Contribution of sea ice microbial production to Antarctic benthic communities is driven by sea ice dynamics and composition of functional guilds

Organic matter produced by the sea ice microbial community (SIMCo) is an important link between sea ice dynamics and secondary production in near‐shore food webs of Antarctica. Sea ice conditions in McMurdo Sound were quantified from time series of MODIS satellite images for Sept. 1 through Feb. 28 of 2007–2015. A predictable sea ice persistence gradient along the length of the Sound and evidence for a distinct change in sea ice dynamics in 2011 were observed. We used stable isotope analysis (δ¹³C and δ¹⁵N) of SIMCo, suspended particulate organic matter (SPOM) and shallow water (10–20 m) macroinvertebrates to reveal patterns in trophic structure of, and incorporation of organic matter from SIMCo into, benthic communities at eight sites distributed along the sea ice persistence gradient. Mass‐balance analysis revealed distinct trophic architecture among communities and large fluxes of SIMCo into the near‐shore food web, with the estimates ranging from 2 to 84% of organic matter derived from SIMCo for individual species. Analysis of patterns in density, and biomass of macroinvertebrate communities among sites allowed us to model net incorporation of organic matter from SIMCo, in terms of biomass per unit area (g/m²), into benthic communities. Here, organic matter derived from SIMCo supported 39 to 71 per cent of total biomass. Furthermore, for six species, we observed declines in contribution of SIMCo between years with persistent sea ice (2008–2009) and years with extensive sea ice breakout (2012–2015). Our data demonstrate the vital role of SIMCo in ecosystem function in Antarctica and strong linkages between sea ice dynamics and near‐shore secondary productivity. These results have important implications for our understanding of how benthic communities will respond to changes in sea ice dynamics associated with climate change and highlight the important role of shallow water macroinvertebrate communities as sentinels of change for the Antarctic marine ecosystem.     

A device for remote sampling of benthic algae under ice

A benthic algae sampling device designed for use through surface ice, uses the principle of pivoting arms. It is designed to be activated below ice sheets and is capable of passing easily through a hole of 11 cm diameter bored by a SIPRE ice auger.     

Negative feedback in the cold: ice retreat produces new carbon sinks in Antarctica

Feedbacks on climate change so far identified are predominantly positive, enhancing the rate of change. Loss of sea‐ice, increase in desert areas, water vapour increase, loss of tropical rain forest and the restriction of significant areas of marine productivity to higher latitude (thus smaller geographical zones) all lead to an enhancement of the rate of change. The other major feedback identified, changes in cloud radiation, will produce either a positive feedback, if high level clouds are produced, or a negative feedback if low level clouds are produced. Few significant negative feedbacks have been identified, let alone quantified. Here, we show that the loss of ice shelves and retreat of coastal glaciers around the Antarctic Peninsula in the last 50 years has exposed at least 2.4 × 10⁴ km² of new open water. We estimate that these new areas of open water have allowed new phytoplankton blooms containing a total standing stock of ～5.0 × 10⁵ tonnes of carbon to be produced. New marine zooplankton and seabed communities have also been produced, which we estimate contain ～4.1 × 10⁵ tonnes of carbon. This previously unquantified carbon sink acts as a negative feedback to climate change. New annual productivity, as opposed to standing stock, amounts to 3.5 × 10⁶ tonnes yr^?1 of carbon, of which 6.9 × 10⁵ tonnes yr^?1 deposits to the seabed. By comparison the total aboveground biomasses of lowland American tropical rainforest is 160–435 tonnes ha^?1. Around 50% of this is carbon. On this basis the carbon held in new biomass described here is roughly equivalent to 6000–17 000 ha of tropical rainforest. As ice loss increases in polar regions this feedback will become stronger, and eventually, over thousands to hundreds of thousands of years, over 50 Mtonnes of new carbon could be fixed annually in new coastal phytoplankton blooms and over 10 Mtonnes yr^?1 locked in biological standing stock around Antarctica.     

