Nord‐ und Südpolarmeer im Klimawandel. Ein biologischer Vergleich

Impacts of climate change on polar seas The polar seas in the Arctic and Antarctic are characterized by extreme cold and the prevalence of sea ice, which provides a unique polar habitat but also strongly affects the pelagic and benthic biota beneath. Life conditions for the marine fauna and flora differ considerably between the Arctic and Southern Oceans, as a result of contrasts in geography, geological history, as well as seasonal dynamics in light regime, sea ice cover and, hence, biological production. Climate change is particularly obvious in the Arctic Ocean and off the Antarctic Peninsula where warming results in a rapid shrinkage of the summer sea ice cover. Such decline threatens the sea‐ice communities and their associated fauna and will also have far reaching effects for the plankton and benthos of the polar seas.     

Diversity and genomics of Antarctic marine micro-organisms

Marine bacterioplanktons are thought to play a vital role in Southern Ocean ecology and ecosystem function, as they do in other ocean systems. However, our understanding of phylogenetic diversity, genome-enabled capabilities and specific adaptations to this persistently cold environment is limited. Bacterioplankton community composition shifts significantly over the annual cycle as sea ice melts and phytoplankton bloom. Microbial diversity in sea ice is better known than that of the plankton, where culture collections do not appear to represent organisms detected with molecular surveys. Broad phylogenetic groupings of Antarctic bacterioplankton such as the marine group I Crenarchaeota, alpha-Proteobacteria (Roseobacter-related and SAR-11 clusters), gamma-Proteobacteria (both cultivated and uncultivated groups) and Bacteriodetes-affiliated organisms in Southern Ocean waters are in common with other ocean systems. Antarctic SSU rRNA gene phylotypes are typically affiliated with other polar sequences. Some species such as Polaribacter irgensii and currently uncultivated gamma-Proteobacteria (Ant4D3 and Ant10A4) may flourish in Antarctic waters, though further studies are needed to address diversity on a larger scale. Insights from initial genomics studies on both cultivated organisms and genomes accessed through shotgun cloning of environmental samples suggest that there are many unique features of these organisms that facilitate survival in high-latitude, persistently cold environments.     

北极浮冰生态学研究进展

近年来随着北极地区的开放和全球变化对北极地区生态环境和海冰现存量的影响日益显现,北极浮冰生态学研究得到了广泛的重视和实质性的进展.最新研究结果显示,浮冰本身包含了一个复杂的生物群落,高纬度浮冰生物群落的初级产量远高于原先的估算,浮冰生物群落在北极海洋生态系统中的作用被进一步确认.但由于对浮冰生物群落的研究受后勤保障条件的制约,目前尚有大量科学问题有待今后进一步深入研究,预期我国科学家将在其中做出贡献.     

Effects of incubation temperature on growth and production of exopolysaccharides by an antarctic sea ice bacterium grown in batch culture

The sea ice microbial community plays a key role in the productivity of the Southern Ocean. Exopolysaccharide (EPS) is a major component of the exopolymer secreted by many marine bacteria to enhance survival and is abundant in sea ice brine channels, but little is known about its function there. This study investigated the effects of temperature on EPS production in batch culture by CAM025, a marine bacterium isolated from sea ice sampled from the Southern Ocean. Previous studies have shown that CAM025 is a member of the genus Pseudoalteromonas and therefore belongs to a group found to be abundant in sea ice by culture-dependent and -independent techniques. Batch cultures were grown at -2 degrees C, 10 degrees C, and 20 degrees C, and cell number, optical density, pH, glucose concentration, and viscosity were monitored. The yield of EPS at -2 degrees C and 10 degrees C was 30 times higher than at 20 degrees C, which is the optimum growth temperature for many psychrotolerant strains. EPS may have a cryoprotective role in brine channels of sea ice, where extremes of high salinity and low temperature impose pressures on microbial growth and survival. The EPS produced at -2 degrees C and 10 degrees C had a higher uronic acid content than that produced at 20 degrees C. The availability of iron as a trace metal is of critical importance in the Southern Ocean, where it is known to limit primary production. EPS from strain CAM025 is polyanionic and may bind dissolved cations such at trace metals, and therefore the presence of bacterial EPS in the Antarctic marine environment may have important ecological implications.     

