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The marine gastropod genus Laevilitorina is exclusive to the Southern Hemisphere, with 21 species from southern South America, Antarctica, Australia, New Zealand, and sub-Antarctic Islands. We present a comprehensive revision of Laevilitorina , using molecular and morphological analyses, to address formally the interspecific divergences within the nominal taxon Laevilitorina caliginosa s.l. We confirm the validity of L. caliginosa and Laevilitorina venusta , and we demonstrate that specimens from the Strait of Magellan and Hornos Island constitute four new species here described: Laevilitorina magellanica sp. nov. Laevilitorina pepita sp. nov. Laevilitorina fueguina sp. nov. and Laevilitorina hicana sp. nov. All six species are clearly distinguishable genetically, morphologically, and through radular tooth shape and configurations. Laevilitorina venusta is broadly distributed across the Antarctic Peninsula, South Georgia, and sub-Antarctic Islands (Marion, Crozet, Kerguelen, and Macquarie), whereas L. caliginosa s.s. appears geographically restricted to Cape Horn, the Falkland/Malvinas Islands, and South Georgia. The identification of populations from Macquarie Island as L. caliginosa is dubious; we suggest that these records are likely to pertain to L. venusta. This detailed revision of Laevilitorina , whereby hidden diversity was detected, significantly enriches our knowledge of the evolutionary history of this group. [ABSTRACT FROM AUTHOR]

Simple Summary: Abatus is a genus of sea urchin that inhabits the Southern Ocean. Among the 11 described species, three shared morphological traits and live in intertidal zones in Patagonia (A. cavernosus), Kerguelen (A. cordatus), Antarctica, and Tierra del Fuego (A. agassizii). The relationships between Abatus species are complicated and have not been clarified yet. This study analyzed shape variation among these species. The shape of 72 individuals from four locations in the South Shetlands, Kerguelen, Patagonia, and Falklands/Malvinas, were evaluated. Differences in shape were found in all four locations. Especially, the Falklands/Malvinas group showed a marked difference in shape compared to other localities. The possibility that the Falklands/Malvinas group shows phenotypic plasticity or represents a distinct evolutionary unit is discussed. Finally, the methodology used in this study proved to be a powerful tool to differentiate these species, highlighting its utility in systematic studies. Abatus is a genus of irregular brooding sea urchins to the Southern Ocean. Among the 11 described species, three shared morphological traits and present an infaunal lifestyle in the infralittoral from the Subantarctic province; A. cavernosus in Patagonia, A. cordatus in Kerguelen, and A. agassizii in Tierra del Fuego and South Shetlands. The systematic of Abatus, based on morphological characters and incomplete phylogenies, is complex and largely unresolved. This study evaluates the shape variation among these species using geometric morphometrics analysis (GM). For this, 72 individuals from four locations; South Shetlands, Kerguelen, Patagonia, and Falklands/Malvinas were photographed, and 37 landmarks were digitized. To evaluate the shape differences among species, a principal component analysis and a Procrustes ANOVA were performed. Our results showed a marked difference between the Falklands/Malvinas and the other localities, characterized by a narrower and more elongated shape and a significant influence of location in shape but not sex. Additionally, the effect of allometry was evaluated using a permutation test and a regression between shape and size, showing significant shape changes during growth in all groups. The possibility that the Falklands/Malvinas group shows phenotypic plasticity or represents a distinct evolutionary unit is discussed. Finally, GM proved to be a powerful tool to differentiate these species, highlighting its utility in systematic studies. [ABSTRACT FROM AUTHOR]

The threat from novel marine species introductions is a global issue. When non‐native marine species are introduced to novel environments and become invasive, they can affect biodiversity, industry, ecosystem function, and both human and wildlife health. Isolated areas with sensitive or highly specialised endemic species can be particularly impacted. The global increase in the scope of tourism and other human activities, together with a rapidly changing climate, now put these remote ecosystems under threat. In this context, we analyse invasion pathways into South Georgia and the South Sandwich Islands (SGSSI) for marine non‐native species via vessel biofouling. The SGSSI archipelago has high biodiversity and endemism, and has historically been highly isolated from the South American mainland. The islands sit just below the Polar Front temperature boundary, affording some protection against introductions. However, the region is now warming and SGSSI increasingly acts as a gateway port for vessel traffic into the wider Antarctic, amplifying invasion likelihood. We use remote Automatic Identification System vessel‐tracking data over a 2‐year period to map vessel movement and behaviour around South Georgia, and across the 'Scotia Sea', 'Magellanic' and northern 'Continental High Antarctic' ecoregions. We find multiple vessel types from locations across the globe frequently now enter shallow inshore waters and stop for prolonged periods (weeks/months) at anchor. Vessels are active throughout the year and stop at multiple port hubs, frequently crossing international waters and ecoregions. Management recommendations to reduce marine invasion likelihood within SGSSI include initiating benthic and hull monitoring at the identified activity/dispersion hubs of King Edward Point, Bay of Isles, Gold Harbour, St Andrews Bay and Stromness Bay. More broadly, regional collaboration and coordination is necessary at neighbouring international ports. Here vessels need increased pre‐ and post‐arrival biosecurity assessment following set protocols, and improved monitoring of hulls for biofouling to pre‐emptively mitigate this threat. [ABSTRACT FROM AUTHOR]