Microbiota within the perennial ice cover of Lake Vida, Antarctica

Lake Vida, located in the McMurdo Dry Valleys, Antarctica, is an 'ice-sealed' lake with approximately 19 m of ice covering a highly saline water column (approximately 245 ppt). The lower portions of the ice cover and the lake beneath have been isolated from the atmosphere and land for circa 2800 years. Analysis of microbial assemblages within the perennial ice cover of the lake revealed a diverse array of bacteria and eukarya. Bacterial and eukaryal denaturing gradient gel electrophoresis phylotype profile similarities were low (<59%) between all of the depths compared (five depths spanning 11 m of the ice cover), with the greatest differences occurring between surface and deep ice. The majority of bacterial 16S rRNA gene sequences in the surface ice were related to Actinobacteria (42%) while Gammaproteobacteria (52%) dominated the deep ice community. Comparisons of assemblage composition suggest differences in ice habitability and organismal origin in the upper and lower portions of ice cover. Specifically, the upper ice cover microbiota likely reflect the modern day transport and colonization of biota from the terrestrial landscape, whereas assemblages in the deeper ice are more likely to be persistent remnant biota that originated from the ancient liquid water column of the lake that froze.     

Microbial loop malfunctioning in the annual sea ice at Terra Nova Bay (Antarctica)

We investigated organic carbon quantity and biochemical composition, prokaryotic abundance, biomass and carbon production in the annual and platelet sea ice of Terra Nova Bay (Antarctica), as well as the downward fluxes of organic matter released by melting ice during early spring. Huge amounts of biopolymeric C accumulated in the bottom layer of the ice column concomitantly with the early spring increase in sympagic algal biomass. Such organic material, mostly accounted for by autotrophic biomass, was characterised by a high food quality and was rapidly exported to the sea bottom during sea ice melting. Prokaryote abundance (up to 1.3 × 10⁹ cells L⁻¹) and extracellular enzymatic activities (up to 24.3 μM h⁻¹ for amino-peptidase activity) were extremely high, indicating high rates of organic C degradation in the bottom sea ice. Despite this, prokaryote C production values were very low (range 5–30 ng C L⁻¹ h⁻¹), suggesting that most of the degraded organic C was not channelled into prokaryote biomass. In the platelet ice, we found similar organic C concentrations, prokaryote abundance and biomass values and even higher extracellular enzymatic activities, but values of prokaryote C production (range 800–4,200 ng C L⁻¹ h⁻¹) were up to three orders of magnitude higher than in the intact bottom sea ice. Additional field and laboratory experiments revealed that the dissolved organic material derived from algae accumulating in the bottom sea ice significantly reduced prokaryote C production, suggesting the presence of a potential allopathic control of sympagic algae on prokaryote growth. This article belongs to a special topic: Five articles on Sea-ice communities in Terra Nova Bay (Ross Sea), coordinated by L. Guglielmo and V. Saggiomo, appear in this issue of Polar Biology. The studies were conducted in the frame of the National Program of Research in Antarctica (PNRA) of Italy.     

A new freshwater oligochaete species (Clitellata: Enchytraeidae) from Livingston Island,Antarctica

The new enchytraeid species Lumbricillus healyae sp. n. is described from freshwater streams, with well-oxygenated and poorly mineralised waters, situated in Byers Peninsula (Livingston Island, South Shetland Islands, Antarctica). Lumbricillus healyae sp. n. is morphologically close to L. antarcticus and L. incisus, and it is mainly distinguished by the structure of the spermatheca with a short, distinct ectal duct, the oval penial bulb (greatest diameter in the transverse body axis) associated with strong dorso-ventral muscular fibres, and a protrusible pseudopenis. A second undetermined Lumbricillus species is described from a small stream. Study specimens are not fully mature; however, the highly irregular form and size of the testis-sac lobes and the absence of a penial bulb encapsulated under a muscular layer are remarkable. It is probably related to a small group of Lumbricillus species reported from the Antarctic maritime region (L. colpites, L. griseus and L. aestum), characterised by the structure of the male duct, which ends in a simple pore surrounded by glands.

