Introduction: Ocean acidification (OA), resulting from the absorption of increasing atmospheric CO₂ by the oceans, represents a major threat to marine organisms. Despite growing concern, the biochemical responses of Antarctic species to OA remain poorly understood.

Methods: This study investigated the impact of OA (pH 7.70 ± 0.09) on the fatty acid (FA) composition of the Antarctic snail Neobuccinum eatoni over a two-month experimental period (December 2015–March 2016). Fatty acid profiles were analyzed in multiple tissues to assess potential alterations induced by low-pH (LpH) conditions.

Results: Significant tissue-specific changes in FA composition were detected, particularly in the mantle and gill. Under LpH exposure, notable modifications occurred in long-chain polyunsaturated fatty acids (LC-PUFAs) such as 22:5n-3, 22:6n-3, and 24:5n-6. Elevated LC-PUFA levels in the mantle suggested a compensatory response to oxidative stress, while shifts in the n-3/n-6 ratios in the gill pointed to potential alterations in immune and anti-inflammatory functions.

Discussion: Indicators of homeoviscous adaptation (HVA), including PUFA/SFA ratios and mean chain length (MCL), revealed biochemical strategies used by N. eatoni to maintain membrane fluidity under acidified conditions. This study provides the first evidence of FA-based responses to elevated pCO_₂ in an Antarctic gastropod, highlighting the potential of fatty acids as sensitive biomarkers of physiological adaptation to environmental stressors.

Guidelines for ecotoxicity testing with Daphnia magna specify particular feeding protocols during the exposure, yet standardization for preexposure feeding remains ambiguous despite its recognized significance in affecting organismal metabolic capacity and tolerance. This ambiguity may contribute to disparate responses and heightened uncertainty in determining the effect concentrations of test chemicals, particularly those inducing metabolic effects through narcosis. Here, we address this gap through a three-step doseresponse experiment with neonates of D. magna subjected to two alternative feeding regimes in the preexposure phase: starved and moderately fed during the first 24 hr after birth. Following this treatment, the daphnids were exposed to narcosis-inducing substances (polycyclic aromatic hydrocarbons; PAHs) for 72 hr before being transferred to clean media with algal food ad libitum for a 48 hr recovery phase. Daphnid survivorship, individual protein content, and body size at the end of each experiment phase-pre-exposure, postexposure and postrecovery-were compared between the treatments. Significant treatment effects were observed, including lower and less variable protein content in the starved daphnids entering the PAH exposure phase, yet higher survivorship and greater recovery potential in these daphnids compared with the fed individuals. Our findings underscore the importance of early-life food access and advocate for mandatory reporting of pre-exposure feeding regimes, particularly when testing substances acting via nonpolar narcosis.

Guidelines for ecotoxicity testing with Daphnia magna specify particular feeding protocols during the exposure, yet standardization for preexposure feeding remains ambiguous despite its recognized significance in affecting organismal metabolic capacity and tolerance. This ambiguity may contribute to disparate responses and heightened uncertainty in determining the effect concentrations of test chemicals, particularly those inducing metabolic effects through narcosis. Here, we address this gap through a three-step dose-response experiment with neonates of D. magna subjected to two alternative feeding regimes in the preexposure phase: starved and moderately fed during the first 24 hr after birth. Following this treatment, the daphnids were exposed to narcosis-inducing substances (polycyclic aromatic hydrocarbons; PAHs) for 72 hr before being transferred to clean media with algal food ad libitum for a 48 hr recovery phase. Daphnid survivorship, individual protein content, and body size at the end of each experiment phase—pre-exposure, postexposure and postrecovery—were compared between the treatments. Significant treatment effects were observed, including lower and less variable protein content in the starved daphnids entering the PAH exposure phase, yet higher survivorship and greater recovery potential in these daphnids compared with the fed individuals. Our findings underscore the importance of early-life food access and advocate for mandatory reporting of pre-exposure feeding regimes, particularly when testing substances acting via nonpolar narcosis.

