Antimalarial secondary metabolites from Morinda lucida
- Authors: Chithambo, Bertha
- Date: 2017
- Subjects: Botanical chemistry , Anthraquinones , Antimalarials , Rubiaceae -- Therapeutic use , Malaria -- Treatment
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/45730 , vital:25535
- Description: Antimalarial activities of secondary metabolites from Morinda lucida (Rubiaceae), were investigated. Even though M. lucida is traditionally used to treat malaria, diabetes, jaundice, hypertension, dysentery and many other diseases, the compounds in this plant have not yet been fully investigated and characterised. Most of the studies that have been done on this plant focused on the medicinal properties of the crude extracts but have not gone further to isolate and characterise the compounds. In this study, the methanol - dichloromethane crude extract from the bark of M. lucida was fractionated into fractions 1-8. Fractions 2-5 were purified in order to isolate active secondary metabolites. The isolated pure compounds were characterised and identified. An in vitro antimalarial assay was carried out on the crude extract, fractions, pure compounds and solutions made from different combinations of pure compounds using the parasite lactate dehydrogenase (pLDH) assay. An IC50 done on the methanolic crude extract gave a value of 25 µg/mL. The % cell viability for the crude extract in cell toxicity assay remained at 100%. Each of the pure compounds tested had very little activity. Their activities were increased when samples from the different compounds were mixed. One of these mixtures reduced malaria viability to about 22 % at 20 µM and gave an IC50 value of 17 µM. Antibacterial assays were also carried out on the crude extract and fractions. Fractions 2 and 3 were relatively active (MIC values ranging between 125-1000 µg/mL) against M. cattarhalis and E. faecalis. Fraction 2 was also the most active on S. typhimurium and S. aureus (MIC value of 1000 µg/mL) compared with the other fractions. This same fraction also showed some activity against M. tuberculosis with MIC90 and MIC99 values of 40.9 and 46.3 µg/mL respectively in an anti-tuberculosis assay.The following compounds, comprising of iridoids (asperuloside and asperulosidic acid), terpenoids (stigmasterol, P-sitosterol, campesterol, lanosterol and cycloartenol) and anthraquinones [5,15-O-dimethylmorindol, 1,7-dihydroxy-2-methoxy-5-(methoxymethyl) anthraquinone and 1,6-dihydroxy-2-methoxy-5-(methoxymethyl)anthraquinone], were isolated. All these compounds have been isolated from different plants before with the exception of 1,7-dihydroxy-2-methoxy-5-(methoxymethyl)anthraquinone and 1,6-dihydroxy-2-methoxy-5-(methoxymethyl)anthraquinone which were tentatively assigned the structures due to insufficient data. To the best of our knowledge, this is the first report on the identification of all of the mentioned compounds, with the exception of ß-sitosterol and stigmasterol, from M. lucida. Molecular docking was performed on one of the isolated anthraquinones (5,15-O- dimethylmorindol) to check if it can bind to cytochrome bci, a known target for atovaquone. This compound interacted with the same amino acids that atovaquone, a well known antimalarial agent, interacted with on cytochrome bc1 indicating a possible similar mode of action.
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Appropriate integration of workers with physical limitations into a manual workplace – development of an assessment tool
- Authors: Pearson, Jessie T
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/8209 , vital:21368
- Description: Background: People with physical limitations can contribute significantly to society and the economy, however, barriers to full and effective participation in the labour market often hinder decent employment. In light of this, placement decisions of impaired workers should be based on detailed information of the nature of the jobs available, as well as individual capabilities of the worker. An ergonomics approach to design attempts to achieve an appropriate balance between the capabilities of the worker and the requirements of the task and uses this balance to improve productivity and encourage physical and mental well-being, job satisfaction and safety. A specific analysis tool which can be applied to various workplaces and jobs, and provide information for decisions regarding placement of physically limited workers, will help to increase the percentage of correct placement in an appropriate workplace, resulting in optimum productivity and worker safety. Methods: An assessment tool which allows matching of job requirements and worker capabilities was developed based on a theoretical framework from Mattison and Goebel (2007), as well as principles defined by Almgren and Schaurig (2012) and Demura and Nakada (2010). The tool assesses range of motion, force and time components of the physical requirements of different tasks involved in the job, as well as movement capabilities and limitations of the worker. The tool was pilot tested in a case study with an above the knee amputee working at a research facility. Results: The tool successfully provided information regarding the matching of the work to the identified job. The output of the tool highlighted two tasks which would place the worker at risk due to physical requirements of the tasks being greater than movement capabilities of the worker. These tasks need to be further investigated to determine if accommodations can be made to assist the worker in safely performing the task, or if the job is not suitable for the worker. Conclusions: The tool developed was useful in providing information to inform appropriate placement of the physically limited worker. Further research needs to be done to validate and determine reliability of the tool.
