Sea ice concentration decline in an important Adélie penguin molt area.

Unlike in many polar regions, the spatial extent and duration of the sea ice season have increased in the Ross Sea sector of the Southern Ocean during the satellite era. Simultaneously, populations of Adélie penguins, a sea ice obligate, have been stable or increasing in the region. Relationships between Adélie penguin population growth and sea ice concentration (SIC) are complex, with sea ice driving different, sometimes contrasting, demographic patterns. Adélie penguins undergo a complete molt annually, replacing all their feathers while fasting shortly after the breeding season. Unlike most penguin species, a majority of Adélies are thought to molt on sea ice, away from the breeding colonies, which makes this period particularly difficult to study. Here, we evaluate the hypothesis that persistent areas of high SIC provide an important molting habitat for Adélie penguins. We analyzed data from geolocating dive recorders deployed year-round on 195 adult penguins at two colonies in the Ross Sea from 2017 to 2019. We identified molt by detecting extended gaps in postbreeding diving activity and used associated locations to define two key molting areas. Remotely sensed data indicated that SIC during molt was anomalously low during the study and has declined in the primary molt area since 1980. Further, annual return rates of penguins to breeding colonies were positively correlated with SIC in the molt areas over 20 y. Together these results suggest that sea ice conditions during Adélie penguin molt may represent a previously underappreciated annual bottleneck for adult survival.

Effect of PAR irradiance intensity on Phaeocystis antarctica (Prymnesiophyceae) growth and DMSP, DMSO, and acrylate concentrations.

Phaeocystis antarctica forms extensive spring blooms in the Southern Ocean that coincide with high concentrations of dimethylsulfoniopropionate (DMSP), dimethylsulfoxide (DMSO), dimethylsulfide (DMS), and acrylate. We determined how concentrations of these compounds changed during the growth of axenic P. antarctica cultures exposed to light-limiting, sub-saturating, and saturating PAR irradiances. Cellular DMSP concentrations per liter cell volume (CV) ranged between 199 and 403 mmol · LCV -1 , with the highest concentrations observed under light-limiting PAR. Cellular acrylate concentrations did not change appreciably with a change in irradiance level or growth, ranging between 18 and 45 mmol · LCV -1 , constituting an estimated 0.2%-2.8% of cellular carbon. Both dissolved acrylate and DMSO increased substantially with irradiance during exponential growth on a per-cell basis, ranging from 0.91 to 3.15 and 0.24 to 1.39 fmol · cell-1 , respectively, indicating substantial export of these compounds into the dissolved phase. Average cellular DMSO:DMSP ratios increased 7.6-fold between exponential and stationary phases of batch growth, with a 3- to 13-fold increase in cellular DMSO likely formed from abiotic reactions of DMSP and DMS with reactive oxygen species (ROS). At mM levels, cellular DMSP and acrylate are proposed to serve as de facto antioxidants in P. antarctica not regulated by oxidative stress or changes in ROS. Instead, cellular DMSP concentrations are likely controlled by other physiological processes including an overflow mechanism to remove excess carbon via acrylate, DMS, and DMSO during times of unbalanced growth brought on by physical stress or nutrient limitation. Together, these compounds should aid P. antarctica in adapting to a range of PAR irradiances by maintaining cellular functions and reducing oxidative stress.

Textile microfibers in wild Antarctic whelk Neobuccinum eatoni (Smith, 1875) from Terra Nova Bay (Ross Sea, Antarctica).

