South Orkney Islands Research Articles

South! Phylogeography of the Antarctic fairy shrimp Branchinecta gaini and its closest Patagonian congener Branchinecta granulosa reveals a long-term association of freshwater fauna with the southern continent

AbstractBranchinecta gaini Daday, 1910 is the southernmost extant Anostracan species occurring in various localities across Maritime Antarctica. Since this region was almost completely glaciated during the Last Glacial Maximum, the identification of potential glacial refugia and the colonization sequence of freshwater habitats within Maritime Antarctica remains primary biogeographic objective for understanding the evolution of the Antarctic environment. To evaluate the history of B. gaini in Maritime Antarctica, we performed phylogeographic analyses of B. gaini and its closest Patagonian congener Branchinecta granulosa Daday, 1902. We sampled 47 populations from all three Antarctic bioregions where B. gaini occurs – South Orkney Islands, North-west and North-east Antarctic Peninsula. B. granulosa was represented by 8 populations from Patagonia. Molecular analyses of two mitochondrial (16S, COI) and one nuclear (ITS2) marker showed low overall mitochondrial variability and the ambiguous nature of ITS2 variability. The species assessment revealed insufficient genetic differentiation between B. gaini and B. granulosa to consider them two separate species. Therefore, the widely accepted idea that there is a species of Branchinecta endemic to Antarctica and sub-Antarctic islands should be omitted, and B. gaini should be synonymized with B. granulosa. Molecular clock analysis of COI for two substitution rates dated the separation of B. gaini from B. granulosa to the Pleistocene (170 – 502 ka BP and 17 – 50 ka BP, respectively). Therefore, Antarctic populations of B. gaini separated from Patagonian B. granulosa before or during the Last Glacial Maximum, indicating an older association with the southern continent than previously anticipated. The geographic distribution of haplotypes further suggests that B. gaini most likely survived at least the last glacial period in an as-yet unknown refugium in Antarctica.

Development observed in the field of the Antarctic bivalve mollusc Aequiyoldia eightsii at Signy Island, South Orkney Islands

ABSTRACT The embryonic development of marine ectotherms has been shown to be strongly temperature dependent across the world's oceans. However, at the coldest sites, in the polar regions, development is even slower than would be predicted on the basis of the temperature dependence of development in warmer waters, and this is thought to be a consequence of changes in physical characteristics of cytoplasm near 0 °C—such as viscosity and osmolyte packing that slow protein folding and increase the likelihood of interference by charged particles, and their effect on protein synthesis. The overwhelming majority of studies of rates of embryonic development have been laboratory-based, with animals either collected directly from the sea and spawned in the laboratory or held first in the laboratory and preconditioned to set environments before spawning. Few studies have assessed development from regularly collected samples and assessed field development, especially from polar latitudes. Here we present data for the Antarctic bivalve mollusc Aequiyoldia eightsii, tracking its development from spawning on 25/26 May to hatching of pelagic veligers on 12 June and the disappearance of pediveliger larvae from the water column at the end of September or early October, 108–114 days later. Larval dry mass was constant at 16.7 µg (SE = 0.19) across the pelagic phase, except for the initial few days after hatching when it was 9.55 µg (SE = 0.60). The difference was likely the calcification of the larval shell. The development time to trochophore was 189 h, and this was in line with previous studies showing larval development at temperatures around 0 °C is around 4–22 times slower than would be predicted from the general effect of temperature on development rates.

Seasonal variation in the stomach microbiota of two sympatrically breeding Pygoscelis penguin species at Signy Island, South Orkney Islands.

The gut microbiomes of Antarctic penguins are important for the fitness of the host birds and their chicks. The compositions of microbial communities in Antarctic penguin guts are strongly associated with the birds' diet, physiological adaptation and phylogeny. Whilst seasonal changes in food resources, distribution and population parameters of Antarctic penguins have been well addressed, little research is available on the stability or variability of penguin stomach microbiomes over time. Here, we focused on two Pygoscelis penguin species breeding sympatrically in the maritime Antarctic and analysed their stomach contents to assess whether penguin gut microbiota differed over three austral summer breeding seasons. We used a high-throughput DNA sequencing approach to study bacterial diversity in stomach regurgitates of Adélie (Pygoscelis adeliae) and chinstrap (Pygoscelis antarctica) penguins that have a similar foraging regime on Signy Island (South Orkney Islands). Our data revealed significant differences in bacterial alpha and beta diversity between the study seasons. We also identified bacterial genera that were significantly associated with specific breeding seasons, diet compositions, chick-rearing stages and sampling events. This study provides a baseline for establishing future monitoring of penguin gut microbiomes in a rapidly changing environment.

