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The ecology of picophytoplankton in a coastal upwelling ecosystem
The dynamic Benguela Upwelling System is one of four major upwelling regions in the world and is subdivided into two sub-systems, the northern and southern Benguela. This current study was conducted within the southern Benguela, which lies between 27°S and 35°S (Orange River Mouth to East London) an...
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| Format: | Thesis |
| Language: | English |
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Department of Biological Sciences
2021
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| _version_ | 1867613146371325952 |
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| access_status_str | Open Access |
| author | Gebe, Zimkhita |
| author2 | Moloney, Coleen |
| author_browse | Gebe, Zimkhita Moloney, Coleen |
| author_facet | Moloney, Coleen Gebe, Zimkhita |
| author_sort | Gebe, Zimkhita |
| collection | Thesis |
| description | The dynamic Benguela Upwelling System is one of four major upwelling regions in the world and is subdivided into two sub-systems, the northern and southern Benguela. This current study was conducted within the southern Benguela, which lies between 27°S and 35°S (Orange River Mouth to East London) and is characterized on the west coast by seasonal, wind-driven, coastal upwelling. The study targeted three picophytoplankton groups, Synechococcus, Prochlorococcus and picoeukaryotes, which are the three most abundant < 2 µm size class phytoplankton. Flow cytometry was employed to enumerate picophytoplankton abundances, using their pigments and cell sizes to identify the different groups. The aim of the study was to investigate the role of picophytoplankton in the southern Benguela coastal upwelling ecosystem. These aims were met by: i) determining the spatiotemporal variability of each of the three picophytoplankton groups over a period of 8 sampling cruises at 44 stations across four latitudinal lines in the study region, ii) determining short-term changes in carbon and nitrogen biomass of picophytoplankton and their growth rates over a 10-day period, using abundance estimates from a station off St. Helena Bay, and iii) estimating mortality of microbial communities in a laboratory study using samples collected from a coastal upwelling environment. Results showed no strong seasonality in picophytoplankton abundances but evidence of latitudinal and zonal effects. Investigations over the short term showed that populations of picophytoplankton in the southern Benguela change on the same timescale of ~3 days as the larger phytoplankton during an upwelling event. Determining mortality rates using a dilution experiment presented some challenges. Instead of increased growth rates, the study showed decreased growth rates as predator numbers decreased. These shortcomings were investigated in a second experiment, which both excluded large predators (<200µm) and also ran a parallel experiment excluding smaller predators (10-200 µm). The last of these experiments resulted in increased growth rates as predator numbers decreased. The complexity of the southern Benguela system, with its pulsed, high productivity and large concentrations of nutrients, traditionally is known to show variability through effects on the biology of large phytoplankton. However, picophytoplankton also were variable in the study area, resulting from bottom up effects of the environment, confounded by biotic factors such as predation, parasitism and competition |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/33737 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:31:30.019Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2021 |
| publishDateRange | 2021 |
| publishDateSort | 2021 |
| publisher | Department of Biological Sciences |
| publisherStr | Department of Biological Sciences |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/33737 The ecology of picophytoplankton in a coastal upwelling ecosystem Gebe, Zimkhita Moloney, Coleen Pfaff, Maya Rocke, Emma Biological Sciences The dynamic Benguela Upwelling System is one of four major upwelling regions in the world and is subdivided into two sub-systems, the northern and southern Benguela. This current study was conducted within the southern Benguela, which lies between 27°S and 35°S (Orange River Mouth to East London) and is characterized on the west coast by seasonal, wind-driven, coastal upwelling. The study targeted three picophytoplankton groups, Synechococcus, Prochlorococcus and picoeukaryotes, which are the three most abundant < 2 µm size class phytoplankton. Flow cytometry was employed to enumerate picophytoplankton abundances, using their pigments and cell sizes to identify the different groups. The aim of the study was to investigate the role of picophytoplankton in the southern Benguela coastal upwelling ecosystem. These aims were met by: i) determining the spatiotemporal variability of each of the three picophytoplankton groups over a period of 8 sampling cruises at 44 stations across four latitudinal lines in the study region, ii) determining short-term changes in carbon and nitrogen biomass of picophytoplankton and their growth rates over a 10-day period, using abundance estimates from a station off St. Helena Bay, and iii) estimating mortality of microbial communities in a laboratory study using samples collected from a coastal upwelling environment. Results showed no strong seasonality in picophytoplankton abundances but evidence of latitudinal and zonal effects. Investigations over the short term showed that populations of picophytoplankton in the southern Benguela change on the same timescale of ~3 days as the larger phytoplankton during an upwelling event. Determining mortality rates using a dilution experiment presented some challenges. Instead of increased growth rates, the study showed decreased growth rates as predator numbers decreased. These shortcomings were investigated in a second experiment, which both excluded large predators (<200µm) and also ran a parallel experiment excluding smaller predators (10-200 µm). The last of these experiments resulted in increased growth rates as predator numbers decreased. The complexity of the southern Benguela system, with its pulsed, high productivity and large concentrations of nutrients, traditionally is known to show variability through effects on the biology of large phytoplankton. However, picophytoplankton also were variable in the study area, resulting from bottom up effects of the environment, confounded by biotic factors such as predation, parasitism and competition 2021-08-12T09:11:03Z 2021-08-12T09:11:03Z 2021 2021-08-10T09:39:58Z Doctoral Thesis Doctoral PhD http://hdl.handle.net/11427/33737 eng application/pdf Department of Biological Sciences Faculty of Science |
| spellingShingle | Biological Sciences Gebe, Zimkhita The ecology of picophytoplankton in a coastal upwelling ecosystem |
| thesis_degree_str | Doctoral |
| title | The ecology of picophytoplankton in a coastal upwelling ecosystem |
| title_full | The ecology of picophytoplankton in a coastal upwelling ecosystem |
| title_fullStr | The ecology of picophytoplankton in a coastal upwelling ecosystem |
| title_full_unstemmed | The ecology of picophytoplankton in a coastal upwelling ecosystem |
| title_short | The ecology of picophytoplankton in a coastal upwelling ecosystem |
| title_sort | ecology of picophytoplankton in a coastal upwelling ecosystem |
| topic | Biological Sciences |
| url | http://hdl.handle.net/11427/33737 |
| work_keys_str_mv | AT gebezimkhita theecologyofpicophytoplanktoninacoastalupwellingecosystem AT gebezimkhita ecologyofpicophytoplanktoninacoastalupwellingecosystem |