Bacterioplankton community composition and activity in the Atlantic Ocean

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

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2007

Author dc:creator

• Heywood, Jane Louise