cu. Likewise, 33.1 and 23.8% less Cu accumulated intracellularly at 25 °C after exposure to 1.6 μM and 3.2 μM Cu, respectively. Additionally, at 25 °C about half of the Cu ions accumulated intracellularly and half extracellularly compared to 15 °C, where Cu accumulated mostly intracellularly at the two highest Cu concentrations. The results presented here provide valuable information to better understand the interactive effects of increased temperature and excess Cu in the stress response of Ectocarpus, suggesting that increased temperature helps to offset the negative impacts of exposure to high Cu concentrations.

SUMMARY This study characterizes the ecophysiological responses and growth dynamics of Nitzschia palea isolated from Salar de Huasco, Chile, a high‐altitude wetland located at 3800 m above sea level. The culture was maintained at 17°C under cool‐white fluorescent light with a 14:10 h light/dark photocycle and a photon flux of 50 μmol photons m − 2 s −1 . The diatom was identified morphologically and genetically, with phylogenetic analysis confirming its close relationship to known N. palea strains. Photophysiological responses were measured along with a series of media and temperature conditions in N. palea strain. Modified f/2 media supplemented with different concentrations of Si, Se and vitamins were tested. Subsequently, growth in the double‐Si f/2 media was assessed at three different temperatures. Lastly, the diatom strain was incubated at 17°C and 27–29°C in f/2 + double‐Si (NN: non‐extra nutrient addition) and a highly eutrophic state of f/2 (WN: with nutrient enrichment addition). The highest growth was observed using the f/2 media WN at 17°C (day 5, 4.46 × 10 5 ± 3.15 × 10 4 SD cells mL −1 ). Temperature significantly influenced growth; 17°C supported higher cell densities and more stable photosynthetic parameters compared 27–29°C. Nutrient enrichment further enhanced photosynthetic efficiency (αETR) and maximal quantum yield ( F v / F m ), particularly under control temperature conditions. Photosynthetic performance, assessed via rapid light‐response curves, showed significant temperature and nutrient dependent variation. Nitzschia palea cultures at 27–29°C exhibited increased in relative maximal ETR (rETR max ,184.1 μmol m −2 s −1 ) compared to control conditions. In nutrient enriched treatments, photosynthetic efficiency peaked on day 5, but declined by day 8. These findings highlight the adaptive capacity of N. palea to fluctuating environmental conditions and underscore its potential as a model organism for studying diatom responses to nutrient and temperature stress in extreme ecosystems.

Gongolaria usneoides is a native brown alga in Europa, known for its high release of phenolics into the water. Rugulopteryx okamurae is a native brown macroalga from Asia but invasive in Europe, causing significant environmental and socioeconomic impacts. It has been observed that in some regions where Gongolaria is present, there is less biomass of Rugulopteryx, and they are often epiphytized by red filamentous algae. The present study aimed to analyze whether phenolics released in the seawater by G. usneoides affect the photosynthetic and biochemical responses in R. okamurae. To analyze the resilience of R. okamurae, algae were cultivated for 5 days in water with different percentages of phenolics released by G. usneoides (exposure phase) (0, 75, 150, 225 and 300 µg mL−1) in laboratory (20 °C, a 12:12 photoperiod, and PAR 190 µmol photons m−2 s−1 for a period of 115 h) and a period in the sun (4 h), followed 2 days cultured under phenolic-free water (recovery phase). Photosynthetic characteristics (Fv/Fm and ETR) and biochemical composition (phenolic, antioxidant activity, C, N and S) were measured (R. okamurae showed considerable photosynthetic declines without recovery when exposed to high concentrations of phenolics (225 and 300 µg mL−1). It can be inferred that the presence of G. usneoides in nature and the release of phenolic compounds by this alga may be affecting the invasive alga R. okamurae, potentially serving as a natural means to decrease or weaken the invasive species.