Impact of the Antarctic benthic fauna on the enrichment of biopolymer degrading psychrophilic bacteria

Stenothermic cold adaptation was a predominant growth characteristic among biopolymer degrading bacteria from Antarctic shelf sediments. Psychrophilic decomposers of protein (gelatin), chitin, and cellulose accounted for up to 84, 93, and 68%, respectively, of 0°C-isolates from selected compartments of the sediments. Macroinvertebrates were recognized as a selective pressure on these fast-growing (zymogenous) psychrophiles. Psychrophilic properties of growth and biopolymer degradation coincided most in the case of proteolytic isolates. On the other hand, the majority of psychrophilic chitin- and cellulose-decomposers showed less efficient biopolymer degradation at environmental temperatures (0°C). Temperature optima of the activities of pertinent depolymerizing enzymes (e.g., scleroprotease) exceeded by far the temperature optima for growth (between 4 and 12°C). Therefore, it appears likely that enhanced rates of enzyme synthesis at low temperatures play a crucial role for the degradation of detrital organic matter in this permanently cold environment.     

Extracellular enzymes produced by microorganisms isolated from maritime Antarctica

Antarctic environments can sustain a great diversity of well-adapted microorganisms known as psychrophiles or psychrotrophs. The potential of these microorganisms as a resource of enzymes able to maintain their activity and stability at low temperature for technological applications has stimulated interest in exploration and isolation of microbes from this extreme environment. Enzymes produced by these organisms have a considerable potential for technological applications because they are known to have higher enzymatic activities at lower temperatures than their mesophilic and thermophilic counterparts. A total of 518 Antarctic microorganisms, were isolated during Antarctic expeditions organized by the Instituto Antártico Uruguayo. Samples of particules suspended in air, ice, sea and freshwater, soil, sediment, bird and marine animal faeces, dead animals, algae, plants, rocks and microbial mats were collected from different sites in maritime Antarctica. We report enzymatic activities present in 161 microorganisms (120 bacteria, 31 yeasts and 10 filamentous fungi) isolated from these locations. Enzymatic performance was evaluated at 4 and 20°C. Most of yeasts and bacteria grew better at 20°C than at 4°C, however the opposite was observed with the fungi. Amylase, lipase and protease activities were frequently found in bacterial strains. Yeasts and fungal isolates typically exhibited lipase, celullase and gelatinase activities. Bacterial isolates with highest enzymatic activities were identified by 16S rDNA sequence analysis as Pseudomonas spp., Psychrobacter sp., Arthrobacter spp., Bacillus sp. and Carnobacterium sp. Yeasts and fungal strains, with multiple enzymatic activities, belonged to Cryptococcus victoriae, Trichosporon pullulans and Geomyces pannorum.     

Altered Sea Ice Thickness and Permanence Affects Benthic Ecosystem Functioning in Coastal Antarctica

Antarctic sea ice and the cold waters surrounding the continent are key elements of the global climate system, influencing heat redistribution, oceanic circulation and the absorption of carbon dioxide from the atmosphere. However, the Southern Ocean is predicted to warm by 1–6°C over the next century, altering sea ice extent, thickness and permanence. To better understand the connections between coastal sea ice conditions and the functioning of Antarctica’s unique marine benthic ecosystems, we performed manipulative experiments on the seafloor at two southwestern Ross Sea sites with contrasting sea ice conditions. Benthic systems at both study sites were net heterotrophic during the study period (early November), with primary production most likely limited by light availability rather than nutrients. There was five times more fresh algal detrital material in benthic sediments at the site with the thinner, snow-free, annually formed sea ice, relative to the site with thicker, multiyear sea ice. This elevated quantity and quality of algal detrital matter corresponded with a significantly greater rate of sediment oxygen utilization by the benthos and an altered pathway of nitrogen regeneration (tighter coupling between nitrification and denitrification). Large benthic animals (brittle stars, Ophionotus victoriae) enhanced the efflux of dissolved inorganic nutrients from the sediment to the water column and played a greater role in nutrient regeneration at the site with more food. Although changes in sea ice characteristics in the Western Ross Sea are difficult to predict at present, large benthic organisms can be expected to have an expanded role in mediating the effects of elevated coastal productivity and detritus supply on ecosystem dynamics in this part of Antarctica.     