Antarctica has been affected directly and indirectly by human pressure for more than two centuries and recently plastic pollution has been recognized as a further potential threat for its unique biodiversity. Global long-range transport as well as local input from anthropogenic activities are potential sources of plastic pollution in both terrestrial and marine Antarctic territories. The present study evaluated the presence of microplastics in specimens of the Antarctic whelk Neobuccinum eatoni, a key species in benthic communities of the Ross Sea, one of the largest marine protected areas worldwide. To this aim, a thermo-oxidative extraction method was applied for microplastic isolation and quantification, and polymer identification was performed by manual µ-FTIR spectroscopy. Textile (semi-)synthetic or composite microfibers (length range: 0.8-5.7 mm) were found in 27.3% of whelk specimens, suggesting a low risk of bioaccumulation along Antarctic benthic food webs in the Ross Sea. Their polymer composition (of polyethylene terephthalate and cellulose-polyamide composites) matched those of outdoor technical clothing in use by the personnel of the Italian "Mario Zucchelli" station near Terra Nova Bay in the Ross Sea. Such findings indicate that sewage from base stations may act as potential local sources of textile microplastic fibers in this remote environment. More in-depth monitoring studies aiming at defining the extent of microplastic contamination related to such sources in Antarctica are encouraged.

A regional-scale approach for modeling primary production and biogenic silica export in the Southern Ocean.

Persistent uncertainties in the representations of net primary production (NPP) and silicate in the Southern Ocean have been noted in recent assessments ofthe ocean biogeochemical components of Earth system models (ESMs). Consequently, more mechanistic studies at the regional scale are required. To reduce these uncertainties, we applied a one-dimensional (1D) marine ecosystem model to different bioregions in the Southern Ocean: the Polar Frontal Zone in the Pacific sector, the seasonal sea ice zone in the northwestern Ross Sea, and the inner shelf of Terra Nova Bay. To make the existing ecosystem model applicable to the Southern Ocean, we modified the phytoplankton physiology (stoichiometry depending on species) and the silicate cycle (dissolution rate of biogenic silica (BSi) depending on latitude) in the model. We quantified and compared seasonal variations in several limitation factors of NPP, namely, iron, irradiance, silicate and temperature, in the three regions. The simulation results showed that dissolved iron plays the most significant role in determining the magnitude of NPP and the phytoplankton community structure during summer. Additionally, the modified model successfully reproduced the vertical flux of BSi and particulate organic carbon (POC). The POC export efficiency was high in the inner shelf zone, which had high levels of iron concentration, NPP, and Phaeocystis biomass. In contrast, BSi export occurred most efficiently in the Polar Frontal Zone, where diatoms are dominant, the BSi dissolution rate is low, and NPP is extremely low. Our results from the integrated mechanistic framework at the regional scale demonstrate which specific processes should be urgently included in ESMs for better representation of the biogeochemical dynamics in the Southern Ocean.

Antarctic ice sheet sensitivity to atmospheric CO2 variations in the early to mid-Miocene.

Geological records from the Antarctic margin offer direct evidence of environmental variability at high southern latitudes and provide insight regarding ice sheet sensitivity to past climate change. The early to mid-Miocene (23-14 Mya) is a compelling interval to study as global temperatures and atmospheric CO2 concentrations were similar to those projected for coming centuries. Importantly, this time interval includes the Miocene Climatic Optimum, a period of global warmth during which average surface temperatures were 3-4 °C higher than today. Miocene sediments in the ANDRILL-2A drill core from the Western Ross Sea, Antarctica, indicate that the Antarctic ice sheet (AIS) was highly variable through this key time interval. A multiproxy dataset derived from the core identifies four distinct environmental motifs based on changes in sedimentary facies, fossil assemblages, geochemistry, and paleotemperature. Four major disconformities in the drill core coincide with regional seismic discontinuities and reflect transient expansion of grounded ice across the Ross Sea. They correlate with major positive shifts in benthic oxygen isotope records and generally coincide with intervals when atmospheric CO2 concentrations were at or below preindustrial levels (∼280 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for substantial ice mass loss during episodes of high (∼500 ppm) atmospheric CO2 These new drill core data and associated ice sheet modeling experiments indicate that polar climate and the AIS were highly sensitive to relatively small changes in atmospheric CO2 during the early to mid-Miocene.

Widespread collapse of the Ross Ice Shelf during the late Holocene.

