Heterotrophic bacterioplankton dynamics have seldom been assessed in the Red Sea, an
exceptionally warm oligotrophic basin, which could be used as a model for the future
ocean. To understand the function of heterotrophic bacteria in biogeochemical cycles and
the flows of matter and energy to higher trophic levels, it is peremptory to understand how
bacterial growth is controlled. Bottom-up (resources availability), top-down (mortality by
predators and viruses) and temperature are the main hypotheses of control of bacterial
activity and stocks. This dissertation aims to assess the spatial-temporal variability of
heterotrophic bacteria and their interactions with diverse sources of dissolved organic
matter (DOM) through the observed effects on bacterial growth rates and productivity in
coastal environments of the central Red Sea. To that end we conducted a total of 66 shortterm
incubations (4-6 days) concurrently with the whole microbial community and
predator-free (by filtration) in various shallow ecosystems characterized by different
dominant sources of DOM. Frequent sampling combined flow cytometry and
biogeochemical analysis allowed us to measure bacterial standing stocks, including the
carrying capacity (maximum abundances), growth rates, characterize DOM concentrations
and lability, assess bacterial DOM consumption rates and biomass production and
ultimately quantify bacterial growth efficiencies. Our findings suggest that although
bacteria seemed to thrive in nutrient-sufficient waters, the central coastal Red Sea is
characterized by unusually low bacterial standing stocks (4.05 ± 0.31 x105 cells ml-1),
probably controlled by protistan grazing. At the same time, bacterioplankton showed high
potential to grow (0.35-1.75 d-1, reaching 4.16 d-1 when dilution and pre-filtration were
performed). Even though the highest specific growth rates were observed during the
warmer periods, we did not find any consistent relationship with temperature. While
temperature seemed not to constrain bacterial specific growth rates, we observed a tight
link between bacterial growth and resource availability in terms of both quantity and
quality. Overall, by surveying one of the warmest marine regions on Earth, this dissertation
provides detailed insights into heterotrophic bacterioplankton dynamics and how bottomup,
top-down and temperature regulate them in tropical waters, a vast geographical
extension of the world oceans that had remained strongly undersampled to date.
| Identifer | oai:union.ndltd.org:kaust.edu.sa/oai:repository.kaust.edu.sa:10754/661943 |
| Date | 03 1900 |
| Creators | Silva, Luis |
| Contributors | Moran, Xose Anxelu G., Biological and Environmental Sciences and Engineering (BESE) Division, Duarte, Carlos M., Daffonchio, Daniele, Gasol, Josep |
| Source Sets | King Abdullah University of Science and Technology |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
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