Morphometric characteristics of Antarctic krill (Euphausia superba) and finfish bycatch in the krill fishery in the waters of South Orkney Islands during the 2022/23 fishing season

Determination of bar spacing of bycatch reduction devices (BRDs) should consider species composition and morphometric characteristics (particularly width) of target species krill and bycatch. This study conducted a scientific investigation of the finfish bycatch in the Antarctic krill (Euphausia superba) trawl fishery by the fishing vessel SHEN LAN in the waters surrounding the South Orkney Islands from December 24, 2022, to February 20, 2023. The results show that scientific observers sampled 676 individuals of finfish bycatch. Of these, 665 were identified to species (17 species from 8 families), while the remaining 11 specimen were juveniles of the Nototheniidae family that could not be identified to the species level. IRI (index of relative importance) calculations showed three dominant (IRI value greater than 1,000) finfish bycatch species (Champsocephalus gunnari, Pseudochaenichthys georgianus, and C. aceratus from the Channichthyidae family) and four important (IRI value between 1,000 and 100) finfish bycatch species (Electrona carlsbergi and Gymnoscopelus nicholsi from the Myctophidae family, Gobionotothen gibberifrons from the Nototheniidae family, and Notolepis coatsi from the Paralepididae family). Our study provides morphometric data (particularly body width) that is crucial to model the potential for bycatch reduction by use of bycatch reduction devices (BRDs) and to determine the appropriate candidate bar spacings for BRD sea trials. Predictions suggest that a 10 mm (the maximum body width of krill) bar spacing releases a significant amount of dominant and important bycatch species (93.94% of C. gunnari, 53.99% of P. georgianus, 76.25% of C. aceratus, and 100% of G. gibberifrons). Reduced fishing pressure would reduce the risks to dominant and important bycatch species to make the krill fishery sustainable. We recommend that future BRD sea trials should initially test a 10 mm bar spacing. If marked loss of krill is observed, wider spacings (e.g. 15 mm) must be tested.

New distributional records of Southern Ocean Isopoda based on vouchers from the Italian National Antarctic Museum (MNA, Section of Genoa).

The order Isopoda Latreille, 1816 consists of species occurring in terrestrial, marine and freshwater environments. In the Southern Ocean (SO), this group is amongst the most speciose and occur at all depths. Isopoda biogeography, despite being studied since the first Antarctic expeditions, is still poorly known from a geographical point of view and shows large occurrence gaps for some groups in specific sectors of the SO. In this paper, we update the isopod checklists of the Ross Sea (RS) and of some peri-Antarctic areas, such as the South Orkney Islands (SOI) and the South Sandwich Islands (SSI), based on the study of museum vouchers curated by the Italian National Antarctic Museum (MNA, Section of Genoa). A total of 279 MNA samples from 15 different expeditions were studied. From this material, consisting of 419 specimens, 41 accepted species distributed in 24 families and 51 genera were identified. Comparing this newly-obtained information with the GBIF (Global Biodiversity Information Facility) and OBIS (Ocean Biodiversity Information System) portal, 15 species are here reported for the first time in the Ross Sea, with five new records in the Ross Sea Marine Protected Area. All records are new for the Terra Nova Bay area, for which a checklist of this group has never been produced before.

Consumption of Antarctic krill Euphausia superba by mackerel icefish, Champsocephalus gunnari off the South Orkney Islands: filling an information gap in the current ecosystem-based management approach

Consumption of Antarctic krill Euphausia superba by mackerel icefish, Champsocephalus gunnari off the South Orkney Islands: filling an information gap in the current ecosystem-based management approach

Physiological parameters of South Georgia Shag (Phalacrocorax georgianus) during breeding in South Orkney Island, Antarctica

Physiological parameters of South Georgia Shag (Phalacrocorax georgianus) during breeding in South Orkney Island, Antarctica

Revealing the variety in phytoplankton communities in waters near the Antarctic Peninsula by high-throughput sequencing

