Annual Bacterioplankton Biomasses and Productivities in a Temperate West Coast Canadian Fjord

Bacterioplankton numbers, biomasses, and productivities, as well as chlorophyll a concentrations and phytoplankton productivities, were assayed from 1 March 1984 to 12 August 1985 through a 250-m-deep seawater column in Howe Sound, a temperate fjord-sound on the southern coast of British Columbia, Canada. Primary production during this 18-month period was 845 g of C m⁻². Bacterial production was assayed over this same period as 193 g of C m⁻² (thymidine incorporation) and 77 g of C m⁻² (frequency of dividing cells). Bacterial productivities per cubic meter were usually greater in the euphotic zone than in deeper aphotic water, but when integrated through the water column, approximately half of the bacterial production occurred in the deeper aphotic portion. Bacterial production occurred throughout the year, although at reduced rates in late fall and early winter; primary production almost ceased during late fall and early winter. Because of this heterotrophic bacterioplankton production was a very large portion of the microbial (bacterial plus phyto-plankton) production at this time. In mid-summer bacterial production was a small proportion of the microbial production. Because of this asynchrony in peaks and troughs of bacterial and phytoplankton production through the year, data comparison is best done over an annual cycle. On this basis the bacterial production in the Howe Sound water column was between 23 and 9% of the phytoplankton production when a bacterial C to biovolume ratio of 0.107 pg of C μm⁻³ was assumed; the corresponding values were 64 and 29% when a ratio of 0.300 pg of bacterial C μm⁻³ was assumed.     

Comparison of Bacterioneuston and Bacterioplankton Dynamics during a Phytoplankton Bloom in a Fjord Mesocosm

The bacterioneuston is the community of Bacteria present in surface microlayers, the thin surface film that forms the interface between aquatic environments and the atmosphere. In this study we compared bacterial cell abundances and bacterial community structures of the bacterioneuston and the bacterioplankton (from the subsurface water column) during a phytoplankton bloom mesocosm experiment. Bacterial cell abundance, determined by flow cytometry, followed a typical bacterioplankton response to a phytoplankton bloom, with Synechococcus and high-nucleic acid content (HNA) bacterial cell numbers initially falling, probably due to selective protist grazing. Subsequently HNA and low-nucleic acid content bacterial cells increased in abundance, but Synechococcus cells did not. There was no significant difference between bacterioneuston and bacterioplankton cell abundances during the experiment. Conversely, distinct and consistent differences between the bacterioneuston and the bacterioplankton community structures were observed. This was monitored simultaneously by Bacteria 16S rRNA gene terminal restriction fragment length polymorphism and denaturing gradient gel electrophoresis. The conserved patterns of community structure observed in all of the mesocosms indicate that the bacterioneuston is distinctive and nonrandom.Determining and understanding both spatial and temporal patterns in bacterioplankton community structure are a core aim of marine microbial ecology (15). Distributions of bacterioplankton over space and time can be correlated to environmental parameters, and subsequent links can therefore be made to ecosystem function. A broad range of spatial studies made on macro- (34), meso- (20), and microscales (27) have shown clear patterns in distribution of the bacterioplankton.The sea surface microlayer is part of the air-sea interface and is generally considered to be the top 1 mm or less of the ocean (26). Surface microlayers have a fundamental role in regulating transport processes between the ocean and the atmosphere (26) and are often referred to as the neuston (28, 31). For more than 25 years it has been hypothesized that the sea surface microlayer is a hydrated gelatinous layer (40) that contains surface-active organic compounds such as carbohydrates, proteins, lipids, and humic substances in relatively high concentrations (17, 45, 48). Recently, gel-like transparent expolymer particles (TEP) have been shown to be enriched in the surface microlayer, supporting the concept of a gelatinous interfacial layer (46).Bacteria present in surface microlayers or the neuston are regarded as the bacterioneuston. There are relatively few studies which have directly compared the community structure of the bacterioneuston with that of the cognate subsurface (bacterioplankton) in the marine environment. Analysis of Bacteria 16S rRNA gene clone libraries constructed using DNA isolated from surface microlayer and subsurface water (<1 m) samples from the North Sea revealed that the bacterioneuston was dominated by two operational taxonomic units which accounted for 81% of clones analyzed (13). Community structure profiling using denaturing gradient gel electrophoresis (DGGE) of the bacterioneuston at three sites around Oahu Island in the Pacific Ocean showed that the bacterioneuston forms consistent and distinct community structures. Conversely, the archaeal community structure of the same samples using Archaea 16S rRNA gene DGGE analysis did not show the same surface microlayer-specific response, indicating that bacteria and archaea respond to their environment in fundamentally different ways in the neuston (7).Other studies have, however, reported no consistent differences between the bacterioneuston and the bacterioplankton. Samples collected from two separate sites in the Mediterranean Sea were analyzed using single-strand conformation polymorphism of Bacteria 16S rRNA genes (1). The authors did not report any significant differences between the surface microlayer and subsurface samples using this community profiling method.Nonmarine studies of the bacterioneuston and Archaea communities in estuarine (10) and freshwater (5, 19) environments have also shown distinct microbial community structures present in the surface microlayer compared to those in subsurface water ≤1 m below.Recurring phytoplankton blooms are a key feature of coastal waters and strongly influence bacterioplankton community structure and succession (4, 14, 38). Phytoplankton blooms stimulate the bacterioplankton by the release of dissolved organic matter (22) or affect bacterioplankton negatively by direct competition for resources (6). Bacterioplankton community structure may also be influenced by grazing flagellates or viral lysis (47).Mesocosm experiments have been used to study plankton ecology for many decades (33). Mesocosms facilitate study of the effects of key environmental parameters, such as temperature, on plankton communities and allow the succession of natural plankton communities that resemble those found in the marine environment (11). The enclosed water mass means that experiments can be designed which manipulate physicochemical parameters to observe biological effects. Furthermore, with replicated mesocosms, the data collected can be analyzed with statistics rigorously. In this study we monitored the dynamics of the bacterioneuston and the bacterioplankton in mesocosms of fjord surface water during an artificially induced phytoplankton bloom and compared bacterial abundances and bacterial community structures in the surface microlayer and subsurface water.     

