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Title: Bacterioplankton community composition and activity in the Atlantic Ocean
Author: Heywood, Jane Louise
ISNI:       0000 0004 2687 7150
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2007
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Temporal and spatial patterns of bacterioplankton in six different provinces of the Atlantic Ocean were examined between 1996 and 2004. The abundance and integrated biomass of three prokaryote groups (Prochlorococcus spp., Synechococcus spp. and heterotrophic bacteria) were used to detect standing stock changes and characterise community structure in the Northern and Southern oligotrophic gyres and in the equatorial region. There was no statistically significant inter-annual variability in Prochlorococcus or Synechococcus abundance or integrated biomass in any of the provinces. The abundance and biomass of the remaining prokaryoplankton was variable but this variation could not be ascribed to seasonal differences and did not follow a clear inter-annual trend. The importance of the microbial loop in recycling organic nutrients in the upper Atlantic Ocean was also studied by comparing ratios of bacterial to primary production in different oceanic provinces. A proportionately higher rate of photosynthetically fixed carbon flowed through the microbial loop in the Northern oligotrophic gyre (22 – 55 %) compared to the other provinces studied. This indicates a difference in energy flow through the ecosystem in different oceanic regions with a greater emphasis on energy flow through the microbial loop in the Northern oligotrophic gyre probably due to reduced grazing of phytoplankton and reduced export production compared to other Atlantic Ocean provinces. The role of defined groups of bacteria in the cycling of nutrients was identified using a combination of flow cytometric sorting with radiotracer uptake and CARD-FISH. The SAR11 clade of bacteria were found to dominate the low nucleic acid group of bacterioplankton and as such it was possible to quantify the activity and abundance of these cells in the Atlantic Ocean. Despite their small genome size, SAR11 bacteria were found to be generally as active as an average bacterioplankton cell and were responsible for between 30 and 50 % of the total community methionine uptake. This research has characterised bacterioplankton composition and activity in Atlantic Ocean provinces thus enabling further understanding of the function and importance of the microbial loop in the upper ocean.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: GC Oceanography