ABSTRACT The waters near the Antarctic Peninsula have always been a hot spot because of their variable and unique oceanographic conditions. To distinguish the differences in phytoplankton communities, we conducted a mesoscale survey during the austral summer of 2018. Samples were collected at 14 stations located in the Drake Passage, South Shetland Islands (SSI) and South Orkney Islands (SOI). A total of 615 operational taxonomic units were extrapolated using V4-5 18S rDNA sequencing collected from the chl a max layers. Three groups (I, II, and III) were divided at a similarity level of 60% by multivariate statistical analysis, and there were significant differences between groups II and III. Generally, diatoms and dinoflagellates predominated among all three groups. Chlorophyta was found in greater abundance near the SSI, whereas pennate diatoms contributed more around the SOI. The different abundance of particular dinoflagellates was the reason for grouping by SIMPER analysis. And Pseudochattonella farcimen, Micromonas sp. and Pyramimonas sp were screened out which inducing dissimilarity were less mentioned in other literatures. Temperature and salinity among stations showed little difference in our study. Phytoplankton assemblage was a complex issue and the factors induced the difference of phytoplankton communities need to further analyze.

New records of demosponges (Porifera) from the South Orkney Islands (Antarctica) with a checklist for the region.

The South Orkney Islands (SOI) is a poorly studied Antarctic archipelago located in the Scotia Arc. In this study, we added 25 Demospongiae species to the SOI known sponge richness, which was previously represented by only 16 species. Of these, 22 species represent new records for SOI region, although they were previously recorded from other Antarctic sectors. Samples were collected during two Argentinean Antarctic Research Cruises onboard RV Puerto Deseado. The most frequently collected species were Artemisina apollinis, Iophon gaussi, I. unicorne, Lissodendoryx (E.) ramilobosa, Myxodoryx hanitschi and Tedania (T.) tantula. Data and illustrations of some rare or uncommon species are provided: Iophon gaussi, Lissodendoryx (E.) anacantha, Microxina charcoti, Raspailia (H.) hentscheli, Haliclona spongiosissima, Haliclona (G.) cf. cucurbitiformis. Although the present results increase substantially the previously known information on sponge species, this is still an underestimation of total richness because certain orders (Tetractinellida, Suberitida, Biemnida, Polymastiida) and classes were not studied during the current investigation, although previous records were included.

Seasonal acoustic presence of marine mammals at the South Orkney Islands, Scotia Sea.

Increased knowledge about marine mammal seasonal distribution and species assemblage from the South Orkney Islands waters is needed for the development of management regulations of the commercial fishery for Antarctic krill (Euphausia superba) in this region. Passive acoustic monitoring (PAM) data were collected during the autumn and winter seasons in two consecutive years (2016, 2017), which represented highly contrasting environmental conditions due to the 2016 El Niño event. We explored differences in seasonal patterns in marine mammal acoustic presence between the two years in context of environmental cues and climate variability. Acoustic signals from five baleen whale species, two pinniped species and odontocete species were detected and separated into guilds. Although species diversity remained stable over time, the ice-avoiding and ice-affiliated species dominated before and after the onset of winter, respectively, and thus demonstrating a shift in guild composition related to season. Herein, we provide novel information about local marine mammal species diversity, community structure and residency times in a krill hotspot. Our study also demonstrates the utility of PAM data and its usefulness in providing new insights into the marine mammal habitat use and responses to environmental conditions, which are essential knowledge for the future development of a sustainable fishery management in a changing ecosystem.

Spatial structuring in early life stage fish diversity in the Scotia Sea region of the Southern Ocean

AbstractThe fish community of the Scotia Sea is diverse and plays key roles in Antarctic food webs and biogeochemical cycling. However, knowledge of the spatial and community structure of their early life stages is limited, particularly in the region surrounding the South Orkney Islands. Here we examine the structure of the early life stage fish community in the epipelagic using data from a basin-scale survey conducted in early 2019, which sampled the top 200 m of the water column. 347 early life stage fish from 19 genera were caught in 58 hauls. A third of all specimens belonged to the genus Notolepis and the nine most common genera comprised over 90% of specimens. Cluster analysis revealed five distinct groupings, the most common were a group dominated by pelagic and shelf slope genera (Notolepis, Muraenolepis and Electrona) found mainly in oceanic waters (depth ≥ 1000 m), and a group dominated by species with demersal or benthopelagic adults (Chionodraco, Chaenocephalus and Nototheniops) found mainly in shelf waters. Bottom depth was the main environmental determinant of community structure, separating the diverse on-shelf assemblage at the South Orkneys from the less species-rich community of widespread oceanic taxa. Our results indicate the highest diversities of early life stages of endemic fish occur on the shelf and near-shelf areas. Dedicated monitoring is recommended to understand the seasonal differences in larval community assemblages and the implications of early life stages fish bycatch within the krill fishery.

