Antarctic Marine Research Articles

Occurrence of microplastics in Antarctic fishes: Abundance, size, shape, and polymer composition

Presence of microplastics (MPs) in Antarctic ecosystems has attracted global attention, due to the potential threat to the Antarctic marine organisms. However, data on the occurrence of MPs in Antarctic fishes remains very limited. This study investigated the abundance and characteristics of MPs in four species of Antarctic fish (n = 114). The highest mean abundance of MPs was detected in Trematomus eulepidotus (1.7 ± 0.61 items/individual), followed by that in Chionodraco rastrospinosus (1.4 ± 0.26 items/individual), Notolepis coatsi (1.1 ± 0.57 items/individual), and Electrona carlsbergi (0.72 ± 0.19 items/individual). MPs in Notolepis coatsi (mean 747 μm) had the highest mean size, followed by that in Trematomus eulepidotus (653 μm), Chionodraco rastrospinosus (629 μm), and Electrona carlsbergi (473 μm). This is possibly attributed to the feeding habits and egestion behaviors of different Antarctic fishes. Fiber was consistently the predominant shape of MPs in Trematomus eulepidotus, Chionodraco rastrospinosus, and Electrona carlsbergi, accounting for 82 %, 76 %, and 60 % of total items of MPs, respectively. Polypropylene, polyamide, and polyethylene were the predominant polymer composition of MPs in Antarctic fishes, collectively contributed 63–86 % of total items of MPs. This may be because these types of MPs have been widely used in global household materials. To our knowledge, this is the most comprehensive study examining the occurrence of MPs in Antarctic fishes. This study provides fundamental data for evaluating the risks of MP exposure for Antarctic fishes.

Sex‐specific mercury levels in skin samples of southern elephant seals (Mirounga leonina) at Isla 25 de Mayo (King George Island), Antarctic Peninsula

AbstractThe southern elephant seal (SES; Mirounga leonina) has a circumpolar distribution, breeding mainly on sub‐Antarctic islands and making long trips between breeding or molting and foraging areas. Most individuals from colonies in the South Shetland Islands (western Antarctic Peninsula; WAP) are distributed in Antarctic Specially Protected Areas (ASPA). Despite these protected habitats, pollutants can reach such remote areas far away from emission sources, affecting local fauna. To assess possible mercury (Hg) contamination in SES, we analyzed skin samples collected from free‐ranging molting individuals using the remote biopsy PAXARMS system in Isla 25 de Mayo/King George Island (62°15′S, 58°39′W; ASPA 132). Hairless skin samples were analyzed to determine total‐Hg (THg) concentrations, which ranged between 145 ng/g and 1,915 ng/g (M = 730, SD = 388 ng/g), showing significant differences between sexes, with adult‐females having higher concentrations (range = 306–1,915, M = 859, SD = 427 ng/g dw) than subadult‐males (range = 145–1,645, M = 629, SD = 329 ng/g dw). These differences may be explained mainly by feeding‐niche partitioning between sexes. Females prefer mesopelagic prey or prey associated with sea‐ice in the WAP, which are enriched in methylmercury. These results provide insight regarding Hg contamination in top Antarctic predators like SES, and the need to monitor for potential effects of Hg contamination in Antarctic marine mammals.

The future of the South Georgia and South Sandwich Islands marine protected area in a changing environment: The choice between industrial fisheries, or ecosystem protection