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Assessing MODIS evapotranspiration data for hydrological modelling in South Africa
- Authors: Mazibuko, Sbongiseni Christian
- Date: 2017
- Subjects: Evapotranspiration , Evapotranspiration -- Measurement , Hydrologic models , Hydrologic models -- South Africa , MODIS (Spectroradiometer)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/8009 , vital:21334
- Description: Evapotranspiration as a major component of the water balance has been identified as a key factor in hydrological modelling. Water management can be improved by means of increased use of reliable methods for estimating evapotranspiration. The limited availability of measured climate and discharge data sets, particularly in the developing world, restricts the reliability of hydrological models in these regions. Furthermore, rapid changes in hydrological systems with increasing development mean uncertainties in water resource estimation are growing. These changes are related to the modification of catchment hydrological processes with increasing human activity. Dealing with data uncertainty and quantifying the impacts of catchment activities are significant challenges that scientists in the field of hydrology face today. Uncertainties in hydrometeorological data are associated with poor observation networks that provide data at point scales which are not adequately representative of the inherent heterogeneity within catchment processes. Using uncertain data in model applications reduces the predictive power of hydrological models as well as the ability to validate the model outcomes. This study examines the potential of using remote sensing-based evapotranspiration data to reduce uncertainty in the climatic forcing data and constraining the output of a rainfall-runoff hydrological model. It is common to use fixed seasonally variable potential evapotranspiration (PET) instead of temporally varying PET data as inputs to standard rainfall-runoff models. Part of the reason is that there are relatively few stations available to measure a variety of meteorological input data needed to compute PET, as well as the apparent lack of sensitivity of rainfall-runoff models to different types of PET inputs. As hydrometeorological data become more readily available through the use of earth observation systems, it is important to determine whether rainfall-runoff models are sensitive to time-varying PET derived from these earth observations systems. Further potential includes the use of actual evapotranspiration (ETa) from this type of data to constrain model outputs and improve model realism. It is assumed that a better representation of evapotranspiration demands could improve the efficiency of models, and this study explores some of these issues. The study used evapotranspiration estimates (PET and ETa) from the MOD16 global product with one of the most widely used hydrological models in South Africa. The investigation included applying the Pitman model in a number of case study catchments located in different climatic regions of the country. The main objectives of the study included (i) the establishment of behavioural model parameter sets that generate acceptable hydrological response under both naturalised and present-day conditions, (ii) the use of time-varying PET estimates derived from MOD16 data to force the model, and (iii) the use of MOD16 ETa estimates to constrain model-simulated ETa. Before examining the use of different PET forcing data in the model, a two-step modelling approached was employed both a single-run and an uncertainty version of the Pitman model. During the first step (using a single-run version), available information on catchment physical properties and regionalised groundwater recharge together with model calibration principles were used to develop model functionality understanding and establish initial parameter sets. The outcomes from the first step were used to define uncertain parameter ranges for the use in the uncertainty version of the Pitman model (second step). Further, catchment water uses were quantified to ensure comparability with present-day flow conditions represented by the stream flow records. The effects of forcing the Pitman model with MOD16-based time-varying PET data inputs were evaluated using static and dynamic sensitivity analysis approaches. In the static approach, parameter sets calibrated using fixed seasonal distributions of PET data remain unchanged when forcing the model with other forms of PET, whereas in the dynamic method, the model is recalibrated with changing PET inputs. In both approaches, model sensitivity was assessed by comparing objective function statistics of reference flow simulations with those simulations incorporating changing PET data inputs. The use of the MOD16 ETa data to constrain model- simulated evapotranspiration losses was conducted by calibrating the parameters such that the simulated-ETa matched the evapotranspiration loss estimated from the MOD16 data. Despite issues around model equifinality and significant uncertainty within water use information, the Pitman model simulations were generally satisfactory and compared with observed stream flow data where available. The use of time-varying PET data does not improve the efficiency of the model when both static and dynamic sensitivity approaches are used. This was highly expected with the static approach where fixed model parameter sets do not account for the changes in evapotranspiration demands. However, with the dynamic approach, it was difficult to conclude why the model efficiency did not improve given the flexibility of the model to achieve appropriate parameter sets to different forms of PET. The study noted that the insensitivity of the model to changes in PET demands could be due to uncertainties in the model structure and MOD16 data. Attempts to constrain the model-simulated actual evapotranspiration with MOD16 ETa estimates were hampered by large errors in the MOD16 data and resulted in the non-closure of the catchment annual water balance, even when likely errors in the other components of the water balance were accounted for. There is still a great deal of work that needs to be done to reduce uncertainties associated with the use of earth observation data in hydrological modelling. This study has identified some of the specific gaps within the application of evapotranspiration data from earth observation information. While the MOD16 data applied with the Pitman model did not achieve improved simulations, the study has demonstrated the enormous potential of the data product in the future should the identified uncertainties be resolved. Lastly, the investigation highlighted some of the possible model structural uncertainties specifically associated with the simplified soil-moisture accounting routines within the model. It is possible that amending the model structure through investigating the dynamics of the relationship between soil moisture and evapotranspiration losses would assist in the improved utilisation of earth observation products related to the MOD16 ET data.
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Assessing selected ecosystem services in urban green spaces in Bulawayo, Zimbabwe
- Authors: Ngulani, Thembelihle Tshandapiwa
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/5856 , vital:20982
- Description: Urbanization has resulted in the building of numerous structures such as buildings and roads which reduces the amount of natural land. Urban space planning has taken this into consideration resulting in planned urban green spaces and remnant land within urban areas. Urban green spaces provide a number of ecosystem services which are beneficial to urban residents. This study sought to determine residents’ use and perception of urban green spaces in Bulawayo, the second largest city in Zimbabwe, and to quantify and value four selected ecosystem services, i.e. carbon sequestration by urban trees, urban heat island amelioration, spiritual services and firewood provision. All ecosystem services were valued using local a variety of direct or substitutive methods. Questionnaires were administered at green spaces to green space users to capture responses on reasons why they use green spaces and their perception of green spaces. Residents’ responses showed that they appreciate green spaces as multidimensional spaces which provide a number of benefits for cultural and provisioning services. The role of the green spaces in providing regulating services was not well appreciated by the residents as they did not directly experience these benefits. An association was revealed between primary purpose of visit to urban green spaces and household income. Residents in areas of medium and high density housing visited green spaces on a daily basis, whereas those in more affluent, low density housing areas visited green spaces less often, i.e. a few times a month Carbon sequestration rate was determined by measuring tree diameter within one year to determine increase in carbon sequestered. Bulawayo’s urban green spaces sequester 3 290 t/C/yr valued at approximately $13 000/yr. There was a significant difference in carbon sequestration by urban trees between formal and informal green spaces with formal green spaces sequestering more carbon. Indigenous trees were shown to sequester more carbon than exotic trees and trees with bigger stem diameter were determined sequester more carbon than trees with small diameter. The effect of urban green spaces on ambient temperature was determined by measuring ambient air temperature in green spaces and built up areas over six months. Urban green spaces in Bulawayo play a role in urban micro-climate regulation by reducing the ambient temperature in the green spaces as well as is built up areas. The mean difference between green spaces and surrounding urban areas was up to 60C, with larger green spaces generally showing larger differences. The green spaces extend their cooling effect to surrounding areas thus reducing the temperatures in surrounding residential areas thus reducing the energy demand used for indoor cooling. To determine why residents worship in green spaces, questionnaires were administered to congregation members to capture reasons why and how often they worship in green spaces, challenges faced by the congregants as well as assistance that can be given by the Bulawayo city council to improve the outdoor worship experience. Green spaces offer ideal places for worship in natural areas for congregants to be in touch with nature. The green spaces are also used by some congregations who ordinarily would worship in buildings but fail to do so due to lack of funds for rent or to purchase or construct a church building to use. The value of Bulawayo’s green spaces spiritual services was determined to be $92.50/ha/yr. Firewood provision was also determined by measuring tree diameter within one year to determine increase in fuelwood. The green spaces showed a significant difference in firewood production among sites. Formal green spaces were shown to produce more firewood as compared to informal green spaces and no difference was determined in growth rates between exotic and indigenous tree species. Bulawayo’s green spaces produce 1.9t/ha/yr of firewood with an ecosystem service value of $340 to $490 /ha/yr. These findings indicate the importance of urban green spaces in Bulawayo. They are multifunctional spaces, providing multiple ecosystem services. The local appreciation of the services provided by urban green spaces differs according to the type of service and location in the city. The value of services provided by green spaces is high, albeit not taken into account in planning decisions.