Physiological and biochemical responses to elevated temperatures were studied in the isomorphic tetrasporophyte (diploid) and gametophyte (haploid) phases of two Antarctic red macroalgal species (Sarcopeltis antarctica, former Gigartina skottsbergii - and Iridaea cordata), assessing whether ploidy affects the responses to extreme and fast warming events. The tetrasporophyte and gametophyte fronds of both species were exposed in the laboratory to 2 °C (control) and 8 °C (warming event) for up to 3 days. Photosynthetic performance and concentrations of chlorophyll a, total carotenoids, and mycosporine-like amino acids (MAAs) were determined. Inter-and intraspecific differences in physiological and biochemical responses to temperature were observed. Temperature increases slightly stimulated photosynthetic activity (Fv/Fm) over 15 % at 8 °C only in gametophytes of both species. Intraspecific variation in the content of MAAs and total carotenoids was also observed, with tetrasporophytes of S. antarctica and gametophytes of I. cordata evidencing a significative 60 % MAA content decrease (accompanied by a slight increase in total carotenoid) at 8 °C. These results highlight the role of carotenoids in the acclimation to elevated temperature and MAA content at the lowest ones. Although some intraspecific differences in the responses of haplo-diplontic life cycle phase were observed, there were low effects of exposure to 8 °C on photochemistry, outlining the physiological tolerance of both ploidy phases of intertidal species to extreme pulses of temperature increases in Antarctica.

Light variability is a key environmental stressor influencing the physiology and productivity of marine macroalgae. This study examined the ecophysiological and biochemical responses of Lessonia spicata (Ochrophyta) during a natural light deprivation event caused by a solar eclipse. We measured the in vivo chlorophyll a (Chla) fluorescence, photoinhibition, and photosynthetic capacity, along with the pigment content, phenolic compound accumulation, and antioxidant capacity, to evaluate short-term photosynthetic adjustments. Dark-adapted conditions during the eclipse peak led to reduced photosynthetic and biochemical activity, while post-eclipse recovery involved the increased accumulation of photosynthetic pigments and photoprotective compounds. Carotenoids showed high antioxidant potential under eclipse exposure, contrasting with declines in chlorophyll content and productivity under pre-eclipse high irradiance. This study provides valuable insights into the rapid acclimation mechanisms of Lessonia spicata to transient light stress, highlighting its sensitivity and resilience to sudden shifts in solar irradiance. These findings contribute to the broader field of marine macroalgal photobiology and stress physiology, enhancing our understanding of how intertidal brown algae adapt to dynamic environmental conditions.

Carbon dioxide (CO2) emissions due to human activities are responsible for approximately 80% of the drivers of global warming, resulting in a 1.1 °C increase above pre-industrial temperatures. This study quantified the CO2 assimilation and productivity of the brown macroalgae Lessonia spicata in the central Pacific coast of Chile, across seasonal and daily cycles, under different environmental stressors, such as temperature and solar irradiance. Measurements were performed using an infra-red gas analysis (IRGA) instrument which had a chamber allowing for precise quantification of CO2 concentrations; additional photophysiological and biochemical responses were also measured. CO2 assimilation, along with the productivity and biosynthesis of proteins and lipids, increased during the spring, coinciding with moderate temperatures (~14 °C) and high photosynthetically active radiation (PAR). Furthermore, the increased production of photoprotective and antioxidant compounds, including phenolic compounds, and carotenoids, along with the enhancement of non-photochemical quenching (NPQ), contribute to the effective photoacclimation strategies of L. spicata. Principal component analysis (PCA) revealed seasonal associations between productivity, reactive oxygen species (ROSs), and biochemical indicators, particularly during the spring and summer. These associations, further supported by Pearson correlation analyses, suggest a high but seasonally constrained photoacclimation capacity. In contrast, the reduced productivity and photoprotection observed in the summer suggest increased physiological vulnerability to heat and light stress. Overall, our findings position L. spicata as a promising nature-based solution for climate change mitigation.

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.

