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In this work, we describe a new sponge species belonging to the genus Coelosphaera Thomson, 1873. It was collected during an Argentinean Summer Antarctic Research Cruise onboard the Research Vessel BPuerto Deseado^ in March 2014, near South Orkney Islands (Antarctica), 60° 53′S42°35′W, 487-m depth. Coelosphaera (Coelosphaera) koltuni sp. nov. is a globular, fistular and hollowshaped sponge, with significantly larger megascleres (almost twice the length) than other Antarctic and New Zealand Coelosphaera species. We provide comparative data of all the described Coelosphaera species, especially those from nearby, SI

Ocean acidification (OA) could become a serious threat for theAntarctic marine ecosystem over coming years, as the solubility of atmosphericCO2 and CaCO3 minerals increases at lower temperatures.We evaluated the effect of OA on the stress response of the limpet Nacella concinna by measuring geneexpression levels. The experiment was performed with the two ecotypes (Littoraland Sublittoral) of the species during 54 days (IPCC 2019 scenario RCP8.5; control, ~375 ppm;low-pH treatment, ~923 ppm). Exposure to low-pH treatment during 15 days triggered thedown-regulation of two heat-shock protein genes (HSP70A, HSP70B) only in sublittoralindividuals. Little variation in the relative expression values of all genes in both ecotypes was observed probably,due to a historicalexposure to the substantial daily naturalpH fluctuations recorded in the study area during the experiment. This study provides relevant baseline data for future OAexperiments on coastal species in Antarctica., SI

Benthic organisms of the Southern Ocean are particularly vulnerable to ocean acidification (OA), as they inhabit cold waters where calcite-aragonite saturation states are naturally low. OA most strongly affects animals with calcium carbonate skeletons or shells, such as corals and mollusks. We exposed the abundant cold-water coral Malacobelemnon daytoni from an Antarctic fjord to low pH seawater (LpH) (7.68 ± 0.17) to test its physiological responses to OA, at the level of gene expression (RT-PCR) and enzyme activity. Corals were exposed in short- (3 days) and long-term (54 days) experiments to two pCO2 conditions (ambient and elevated pCO2 equaling RCP 8.5, IPCC 2019, approximately 372.53 and 956.78 μatm, respectively). Of the eleven genes studied through RT-PCR, six were significantly upregulated compared with control in the short-term in the LpH condition, including the antioxidant enzyme superoxide dismutase (SOD), Heat Shock Protein 70 (HSP70), Toll-like receptor (TLR), galaxin and ferritin. After long-term exposure to low pH conditions, RT-PCR analysis showed seven genes were upregulated. These include the mannose-binding C-Lectin and HSP90. Also, the expression of TLR and galaxin, among others, continued to be upregulated after long-term exposure to LpH. Expression of carbonic anhydrase (CA), a key enzyme involved in calcification, was also significantly upregulated after long-term exposure. Our results indicated that, after two months, M. daytoni is not acclimatized to this experimental LpH condition. Gene expression profiles revealed molecular impacts that were not evident at the enzyme activity level. Consequently, understanding the molecular mechanisms behind the physiological processes in the response of a coral to LpH is critical to understanding the ability of polar species to cope with future environmental changes. Approaches integrating molecular tools into Antarctic ecological and/or conservation research make an essential contribution given the current ongoing OA processes.

Simple Summary Compared to more accessible sites, organisms inhabiting Antarctic waters have been poorly investigated. This study provides the first molecular resource (transcriptome from whole individual) for the eucalanoid copepod Rhincalanus gigas, one of the predominant zooplankton species of Antarctic waters. Sequence analyses identified possible adaptation strategies adopted by the organism to cope with cold environments. Among those, we identified in R. gigas transcriptome three predicted genes encoding for antifreeze proteins and gene duplication within the glutathione metabolism pathway. This new molecular resource, provided here, will be useful to study the physiology, ecology, and biology of R. gigas and it increases the information available for polar environments. Abstract Antarctic waters are the largest almost untapped diversified resource of our planet. Molecular resources for Antarctic organisms are very limited and mostly represented by sequences used for species genotyping. In this study, we present the first transcriptome for the copepod Rhincalanus gigas, one of the predominant zooplankton species of Antarctic waters. This transcriptome represents also the first molecular resource for an eucalanoid copepod. The transcriptome is of high quality and completeness. The presence of three predicted genes encoding antifreeze proteins and gene duplication within the glutathione metabolism pathway are suggested as possible adaptations to cope with this harsh environment. The R. gigas transcriptome represents a powerful new resource for investigating the molecular basis associated with polar biological processes and ecology.

