Showing items 841 - 860 of 1292

Your selections:

Reactions towards the synthesis of the uncommon P57 cymarose moiety

  • Authors: Mahanjana, Lungelwa
  • Date: 2013
  • Subjects: Chemistry, Organic , Organic compounds -- Synthesis
  • Language: English
  • Type: Thesis , Masters , MTech
  • Identifier: http://hdl.handle.net/10948/6711 , vital:21136
  • Description: The work described in this study aims to investigate methods that will improve a lengthy synthetic pathway in the synthesis of the P57 cymarose moiety, and to examine the conformational structure of certain glycosides in order to shed light on the problematic stereochemical issues surrounding the formation of the cymarose glycosyl donor. The cymarose moiety forms part of the trisaccharide derivative present in P57, an appetite suppressant molecule. Modification of reaction steps in the conversion of the stereochemistry at C-3 of a previously reported synthesis of the P57 cymarose moiety was carried out. The first step was the selective oxidation of D-glucal using Pd/C in the presence of acetonitrile. These reaction conditions are more appropriate for the oxidation step to avoid decomposition of the formed molecules. Successive protection of the free OH groups was followed by NaBH4 reduction under stereo-controlled conditions, influenced by CeCl3•7H2O. However, the reduced product could not be isolated from the starting material and this led to ambiguous results when attempting to confirm whether the conversion of the stereochemistry at C-3 had occurred or not. The effect of reaction conditions, such as change in reaction temperature, during the preparation of the cymarose glycosyl donor was studied in order to find suitable reaction conditions to produce α,β-allo derivatives with high stereoselectivity. Compared to the reported synthetic method, this set-up gave improved yields with, unfortunately, similar or slightly lower selectivity to the formation of α-altro:α,β-allo derivative. Examination of the conformational structure of the allal derivative, in order to understand the mechanism at work during the placement of the directing group at C-2, was carried out using molecular modelling. The mechanistic implications of this very short study are discussed and it provides some insights into the likely pathway of the iodination reaction and its selectivity in particular, to the D-allose system.
  • Full Text:
  • Date Issued: 2013

Relating vegetation condition to grazing management systems in the central Keiskamma catchment, Eastern Cape Province, South Africa

  • Authors: Ndou, Naledzani Nyahman
  • Date: 2013
  • Subjects: Grazing -- Management , Grazing -- South Africa -- Management , Vegetation and climate -- South Africa -- Eastern Cape
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10673 , http://hdl.handle.net/10948/d1020645
  • Description: Vegetation degradation in South Africa has been identified as a serious environmental problem, especially impacting communal areas. This study investigated the spatial distribution of vegetative condition, along with related changes, deterioration and trends, across the communal villages of the central Keiskamma catchment, Eastern Cape Province. The principal hypothesis of this study was that differences in grazing management strategies may explain the variations in vegetation condition within these communal areas. This investigation assessed the status and condition of vegetation in relation to local institutional grazing management systems, in association with factoring in relevant topographical and physical elements. Topographic homogeneity of the study area was tested by extracting topographic parameters from a DEM and performing a Chi squared test. Remote sensing techniques were used to analyse the spatial and temporal variations in vegetation condition between the villages. Landsat TM images, from 1984 and 1999, in conjunction with SPOT imagery of 2011, were used to assess the spatial trends in vegetation. Land use and cover maps were generated, comprising five categories of land cover, viz. intact vegetation; transformed vegetation; degraded vegetation; bare surfaces; and water. The classification of the images was achieved using the supervised object-oriented classification techniques, which aggregates pixels of each class into homogeneous objects. Information regarding existence and functionality of local institutional structures was obtained through structured interview method. Vegetation condition was correlated to grazing management systems, with the logistic regression confirming a significant relationship between vegetation condition and grazing management systems. Analysis of vegetation condition trends revealed a decline in pristine vegetation with an increase in degraded vegetation and exposed soil throughout the villages. However, it was observed that the decrease in pristine vegetation, with the associated increase in degraded vegetation and soil, do not occur evenly among the villages of the central Keiskamma catchment; the communal areas surrounding certain villages exhibited severe degradation of soil and vegetation, while other villages demonstrated less or minimal deterioration in their environs. The topographic homogeneity of the study locale lent credence to the theory that the uneven distribution of vegetation conditions between the villages is not controlled by topographic factors. Analysis of the data, collected through interviews, revealed differences in the functionality of institutional structures between villages. A statistically significant correlation between the vegetative condition and implementation of grazing management systems, supports the postulated concept that the variances in vegetation condition of the central Keiskamma catchment reflect the efficacy or inefficiency of the settlements‘ grazing management systems. Through gathering, analysing and assessing all the data, a conclusion was drawn, which advances that the primary requirement for remedial action in reversing the current decline in vegetation condition is strengthening the local institutional management regimes throughout all villages under study.
  • Full Text:
  • Date Issued: 2013

Revision of Aloiampelos Klopper & Gideon F.Sm. (xanthorrhoeaceae subfam. asphodeloideae)

  • Authors: Ellis, Kristen
  • Date: 2013
  • Subjects: Xanthorrhoeaceae , Asparagales
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10642 , http://hdl.handle.net/10948/d1020955
  • Description: The genus Aloiampelos Klopper & Gideon F.Sm., previously treated as Aloe L. Ser. Macrifoliae (Sect. Prolongatae), comprises seven species with barely succulent leaves that are popularly known as rambling, scrambling or climbing aloes, because they make use of surrounding trees and shrubs for support. The rambling aloes are centered in the Eastern Cape but some species have disjunct distributions in the Western Cape and KwaZulu-Natal. Many are widely used in gardens and landscaping. With their rambling habit and weakly succulent leaves, the genus is widely considered to be an old lineage among alooid genera. Species concepts within the genus remain contentious, with disagreement amongst taxonomists with respect to the recognition of some taxa at the rank of variety. Morphology, historical taxonomy, palynology and phylogenetics of the genus were investigated. The occasional presence of minute cilia on the sheathing leaf bases and distinct lineation of the leaf sheaths of Aloiampelos tenuior var. decidua and Aloiampelos tenuior var. rubriflora were the most important outcomes of the morphological study. The pollen grains of all species studied were very similar in grain shape and exine surface pattern, with only minor differences in grain size. Ordination analyses showed that grain length and muri length were useful at the infraspecific level, with Aloiampelos tenuior “orange” separating clearly from the other varieties. Pollen morphology was therefore not informative as a taxonomic character at species level when used in isolation, but may be useful when used in conjunction with other characteristics. Preliminary analyses of two plastid barcoding regions (matK and rbcL) and nuclear ITS have confirmed that Aloiampelos is monophyletic. These barcoding markers were not informative in assessing the species boundaries among the closely related taxa in the genus and morphological assessments were therefore used to elucidate relationships at the species rank. A key is given for the genus, integrating the findings of the study.
  • Full Text:
  • Date Issued: 2013