Warming oceans are reshaping coastal ecosystems, yet the thermal sensitivity of many foundation macroalgae remains poorly constrained. Under SSP2-4.5, sea surface temperatures are expected to rise by ~2.7 °C by 2100, with unknown consequences for the canopy-forming kelp Lessonia spicata. We exposed thalli to control (15 °C) and warming (18 °C) conditions for 14 days to simulate near-future thermal scenarios, assessing photophysiology, oxidative stress and pigment composition. Warming caused marked declines in Fv/Fm and ETRmax and increased NPQmax, signaling reduced photochemical efficiency and enhanced thermal energy dissipation. Simultaneously, pigment concentrations decreased, ROS and MDA accumulated, and antioxidant capacity dropped, indicating rapid disruption of cellular redox homeostasis. Our results demonstrate that even modest warming consistent with mid-century projections triggers immediate photophysiological impairment and oxidative stress in L. spicata. These mechanistic insights highlight potential vulnerability of kelp forests in central Chile as ocean temperatures continue to rise.

High-altitude wetland holds unique peatland ponds subjected to extreme diel environmental condition changes. Herein, we evaluate the response of photoautotrophic and nitrification activities and compare it with bacteria and archaea composition shifts in sediment and water changes during key hours of the day. Results indicate the presence of photo-inhibition, including ammonia oxidizers, but a high recovery of photosynthetic activities in the microbial mat and of potential specific functional groups towards the afternoon. The microbial community was composed of 45 phyla, mainly proteobacteria from Alpha-, Delta-, and Gammaproteobacteria and Bacteroidota in the water and sediments, and these later groups were notoriously enriched during the afternoon. The microbial community composition changes were associated with chlorophyll a, nutrients, and greenhouse gases reservoir variability, including methane potential release towards the atmosphere at hours of high radiation. Peatland pond microbial communities and their biogeochemical contribution change in a complex interplay coupled by time to environmental conditions predominantly driven by the extreme solar radiation.

Seawater desalination by reverse osmosis is growing exponentially due to water scarcity. Byproducts of this process (e.g. brines), are generally discharged directly into the coastal ecosystem, causing detrimental effects, on benthic organisms. Understanding the cellular stress response of these organisms (biomarkers), could be crucial for establishing appropriate salinity thresholds for discharged brines. Early stress biomarkers can serve as valuable tools for monitoring the health status of brine-impacted organisms, enabling the prediction of long-term irreversible damage caused by the desalination industry. In this study, we conducted laboratory-controlled experiments to assess cellular and molecular biomarkers against brine exposure in two salinity-sensitive Mediterranean seagrasses: Posidonia oceanica and Cymodocea nodosa. Treatments involved exposure to 39, 41, and 43 psu, for 6 h and 7 days. Results indicated that photosynthetic performance remained unaffected across all treatments. However, under 43 psu, P. oceanica and C. nodosa exhibited lipid oxidative damage, which occurred earlier in P. oceanica. Additionally, P. oceanica displayed an antioxidant response at higher salinities by accumulating phenolic compounds within 6 h and ascorbate within 7 d; whereas for C. nodosa the predominant antioxidant mechanisms were phenolic compounds accumulation and total radical scavenging activity, which was evident after 7 d of brines exposure. Finally, transcriptomic analyses in P. oceanica exposed to 43 psu for 7 days revealed a poor up-regulation of genes associated with brassinosteroid response and abiotic stress response, while a high down-regulation of genes related to primary metabolism was detected. In C. nodosa, up-regulated genes were involved in DNA repair, cell cycle regulation, and reproduction, while down-regulated genes were mainly associated with photosynthesis and ribosome assembly. Overall, these findings suggest that 43 psu is a critical salinity-damage threshold for both seagrasses; and despite the moderate overexpression of several transcripts that could confer salt tolerance, genes involved in essential biological processes were severely downregulated.