South Georgia and the South Sandwich Islands (SGSSI) comprise an Overseas Territory of the UK. For over two centuries, the islands and surrounding waters were subject to serial over-exploitation of commercially valuable marine species. First seals, then whales, and later some species of fish were harvested to virtual economic extinction. Today, exploitation is strictly regulated: through the multilateral Convention on the Conservation of Antarctic Marine Living Resources; through the commercial whaling moratorium of the International Whaling Commission; and now, increasingly, through local sovereign government legislation. Commercial fisheries still operate for three species of fish and one species of crustacean, Antarctic krill. Here, I consider aspects of these fisheries, to help inform the current review of the SGSSI Marine Protected Area (MPA), highlighting how future management must take into account important ongoing changes in this biodiverse ecosystem. Two issues are of paramount importance: ongoing recovery of baleen whale species; and climate change. Both increase uncertainty for fisheries managers, so that considerations about their implications must now be directly included into the management of harvested and dependent species. With the recovery of some previously exploited species, and ongoing recovery of others, the MPA could now be managed with additional ecologically-appropriate large no-take areas, commensurate with increasing levels of ocean protection advocated for by a growing number of scientists and governments. Spatial protection reflecting the habitat use of baleen whales and their prey, krill, would, through umbrella protection, also protect other biodiversity integral to the operation of the marine ecosystem.

Quantifying circumpolar summer habitat for Antarctic krill and Ice krill, two key species of the Antarctic marine ecosystem

AbstractAntarctic krill (Euphausia superba) and Ice krill (Euphausia crystallorophias) are key species within Southern Ocean marine ecosystems. Given their importance in regional food webs, coupled with the uncertain impacts of climate change, the on-going recovery of krill-eating marine mammals, and the expanding commercial fishery for Antarctic krill, there is an increasing need to improve current estimates of their circumpolar habitat distribution. Here, we provide an estimate of the austral summer circumpolar habitat distribution of both species using an ensemble of habitat models and updated environmental covariates. Our models were able to resolve the segregated habitats of both species. We find that extensive potential habitat for Antarctic krill is mainly situated in the open ocean and concentrated in the Atlantic sector of the Southern Ocean, while Ice krill habitat was concentrated more evenly around the continent, largely over the continental shelf. Ice krill habitat was mainly predicted by surface oxygen concentration and water column temperature, while Antarctic krill was additionally characterized by mixed layer depth, distance to the continental shelf edge, and surface salinity. Our results further improve understanding about these key species, helping inform sustainable circumpolar management practices.

Quantifying microplastics in fjords along the Western Antarctic Peninsula

Microplastics are ubiquitous around the world. Microplastics have been documented around the Southern Ocean, in coastal sediments and in Antarctic marine organisms, however microplastics data for Antarctic waters remain scarce. Microplastics concentrations were characterized from fjord habitats on the Western Antarctic Peninsula where most glaciers are rapidly retreating. Water samples were collected from 2017 to 2020 from surface and benthos, vacuum-filtered, quantified to determine the classification of microplastic, color, and size. Micro-FTIR spectrophotometry was utilized to confirm chemical composition. Comparisons over time and location were made for average microplastic per liter. Despite the new emergent youth and remoteness of these habitats, it was determined that all fjord habitats had microplastics present each year sampled and increased from 2017 to 2020 in each fjord. Despite physical ‘barriers’ such as the Antarctic Circumpolar Current (and particularly its strongest jet, the Polar Front), microplastics are clearly present and increasing in even recent habitats.

Unraveling the functional diversity of macrobenthic community from Prydz Bay, Indian sector of the Southern Ocean

Antarctic marine ecosystems show rich macrobenthic diversity with a high level of endemism and biomass which is under the threat of global climate change. Till date, information regarding the structure of macrobenthic communities from Prydz Bay is extremely meagre. The present study investigates the spatial pattern of macrobenthic communities, and their response to environmental factors from Prydz Bay complemented with trait-based functional diversity patterns. Samples were collected from 8 stations during the 11th Indian scientific expedition to the Southern Ocean. A total of 57 species of macrobenthos belonging to 8 phyla and 33 families were identified. The macrobenthic communities were dominated by families, Lumbrineridae, Glyceridae, Ophiuridae, and Epimeriidae. Macrobenthos abundance in the study area ranged from 0 to 1592 indv.m-2, whereas biomass ranged from 0 to 1210.2 g m-2. CLUSTER analysis divided the entire macrobenthic community into four groups based on 13.5% similarity. SIMPER analysis delineated species Nacella kerguenlensis and Rossella antarctica as the main contributors for establishing similarity in macrobenthic community composition across the groups. Canonical correspondence analysis (CCA) showed environmental variables like clay %, depth, and sediment total organic carbon as the governing factors in structuring the composition of macrobenthic species. Biological trait analysis (BTA) was performed to visualize the functional diversity of the total macrobenthic population based on morphological and ecological characteristics. A total of 23 traits in 6 categories were used to assess the functional diversity of the study area. The most widespread trait categories were epifaunal environmental position, motile locomotion strategy, sexual brooder and spawner, burrowing living habitat, predatory and detritivore feeding strategies. Investigating the functional diversity of macrobenthic assemblages using BTA represents a novel step towards evaluating the ecological status of the benthic realm of Prydz Bay. RLQ approach in combination with fourth-corner analysis was used to evaluate the relationships among biological traits, macrobenthic species and environmental parameters.The RLQ analysis revealed the positive association of tube dwelling and burrowing polychaetes with silty substratum, and the sessile organisms were found to be negatively correlated with the presence of carnivores/predators. The present study gives a comprehensive understanding about the macrobenthic community structure along with biological trait categories from Prydz Bay.