HISTORICAL HERITAGE IN ANTARCTICA, THE CASA MONETA MUSEUM: A FIRST APPROACH TO THE CHARACTERIZATION OF XYLOPHAGOUS FUNGI AND THEIR POTENTIAL ROLE IN WOOD DAMAGE

The Casa Moneta Museum is located at the base located at an isthmus located on Laurie Island in the South Orkney Islands archipelago. Currently, the museum shows signs of deterioration of the wood (discoloration, fibrous appearance and presence of mycelium) and it is necessary to characterize this mycobiota to analyze the potential role in the biodegradation process. An assessment of the potential risk associated with fungal communities could provide valuable information for taking conservation action at the Casa Moneta Museum. The aim of this work was to evaluate the extracellular oxidase production of fungi recovered from deteriorated wood at the museum and to analyze the biodegradation risk index of three sampled sites in the building. The enzymatic profile showed the potential degradation of Cadophora spp. and Tulasnella albida strains. The analysis performed integrated data on several parameters like occurrences, species diversity, dominant species, wind direction, relative humidity, growth temperature, type of dispersion propagules and substrate, indicating Site 2 has a major biodegradation risk index which suggests that this site should be the immediate target for conservation efforts.

Temperature variation in the South Orkney Islands, maritime Antarctic

AbstractMeteorological records at Signy Station in the South Orkney Islands (SOIs) have recently been digitized to cover the period of 1947–1995. This study compares the newly available near‐surface air temperatures at Signy with those from a nearby station, Orcadas and with reanalysis datasets to provide a more comprehensive picture of the weather and climate variability in the SOIs. Temperatures from both stations show a higher degree of variability in winter than summer, but the variability differs in terms of its relationship to the dominant wind directions and sea ice influences. The two stations differ markedly in terms of their respective warm temperature events, largely due to orography‐induced föhn winds at Signy Station as northwesterlies flow over Coronation Island. ERA5 reproduces the monthly to annual averages exceedingly well but underestimates both cold and warm tails of station temperatures. Temperature trends in the SOIs are also considered in terms of changes in large‐scale circulation and the sea surface temperature over the Brazil‐Falkland Confluence. However, caution is required in interpreting the long‐term temperature trends estimated from reanalysis data as most of the reanalyses show a cold bias before 1979, which is most likely caused by misrepresentation of the sea ice.

Ectoparasite infestation and host–parasite trophic relationship for Champsocephalus gunnari (Lonnberg, 1905) at South Orkney Islands, Antarctica

Ectoparasite infestation and host–parasite trophic relationship for Champsocephalus gunnari (Lonnberg, 1905) at South Orkney Islands, Antarctica

Top-down control over dissolved organic carbon in the bottom water of the Weddell Sea and its implication for the continental shelf pump

Dense water out of the Antarctic shelves is expected to drive the transport of carbon into the deep Southern Ocean via the formation of Antarctic Bottom Water. However, bottom water formation’s capacity to sequester carbon into the deep ocean is poorly constrained. Here, dissolved organic carbon (DOC), dissolved black carbon (DBC), and particulate organic carbon (POC) were examined to reveal the influence of the Weddell Sea Deep Water (WSDW) on DOC transport during its flowing out of the Weddell Sea. High DOC concentrations (>60 μM-C) and low DBC/DOC ratios (<1.5%) were observed in surface water near the South Orkney Islands, ascribing to sea ice melt-induced phytoplankton blooms. Seawater at the mid-deep depths exhibited a higher DOC concentration (averaging 48.1 ± 3.7 μM-C) than the incoming water source, resulting from the release of DOC from sinking particles. Bottom water had higher DOC concentration compared to the mid-deep layer water (t-test, p < 0.005), while the DBC concentrations were comparable. In addition, the excess DOC (relative to WSDW) in bottom water showed a close relation with POC in surface water. These results reveal a top-down control over the DOC concentration in bottom water through a quick sinking of diatom detritus and subsequently solubilization in bottom water and/or sediment. With an estimate, the WSDW carries 5.1 ± 2.8 Tg-C/yr of excess DOC out of the Powell Basin, representing an important carbon source to the deep Southern Ocean. This study highlights the key role of the Antarctic continental shelf pump in carbon sequestration.