Broadscale patterns in the distribution of aquatic and terrestrial vegetation at three ice-free regions on Ross Island,Antarctica

Distribution patterns are presented for selected aquatic algae, and terrestrial algae, mosses and lichens, at three large, coastal ice-free regions on Ross Island. Each region is unique in certain aspects of its vegetation. The variation in areal and quantitative occurrence of different components of the vegetation in diverse ponds and streams, and over exposed ground surfaces, is related to the levels of marine salts in the environment, fertilisation by birds, water availability, substratum type and degree of exposure. A comparison is made with other antarctic, coastal, ice-free regions where similar broadscale patterns have been recognised.     

Bacterial community along a historic lake sediment core of Ardley Island, west Antarctica

The bacterial community in a historic lake sediment core of Ardley Island, Antarctica, spanning approximately 1,600 years, was investigated by molecular approaches targeting the 16S rRNA gene fragments. The cell number in each 1 cm layer of the sediment core was deduced through semi-quantification of the 16S rRNA gene copies by quantitative competitive PCR (QC-PCR). It was found that the total bacterial numbers remained relatively stable along the entire 59 cm sediment core. Denaturing Gradient Gel Electrophoresis (DGGE) analysis and sequencing of PCR-amplified 16S rRNA gene fragments were performed to analyze the bacterial diversity over the entire column. Principle coordinates analysis suggested that the bacterial communities along the sediment core could be separated into three groups. There were obvious bacterial community shift among groups of 1–20 cm, 21–46 cm and 46–59 cm. Diversity indices indicated that the bacterial community in the 21–46 cm depth showed the highest species diversity and uniformity. The main bacterial groups in the sediments fell into 4 major lineages of the gram-negative bacteria: the α, γ and δ subdivision of Proteobacteria, the Cytophaga-Flavobacteria-Bacteroides, and some unknown sequences. The gram-positive bacteria Gemmatimonadetes, Firmicutes and Actinobacteria were also detected. The results demonstrated the presence of highly diverse bacterial community population in the Antarctic lake sediment core. And the possible influence of climate and penguin population change on the bacterial community shift along the sediment core was discussed.Shengkang Li and Xiang Xiao contributed equally to this paper     

Albino Weddell seal at Cape Shirreff,Livingston Island,Antarctica

To our knowledge, this paper is the first record/report of a juvenile light-coloured Weddell seal (Leptonychotes weddellii) at Cape Shirreff, Livingston Island in January 1998, determining that it was an albino individual. Based on available literature, three cases of albino seals have been reported exclusively for Harbour seal pups, and no albino has been reported for Antarctic pagophilic true seals. Therefore, this is the first confirmed case of albinism in Antarctic pagophilic true seals species, indicating that this phenomenon is indeed of a rare occurrence.

Macrofaunal shallow benthic communities along a discontinuous annual cycle at Admiralty Bay,King George Island,Antarctica

Temporal variations in composition and density of the benthic macrofauna at two stations (12 and 25 m depth) were studied in Admiralty Bay, King George Island, Antarctica. Samples where carried out using an van Veen sampler between March and December 1999 (winter) and December 2000 and March 2001 (summer), comprising a discontinuous annual cycle. Sediment organic matter showed a marked seasonal cycle, with lowest values at middle winter. Communities showed little variations in density and composition. Temporal variations were not detected at 25 m depth. Variations at 12 m were related to one iceberg impact and to wind generated hydrodinamism, as a function of wind direction, intensity and fetch. As winter scarcity of primary production did not seem to affect macrofaunal community densities, nutrient availability for the benthos in winter can be related to the remineralization of sediment organic matter by bacterial activity.