Transcriptome analysis reveals genes connected to temperature adaptation in juvenile antarctic krill Euphausia superba

BackgroundThe Antarctic krill, Euphausia superba (E. superba), is a key organism in the Antarctic marine ecosystem and has been widely studied. However, there is a lack of transcriptome data focusing on temperature responses.MethodsIn this study, we performed transcriptome sequencing of E. superba samples exposed to three different temperatures: −1.19 °C (low temperature, LT), − 0.37 °C (medium temperature, MT), and 3 °C (high temperature, HT).ResultsIllumina sequencing generated 772,109,224 clean reads from the three temperature groups. In total, 1,623, 142, and 842 genes were differentially expressed in MT versus LT, HT versus LT, and HT versus MT, respectively. Moreover, Kyoto Encyclopedia of Genes and Genomes analysis revealed that these differentially expressed genes were mainly involved in the Hippo signaling pathway, MAPK signaling pathway, and Toll−like receptor signaling pathway. Quantitative reverse-transcription PCR revealed that ESG037073 expression was significantly upregulated in the MT group compared with the LT group, and ESG037998 expression was significantly higher in the HT group than in the LT group.ConclusionsThis is the first transcriptome analysis of E. superba exposed to three different temperatures. Our results provide valuable resources for further studies on the molecular mechanisms underlying temperature adaptation in E. superba.

Scoping intergenerational effects of nanoplastic on the lipid reserves of Antarctic krill embryos

Antarctic krill (Euphausia superba) plays a central role in the Antarctic marine food web and biogeochemical cycles and has been identified as a species that is potentially vulnerable to plastic pollution. While plastic pollution has been acknowledged as a potential threat to Southern Ocean marine ecosystems, the effect of nanoplastics (<1000 nm) is poorly understood. Deleterious impacts of nanoplastic are predicted to be higher than that of larger plastics, due to their small size which enables their permeation of cell membranes and potentially provokes toxicity. Here, we investigated the intergenerational impact of exposing Antarctic krill to nanoplastics. We focused on whether embryonic energy resources were affected when gravid female krill were exposed to nanoplastic by determining lipid and fatty acid compositions of embryos produced in incubation. Embryos were collected from females who had spawned under three different exposure treatments (control, nanoplastic, nanoplastic + algae). Embryos collected from each maternal treatment were incubated for a further 6 days under three nanoplastic exposure treatments (control, low concentration nanoplastic, and high concentration nanoplastic). Nanoplastic additions to seawater did not impact lipid metabolism (total lipid or fatty acid composition) across the maternal or direct embryo treatments, and no interactive effects were observed. The provision of a food source during maternal exposure to nanoplastic had a positive effect on key fatty acids identified as important during embryogenesis, including higher total polyunsaturated fatty acids (PUFA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) when compared to the control and nanoplastic treatments. Whilst the short exposure time was ample for lipids from maternally digested algae to be incorporated into embryos, we discuss why the nanoplastic-fatty acid relationship may be more complex. Our study is the first to scope intergeneration effects of nanoplastic on Antarctic krill lipid and fatty acid reserves. From this, we suggest directions for future research including long term exposures, multi-stressor scenarios and exploring other critical energy reserves such as proteins.