Mollusca collected by Agassiz trawl from the 2016 SO-AntEco (JR15005) expedition to the South Orkney Islands, Antarctica - data.

This dataset contributes to the knowledge of macro- and megafaunal Mollusca associated with a range of benthic habitat types in the South Orkney Islands, Antarctica, an exceptionally diverse region of the Southern Ocean. The information presented is derived from Agassiz trawl samples collected on the archipelago's shelf plateau and slope, within and outside of the South Orkney Islands Southern Shelf Marine Protected Area (SOISS MPA). Sampling was conducted in the framework of the British Antarctic Survey/SCAR "South Orkneys - State of the Antarctic Ecosystem" (SO-AntEco) project aboard RRS James Clark Ross during expedition JR15005 in Austral summer 2016. This dataset is published by the British Antarctic Survey under the licence CC-BY 4.0. We would appreciate it if you could follow the guidelines from the SCAR Data Policy (SCAR 2023) when using the data. If you have any questions regarding this dataset, do not hesitate to contact us via the contact information provided in the metadata or via data-biodiversity-aq@naturalsciences.be. Issues with the dataset can be reported at https://github.com/biodiversity-aq/data-publication/. This dataset is part of the Biodiversity, Evolution and Adaptation Project of the Environmental Change and Evolution Program of the British Antarctic Survey. The cruise report of the expedition is available at https://www.bodc.ac.uk/resources/inventories/cruise_inventory/reports/jr15005.pdf. We report occurrences of Mollusca from individual samples taken with a 2 m-wide Agassiz trawl (AGT) in the framework of the February - March 2016 research expedition JR15005 of RRS James Clark Ross to the SOISS MPA and adjacent shelf and slope areas. Of 78 successful AGT deployments, 44 trawls at depths ranging from 235-2194 m yielded living Mollusca, totalling 2276 individuals, 67 morphospecies and 163 distributional records. One hundred and fifteen empty shells were also collected and recorded in the dataset. Three morphospecies (one Bivalvia and two Gastropoda) were sampled exclusively as empty shells, yielding a total of 70 morphospecies and 2391 specimens represented in the dataset. All specimens were preserved in 96% undenatured ethanol and are stored as vouchers in the collections of the British Antarctic Survey (BAS), Cambridge, United Kingdom. The publication of this dataset aims at increasing the knowledge on the biodiversity, abundance and geographical and bathymetric distribution of larger-sized epi- and shallow infaunal Mollusca of the South Orkney Islands.

Extreme warm events in the South Orkney Islands, Southern Ocean: Compounding influence of atmospheric rivers and föhn conditions

AbstractExtreme warm events in the South Orkney Islands (SOIs) are investigated using synoptic observations from Signy and Orcadas stations for 1947–1994 and 1956–2019 respectively. Defining the extremes as temperatures exceeding the 95th percentile of the temperature distribution, we reveal the characteristics and associated drivers of the warm events, especially the top 10 events in both summer and winter. At both stations, extreme warm events often involve a combined effect of atmospheric rivers (ARs) and localised föhn warming, with distinct characteristics due to the station locations relative to Coronation Island, the largest and highest island of the SOIs. For example, warm events at Signy are warmer (by an average of around 3°C) than the corresponding concurrent temperatures at Orcadas. The number of warm events per year has significantly increased over the record periods at both stations, which could potentially impact ecosystems by increasing melting of snow and ice. Extreme warm events at Signy are dominated by föhn warming in combination with ARs originating from the Southern Atlantic Ocean, where warm, moisture‐rich air is rapidly advected towards the islands by enhanced northerly winds. By contrast, the Orcadas warm extremes involve both warm‐air advection and föhn warming associated with enhanced northwesterlies/westerlies with ARs originating in the Pacific Ocean that travel across the Drake Passage. Simulation of one of the top 10 warm events for Signy station using a 1‐km grid spacing configuration of the atmosphere‐only UK Met Office Unified Model is used to disentangle the role of local versus large‐scale forcing. We find that the majority of the warming can be attributed to föhn effects for the case study. These results demonstrate the complexity of Antarctic temperature extremes.

