Browsing by Author "Pfaff, Maya C"

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    Fast food : the transport of particulate organic matter over an upwelling event on the west coast of southern Africa
    (2007) Biccard, Aiden; Branch, George M; Pfaff, Maya C
    Differences in transport, composition and supply of particulate organic matter (POM), as a food source for coastal consumers, were investigated between an exposed headland (Cape Columbine) and a sheltered bay (Elandsbaai) in the southern Benguela. Physical data, in agreement with previous studies, showed that Cape Columbine is situated within an upwelling center and Elandsbaai within an upwelling shadow. Three distinct oceanographic conditions, upwelling, relaxation and downwelling, were discemable from wind, current and temperature data at each site. Upwelling was most prevalent at Cape Columbine in contrast to relaxation at Elandsbaai. Significant differences (P < 0.00001) in chlorophyll a concentration, quantities of organic carbon and % kelp-derived carbon were found between the two sites. In addition, significant differences (P < 0.0001) in chlorophyll a concentration, quantities of organic carbon and % kelp-derived carbon were found between the different oceanographic conditions: upwelling, relaxation and downwelling. A significant interaction (P < 0.00001) for % kelp-derived carbon was found between site and oceanographic conditions. Tests within study sites revealed significantly higher chlorophyll a concentrations in the euphotic zone, as expected. Furthermore, chlorophyll a concentrations showed a significant decrease with distance offshore at Elandsbaai. Percentage contribution of kelp-derived carbon (max = 36%) to POM was lower than predicted and surprisingly lower than values reported in previous works (77%). No stratification of kelp-derived matter or organic carbon was observed in the water column at both sites. It is likely that sampling stations were too shallow i.e. water column was well mixed as a results of nearshore turbulence. In terms of food supply to coastal consumers, upwelling episodes at Cape Columbine resulted in significantly high import of kelp matter into the nearshore water column. In contrast, phytoplankton, constituted the primary food source for both sites during relaxation and downwelling episodes. It is clear that different oceanographic conditions between an exposed headland and a sheltered bay have profound implications regarding the transport, composition and supply of POM, as a source of food to coastal communities.
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    The interactive effects of disturbance and nutrient enrichment on species diversity and biomass of intertidal rocky-shore communities
    (2005) Pfaff, Maya C; Branch, George M
    Unimodal patterns of diversity along gradients of both disturbance and productivity rank amongst the most celebrated generalizations in ecology, known as the Intermediate Disturbance Hypothesis (IOH) and Productivity Diversity Hypothesis. However, doubt about their generality has arisen from studies that have failed to confirm the predicted patterns. Models suggest the interactive effects of disturbance and productivity on diversity to be responsible for the variability of diversity patterns.
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    Microbial biodiversity in the southern Indian Ocean and Southern Ocean
    (2017) Flaviani, Flavia; Rybicki, Edward P; Schroeder, Declan; Pfaff, Maya C
    The multi-phylotype and ecologically important community of microbes in aquatic environments ranges from the numerically dominant viruses to the diverse climate-change regulating phytoplankton. Recent advances in next generation sequencing are starting to reveal the true diversity and biological complexity of this previously invisible component of Earth's hydrosphere. An increased awareness of this microbiome's importance has led to the rise of microbial studies with marine environmental samples being collected and sequenced daily around the globe. Despite the rapid advancement in knowledge of marine microbial diversity, technical difficulties have constrained the ability to perform basin wide physical and chemical oceanographic assessments in tandem with microbiological screening with the majority of studies only looking at a single component of the microbial community. In this study the full microbial diversity, from viruses to protists, was characterised within the southern Indian Ocean and the Southern Ocean from a small volume of seawater collected using the same CTD equipment used by oceanographers. Throughout this study it will be demonstrated how this small volume is sufficient to describe the core microbial taxa in the marine environment. The application of a bespoke bioinformatics pipeline, integrated with sequencing replication, improved the description of the dominant core microbiome whilst removing OTUs present due to PCR and sequencing artefacts thereby improving the accurate description of rare phylotypes. Analyses confirmed the dominance of Cyanobacteria, Alphaproteobacteria and Gammaproteobacteria in the pelagic prokaryotic microbiome, while the Stramenopiles-Alveolata-Rhizaria (SAR) cluster dominates the eukaryotic microbiome. A decrease in the SAR community will be reported for the Southern Ocean with a concomitant increase in the haptophyte community. Whilst the virome confirmed the dominance of tailed phages and giant viruses across all stations, there was a significant variation caudoviruses and Nucleocytoplasmic Large DNA viruses (NCLDV) across defined biogeographical boundaries. The described method will allow the characterisation of the microbial biodiversity as well as future integration with oceanographic data with a much reduced sampling effort. The characterisation of the whole microbial community from a single water sample will improve the understanding of microbial interactions and represent a step towards in the inclusion of viruses into biogeochemical models.