Rhenium (I), (III) and (V) complexes with potentially multidentate N, O-Donor ligands

  • Authors: Habarurema, Gratien
  • Date: 2013
  • Subjects: Rhenium , Ligands
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10441 , http://hdl.handle.net/10948/d1020952
  • Description: This study investigates the coordination modes of potential multidentate N,O-donor Schiff base ligands to the [ReVO]3+ and fac-[ReI(CO)3]+ cores. The project is aimed at the synthesis of tridentate, tetradentate and pentadentate Schiff bases ligands derived from the condensation reactions of benzaldehyde with different primary amines. The structures of these Schiff bases and their complexes were confirmed by using physical characterization methods, namely melting points, UV-Visible, UV-emission, 1H NMR and IR spectroscopy, X-ray diffractometry and elemental analysis. To further understand the coordination chemistry of rhenium, the prepared diiminediphenol N2O2-donor Schiff base ligand N N′-o-phenylene-bis(salicylaldimine) (H2salphen) was reacted with trans-[ReOCl3(PPh3)2] to yield cis-[ReCl2(ophsal)(PPh3)], whereas its reaction with trans-[ReOBr3(PPh3)2] resulted in the formation of the cis-[ReBr2(aphsal)(PPh3)].2CH3CN complex. In the above complexes the H2salphen ligand was cleaved leading to the coordinated tridentate ophsal NO2- and aphsal N2O-donor ligands. The reaction of H3aphsal with trans-[ReOBr3(PPh3)2] in toluene led to an unexpected compound, trans- [{[ReBr(aphsal)(PPh3)2]Br}{[ReBr(aphsal)(PPh3)2](ReO4)}] with an imido [ReNR]3+core. The ligand aphsal was coordinated tridentately with the doubly deprotonated amino nitrogen leading to Re(V)-imido complexes. The reaction of 2-((Z)-(2-aminoethylimino)methyl)phenol (H3amphol) with [Re(CO)5Cl] led to the rhenium(I) product fac-[Re(CO)3(H3amphol)] with H3amphol coordinated as a monoanionic tridentate chelate through its phenolate oxygen and amino nitrogen atoms. The X-ray crystal structures showed that all complexes display a distorted octahedral geometry around the central rhenium atom. The reaction of 2,6-bis(2-hydroxyphenylimino)pyridine (H2hpp) with cis-[ReO2I(PPh3)2] resulted in the reduced Re(III) product trans-[Re(hpp)(PPh3)2]I, while trans-[Re(hpp)(PPh3)2](ReO4) was isolated from its reaction with trans-[ReOCl3(PPh3)2]. The H2hpp ligand acts as a pentadentate N3O2-donor ligand where the two phenolic protons undergo deprotonation and its three nitrogens act as neutral donor atoms. Both compounds resulted from a disproportionation reaction characterized by the produced perrhenate counter-ion. The complex fac-[Re(CO)3(H2hpp)Cl] was prepared from [Re(CO)5Cl] and H2hpp in toluene. The H2hpp ligand acted as a neutral bidentate N,N-donor chelate. The metal is coordinated to three carbonyl donors in a facial orientation, two neutral nitrogen atoms and a chloride ligand. The reactions of the potentially tetradentate ligand N,N'-ethylenebis(salicylideneimine) (H2salen) with different rhenium(V) precursors resulted in the formation of two dimeric oxorhenium (V) compounds. In the reaction of H2salen with trans-[ReOCl3(PPh3)2] in ethanol, the highly unusual distorted dimeric complex (μ-salen)[ReOCl2(PPh3)]2 was isolated, in which salen2- is coordinated as a tetradentate to two oxorhenium(V) centres, and salen2- is present as a bidentate monoanionic ligand on each rhenium center. The reaction of cis- [ReO2I(PPh3)2] with H2salen led to the formation of the neutral dimeric oxorhenium(V) complex (μ-O)[ReO(salen)]2 in which the tetradentate chelate salen acts as a tetradentate dianionic ligand through its phenolate oxygens and nitrogen atoms of the azomethine groups. In its reaction with H2hmp the compound (μ-O)[ReO(hmp)]2 was isolated. In this product the pentadentate ligand H2hmp coordinated as tetradentate via its phenolic oxygen and nitrogen atoms. The reaction of the potentially tetradentate N1,N2-bis(aminobenzylidene)-1,2-ethylenediamine (H2amben) with trans-[ReOCl3(PPh3)2] led to the formation of the monocationic square-pyramidal complex salt [ReO(amben)](ReO4.
  • Full Text:
  • Date Issued: 2013

Sedimentology and sequence stratigraphy of the Congo and Kalahari basins of South Central Africa and their evolution during the formation and break-up of West Gondwana

