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.

Marine phytoplankton can utilize different strategies to cope with ocean warming and freshening from glacial melting in polar regions, which are disproportionally impacted by global warming. In the present study, we investigated the individual and combined effects of a 4 °C increase in seawater temperature (T+) and a 4 psu decrease in salinity (S−) from ambient values on biomass, nutrient use, fatty acid composition and lipid damage biochemistry of natural phytoplankton assemblages from Potter Cove (25 de Mayo/King George Island, Antarctica). Experiments were conducted by exposing the assemblages to four treatments during a 7-day incubation period using microcosm located along shore from January 23 to 31, 2016. The N:P ratio decreased in all treatments from day 4 onwards, but especially under high temperature (T+). Lipid damage was mainly detected under S0T+ and S−T+ conditions, and it decreased when the production of the antioxidant α-tocopherol increased. This antioxidant protection resulted in a build-up of phytoplankton biomass, especially at T+. Under the combined effect of both stressors (S−T+), the concentration of ω3 fatty acids increased, potentially leading to higher-quality FA composition. These results, which were related to the dominance of sub-Antarctic species in phytoplankton assemblages, contribute to the understanding of the potential consequences of ocean warming and increase seawater freshening on the trophic webs of the Southern Ocean.

On the southern Patagonian shelf (Argentina, 47 degrees-55 degrees S) phyto- and protozooplankton are key structural and functional components of a complex trophic web that sustains commercially important species. During late summer 2004, spatial structure, assemblage species and their association with environmental characteristics of water masses were studied for the 2-200 mu m phyto- and protozooplankton communities. Ultraplankton 2-5 mu m was the most abundant size-fraction (90%), followed by the lower nanoplankton 5-10 mu m (7.5%), the larger nanoplankton 10-20 mu m (1.5%), and microplankton 20-200 mu m (1%). Several of the 319 morpho-species found are potentially toxic taxa (the dinoflagellates Alexandrium tamarense, Protoceratium reticylatum, Dinophysis acuminata, Prorocentrum cordatum, Karenia and amphidomataceans and the diatom genus Pseudo-nitzschia), and this is important since the area sustains significant fisheries. A ultraphytoeukaryotic coccal cell (probably chlorophyte/prasinophyte) (3 mu m), P. cordatum, and a microplankton naked ciliate were the morpho-species with the highest abundance and occurrence. Abundance and biodiversity patterns indicated that the plankton community structure was heterogeneous vertically, cross-shelf, and along-shelf, suggesting shifts in community structure over the region. Five areas with dissimilar plankton assemblages were defined, each corresponding to different environments. Depth, bathymetry, latitude and temperature were the most explanatory variables for the assemblage distribution patterns observed. This south Patagonian region possesses important fisheries and, considering expected environmental changes, our results help to understand the spatial structure of plankton communities over a broad size spectrum.

The copepod community structure, with special emphasis on small-sized species, was studied over the southern Patagonian shelf in late summer 2004, applying the first plankton sampling in the region with a fine-mesh (66 μm) net. The key role of the copepods Drepanopus forcipatus and Calanus australis was confirmed, but also the high abundance and frequency of occurrence of the microcopepods Oithona helgolandica and Microsetella norvegica and of the medium-sized copepod Ctenocalanus vanus were revealed. Copepod community structure was nearly homogenous over the entire study area. Drepanopus forcipatus, O. helgolandica and M. norvegica were identified as the typical species of the region, although secondarily C. australis and Oithona atlantica also contributed significantly to community similarity across the area. The study of interspecific relationships of dominant copepods indicated that D. forcipatus and C. australis were associated positively with O. helgolandica, while C. vanus, and M. norvegica constituted a separate assemblage with Clausocalanus brevipes and O. atlantica. The importance of fine-mesh-size nets for collecting the smaller size fractions of mesozooplankton and for accurately portraying the mesozooplankton assemblage structure in the area is stressed by this study.