Bacterioplankton Community Shifts in an Arctic Lake Correlate with Seasonal Changes in Organic Matter Source

Seasonal shifts in bacterioplankton community composition in Toolik Lake, a tundra lake on the North Slope of Alaska, were related to shifts in the source (terrestrial versus phytoplankton) and lability of dissolved organic matter (DOM). A shift in community composition, measured by denaturing gradient gel electrophoresis (DGGE) of 16S rRNA genes, occurred at 4°C in near-surface waters beneath seasonal ice and snow cover in spring. This shift was associated with an annual peak in bacterial productivity ([¹⁴C]leucine incorporation) driven by the large influx of labile terrestrial DOM associated with snow meltwater. A second shift occurred after the flux of terrestrial DOM had ended in early summer as ice left the lake and as the phytoplankton community developed. Bacterioplankton communities were composed of persistent populations present throughout the year and transient populations that appeared and disappeared. Most of the transient populations could be divided into those that were advected into the lake with terrestrial DOM in spring and those that grew up from low concentrations during the development of the phytoplankton community in early summer. Sequencing of DNA in DGGE bands demonstrated that most bands represented single ribotypes and that matching bands from different samples represented identical ribotypes. Bacteria were identified as members of globally distributed freshwater phylogenetic clusters within the α- and β-Proteobacteria, the Cytophaga-Flavobacteria-Bacteroides group, and the Actinobacteria.     