Depth drives the distribution of microbial ecological functions in the coastal western Antarctic Peninsula.

The Antarctic marine environment is a dynamic ecosystem where microorganisms play an important role in key biogeochemical cycles. Despite the role that microbes play in this ecosystem, little is known about the genetic and metabolic diversity of Antarctic marine microbes. In this study we leveraged DNA samples collected by the Palmer Long Term Ecological Research (LTER) project to sequence shotgun metagenomes of 48 key samples collected across the marine ecosystem of the western Antarctic Peninsula (wAP). We developed an in silico metagenomics pipeline (iMAGine) for processing metagenomic data and constructing metagenome-assembled genomes (MAGs), identifying a diverse genomic repertoire related to the carbon, sulfur, and nitrogen cycles. A novel analytical approach based on gene coverage was used to understand the differences in microbial community functions across depth and region. Our results showed that microbial community functions were partitioned based on depth. Bacterial members harbored diverse genes for carbohydrate transformation, indicating the availability of processes to convert complex carbons into simpler bioavailable forms. We generated 137 dereplicated MAGs giving us a new perspective on the role of prokaryotes in the coastal wAP. In particular, the presence of mixotrophic prokaryotes capable of autotrophic and heterotrophic lifestyles indicated a metabolically flexible community, which we hypothesize enables survival under rapidly changing conditions. Overall, the study identified key microbial community functions and created a valuable sequence library collection for future Antarctic genomics research.

Temperature-Related Short-Term Succession Events of Bacterial Phylotypes in Potter Cove, Antarctica.

In recent years, our understanding of the roles of bacterial communities in the Antarctic Ocean has substantially improved. It became evident that Antarctic marine bacteria are metabolically versatile, and even closely related strains may differ in their functionality and, therefore, affect the ecosystem differently. Nevertheless, most studies have been focused on entire bacterial communities, with little attention given to individual taxonomic groups. Antarctic waters are strongly influenced by climate change; thus, it is crucial to understand how changes in environmental conditions, such as changes in water temperature and salinity fluctuations, affect bacterial species in this important area. In this study, we show that an increase in water temperature of 1 °C was enough to alter bacterial communities on a short-term temporal scale. We further show the high intraspecific diversity of Antarctic bacteria and, subsequently, rapid intra-species succession events most likely driven by various temperature-adapted phylotypes. Our results reveal pronounced changes in microbial communities in the Antarctic Ocean driven by a single strong temperature anomaly. This suggests that long-term warming may have profound effects on bacterial community composition and presumably functionality in light of continuous and future climate change.

Mitochondrial Heteroplasmy and PCR Amplification Bias Lead to Wrong Species Delimitation with High Confidence in the South American and Antarctic Marine Bivalve Aequiyoldia eightsii Species Complex.

The species delimitation of the marine bivalve species complex Aequiyoldia eightsii in South America and Antarctica is complicated by mitochondrial heteroplasmy and amplification bias in molecular barcoding. In this study, we compare different data sources (mitochondrial cytochrome c oxidase subunit I (COI) sequences; nuclear and mitochondrial SNPs). Whilst all the data suggest that populations on either side of the Drake Passage belong to different species, the picture is less clear within Antarctic populations, which harbor three distinct mitochondrial lineages (p-dist ≈ 6%) that coexist in populations and in a subset of individuals with heteroplasmy. Standard barcoding procedures lead to amplification bias favoring either haplotype unpredictably and thus overestimate the species richness with high confidence. However, nuclear SNPs show no differentiation akin to the trans-Drake comparison, suggesting that the Antarctic populations represent a single species. Their distinct haplotypes likely evolved during periods of temporary allopatry, whereas recombination eroded similar differentiation patterns in the nuclear genome after secondary contact. Our study highlights the importance of using multiple data sources and careful quality control measures to avoid bias and increase the accuracy of molecular species delimitation. We recommend an active search for mitochondrial heteroplasmy and haplotype-specific primers for amplification in DNA-barcoding studies.

