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The 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. [ABSTRACT FROM AUTHOR]

The Black-browed Albatross (BBA), Thalassarche melanophris, is one of the most abundant and widespread pelagic seabirds in the southern hemisphere, considered an indicator species of climate change in Antarctica. In addition to the known negative interactions with fisheries, other threats may act indirectly on this species whose effects have not yet been evaluated, such as increased sea surface temperature due to climate change. Under the assumption that carbon emissions modify the distribution of BBA, we modeled the environmental suitability and inferred BBA distribution under future climate scenarios for 2050 and 2100. We used 23 years of observation data (1991–2020) from research vessels in the Southwest Atlantic Ocean and Antarctica to estimate habitat suitability and predict change in suitability for the two future time ranges (2040–2050 and 2090–2100) under four representative concentration pathway scenarios: optimistic, intermediate pessimistic. Our projections predict a reduction in the total habitat suitability for BBA by 8% and 31.4% by 2050 and 2100, respectively, in the worst-case scenario compared to the present. Our study enhances understanding of the factors driving distribution dynamics for the species and aid in the development of conservation areas under future global change scenarios. [ABSTRACT FROM AUTHOR]

Monitoring of early euphausiid larvae provides valuable information on the mechanisms involved in recruitment to the adult populations. As the Antarctic is undergoing rapid environmental change, these mechanisms are key to ecosystem-based management of the krill fishery. We analyzed the distribution and abundance of early euphausiid larvae (calyptopes I to late furciliae) from 76 plankton samples from surface to 300 m depth in the Atlantic sector in January 2011 in relation with a previous survey and published information. Thysanoessa macrura (mean density: 209 ind m−2) dominated the sampling while Euphausia superba (mean density: 13.63 ind m−2) and Euphausia frigida (mean density: 10.05 ind m−2) were also present. T. macrura density increased while E. superba experienced a high decrease respect to historical data. Clustering of stations and correspondence analysis showed that the associations of larvae and water masses are in agreement with literature reports, so the differences on the abundance of early larvae are within the observed variability and cannot be attributed to any single factor, suggesting that it is due to more subtle changes such as the stability of the water column and/or vorticity in the fronts. [ABSTRACT FROM AUTHOR]

To investigate whether impacts of reported climate change in the Antarctic marine environment have affected mesozooplankton populations, we compared the summertime abundances of four species of large calanoid copepods from samples taken during the Discovery Investigations (1926-1938) and contemporary times (1996-2013). Discovery samples were obtained using an N70V closing net fished vertically through three depth horizons encompassing the top 250 m of the water column, whereas contemporary samples were obtained using a Bongo net fished vertically through 200-0 m. Data from a previous study comparing catch efficiencies of the two nets were used to generate calibration factors which were applied to the N70V abundances. Following further corrections for net depth differences and seasonal biases in sampling frequency, three of the four species, Calanoides acutus, Rhincalanus gigas and Calanus simillimus, were found to be between ~ 20-55% more abundant in contemporary times than they were 70 years ago. Calanus propinquus was marginally more abundant in the Discovery era. These results were robust to sensitivity analyses for the net calibration factor, seasonal bias and net depth corrections. Although near-surface ocean temperatures within the Scotia Sea have increased by up to 1.5 °C during the last 70 years, we conclude that the most likely causes of increased copepod abundances are linked to changes in the food-web. In particular, we discuss the reported decrease in krill abundance in the South Atlantic that has potentially increased the amount of food available to copepods while at the same time decreasing predator pressure. [ABSTRACT FROM AUTHOR]