Phenotypic Plasticity of Southern Ocean Diatoms: Key to Success in the Sea Ice Habitat?

Diatoms are the primary source of nutrition and energy for the Southern Ocean ecosystem. Microalgae, including diatoms, synthesise biological macromolecules such as lipids, proteins and carbohydrates for growth, reproduction and acclimation to prevailing environmental conditions. Here we show that three key species of Southern Ocean diatom (Fragilariopsis cylindrus, Chaetoceros simplex and Pseudo-nitzschia subcurvata) exhibited phenotypic plasticity in response to salinity and temperature regimes experienced during the seasonal formation and decay of sea ice. The degree of phenotypic plasticity, in terms of changes in macromolecular composition, was highly species-specific and consistent with each species’ known distribution and abundance throughout sea ice, meltwater and pelagic habitats, suggesting that phenotypic plasticity may have been selected for by the extreme variability of the polar marine environment. We argue that changes in diatom macromolecular composition and shifts in species dominance in response to a changing climate have the potential to alter nutrient and energy fluxes throughout the Southern Ocean ecosystem.     

CYANOBACTERIAL DOMINANCE OF POLAR FRESHWATER ECOSYSTEMS: ARE HIGH-LATITUDE MAT-FORMERS ADAPTED TO LOW TEMPERATURE?1

Although it is generally believed that cyanobacteria have high temperature optima for growth (> 20° C), mat-foming cyanobacteria are dominant in many types of lakes, streams, and ponds in the Arctic and Antarctic. We studied the effect of temperature on growth (μ) and relative pigment composition of 27 isolates of cyanobacteria (mat-forming Oscillatoriaceae) from the Arctic, subarctic, and Antarctic to investigate whether they are a) adapted to the low temperature (i.e. psychrophilic) or b) tolerant of the low temperature of the polar regions (i.e. psychrotrophic). We also derived a parabolic function that describes both the rise and the decline of cyanobacterial growth rates with increasing temperature. The cyanobacteria were cultured at seven different temperatures (5°-35° C at 5° C intervals), with continuous illumination of 225 μmol photons.m⁻².s⁻¹. The parabolic function fits the μ-temperature data with 90% confidence for 75% of the isolates. Among the 27 isolates of cyanobacteria studied, the temperature optima (T_opt) for growth ranged from 15° to 35° C, with an average of 19.9° C. These results imply that most polar cyanobacteria are psychrotrophs, not psychrophiles. The cyanobacteria grew over a wide temperature range (typically 20° C) but growth rates were low men at T_opt (average μ_max of 0.23 ± 0.069 d⁻¹). Extremely slow growth rates at low temperature and the high temperature for optimal growth imply that the cyanobacteria are not adapted genetically to cold temperatures, which characterize their ambient environment. Other competitive advantages such as tolerance to desiccation, freeze—thaw cycles, and bright, continuous solar radiation may contribute to their dominance in polar aquatic ecosystems.     