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Response of nematode communities after large‐scale ice‐shelf collapse events in the Antarctic Larsen area

Owing to large‐scale ice‐shelf disintegration events, the Antarctic Larsen A and B areas recently became ice‐free. During the ANT‐XXIII/8 Polarstern campaign, this region was sampled for the first time. Our study is the first to investigate benthic communities in this area and their response to the collapse of ice shelves in the Antarctic. The nematofauna appears to be strongly influenced by the sudden ice‐cover removal, although its response differs from that of the macro‐ and megabenthos. Our results indicate that precollapse, sub‐ice communities were impoverished and characterized by low densities, low diversity and high dominance of a few taxa. This might still be visible at a station located deep inside the Larsen B embayment, where Halomonhystera was dominant. Post‐collapse recolonization of the ‘inner’ stations, i.e. those located furthermost from the former ice‐shelf edge, is believed to be a long‐time process. At the time of sampling, community structure at the inner stations was not or only slightly influenced by colonization, and might be structured by local environmental conditions. Our results indicate that a locally increased food supply after ice‐cover removal could provoke a faster, local response of the nematode assemblages compared with the response due to recolonization. Thalassomonhystera is recognized as an opportunist, taking advantage of increased food supply at inner stations A_South and B_North. Communities living close to the former ice‐shelf edge are believed to be at an intermediate or late stage of succession, with a dominance of Microlaimus, a common Antarctic genus and quick colonizer. Densities here were comparable with those at other Antarctic stations, whereas they were considerably decreased at the inner stations. In general, the collapse of the Larsen ice shelves initially has a positive effect on the shelf nematode fauna in the area, both in terms of abundance and diversity.     

The response of two estuarine benthic communities to the quantity and quality of food

Experimental manipulations of food supply were performed on soft sediment cores from two European estuaries, the Westerscheldt and the Gironde, with a view to determining benthic macrofaunal community response. Over a period of twenty weeks in a laboratory mesocosm system, both communities showed losses in terms of numbers of individuals and small, but non-significant, losses in terms of numbers of species. Whereas no effect of the different types of foods or the dose levels at which they were supplied was detected for the Westerscheldt benthic community, that of the Gironde showed some significant response. This was largely attributed to the differential mortality of spionid polychaetes across the dose levels used, with the highest dose, equivalent to 200 g C m^–2 yr^–1, only just maintaining their initial population densities. The results are discussed in terms of the importance of lateral advection of food particles at the benthic boundary layer and the general insufficiency of many estimates of carbon input to shallow benthic systems.     

Spatial variability in the distribution of dominant shallow-water benthos at Adelaide Island, Antarctica

Studies from temperate and tropical regions have shown that variability in the distribution of benthos exists at different spatial scales. There are very few similar studies from polar systems, the shallows of which represent some of the most intensely disturbed habitats on the planet. Variability in the abundances of the five most common macrofauna was examined at three spatial scales, metres, tens of metres and hundreds of metres, in the shallows (5-25 m depth) of Adelaide Island, West Antarctic Peninsula. Whilst significant community change occurs along a depth gradient at the study sites, not all of the common species studied showed clear depth-related patterns of distribution. Furthermore, although abundance patterns varied between the organisms, consistent depth-related trends in the spatial scale contributing most to the variability were observed for four of the five species. For four species the relative importance of large-scale variability (between sites) decreased from 5 to 25 m depth, whilst small-scale variability (between replicates) increased along the depth gradient. Variation between sites is probably largely driven by ice disturbance, which becomes less frequent with depth. Conversely, small-scale patchiness is promoted by biological interactions, which become relatively more influential as community complexity and species richness increase along the depth gradient.     

The Bryophytes of the King George Island,Antarctica

After examining the moss collections from the King George Island collected by Dr. Wei Jiang-chun and Mr. Li Zhen-pei in 1983–1984 and 1985 separately, we find 7 species of the mosses, which belong to 4 families and 6 genera. Some of them such as the mosses of Calliergon and Drepanocladus favour moist habitats, whereas Andreaea obovata indicates the dry rocky substratum. Barbula unguiculata and Tortula ruralis could suffer non-permanent dry condition. Geographically, except Andreaea obovata and Calliergon stramineum the other mosses are almost cosmopolitans. They probably distributed to the King George Island before Antarctica drifting to the recent position, and the strong wind was also possible to blow the spores of mosses to Antarctica.     