The stability of modern ice shelves is threatened by atmospheric and oceanic warming. The geologic record of formerly glaciated continental shelves provides a window into the past of how ice shelves responded to a warming climate. Fields of deep (-560 m), linear iceberg furrows on the outer, western Ross Sea continental shelf record an early post-Last Glacial Maximum episode of ice-shelf collapse that was followed by continuous retreat of the grounding line for ∼200 km. Runaway grounding line conditions culminated once the ice became pinned on shallow banks in the western Ross Sea. This early episode of ice-shelf collapse is not observed in the eastern Ross Sea, where more episodic grounding line retreat took place. More widespread (∼280,000 km(2)) retreat of the ancestral Ross Ice Shelf occurred during the late Holocene. This event is recorded in sediment cores by a shift from terrigenous glacimarine mud to diatomaceous open-marine sediment as well as an increase in radiogenic beryllium ((10)Be) concentrations. The timing of ice-shelf breakup is constrained by compound specific radiocarbon ages, the first application of this technique systematically applied to Antarctic marine sediments. Breakup initiated around 5 ka, with the ice shelf reaching its current configuration ∼1.5 ka. In the eastern Ross Sea, the ice shelf retreated up to 100 km in about a thousand years. Three-dimensional thermodynamic ice-shelf/ocean modeling results and comparison with ice-core records indicate that ice-shelf breakup resulted from combined atmospheric warming and warm ocean currents impinging onto the continental shelf.

Antarcticibacterium flavum gen. nov., sp. nov., isolated from marine sediment.

A Gram-stain-negative, strictly aerobic, yellow-pigmented, non-gliding, oval to rod-shaped bacterial strain, designated JB01H24T, belonging to the family Flavobacteriaceae, was isolated from marine surface sediment collected from the Ross Sea, Antarctica. Strain JB01H24T grew at 4-40 °C (optimum 25-30 °C), pH 7.0-9.0 (optimum 7.5-8.0), and in the presence of 0-8 % NaCl (optimum 3 %, w/v). Phylogenetic analysis based on 16S rRNA gene sequences showed that strain JB01H24T formed an independent linkage within the family Flavobacteriaceae and was closely related with the genus Gillisia. Strain JB01H24T exhibited 16S rRNA gene sequence similarities of 95.3-91.5 % and 94.9-94.0 % to the type strains of the genera Gillisia and Salinimicrobium, respectively. The major fatty acids (>5 %) were iso-C15 : 0, summed feature 3 (C16 : 1ω6c and/or C16 : 1ω7c), anteiso-C15 : 0, iso-C15 : 1 G and summed feature 9 (iso-C17 : 1ω9c and/or 10-methyl C16 : 0). The major polar lipids were phosphatidylethanolamine, seven unidentified lipids, two unidentified aminolipids and an unidentified aminophospholipid. Strain JB01H24T contained menaquinone-6 as the only ubiquinone. The DNA G+C content was 42.4 mol%. On the basis of phylogenetic, physiological and chemotaxonomic properties, strain JB01H24T is considered to represent a novel species of a new genus within the family Flavobacteriaceae, for which the name Antarcticibacterium flavum gen. nov., sp. nov. is proposed. The type strain of Antarcticibacterium flavum is JB01H24T (=GDMCC 1.1229T=KCTC 52984T).

Gramella antarctica sp. nov., isolated from marine surface sediment.