  • Authors: Linol, Bastien
  • Date: 2013
  • Subjects: Sedimentary basins -- Africa , Sedimentology
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: vital:10655 , http://hdl.handle.net/10948/d1012148 , Sedimentary basins -- Africa , Sedimentology
  • Description: The high elevated (ca. 1100 m) continental Kalahari Basin (KB) of southern Africa and the linked lower lying (ca. 400 m) Congo Basin (CB) of central Africa preserve in their interiors extensive sedimentary rock sequences and sediments that represent a unique record of the Phanerozoic geodynamic and climatic evolution of sub-Saharan Africa. In this thesis, field observations and new borehole data from the Democratic Republic of Congo (DRC) and Botswana are integrated with new paleontology and geochronology to present a substantially revised stratigraphy for the CB, and south-central Africa in general. This work also introduces a new multiphase model for the subsidence and uplift history of the CB, and improves correlations with the Cape-Karoo Basin (CKB) of South Africa and the Paraná Basin (PB) of south-east Brazil. Four deep boreholes, each between 2 and 4.5 km deep, drilled in the centre of the CB in the 1950’s and 1970’s are re-examined together with the colonial literature (in French) and available seismic data. This stratigraphic and basin analysis is complemented with new U-Pb dates of detrital zircons from core-samples of two of the boreholes (Samba and Dekese), as well as from samples collected during field work in the Kwango region of the south-west DRC. This work, for the first time, constrains the maximum ages and source provenances of the successions in the CB. Following the Pan African orogens (ca. 650-530 Ma), extensive sequences of red beds were deposited by regional paleocurrents to the south. These are now best preserved (1 km thick) along the West Congo, Oubanguides, and Lufilian Belts surrounding the CB. Overlying a hiatus that represents most of the early-Paleozoic, is a 1 to 3 km thick succession of easterly derived glacial, and then continental sequences of the Karoo Supergroup. This succession records the first main episode of subsidence [10-15 m/Ma], interrupted by a phase of uplift that is likely related to far-field intracontinental deformation within Gondwana supercontinent during the Variscan and Cape Fold orogenies (ca. 250-330 Ma) at its peripheries. Detrital zircons from the lower Karoo diamictites are dated at 1.85-2.05 Ga and 1.37- 1.42 Ga, and thus sourced from Paleoproterozoic (Eburnean) and mid-Mesoproterozoic (Kibaran type-I) basement rocks in Uganda and Tanzania. Zircons from all the other successions in the CB date predominantly at 950-1050 Ma and 500-800 Ma. These are derived from sediment recycling of late-Mesoproterozoic (Kibaran type-II) and late- Neoproterozoic (Pan African) sources in the Central African Republic (CAR) and Chad. A distinct unconformity across the Karoo Supergroup in the CB is overlain by 500- 1000 m Jurassic-Cretaceous sequences, here named the Congo Supergroup. During initial rapid subsidence [10-50 m/Ma], late-Jurassic (Kimmeridgian) shallow marine to continental sedimentation attests to a short transgression of proto-Indian Ocean waters into the northern CB (at 160 m above present day sea-level), succeeded by widespread deposition of aeolian dunes that extend from the southern CB to the PB in South America. The youngest zircons from these aeolian sediments in the CB date at 190 Ma and 240-290 Ma, and most likely indicate the influence of extensive silicic volcanic ash derived from the proto-Andes along the south-western margin of Gondwana. Two superimposed mid-Cretaceous (Albian-Cenomanian) lacustrine sequences in the central CB record a succeeding, slower [10-15 m/Ma], phase of basin subsidence during the opening of the South Atlantic (ca. 85-135 Ma). These Cretaceous sequences are in turn truncated by another regional peneplanation surface covered by Cenozoic (Eocene) silcretized sands and alluviums of the Kalahari Group, only 50-250 m thick in the centre of the CB. Southward, on top of the Kalahari Plateau in the central desert region of north-west Botswana, new boreholes intercepted laterally equivalent condensed lacustrine carbonates and calcretes (20-50 m thick) covered by sands. These terrestrial sequences are key archives of late-Mesozoic – Cenozoic paleo-climate changes, yet they remain stratigraphically unresolved. This new analysis of the Phanerozoic continental basins of south-central Africa and their equivalents in South America, opens a fresh continental-scale window into how West Gondwana break-up and concomitant epeirogenic uplifts of Kalahari (>2 km) and Congo (>200 m) are linked to interactions between the lithosphere and mantle geodynamics, and how these processes likely affected global climate changes.
  • Full Text:
  • Date Issued: 2013

Single-end reflectometric measurements of polarization-mode dispersion in single-mode optical fibres

  • Authors: Fosuhene, Samuel Kofi
  • Date: 2013
  • Subjects: Fiber optics , Polarization (Light) , Optical measurements
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: http://hdl.handle.net/10948/6280 , vital:21069
  • Description: In this thesis two novel single-end methods are applied to measure and characterize polarization mode dispersion in single mode optical fibres. Polarization mode dispersion (PMD) is an important factor negatively affecting the successful implementation of high speed long haul optical fibre networks operating at bit rates of 10Gb/s and above. PMD measurements are thus important for quality control during manufacturing and cabling processes. It is also useful for network operators planning to upgrade bitrates in existing networks to 10Gb/s and beyond. In an optical fibre link, sections with particularly high PMD may act to increase the entire PMD of the link. Identifying and replacing such sections can greatly reduce the PMD of the link. PMD measurements can be forward or single-end. In forward measurements, both ends of the fibre are used for input and detection. In single-end configuration, only one end of the fibre is used. For this reason, single-end measurements are more practical for the field where fibre ends are situated several kilometres apart. Single-end techniques can be implemented with a continuous wave for non-local PMD measurements (by Fresnel reflection). If a pulsed wave is used, local measurements can be achieved (by total power due to Rayleigh scattering). Two single-end schemes, one based on Fresnel reflection and the other due to Rayleigh scattering have been applied to measure non-local and local PMD of standard single mode optical fibres. For the non-local PMD measurements, the general interferometric technique (GINTY) was modified to operate in a round-trip configuration. In this configuration, the fibre was treated as a concatenation of two identical fibre segments. Three different sets of fibres were investigated, each set representing a particular mode coupling regime. For polarization maintaining fibres, (PMFs), with no mode coupling, a factor of two was found between forward and single-end measurements. For long single mode fibres in the long length regime, the factor was 1.4. For a combination of PMF and single mode fibres, a factor of 1.6 was obtained. The method which is accurate, repeatable, low cost and robust is very suitable for field applications. The second method is the polarization optical time domain reflectometric (P-OTDR) technique. This technique performs local birefringence measurements by measuring the evolution of the states of polarization (SOP). The birefringence information from such measurements was extracted and analysed to characterise four different fibres. Beat lengths and correlation lengths extracted from the P-OTDR were used to calculate the differential group delay (DGD) of the fibres. Next an expression for the root-mean-square differential group delay was derived and applied to the birefringence measurements to calculate the DGDs at a single wavelength. This method which operates at a single wavelength has a huge advantage. Firstly it is able to measure completely all the fibre characteristic parameters. Secondly it can measure mean DGD, root mean square DGD and instantaneous DGD. A plot of instantaneous DGD vs. length enables one to identify and eliminate sections with particularly high DGD. Finally since the P-OTDR system operates with a single wavelength, real time monitoring of PMD is possible via multiplexing. The results obtained are repeatable, accurate and are in good agreement with the standard Jones Matrix Eigenanalysis (JME) technique.
  • Full Text:
  • Date Issued: 2013

Social network analysis of stakeholders in the Duiwenhoks Water Catchment

  • Authors: Whyte, Michelle
  • Date: 2013
  • Subjects: Conservation of natural resources -- South Africa , Conservation plants
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10756 , http://hdl.handle.net/10948/d1020995
  • Description: Social-ecological systems are facing complex social, political, economic and environmental problems beyond the capacity of one group of stakeholders or organization to solve in isolation. Ecosystem degradation causes major environmental and economic concern, due to the loss of ecosystem services which river and wetland ecosystems provide. Stakeholder communities who depend on natural resources need to identify the social processes which are underlying causes to unsuccessful natural resource management and thus environmental degradation. The study is primarily aimed at identifying and understanding the structural and functional properties of the stakeholder network in the Duiwenhoks River catchment in the Western Cape, South Africa. Through analyzing the social network properties the study identifies and describes the main stakeholders involved with natural resource management in the Duiwenhoks water catchment area. How the individual actors from the diverse stakeholder groups are connected through communication ties were assessed. Furthermore, issues and factors which limit the effectiveness of the social network were identified. The main factors include a lack of communication and collaboration between key local resource users and governance officials caused by conflicting perspectives regarding resource management and societal conflicts caused by asymmetries in power distribution favoring government institutions. The lack of collaboration between stakeholders was identified as a contributing factor that links to the resource degradation experienced in the catchment. Ultimately means of overcoming the limitations to effective social networking, in order to manage the challenges related to natural resource management were identified. Management recommendations include the development of bridging ties and collaboration between diverse stakeholders, whilst facilitating participatory processes aimed at participatory problem solving and adaptive co-management of natural resources. Government institutions were identified as being dominant stakeholders in the network and should be mobilized to perform a stronger bridging role to connect disconnected actors. The findings of the study may inform future efforts of researchers and facilitators to implement strategies which promote social networking, social learning and ultimately adaptive co-management in the study area or other similar social-ecological systems. Ultimately, collaboration can be achieved between the diverse stakeholders to successfully improve ecosystem management and resilience in the Duiwenhoks water catchment.
  • Full Text:
  • Date Issued: 2013