DGGE fingerprinting of bacteria in soils from eight ecologically different sites around Casey Station,Antarctica

Bacterial community structures in soils collected from eight sites around Casey Station, Antarctica, were investigated using denaturing gradient gel electrophoresis (DGGE) of amplified 16S rRNA gene fragments. Higher bacterial diversity was found in soils from protected or relatively low human-impacted sites in comparison to highly impacted sites. However, the highest diversity was detected in samples from Wilkes Tip, a former waste disposal site that has been undisturbed for the last 50 years. Comparison of community structure based on non-metric multidimensional scaling plots revealed that all sites, except the hydrocarbon-contaminated (oil spill) site, were clustered with a 45% similarity. A total of 23 partial 16S rRNA gene sequences were obtained from the excised DGGE bands, with the majority of the sequences closely related to those of the Cytophaga–Flexibacter–Bacteroides group. No significant correlation was established between environmental variables, including soil pH, electrical conductivity, carbon, nitrogen, water content and heavy metals, with bacterial diversity across the eight study sites.     

Observations of seasonal changes in diatoms at inshore localities near Davis Station,East Antarctica

Seventy-five diatom taxa were identified from net plankton samples collected inshore during winter, spring and summer 1977–8 near Davis Station, East Antarctica. Species richness was found to be higher in winter than in summer; this is the first time this trend has been reported in antarctic coastal regions.When these taxa were grouped according to the general habitats in which they normally occur, the benthic assemblages dominated the planktonic ones.Of the plankton, most species were of oceanic origin in winter and late summer and are thought to have been swept inshore by a cyclonic gyre which is known to occur in summer but has not been studied in winter.     

Response of Antarctic benthic communities to disturbance: first results from the artificial Benthic Disturbance Experiment on the eastern Weddell Sea Shelf, Antarctica

The long-term benthic disturbance experiment (BENDEX) was started on the eastern Weddell Sea shelf off Austasen (Antarctica) during ‘Polarstern’ cruise ANT XXI/2 in December 2003 to simulate the impact of grounding icebergs on the seabed and follow the steps and timescales of recovery of disturbed benthos and demersal fish communities. Here, we report the basic approach and first results for this experimental field study. By means of 11 densely-placed hauls with a modified bottom trawl, a seabed area of approximately 100 × 1000 m was artificially scoured to inflict a similar damage to the benthic habitats as a grounding iceberg. Before the disturbance event and 11 days after it, the seafloor communities were sampled (invertebrate assemblages by multibox corers, the fish fauna by trawl hauls) and comparatively analyzed. Sediment texture and chemistry was not significantly altered by the heavy disturbance inflicted by repeated trawling, whereas the fauna was negatively affected. Invertebrate benthic biomass was drastically reduced by a factor of 10, while mean abundances were only slightly reduced. Demersal fish biomass and abundance were slightly but not significantly smaller after the disturbance. Effects of disturbance became more evident in the composition of the fish fauna, with Trematomus pennelli and T. hansoni being dominant at disturbed sites, whereas Chionodraco myersi was the dominant species in trawl catches from undisturbed stations.     