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Assessing the physical fitness level of children with intellectual disability in the Grahamstown region of the Eastern Cape, and subsequently designing, implementing and evaluating the efficacy of an exercise intervention
- Authors: Parsons, Samantha Lee
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/19723 , vital:22478
- Description: Background: Extensive research has addressed physical fitness as an agent in promoting health and well-being; however, there is little research on this topic for special populations, such as individuals with intellectual disability and even less relating to the South African context. Children with intellectual disability attending special need schools in disadvantaged communities in the Eastern Cape have lacked the opportunity to participate in structured physical education programs. Implementing a solution to this problem was seen to be a challenge, due to the lack of informative research and available data. Aims: The purpose of this research was two-fold; firstly, it aimed to identify the physical fitness levels of the intellectually disabled children in the Grahamstown region of the Eastern Cape province of South Africa; and secondly, it aimed to implement and evaluate the efficacy of an exercise intervention programme on physical fitness in a local school for children with intellectual disability. Phase 1: The descriptive study compared basic anthropometric as well as physical fitness measures from a sample of participants with intellectual disability (n=29) with a comparable sample of typically developed children (n=25). There were 15 males and 14 females in the intellectually disabled sample group, with an average age of 10.69 ± 1.26 years, and the typically developed sample had 13 males and 12 females, with an average age of 10.51 ± 0.74 years. The anthropometric measures included stature and mass; while the health-related physical fitness components included cardiorespiratory endurance, muscular endurance, strength, body composition, and flexibility; and the skill-related physical fitness components were balance, agility, speed, power, coordination and reaction time. The results revealed that the children with intellectual disability were significantly shorter in stature and lighter in mass (p <0.001) compared to their typically developed peers. Muscular endurance and strength, balance, speed, power, coordination and reaction time were poorer among those with intellectual disabilities (p <0.05). Cardiorespiratory endurance, flexibility and agility were similar between groups. Results of the correlation analyses determined significant (p <0.05) relationships between certain health-related and/or skill-related physical fitness components, which were instrumental for selecting measures for Phase 2. The physical fitness components that had the most significant (p <0.05) correlations were speed with five significant correlations, both muscular endurance and balance with six, coordination with seven, and power with eight significant correlations of the eleven physical fitness components. The comparative results, in conjunction with the correlations, determined that the most suitable physical fitness components to be implemented in the exercise intervention for Phase 2 were muscular endurance, balance, and power. Phase 2: The intervention study was a case-control study (intervention group: n = 16; control group: n = 15), whereby the intervention group was exposed to an 8-week multi-modal exercise intervention training muscular endurance, balance and power. Pre-and post-intervention measures were performed using the same eleven physical fitness tests as in Phase 1. The interaction effects and effect sizes were determined and the results showed significant improvements and large effect sizes for the intervention group’s performance of muscular endurance (p=0.026; d=0.617) and power (p<0.000; d=0.999), whereas no significant changes were found for balance. Furthermore, the exercise intervention also impacted the overall level of physical fitness, as significant changes were found for cardiorespiratory endurance (p<0.001; d=0.98), strength (p=0.021; d=0.654) and flexibility (p=0.032; d=586). In conclusion, the exercise intervention was effective for improving the intellectually disabled participants’ muscular endurance and power but not found effective for balance.
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Assessing the potential impact of climate change in the south-eastern Great Escarpment, Southern Africa
- Authors: Bentley, Luke Kinross
- Date: 2017
- Subjects: Mountain plants -- Climatic factors -- Drakensberg Mountains , Mountain biodiversity -- Drakensberg Mountains , Climatic changes -- Drakensberg Mountains , Rain and rainfall -- Drakensberg Mountains , Plant diversity -- Climatic factors -- Drakensberg Mountains
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/4657 , vital:20709
- Description: Rapid, anthropogenic climate change is a contemporary phenomenon which is threatening natural ecosystems. Mountains are globally important, housing high levels of plant and animal biodiversity, as well as being important suppliers of water with 50% of mountainous regions being essential for the provision of water to downstream inhabitants. Owing to their importance, an assessment of the historical, current and potential impacts of climate change on the south-eastern Great Escarpment encompassing South Africa and Lesotho is necessary and is the primary aim of this thesis. In order to assess the historical and current impacts of climate change, historical rainfall records were collected from 78 sites throughout the Eastern Cape. These records were used to determine rainfall trends and trends in the frequency of daily extreme events. Climate change projections predict increasing trends in summer and annual rainfall, and a marginal increase to a slightly decreasing trend in winter rainfall, depending on if statistically downscaled or dynamically downscaled projections are examined. Extreme events are also predicted to increase in frequency. Results showed trends which generally agree with the predictions, except for extreme events for which there was insufficient data to support the projections. This has implications for farmers in the area and validates the downscaled Regional Climate Models (RCMs) to be used for the predictive analysis determining the potential future impacts of climate change on plant species' distributions in the south-eastern Great Escarpment. In order to assess montane plant species to future climate predictions, occurrence records of 46 species were correlated to rainfall and temperature predictor variables and predictions for species richness and beta diversity were made for current and future climates. This predictive analysis used and compared two correlative species distribution modelling methods - one method used one correlating algorithm in a nuanced manner and the other method used five correlating algorithms in an ensemble. A trend of range restriction to higher elevations for the 46 species analysed was as expected from a warming climate. The nuanced, single algorithm modelling method produced less conservative models. The predicted trend of an elevational increase in montane vegetation in this region points to Lesotho and the Drakensberg highlands as being an important refugium for montane plant taxa of the southeastern Great Escarpment. The Maloti Drakensberg Transfrontier Conservation Area hence needs to be expanded and its mandate properly enforced to protect this region adequately.