A Gram-stain-negative, aerobic, yellow-coloured, motile by gliding, rod-shaped bacterial strain, designated R17H11T, was isolated from surface sediment collected from the Ross Sea, Antarctica. Growth optimally occurred at 25-30 °C, at pH 7.0-7.5 and in the presence of 3 % NaCl (w/v). Phylogenetic trees based on 16S rRNA gene sequences indicated that strain R17H11T clustered together with Gramella flava JLT2011T and fell within the genus Gramella. Strain R17H11T shared the highest 16S rRNA gene similarities (96.1 and 96.0 %) with the type strains of Gramella forsetii and G. flava, and 92.6-95.5 % similarities with those of other known Gramella species. Strain R17H11T contained menaquinone-6 as the only isoprenoid quinone. The major fatty acids (>5 %) were summed feature 3 (17.5 %, comprising C16 : 1ω7c and/or C16 : 1ω6c), iso-C15 : 0 (14.0 %), summed feature 9 (11.8 %, comprising 10-methyl C16 : 0 and/or iso-C17 : 1ω9c), iso-C17 : 0 3-OH (11.8 %), iso-C16 : 0 (7.4 %), C17 : 1ω6c (6.9 %) and anteiso-C15 : 0 (5.1 %). The major polar lipids were phosphatidylethanolamine, four unidentified lipids, an unidentified aminolipid, an unidentified aminophospholipid and an unidentified glycolipid. The DNA G+C content of strain R17H11T was 38.6 mol%. On the basis of the phylogenetic, physiological and chemotaxonomic characteristics, strain R17H11T represents a novel species in the genus Gramella, for which the name Gramellaantarctica sp. nov. is proposed. The type strain of the novel species is R17H11T (=GDMCC 1.1208T=KCTC 52925T).

Arenibacter catalasegens sp. nov., isolated from marine surface sediment, and emended description of the genus Arenibacter.

A Gram-staining-negative, aerobic, non-motile, rod-shaped bacterium, designated as P308H10T, was isolated from surface sediment of the Southern Indian Ocean. Growth occurred at 4-36 °C (optimum 20-25 °C), pH 6.0-8.5 (optimum 7.5-8.0) and in the presence of 1-8 % (w/v) NaCl (optimum 2-3 %). Phylogenetic analysis based on 16S rRNA gene sequences showed that strain P308H10T lies within the clade of members of the genus Arenibacter and is closely related to Arenibacterhampyeongensis HP12T (98.0 %), Arenibacterechinorum KMM 6032T (98.4 %), Arenibacterpalladensis LMG 21972T (97.9 %), Arenibactertroitsensis KMM 3674T (97.9 %) and 'Arenibacter algicola' TG409 (98.1 %). The average nucleotide identity and digital DNA-DNA hybridization values between strain P308H10T and the five reference strains were 85.9-80.6 % and 30.2-23.6 %, respectively. The major fatty acids (>10 %) of strain P308H10T were summed feature 3, iso-C17 : 0 3-OH, iso-C15 : 1 G and iso-C15 : 0. The major polar lipids comprised phosphatidylethanolamine, five unidentified aminolipids and four unidentified lipids. The only respiratory quinone was menaquinone-6. The genomic DNA G+C content was 38.2 mol%. On the basis of the phenotypic, phylogenetic and chemotaxonomic data presented, strain P308H10T represents a novel species of the genus Arenibacter, for which the name Arenibacter catalasegens sp. nov. is proposed. The type strain is P308H10T (=GDMCC 1.1230T=KCTC 52983T). An emended description of the genus Arenibacter is also proposed.

The extraordinary longevity of kleptoplasts derived from the Ross Sea haptophyte Phaeocystis antarctica within dinoflagellate host cells relates to the diminished role of the oxygen-evolving Photosystem II and to supplementary light harvesting by mycosporine-like amino acid/s.

The haptophyte Phaeocystis antarctica and the novel Ross Sea dinoflagellate that hosts kleptoplasts derived from P. antarctica (RSD; R.J. Gast et al., 2006, J. Phycol. 42 233-242) were compared for photosynthetic light harvesting and for oxygen evolution activity. Both chloroplasts and kleptoplasts emit chlorophyll a (Chl a) fluorescence peaking at 683nm (F683) at 277K and at 689 (F689) at 77K. Second derivative analysis of the F689 band at 77K revealed two individual contributions centered at 683nm (Fi-683) and at 689 (Fi-689). Using the p-nitrothiophenol (p-NTP) treatment of Kobayashi et al. (Biochim. Biophys. Acta 423 (1976) 80-90) to differentiate between Photosystem (PS) II and I fluorescence emissions, we could identify PS II as the origin of Fi-683 and PS I as the origin of Fi-689. Both emissions could be excited not only by Chl a-selective light (436nm) but also by mycosporine-like amino acids (MAAs)-selective light (345nm). This suggests that a fraction of MAAs must be proximal to Chls a and, therefore, located within the plastids. On the basis of second derivative fluorescence spectra at 77K, of p-NTP resolved fluorescence spectra, as well as of PSII-driven oxygen evolution activities, PS II appears substantially less active (~1/5) in dinoflagellate kleptoplasts than in P. antarctica chloroplasts. We suggest that a diminished role of PS II, a known source of reactive oxygen species, and a diminished dependence on nucleus-encoded light-harvesting proteins, due to supplementary light-harvesting by MAAs, may account for the extraordinary longevity of RSD kleptoplasts.