Baccharis macraei Hook. & Arn (Asteraceae), commonly known as Vautro, is found in the coastal areas of central-southern Chile, including the industrial zone of Quintero-Puchuncaví, known for the contamination of its soils with heavy metals, which together with other factors generate abiotic stress in plant species, against which they present defensive mechanisms. For this reason, the objective was to evaluate the effect of abiotic stress generated by the proximity of B. macraei to the industrial complex by assessing the physiological and metabolic states reported by the extracts and compounds isolated from the species, as well as the photosynthetic capacity, metal content and production, and antioxidant activity and cytotoxicity against tumorigenic cell lines of the phytoconstituents. To this end, B. macraei was collected at two different distances from the industrial complex, observing that the closer the species is, the greater the concentration of copper in the soil, generating a decrease in the rate of electron transport in situ, but an increase in antioxidant activity with low cytotoxicity. This activity could be due to the presence of flavonoids such as Hispidulin, Cirsimaritina, and Isokaempferida, as well as monoterpenes, oxygenated and non-oxygenated sesquiterpenes identified in this study.

Seagrasses, which are considered among the most ecologically valuable and endangered coastal ecosystems, have a narrowly limited distribution in the south-east Pacific, where Zostera chilensis is the only remaining relict. Due to water scarcity, desalination industry has grown in the last decades in the central-north coasts of Chile, which may be relevant to address in terms of potential impacts on benthic communities due to their associated high-salinity brine discharges to subtidal ecosystems. In this work, we assessed ecophysiological and cellular responses to desalination-extrapolable hypersalinity conditions on Z. chilensis. Mesocosms experiments were performed for 10 days, where plants were exposed to 3 different salinity treatments: 34 psu (control), 37 psu and 40 psu. Photosynthetic performance, H2O2 accumulation, and ascorbate content (reduced and oxidized) were measured, as well as relative gene expression of enzymes related to osmotic regulation and oxidative stress; these, at 1, 3, 6 and 10 days. Z. chilensis showed a decrease in photosynthetic parameters such as electron transport rate (ETRmax) and saturation irradiance (EkETR) under hypersalinity treatments, while non-photochemical quenching (NPQmax) presented an initial increment and a subsequent decline at 40 psu. H2O2 levels increased with hypersalinity, while ascorbate and dehydroascorbate only increased under 37 psu, although decreased along the experimental period. Increased salinities also triggered the expression of genes related to ion transport and osmolyte syntheses, but salinity-dependent up-regulated genes were mostly those related to the reactive oxygen species metabolism. The relict seagrass Z. chilensis has shown to withstand increased salinities that may be extrapolable to desalination effects in the short-term. As the latter is not fully clear in the long-term, and considering the restricted distribution and ecological importance, direct brine discharges to Z. chilensis meadows may not be recommended.

Desalination residual brines are mostly discharged to marine environments, which can produce osmotic stress on sensitive benthic organisms. In this investigation, we performed transplantation experiments nearby desalination plants using two brown macroalgae species from a cosmopolitan genus: Dictyota kunthii (Chile) and Dictyota dichotoma (Spain). Parameters related to photosynthetic activity and oxidative stress were evaluated at 3 and 7 days for D. kunthii, and 3 and 6 days for D. dichotoma; each at 2 different impacted sites and 1 control. We observed that brine exposition at both impacted sites in Chile generated a marked stress response on D. kunthii, reflected in a decrease of primary productivity (ETRmax), light requirement (Ek(ETR)), and an excessive thermal dissipation (NPQ(max)), especially at 7 days. In D. dichotoma, similar impaired photosynthetic activity was recorded but only at the highest brine influence site during day 3. Regarding oxidative stress, both species displayed high levels of H2O2 when exposed to brine-influenced sites. Although in D. kunthii H2O2 content together with lipid peroxidation was higher after 3 days, these returned to baseline values towards day 7; instead, D. dichotoma H2O2 levels increased only at day 6. This easy and practical approach has proven to provide valuable data to address potential impacts of brine discharges at global scale coastal ecosystems.