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Automation of source-artefact classification
- Authors: Sebokolodi, Makhuduga Lerato Lydia
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/4920 , vital:20743
- Description: The high sensitivities of modern radio telescopes will enable the detection of very faint astrophysical sources in the distant Universe. However, these high sensitivities also imply that calibration artefacts, which were below the noise for less sensitive instruments, will emerge above the noise and may limit the dynamic range capabilities of these instruments. Detecting faint emission will require detection thresholds close to the noise and this may cause some of the artefacts to be incorrectly detected as real emission. The current approach is to manually remove the artefacts, or set high detection thresholds in order to avoid them. The former will not be possible given the large quantities of data that these instruments will produce, and the latter results in very shallow and incomplete catalogues. This work uses the negative detection method developed by Serra et al. (2012) to distinguish artefacts from astrophysical emission in radio images. We also present a technique that automates the identification of sources subject to severe direction-dependent (DD) effects and thus allows them to be flagged for DD calibration. The negative detection approach is shown to provide high reliability and high completeness catalogues for simulated data, as well as a JVLA observation of the 3C147 field (Mitra et al., 2015). We also show that our technique correctly identifies sources that require DD calibration for datasets from the KAT-7, LOFAR, JVLA and GMRT instruments.
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Biogeomorphic aspects of lichen colonisation in part of western Dronning Maud Land, Antarctica
- Authors: Ayres, Gabrielle Alexzena
- Date: 2017
- Subjects: Lichen communities -- Queen Maud Land , Lichens -- Ecology -- Queen Maud Land , Polar regions , Ecology -- Polar regions , Antarctica , Ecology -- Antarctica
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/19713 , vital:22477
- Description: Ice-free regions in Antarctica provide natural laboratories for investigating and modelling change in landscapes and ecosystems. The terrestrial ecosystems in western Dronning Maud Land are potentially critical to improve current understanding of polar ecosystems, however, they remain poorly represented and under-protected. Lichen habitats were used to elucidate geomorphic-biological feedbacks that shape the landscape’s topography and biodiversity, which in turn promote environmental heterogeneity. Environmental parameters acting on two landforms were measured to determine the colonisation and growth of lichens in niche habitats. The habitats were identified and characterised, and topographic heterogeneity was found to control lichen colonisation. Micro-topographical niches provide the most stable environments for colonisation, and are preferred habitats. Lichen-habitat interactions were species specific, and closely related to insolation and moisture availability. The bidirectional relationships between rock weathering and lichen colonisation was ascertained. Results showed that lichens are good indicators of landform heterogeneity, but also promote landform heterogeneity. Given the habitat preferences of specific lichen species, they provide proxy to evaluating environmental responses, especially environmental change. The findings of this research are to be used as baseline data for future studies exploring ecosystem development in emerging landforms.
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Browsing as a demographic bottleneck in a semi-arid savanna: the effect of size and age on compensatory responses of Vachellia karroo seedlings after simulated herbivory
- Authors: Perumal, Lavinia
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/4899 , vital:20741
- Description: Savannas are characterised by a continuous grass layer with scattered trees at varying densities. This vegetation structure is determined by several interacting factors, including fire, herbivory, resource competition and atmospheric CO2 concentration. The preservation of savanna biomes is important and a shift towards a woody biome threatens savanna globally. Bush encroachment which describes the shift towards domination of savannas by C3 woody plants, is especially acute in southern Africa. In semi-arid rangelands, encroachment progresses to dense thickets dominated by thorny and unpalatable bushes and trees. There is evidence that bush encroachment is driven by a reduction in fire and browsing events as well as their interaction. Despite browsing having strong effects on African savannas its isolated role in maintaining tree-grass coexistence has not received as much attention as the role of fire. Therefore the overall aim of this study was to examine the effects of browsing on seedlings of a commonly encroaching species, Vachellia karroo. Browsing was hypothesized to be a demographic release bottleneck for bush encroachment in a semiarid (MAP ~550mm) savanna in the Eastern Cape of South Africa, where fire has been historically rare. In a single study I explored the fate of V. karroo seedlings (less than a year old) following browsing in sub canopy and inter canopy microhabitats. Additionally, I explored how the fate of a seedling changed under high and low tree cover. Firstly, I investigated the type, intensity and frequency of herbivory, from both small and large herbivores, which seedlings were subjected to. Results revealed that browsing was severe and frequent with the majority of seedlings browsed more than twice over a 12 month period. Large browsers such as kudu and impala caused high seedling mortality (46%) while smaller browsers such as invertebrates were more effective at suppressing growth. Microhabitat had little impact on seedling survival, but significantly influenced plant compensatory growth. Reduced seedling growth following browsing was observed in the sub-canopy in comparison to seedling growth in full sunlight in the intercanopy, suggesting V.karroo may be shade intolerant. Secondly, the effect of tree cover on browsed seedlings was determined by quantifying browsing frequency and intensity at high and low tree cover. No differences in browsing intensity and frequency were observed between high and low tree cover. However, high tree cover due to bush encroachment limited seedling above ground growth. The aim of the second study was to investigate how V.karroo survival and growth were influenced by its age and size following simulated browsing. I explored this aim through field and greenhouse experiments. I was particularly interested in testing how plant sensitivity to varying defoliation intensities of repeated browsing varied with plant age (known ages of 6, 12, 16 and 30 weeks). There were large differences in mortality between the different age groups. Furthermore, age interacted with repeated browsing and negatively influenced seedling survival and regrowth. Older seedlings (16 and 30 week old) had greater survival and higher browsing frequencies resulted in greater mortality and reduced growth. The threshold age after which seedlings become more tolerant to herbivory occurs at an age of 28 weeks. Seedlings less than six weeks old experiencing intense (100 % defoliation)browsing had a very low probability (33%) of survival following just a single defoliation. Interestingly, all 16 week old seedlings regrew most of their foliage following a moderate (50%) defoliation with some plants overcompensating for leaf loss. The field study revealed two distinct demographic stages based on age and size (seedlings< 9 mm and saplings >9 mm in stem basal diameter (SBD)). Browsing had a strong negative effect on seedlings, resulting in reduced investment in leaf biomass. These findings suggest plant size and age can be used as robust predictors of a plants vulnerability to browsing. An increase in tree cover requires successful transitions of seedlings to saplings (also known as release). The results of this study suggest that in semi-arid savannas, browsing can impact tree cover through imposing a release bottleneck for tree seedlings and to lesser extent saplings. By limiting tree growth plants are kept in a disturbance trap and will therefore be exposed to not only browsers but fire. These findings also have important implications for tree-grass coexistence dynamics, suggesting that specific size and browsing thresholds should be considered in savanna management.