Phylogenetic Composition of Bacterioplankton Assemblages from the Arctic Ocean

We analyzed the phylogenetic composition of bacterioplankton assemblages in 11 Arctic Ocean samples collected over three seasons (winter-spring 1995, summer 1996, and summer-fall 1997) by sequencing cloned fragments of 16S rRNA genes. The sequencing effort was directed by denaturing gradient gel electrophoresis (DGGE) screening of samples and the clone libraries. Sequences of 88 clones fell into seven major lineages of the domain Bacteria: α (36%)-, γ (32%)-, δ (14%)-, and (1%)-Proteobacteria; Cytophaga-Flexibacter-Bacteroides spp. (9%); Verrucomicrobium spp. (6%); and green nonsulfur bacteria (2%). A total of 34% of the cloned sequences (excluding clones in the SAR11 and Roseobacter groups) had sequence similarities that were <94% compared to previously reported sequences, indicating the presence of novel sequences. DGGE fingerprints of the selected samples showed that most of the bands were common to all samples in all three seasons. However, additional bands representing sequences related to Cytophaga and Polaribacter species were found in samples collected during the summer and fall. Of the clones in a library generated from one sample collected in spring of 1995, 50% were the same and were most closely affiliated (99% similarity) with Alteromonas macleodii, while 50% of the clones in another sample were most closely affiliated (90 to 96% similarity) with Oceanospirillum sp. The majority of the cloned sequences were most closely related to uncultured, environmental sequences. Prominent among these were members of the SAR11 group. Differences between mixed-layer and halocline samples were apparent in DGGE fingerprints and clone libraries. Sequences related to α-Proteobacteria (dominated by SAR11) were abundant (52%) in samples from the mixed layer, while sequences related to γ-proteobacteria were more abundant (44%) in halocline samples. Two bands corresponding to sequences related to SAR307 (common in deep water) and the high-G+C gram-positive bacteria were characteristic of the halocline samples.     

Building an indicator to characterize the thermal conditions for plant growth on an Arctic archipelago,Svalbard

Plant growth in the Arctic is strictly dependant on thermal conditions. The purpose of our study is therefore to calculating temperature distributions on the Svalbard archipelago at a relatively high spatial resolution. The model is designed to reflect both the length of the growing season and the temperature sum for a given area (i.e. growing degree-days (GDD)). GDD on Svalbard is defined as the cumulative sum of positive mean daily temperatures in the months of June, July and August. The temperature distribution of GDD for the entire archipelago is calculated from both local and regional information. Local information is derived from data collected in a small area in northwestern Spitsbergen (Kongsfjorden) where a network of 45 thermal sensors recorded air temperatures for five years (2001–2005). A local GDD parameter is computed by a linear combination of elevation, valley depth and NDVI (normalized difference vegetation index). Then this local GDD is applied to the whole of Svalbard (GDD1) and refined stepwise by adding environmental variables such as cloud fraction, land surface temperature, sea surface temperature, distance to the ocean and number of snow-free days. Because the official network of climatological stations on Svalbard is not dense enough and sufficiently well-distributed across the archipelago to enable spatial interpolations for four years only (2011–2014), all outputs are statistically evaluated and adjusted using the values recorded at 9 (2011), 12 (2012) and 13 (2013–2014) meteorological stations (GDD_ref) and used as a set of evaluation data. The final model (GDD_mean), which is the mean of the annual models estimated by regression (GDD_est), performs well: the central parts of Spitsbergen, known for its comparatively high temperatures, contrast with the colder northern and eastern parts of the archipelago.     

Spatio-Temporal Monitoring and Ecological Significance of Retrievable Pelagic Heterotrophic Bacteria in Kongsfjorden,an Arctic Fjord

Kongsfjorden is a glacial fjord in the Arctic that is influenced by both Atlantic and Arctic water masses. In the present report retrievable heterotrophic bacteria isolated from two distinct zones (outer and inner fjord) of Kongsfjorden was studied during summer to fall of 2012. 16S rRNA gene sequences of the retrievable heterotrophic bacteria corresponded to γ-proteobacteria (13 phylotypes), α-proteobacteria (3 phylotypes), Bacteroidetes (4 phylotypes) and Actinobacteria (2 phylotypes). The heterotrophic bacterial community structure was fundamentally different in different months which could be linked to changes in the water masses and/or phytoplankton bloom dynamics. It is hypothesized that monitoring the retrievable heterotrophic bacterial assemblage in the fjord would give valuable insights into the complex ecological role they play under extreme and dynamic conditions.     

Arctic Gasteromycetes II. Calvatia in Greenland, Svalbard and Iceland

Species of Calvatia (Lycoperdaceae) from arctic and subarctic regions are described. The diagnostic characters in Calvatia are discused with emphasis on strutures of peridium and capillitium and colour of gleba. Ten species are recognized. Three species: C. Candida, C. excipuliformis, C. utriformis are confined to subarctic stations, while seven species have their main distribution in the arctic zones. Three of these are new species: C. connivens, C. horrida, C. septentrionalis , while three other species are redefined after studies of type material: C. arctica, C. bellii and C. turneri. Several specimens studied show characters pointing to a hybrid origin.     