Myctophid fish play an important role in the Southern Ocean pelagic food web. The lanternfish Krefftichthys anderssoni is one of the most common myctophids in the region, but its ecology is poorly known. This study examines spatial and temporal patterns in the species distribution of density, life cycle, population structure and diet using samples collected by mid-water trawl nets deployed in different seasons across the Scotia Sea. Virtually absent from the sea-ice zone, the species was most abundant in the northern Scotia Sea around the Georgia Basin at depths below 400 m that are associated with the Circumpolar Deep Water. The species migrated during night from waters deeper than 700 m to waters above the 400 m following their main prey species: the copepods Rhincalanus gigas and Calanoides acutus and euphausiids of the Thysanoessa genus. Larvae length distribution and post-larvae length-frequency analyses suggested a life cycle of ~3 years with spawning and recruitment strongly connected with APF and the South Georgia shelf. Our results show that species spatial distribution, population structure and diet changed both seasonally and ontogenetically. This study is the most comprehensive examination of the ecology of K. anderssoni in the Southern Ocean to date and contributes to resolving how pelagic food webs and ecosystems operate in the region. [ABSTRACT FROM AUTHOR]

Reproductive capacity can influence distribution and abundance over large spatial scales through larval dispersal, even when adult stages remain isolated following settlement. We examined size distribution, reproductive traits and age structure in Scotia Sea icefish, Chaenocephalus aceratus, an abundant benthic species with a long larval pelagic phase found on continental shelves along the Southern Scotia Ridge. In particular, we compared life history strategies between fish caught during surveys undertaken off the South Orkney Islands (SOI) and South Shetland Islands (SSI). Results corroborated regional separation after settlement and suggested distinct life history strategies, in which fish from SOI invested much less in reproduction, and somewhat more in somatic growth earlier in their life history. Compared to SSI, body weight increased faster with length and absolute fecundity was 46 % lower and increased more slowly with size for SOI population. In addition, the proportion of spawning cohorts and L was lower and k higher for SOI. The differences appeared to be a phenotypic response to environmental conditions related to regional hydrography. Lower reproductive capacity around the SOI, and strong eastward flow in the large-scale circulation, suggests that the SSI may be more important in influencing distributions and abundance of icefish along the Southern Scotia Ridge. [ABSTRACT FROM AUTHOR]

Gymnoscopelus braueri, Gymnoscopelus fraseri and Gymnoscopelus nicholsi are common in the Southern Ocean mesopelagic fish community. However, their ecology is poorly understood in the region. This study investigated spatial and temporal patterns in their abundance, population structure and diets at different times of year within the Scotia Sea to ascertain their functional role in the pelagic food web. G. braueri was the most abundant species (0.07-0.17 ind. 1,000 m) throughout the Scotia Sea. G. fraseri was absent from the sea-ice sectors and occurred mostly around the Antarctic Polar Front (APF), comprising densities of 0.01-0.04 ind. 1,000 m. G. nicholsi occurred in low abundance (<0.01 ind. 1,000 m) throughout the region. G. braueri and G. fraseri had a lifespan of ~4 and 3 years, respectively, but spatial variation in their population structures was evident and recruitment appeared to occur only around the APF. G. nicholsi had a lifespan of >4 years. There was evidence of seasonal variation in depth distribution, size-related sexual dimorphism and vertical segregation in size classes for each species. Overall, diets were dominated by copepods ( Metridia spp., Rhincalanus gigas, Pleuromamma robusta) and euphausiids ( Thysanoessa spp. and Euphausia superba), although G. fraseri did not predate E. superba. Regional, seasonal and ontogenetic patterns in diet were evident for all species. This study provides new insight into the ecology of these Gymnoscopelus species in the Scotia Sea. Such details contribute towards resolving how pelagic food webs are structured in the Southern Ocean and their sensitivity to ongoing environmental change. [ABSTRACT FROM AUTHOR]