12 pages, 4 figures, 3 tables, supplementary material http://journal.frontiersin.org/article/10.3389/fmicb.2017.00241/full#supplementary-material, During the Austral summer 2009 we studied three areas surrounding the Antarctic Peninsula: the Bellingshausen Sea, the Bransfield Strait and the Weddell Sea. We aimed to investigate, whether viruses or protists were the main agents inducing prokaryotic mortality rates, and the sensitivity to temperature of prokaryotic heterotrophic production and mortality based on the activation energy (Ea) for each process. Seawater samples were taken at seven depths (0.1–100 m) to quantify viruses, prokaryotes and protists abundances, and heterotrophic prokaryotic production (PHP). Viral lytic production, lysogeny, and mortality rates of prokaryotes due to viruses and protists were estimated at surface (0.1–1 m) and at the Deep Fluorescence Maximum (DFM, 12–55 m) at eight representative stations of the three areas. The average viral lytic production ranged from 1.0 ± 0.3 × 107 viruses ml−1 d−1 in the Bellingshausen Sea to1.3 ± 0.7 × 107 viruses ml−1 d−1 in the Bransfield Strait, while lysogeny, when detectable, recorded the lowest value in the Bellingshausen Sea (0.05 ± 0.05 × 107 viruses ml−1 d−1) and the highest in the Weddell Sea (4.3 ± 3.5 × 107 viruses ml−1 d−1). Average mortality rates due to viruses ranged from 9.7 ± 6.1 × 104 cells ml−1 d−1 in the Weddell Sea to 14.3 ± 4.0 × 104 cells ml−1 d−1 in the Bellingshausen Sea, and were higher than averaged grazing rates in the Weddell Sea (5.9 ± 1.1 × 104 cells ml−1 d−1) and in the Bellingshausen Sea (6.8 ± 0.9 × 104 cells ml−1 d−1). The highest impact on prokaryotes by viruses and main differences between viral and protists activities were observed in surface samples: 17.8 ± 6.8 × 104 cells ml−1 d−1 and 6.5 ± 3.9 × 104 cells ml−1 d−1 in the Weddell Sea; 22.1 ± 9.6 × 104 cells ml−1 d−1 and 11.6 ± 1.4 × 104 cells ml−1 d−1 in the Bransfield Strait; and 16.1 ± 5.7 × 104 cells ml−1 d−1 and 7.9 ± 2.6 × 104 cells ml−1 d−1 in the Bellingshausen Sea, respectively. Furthermore, the rate of lysed cells and PHP showed higher sensitivity to temperature than grazing rates by protists. We conclude that viruses were more important mortality agents than protists mainly in surface waters and that viral activity has a higher sensitivity to temperature than grazing rates. This suggests a reduction of the carbon transferred through the microbial food-web that could have implications in the biogeochemical cycles in a future warmer ocean scenario, This study was supported by the following projects: ATOS (POL2006-00550/CTM, P.I.: CD.) funded by the Spanish Ministerio de Ciencia e Innovación, YC work was supported by a Ph.D. fellowship from the MINECO (FPI grant)

To study how natural Southern Ocean phytoplankton communities acclimate to rapid fluctuations in irradiance levels that result from deep wind-driven mixing of the upper water column, we measured their fluorescence properties (Fv:Fm, maximum quantum yield of photosystem II; and qN, non-photochemical quenching) and pigment composition. Values of Fv:Fm were low (, 0.46) and qN was high (. 0.67) throughout the upper mixed layer (UML). Short-term (20-min) exposure to incident surface irradiance strongly reduced Fv:Fm and recovery was slow under subsequent incubation at low irradiance. This suggests that phytoplankton cells are frequently photodamaged when mixed up to the surface from depth. Recovery of Fv:Fm was suppressed when lincomycin was added, inhibiting synthesis of the photosystem II reaction center D1 protein. This indicates that D1 protein repair is crucial in maintaining photosynthetic performance under fluctuating irradiance levels. Regions within the Antarctic Circumpolar Current (ACC) with a deep UML had lower depth-integrated phytoplankton biomass than regions close to the Antarctic continent with a shallow UML. Surprisingly, the depth-averaged light level within the UML in these latter regions was lower than in the ACC. Thus, it appears that photodamage incurred during the high irradiance portion of the vertical mixing cycle, rather than light limitation, controls phytoplankton growth in regions of the Southern Ocean with a deep UML. This concept represents a shift from the widely accepted paradigm that phytoplankton growth in the open Southern Ocean is limited by low levels of light or inadequate iron supply. The Southern Ocean (south of 44uS) is an important component of the global carbon cycle due to its large size and unique physical and chemical characteristics. Recent studies indicate that some regions of the Southern Ocean are a strong sink for anthropogenic CO2 (Arrigo et al. 2008; Gruber et al. 2009) and that its lower latitudes are important areas of anthropogenic CO2 storage (Sabine et al. 2004). In regions south of the Polar Front, major inorganic nutrients such as nitrate, phosphate, and silicate are seldom fully utilized, but low trace metal concentrations, especially of iron (Fe), limit phytoplankton growth in large areas of the Southern Ocean (Martin et al. 1990; Boyd et al. 2007), making it the largest of the three high nutrient– low chlorophyll (HNLC) regions of the global ocean. In addition, phytoplankton productivity is light limited in many areas of the Southern Ocean because weak water column stratification and strong winds create deep mixed layers, especially in the vicinity of the Antarctic Circumpo