Ocean acidification (OA) and ocean warming (OW) are likely to alter the biochemical composition of certain organisms as a physiological response to these changing environmental conditions. Given the importance of fatty acids (FA) in energy transfer within marine food webs, this two-month laboratory study examines the response of two calcifying species from Potter Cove (Antarctica) - the bivalve Aequiyoldia eightsii and the coral Malacobelemnon daytoni - to predicted OA and OW, focusing on their FA profiles. Neither species showed significant changes compared to the control group in the composition of FA ratios associated with immune function and cell membrane fluidity in response to either OA or OW. Additionally, the FA composition related to inflammatory responses remained largely unaffected by the stressors, although the 20:5n-3 FA was negatively impacted in A. eightsii under high-temperature conditions. Overall, the FA composition in these species appears robust to near-future environmental changes.

The risk assessment of chemicals relies on multiple tools to quantify the ecological responses of ecosystems to existing chemical pollution. These tools are broadly categorized into three major groups: toxic pressure assessments, bioassays, and ecological monitoring. Here, we examine the strengths and limitations of these approaches, their current level of implementation for freshwater ecosystems across Europe, and their ability to evaluate the impacts of chemicals under field conditions. Additionally, we analyze the correspondence between results obtained from these tools when applied to a monitoring dataset from German streams. Our evaluation showed that no single tool can perfectly characterize the environmental impacts of chemical mixtures. However, each provides distinct lines of evidence, enabling the identification of chemicals driving ecological risks and the biological endpoints most likely to be affected, with ecological monitoring tools having the potential to show long-term ecosystem impairment. Finally, we propose recommendations to better understand the discrepancies between the outcomes of different methods and explore their potential integration into a unified water quality evaluation framework.

Plastic contamination in the Southern Ocean is a growing issue. This study provides the first comprehensive analysis of marine microplastics (MPs) (0.1–5 mm) in surface sediments in Potter Cove and nearby areas around Argentina's Carlini station (25 de Mayo/King George Island, South Shetlands). Sediment samples from 31 sites (2020−2022) were collected to examine whether MP pollution originates from station activities or ocean currents. All samples contained MPs, averaging 0.18 ± 0.12 MPs/g of sediment, mainly microfibers (MFs) and irregular microfragments (MFRs) (0.11–6.23 mm) and irregular microfragments (MFRs) (0.09–4.57 mm). Infrared spectroscopy identified 13 polymer types, including cellulosic materials, polyester, and polyamide, with most MPs < 1 mm, showing aging signs, similar to laundry wear. This widespread distribution suggests contamination may stem from both local activities and external sources. Findings underscore the urgent need for MP pollution management and further research to identify sources and develop effective mitigation strategies.

Plastic pollution in the Southern Ocean around Antarctica is a growing concern, but many areas in this vast region remain unexplored. This study provides the first comprehensive analysis of marine microplastic (MPs) concentrations in Potter Cove, located near the Argentinian Carlini research station on 25 de Mayo/King George Island, Antarctica. Water samples were collected at 14 sites within the cove, representing various influences from the station's activities. Two sampling methods were used: a 5 L Niskin bottle and an in-situ filtering device called Microfilter, allowing for large water volumes to be filtered. MPs were found in 100 % of the samples. Microfilter samples ranged from 0.02 to 2.14 MPs/L, with a mean concentration of 0.44 ± 0.44 MPs/L. Niskin bottle samples showed concentrations from 0.40 to 55.67 MPs/L, with a mean concentration of 19.03 ± 18.21 MPs/L. The dominant types of MPs were anthropogenic black, transparent, and pink microfibers (MFs) measuring between 0.11 and 3.6 mm (Microfilter) and 0.06 to 7.96 mm (Niskin bottle), with a median length of 0.01 mm for both methods. Transparent and black irregular microfragments (MFRs) with diameters from 0.10 to 5.08 mm and a median diameter of 0.49 mm were also prevalent. FTIR-spectroscopy revealed the presence of 14 types of polymers. Cellulose-based materials and polyethylene terephthalate were the most abundant in MFs, while polyurethanes and styrene-based copolymers dominated in MFRs. MPs were more abundant near the Carlini station. Compared to other coastal Antarctic areas, the MPs in the cove were relatively abundant and mostly smaller than 1 mm. Local activities on the island were identified as the primary source of MPs in the cove, and the cyclonic water circulation likely affects the distribution of small-sized particles. To protect the ecosystem, reducing plastic usage, improving waste management, regulating MPs debris, and enhancing wastewater practices are essential.