Statistical analysis of electricity demand profiles

  • Authors: Mangisa, Siphumlile
  • Date: 2013
  • Subjects: Electric power consumption -- Forecasting , Energy consumption , Electric power consumption
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10572 , http://hdl.handle.net/10948/d1011548 , Electric power consumption -- Forecasting , Energy consumption , Electric power consumption
  • Description: An electricity demand profile is a graph showing the amount of electricity used by customers over a unit of time. It shows the variation in electricity demand versus time. In the demand profiles, the shape of the graph is of utmost importance. The variations in demand profiles are caused by many factors, such as economic and en- vironmental factors. These variations may also be due to changes in the electricity use behaviours of electricity users. This study seeks to model daily profiles of energy demand in South Africa with a model which is a composition of two de Moivre type models. The model has seven parameters, each with a natural interpretation (one parameter representing minimum demand in a day, two parameters representing the time of morning and afternoon peaks, two parameters representing the shape of each peak, and two parameters representing the total energy per peak). With the help of this model, we trace change in the demand profile over a number of years. The proposed model will be helpful for short to long term electricity demand forecasting.
  • Full Text:
  • Date Issued: 2013

Statistical model for risk diversification in renewable energy

  • Authors: Ahame, Edmund
  • Date: 2013
  • Subjects: Renewable energy sources -- Statistics , Diversification in industry
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10564 , http://hdl.handle.net/10948/d1008399 , Renewable energy sources -- Statistics , Diversification in industry
  • Description: The growth of the industry and population of South Africa urges to seek new sources of electric power, hence the need to look at alternative power sources. Power output from some renewable energy sources is highly volatile. For instance power output from wind turbines or photovoltaic solar panels fluctuates between zero and the maximum rated power out. To optimize the overall power output a model was designed to determine the best trade-off between production from two or more renewable energy sources putting emphasis on wind and solar. Different measures of risk, such as coefficient of variation (CV) and value at risk (VAR), were used to determine the best hybrid renewable energy system (HRES) configuration. Depending on the investors’ expected returns (demand) and risk averseness, they will be able to use the model to choose the best configuration that suites their needs. In general it was found that investing in a diversified HRES is better than investing in individual power sources.
  • Full Text:
  • Date Issued: 2013

Strategic adaptive management and the efficiency of invasive alien plant management in South African national parks

  • Authors: Loftus, Wynand Johan
  • Date: 2013
  • Subjects: Biodiversity -- South Africa -- Management , Alien plants -- South Africa , Invasive plants -- South Africa , Ecosystem management
  • Language: English
  • Type: Thesis , Masters , MTech
  • Identifier: vital:10755 , http://hdl.handle.net/10948/d1020089
  • Description: It is well known that invasive alien plants (IAPs) pose a significant threat to natural biodiversity and human well-being. Through various pressures exerted on natural ecosystems, IAPs decrease and alter natural processes that provide important ecosystems services and livelihoods to human communities. These plants also displace and out-compete natural plant communities in the areas in which they invade. Management of IAPs is a complex issue with social, environmental and financial challenges. The long-term sustainable management of IAPs requires a management approach that monitors and measures the outcomes of current management practices, and considers the lessons learnt in future decision making. Adaptive management is such an approach and is characterised by monitoring, assessment, reflection and adaptation. In this dissertation I explore IAP management within the South African National Parks (SANParks) organisation. I focus on the quality of the available IAP clearing data for monitoring and environmental decision-making and explore how strategic adaptive management (SAM) is being applied to IAP management. Strategic adaptive management is a form of adaptive management that SANParks adopted to deal with the inherent unpredictability of the social ecological systems they manage, and is primarily a learning-by-doing approach. In chapter one I describe the various impacts that IAPs have on natural environments. I also discuss management of IAPs, the national Working for Water (WfW) programme and how SANParks control IAPs in partnership with WfW. Clearing of IAPs within the borders of SANParks is funded by the Department of Environmental Affairs‘ (DEA) Natural Resource Management programmes and carried out through the Working for Water programme, under SANParks‘ Biodiversity Social Projects programme and is done on a contract basis. Contract data are stored in the Working for Water Information Management System (WIMS) database. Although IAP clearing is well established, the efficiency of overall clearing operations within the parks, and quality and reliability of the data available in the WIMS, needs to be examined. In Chapter two, I (i) assess the status of IAP clearing and the direct clearing costs in each of the five national parks (costs are inflated to 2012 equivalents using the consumer price index), (ii) assess the accuracy of workload estimations for WfW IAP clearing, and (iii) discuss the utility of WIMS as a system to collate and store accurate data for monitoring purposes, focusing on the integrity and reliability of the data, the accuracy of density estimations and whether it can inform sound decision making. The planning of future clearing contracts lacks efficiency due to inaccuracies and unreliability of input data, specifically estimates of invasive alien plant density. The accuracy of density estimation and cost of clearing varies greatly between parks and does not appear to reflect the reality on the ground. In Chapter 3, through an interview process with IAP managers, I 1) unpack the steps in the SAM ‗cycle‘ and investigate the effectiveness of implementation of each step according to respondents; 2) assess the barriers that are currently keeping managers from implementing effective IAP management; 3) discuss whether learning and adaptation is taking place, and 4) discuss how the SAM process can be modified to promote its effectiveness.
  • Full Text:
  • Date Issued: 2013

Structural analysis of synthetic ferrihydrite nanoparticles and its reduction in a hydrogen atmosphere