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Calibration and imaging with variable radio sources
- Authors: Mbou Sob, Ulrich Armel
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/37977 , vital:24721
- Description: Calibration of radio interferometric data is one of the most important steps that are required to produce high dynamic range radio maps with high fidelity. However, naive calibration (inaccurate knowledge of the sky and instruments) leads to the formation of calibration artefacts: the generation of spurious sources and the deformations in the structure of extended sources. A particular class of calibration artefacts, called ghost sources, which results from calibration with incomplete sky models has been extensively studied by Grobler et al. (2014, 2016) and Wijnholds et al. (2016). They developed a framework which can be used to predict the fluxes and positions of ghost sources. This work uses the approach initiated by these authors to study the calibration artefacts and ghost sources that are produced when variable sources are not considered in sky models during calibration. This work investigates both long-term and short-term variability and uses the root mean square (rms) and power spectrum as metrics to evaluate the “quality” of the residual visibilities obtained through calibration. We show that the overestimation and underestimation of source flux density during calibration produces similar but symmetrically opposite results. We show that calibration artefacts from sky model errors are not normally distributed. This prevents them from being removed by employing advanced techniques, such as stacking. The power spectrums measured from the residuals with a variable source was significantly higher than those from residuals without a variable source. This implies advanced calibration techniques and sky model completeness will be required for studies such as probing the Epoch of Reoinization, where we seek to detect faint signals below thermal noise.
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Cardiovascular disease risk in Black and Caucasian females: an Eastern Cape sample
- Authors: Remsing, Sandra Claudia
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/40737 , vital:25021
- Description: The purpose of this study was to investigate cardiovascular disease risk in Black and Caucasian urban working females of the Makana region of the Eastern Cape. One- hundred and sixty six age-matched urban-working individuals (Black n = 88; Caucasian n = 78) voluntarily participated in this cross-sectional study. Cardiovascular disease risk was assessed in four categories: 1) obesity, classified as ‘morphological risk’, 2) blood pressure, classified as ‘cardiovascular risk’, 3) diet, physical activity, smoking, and alcohol consumption, classified as ‘lifestyle risk’, and 4) education and income, classified as ‘socioeconomic factors’. Results showed that Black females were significantly (p<0.01) heavier than Caucasian females and categorized as ‘obese’ according to BMI classifications (31.19 ± 8.09 kg.m2 and 25.90 ±4.67 kg.m2, respectively). Black females also presented with significantly (p<0.01) higher waist circumferences and waist-to-stature ratios, further confirming the obesity prevalence in this group. When accounting for those who were on anti-hypertensive mediation, Black females additionally presented with significantly (p<0.05) higher blood pressure, categorizing them as ‘pre-hypertensive’ (MAP = 98 ± 16 mmHg and 85 ± 11 mmHg, respectively). These results therefore placed Black females at increased cardiovascular disease risk compared to Caucasian females. With respect to lifestyle factors, Black females consumed significantly (p<0.05) more kilojoules carbohydrates, and total sugar than Caucasian females, and expended more physical activity MET- minutes per week (2688.86 ± 1486.56 MET-minutes and 1828.27 ± 2238.10 MET- minutes, respectively). However, reduced validity of physical activity data as well as poor dietary recall limited the interpretations of these findings. In addition, despite significant differences between smoking and alcohol consumption between groups, the majority of both Black and Caucasian females reported being non-smokers and consumed alcohol minimally. Thus, these were concluded to be unlikely contributors to cardiovascular disease risk in these samples. Socioeconomic results nevertheless expectedly showed that Black females were significantly (p<0.05) less educated, and subsequently earned lower incomes. It was thus concluded that this may be a likely contributor to higher cardiovascular risk in Black females. Future recommendations include the incorporation of exercise intensity measures as well as objective measures of habitual diet. This is in order to get a clearer understanding of the impact of these lifestyle factors on cardiovascular disease risk.
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Characterisation, antimalarial and biological activities of secondary metabolites from leaves of anonidium mannii
- Authors: Makoni, Pfungwa Gervase
- Date: 2017
- Subjects: Anonidium mannii -- Therapeutic use , Botanical chemistry , Annonaceae -- Therapeutic use , Apocynaceae -- Therapeutic use , Malaria -- Chemotherapy , Tuberculosis -- Chemotherapy , Bacterial diseases -- Chemotherapy , Cancer -- Chemotherapy
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/4797 , vital:20725
- Description: Anonidium mannii is a plant of the Annonaceae genus which is used traditionally in Africa for the treatment of gonorrhoea, malaria, cancer, skin inflammation and dysentery. In this study we will evaluate antimalarial, antifungal, anti - tuberculosis, antibacterial activities and cytotoxicity of different fractions in order to provide a scientific rationale for the traditional use of Anonidium mannii as well as provide possible novel drugs in the treatment of multi drug resistant strains of parasites and bacteria. Extracts from dried leaves were obtained by using solvent extraction and different fractions obtained using column chromatography eluted with solvents of varying polarities to obtain a wide range of metabolites. The antimalarial activity of the various fractions and some pure compounds was evaluated using plasmodium lactate dehydrogenase (pLDH) assay. Cytotoxicity was evaluated using HeLa cells while anti – tuberculosis assay was evaluated using the green fluorescent protein. Antibacterial activity of the extracts was evaluated using micro-dilution assay against Gram-positive (Staphylococcus aureus and Enterococcus faecalis) bacteria and Gram-negative (Escherichia coli and Salmonella typhi) bacteria. Antifungal activity was evaluated against Candida albicans. The antimalarial assays yielded some fractions with promising IC50 values. The selected fractions yielded activities ranging between 0.73 μg/mL and 20.23 μg/mL. The fraction with the best activity was obtained from a hexane/ethyl acetate fraction. AM1C, a cholestane, showed the best activity from the pure metabolites that were screened. AM3C, stigmasterol, a pure compound gave the best antifungal activity with an MIC of 0.063 μg/mL. AM9C another pure compound (sterol) showed the best activity against S. typhi with a value of 0.031 μg/mL. AM2C a pure compound showed an activity of 0.063 μg/mL against E. faecalis. The best cytotoxicity was demonstrated by the fraction C2AM3P with a cell viability of 7.1 ± 0.2 % while AM1C had a viability of 20.2 ± 1.2 %. Several pure metabolites were isolated and four of these were positively identified as steroids. Of these steroids the structure of three novel metabolites from A. mannii was deduced. The study showed promising antibacterial, antifungal, anti – tuberculosis, antimalarial and anticancer activity of A. mannii. These results validate the use of A. manni against cancer, skin inflammation which is caused by fungus, malaria and bacterial diseases.