Some worldwide marine regions have been invaded by introduced species more than others, and those accruing a large number of introduced species are identified as hotspot areas. The southern Southwest Atlantic (SWA) is a vast region that has a variety of heterogeneous environments that are affected by different environmental and anthropogenic drivers and have been colonized by many introduced species. Nevertheless, a comprehensive analysis considering all these aspects together to identify hotspots of introduced species has not been developed, nor has a statistically based procedure to define and identify these hotspots been produced. Therefore, the main objectives of this study were to (1) quantify the spatial richness of introduced species (ISR) in the SWA, (2) identify introduced species hotspots, (3) explore the environmental and anthropogenic drivers that explain the ISR pattern and the assemblage composition of introduced species in these hotspots, and (4) assess the variation in the assemblage species composition among the introduced species in the identified hotspots. Six different hotspots were identified. The ISR in these hotspots was significantly explained by a set of environmental (maximum and minimum sea surface temperature, distance to shore, maximum salinity) and anthropogenic drivers (maritime traffic density, distance to the nearest port). Assemblage composition was related only to the environmental predictors. The variation in assemblage composition showed heterogeneity among introduced species hotspots. Our study shows that mapping introduced species hotspots and identifying them through spatial statistics facilitates the synthesis and integration of information objectively. This represents a cutting-edge approach to prioritize areas for management and adopt policies for the SWA.

Southern Ocean organisms are considered particularly vulnerable to Ocean acidification (OA), as they inhabit cold waters where calcite-aragonite saturation states are naturally low. It is also generally assumed that OA would affect calcifying animals more than non-calcifying animals. In this context, we aimed to study the impact of reduced pH on both types of species: the ascidian Cnemidocarpa verrucosa sp. A, and the bivalve Aequiyoldia eightsii, from an Antarctic fjord. We used gene expression profiling and enzyme activity to study the responses of these two Antarctic benthic species to OA. We report the results of an experiment lasting 66 days, comparing the molecular mechanisms underlying responses under two pCO2 treatments (ambient and elevated pCO2). We observed 224 up-regulated and 111 down-regulated genes (FC >= 2; p-value <= 0.05) in the ascidian. In particular, the decrease in pH caused an upregulation of genes involved in the immune system and antioxidant response. While fewer differentially expressed (DE) genes were observed in the infaunal bivalve, 34 genes were up -regulated, and 69 genes were downregulated (FC >= 2; p-value <= 0.05) in response to OA. We found down -regulated genes involved in the oxidoreductase pathway (such as glucose dehydrogenase and trimethyl lysine dioxygenase), while the heat shock protein 70 was up-regulated. This work addresses the effect of OA in two common, widely distributed Antarctic species, showing striking results. Our major finding highlights the impact of OA on the non-calcifying species, a result that differ from the general trend, which describes a higher impact on calcifying species. This calls for discussion of potential effects on non-calcifying species, such as ascidians, a diverse and abundant group that form extended three-dimensional clusters in shallow waters and shelf areas in the Southern Ocean.

Deep-sea benthic communities from the Weddell Sea, Antarctica, were sampled in January–April 2005 in an area located between 61°S–70°S and 0°W–49°W. We found a total of eight ascidian species that belong to five different families, of which one corresponded to a new species. These were: Protoholozoa pedunculata Kott, 1969; Corynascidia suhmi Herdman, 1882; Styela andeepensis Maggioni & Tatián sp. nov.; Culeolus suhmi Herman, 1881; Culeolus anonymus Monniot F. & Monniot C., 1976; Culeolus likae Sanamyan K. & Sanamyan N., 2002; Oligotrema lyra (Monniot C. & Monniot F., 1973) and Asajirus indicus (Oka, 1913). We report: the extension of the known distribution ranges of P. pedunculata, Corynascidia suhmi, Culeolus suhmi, C. likae and A. indicus, being the first time they are collected from the Weddell Sea; and the shallowest record of C. likae. Six species were added to the list of ascidians of the Weddell Sea, being all deep-sea representatives. While the total number of ascidian species augmented from 43 to 49, the number of deep-sea representatives increased from 23 to 29. Our findings, thus, reinforce the need of performing more deep-sea prospections in the area.