Transcriptomic response of the Antarctic pteropod Limacina helicina antarctica to ocean acidification.

BACKGROUND: Ocean acidification (OA), a change in ocean chemistry due to the absorption of atmospheric CO2 into surface oceans, challenges biogenic calcification in many marine organisms. Ocean acidification is expected to rapidly progress in polar seas, with regions of the Southern Ocean expected to experience severe OA within decades. Biologically, the consequences of OA challenge calcification processes and impose an energetic cost. RESULTS: In order to better characterize the response of a polar calcifier to conditions of OA, we assessed differential gene expression in the Antarctic pteropod, Limacina helicina antarctica. Experimental levels of pCO2 were chosen to create both contemporary pH conditions, and to mimic future pH expected in OA scenarios. Significant changes in the transcriptome were observed when juvenile L. h. antarctica were acclimated for 21 days to low-pH (7.71), mid-pH (7.9) or high-pH (8.13) conditions. Differential gene expression analysis of individuals maintained in the low-pH treatment identified down-regulation of genes involved in cytoskeletal structure, lipid transport, and metabolism. High pH exposure led to increased expression and enrichment for genes involved in shell formation, calcium ion binding, and DNA binding. Significant differential gene expression was observed in four major cellular and physiological processes: shell formation, the cellular stress response, metabolism, and neural function. Across these functional groups, exposure to conditions that mimic ocean acidification led to rapid suppression of gene expression. CONCLUSIONS: Results of this study demonstrated that the transcriptome of the juvenile pteropod, L. h. antarctica, was dynamic and changed in response to different levels of pCO2. In a global change context, exposure of L. h. antarctica to the low pH, high pCO2 OA conditions resulted in a suppression of transcripts for genes involved in key physiological processes: calcification, metabolism, and the cellular stress response. The transcriptomic response at both acute and longer-term acclimation time frames indicated that contemporary L. h. antarctica may not have the physiological plasticity necessary for adaptation to OA conditions expected in future decades. Lastly, the differential gene expression results further support the role of shelled pteropods such as L. h. antarctica as sentinel organisms for the impacts of ocean acidification.

The challenges of detecting subtle population structure and its importance for the conservation of emperor penguins.

Understanding the boundaries of breeding populations is of great importance for conservation efforts and estimates of extinction risk for threatened species. However, determining these boundaries can be difficult when population structure is subtle. Emperor penguins are highly reliant on sea ice, and some populations may be in jeopardy as climate change alters sea-ice extent and quality. An understanding of emperor penguin population structure is therefore urgently needed. Two previous studies have differed in their conclusions, particularly whether the Ross Sea, a major stronghold for the species, is isolated or not. We assessed emperor penguin population structure using 4,596 genome-wide single nucleotide polymorphisms (SNPs), characterized in 110 individuals (10-16 per colony) from eight colonies around Antarctica. In contrast to a previous conclusion that emperor penguins are panmictic around the entire continent, we find that emperor penguins comprise at least four metapopulations, and that the Ross Sea is clearly a distinct metapopulation. Using larger sample sizes and a thorough assessment of the limitations of different analytical methods, we have shown that population structure within emperor penguins does exist and argue that its recognition is vital for the effective conservation of the species. We discuss the many difficulties that molecular ecologists and managers face in the detection and interpretation of subtle population structure using large SNP data sets, and argue that subtle structure should be taken into account when determining management strategies for threatened species, until accurate estimates of demographic connectivity among populations can be made.