Managing for climate resilient fisheries: Applications to the Southern Ocean

Climate change is having profound effects on populations of fished species and the ecosystems on which they depend, lending to a growing body of work that advocates for climate resilience to be a priority in fishery management. Here, we provide a comprehensive analysis of the tools needed to manage for climate resiliency. The Antarctic region is among the most vulnerable to climate change, and thus, we then consider climate resilient management tools utilized by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), the body responsible for the management of Antarctic marine living resources as part of the Antarctic Treaty System. We note progress, gaps, and opportunities for implementation. Across the literature, ecosystem-based management was cited as an appropriate tool for climate resilience of marine ecosystems, as was the use of climate model outputs (projections and simulations), marine protected areas (MPAs), and dynamic stock assessments. CCAMLR has a unique position where its Convention effectively mandates the principles of an ecosystem-based precautionary approach for managing fisheries, and many of its Member States have been advocating for climate initiatives within this approach. While CCAMLR has made limited overall progress towards ensuring climate resilience, it has advanced in some areas, such as MPA implementation, developing a risk assessment for krill, and including statements on climate change in fishery reports, although there is much work to be done. While climate change remains a worldwide issue that must be addressed on a global scale, CCAMLR holds the responsibility for adaptively managing Southern Ocean marine living resources for climate resilience.

Commercial krill fishing within a foraging supergroup of fin whales in the Southern Ocean.

Commercial krill fishing within a foraging supergroup of fin whales in the Southern Ocean.

Low-Molecular-Mass Fragments of Collagen Improve Parameters Related to Mass and Inflammation of the Adipose Tissue in the Obese Rat.

Despite clearly recognized links between increased body mass and increased risk for various pathological conditions, therapeutic options to treat obesity are still very limited. The aim of the present study is to explore the effect of low-molecular-mass collagen fragments obtained from the scales of Antarctic wild marine fish on rats' visceral and subcutaneous white adipose tissue in a high-calorie diet-induced obesity model. The study was conducted on outbred rats, which were divided into 3 experimental groups: (i) control, consuming standard food (3.81 kcal/g), (ii) obese group, consuming a high-calorie diet (5.35 kcal/g), and (iii) obese group, consuming a high-calorie diet (5.35 kcal/g) with intragastric administration of low-molecular-mass collagen fragments (at a dose 1 g/kg of body mass during 6 weeks). Low-molecular-mass collagen fragments were obtained by a procedure that included collagen extraction from fish scales and enzymatic hydrolysis with pepsin. Apart from hematoxylin and eosin staining, fibrosis level was assessed by histochemical Van Gieson's trichrome picrofuchsin staining, and mast cells were analysed by toluidine blue O staining. Group treated with low-molecular-mass fragments of collagen exhibited decreased rate of mass gain, relative mass, area occupied by collagen fibre of both visceral and subcutaneous adipose tissue, and cross-sectional area of both visceral and subcutaneous adipocytes. Treatment with low-molecular-mass fragments of collagen reduced the infiltration of immune cells, number of mast cells and their redistribution back to the septa. This was also accompanied by a decreased number of the crown-like structures formed by the immune cells, which are markers of chronic inflammation that accompanies obesity. This is the first study that reports the anti-obesity effect of low-molecular-mass fragments produced as a result of controlled hydrolysis of collagen from the scales of Antarctic wild marine fish in the in vivo model. Another novelty of this work is the observation that the tested collagen fragments not only reduce the body mass, but also improve the morphological and inflammatory parameters (decrease in the number of crown-like structures, immune cell infiltration, fibrosis and mast cells). Altogether, our work suggests that low-molecular-mass collagen fragments are a promising candidate for amelioration of some comorbidities linked to obesity.

Organic or junk food? Microplastic contamination in Antarctic krill and salps.