Biological invasions are one of the main drivers of global biodiversity decline. At the same time, glacial retreat induced by climate warming is occurring at an alarming rate across the globe, threatening unique taxa and ecosystems. However, we know little about how introduced species contribute to the dynamics of colonisation in newly-deglaciated forelands. To answer this question, detailed inventories of plant and invertebrate communities were undertaken during two summer field seasons in the forelands of three tidewater and three inland glaciers that are retreating on the sub-Antarctic Island of South Georgia. The vascular plant communities present included a large proportion of South Georgia's native flora. As expected, plant richness and cover increased with time since deglaciation along a deglaciation chronosequence. Introduced plants were well represented in the study sites and two species (Poa annua and Cerastium fontanum) were amongst the earliest and most frequent colonisers of recently-deglaciated areas (occurring on more than 75% of transects surveyed). Introduced arthropods were also present around tidewater glaciers, including an important predatory species (Merizodus soledadinus) with known detrimental impacts on native invertebrate communities. Our study provides a rare and detailed picture of developing novel communities along a deglaciation chronosequence in the sub-Antarctic. Introduced species are able to track glacial retreat on South Georgia, indicating that further local colonisation and spread are inevitable as the region's climate continues to warm. [ABSTRACT FROM AUTHOR]

South Georgia is a heavily glaciated sub‐Antarctic island in the Southern Ocean. Cumberland Bay is the largest fjord on the island, split into two arms, each with a large marine‐terminating glacier at the head. Although these glaciers have shown markedly different retreat rates over the past century, the underlying drivers of such differential retreat are not yet understood. This study uses observations and a new high‐resolution oceanographic model to characterize oceanographic variability in Cumberland Bay and to explore its influence on glacier retreat. While observations indicate a strong seasonal cycle in temperature and salinity, they reveal no clear hydrographic differences that could explain the differential glacier retreat. Model simulations suggest the subglacial outflow plume dynamics and fjord circulation are sensitive to the bathymetry adjacent to the glacier, though this does not provide persuasive reasoning for the asymmetric glacier retreat. The addition of a postulated shallow inner sill in one fjord arm, however, significantly changes the water properties in the resultant inner basin by blocking the intrusion of colder, higher salinity waters at depth. This increase in temperature could significantly increase submarine melting, which is proposed as a possible contribution to the different rates of glacier retreat observed in the two fjord arms. This study represents the first detailed description of the oceanographic variability of a sub‐Antarctic island fjord, highlighting the sensitivity of fjord oceanography to bathymetry. Notably, in fjords systems where temperature decreases with depth, the presence of a shallow sill has the potential to accelerate glacier retreat. Plain Language Summary: Cumberland Bay, a fjord on the sub‐Antarctic island of South Georgia, is split into two arms, each with a large marine‐terminating glacier. One of these glaciers is retreating much faster than the other, possibly due to differences in oceanography between the arms. Here, we investigate how the oceanography in Cumberland Bay varies seasonally and with the seabed depth by using oceanographic data and numerical ocean simulations. We find that the properties of buoyant plumes, which arise from meltwater entering the ocean from beneath the glacier, are sensitive to the seabed depth near the glaciers, resulting in strong differences in ocean flow between the fjord arms. Assuming higher ocean temperatures increase glacier melting, we find that the presence of a near‐glacier shallow sill likely increases melting by blocking deeper, colder waters and trapping warmer surface waters close to the glacier. As a shallow sill is likely to be present near the rapidly retreating glacier only, this result offers a persuasive explanation for the observed glacier retreat. Understanding the variability in oceanography and glacier retreat is important as they directly impact the marine ecosystem at South Georgia by influencing the availability of nutrients for primary production and food availability for higher predators. Key Points: Observational data and a new high‐resolution model are combined to describe oceanographic variability in Cumberland Bay, South GeorgiaWe show that the properties of buoyancy‐driven outflow plumes are sensitive to bathymetry and drive spatial differences between fjord armsWe highlight that the presence of a postulated inner sill may be a key factor in the observed rapid glacier retreat [ABSTRACT FROM AUTHOR]