Environmental and behavioural drivers of Antarctic krill distribution at the South Orkney Islands: A regional perspective

Antarctic krill (Euphausia superba) is a key species in the marine ecosystem of the Southern Ocean, but is also the target of a commercial fishery, with an important fishing ground in the South Orkney Islands region. The potential for competition for krill between predators and the fishery requires risk management strategies for the fishery, underpinned by an understanding of the key physical and behavioural drivers of krill movement and retention in target areas. Here, we present the results of a regional modelling study, combining a high-resolution ocean-sea ice model and an individual-based model parameterised for krill, to elucidate the roles of oceanographic variability and krill behaviour on patterns of transport and retention on and around the South Orkney Plateau. Simulations suggest that oceanic transport from sources around the Antarctic Peninsula is restricted by the northward flowing Antarctic Slope Current. Around the South Orkney Plateau, anticyclonic flows associated with the Weddell Front and the shelf edge transport krill rapidly towards the main fishing grounds to the northwest of the plateau. Transport onto the shelf and subsequent retention are influenced by the strength and direction of regional winds; weaker on-shelf transport and shorter retention times are associated with stronger westerly and northerly winds. The incorporation of sea-ice associated behaviour, whereby krill are moved with sea ice when sea ice is present, significantly modifies the patterns from purely oceanic transport; it reduces the influence of strong regional oceanic flows and increases transport of krill to the South Orkneys region from the Antarctic Peninsula. The inclusion of diel vertical migration also modifies predicted patterns from oceanic transport, but to a lesser extent, and moderates the impact of including sea-ice associated behaviour. We highlight the importance of understanding the behaviour of krill, including age-dependent behavioural changes in response to sea ice conditions, for modelling and management of Antarctic krill populations.

Structure and Spatial Distribution of Mesozooplankton Communities in the Atlantic Sector of the Southern Ocean

In this paper, the composition and patterns of spatial distribution of mesozooplankton communities in the waters of the Bransfield Strait, the Antarctic Sound, the Powell Basin of the Weddell Sea and the waters off the Antarctic Peninsula and South Orkney Islands during the austral summer of 2022 are presented. Among the mesozooplankton communities two groups were found to be the most abundant: copepods Calanoides acutus, Metridia gerlachei and Oithona spp., and euphausiids Euphausia superba. The maximum abundance and biomass of the mesozooplankton were found in the warm Antarctic surface deep-sea water off the South Orkney Islands. The minimum values, respectively, were found in the cold modified Weddell Sea waters off the Antarctic Peninsula. Copepods was concentrated in the Bransfield Strait near the South Shetland Islands with sea surface temperature (SST) of –0.5–0.5°С and sea surface salinity (SSS) of 34.5–34.6‰; and the krill E. superba eggs and larvae at different development stages was concentrated in the waters off the South Orkney Islands with SST values of 1–2°С and SSS values of 34.3–34.5‰. Four groups of mesozooplankton communities at different composition, abundance, and taxa dominance were identified. The results of this and future study have practical implications for monitoring the state of the changing ecosystem of the Southern Ocean.

Modeling of the Distribution and Relationship with Abiotic Environmental Factors of Juvenile and Adult Antarctic Krill &lt;i&gt;Euphausia superba&lt;/i&gt; Based on Actual Hydrophysical Measurements

The results of statistical processing of the occurrence of krill individuals depending on some environmental factors, based on the actual data of hydrophysical measurements, at the studied stations in the Powell Basin of the Weddell Sea, the Bransfield Strait and Antarctic Sound, as well as off the South Orkney Islands in the austral summer of 2022 are discussed. Data were obtained on the association of the main abiotic environmental factors and their values, which are optimal for juvenile and mature krill individuals, and a number of abiotic environmental factors that affect the distribution of Antarctic krill in the studied region were identified. The results of such statistical modeling are important for monitoring the state of Antarctic ecosystems and their components under changing environmental factors, including current trends in climate change.