Drepanopus forcipatus and Calanus australis are key planktonic copepods on the southern Patagonian shelf. Their feeding and reproductive patterns and population status were investigated during late summer, when environmental conditions may be critical. The presence of food in the gut and food-pellet length were recorded in adult females and the most abundant copepodite stages. Diet composition was also studied in adult females. Female reproductive status was evaluated by gonad staging. Despite generally low feeding conditions and decreasing seasonal temperature, both copepods fed to some degree. The most numerous copepodites and adult females of both species showed similarly low feeding activity. About half of the adult females of the two species and C5s of C. australis contained food in their guts, but the proportion of fed C4-females of D. forcipatus was much lower. All copepods were generally feeding at low or intermediate levels. Gonad stage distribution and population structure showed low but still ongoing reproduction in both species. Gut content findings suggest a preference for smaller nanoplanktonic particles, especially dinoflagellates by D. forcipatus, and for autotrophic prey, particularly large diatoms by C. australis. The feeding and reproduction patterns of the two copepods were likely influenced by the distributions of potential food resources and temperature.

A strong interest in the southern Patagonian shelf has emerged in recent years, along with the increasing recognition of its high biological productivity. Knowledge of the pelagic food web structure that supports the richness of this system is still developing, but there are indications that mesozooplankton occupy a pivotal position, as consumers of smaller plankton and as vital prey for fish and squid. All plankton communities in the size 2μm–20mm, total and size-fractioned chlorophyll a (Chl a), nutrients and hydrology were surveyed simultaneously in October 2005 between 47°S–55°S. Picoplankton, nanoplankton and microplankton were taxonomically and functionally (autotrophs, heterotrophs) sorted within each size fraction. Plankton data and trophic relationships were examined through multivariate statistics. At that time fairly homogeneous thermal conditions prevailed over most of the shelf but weak saline horizontal gradients were evident. N/P ratios indicated no N or P limitation for phytoplankton. Surface concentrations of total Chl a were particularly high in the Grande Bay area at ca. 51°S near shore (28.6mgm−3) and at ca. 47°S on the shelf-break (7.7mgm−3). At both locations the contribution of the Chl a>5μm fraction was remarkably high. The dinoflagellate Prorocentrum minimum (10·106cellsL−1) and the diatom Thalassiosira cf. oceanica (1.3·106cellsL−1) were respectively blooming at these sites. Otherwise <10μm plankton prevailed overall. Copepods largely dominated the >200μm fraction. Three mesozooplankton assemblages typical of the inner, middle, and outer shelf were identified. The inner and middle shelf assemblages overlapped slightly but were spatially separated from the outer shelf community. Adults and late copepodids of Drepanopus forcipatus were typical of the inner shelf assemblage. Middle-shelf species included the copepod Ctenocalanus vanus, the amphipod Themisto gaudichaudii and the chaetognath Sagitta tasmanica, while an assortment of taxa characterized the outer sector. Latitudinal patterns in mesozooplankton community composition were less noticeable than cross-shelf patterns. No clear distribution of phytoplankton and protozooplankton assemblages was apparent when the whole <200μm plankton community structure was considered. In contrast, communities in the optimal size food for copepods (>10–200μm) were slightly different across shelf. Overall, spatial patterns of mesozooplankton and food availability matched weakly, suggesting a poor coupling between consumers and their prey communities at the time. Significant correlations were found particularly with large autotrophs and heterotrophs.

Three representative copepods occurring in the southern Patagonian shelf, i.e., Calanus australis, Drepanopus forcipatus and Oithona helgolandica were sampled by the first time with paired nets of 66 and 150µm mesh size. The stage-specific estimates of abundance of their populations were statistically analyzed to assess differences in the catchability by both plankton nets. Differences between nets were significant only for smaller developmental stages and species, with higher catchabilities by the 66µm net, while no differences were detected for most of the stages of the medium and large size species. A significant effect of the spatial distribution on the estimates of abundance was detected for the majority of the species and stages but the interaction between mesh size and spatial distribution was not significant. This means that differences between both nets were maintained across the latitudinal gradient. Our results strongly suggest the convenience of using the 66µm plankton net to estimate the abundance of the three copepods' populations. Furthermore, we propose a correction factor to adjust past estimates of abundances from 150µm mesh collections.

A rich benthic filter-feeding community is present at Potter Cove, South Shetland, in spite of some usually unfavorable conditions affecting their feeding ecology, such as low phytoplankton production in summer and high sedimentation rates. However, organic material that could fuel the benthic system, such as macroalgal fragments, was detected in the water-bottom interface year-round. Mean assimilation efficiency of several sizes of macroalgal particles under different inorganic particulate percentages varied between 26–51% in a clam, and 26–72% in two ascidian species. Estimated particle flux (feces) produced by ascidians varied according to species and abundance. The C:N ratio of feces was relatively high. Plasticity and profit from the available food sources contribute to the success of the filter-feeding community in Potter Cove.