The Contributions of Sea Ice Algae to Antarctic Marine Primary Production

The seasonally ice-covered regions of the Southern Ocean havedistinctive ecological systems due to the growth of microalgaein sea ice. Although sea ice microalgal production is exceededby phytoplankton production on an annual basis in most offshoreregions of the Southern Ocean, blooms of sea ice algae differconsiderably from the phytoplankton in terms of timing and distribution.Thus sea ice algae provide food resources for higher trophiclevel organisms in seasons and regions where water column biologicalproduction is low or negligible. A flux of biogenic materialfrom sea ice to the water column and benthos follows ice melt,and some of the algal species are known to occur in ensuingphytoplankton blooms. A review of algal species in pack iceand offshore plankton showed that dominance is common for threespecies: Phaeocystis antarctica, Fragilariopsis cylindrus andFragilariopsis curta. The degree to which dominance by thesespecies is a product of successional processes in sea ice communitiescould be an important in determining their biogeochemical contributionto the Southern Ocean and their ability to seed blooms in marginalice zones.     

Phylogenetic Diversity of Numerically Important Arctic Sea-Ice Bacteria Cultured at Subzero Temperature

Heterotrophic bacteria in sea ice play a key role in carbon cycling, but little is known about the predominant players at the phylogenetic level. In a study of both algal bands and clear ice habitats within summertime Arctic pack ice from the Chukchi Sea, we determined the abundance of total bacteria and actively respiring cells in melted ice samples using epifluorescence microscopy and the stains 4', 6'-diamidino-2-phenylindole 2HCl (DAPI) and 5-cyano-2,3-ditolyl tetrazolium chloride (CTC), respectively. Organic-rich and -poor culturing media were used to determine culturable members by plating (at 0 degrees C and 5 degrees C) and most-probable-number (MPN) analyses (at -1 degrees C). Total bacterial counts ranged from 5.44 x 10(4) ml(-1) in clear ice to 2.41 x 10(6) ml(-1) in algal-band ice samples, with 2-27% metabolically active by CTC stain. Plating and MPN results revealed a high degree of culturability in both types of media, but greater success in oligotrophic media (to 62% of total abundance) and from clear ice samples. The bacterial enumeration anomaly, commonly held to mean 相似文献   

Widespread distribution in polar oceans of a 16S rRNA gene sequence with affinity to Nitrosospira-like ammonia-oxidizing bacteria

We analyzed the phylogenetic compositions of ammonia-oxidizing bacteria of the beta subclass of Proteobacteria from 42 Southern Ocean samples. We found a Nitrosospira-like 16S rRNA gene sequence in all 20 samples that yielded PCR products (8 of 30 samples from the Ross Sea and 12 of 12 samples from the Palmer Peninsula). We also found this sequence in Arctic Ocean samples, indicating a transpolar, if not global, distribution; however, slight differences between Arctic and Antarctic sequences may be evidence of polar endemism.     

Abundance and function of bacteria in the Southern Ocean.

The very low water temperatures existing in polar oceans that experience seasonal advance and retreat of pack ice do not inhibit the presence of large bacterial populations. Bacteria may contribute significantly to the energy transfers within the Southern Ocean. In the last decades, notable progress has been made in the knowledge of the role of marine bacteria in the Southern Ocean. A short overview of the abundance and function ofAntarctic marine bacteria is given, with respect to metabolic activity. The importance of spatial and temporal variability is described. The ecological function of Antarctic marine bacterioplankton is discussed. Depending on food web structure, bacteria may be either a link in food webs supporting metazoan production, or a sink where bacterial production is metabolised by microorganisms. In the more oligotrophic areas and during certain periods of the year bacterial biomass dominates phytoplankton. The microbial food web is therefore the dominant pathway for carbon and energy flow in Antarctic seawater.     

The overwintering strategy of Antarctic krill under the pack-ice of the Weddell Sea

Summary Antarctic krill (Euphausia superba Dana) occurs in enormous swarms in Antarctic waters during the ice-free summer months. The winter whereabouts of this stock were hitherto unknown. Evidence collected during the Winter Weddell Sea Project 1986 (WWSP'86, G. Hempel 1988) covering a large area of the eastern and southern Weddell Sea indicates that the seasonal sea ice cover sustains the bulk of the krill population. Results presented here, show that known aspects of krill morphology and behavior are actually adaptations to the ice habitat, suggesting that the dominance of krill in the Antarctic marine ecosystem is a result of its capacity to grow and reproduce in the water column in summer, and find both food and shelter in the ice cover during the rest of the year. This conclusion has far-reaching implications for our understanding of Southern Ocean biology and ecology.     