In many areas of the Antarctic and Subantarctic, king crabs records are still fragmentary. New data on the distribution of Lithodidae in the Scotia Sea and the adjacent area of the south-west Atlantic and the south-east Pacific have been collected during exploratory pot fishing in the year 2010 and are also based on some earlier collections that are deposited in Russian museums. The occurrence of Lithodes macquariae off Peter I Island is confirmed. Lithodes confundens, Lithodes turkayi and Neolithodes diomedeae were found in abundance on the Northern Scotia Ridge at a depth of, respectively, 315-775, 315-1,410 and 840-1,300 m. Paralomis formosa was recorded for the first time on the shelf of the South Orkney Islands, which is the southernmost record of this species. New material and literature data demonstrate the existence of two discontinuous lithodid faunas: the Antarctic Pacific fauna that extends up to the western Antarctic Peninsula and the Magellanic-Scotia fauna. The origin of this faunal discontinuity is discussed. The molecular barcodes (subunit I of the mitochondrial cytochrome-oxidase gene-COI) data for N. diomedeae and L. turkayi are provided for the first time. COI gene tree suggests that two main Subantarctic/Antarctic lineages of Lithodes, i.e. a pair Lithodes santolla/ L. confundens and L. turkayi (with possibly closely related Lithodes murrayi and L. macquariae) are phylogenetically distant from each other as well as with low-latitude Pacific and Atlantic species of this genus. [ABSTRACT FROM AUTHOR]

The Scotia Sea is one of the most productive regions of the Southern Ocean, but its surface waters are experiencing a rapid increase in temperature, which may be changing the behaviour and distribution of many myctophids and their prey species. Electrona antarctica and Electrona carlsbergi are two of the most abundant myctophids in the region, but their ecology is poorly understood and their response to ongoing environmental change is difficult to determine. This study investigated spatial and temporal patterns in their abundance, population structure and diets using mid-water trawl nets deployed across the Scotia Sea during spring, summer and autumn. E. antarctica was the most numerically abundant species (0.09-0.21 ind. 1,000 m), with greatest concentrations occurring in the sea-ice sectors. E. carlsbergi occurred in more northern regions, comprising densities of 0.02-0.11 ind. 1,000 m. There was evidence of seasonal variation in depth distribution, size-related sexual dimorphism and size-specific vertical stratification for both species. Latitudinal trends in sex ratio and female body size were apparent for E. antarctica. Its diet varied between regions, seasons and size classes, but overall, Euphausia superba, Metridia spp. and Themisto gaudichaudii were the dominant prey items. E. carlsbergi appeared not to recruit in the Scotia Sea. Its diet was dominated by copepods, particularly Rhincalanus gigas and Metridia spp., but regional, seasonal and ontogenetic variations were evident. This study contributes to our understanding of how mid-water food webs are structured in the Southern Ocean and their sensitivity to ongoing environmental change. [ABSTRACT FROM AUTHOR]

The Antarctic marine environment is extreme in its low temperatures and short periods of primary productivity. Invertebrates must therefore adapt to maximise reproductive output where low temperature and limited food slow larval development. Brooding is a common reproductive trait in Antarctic marine bivalves; larval development occurs within the mantle cavity, and larvae are released as fully developed young. Lissarca miliaris is a small, short-lived, shallow-water brooding bivalve of circum-Antarctic distribution and found most abundant in the sub-Antarctic Magellan Region and islands of the Scotia Arc. Here, an unusual hermaphrodite reproductive trait is described for L. miliaris from King George Island (62°14′S, 58°38′W) and Signy Island (60°42′S, 45°36′W), Antarctica, using histological and dissection techniques. Specimens demonstrate simultaneous and sequential hermaphrodite traits; male and female gonads develop simultaneously, but the production of oocytes is reduced while testes are ripe. Functional females are more abundant in specimens above 3 mm shell length, although male reproductive tissue persists and functional males are found in all size classes. The number of previtellogenic oocytes produced by far exceeds the number of oocytes extruded and brooded, which may indicate an ancestral link to a planktotrophic past. Hermaphroditism in L. miliaris maximises reproductive efficiency in a short-lived species, in which the female's capacity to brood its young is limited, and demonstrates a specialised adaptation to a cold stenothermal and food-limited environment prevailing in the Southern Ocean. [ABSTRACT FROM AUTHOR]