  • Authors: Masina, Colani John
  • Date: 2013
  • Subjects: Ferric hydroxides , Minerals -- Analysis , Nanoparticles
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: vital:10555 , http://hdl.handle.net/10948/d1020796
  • Description: Ferrihydrite (FHYD), a nanocrystalline material has long been described as a poorly crystalline disordered mineral mainly due to its small crystal size which is typically 2−6 𝑛𝑚. The three-dimensional structure of the mineral has long been described by a multi-phase structural model that consists of Fe3+ only in octahedral (Oh) coordination. In this model ferrihydrite is described as a mixture of two major phases (akaganeite/goethite-like f-phase and feroxyhite-like d-phase) and a minor ultradispersed nanohematite phase. This model has been recently challenged and a new, single-phase model was proposed, having a basic structural motif closely related to the Baker-Figgs δ-Keggin cluster and is isostructural with the mineral akdalaite, Al10O14(OH)2. In its ideal form, the proposed new structure of FHYD consist of 80 % Oh and 20 % tetrahedral (Td) Fe3+ polyhedra which can be adequately described by a single-domain model with the hexagonal spacegroup 𝑃63𝑚𝑐 and unit cell dimensions 𝑎=5.95 Å and 𝑐=9.06 Å. In this study, nanoparticles of 2-line FHYD (FHYD2), 2-line FHYD deposited onto SiO2 (FHYD2/SiO2) and 6-line FHYD (FHYD6) synthesised using rapid hydrolysis of Fe(NO3)3.9H2O solutions were characterized using X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), Mössbauer spectroscopy (MS) as well as magnetization and magnetic susceptibility measurements. The coordination environment of iron atoms in the structure of FHYD was investigated using TEM and MS. The thermal transformation of FHYD nanoparticles was monitored through changes in the magnetization as a function of temperature and the reduction behaviour in hydrogen environment was studied using temperature programmed reduction (TPR), in-situ XRD and MS. Electron diffraction, TEM/ scanning TEM (STEM) imaging, and electron energy loss (EELS) measurements were carried out on three different microscopes viz. JEOL JEM-2100 LaB6 TEM, aberration corrected Schottky-FEG JEOL JEM-ARM200F HRTEM and cold-FEG Zeiss SESAM TEM. EELS studies were concentrated mainly on the iron 𝐿-edge of FHYD and iron oxides reference spectra with well known crystal structures. The iron oxide Fe 𝐿-edge is usually characterized by two intense sharp peaks termed “white lines”. The fine structures introduced by the crystal field effect on the 𝐿- edge contain information that is highly specific to the Fe3+ site symmetry.
  • Full Text:
  • Date Issued: 2013

Sustainable harvesting of wild populations of Cyclopia intermedia in Kouga, Eastern Cape, South Africa

  • Authors: Barnardo, Nadia
  • Date: 2013
  • Subjects: Wild plants, Edible -- South Africa -- Eastern Cape , Rooibos tea industry -- South Africa -- Eastern Cape
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10639 , http://hdl.handle.net/10948/d1020195
  • Description: Cyclopia intermedia E. Mey is harvested from the wild to produce honeybush tea. The presence of a lignotuber and its slow growth seems to hinder the cultivation of this species and wild harvesting is likely to continue. Species distribution modelling indicated that C. intermedia has a climate envelope that spans from the Eastern Cape to the Western Cape along the Cape Fold mountains. This regional distribution is threatened under future climate change scenarios with a range loss and shift identified for climate conditions predicted for 2050. More specifically, its niche was identified as south-facing slopes with sandy to loamy sand soils and water holding capacity that is higher than the surrounding areas. Some keystone Fynbos species were found to share this niche: Leucadendron salignum, Leucospermum cuneiforme, Protea neriifolia, Protea repens, Elegia filacea and Rhodocoma fruticosa. Cyclopia intermedia grows throughout the summer with flowering buds developing in autumn. These enlarge during winter with the flowers opening in early spring. Pods develop in November and seed set occurs during December. Harvesting plants increases their fecundity with cut plants producing more than twice the number of pods and seeds compared to their non-harvested counterparts. This is because resprouting plants produce more flowering stems than uncut plants. Controlled harvesting or localised short-cycle burning could be considered as a management option to improve fecundity of declining Cyclopia intermedia populations in protected areas. C. intermedia harvesting could occur every third year and stem colour was identified as a measure of harvest maturity. Where at least 30 percent of the population has orange (RHS colour 163A) stems the population is suitable for harvesting.
  • Full Text:
  • Date Issued: 2013

Synthesis and characterisation of oxorhenium(V) and tricarbonylrhenium(I) complexes with biologically active N, O and N, S-Donor ligands

  • Authors: Mukiza, Janvier
  • Date: 2013
  • Subjects: Rhenium , Rhenium compounds , Ligands
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10437 , http://hdl.handle.net/10948/d1020769
  • Description: This study investigated the synthesis of rhenium(I) and rhenium(V) complexes with a variety of multidentate NS, NSO, NO and SO-donor ligands. It also investigated the synthesis of dinuclear dihalogeno- and trihalogeno-bridged rhenium(I) complexes based on the fac-[Re(CO)3]+ core. The reactions of hydrated folic acid with [Re(CO)5X] (X = Cl, Br) were studied, and the complexes [Re(CO)3(H2O)3]+[Re2(μ-X)3CO)6]−.5H2O [X= Br (1), Cl(2)] were isolated. The reaction of orotic acid potassium salt [Re(CO)5Br] was performed, and the complex [Re2(μ-Br)2(CO)8] was isolated. The reaction of bis(piperidin-1- yl)methanone with [Re(CO)5Cl] followed by recrystallisation of the resulting precipitate in dichloromethane/acetontrile resulted in the complex [Re2(μ- Cl)2(CO)6(MeCN)2]. The X-ray crystal structures show that all these complexes display a distorted octahedral geometry around the central rhenium atoms. The reactions of aroylhydrazone-based ligands such as 3-((pyridin- 2yl)methyleneamino)-2,3-dihydro-2-pyridin-2yl)quinazolin-4-(1H)-one (Hppq) and N-(di(pyridin-2-yl)methylene)benzohydrazide (Hdpmb) with [Re(CO)5Cl] were studied and led to the formation of the complexes [Re(CO)3Cl(Hdpmb)] and [Re(CO)3Cl(Hppq)]. The Hdpmb and Hppq coordinated to the fac-[Re(CO)3]+ core as neutral bidentate chalates via the pyridinic nitrogens (for Hdpmb) and via imino and pyridinic nitrogens for Hppq. The X-ray crystal structures show that the geometry around the rhenium in both complexes is a distorted octahedral. The treatment of the dithizone (H2dz) ligand with rhenium(V) precursors containing a triphenylphosphine group (PPh3) led to the decomposition of dithizone. The decomposition product reacted with the triphenylphosphine group and generated a new ligand triphenylphosphazeno-N-phenylmethanethiohydrazide (H2L). The reaction of trans-[ReOX3(PPh3)2] (X = Cl, Br) with dithizone (H2dz) led to the complex [ReO(dz)2][ReO(HL)2]. The reaction of trans-[ReOI2(OEt)(PPh3)2] with H2dz led to the same product. The reaction of cis-[ReO2I(PPh3)2] with H2dz in methanol led to [ReO(dz)2][ReO(HL)2](MeOH)2 in which methanol bonded to HLvia hydrogen bonds. The H2dz was doubly deprotonated and coordinated to the [ReO]3+ moiety via a thiolate sulfur and deprotonated hydrazinic nitrogen to yield [ReO(dz)2]−, while the H2L was singly deprotonated and coordinated to [ReO]3+ moiety via the neutral sulfur atom and deprotonated hydrazinic nitrogen to yield [ReO(HL)2]+. The X-ray crystal structure show that in both [ReO(HL)2]+ and [ReO(dz)2]−, the rhenium atoms are five-coordinated and adopt a distorted squarebased pyramidal geometry. The reaction of thiosemicarbazones such as salcylidene-4- phenylthiosemicarbazide (H3salpt) with cis-[ReO2I(PPh3)2] was investigated and led to the complex [ReO(Hsalpt)(H2salpt)]. The X-ray study reveals that Hsalpt is present as a tridentate chelate coordinating via the thiolate sulfur, imino nitrogen and phenolic oxygen, while H2salpt coordinates as a bidentate chelate via the thiolate sulfur and imino nitrogen atoms. The geometry around rhenium is distorted octahedral. The coordination mode of the benzoylthiourea derivatives 4-tert-butyl-N- (diphenylcarbamothioyl)benzamide (Htpb) and N-(diethylcarbamothioyl)benzamide (Heb) to the [Re2O3]4+ and fac-[Re(CO)3]+ cores were investigated. The reaction of [Re(CO)5Cl] in presence of sodium acetate with Htpb led to the dimeric complex [Re(CO)3(tpb)]2 in which the tpb coordinated to the fac-[Re(CO)3]+ core via the ketonic oxygen and bridging thiolate sulfur. The same reaction with Heb led to the monomeric complex [Re(CO)3(eb)(Heb)], in which the eb coordinates to the fac-[Re(CO)3]+core via thiolate sulfur and ketonic oxygen with Heb binding via the neutral sulfur atom. The reaction of Heb with cis-[ReO2I(PPh3)2] at room temperature with excess of sodium acetate led to the dimeric complex (μ-O)[ReO(eb)2]2 in which Heb is present as a monoanionic (deprotonated) bidentate with coordination through the thiolate sulfur and ketonic oxygen.
  • Full Text:
  • Date Issued: 2013

