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Title: Investigation of the environmental control on the phytoplankton and bacterioplankton in two contrasting temperate estuaries
Author: Alshatti, Amani Ebraheem
ISNI:       0000 0004 6496 4511
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2017
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Frequent measurements of the physical-chemical parameters and biological components of estuaries are key for assessing the ecological status of these transitional waters. Little is known about the microbial community composition of two temperate South Coast UK estuaries, Southampton Water and Christchurch Harbour (Mudeford Quay). The aim of this research project was to investigate how changes in the abundance and dynamics of the dominant phylogenetic heterotrophic bacteria populations relate to major physical-chemical parameters during phytoplankton bloom periods in the spring and summer months in these two estuaries. During 2013 in Southampton Water, the spring phytoplankton bloom occurred when the water temperature was below 10°C whereas in Christchurch Harbour it occurred at 14°C, and in the following years in Southampton Water at 14 °C and 15 °C, in 2014 and 2015, respectively. The spring bloom chlorophyll a concentrations in Southampton Water never exceeded 10 μg L‐1 in all three years while in Christchurch Harbour a major peak in spring 2013 reached 44 μg L‐1. Surface salinity in Southampton Water showed a narrow range of 27-33 whereas, at Mudeford Quay at the entrance to Christchurch Harbour a much larger range was detected of 1.3-22. The concentration of inorganic nutrients detected between the two estuaries for nitrate, phosphate and silicate had a much higher range in Christchurch Harbour compared to Southampton Water reflecting the contribution from different river sources. Identifying the biological components the influence of the physical-chemical controls affecting their dynamics and succession. The phytoplankton community in Southampton Water was assessed from HPLC pigment analysis coupled with microscopic counts, and indicated diatoms (Skeletonema sp., Thalassiosira sp., and Chaetoceros sp.) dominated the spring bloom and dinoflagellates dominated summer bloom with major species Scripsiella sp. and Prorocentrum sp. Nucleic acid staining (DAPI and SYBR Green I) was applied to 1% (PFA) preserved water samples for total enumeration of bacterioplankton. A cytosense flow cytometry slightly overestimated the concentration of bacteria compared to DAPI cell counts determined using a fluorescent microscope mainly during the phytoplankton spring and summer blooms but overall with significant correlation between the two methods for Southampton Water and Christchurch Harbour (r =0.87, r = 0.85, p < 0.0001, n = 32 respectively). Fluorescence in situ hybridization (FISH) with oligonucleotide probes was used to determine the abundance and dominance of various heterotrophic bacteria groups in samples from both estuaries and theses related to environmental conditions. Beta proteobacteria showed a strong negative significant correlation with salinity (r = ‐0.95, p < 0.0001, n = 29) in the two estuaries indicating they favour fresh water systems. Alpha‐, and Gamma proteobacteria were detected with variable significant correlation with temperature and salinity. However, only a moderate correlation was observed between the phylogenetic groups and Chl‐a concentrations highlighting the fact that heterotrophic bacteria may utilize organic carbon from other sources in the estuarine system. A principal component analysis (PCA), indicated temperature to be the most influence on bacteria domain levels (Eubacteria and Euryarchaea). Whereas, at phylogenetic class level proteobacterial phyla, salinity and Chl‐a were the most influence on their abundance and succession.
Supervisor: Purdie, Duncan Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available