The process of egg release is a complex and crucial step in the life cycle of euphausiids, especially with regards mortality and recruitment success. We examined this process in Antarctic krill ( Euphausia superba) in terms of the functioning of the female genital apparatus and associated swimming behaviour. A tethering technique combined with video analysis was used to make observations of three females during the release process. We found eggs were steadily extruded over a period of up to 10 h, during which time the krill released between 1,600 and 4,000 eggs and the ovary reduced by a half in length and a third in height. Eggs were mainly released individually or, less commonly, in batches of between 2 and 4 eggs. Release rates were between 5 and 30 eggs min−1. The steady release of eggs fits well with histological evidence that mature oocytes must pass individually through tight genital ducts with narrow apertures, before coming in to close contact with the sperm plug for fertilisation , and then expulsion from the thelycum as fertilised eggs. During spawning, the female alternated between slow and rapid rates of pleopod beating with egg release occurring at the moment of beat acceleration. At the point of release, the descent of the egg was accelerated through downward beats of the 7th thoracic leg. The cyclic pattern in pleopod beat-rate during spawning may alter swimming performance and contribute to the widely reported sex- and maturity-based biases within krill swarms. [ABSTRACT FROM AUTHOR]

Ontogenetic, inter-annual and regional variations in diet were investigated for mackerel icefish, Champsocephalus gunnari, in three successive summer seasons around South Georgia. Stomach contents from 2239 C. gunnari (130–560 mm total length) were examined. A bootstrapping technique was used to calculate confidence intervals for an index of relative importance of prey categories (% IRIDC). Diet varied significantly between years and age classes but there was little regional difference in diet. In general, diet was dominated by krill, Euphausia superba and by the amphipod Themisto gaudichaudii. Smaller (younger) fish tended to prey on a higher proportion of T. gaudichaudii and small euphausiids such as Thysanoessa sp. and took smaller quantities of E. superba. In a season of poor krill availability (summer of 2003–2004) the proportion of krill in the diet, stomach fullness and fish condition (indicated by length–weight relationships) were significantly lower than in the other summer seasons. A large reduction (>80%) in the estimated annual (2005) biomass of the C. gunnari stock directly followed the season of poor krill availability. This decline was largely because of mortality of 2+ and 3+ fish, which were more krill dependent than 1+ fish. Younger fish appear to have survived, leading to an increase in the estimated population biomass in 2006. [ABSTRACT FROM AUTHOR]

The mesopelagic fish community of the northern Scotia Sea was investigated during the austral autumn using multi-frequency acoustics, opening and closing nets and pelagic trawls fished from the surface to 1,000 m. The Family Myctophidae (15 species in 5 genera) dominated the ichthyofauna, with larval notothenids caught over the South Georgia shelf and bathylagids and stomiids abundant in deeper hauls. The biomass of myctophids was estimated to be 2.93 g wet weight 1,000 m−3, with Electrona carlsbergi, E. antarctica, Protomyctophum bolini, P. choriodon, Gymnoscopelus braueri, G. fraseri, G. nicholsi and Krefftichthys anderssoni, being the most abundant species. Analysis of community structure indicated a high level of depth stratification within the myctophids, with evidence of diurnal vertical migration in some, but not all, species. Length-frequencies of G. braueri, G. nicholsi, E. antarctica and K. anderssoni were multimodal, suggesting that all life stages may be present in the northern Scotia Sea. In contrast, P. choriodon, P. bolini, G. fraseri and E. carlsbergi had unimodal distributions despite having multi-year lifecycles, indicating that they probably migrate into the region from warmer areas to the north. [ABSTRACT FROM AUTHOR]