Nitrogen fixation in Arctic vegetation and soils from Svalbard,Norway

Nitrogen fixation was measured by the acetylene reduction method in a high Arctic ecosystem at Kongsfjorden, Spitsbergen (79°N, 12°E). The most important source of biologically fixed nitrogen was found in cyanobacteria either as free living colonies ofNostoc sp. in wet unvegetated or sparsely vegetated grounds or growing as epiphytes on bryophytes. Fixation associated with plant roots or in soil and peat samples had little or no significance for nitrogen input to the ecosystem. The ability to support an epiphytic flora of nitrogen-fixing cyanobacteria varied greatly between bryophyte species.Calliergon richardsonii andSanionia uncinata seemed especially well adapted for harbouring epiphytic cyanobacteria, but the extent of nitrogen fixation varied with the growing location. The rate of nitrogen fixation was greatly influenced by grazing by geese. In a geese-grazing area values were found with a maximum of 693.6±1.5 nmol C₂H₄ h⁻¹ g (dry weight)⁻¹ while the maximum value for ungrazed areas was 65.3±16.6 nmol C₂H₄ h⁻¹ g (dry weight)⁻¹. In the grazed area cyanobacteria were also found fixing nitrogen epiphytically on grass. The high plant productivity, supporting heavy grazing, clearly indicates an effective transfer of fixed nitrogen to the plant community. Under cliffs harbouring colonies of birds, the biological nitrogen fixation was inhibited by bird droppings.     

Epidermal UV-screening in vascular plants from Svalbard (Norwegian Arctic)

Stratospheric ozone depletion is most pronounced at high latitudes, and the concurring increased UV-B radiation might adversely affect plants from polar areas. However, vascular plants may protect themselves against UV-B radiation by UV-absorbing compounds located in the epidermis. In this 3-year study, epidermal UV-B (_max 314 nm) and UV-A (_max 366 nm) screening was assessed using a fluorescence method in 12 vascular species growing in their natural environment at Svalbard. The potential for acclimation to increased radiation was studied with artificially increased UV-B, simulating 11% ozone depletion. Open-top chambers simulated an increase in temperature of 2–3°C in addition to the UV-B manipulation. Adaxial epidermal UV-B transmittance varied between 1.6 and 11.4%. Artificially increased UV-B radiation and temperature did not consistently influence the epidermal UV-B transmittance in any of the measured species, suggesting that they may not have the potential to increase their epidermal screening, or that the screening is already high enough at the applied UV-B level. We propose that environmental factors other than UV-B radiation may influence epidermal UV-B screening.     

Environmental drivers of macroinvertebrate communities in high Arctic rivers (Svalbard)

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Molecular diversity and temporal variation of picoeukaryotes in two Arctic fjords,Svalbard

Picoeukaryotes (protists <3 μm) form an important component of Arctic marine ecosystems, although knowledge of their diversity and ecosystem functioning is limited. In this study, the molecular diversity and autotrophic biomass contribution of picoeukaryotes from January to June 2009 in two Arctic fjords at Svalbard were examined using 18S environmental cloning and size-fractioned chlorophyll a measurements. A total of 62 putative picoeukaryotic phylotypes were recovered from 337 positive clones. Putative picoeukaryotic autotrophs were mostly limited to one species: Micromonas pusilla, while the putative heterotrophic picoeukaryote assemblage was more diverse and dominated by uncultured marine stramenopiles (MAST) and marine alveolate groups. One MAST-1A phylotype was the only phylotype to be found in all clone libraries. The diversity of picoeukaryotes in general showed an inverse relationship with total autotrophic biomass, suggesting that the conditions dominating during the peak of the spring bloom may have a negative impact on picoeukaryote diversity. Picoplankton could contribute more than half of total autotrophic biomass before and after the spring bloom and benefited from an early onset of the growth season, whereas larger cells dominated the bloom itself.     

