Near-real time foF2 predictions using neural networks
- Authors: Oyeyemi, E O , McKinnell, Lee-Anne , Poole, Allon W V
- Date: 2006
- Language: English
- Type: text , Article
- Identifier: vital:6804 , http://hdl.handle.net/10962/d1004167
- Description: This paper describes the use of the neural network (NN) technique for the development of a near-real time global foF2 (NRTNN) empirical model. The data used are hourly daily values of foF2 from 26 worldwide ionospheric stations (based on availability) during the period 1976–1986 for training the NN and between 1977 and 1989 for verifying the prediction accuracy. The training data set includes all periods of quiet and disturbed geomagnetic conditions. Two categories of input parameters were used as inputs to the NN. The first category consists of geophysical parameters that are temporally or spatially related to the training stations. The second category, which is related to the foF2 itself, consists of three recent past observations of foF2 (i.e. real-time foF2 (F0), 2 h (F−2) and 1 h (F−1) prior to F0) from four control stations (i.e. Boulder (40.0°N, 254.7°E), Grahamstown (33.3°S, 26.5°E), Dourbes (50.1°N, 4.6°E) and Port Stanley (51.7°S, 302.2°E). The performance of the NRTNN was verified under both geomagnetically quiet and disturbed conditions with observed data from a few verification stations. A comparison of the root mean square error (RMSE) differences between measured values and the NRTNN predictions with our earlier standard foF2 NN empirical model is also illustrated. The results reveal that NRTNN will predict foF2 in near-real time with about 1 MHz RMSE difference anywhere on the globe, provided real time data is available at the four control stations. From the results it is also evident that in addition to the geophysical information from any geographical location, recent past observations of foF2 from these control stations could be used as inputs to a NN for near-real time foF2 predictions. Results also reveal that there is a temporal correlation between measured foF2 values at different locations.
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- Date Issued: 2006
New and improved : Linda in Java
- Authors: Wells, George C
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6613 , http://hdl.handle.net/10962/d1011511 , http://www.sciencedirect.com/science/article/pii/S0167642305000869
- Description: This paper discusses the current resurgence of interest in the Linda coordination language for parallel and distributed programming. Particularly in the Java field, there have been a number of developments over the past few years. These developments are summarised together with the advantages of using Linda for programming concurrent systems. Some problems with the basic Linda approach are also discussed and a novel solution to these is presented. The power and flexibility of the proposed extensions to the Linda programming model are illustrated by considering a number of example applications, including a detailed case study of visual language parsing.
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- Date Issued: 2006
Non-steroidal anti-inflammatory agents, tolmetin and sulindac, inhibit liver tryptophan 2,3-dioxygenase activity and alter brain neurotransmitter levels
- Authors: Dairam, A , Antunes, Edith M , Saravanan, K S , Daya, Santylal
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6358 , http://hdl.handle.net/10962/d1006050 , http://dx.doi.org/10.1016/j.lfs.2006.07.028
- Description: Hepatic tryptophan 2,3-dioxygenase (TDO) is one of the rate-limiting enzymes in tryptophan catabolism and plays an important role in regulating the physiological flux of tryptophan into relevant metabolic pathways. In this study, we determined the effect of the non-steroidal anti-inflammatory agents, tolmetin and sulindac, on rat liver TDO activity and the subsequent changes in the hippocampal and striatal neurotransmitter levels. The amount of melatonin produced by the pineal gland was also measured using high performance liquid chromatography (HPLC). Treatment of rats with tolmetin or sulindac (5 mg/kg/bd for 5 days) significantly inhibited liver TDO activity. The results show that whilst tolmetin and sulindac increase serotonin levels in the hippocampus, these agents also significantly reduce dopamine levels in the striatum. Tolmetin, but not sulindac, increased the amount of melatonin produced by the pineal gland. The results of this study suggest that whilst tolmetin and sulindac may be beneficial for patients suffering from depression, these agents also have the potential to induce adverse effects in patients suffering with neurological disorders such as Parkinson's disease.