Microplastics (MP) have been reported in Southern Ocean (SO), where they are likely to encounter Antarctic zooplankton and enter pelagic food webs. Here we assess the presence of MP within Antarctic krill (Euphausia superba) and salps (Salpa thompsoni) and quantify their abundance and type by micro-Fourier transform infrared microscopy. MP were found in both species, with fibres being more abundant than fragments (krill: 56.25% and salps: 22.32% of the total MP). Polymer identification indicated MP originated from both local and distant sources. Our findings prove how in situ MP ingestion from these organisms is a real and ongoing process in the SO. MP amount was higher in krill (2.13 ± 0.26 MP ind-1) than salps (1.38 ± 0.42 MP ind-1), while MP size extracted from krill (130 ± 30 µm) was significantly lower than MP size from salps (330 ± 50 µm). We suggest that differences between abundance and size of MP ingested by these two species may be related to their food strategies, their ability to fragment MP as well as different human pressures within the collection areas of the study region. First comparative field-based evidence of MP in both krill and salps, two emblematic zooplankton species of the SO marine ecosystems, underlines that Antarctic marine ecosystems may be particularly sensitive to plastic pollution.

The 2018 Judgment by the European Court of Justice on Antarctic MPAS and Its Possible Significance to the Antarctic Treaty System

The CJEU’s decision in the Antarctic Marine Protected Areas (MPAs) case offered an opportunity to explore the area where EU Law and the Antarctic Treaty System overlap: in the forum of the CAMLR Commission. From the point of view of EU Law, CCAMLR is a so-called ‘mixed agreement’, meaning that its scope includes areas where both the European Union and its Member States are competent. This article explains how the Court resolved the question of the joint representation of a common standpoint in a forum where the Union has no autonomous position, and then goes on to explore the significance that the decision could have for the Antarctic Treaty System.

Evaluation of Antimicrobial Properties and Potential Applications of Pseudomonas gessardii M15 Rhamnolipids towards Multiresistant Staphylococcus aureus

Staphylococcus aureus is a Gram-positive opportunistic human pathogen responsible for severe infections and thousands of deaths annually, mostly due to its multidrug-resistant (MDR) variants. The cell membrane has emerged as a promising new therapeutic target, and lipophilic molecules, such as biosurfactants, are currently being utilized. Herein, we evaluated the antimicrobial activity of a rhamnolipids mixture produced by the Antarctic marine bacterium Pseudomonas gessardii M15. We demonstrated that our mixture has bactericidal activity in the range of 12.5-50 µg/mL against a panel of clinical MDR isolates of S. aureus, and that the mixture eradicated the bacterial population in 30 min at MIC value, and in 5 min after doubling the concentration. We also tested abilities of RLs to interfere with biofilm at different stages and determined that RLs can penetrate biofilm and kill the bacteria at sub-MICs values. The mixture was then used to functionalize a cotton swab to evaluate the prevention of S. aureus proliferation. We showed that by using 8 µg of rhamnolipids per swab, the entire bacterial load is eradicated, and just 0.5 µg is sufficient to reduce the growth by 99.99%. Our results strongly indicate the possibility of using this mixture as an additive for wound dressings for chronic wounds.

New Pyrroline Isolated from Antarctic Krill-Derived Actinomycetes Nocardiopsis sp. LX-1 Combining with Molecular Networking