Dimethylsulfoniopropionate and Methanethiol Are Important Precursors of Methionine and Protein-Sulfur in Marine Bacterioplankton

Organic sulfur compounds are present in all aquatic systems, but their use as sources of sulfur for bacteria is generally not considered important because of the high sulfate concentrations in natural waters. This study investigated whether dimethylsulfoniopropionate (DMSP), an algal osmolyte that is abundant and rapidly cycled in seawater, is used as a source of sulfur by bacterioplankton. Natural populations of bacterioplankton from subtropical and temperate marine waters rapidly incorporated 15 to 40% of the sulfur from tracer-level additions of [³⁵S]DMSP into a macromolecule fraction. Tests with proteinase K and chloramphenicol showed that the sulfur from DMSP was incorporated into proteins, and analysis of protein hydrolysis products by high-pressure liquid chromatography showed that methionine was the major labeled amino acid produced from [³⁵S]DMSP. Bacterial strains isolated from coastal seawater and belonging to the α-subdivision of the division Proteobacteria incorporated DMSP sulfur into protein only if they were capable of degrading DMSP to methanethiol (MeSH), whereas MeSH was rapidly incorporated into macromolecules by all tested strains and by natural bacterioplankton. These findings indicate that the demethylation/demethiolation pathway of DMSP degradation is important for sulfur assimilation and that MeSH is a key intermediate in the pathway leading to protein sulfur. Incorporation of sulfur from DMSP and MeSH by natural populations was inhibited by nanomolar levels of other reduced sulfur compounds including sulfide, methionine, homocysteine, cysteine, and cystathionine. In addition, propargylglycine and vinylglycine were potent inhibitors of incorporation of sulfur from DMSP and MeSH, suggesting involvement of the enzyme cystathionine γ-synthetase in sulfur assimilation by natural populations. Experiments with [methyl-³H]MeSH and [³⁵S]MeSH showed that the entire methiol group of MeSH was efficiently incorporated into methionine, a reaction consistent with activity of cystathionine γ-synthetase. Field data from the Gulf of Mexico indicated that natural turnover of DMSP supplied a major fraction of the sulfur required for bacterial growth in surface waters. Our study highlights a remarkable adaptation by marine bacteria: they exploit nanomolar levels of reduced sulfur in apparent preference to sulfate, which is present at 10⁶- to 10⁷-fold higher concentrations.     

Higher phytosociological syntaxa on Svalbard and their use in subdivision of the Arctic

Idealized distributions of phytosociological syntaxa are arranged along topographical gradients on siliceous and carbonaceous substrates in the northern arctic tundra zone of Svalbard. Two alliances (Luzulion arcuatae all. prov. and Papaverion dahliani Hoffm. 68 all. prov. em.) and three associations (Gymnomitrio corallioidis - Luzule-tum arcuatae ass. prov., Cetrario nivalis - Luzuletum arcuatae ass. prov. and Raco-mitrio lanuginosi — Luzuletum arcuatae ass. prov.) are proposed. Luzulion arcticae (Nordh. 36) Gjaerev. 56 and Polytrichion norvegici Gjierev. 49 described from Scandinavia are supposed to be important syntaxa on Svalbard. A subdivision of the Arctic into four zones, arctic polar desert zone, and northern, middle, and southern arctic tundra zones, is proposed. These zones and the transitional hemiarctic zone are defined and mapped in Europe and adjacent areas according to phytosociological criteria. They are also compared with alpine belts of Fennoscandia. The following zonal syntaxa are proposed for Europe and Greenland: Phyllodoco — Vaccinion in the hemiarctic zone, Loiseleurio — Diapension in the southern arctic tundra zone, Kobre-sio — Dryadion (Tetragono — Dryadetum) in the middle arctic tundra zone, Luzulion arcticae in the northern arctic tundra zone, and Papaverion dahliani in the arctic polar desert zone.     

Phytochemical profiles and antioxidant potential of four Arctic vascular plants from Svalbard

Environmental stress in the Arctic region leads to damage in plant membranes as a result of oxidation processes. To withstand these stress conditions, plants are expected to produce antioxidants that differ from phenolics. Here, we investigated the chemical composition and antioxidative activities of four Arctic flowering plant species (Dryas octopetala, Carex rupestris, Silene uralensis and Deschampsia alpina.) through in vitro measurements of the free radical scavenging activities (FRS), inhibition of lipid peroxidation (ILP) and trolox equivalent antioxidant capacities (TEAC). D. octopetala exhibited the highest ILP (76.45?%) and FRS (86.58?%) activities. The TEAC values were higher than those of the Trolox vitamin E standard in all four species. Overall, the antioxidative activity was highest in D. octopetala, followed by C. rupestris, S. uralensis and D. alpina. Electrospray ionization tandem mass spectrometric (ESI–MS/MS) analysis of methanolic extracts of these plants revealed the presence of organoselenides, linear alkylbenzenesulfonates (LAS) and oligosaccharides, some of which are reported as antioxidants in the literature. Hence, it is likely that the antioxidant activities exhibited by these plants are not only related to the production of phenolics. This is the first report of the antioxidant potential of four Arctic flowering plants and the presence of selenides in D. octopetala and S. uralensis, and the production of LAS in C. rupestris. Our findings suggest that these plants can be used as nutraceutical sources of selenium and as biomarkers for environmental pollution.     