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- Date Issued: 2006
Novel amperometric glucose biosensor based on an ether-linked cobalt(II) phthalocyaninecobalt(II) tetraphenylporphyrin pentamer as a redox mediator
- Authors: Ozoemena, Kenneth I , Nyokong, Tebello
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6583 , http://hdl.handle.net/10962/d1004148
- Description: The development of cobalt(II) phthalocyanine–cobalt(II) tetra(5-phenoxy-10,15,20-triphenylporphyrin), (CoPc–(CoTPP)[subscript 4]) pentamer as a novel redox mediator for amperometric enzyme electrode sensitive to glucose is described. A glassy carbon electrode (GCE) was first modified with the pentamer, then followed by the immobilization onto the GCE–CoPc–(CoTPP)[subscript 4] with glucose oxidase (GOx) through cross-linking with glutaraldehyde in the presence of bovine serum albumin (BSA) and Nafion® cation-exchange polymer. The proposed biosensor displayed good amperometric respose charateristics to glucose in pH 7.0 PBS solution; such as low overpotentials (+400 mV versus Ag|AgCl), very fast amperometric response time (~5 s), linear concentration range extended up to 11 mM, with 10 μM detection limit. The biosensor exhibited electrochemical Michaelis–Menten kinetics and showed an average apparent Michaelis–Menten constant (K′M) of 14.91 ± 0.46 mM over a storage period of 2 weeks.
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- Date Issued: 2006
Observations of the habitats and biodiversity of the submarine canyons at Sodwana Bay
- Authors: Sink, K J , Boshoff, W , Samaai, Toufiek , Timm, P G , Kerwath, S E
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6771 , http://hdl.handle.net/10962/d1008065
- Description: The discovery of coelacanths, Latimeria chalumnae, in Jesser Canyon off Sodwana Bay in northern KwaZulu-Natal in 2000 triggered renewed interest in the deep subtidal habitats associated with submarine canyons. Information stemming from three recreational Trimix diving expeditions in Wright and Jesser canyons between April 1998 and June 2001 revealed distinct and diverse invertebrate and fish communities in the canyons of the Greater St Lucia Wetland Park (GSLWP). In total, 69 invertebrate taxa were collected from Wright Canyon, including at least 15 new records for South Africa plus 11 potential new species and 16 range or depth extensions. Divers documented the first five coelacanth specimens and obtained information on fish distribution and abundance. Five different habitat types were recognized supporting distinct biological communities; the sandy plains outside of the canyons, scattered rock outcrops within the sandy plains, the canyon margin, canyon walls and caves and overhangs. The canyon margin is the richest habitat and supports dense communities of invertebrate suspension feeders, as well as a diverse and abundant fish fauna. Dominant canyon invertebrates included sponges, black corals, gorgonians, alcyonarian soft corals and stylasterine lace corals. These invertebrates support a diverse epifauna including basket- and brittlestars, winged oysters and other molluscs. The canyons within the GSLWP protect large populations of commercially important linefish species including the sparids, Chrysoblephus puniceus, C. anglicus, Polysteganus praeorbitalis and P. caeruleopunctatus, as well as several species of serranids and lutjanids. Additional biological sampling and standardized quantitative sampling within the canyons and deep reefs is required to develop a better understanding of their biological communities and the factors that shape them.
- Full Text:
- Date Issued: 2006
Oceanographic environment of the Sodwana Bay coelacanths (Latimeria chalumnae), South Africa
- Authors: Roberts, M J , Ribbink, Anthony J , Morris, T
- Date: 2006
- Language: English
- Type: text , Article
- Identifier: vital:7156 , http://hdl.handle.net/10962/d1011883
- Description: Trimix scuba divers discovered coelacanths in Jesser Canyon at a depth of 104 m on the northern KwaZulu-Natal (KZN) coast (Sodwana Bay) in October 2000. The existence of these animals at such a shallow depth and in the swift and powerful Agulhas Current led to a suggestion that this might be an isolated group swept well away from the main population in the Comoros, where they live at depths of 200–350 m with little current. Subsequent observations from three manned submersible surveys and one remotely operated vehicle expedition together with recreational diver observations indicate that the South African population of coelacanths has at least 26 individuals, mostly occupying the depth range of 104–140 m in canyons. Seventeen CTD sections collected during four cruises in 2002 and 2003 indicate the temperature range in this habitat to be similar to that found in the Comoros Islands (that is, 15–22°C cf. 15–19°C in the Comoros). However, a 2.5-month-long time series of hourly data collected by a thermistor array deployed near a known coelacanth cave in Wright Canyon indicated greater variation than anticipated, with temperature changes between 16°C and 24°C occurring in a day. Dissolved oxygen levels in this depth zone were found to range between 3.0 ml l[superscript (–1)] and 4.8 ml l[superscript (–1)] compared to 3.5 ml l[superscript (–1)] in the Comoros. The low oxygen values along this coast are a result of the shallow oxygen minimum, which becomes shallower in the southwest Indian Ocean, particularly in the Agulhas Current, than in tropical latitudes. Current velocities measured using a ship-borne ADCP in the depth range 100–140 m at Sodwana were considerably higher than those measured in the Comoros habitat (20–60 cm s[superscript (–1)] cf. 3–4 cm s[superscript (–1)]) and may be an important factor explaining the coelacanths’ occupation of the canyons found along the northern KZN shelf-break.