Notes on the biology of sea ice in the Arctic and Antarctic

The sea ice which covers large areas of the polar regions plays a major role in the marine ecosystem of both the Arctic and Southern Oceans. Not only do warmblooded animals depend on sea ice as a platform, but the sympagic organisms living internally within the sea ice or at the interfaces ice/snow and ice/water provide a substantial part of the total primary production of the ice covered regions. In addition sea ice organisms are an important food source for a variety of pelagic animals and may initiate phytoplankton spring blooms after ice melt by seeding effects.Sea ice organisms often are enriched by some orders of magnitude if the same volume of melted ice is compared to that of the underlying water column. Three hypotheses try to explain this discrepancy and are discussed. Investigations on the nutrient chemistry within the sea ice system and in-situ observations still are rare. Intense growth of sympagic organisms can result in nutrient deficiencies, at least in selected habitats. Advances in endoscopie methods may lead to a better understanding of the life within the sea ice.Paper presented at the Symposium on Polar regions: the challenge for biological and ecological research organised by the Swiss Committee for Polar Research, Basel on 2 October 1992     

Bacteria beneath the West Antarctic Ice Sheet

Subglacial environments, particularly those that lie beneath polar ice sheets, are beginning to be recognized as an important part of Earth's biosphere. However, except for indirect indications of microbial assemblages in subglacial Lake Vostok, Antarctica, no sub-ice sheet environments have been shown to support microbial ecosystems. Here we report 16S rRNA gene and isolate diversity in sediments collected from beneath the Kamb Ice Stream, West Antarctic Ice Sheet and stored for 15 months at 4°C. This is the first report of microbes in samples from the sediment environment beneath the Antarctic Ice Sheet. The cells were abundant (∼10⁷ cells g⁻¹) but displayed low diversity (only five phylotypes), likely as a result of enrichment during storage. Isolates were cold tolerant and the 16S rRNA gene diversity was a simplified version of that found in subglacial alpine and Arctic sediments and water. Although in situ cell abundance and the extent of wet sediments beneath the Antarctic ice sheet can only be roughly extrapolated on the basis of this sample, it is clear that the subglacial ecosystem contains a significant and previously unrecognized pool of microbial cells and associated organic carbon that could potentially have significant implications for global geochemical processes.     

The draft genome of Planococcus donghaensis MPA1U2 reveals nonsporulation pathways controlled by a conserved Spo0A regulon

The Planococcaceae are extreme survivors, having been cultured from environments such as deep sea sediments, marine solar salterns, glaciers, permafrost, Antarctic deserts, and sea ice brine. The family contains both sporulating and nonsporulating genera. Here we present the unclosed, draft genome sequence of Planococcus donghaensis strain MPA1U2, a nonsporulating psychrotrophic bacterium isolated from surface coastal water of the Pacific Ocean.     

Retention of ice-associated amphipods: possible consequences for an ice-free Arctic Ocean

Recent studies predict that the Arctic Ocean will have ice-free summers within the next 30 years. This poses a significant challenge for the marine organisms associated with the Arctic sea ice, such as marine mammals and, not least, the ice-associated crustaceans generally considered to spend their entire life on the underside of the Arctic sea ice. Based upon unique samples collected within the Arctic Ocean during the polar night, we provide a new conceptual understanding of an intimate connection between these under-ice crustaceans and the deep Arctic Ocean currents. We suggest that downwards vertical migrations, followed by polewards transport in deep ocean currents, are an adaptive trait of ice fauna that both increases survival during ice-free periods of the year and enables re-colonization of sea ice when they ascend within the Arctic Ocean. From an evolutionary perspective, this may have been an adaptation allowing success in a seasonally ice-covered Arctic. Our findings may ultimately change the perception of ice fauna as a biota imminently threatened by the predicted disappearance of perennial sea ice.     