Arenibacter antarcticus sp. nov., isolated from marine sediment.

A strictly aerobic, Gram-stain-negative, pale-golden, rod-shaped bacterium, designated as R18H21T, was isolated from marine sediment collected from the Ross Sea, Antarctica. Strain R18H21T grew at 4-40 °C (optimum 25 °C), at pH 6.3-9.2 (optimum 7.5-8.5) and in 0.5-6 % (w/v) NaCl (optimum 2 %). Phylogenetic analyses based on 16S rRNA gene sequences showed that strain R18H21T belonged to the genus Arenibacter, with the highest similarity to two type strains, Arenibacter latericius KMM 426T (96.6 %) and Arenibacter certesii KMM 3941T (96.6 %), and lower similarities (95.2-95.9 %) to five other members of the genus Arenibacter. The major fatty acids were iso-C17 : 0 3-OH, Summed Feature 3 (C16 : 1ω6c and/or C16 : 1ω7c), iso-C15 : 0, iso-C15 : 1 G. The major polar lipids were phosphatidylethanolamine, an unidentified aminolipid and an unidentified phospholipid. The respiratory quinone of strain R18H21T was menaquinone-6. The DNA G+C content was 40.0 mol%. Based on phylogenetic, physiological and chemotaxonomic features, strain R18H21T has been classified as a novel species in the genus Arenibacter, for which the name Arenibacterantarcticus sp. nov. is proposed. The type strain of the novel species is R18H21T (=GDMCC 1.1159T=KCTC 52924T).

Aurantimonas aggregata sp. nov., isolated from deep-sea sediment.

A novel bacterium, designated R14M6T, was isolated from deep-sea sediment collected from the Ross Sea, Antarctica. Cells are Gram-stain-negative, aerobic, pale yellow, short-rod-shaped, polar-flagellated and aggregate-forming. Growth occurs at 4-36 °C, pH 6.0-8.3, and in 1-15 % (w/v) NaCl. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain R14M6T clustered together with Aurantimonas endophytica EGI6500337T and fell within the genus Aurantimonas. The 16S rRNA gene sequence of strain R14M6T shared similarity with A. endophytica EGI6500337T (99.15 %), A. manganoxydans DSM 21871T (97.73 %), A. coralicida DSM 14790T (97.58 %) and 'A. litoralis' KCTC 12094 (97.51 %). The DNA-DNA relatedness values between strain R14M6T and A. endophytica EGI6500337T, A. coralicida DSM 14790T, A. manganoxydans DSM 21871T and 'A. litoralis' KCTC 12094 were 36.9±4.5, 27.6±2.8, 29.6±1.2 and 25.2±2.4 % respectively. The major fatty acid of strain R14M6T was C18 : 1ω7c. The major polar lipids were phosphatidylcholine, diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and an unidentified aminolipid. Strain R14M6T contained Q-10 as the dominant isoprenoid quinone. The DNA G+C content of strain R14M6T was 67.4 mol%. Based on the phylogenetic, physiological and chemotaxonomic analyses, strain R14M6T represents a novel species of the genus Aurantimonas, for which the name Aurantimonas aggregata sp. nov. is proposed. The type strain is R14M6T (=GDMCC 1.1202T=KCTC 52919T).

Coping with the loss of large, energy-dense prey: a potential bottleneck for Weddell Seals in the Ross Sea.