Survey of moss-dwelling bdelloid rotifers from middle Arctic Spitsbergen (Svalbard)

A survey of bdelloid rotifers from moss and lichen samples collected in the middle Arctic tundra subzone of Spitsbergen (Svalbard) revealed an unexpected high species richness of 52 taxa, of which 18 fully identified species are new for the region. About one-fifth of the European bdelloid species are present. Moisture regime and geographic localization of the moss appeared the most important ecological features driving differences in species composition between samples.     

Glacier ecosystem response to episodic nitrogen enrichment in Svalbard, European High Arctic

We describe the climatology, hydrology and biogeochemistry of an extreme nitrogen deposition event that occurred in the highly glacierised environment of the European High Arctic during June 1999. Meteorological analysis, three-dimensional air mass trajectories and a 3D transport model show that blocking high pressures over Scandinavia and the rapid advection of western European pollution toward Svalbard were sufficient to cause the most concentrated (1.15 ppm NO₃–N and 1.20 ppm NH₄–N), high magnitude (total 26 mm and up to 2.4 mm h^?1 at 30 m above sea level) nitrogen deposition event on record in this sensitive, high Arctic environment (78.91° N, 11.93° E). Since the event occurred when much of the catchment remained frozen or under snow cover, microbial utilisation of nitrogen within snowpacks and perennially unfrozen subglacial sediments, rather than soils, were mostly responsible for reducing N export. The rainfall event occurred long before the annual subglacial outburst flood and so prolonged (ca. 10 day) water storage at the glacier bed further enhanced the microbial assimilation. When the subglacial outburst eventually occurred, high runoff and concentrations of NO₃ ^? (but not NH₄ ⁺) returned in the downstream rivers. Assimilation accounted for between 53 and 72% of the total inorganic nitrogen deposited during the event, but the annual NO₃ ^? and NH₄ ⁺ runoff yields were still enhanced by up to 5 and 40 times respectively. Episodic atmospheric inputs of reactive nitrogen can therefore directly influence the biogeochemical functioning of High Arctic catchments, even when microbial activity takes place beneath a glacier at a time when terrestrial soil ecosystems remain frozen and unresponsive.     

Distribution and diversity of sipunculan fauna in high Arctic fjords (west Svalbard)

Sipuncula is a relatively species poor and generally rarely investigated phylum; nonetheless, it may play a considerable role in the ecosystem. During this study sipunculan species distribution patterns in four fjords of west Spitsbergen (Kongsfjorden, Hornsund, Isfjorden and van Mijenfjorden) were examined. Material was collected during ten cruises undertaken from 1997 to 2006. A total of 381 samples were taken at 132 stations located in the four fjords and, a total number of 920 sipunculans specimens were found in 114 of those samples. The highest sipunculan species richness was observed in Hornsund (six species), followed by Kongsfjorden and Isfjorden (five species in each fjord). Sipunculan fauna in all fjords was strongly dominated by Golfingia vulgaris (80% of all sipunculan individuals in Kongsfjorden), and Golfingia margaritacea (84% in van Mijenfjorden and 40% in Hornsund) or Nephasoma diaphanes (54% in Isfjorden). Locally, sipunculans were found in high densities (max. 62 ind. 0.1 m⁻² and up to 11% of macrobenthic densities) and biomass (max. 110.87 g 0.1 m⁻² and up to 80% of total fauna biomass). At such sites, sipunculans may play an important role in bioturbation of sediments and as a food source for higher trophic levels. Sipunculans did not occur within close proximity of the glacier where they might be eliminated due to high sedimentation rate and low amounts of organic matter. Because of their importance in benthic systems, a need to include sipunculans in routine macrobenthic surveys is emphasized.