- Full Text:
- Date Issued: 2006
Oceanographic environment of the Sodwana Bay coelacanths (Latimeria chalumnae), South Africa
- Authors: Roberts, M J , Ribbink, A J , Morris, T
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:7126 , http://hdl.handle.net/10962/d1010633
- Description: Trimix scuba divers discovered coelacanths in Jesser Canyon at a depth of 104 m on the northern KwaZulu-Natal (KZN) coast (Sodwana Bay) in October 2000. The existence of these animals at such a shallow depth and in the swift and powerful Agulhas Current led to a suggestion that this might be an isolated group swept well away from the main population in the Comoros, where they live at depths of 200–350 m with little current. Subsequent observations from three manned submersible surveys and one remotely operated vehicle expedition together with recreational diver observations indicate that the South African population of coelacanths has at least 26 individuals, mostly occupying the depth range of 104–140 m in canyons. Seventeen CTD sections collected during four cruises in 2002 and 2003 indicate the temperature range in this habitat to be similar to that found in the Comoros Islands (that is, 15–22°C cf. 15–19°C in the Comoros). However, a 2.5-month-long time series of hourly data collected by a thermistor array deployed near a known coelacanth cave in Wright Canyon indicated greater variation than anticipated, with temperature changes between 16°C and 24°C occurring in a day. Dissolved oxygen levels in this depth zone were found to range between 3.0 ml l[superscript (–1)] and 4.8 ml l[superscript (–1)] compared to 3.5 ml l[superscript (–1)] in the Comoros. The low oxygen values along this coast are a result of the shallow oxygen minimum, which becomes shallower in the southwest Indian Ocean, particularly in the Agulhas Current, than in tropical latitudes. Current velocities measured using a ship-borne ADCP in the depth range 100–140 m at Sodwana were considerably higher than those measured in the Comoros habitat (20–60 cm s[superscript (–1)] cf. 3–4 cm s[superscript (–1)]) and may be an important factor explaining the coelacanths’ occupation of the canyons found along the northern KZN shelf-break.
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- Date Issued: 2006
Olive Schreiner at 150: some thoughts on re-editing Cronwright's The Reinterment on Buffelskop
- Authors: Walters, Paul S , Fogg, W Jeremy M
- Date: 2006
- Language: English
- Type: text , Article
- Identifier: vital:6124 , http://hdl.handle.net/10962/d1004708
- Description: [From the introduction]: The original edition of Cronwright’s The Reinterment on Buffelskop (1983) was produced by Guy Butler and Nick Visser to commemorate the centenary of the 1883 publication of The Story of an African Farm. The Butler-Visser text was a photographic reproduction of a typed carbon copy of the first part of Cronwright’s extant diaries plus a special diary he had kept covering in detail the events of the actual reinterment. (The originals are now at the National English Literary Museum [NELM].) Butler included a comprehensive and illuminating introduction to these texts, as well as – under separate soft cover – a set of “Provisional Notes” which draw deeply on his own and his family’s accumulated knowledge of Cradock, its environs and inhabitants. In addition, Butler and Visser included two passages excised by Cronwright from the typescript of his Life of Olive Schreiner: a word picture of Charles Heathcote, and the longer account of “The Nienaber Incident” – pages which deal with the execution of three innocent men at De Aar on 19 March 1901, and Cronwright’s subsequent attempts at legal reparation for them and their families. The substantive text of the Butler-Visser edition is often difficult to read because of the method of reproduction; moreover, because it also reproduces Cronwright’s emendations (in ink) of the typescript, it is frankly uninviting. Thus, when the NELM Council proposed a publication commemorating the 150th anniversary of Olive Schreiner’s birth on 24 March 1855, it seemed appropriate that a second attempt be made to give students of Olive Schreiner’s works easier access to Cronwright’s detailed account of this “bizarre, romantic” episode. Furthermore, from the perspective of text history, the typescript of the Reinterment antedates both Cronwright’s Life and The Letters of Olive Schreiner. Parts of it are clearly Cronwright’s preliminary ‘notes towards’ his Life, and, as Butler hypothesizes, the whole of the Reinterment might have been intended as a separate (and earlier) publication. Finally, the sarcophagus on Buffelskop is one of South Africa’s more noteworthy literary shrines: while the idea of re-editing an account of Olive Schreiner’s reinterment might be thought to be a futile exercise in intellectual recycling, our intention is that both husband and wife should live again through a rediscovery of the thoughts and feelings that led them to this dramatic final resting-place.