Extraction of Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea began in 1997, following a management plan that targets the largest fish with a goal of reducing the spawning biomass by 50% over 35 yr. We investigate the potential long-term consequences of the reduced availability of this prey for Weddell seals (Leptonychotes weddellii). Energy demands in seals are acute, especially immediately following lactation, when females must recover substantial mass and cope with molting costs. We tested the hypothesis that toothfish are critically important for adult female seals during this period. Toothfish body mass is three orders of magnitude greater, and its energy density nearly double that of the most common seal prey, Antarctic silverfish (Pleuragramma antarcticum). Reduction or elimination of toothfish consumption could impair a female's ability to sufficiently recover and successfully produce a pup in the following pupping season. Our goals are to (1) illustrate mechanisms and conditions whereby toothfish depletion might plausibly affect seal population trends; (2) identify measurable parameters of the seals' ecology that may help better understand the potential negative impact of toothfish depletion on seal populations; and (3) promote a precautionary management approach for the fishery that includes monitoring of seal populations We constructed a set of inter-linked models of seal diving behavior, physiological condition, and demography based on existing information. We evaluate the effect of the following factors on seal mass recovery and intrinsic population growth rates: fishery depletion rate, daily diving limits, probability of a successful dive, and body mass recovery target. We show that loss of toothfish has the greatest potential impact on seal populations' growth rate. Under some scenarios, populations may decrease at >10% per year. Critical parameters to better understand fishery impacts include prevalence and size of toothfish in the seals' diet; the relationship between diet and the rate of mass recovery; and female breeding propensity in relation to body condition at the end of the molting period. Our results lend support to concerns about the potential negative impact of toothfish extraction in the Ross Sea; and to advocate for a precautionary management approach by the fishery.

Patterns of age-related change in reproductive effort differ in the pre-natal and post-natal periods in a long-lived mammal.

Age-related changes in maternal reproductive allocation for long-lived species are a key prediction from life-history theory. Theoretical and empirical work suggests that allocation may increase with age due to constraint (increases with experience) or restraint (increases with age in the face of declining residual reproductive value), and may decrease among the oldest aged animals due to senescence in reproductive function. Here, we use a hierarchical modelling approach to investigate the age-related patterns of change in maternal reproductive effort in the Weddell seal, a long-lived marine mammal with a protracted period of maternal care during which mothers allocate a large proportion of body mass while feeding little. We find that maternal allocation increases with age for young mothers during both the pre-natal and post-natal periods. In contrast, older mothers demonstrate a senescent decline in pre-natal allocation but allocate more of their declining resources to their offspring during the post-natal period. We also find strong evidence for the importance of individual effects in reproductive allocation among mothers: some mothers consistently produce heavier (or lighter) pups than expected. Our results indicate that maternal allocation changes over a mother's reproductive life span and that age-specific differences differ in notable ways in pre-natal and post-natal periods.

Too much of a good thing: sea ice extent may have forced emperor penguins into refugia during the last glacial maximum.

The relationship between population structure and demographic history is critical to understanding microevolution and for predicting the resilience of species to environmental change. Using mitochondrial DNA from extant colonies and radiocarbon-dated subfossils, we present the first microevolutionary analysis of emperor penguins (Aptenodytes forsteri) and show their population trends throughout the last glacial maximum (LGM, 19.5-16 kya) and during the subsequent period of warming and sea ice retreat. We found evidence for three mitochondrial clades within emperor penguins, suggesting that they were isolated within three glacial refugia during the LGM. One of these clades has remained largely isolated within the Ross Sea, while the two other clades have intermixed around the coast of Antarctica from Adélie Land to the Weddell Sea. The differentiation of the Ross Sea population has been preserved despite rapid population growth and opportunities for migration. Low effective population sizes during the LGM, followed by a rapid expansion around the beginning of the Holocene, suggest that an optimum set of sea ice conditions exist for emperor penguins, corresponding to available foraging area.

Selective feeding and foreign plastid retention in an Antarctic dinoflagellate.