南极恩克斯堡岛土壤中可培养细菌多样性

【背景】南极地区环境苛刻植被稀少,无冰区面积约占其总面积的0.4%,但是土壤中存在着丰富的微生物群落,对于极地微生物资源仍需要进一步挖掘。【目的】获得南极恩克斯堡岛土壤中可培养细菌多样性信息。【方法】对来源于南极恩克斯堡岛的5个土壤样品采用直接涂布、微好氧富集和有氧富集后涂布3种方法进行细菌分离培养。【结果】共获得144株可培养细菌,分布于5门30个属。这些菌株来自变形菌门(Proteobacteria,38.9%)、放线菌门(Actinobacteria,34.0%)、厚壁菌门(Firmicutes,22.2%)、异常球菌-栖热菌门(Deinococcus-Thermus,3.5%)、拟杆菌门(Bacteroidetes,1.4%)等。不同土壤样品中可培养细菌多样性存在差异。企鹅粪土中Bacillus是主要属类;Pseudomonas、Streptomyces在植被覆盖区土壤中是优势菌属;Psychrobacter在湖水边土壤中是优势属类,Flavobacterium、Chryseobacterium仅从该样品中分离得到;放线菌门类在干燥土壤样中占优势,Pseudarthrobacter、Rhodococcus、Microbacterium等属仅从这类干燥样品中分离出。经16S rRNA基因序列对比发现,有2株菌为潜在新种。【结论】南极恩克斯堡岛土壤中存在可开发利用的菌种资源,本文为研究该地细菌多样性提供一定的基础数据。     

Diversity of benthic macrofauna in the eastern English Channel: comparison among and within communities

The diversity of benthic macrofaunal assemblages in the eastern English Channel is described from 707 samples collected with a Rallier-du-Baty dredge during 1971–1975. Four assemblages were primarily defined by means of multivariate data analyses and clustering methods: the Abra alba community, the Ophelia borealis community, the pebbles community and a mixed assemblage of the first three communities. Spatial heterogeneity of these communities is significantly correlated with sedimentary characteristics, although local variability appears to be controlled by both physical and biological processes. Ecological diversity of these communities was analysed considering species richness (S), the Shannon diversity index (H), and rank-frequency diagrammes (RFD). These analyses were performed at two spatial scales: for a single sample, and for a 'site of 10 pooled samples. Thus, several sites were chosen in order to compare diversity patterns and species quantitative structure among and within the communities. The greatest species richness was recorded for the pebbles (57–69) and the A. alba (63–79) communities. In the former, high values may be due to the complexity of microhabitats and the large flux of food related to strong currents. In the latter, both organic matter and terrestrial inputs associated with the mud favour the presence of deposit-feeder organisms. No clear trend was observed among and within the community sites in terms of the species quantitative structure. Thus, convex RFD shapes were observed in three assemblages: the mixed assemblage (offshore site), the A. alba (North Sea), and the pebbles (Normandy coast). Sigmoid shapes were observed in the pebbles (Dover Strait) and A. alba (English coast) communities. Presumably, these shapes can be caused by the combined action of physical (strong currents, substrate stability, mud content in the sediments) and biological factors (co-occurrence of species from different communities, strong species recruitment, relative dominance of carnivorous species).     

Stratification and dynamics of microbial loop communities in Lake Fryxell, Antarctica

1. Lake Fryxell, situated in the McMurdo Dry Valleys, Antarctica, offers the opportunity to study microbial loop processes in the absence of crustacean zooplankton and other higher organisms. This is the first study of Lake Fryxell to provide detailed temporal and vertical variations of microbial loop organisms.
2. Protozoan communities are concentrated around the chemocline (9–10 m) in Lake Fryxell. Phototrophic nanoflagellates (PNAN), heterotrophic nanoflagellates (HNAN) and ciliates formed deep maxima of 14 580, 694 and 58 cells mL−1 respectively. Although abundance and biomass at the chemocline was high, diversity of protozoa was low, Plagiocampa accounting for> 80% of the total ciliate biomass.
3. In the mixolimnion (4.5–8 m), protozoa were less abundant, but more diverse, with 24 ciliate morphotypes being identified within this region of the water column. Inter-annual variability of protozoan biomass and abundance was greater in the mixolimnion than at the chemocline due to more variable nutrient and prey concentrations.
4. Physicochemical gradients in Lake Fryxell were very stable because the perennial ice cover reduced wind driven currents. As a consequence, ciliate species occurred in distinct depth strata, Monodinium being most abundant directly beneath the ice cover, Askenasia having maximum abundance at 8 m and Plagiocampa dominating ciliate biomass at the chemocline. The lack of vertical mixing reduced seasonal successions of PNAN and ciliate species. Three cryptophyte species dominated the PNAN community at all times (>79% of total biomass).