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Characterization of the distribution of platinum group elements in sulphide ores within the Merensky Reef at Modikwa and Two Rivers Platinum Mines, Eastern Bushveld Complex, South Africa
- Authors: Zilibokwe, Nosibulelo Julie
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/7938 , vital:21326
- Description: The distribution of the platinum group element (PGE), in the Merensky Reef was characterized by, first determining the occurrence of the platinum group minerals (PGM), then by establishing the PGE concentration in the base metal sulphides (BMS) associated with the PGE mineralization in the Merensky Reef from selected borehole intersections, at the Two Rivers (TRP) and Modikwa Platinum Mines in the Eastern Bushveld Complex. A mineral liberation analyser (MLA) was then used to identify the PGM phases; their silicate and base metal associations; and their grain size distribution. Electron microprobe quantitative analysis and mapping were then used to determine the compositional variation of the PGM and the PGE elemental distribution in the BMS, respectively. The study showed that the BMS including pyrrhotite, pentlandite, and chalcopyrite were the principal sulphides, where pyrrhotite was most prominent with minor quantities of pyrite. Orthopyroxene, clinopyroxene and plagioclase were the most abundant primary silicate minerals identified, while secondary silicates identified included talc, serpentine and amphibole. Platinum group minerals showed three distinct groups with respect to the mineralogical association with the PGE; (i) BMS association; (ii) chromite association; and (iii) silicate association. Of the BMS, chalcopyrite showed the most dominant association with the PGMs. All samples from both mines exhibited a wide range of PGMs, including maslovite, braggite, cooperate, laurite and PGE alloys such as ferroplatinum as well as other unidentified platinum and palladium sulphides, arsenides and bismuthides, while gold was present as electrum. The PGMs ranged in size from less than a micron to about 125 microns with an average of 20 microns. The close association of PGM with BMS along the margins of sulphides indicates that the PGMs were derived from the sulphide melt. PGE distribution in the sulphides at Modikwa showed pentlandite contained the highest concentrations of palladium (up to 379 ppm) and chalcopyrite hosting the highest rhodium concentrations (up to 793 ppm). Samples from Two Rivers revealed pentlandite as the principal host to both palladium and rhodium, with concentrations reaching up to 695 and 930 ppm, respectively. Magnetite at both Modikwa and Two Rivers showed significant rhodium content, reaching up to 982 and 930 ppm, respectively. The pyrrhotite compared to other sulphides contained all the elements found in the platinum group (PPGE), namely, platinum, palladium and rhodium, with all the platinum identified found in the pyrrhotite. The concentrations for the iridium group (IPGE) namely, iridium, osmium, and ruthenium were below the detection limit. The PGE mineralization in the stratigraphy varied within each mine. The mineralization revealed top loading in the central sector (Modikwa) and bottom loading in the southern sector (Two Rivers). The sequence of the Merensky Reef at the two sectors of the Eastern Bushveld Complex showed a remarkable similarity in their mineralogy suggesting that these two sectors were formed from the same liquid or formed simultaneously within a single magma chamber; however the PGE distribution within the stratigraphy may have been controlled by the presence of cumulate sulphides.
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Characterization of the Mitochondrial Plasmodium falciparum heat shock protein 70
- Authors: Nyakundi, David Onchong’a
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/44449 , vital:25408 , https://doi.org/10.21504/10962/44448
- Description: Malaria remains a global health problem and accounts for many deaths and illnesses in subSaharan Africa. Plasmodium falciparum, the causative agent of the most fatal form of malaria, expresses a repertoire of heat shock proteins for cytoprotection, survival and pathogenesis. The parasite genome encodes six Hsp70 proteins found in various cell compartments. However, the putative parasite mitochondrial Hsp70 (PfHsp70-3) has not been investigated. The J-proteins, Pfj1 and PFF1415c, were proposed to function as co-chaperones of PfHsp70-3. The biochemical characterization of PfHsp70-3 was initially complicated by the fact that the protein was insoluble when expressed in E. coli cells. Various approaches to solubilize it resulted in inactive protein. A general characteristic of eukaryotic mitochondrial Hsp70s is their insolubility and their reliance on an Hsp70 escort protein (Hep) for solubility and ultimate functions. In this study, a putative Hep protein was identified in the genome of P. falciparum that is referred to as PfHep1. Coexpression of PfHep1 with PfHsp70-3 resulted in soluble and biochemically active PfHsp70-3. Size exclusion chromatography was employed to separate PfHsp70-3 from PfHep1 after coexpression. PfHep1 suppressed thermally induced aggregation of PfHsp70-3 but not the aggregation of malate dehydrogenase or citrate synthase, thus showing specificity for PfHsp70-3. Zinc ions were also found to be essential for maintaining the functions of PfHep1, as EDTA chelation abrogated its abilities to suppress the aggregation of PfHsp70-3. Furthermore, PfHep1 did not stimulate the basal ATPase or increase refoldase activities of PfHsp70-3 hence displaying no co-chaperone roles. The full-length putative mitochondrial type I J protein, Pfj1, could not be produced in E.coli but a truncated protein containing the J-domain was produced which stimulated both the ATPase and refoldase activities of PfHsp70-3. Further, this study demonstrated that both PfHep1 and PfHsp70-3 localized to the mitochondrion in the erythrocytic stage of P. falciparum development thus confirming in silico predictions of their localization. Besides, PfHsp70-3 was expressed during all stages of the intraerythrocytic cycle of parasite development and was heat inducible. Generally, the data obtained in this study will enhance the existing knowledge on the biology of the parasite mitochondrial chaperone functions and open the possible avenue of drug targeting considering the specificity of PfHsp70- 3 and PfHep1 partnerships.