Fishery discards supplement food for many seabirds, but the impacts of declining discards are poorly understood. Discards may be beneficial for some populations but have negative impacts by increasing bycatch risk or because they are junk-food. The Falkland Islands support > 70% of global black-browed albatross Thalassarche melanophris populations, which feed on discards. However, the effect of discards on population demographics, and implications of fishery management changes, are unknown. We analysed stomach contents of black-browed albatross chicks across eight breeding seasons (2004–2020) from New Island, Falkland Islands, to assess variation in discard consumption and how this relates to foraging conditions and breeding success. Across years, 68%–98% of samples contained natural prey, whilst 23%–88% of samples contained fishery discards. Discard consumption was positively related to fishery catches of hoki Macruronus magellanicus and sea surface temperature anomalies SSTA (°C), and negatively related to breeding success. These results suggest a diet-switching behaviour for Falkland Islands albatrosses, whereby birds switch from preferred natural prey to suboptimal discards when environmental conditions, and hence natural feeding opportunities, are unfavourable. Crucially, this study highlights that fishery discards do not compensate for poor natural foraging conditions for breeding albatrosses in the long term. [ABSTRACT FROM AUTHOR]

Biological invasions represent a growing threat to islands and their biodiversity across the world. The isolated sub‐Antarctic island of South Georgia in the South Atlantic Ocean is a highly protected area that relies on effective biosecurity including prevention, surveillance and eradication to limit the risk of biological invasions. Based on an opportunistic field discovery, we provide the first report of an introduced ladybird beetle on South Georgia. All specimens discovered belong to the Eurasian species Coccinella undecimpunctata Linnaeus (1758) (Coleoptera: Coccinellidae). Tens of individuals of both sexes were discovered at a single location, indicating that the species may already be established on South Georgia. Transport connectivity with this site suggests that the species most likely arrived recently from the Falkland Islands as a stowaway on a ship. We discuss the implications of our discovery for the continued development of South Atlantic biosecurity. [ABSTRACT FROM AUTHOR]

Members of the sea anemone genus Metridium are abundant in temperate rocky habitats and fouling communities. Their biogeographic history is expected to reflect changes in currents and habitats that have influenced benthic communities, such as the climate-influenced changes that occurred during the Last Glacial Maximum. More recently, however, anthropogenic influences such as shipping transportation and the creation of artificial habitat have altered and affected the composition of modern-day marine communities. Here we use sequence-capture data to examine the genetic structure of Metridium across its shallow-water distribution to (1) evaluate species boundaries within Metridium , (2) elucidate the dispersal history of Metridium between and among oceans, and (3) assess the influence of anthropogenic movement on modern-day populations. We find strong evidence for two species within Metridium : M. farcimen and M. senile. Dispersal from the Pacific to the Atlantic included a subsequent isolation of a small population in or above the Bering Sea, which has presumably moved southward. Within the native range of M. senile , admixture is prevalent even between oceans as a result of anthropogenic activities. The nonnative populations in Chile and the Falkland Islands came from at least two distinct introduction events originating from both coasts of the United States in the North Pacific and North Atlantic Oceans. Hybridization between M. senile and M. farcimen is documented as occurring in anthropogenically influenced habitats. The heavy influence from anthropogenic activities will continue to impact our understanding of marine organisms, particularly within the native range and for those that are easily transported across long distances. [ABSTRACT FROM AUTHOR]

Littorinid snails are present in most coastal areas globally, playing a significant role in the ecology of intertidal communities. Laevilitorina is a marine gastropod genus distributed exclusively in the Southern Hemisphere, with 21 species reported from South America, the sub-Antarctic islands, Antarctica, New Zealand, Australia and Tasmania. Here, an updated database of 21 species generated from a combination of sources is presented: 1) new field sampling data; 2) published records; 3) the Global Biodiversity Information Facility (GBIF) and The Atlas of Living Australia (ALA), to provide a comprehensive description of the known geographic distribution of the genus and detailed occurrences for each of the 21 species. The database includes 813 records (occurrences), 53 from field sampling, 174 from the literature, 128 from GBIF, and 458 from ALA. West Antarctica had the highest species richness (8 species), followed by sub-Antarctic islands of New Zealand (4 species) and the south-east shelf of Australia (4 species). The provinces of Magellan, New Zealand South Island, and sub-Antarctic Islands of the Indian Ocean include two species each. This study specifically highlights reports of L. pygmaea and L. venusta, species that have been almost unrecorded since their description. Recent advances in molecular studies of L. caliginosa showed that this species does not correspond to a widely distributed taxon, but to multiple divergent lineages distributed throughout the Southern Ocean. Ongoing molecular and taxonomic studies are necessary for a better understanding of the diversity and biogeography of this genus. [ABSTRACT FROM AUTHOR]