Levels of infestation by the suctorian Ephelota sp. were determined in Antarctic krill taken in the north-eastern region of the Scotia sea, close to the island of South Georgia. Individuals caught in summer between 2002 and 2004 were measured for body length, eye diameter, moult stage, sex, sexual maturity and number of suctorian parasites. All krill samples were found to contain at least two modal size-classes and the complete range of maturity- and moult stages. Sample analysis for the different characters identified moult stage as an important determinant of infestation by Ephelota sp., with 66% of those about to moult (pre-moult individuals) being infested compared with 0% of post-moult individuals. Multiple Correspondence Analysis also identified a strong link between age and degree of suctorian infestation with large-eyed (and hence old) males having very high numbers of suctorian bodies. Moulting is costly in terms of energy and vulnerability, but it is believed that krill moult at relatively high rates throughout their life to facilitate growth and “shrinkage”. Here, we demonstrate that the control of external parasitism is also a major advantage of moulting at high frequency. The capacity of krill to maintain a high moult rate decreases with age, leading to older krill enduring higher parasitic loads. [ABSTRACT FROM AUTHOR]

The bivalve Lissarca notorcadensis is one of the most abundant species in Antarctic waters and has colonised the entire Antarctic shelf and Scotia Sea Islands. Its brooding reproduction, low dispersal capabilities and epizoic lifestyle predict limited gene flow between geographically isolated populations. Relationships between specimens from seven regions in the Southern Ocean and outgroups were assessed with nuclear 28S rDNA and mitochondrial cytochrome oxidase subunit I (COI) genes. The 28S dataset indicate that while Lissarca appears to be a monophyletic genus, there is polyphyly between the Limopsidae and Philobryidae. Thirteen CO1 haplotypes were found, mostly unique to the sample regions, and two distinct lineages were distinguished. Specimens from the Weddell and Ross Sea form one lineage while individuals from the banks and islands of the Scotia Sea form the other. Within each lineage, further vicariance was observed forming six regionally isolated groups. Our results provide initial evidence for reproductively isolated populations of L. notorcadensis. The islands of the Scotia Sea appear to act as centres of speciation in the Southern Ocean. [ABSTRACT FROM AUTHOR]

We describe in situ observations on nesting by the Scotia Sea (or blackfin) icefish Chaenocephalus aceratus (Lönnberg) that constitute the first substantive evidence of egg brooding and parental care by species of the family Channichthyidae. At Boutetoya Island six fish, all apparently male, were observed guarding egg nests at depths of 141–148 m during an ROV deployment. Eggs were laid as aggregated, round masses (~20–25 cm diameter) in shallow, circular depressions (~1-m diameter, ~20-cm depth) that were probably excavated by the parent(s) to protect the nests. The fish guardians remained tenaciously in contact with the eggs despite disturbances caused by the ROV, reacting to this threat with stress and defense behaviors. Because brooding fishes are more susceptible to the population impacts from trawl fisheries, we argue that this life history should be kept in mind in designing management schemes. [ABSTRACT FROM AUTHOR]

Two specimens of Campylonotus arntzianus sp. nov. were caught in the Antarctic Scotia Sea off Saunders Island (57°40.31'S, 26°27.81'W) using an Agassiz trawl at one station (depth: 475–589 m). The new species described here is the fifth representative of the monogeneric family Campylonotidae, and the first of the family south of the Antarctic Convergence. Campylonotus arntzianus sp. nov. is a shrimp of about 5 cm in total length. Due to similarities in adult morphology, C. arntzianus sp. nov. seems to be closely related to C. capensis, a deep-sea species from the Southern Atlantic Ocean. A simple key for the species identification of the Campylonotidae is provided. [ABSTRACT FROM AUTHOR]

Paraliparis orcadensis, from the South Orkney Islands (Scotia Sea), at 1.253 m depth, differs from all other congeneric species by the following combination of characters: a suture between upper and lower hypural plates, P 19 (13 + 3 + 3), none rudimentary, shortest notch ray 6.0% standard length, head length 15.6% standard length, short maxillary, gill slit above P base, three radials, symphyseal pores very closely set and body uniformly dark-grey coloured. Relationships of this new species with P. cerasinus, P. devriesi, P. mawsoni and P. tetrapteryx are discussed. [ABSTRACT FROM AUTHOR]