Synthesis of fluorescent polymers with coumarin backbones by "click" polymerization

  • Authors: Okerio, Jaspher Mosomi
  • Date: 2013
  • Subjects: Polymerization , Fluorescent polymers
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10431 , http://hdl.handle.net/10948/d1020132
  • Description: Click chemistry is one of the growing areas of research which is applied in the design and synthesis of a wide range of polymeric architectures. This investigation focuses on the synthesis of fluorescent coumarin based polymers by “click” A-B step growth polymerization process and evaluation of their photophysical properties. Non-fluorescent azide-alkyne functionalized coumarin-based monomers were synthesized in multiple steps from 2,4-dihydroxybenzaldehyde in reasonable yields. Polymers with coumarin backbone were synthesized from azide-alkyne functionalized coumarin monomers via the Cu(I) catalyzed 1,3-dipolar cycloaddition reaction between azides and alkynes, a typical click reaction, to form polymers whose repeating units are connected by a 1,2,3-triazole ring. The structures of the synthesized polymers were confirmed by NMR and FT-IR spectroscopy. Finally, the photophysical properties of the synthesized monomers and polymers were evaluated in DMF. All coumarin based monomers showed reduced fluorescent properties due to the quenching effect from the azido group. Although all polymers absorbed at maximum wavelength of 340 nm, a characteristic for coumarin chromophore, the homo-polymers emitted at a shorter wavelength of 413 nm as compared to the co-polymers which emitted at 421 nm.
  • Full Text:
  • Date Issued: 2013

Synthesis of fluorescent polymers with pendant triazole-substituted coumarin side-chains via a combination of click chemistry and raft-mediated polymerization

  • Authors: Wali, Nwabisa Whitney
  • Date: 2013
  • Subjects: Fluorescent polymers , Polymerization , Macromolecules -- Synthesis
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10432 , http://hdl.handle.net/10948/d1020142
  • Description: This research project focuses on the synthesis of fluorescent polymers with pendant triazole-substituted coumarin side chain units. Copper(I)-catalyzed Huisgen’s 1,3-dipolar cycloaddition of alkynes with azides to form a 1,2,3-triazole ring, a typical example of “click” reaction, has been utilized for the synthesis of a novel vinyl monomer, 2-oxo-3-(4- vinyl-1H-1,2,3-triazol-1-yl)-2H-chromen-7-yl acetate 62. The monomer and its precursors were synthesised and characterized using 1D- and 2D-NMR and FT-IR. Coumarin-containing triazole polymers were synthesised using free radical polymerization. Reversible Addition-Fragmentation Chain Transfer (RAFT)-mediated polymerization was used to synthesise well defined coumarin-containing triazole polymers with moderate PDI values. The polymers were characterised using 1H-NMR and FT-IR. Modelling of the monomer precursor 61 and the monomer 62 at DFT level of approximation provided useful insights into possible conformations adopted by the monomer precursor 61 and the monomer 62. The photophysical properties of the novel monomer and the synthesised polymers were investigated in a polar solvent.
  • Full Text:
  • Date Issued: 2013

Synthesis, optical and morphological characterization of CdSe/ZnSe quantum dots for cytotoxicity studies

  • Authors: Nkaule, Anati Nomxolisi
  • Date: 2013
  • Subjects: Quantum dots , Quantum dots -- Optical properties
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10434 , http://hdl.handle.net/10948/d1020637
  • Description: Colon cancer (CC) ranks high in morbidity and mortality amongst the most frequent occurring cancers worldwide. Mortality rates are mostly caused by mis-diagnosis and the poor efficacy of treatment. The aim of this study was to enhance our insights of quantum dots, for early detection and targeted drug delivery, thereby reducing toxicity to normal cells and reducing side effects that are caused by previous colon cancer medicine. The synthesis, characterization and cytotoxicity studies of CdSe/ZnSe quantum dots (QDs), nanocrystals are reported. Toxicological properties of the Cd2+ core are reduced by capping quantum dots with ZnSe, varying chain length and functional group ligands. Fluorescence wavelength and their size is improved by varying Cd2+ source and varying nanocrystal synthesis growth temperature. CdSe/ZnSe quantum dots are characterized with FT-IR to elucidate their structure. High-resolution transmission electron microscopy (HRTEM), X-Ray Diffraction (EDX), Photoluminescence spectroscopy (PL) and Ultraviolet-visible spectroscopy (UV-Vis) are used to measure their size and composition. Ligand exchange reactions are conducted with the use of 3-Mercaptopropanoic acid (3-MPA) to facilitate bio-compatibility and stability of CdSe/ZnSe QDs. Temperature stability of various ligand capped and stabilized CdSe/ZnSe QDs are measured by using thermogravimetric analysis (TGA). Caco-2 cell line is cultured from colon cancer, and cytotoxic studies are conducted to test for cell viability of various capped 3-Mercaptopropanoic acid (3-MPA) CdSe/ZnSe quantum dots at various concentrations. Myristic acid capped CdSe/ZnSe quantum dots produce high fluorescing mono-disperse quantum dots. The capping material, synthesis temperature and Cd2+ source of CdSe/ZnSe QDs affect fluorescence wavelength and thermal stability of quantum dots. Fluorescence wavelength is improved by using CdCl2.7H2O source of Cd2+. Cytotoxicity was found to be dependent on the concentration and the capping material of quantum dots. CdSe/ZnSe quantum dots toxicity is adjusted and reduced by varying the length, size and type of the capping ligand on the surface of quantum dots.
  • Full Text:
  • Date Issued: 2013

