- Title
- Zooplankton dynamics of Algoa Bay (South Africa) under varying oceanographic conditions
- Creator
- Bizani,Mfundo
- Subject
- Marine zooplankton -- South Africa
- Subject
- Climate changes
- Date Issued
- 2022-04
- Date
- 2022-04
- Type
- Doctoral theses
- Type
- text
- Identifier
- http://hdl.handle.net/10948/55943
- Identifier
- vital:54554
- Description
- the ecological significance of ocean plankton in terms of nutrient cycling and energy transfer is widely recognised, as is their mechanistic link with both oceanographic processes and climate. Consequently, plankton are widely regarded as sentinels of climate change, principally owing to their responsiveness to changing environmental conditions. Developing an understanding of the ecological as well as socio-economic consequences associated with changes in marine plankton dynamics has emerged as a key issue worldwide. Though many exciting advances in this respect have been attained with the aid of long-term plankton time series (>50 y), global environmental datasets and innovative meta-analyses, building deep knowledge of regional bio-physical dynamics and responses to specific perturbed states remains an essential component of the collective effort. Algoa Bay, situated on the warmtemperate south-east coast of South Africa presents a unique opportunity to study key elements of plankton ecology relevant to climate change problems in the regional sense. The embayment is locally subjected to frequent wind-driven upwelling and regionally, to periodic mesoscale oceanographic forcing (e.g., large solitary meanders, Agulhas Current intrusions), all of which culminate in a complex physical and biogeochemical environment. Using zooplankton as the focal component and drawing from a multi-year monthly dataset incorporating a bay-scale sampling framework, the present study addressed three key hypotheses pertaining to 1) drivers of spatio-temporal variability, 2) biomass rate of change over temporal scales using time-series analyses, and 3) community responses to a bay-scale biological perturbation event. Zooplankton biomass exhibited prominent seasonal patterns with bimodal peaks corresponding with near-consistent year-to-year autumn and spring blooms. Overall, the spatial trend showed no heterogeneity, though statistical significance between-station variability was noted per season. An analytical framework involving generalised additive models revealed zooplankton spatial heterogeneity in Algoa Bay to be a function of seasonal variation in a suite of physicochemical variables, including the combined effects of temperature, salinity, dissolved oxygen, total nitrogen and silicate, but not ammonium, phosphate or chlorophyll-a (as proxy for phytoplankton). Fronts (including river plumes), warm water intrusion from the Agulhas Current, and wind-driven upwelling were postulated to be key driving forces. Structural breaks analysis performed on station-specific time series revealed significant incremental increases in zooplankton biomass over time, which in turn, corresponded with a gradual decrease in thermocline depth. The most pronounced increasing effect was associated with a period (2013– 14) of amplified land-derived nutrient input and increasing harmful algal bloom (HAB) activity.
- Description
- Thesis (PhD) -- Faculty of Science, School of Environmental Sciences, 2022
- Format
- computer
- Format
- online resource
- Format
- 1 online resource (xiii, 134 pages)
- Format
- Publisher
- Nelson Mandela University
- Publisher
- Faculty of Science
- Language
- English
- Rights
- Nelson Mandela University
- Rights
- All Rights Reserved
- Rights
- Open Access
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | SOURCE1 | Bizani, M.pdf | 6 MB | Adobe Acrobat PDF | View Details Download |