A glimpse of the diversity of complex polysaccharide-degrading culturable bacteria from Kongsfjorden,Arctic Ocean

Cold-adapted, complex polysaccharide-degrading marine bacteria have important implications in biogeochemical processes and biotechnological applications. Bacteria capable of degrading complex polysaccharide substrates, mainly starch, have been isolated from various cold environments, such as sea ice, glaciers, subglacial lakes, and marine sediments. However, the total diversity of polysaccharide-degrading culturable bacteria in Kongsfjorden, Arctic Ocean, remains unexplored. In the study reported here, we tested 215 cold-adapted heterotrophic bacterial cultures (incubated at 4 and 20 °C, respectively) isolated from Kongsfjorden, for the production of cold-active extracellular polysaccharide-degrading enzymes, including amylase, pectinase, alginase, xylanase, and carboxymethyl (CM)-cellulase. Our results show that 52 and 41% of the bacterial isolates tested positive for extracellular enzyme activities at 4 and 20 °C, respectively. A large fraction of the bacterial isolates (37% of the positive isolates) showed multiple extracellular enzyme activities. Alginase and pectinase were the most predominantly active enzymes, followed by amylase, xylanase, and CM-cellulase. All isolates which tested positive for extracellular enzyme activities were affiliated to microbial class Gammaproteobacteria. The four genera with the highest number of isolates were Pseudomonas, followed by Psychrobacter, Pseudoalteromonas, and Shewanella. The prevalence of complex polysaccharide-degrading enzymes among the isolates indicates the availability of complex polysaccharide substrates in the Kongsfjorden, likely as a result of glacial melting and/or macroalgal load. In addition, the observed high functional/phenotypic diversity in terms of extracellular enzyme activities within the bacterial genera indicates a role in regulating carbon/carbohydrate turnover in the Kongsfjorden, especially by reducing recalcitrance.     

The association of Antarctic krill Euphausia superba with the under-ice habitat

The association of Antarctic krill Euphausia superba with the under-ice habitat was investigated in the Lazarev Sea (Southern Ocean) during austral summer, autumn and winter. Data were obtained using novel Surface and Under Ice Trawls (SUIT), which sampled the 0-2 m surface layer both under sea ice and in open water. Average surface layer densities ranged between 0.8 individuals m(-2) in summer and autumn, and 2.7 individuals m(-2) in winter. In summer, under-ice densities of Antarctic krill were significantly higher than in open waters. In autumn, the opposite pattern was observed. Under winter sea ice, densities were often low, but repeatedly far exceeded summer and autumn maxima. Statistical models showed that during summer high densities of Antarctic krill in the 0-2 m layer were associated with high ice coverage and shallow mixed layer depths, among other factors. In autumn and winter, density was related to hydrographical parameters. Average under-ice densities from the 0-2 m layer were higher than corresponding values from the 0-200 m layer collected with Rectangular Midwater Trawls (RMT) in summer. In winter, under-ice densities far surpassed maximum 0-200 m densities on several occasions. This indicates that the importance of the ice-water interface layer may be under-estimated by the pelagic nets and sonars commonly used to estimate the population size of Antarctic krill for management purposes, due to their limited ability to sample this habitat. Our results provide evidence for an almost year-round association of Antarctic krill with the under-ice habitat, hundreds of kilometres into the ice-covered area of the Lazarev Sea. Local concentrations of postlarval Antarctic krill under winter sea ice suggest that sea ice biota are important for their winter survival. These findings emphasise the susceptibility of an ecological key species to changing sea ice habitats, suggesting potential ramifications on Antarctic ecosystems induced by climate change.