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Chemical composition of leaf essential oils of Lantana camara varieties in South Africa and their effect on the behavioural preference of Falconia intermedia
- Authors: Ngxande-Koza, Samella W
- Date: 2017
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/4877 , vital:20739
- Description: Lantana camara L. (Verbenaceae) is one the most problematic invaders in South Africa invading forest edges, sand dunes, and shorelines by forming impenetrable thickets. Lantana camara invasions degrade natural biodiversity, reduce the value of land and consequently it has been a target for biological control, over the last 50 years in South Africa. Studies that have reported on chemical profile of Lantana camara have been conducted around the world but not in South Africa. Hence, the first aim of the current study was to identify the chemical baseline of L. camara varieties in the Eastern Cape, South Africa. Recent studies have shown that feeding by one of the agents released against L. camara, Falconia intermedia (Distant) (Hemiptera: Miridae), induces anti-herbivory response through increased leaf toughness and trichome density. A preliminary study conducted also reported the production of volatile chemicals by one variety, Whitney Farm, due to feeding by the mirids. Therefore, the second aim was to determine the induced changes in chemical compounds of L. camara varieties after feeding by F. intermedia. A third aim was to determine the effect these chemical compounds have on the behaviour of F. intermedia. To identify the chemical baseline of L. camara varieties, the essential oils of four L. camara varieties (East London, Port Alfred, Whitney Farm and Heather Glen) were analysed using gas chromatography mass spectrometry (GC-MS) and that resulted to the identification of 163 constitutive and 75 induced chemicals across the varieties tested. Lantana camara varieties showed different chemical classes but were highly dominated by terpenes. A great variation in the number of constitutive chemical compounds was found in all the varieties. There were 56 constitutive chemical compounds in the Whitney Farm variety, 41 in the East London variety, 36 in the Heather Glen variety and 30 in the Port Alfred variety. The Whitney Farm variety had the highest number (22) of unique constitutive chemicals identified when compared with other varieties. This indicates the chemical distinctiveness of the Whitney Farm variety from the other varieties. In the varieties tested, there were common chemical compounds identified in constitutive and induced (discussed below) states of the plants such as caryophyllene, hexane, naphthalene, copaene and a-caryophyllene. Besides naphthalene, the majority of chemical compounds in South African L. camara varieties were similar to compounds that have been identified across the world, suggesting that they are closely related. The expression of naphthalene in these varieties may be due to changes in the chemicals expressed over evolutionary time as predicted by the Novel Weapons Hypothesis. Amongst the varieties, a great variation in chemical compounds and their concentrations was shown in the induced states of the plants. The concentration of constitutive caryophyllene ranged from (3.13 - 15.7) %, to (4.02 - 11.10) % after feeding. The concentration of constitutive hexane ranged from (6.13 - 71.19) %, to (33.3 - 75.8) % after feeding. The concentration of constitutive naphthalene ranged from (0.21 - 4.79) %, to (0.92 - 2.11) % after feeding. The concentration of constitutive copaene ranged from (0.57 - 1.57) %, to (1.20 - 2.72) %. Lastly, the concentration of constitutive a-caryophyllene ranged from (1.18 - 9.03) %, to (0.78 - 5.48) % after feeding. The changes in chemical concentrations in lantana varieties indicated that feeding by the mirid on L. camara varieties causes an induction by either reducing or increasing the chemical concentrations. To determine the effect of the identified compounds on the behaviour of F. intermedia adults, olfactometer bioassays were conducted using a Y-tube technique. A significantly higher proportion of F. intermedia were attracted to undamaged leaves over damaged leaves and purified air. Undamaged leaves attracted 52 % of F. intermedia from the East London variety, 62.5 % from the Port Alfred variety, 56 % from the Whitney Farm variety, 58 % from the Lyndhurst variety and 54.5 % from the Heather Glen variety in dual choice trials versus damaged leaves. Furthermore, a significantly higher proportion of F. intermedia were attracted to damaged leaves over purified air. Damaged leaves attracted 67 % of F. intermedia from the East London variety, 67 % from the Port Alfred variety, 65.9 % from the Whitney Farm variety, 65.3 % from the Heather Glen variety and 64.5 % from the Lyndhurst variety. Olfactometer bioassays were also conducted using purified standard compounds of four chemical compounds identified from essential oils, hexane was used as a positive control as it is reported to be an insect attractant in literature. Hexane was highly attractive to the mirids compared to three standard compounds caryophyllene, caryophyllene oxide and naphthalene at the rate of 80 %, 73 % and 80 %, respectively. The standard compounds tested against F. intermedia are major compounds contained by L. camara varieties and they have proven to have a repellent effect. This may indicate that after feeding by F. intermedia, the major compounds expressed by the plant varieties repel F. intermedia contributing to the invasiveness of this weed. The increased expression of hexane and caryophyllene after feeding may also indicate increased attraction to some insects, opening up the potential for third trophic level interactions in varieties where this is the case. This is the first study on the chemical composition of essential oils of L. camara in South Africa. Therefore, we recommend that where appropriate chemical profile studies of the invasive alien plants should be considered during host specificity testing, and the vital role of chemical compounds on agent-weed interactions must be taken into consideration with other factors before and after the biological control agents are released.
