4 results for Archer, Stephen David James

  • Characterization of the bacterioplankton communities in the melt-water ponds of Bratina Island, Victoria Land, Antarctica

    Archer, Stephen David James (2011)

    Masters thesis
    University of Waikato

    Antarctic ecosystems (such as the ponds by Bratina Island, Antarctica) provide an excellent opportunity to examine organisms that can live in one of the most extreme and geochemically varied environments in the world. These ponds are of interest as each one can vary greatly in size, depth, and age as well as profiles of dissolved oxygen, metal concentrations, pH and salinity. Even within ponds geochemically distinct stratified layers can form which can greatly influence their microbial communities. There are a number of studies which indicate that microbial populations found in Antarctic ponds will be highly diverse and variable due to the uniqueness of the environment. This study aims to increase our knowledge of microbial biodiversity and the environmental factors which structure them, in particular the stratification transition zones within ponds water columns. A thorough set of biological samples were taken from five selected ponds during mid-summer in the 09-10 season to complement those taken during the winter freeze-up in the 07-08 extended season by Hawes and co-workers. Oxygen concentration, pH, conductivity and temperature of each pond water sample were measured in the field and water samples were taken back to the University of Waikato for further analysis. This research primarily used the DNA fingerprinting technique ARISA, matched with geochemistry to identify and characterise the resident and functional members of the microbial community and understand how the community is structured in relation to environmental conditions. We found that the planktonic populations of the Bratina Island ponds do vary between ponds, that each pond has its own chemical signature and that populations do change with depth. One of the studied ponds, Egg, was found to have an extreme chemical stratification leading to significantly different populations at each depth. Data analysis using BEST analysis determined that the changes in the bacterial populations in Egg are primarily in relation to the pH and conductivity at each depth which changes dramatically in the lower depths.

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  • Geochemical, Spatial, and Temporal Drivers of Microbial Community Heterogeneity in the Meltwater Ponds of Antarctica

    Archer, Stephen David James (2015)

    Doctoral thesis
    University of Waikato

    Antarctic meltwater ponds are an abundant, dynamic and sensitive yet poorly understood ecosystem. In this thesis, bacterial communities from surface waters, the water column and benthic zone in geochemically variable meltwater ponds in the Ross Sea Region of Antarctica were investigated. The primary objective of this research was to provide a detailed description of the community composition and to determine the temporal, geochemical and geomorphological drivers of community structure. A coordinated comparable analysis method was used for all samples so that, although separated into the previously mentioned zones, findings could be directly compared across studies. Bacterial community structure between samples was initially investigated by Automated Ribosomal Intergenic Spacer Analysis (ARISA) of the 16S rRNA gene which, combined with in-situ collected geochemistry data was used to identify trends requiring high throughput sequencing (454 pyrosequencing of the V5-V6 hypervariable region of the 16S rRNA gene) analysis coupled with nutrient and elemental data. A preliminary study in December 2009 compared the water columns of five geochemically distinct ponds. Communities between ponds were distinct, their structure driven primarily by pH and conductivity. One geochemically stratified pond formed distinct surface and bottom clusters with increasing diversity and changes to phyla structure with depth. Temporal and geomorphological (Bratina Island and Miers Valley) drivers of variation in the microbial community structure between the surface waters of 41 ponds were examined. Conductivity was identified as the most significant driver across all ponds for the dominant cosmopolitan community, however trace elements were more significant drivers of community structure for the unique community (those sequences absent in at least one pond). Pronounced variation was identified between December and January samples and although the bacterial components of the community were similar between January 2012 and 2013 the community structure varied significantly. Despite different environments, communities from the Miers Valley were not well differentiated from Bratina Island, suggesting biological exchange between locations. The stratified water column of six Bratina Island and two Miers Valley ponds was investigated. Strongly geochemically stratified ponds exhibited a heterogeneous vertical community structure related to conductivity and dissolved oxygen. Variation in community structure was primarily driven by the abundance of a small number of cosmopolitan OTUs that changed with depth. Although the biological constituents were the same, minor variation in community structure was identified within Huey pond between years (2012 and 2013). Variation between Huey pond (Bratina Island) and Morepork pond (Miers Valley) was correlated with variation of iron and mercury concentration. Lastly the benthic zone of six ponds from Bratina Island and six from the Miers Valley was examined. The community structure was highly heterogeneous and diverse with 21 phyla identified. No distinction was identified between the two locations with the majority of pyrosequencing reads shared. Potassium, sodium and cobalt were identified as the most significant explanatory variables to the cosmopolitan community and aluminium, uranium and magnesium to the unique community. This study has granted an unprecedented understanding of the bacterial communities in the meltwater ponds of the Ross Sea Region. Geochemical inter pond heterogeneity is matched with an equally heterogeneous bacterial communities, primarily driven by conductivity. Although harboring a complex and diverse community the majority is comprised of a small number of shared OTUs across spatial and temporal scales.

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  • Characterisation of bacterioplankton communities in the meltwater ponds of Bratina Island, Victoria Land, Antarctica

    Archer, Stephen David James; McDonald, Ian R.; Herbold, Craig W.; Cary, S. Craig (2014)

    Journal article
    University of Waikato

    A unique collection of Antarctic aquatic environments (meltwater ponds) lies in close proximity on the rock and sediment-covered undulating surface of the McMurdo Ice Shelf, near Bratina Island (Victoria Land, Antarctica). During the 2009–10 mid-austral summer, sets of discrete water samples were collected across the vertical geochemical gradients of five meltwater ponds (Egg, P70E, Legin, Salt and Orange) for geochemical and microbial community structure analysis. Bacterial DNA fingerprints (using Automated Ribosomal Intergenic Spacer Analysis) statistically clustered communities within ponds based on ANOSIM (R = 0.766, P = 0.001); however, one highly stratified pond (Egg) had two distinct depth-related bacterial communities (R = 0.975, P = 0.008). 454 pyrosequencing at three depths within Egg also identified phylum level shifts and increased diversity with depth, Bacteroidetes being the dominant phyla in the surface sample and Proteobacteria being dominant in the bottom two depths. BEST analysis, which attempts to link community structure and the geochemistry of a pond, identified conductivity and pH individually, and to a lesser extent Ag109, NO2 and V51 as dominant influences to the microbial community structure in these ponds. Increasing abundances of major halo-tolerant OTUs across the strong conductivity gradient reinforce it as the primary driver of community structure in this study

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  • Benthic microbial communities of coastal terrestrial and ice shelf Antarctic meltwater ponds.

    Archer, Stephen David James; McDonald, Ian R.; Herbold, Craig W.; Lee, Charles Kai-Wu; Cary, S. Craig (2015)

    Journal article
    University of Waikato

    The numerous perennial meltwater ponds distributed throughout Antarctica represent diverse and productive ecosystems central to the ecological functioning of the surrounding ultra oligotrophic environment. The dominant taxa in the pond benthic communities have been well described however, little is known regarding their regional dispersal and local drivers to community structure. The benthic microbial communities of 12 meltwater ponds in the McMurdo Sound of Antarctica were investigated to examine variation between pond microbial communities and their biogeography. Geochemically comparable but geomorphologically distinct ponds were selected from Bratina Island (ice shelf) and Miers Valley (terrestrial) (s correlation coefficient of 0.632 and 0.806, respectively). These results indicate that the microbial communities in meltwater ponds are easily dispersed regionally and that the local geochemical environment drives the ponds community structure.

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