Senecio fistulosus, an endemic plant in Chile, is highly regarded for its medicinal properties and is popular in alternative medicine. It thrives even in polluted areas, like Puchuncaví Valley, Chile. Therefore, the study aimed to assess the impact of industrial pollution in Puchuncaví Valley, Chile, on the phytoconstituent content, as well as the antioxidant and cytotoxic activities, of S. fistulosus. Phenols, flavonoids, and anthraquinones content were measured, alongside the assessment of antioxidant activities. Additionally, a GC-MS analysis was conducted to profile the phytoconstituents, while the cytotoxic potential was evaluated in HT-29 and MCF-7 and cell line non-tumorigenic MCF-10. The Wild sample exhibited a greater concentration of phytoconstituents (0 to 169.48 mg·L−1) compared to the Commercial control (0 to 95.38 mg·L−1), directly correlating with its antioxidant activity. While the Wild species showed cytotoxic activity, the Commercial control demonstrated cytotoxic effects on MCF-10 and MCF-7. Noteworthy compounds identified were hexadecanoic acid (12.76 to 19.57% relative area) and (Z,Z,Z)-9,12,15-octadecatrienoic acid (18.36% relative area), with anticancer properties. In conclusion, the abiotic stress experienced by S. fistulosus led to higher phytoconstituent content and improved antioxidant activity when contrasted with the Commercial control. The Commercial species showed increased cytotoxic activity against both tumorigenic and non-tumorigenic cell lines.

Photosynthesis, growth and biochemical composition of the biomass of the freshwater microalga Chlamydopodium fusiforme cultures outdoors in a thin-layer cascade were investigated. Gross oxygen production measured off-line in samples taken from the outdoor cultures was correlated with the electron transport rate estimated from chlorophyll a fluorescence measurements. According to photosynthesis measurements, a mean of 38.9 ± 10.3 mol of photons were required to release one mole of O2, which is 4.86 times higher than the theoretical value (8 photons per 1 O2). In contrast, according to the fluorescence measurements, a mean of 11.7 ± 0.74 mol of photons were required to release 1 mol of O2. These findings indicate that fluorescence-based photosynthesis rates may not be fully replace oxygen measurements to evaluate the performance of an outdoor culture. Daily gross biomass productivity was 0.3 g DW L−1 day−1 consistently for 4 days. Biomass productivity was strongly affected by the suboptimal concentration at which the culture was operated and by the respiration rate, as the substantial volume of culture was kept in the dark (about 45

The Antarctic Peninsula is experiencing one of the highest warming rates globally. In polar regions, macroalgae thrive under extreme environmental conditions, which could worsen because of future climate change scenarios, including increased ultraviolet exposure, extremely low light availability, and fluctuating temperatures, particularly in the intertidal zones. To investigate the potential role of photoprotective and antioxidant mechanisms in response to future increases in sea surface temperatures caused by climate change, we conducted laboratory experiments using three intertidal macroalgae model species: Adenocystis utricularis (Ochrophyta, Phaeophyceae), Pyropia endiviifolia (Rhodophyta, Bangiophyceae), and Monostroma hariotii (Chlorophyta, Ulvophyceae). These algae were collected in Punta Artigas (King George Island, Antarctica) and acclimated at 2°C for 48 h. They were then assessed in laboratory experiments for up to 5 days under two treatments: (1) control conditions at 2°C and (2) elevated tem.perature conditions at 8°C, representing the most negative increment in SSTs estimated by the end of the 21st century. Carbon, nitrogen, pigments (chlorophylls and carotenoids), mycosporine-like amino acids (MAAs), and phenolic compounds were quantified after 3 and 5 days of exposure. For M. hariotii, elevated temperatures led to an increase in the C/N ratio, total antioxidant capacity, and levels of nitrogen, total carotenoids, chlorophyll-a, pigments (chlorophyll-b and violaxanthin), and phenolic compounds. For A. utricularis, elevated temperatures led to elevated C/N ratio and levels of chlorophyll-a and carotenoids (fucoxanthin and β-carotene). For P. endiviifolia, elevated temperatures resulted in elevated levels of carotenoids (lutein and β-carotene), phenolic compounds, and MAAs (porphyra-334, shinorine, and palythine). Thus, our study suggests that increasing water temperatures due to global warming can enhance the photoprotective abilities of three Antarctic intertidal macroalgae (M. hariotii, A. utricularis, and P. endiviifolia), with each species showing specific responses.