Antarctic krill (Euphausia superba) of the Euphausiidae family comprise one of the largest biomasses in the world and play a key role in the Antarctic marine ecosystem. However, the study of E. superba-derived microbes and their secondary metabolites has been limited. Chemical investigation of the secondary metabolites of the actinomycetes Nocardiopsis sp. LX-1 (in the family of Nocardiopsaceae), isolated from E. superba, combined with molecular networking, led to the identification of 16 compounds a-p (purple nodes in the molecular network) and the isolation of one new pyrroline, nocarpyrroline A (1), along with 11 known compounds 2-12. The structure of the new compound 1 was elucidated by extensive spectroscopic investigation. Compound 2 exhibited broad-spectrum antibacterial activities against A. hydrophila, D. chrysanthemi, C. terrigena, X. citri pv. malvacearum and antifungal activity against C. albicans in a conventional broth dilution assay. The positive control was ciprofloxacin with the MIC values of <0.024 µM, 0.39 µM, 0.39 µM, 0.39 µM, and 0.20 µM, respectively. Compound 1 and compounds 7, 10, and 11 displayed antifungal activities against F. fujikuroi and D. citri, respectively, in modified agar diffusion test. Prochloraz was used as positive control and showed the inhibition zone radius of 17 mm and 15 mm against F. fujikuroi and D. citri, respectively. All the annotated compounds a-p by molecular networking were first discovered from the genus Nocardiopsis. Nocarpyrroline A (1) features an unprecedented 4,5-dihydro-pyrrole-2-carbonitrile substructure, and it is the first pyrroline isolated from the genus Nocardiopsis. This study further demonstrated the guiding significance of molecular networking in the research of microbial secondary metabolites.

A novel promising laccase from the psychrotolerant and halotolerant Antarctic marine Halomonas sp. M68 strain.

Microbial communities inhabiting the Antarctic Ocean show psychrophilic and halophilic adaptations conferring interesting properties to the enzymes they produce, which could be exploited in biotechnology and bioremediation processes. Use of cold- and salt-tolerant enzymes allows to limit costs, reduce contaminations, and minimize pretreatment steps. Here, we report on the screening of 186 morphologically diverse microorganisms isolated from marine biofilms and water samples collected in Terra Nova Bay (Ross Sea, Antarctica) for the identification of new laccase activities. After primary screening, 13.4 and 10.8% of the isolates were identified for the ability to oxidize 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and the dye azure B, respectively. Amongst them, the marine Halomonas sp. strain M68 showed the highest activity. Production of its laccase-like activity increased six-fold when copper was added to culture medium. Enzymatic activity-guided separation coupled with mass spectrometry identified this intracellular laccase-like protein (named Ant laccase) as belonging to the copper resistance system multicopper oxidase family. Ant laccase oxidized ABTS and 2,6-dimethoxy phenol, working better at acidic pHs The enzyme showed a good thermostability, with optimal temperature in the 40-50°C range and maintaining more than 40% of its maximal activity even at 10°C. Furthermore, Ant laccase was salt- and organic solvent-tolerant, paving the way for its use in harsh conditions. To our knowledge, this is the first report concerning the characterization of a thermo- and halo-tolerant laccase isolated from a marine Antarctic bacterium.

Cryptophytes: An emerging algal group in the rapidly changing Antarctic Peninsula marine environments.

The western Antarctic Peninsula (WAP) is a climatically sensitive region where foundational changes at the basis of the food web have been recorded; cryptophytes are gradually outgrowing diatoms together with a decreased size spectrum of the phytoplankton community. Based on a 11-year (2008-2018) in-situ dataset, we demonstrate a strong coupling between biomass accumulation of cryptophytes, summer upper ocean stability, and the mixed layer depth. Our results shed light on the environmental conditions favoring the cryptophyte success in coastal regions of the WAP, especially during situations of shallower mixed layers associated with lower diatom biomass, which evidences a clear competition or niche segregation between diatoms and cryptophytes. We also unravel the cryptophyte photo-physiological niche by exploring its capacity to thrive under high light stress normally found in confined stratified upper layers. Such conditions are becoming more frequent in the Antarctic coastal waters and will likely have significant future implications at various levels of the marine food web. The competitive advantage of cryptophytes in environments with significant light level fluctuations was supported by laboratory experiments that revealed a high flexibility of cryptophytes to grow in different light conditions driven by a fast photo-regulating response. All tested physiological parameters support the hypothesis that cryptophytes are highly flexible regarding their growing light conditions and extremely efficient in rapidly photo-regulating changes to environmental light levels. This plasticity would give them a competitive advantage in exploiting an ecological niche where light levels fluctuate quickly. These findings provide new insights on niche separation between diatoms and cryptophytes, which is vital for a thorough understanding of the WAP marine ecosystem.