Marine benthic (epilithic) diatom communities along the coast of South Africa: A contribution to their diversity, spatio-temporal variations, and ecology
- Authors: Cotiyane-Pondo, Phumlile
- Date: 2023-12
- Subjects: Marine ecology , Marine biodiversity , Coastal ecology
- Language: English
- Type: Doctorate Dissertation , text
- Identifier: http://hdl.handle.net/10948/62453 , vital:72754
- Description: Diatoms remain one of the most diverse and ecologically important microorganisms within microphytobenthos. The highly variable South African coastline, comprised of heterogeneous rocky intertidal habitats provides the ideal study area to investigate epilithic microphytobenthos and their associated influential drivers. In South Africa, in-depth taxonomic research on marine littoral diatoms exists, however, quantitative research and knowledge on their abundance, diversity, community composition and distribution remain limited. Thus, the main aim of this research was to explore the spatial and temporal variability of marine benthic (epilithic) diatoms, in relation to the variable physico-chemical conditions in the nearshore intertidal environments along the coastline of South Africa. To achieve this, field-based observational (natural substrata) and experimental (artificial substrata) studies were conducted on selected locations around the coastline, with a large focus on south coast localities. For the Spatial studies, large (i.e., encompassing all three biogeographical regions) and small-scale (i.e., coastal island in the warm temperate region) surveys of epilithic diatom assemblages from natural rocky substrata were conducted. Large-scale investigation results revealed highly variable diatom assemblages, diversity and distribution, with compositional differences observed between the coastal sections (around the coastline). A total of 85 diatom taxa from 31 genera were observed at 15 sites, and the number of taxa varied un-systematically along coastline. Genera with noticeable contribution included Nitzschia, Cocconeis and Achnanthes. On the coastal Bird Island (small-scale), similar variability was observed, but with a much higher diatom diversity and number of rarely observed species (e.g. Actinoptychus senarius (Ehrenberg) Ehrenberg, Cocconeis capensis (Cholnoky) Witkowski, Fragilariopsis kerguelensis (O’Meara) Hustedt, Striatella unipunctata (Lyngbye) Agardh. Seventy-two (72) species from 35 genera were recorded with a varied abundance and diversity around the island. The study also revealed a high contribution of typical benthic diatom species to the surf zone environment around the island. To study temporal variations, medium-term compositional differences on natural substrata were assessed monthly over an annual cycle at a single site. A paucity of diatom material was evident during this study and observations indicated a trend of presence and absence of diatom taxa from the study site. Nineteen (19) diatom genera were identified and those observed, albeit as one or two individual valves, included taxa from several genera including Biddulphia, Diploneis, Campyloneis, Trachyneis and Triceratium. Noteworthy was a seasonal increase in the number of diatom valves encountered, with the highest diatom abundance observed during spring (September) and the genera Cocconeis, Grammatophora and Navicula appearing regularly. To complement the sparse data from the long-term temporal study, a short-term experimental study on artificial substrata (Plexiglass) revealed rapid temporal variations of benthic diatom assemblages. The composition differed spatio-temporally during the experimental period, with fluctuating species occurrences and abundances between the two study sites. The experimental study also revealed the highest number of diatom species observed during this research (134 species belonging to 44 genera). While Cocconeis (13 species) and Nitzschia (9 species) were the dominant genera, 48% of the diatomcomposition was composed of rarely observed taxa that included Cocconeis testudo Giffen, Donkinia sp., Paralia sulcata (Ehrenberg) Cleve. Regarding environmental drivers, the findings indicated the importance of temperature and nutrients in driving diatom spatial abundance and composition along the coastline, as well as the island. However, the potential influence of the interplay between measured variables and unexplored coastal oceanographic processes (e.g., wave action) was noted. Temporally, from the annual study, the nature of the rocky substrate (rock type) rather than environmental conditions was postulated to have been the influential factor that resulted in the low diatom abundance data, however this requires further in-depth investigations on the influence of rock microtopography on microphytobenthos in this region. Contrastingly, the experimental study results indicated environmental variables having varying influences on the diatom diversity indices, however, study site and sampling occasion were revealed as the most important predictors of the observed variability. Further, site-specific biofilm processes, including biological interaction (e.g. grazing), were shown to alter biofilm succession, thus influencing the observed diatom assemblages. Overall, this research provided new and relevant knowledge on the variability of benthic (epilithic) diatom composition, biodiversity and distribution along the coastline, further contributing to our understanding of marine benthic diatoms ecology, their ecological role in the context of intertidal food web and their potential as bioindicators of change in the coastal ecosystems in Southern Africa. , Thesis (PhD) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-12
Exploring and contextualising the predominant coastal and marine environmental worldview orientations of millennial South Africans
- Authors: van Rooyen, Rize Dorothea
- Date: 2022-12
- Subjects: Coastal ecology , Marine ecology , Generation Y -- South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/62484 , vital:72764
- Description: The increase in human activities within the marine and coastal environments has introduced new stressors to the ocean’s ecosystems. Despite the increasing specification of coastal and marine environments within South African management policy and programmes, marine issues as well as ocean and coastal-related environmental inspections still lag behind terrestrial issues. Previous research identified the importance of including contextual factors within the study of environmental worldviews and behaviour. The present study aimed to address the identified needs within South African environmental management frameworks for proactive approaches, with consideration to the values and beliefs of the citizens of South Africa as specified in the National Environmental Management Act. The study specifically explores the coastal and marine environmental worldviews of a sample of South African millennials with reference to the contextual constraints, which influence their environmental perceptions and behaviours. This generation constitutes 26.4% of South Africa’s population and, according to literature, is largely underrepresented within environmental discourse. This exploratory-descriptive study utilised four research phases to contextualise the coastal and marine environmental worldviews of nine millennial South Africans, namely, a systematic review of 1236 academic articles, an observation and analysis of 50 environmentally focused Tweets from South African news media outlets, and the subsequent engagements, the distribution of a compiled coastal and marine environmental worldview scale to a sample of nine millennial South Africans and, finally, a set of phenomenological interviews with nine millennial South Africans to discuss the contextual constraints to pro-environmental behaviours. The findings of the study resulted in the provision of a theoretical model regarding the antecedents to environmental behaviour, which addressed the complexity of antecedent attributes omitted in contemporary theory. Additionally, the findings provided a framework of contextual attributes from which to address South African coastal and marine environmental worldviews. The findings further provided baseline information for proactive, informed, as well as participatory decisions and programmes for policy, development, and conservation. The present study represented a novel contribution to academic knowledge through its provision of a theoretical and contextual framework from which to study the antecedents of environmental behaviour. It further presents a novel contribution to development practice, allowing for proactive approaches to environmental management. , Thesis (D.Phil) -- Faculty of Business and Economic Sciences , School of Economics, Development & Tourism, 2022
- Full Text:
- Date Issued: 2022-12