The peridinin-containing plastid found in most photosynthetic dinoflagellates is thought to have been replaced in a few lineages by plastids of chlorophyte, diatom, or haptophyte origin. Other distinct lineages of phagotrophic dinoflagellates retain functional plastids obtained from algal prey for different durations and with varying source species specificity. 18S rRNA gene sequence analyses have placed a novel gymnodinoid dinoflagellate isolated from the Ross Sea (RSD) in the Kareniaceae, a family of dinoflagellates with permanent plastids of haptophyte origin. In contrast to other species in this family, the RSD contains kleptoplastids sequestered from its prey, Phaeocystis antarctica. Culture experiments were employed to determine whether the RSD fed selectively on P. antarctica when offered in combination with another polar haptophyte or cryptophyte species, and whether the RSD, isolated from its prey and starved, would take up plastids from P. antarctica or from other polar haptophyte or cryptophyte species. Evidence was obtained for selective feeding on P. antarctica, plastid uptake from P. antarctica, and increased RSD growth in the presence of P. antarctica. The presence of a peduncle-like structure in the RSD suggests that kleptoplasts are obtained by myzocytosis. RSD cells incubated without P. antarctica were capable of survival for at least 29.5 months. This remarkable longevity of the RSD's kleptoplasts and its species specificity for prey and plastid source is consistent with its prolonged co-evolution with P. antarctica. It may also reflect the presence of a plastid protein import mechanism and genes transferred to the dinokaryon from a lost permanent haptophyte plastid.

Planktonic, benthic and sympagic copepods collected from the desalination unit of Mario Zucchelli Research Station in Terra Nova Bay (Ross Sea, Antarctica).

Background: Distributional data on planktonic, benthic and sympagic copepods collected in the framework of the XXXIVth Expeditions of the Italian National Antarctic Programme (PNRA) to the Ross Sea sector from 2018-2019 are here provided. These occurrences correspond to specimens collected from the 25 µm filters used in the desalination plant of the Italian research station "Mario Zucchelli" (MZS), located in the Terra Nova Bay area (TNB; Ross Sea, Antarctica). This dataset is a contribution to the Antarctic Biodiversity Portal, the thematic Antarctic node for both the Ocean Biogeographic Information System (AntOBIS) and the Global Biodiversity Information Facility Antarctic Biodiversity Information Facility (ANTABIF). The dataset was uploaded and integrated with the SCAR-AntOBIS database (the geospatial component of SCAR-MarBIN). Please follow the guidelines from the SCAR Data Policy (ISSN 1998-0337) when using the data. If you have any questions regarding this dataset, please 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 the biodiversity-aq GitHub project. New information: We describe the diversity of marine copepods Terra Nova Bay sampled by the filters installed in the desalination unit (DU) of the Italian research station "Mario Zucchelli" described in recent work. The opening of the intake pipe of the DU is positioned at a depth of 4 m and allowed a total of 2,116 specimens to be sampled and recognised. In addition, new occurrence records of copepod genera and species are reported in the same zone. We provide an overview of the marine copepod diversity reported for TNB. The total of 2,116 individuals corresponds to 14 genera and 15 species and is represented by 136 occurrence records in this dataset. Around 52% of the total number of species are new records for the TNB area. The publication of this data paper was funded by the Belgian Science Policy Office (BELSPO, contract n°FR/36/AN1/AntaBIS) in the Framework of EU-Lifewatch as a contribution to the SCAR Antarctic biodiversity portal (biodiversity.aq).

Geographical distribution of the mesozooplankton community in highly productive coastal polynyas of the Ross Sea region marine protected area (RSR MPA) during early summer.

We investigated the recent spatial variation in the mesozooplankton community on the broad shelf of the RSR MPA during the bloom season. The mesozooplankton community was geographically divided into three regions: the Terra Nova Bay polynya, the Ross Sea polynya, and the marginal polynya. Larval euphausiids were dominant in the two polynya regions, whereas copepods were predominant in the marginal polynya region. Salinity, sea ice, and dissolved oxygen related to the different water mass compositions were the most significant factors distinguishing the mesozooplankton community. The key environmental variable separating the three groups was salinity. In accordance with the relatively high mesozooplankton abundance in the polynya regions, the occurrence and size of the polynyas in the December Ross Sea are thought to affect the spatial distribution of mesozooplankton. Consequently, this study indicates that two polynyas in the Ross Sea are vital habitats for krill during summer. Our observation results provide fundamental information for evaluating marine ecosystems and establishing a management plan for the RSR MPA.