Technology transfer of antibacterial oral solid dosage form in a pharmaceutical industry

  • Authors: Ramloll, Jason
  • Date: 2013
  • Subjects: Clinical pharmacology Pharmacy -- Research , Pharmaceutical industry
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/47913 , vital:40398
  • Description: Technology transfer (TT) looks at the transfer of intellectual property from one manufacturing site to another. If carried out successfully, a TT can increase the leveraging capability of the company acquiring the intellectual property together with its brand strength. This in turn aids in a decreased time to market of the final dosage form produced. The aim of the research was to assess the TT of an antibacterial oral solid dosage form from one manufacturing site to another. An expected change of manufacturing equipment from a single-pot to a multi-phase system took place due to the equipment available at the receiving unit. The assessment done by the researcher was performed in the capacity of an observer. The assessment of the TT was performed by observing the critical stages during the transfer process, namely the development and validation stages. Prior to the start of the development stage, a characterisation of innovator was performed. At this stage, innovator batches received from the Sending Unit (SU) were characterised to allow for a means of comparison. The development stage allows for the determination of the robustness of the formulation to be used whilst the validation stage will look at the reproducibility of the chosen formulation. During the development stage, small scale trials were manufactured with amendments made to the original formulation. The amendments allowed for a formulation more comparable to the innovator product with regards to its dissolution profile. The comparable batch produced at a small scale was then up-scaled to a production scale batch and these were compared to the innovator products. The amendments made were on the amount of granulation fluid and binder as well as the method of addition of the disintegrant. When a large scale batch comparable to that of the innovator product was produced, the validation stage was started. With the aim of showing reproducibility of the Receiving Unit (RU) at producing large scale batches, three batches were produced. These were tested for all critical parameters, namely through the loss on drying, particle size distribution, hardness, disintegration and dissolution tests and, the results of the tests were compared to the specifications set by the SU. They were also compared to each other, enabling statistical determination of any significant difference across the batches through the use of comparative statistical analyses. Comparison of batches, at the development and validation stage, was done using the dissolution potential of the batches. These were performed through the use of statistical analyses. The RU made use of the similarity factor (F2) to compare the dissolution profiles. For the purpose of this research, the 1-Way analysis of variance was also used, which compared to the similarity factor, took in consideration the level of variance of the batches produced. Results and discussion: During the development stage amendments were made to produce a batch comparable to the innovator product. The amendments that led to the production of a comparable batch consisted of an extra 14 % of granulation fluid as well as 50 % of the disintegrant being added intra-granularly with the other 50 % added extra-granularly. The amendments were added on top of the amount suggested by the SU. This formulation was used and three batches produced consecutively. On comparison to the specifications set by the SU, the three batches were seen to be within the specifications. On comparison to each other, the dissolution profiles were seen to be different. Conclusion and recommendation: The development stage producing batches within the specifications set by the SU but also comparable with regards to its dissolution profile, was seen to be successful. The validation stage was seen to be unsuccessful. Even though the results of the critical parameters were within specifications, when compared to each other, the batches were seen to be significantly different. This led to the research looking at the TT as a whole as being unsuccessful. The researcher then determined what stage could be improved and how this could be done. The various stages seen as having associated problems were determined and ways to mitigate those were determined. A guideline in the form of a flow chart was proposed to aid a manufacturing facility undertaking a TT to shorten the period of time to completion as well as increase the chance of success.
  • Full Text:
  • Date Issued: 2013

The contribution of submerged macrophytes and macroalgae to nutrient cycling in the Great Brak Estuary

  • Authors: Human, Lucienne Ryno Daniel
  • Date: 2013
  • Subjects: Nutrient cycles -- South Africa -- Great Brak Estuary , Microalgae -- South Africa -- Great Brak Estuary , Estuarine ecology -- South Africa -- Great Brak Estuary
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: vital:10364 , http://hdl.handle.net/10948/d1021102
  • Description: An ecological reserve study by the Department of Water Affairs on the Great Brak Estuary stated that there was a need to determine how much nitrogen and phosphorus was flowing through the estuary as well as how effective the macroalgae were at removing N and P. The objective of this study was to investigate the physico-chemical characteristics in the estuary and the influence of these on the submerged macrophytes and macroalgae. A nutrient budget for the estuary was developed in order to quantify the contribution of the submerged macrophytes and macroalgae relative to other contributing sources. The Wolwedans Dam located 3 km upstream from the estuary has reduced the amount of freshwater flow to the estuary by as much as 56 percent. The estuary has been allocated 2 x 106 m3 per annum of freshwater (ecological reserve) that is used to breach the mouth once or twice a year in spring or summer. Even though this water has been made available it is not sufficient to flush the estuary. Reduced flushing has led to an accumulation of organic matter and degradation in the water quality. Physico-chemical measurements between September 2010 and July 2012 showed that dissolved oxygen values were generally below 6 mg l-1. The average NH4+ concentration in the estuary was 7 μM and increased with depth to 12 μM at 2 m depths. Concentrations >45 μM were found in February and April 2011 at the 5 m deep hole at 3.4 km upstream. Negative correlations between dissolved oxygen and NH4+ during November 2010, February 2011, April 2011 and July 2011 (r = -0.68; -0.67; -0.63; -0.96) indicated that remineralisation of organic matter had occurred. Soluble reactive phosphorus (SRP) followed a similar trend to the NH4+ and was generally below 1 μM in the water column for most months, and had peaks at 1.0 km and 3.4 km in the bottom water. The abundance of submerged macrophytes and macroalgae below the N2 bridge were mostly influenced by mouth state and river inflow. During the closed phase the dominant macroalga Cladophora glomerata had an area cover ranging from 3000 to 6000 m2 while Zostera capensis and Ruppia cirrhosa covered an area of 2000 to 3500 m2 and 1500 to 2900 m2, respectively. After an artificial breach in February 2011, water drained out of the estuary leaving the alga stranded on the marshes and as the flood tide entered the macroalga was once again redistributed in the lower reaches. The alga utilised the available nutrients in the water column and expanded its area cover from 35000 m2 in February 2011 to 64000 m2 in March 2011. However, after the floods in June 2011, Cladophora glomerata had been washed out of the system while the submerged macrophytes responded positively extending their area cover. By comparing the artificial breach with the natural breach, and the effect on the estuary, an important observation was highlighted. Increasing the current allocated ecological reserve, and using a larger volume of water to breach the mouth artificially, would result in better scouring of sediment and associated organic matter out of the estuary. This would enable better oxygenation of the water column, reduce remineralisation and minimise algal blooms.
  • Full Text:
  • Date Issued: 2013