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Comparative localization studies of P.falciparum ADP-ribosylation factor proteins in P.falciparum parasites and hela cells using GFP tagged constructs
- Authors: Swart, Tarryn
- Date: 2017
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3537 , vital:20519
- Description: Expected release date-December 2018
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Density-dependent effects on body size, Philopatry, and dispersal in the Damaraland mole-rat (Fukomys damarensis)
- Authors: Finn, Kyle T
- Date: 2017
- Subjects: Fukomys damarensis , Fukomys damarensis -- Reproduction , Fukomys damarensis -- Growth , Rodents -- Reproduction -- South Africa -- Northern Cape , Rodents -- Growth -- South Africa -- Northern Cape , Rodent populations -- South Africa -- Northern Cape
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/50495 , vital:25993
- Description: Population density may exert changes in a variety of behavioural and physiological characters in animals. However, the effects of density-dependence and dispersal are poorly studied in subterranean rodents due to the difficulties involved in observing such effects in wild populations. Using the cooperative breeding Damaraland mole-rat (Fukomys damarensis) as a model species, the effects of population density on body size, growth rates, group size, recruitment, philopatry and dispersal were investigated at two sites (one with low density and one with high density) in the Northern Cape of South Africa. Group size, litter size and the probability of recapture were independent of population density. However, individual body size, recruitment, dispersal rate and dispersal distance were density-dependent. Individuals were significantly larger, juveniles exhibited a significantly higher growth rate, and juvenile recruitment was significantly greater when population density was low. At higher densities, significantly more individuals were lost between capture events which may be indicative of increased rates of dispersal. Mean dispersal distances in mole-rats were reduced at higher densities and increased at lower densities. While both sexes dispersed equally, males were significantly more likely to join an established colony and females created new burrow systems. In addition, four times as many single females were found when population density was low. The apparent differences in the study populations may be attributed to variable annual rainfall or food availability. The greater annual rainfall at the high-density site may provide better habitat conditions and therefore result in an increase in the population density and an increased dispersal rate due to the relaxed ecological constraints such as reduced energetic costs to burrowing. However, the larger body size found at the low-density site may indicate that the available food at that location is of better quality. This study revealed that mole-rats were able to disperse over 1km and therefore a much larger study area would be required in capture-mark-recapture studies to ensure the recapture of the majority of dispersers. Lastly, a surprising find of this study was that females may survive a solitary existence for over two years while awaiting the arrival of a mate.
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Development and validation of an In Vitro Release Test (IVRT) to investigate the release of miconazole nitrate from topical cream formulations
- Authors: Purazi, Potiwa
- Date: 2017
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/65223 , vital:28711
- Description: Expected release date-May 2019
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Diurnal and nocturnal activity patterns and habitat use of Algoa Bay’s rocky reef fish community
- Authors: Juby, Roxanne
- Date: 2017
- Subjects: Reef fishes -- Effect of light on , Reef fishes -- South Africa , Underwater videography in wildlife monitoring -- South Africa -- Tsitsikamma
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/44827 , vital:25445
- Description: Distinct day-night changes in ambient light are recognised as an important driver of animal activity patterns, with predictable changes to the structure and composition of animal communities between day and night. While day-night variation in the structure of animal communities has been well researched for terrestrial organisms and shallow marine fish communities around the world, there has been limited research of this type conducted on South Africa’s rocky reef fish communities. Consequently, we have a poor understanding of how nocturnal reef fish communities are structured and the day-night activity patterns of species inhabiting both shallow (10-30m) and deep-aphotic (55-100m) reefs. This research was conducted at two warm-temperate South African rocky reefs situated in Algoa Bay. The importance of natural ambient light in shaping the distribution of reef fish communities at shallow and deep-aphotic reef sites was demonstrated using baited remote underwater stereo-video systems (stereo-BRUVs). Distinct day and night fish communities were sampled at shallow and deep-aphotic reef sites. These differences were driven by significant changes in species richness (p < 0.001), species abundance (p < 0.001) and community composition (p < 0.001). These shifts appeared to be driven by day-night activity patterns that were the result of increased detectability of certain species at either day or night. The majority of species belonging to the family Sparidae showed evidence of strict diurnal activity, with their activity being further restricted to shallow reefs. These species showed evidence that they may enter micro-habitats within the reef at night. Similar activity patterns were shown for other top predatory teleost species and low level consumers, with substantial reductions in abundances, or no recordings at night throughout this study. Shallow reefs at day harboured the most diverse fish community. It is therefore hypothesised that this habitat was associated with conditions that offered improved access to resources for many visual species. In addition, the diverse community inhabiting shallow reefs at day is associated with a high risk of negative interspecies interactions, such as competition and predation. It is hypothesised that the biotic conditions associated with shallow reefs at day drove three movement patterns identified in this study; Pagellus bellottii natalensis showed evidence of movement onto shallow reefs at night from adjacent sandy flats, while Pterogymnus laniarius and Squalus sp. 1 showed evidence of movement onto shallow reefs at night from the deep- aphotic reefs that remain dark throughout the diel cycle. It is further hypothesised that other species which showed evidence for nocturnal activity, i.e. Galeichthys ater, Eptatretus hexatrema and Haploblepharus edwardsii, may enter sheltered micro-habitats within the reef during day light hours. These findings have highlighted the complex patterns that have evolved within marine fish to allow multiple species to coexist and exploit productive reef ecosystems by partitioning resource use and activity patterns at day or night, between depth zones and habitat types.
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Early stage ichthyofauna from shallow water habitats of the Angola-Benguela frontal zone
- Authors: Farthing, Matthew William
- Date: 2017
- Subjects: Fishes -- Larvae -- South Africa -- Atlantic coast , Fishes -- Larvae -- Angola -- Atlantic coast , Striped mullet -- Angola -- Atlantic coast
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/50442 , vital:25988
- Description: Early stage fishes (larvae and early juveniles) were collected from an array of shallow water (±1.5m) habitats on the warm-temperate southern Angolan coastline between June 2014 and June 2015. This study, the first assessment of the early stages of coastal fishes in Angola, provides important new understanding of non-estuarine shallow water nursery habitat use by coastal fishes from the region. In total, 51 species from 18 teleost families were observed. The exposed surf zone was dominated by postflexion larvae, while the moderately exposed beach and sheltered bay were dominated by early juveniles. Both fish density and diversity peaked in the wet season (Feb – Apr 2015) for all habitats, attributed to the influx of summer spawning species. Diplodus sargus dominated catches from the exposed surf zone, and the timing of observations supports the growing consensus that sparid spawning is dictated by temperature, not season. The similitude of the observed species to those observed in warm temperate South Africa highlights the historical connection of the warm-temperate study area with warm-temperate South Africa, prior to the formation of the Benguela Current as a vicariant barrier. The classification of the study assemblage into established estuarine utilization categories showed that the surf zone hosted more exclusively marine species than comparable surf zones in South Africa, attributed to the absence of estuaries in southern Angola. However, the observation of the marine estuarine dependent Mugil cephalus in this study area devoid of estuaries suggests that estuarine dependency may be regionally specific for some taxa. It appears that the warm, sheltered, nutrient rich waters of Tombua Bay provide typically estuarine associated taxa with a suitable alternative, non-estuarine nursery habitat. This study provides evidence that the importance of estuaries as critical nursery habitats has been overemphasized for some warm-temperate coastal fishes. However, the absence of other marine estuarine dependent species from the study area suggests that some warm-temperate taxa do intrinsically rely on estuarine function for survival.
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