The diet of the Subantarctic (A. Tropicalis) and Antarctic (A. Gazella) Fur seal at Marion Island

  • Authors: Mgibantaka, Nonkoliso Felicia
  • Date: 2013
  • Subjects: Southern fur seals -- Feeding and feeds -- Antarctica , Seals (Animals) -- Antarctica , Marine ecology
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10729 , http://hdl.handle.net/10948/d1021104
  • Description: Studying the diet of marine top predators is important for understanding the trophic ecology of the predators but also the distribution, abundance and seasonal variation of prey species. Dietary studies on subantarctic fur seals (Arctocephalus tropicalis) and Antarctic fur seals (A. gazella) is important for assessing their role as predators in the Southern Ocean. Seven hundred and sixty four scats were collected from an A. tropicalis colony at Cape Davis while 659 scats were collected from an A. gazella colony at Watertunnel stream from April 2006 to March 2010. Hard remains such as fish otoliths and cephalopod beaks were used for identification and quantification of prey. A. tropicalis diet comprised of three animal groups (fish, cephalopod and crustaceans) while A. gazella diet was made up of four animal groups (fish, cephalopods, crustaceans and seabirds). Fish contributed substantially more than other prey items in the diet of both fur seal species over the study period. Both species fed predominantly on fish of the family Myctophidae which constituted a numerical abundance of 98.9 percent in scats for both species combined. A. tropicalis fed on fish prey species from eight families, namely: Myctophidae, Notosudidae, Paralepididae, Nototheniidae, Bathylagidae, Chlorophthalmidae, Sternoptychidae and Photichthyidae while A. gazella fed on fish from six of these families, with Chlorophthalmidae and Photichthyidae not represented in its diet. Cephalopods and crustaceans were found in low numbers in the diet of both seal species and seabird remains were only found in the diet of A. gazella. Numerically, the most dominant species were from the genus Gymnoscopelus followed by Protomyctophum and then Electrona. In the diet of A. tropicalis, Gymnoscopelus contributed 66 percent, Protomyctophum 18 percent and Electrona 5.9 percent while in the diet of A. gazella Gymnoscopelus, Protomyctophum and Electrona contributed 59.43 percent, 20.24 percent and 14.24 percent respectively. Gymnoscopelus species comprised G. piabilis, G. bolini, G. braueri, G. fraseri, and G. nicholsi; Protomyctophum comprised Protomyctophum bolini, P. choriodon and P. tenisoni while Electrona comprised Electrona antarctica, E. carlsbergi and E. subaspera. Gymnoscopelus piabilis was the most dominant species from this genus while Electrona carlsbergi and Protomyctophum tenisoni dominated the genus Electrona and Protomyctophum respectively. The total number of fish species utilised by A. tropicalis was twenty four while twenty three fish species were identified in A. gazella diet. Bathysauropsis gracilis only featured in the diet of A. tropicalis while Lampanyctus ater and Lepidonotothen larseni were only found in the diet of A. gazella. To compare the diet of the seal species between seasons, a year was divided into three seasons, early summer, late summer and winter. Their diet was also compared between years from 2006 to 2010. Myctophid fish species showed substantial seasonal and annual fluctuations in the diet of the two fur seal species. E. carlsbergi, G. nicholsi and G. piabilis increased in numerical abundance in winter while Melectrona ventralis increased in late summer. The numerical abundance of G. fraseri and P. tenisoni increased in early summer. Generally, the two fur seal species fed on the same prey species. However, there was a significant difference when the diet of both fur seals was compared seasonally. There was no significant difference when the diet of A. gazella was compared annually, although such a difference was apparent for A. tropicalis.
  • Full Text:
  • Date Issued: 2013

The diversity and distribution patterns of intertidal fish in the Agulhas bioregion

  • Authors: Roux, Maryanne
  • Date: 2013
  • Subjects: Intertidal fishes , Marine fishes -- South Africa
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10723 , http://hdl.handle.net/10948/d1019712
  • Description: This study aimed to expand the existing knowledge on the diversity and distribution patterns of intertidal fishes in the Sardinia Bay MPA and adjacent open access areas. It focussed particularly on in intertidal fish communities along the Agulhas Bioregion coast which has been understudied, especially in recent years. Typical resident species belonging to the family Clinidae were the most abundant, conforming to previous studies. Species from the family Gobiidae were the second most abundant in this study but this family was not previously recorded as being abundant. Transient species were unimportant in the current study which is in contrast to previous studies in the region and suggests a change in species composition. Certain transient species utilised intertidal rockpools as part of their nursery areas in the Eastern Cape, as has previously been found around Algoa Bay. A decrease in species richness from east to west was recorded in this study which has been noted by previous authors and the diversity and distribution patterns of the intertidal fish in the current study conformed to patterns found previously. The position of the biogeographic boundary between the Agulhas and Natal Bioregions could not be confirmed but Wavecrest (along the Transkei coastline) appeared to be part of a transition zone rather than a fixed break. More sampling around this area is recommended to determine the location and understand the dynamic nature of this boundary. The fish species were found to be vertically distributed across the shore with most of the resident species being more abundant across the low shore while the transient species were more abundant in the middle to low shore pools. This vertical distribution has been found at many sites around the world. The volume of the pools proved to be the primary controlling factor while the effect of temperature on vertical distribution could not be demonstrated. The benefits of the Sardinia Bay Marine Protected Area on this unexploited community of fishes could not be demonstrated but the long term benefit of protection has yet to be shown. Results from this study suggest that despite the correspondence with general biogeographic trends, the intertidal fish community has changed in composition (at least in terms of transient species) during the last 30 years and the cause for these changes may in part be reduced recruitment from exploited linefish.
  • Full Text:
  • Date Issued: 2013
  • Disclaimer
  • Privacy
  • Copyright
  • Contact