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- Date Issued: 2006
On the correlation between annealing and variabilities in pulsed-luminescence from quartz
- Authors: Chithambo, Makaiko L
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6797 , http://hdl.handle.net/10962/d1003923
- Description: Properties of luminescence lifetimes in quartz related to annealing between 500 and 900ºC have been investigated. The luminescence was pulse-stimulated at 470 nm from sets of granular quartz annealed at 500, 600, 700, 800, and 900ºC. The lifetimes decrease with annealing temperature from about 42 to 33 µѕ when the annealing temperature is increased from 500 to 900ºC. Luminescence lifetimes are most sensitive to duration of annealing at 600ºC, decreasing from 40.2 ± 0.7 µѕ by as much as 7 µѕ when the duration of annealing is changed from 10 to 60 min. However, at 800–900ºC lifetimes are essentially independent of annealing temperature at about 33 µѕ. Increasing the exciting beta dose causes an increase in the lifetimes of the stimulated luminescence in the sample annealed at 800ºC but not in those annealed at either 500 or 600ºC. The temperature-resolved distribution of luminescence lifetimes is affected by thermal quenching of luminescence. These features may be accounted for with reference to two principal luminescence centres involved in the luminescence emission process.
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- Date Issued: 2006
Preferential electrosorption of cobalt (II) tetra-aminophthalocyanine at single-wall carbon nanotubes immobilized on a basal plane pyrolytic graphite electrode
- Authors: Ozoemena, Kenneth I , Pillay, J , Nyokong, Tebello
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6584 , http://hdl.handle.net/10962/d1004160
- Description: This communication describes the preferential electrosorption of cobalt (II) tetra-aminophthalocyanine (CoTAPc) (rather than the expected electropolymerisation) onto a SWCNT immobilized on a basal plane pyrolytic graphite electrode (BPPGE). Cyclic voltammetric and electrochemical impedance spectroscopic data revealed that the electrosorbed CoTAPc is highly stable, well organized with comparable electron-transfer rate constant in ferricyanide solution (k[subscript app] ~ 6 × 10[superscript (−5)] cm s[superscript (−1)] order) to that of the SWNCT. Electrochemical kinetics of the electrosorbed CoTAPc yielded k[subscript s] of 0.169 s[superscript (−1)] and 832.2 s[superscript (−1)] for the cathodic and anodic reactions, respectively, indicative of different rate-determining steps for the cathodic and anodic reactions. Strong π-stacking interactions between CoTAPc and the sidewalls of the SWCNTs, with possible synergistic covalent interactions, are explained as responsible for the preferential electrosorption process. Both BPPGE-SWCNT-CoTAPc[subscript (ads)] and BPPGE-SWCNT showed comparable electrocatalytic responses towards the detection of 2-(diethylamino) ethanethiol (DEAET).
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- Date Issued: 2006
Professionalism and training for mass communication: challenges and opportunities for Southern Africa
- Authors: Berger, Guy
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6332 , http://hdl.handle.net/10962/d1008477
- Description: [From OPENSPACE Editor Alice Kanengoni's editorial]: Closely linked to a critical media citizenry that can demand better of the media, is the challenge of professionalism and training in the region. Professor Guy Berger illuminates the challenges that the region faces in this regard, a key one being the ability to to match the inputs with the outcomes ... where measuring whether the quality of media products is directly linked to the inputs in training needs to be explored further.
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- Date Issued: 2006
Professor Emeritus Denis William Ewer MBE FRSSAf 1913 - 2009: biographical memoir
- Authors: Hodgson, Alan N
- Date: 2006
- Language: English
- Type: text , Article
- Identifier: vital:6884 , http://hdl.handle.net/10962/d1011643
- Description: Denis Ewer went to University College School in London. In 1931 he entered Trinity College, Cambridge (his father had studied mathematics at Trinity) where he read for the Natural Science Tripos, obtaining a B.A. in 1934. In his second year at Cambridge he gained the nickname of 'Jakes' via a literary route (his father's nickname also had literary origins). The word 'ewer' can mean a jug, chamber pot, or jerry, and hence the progress to 'jakes', Elizabethan English for an outside lavatory. It was at Cambridge that he also met the future communist spy, Kim Philby. After graduating, Jakes Ewer moved to the University of Birmingham where he undertook his doctoral studies (graduating PhD in 1940) under H. Munro Fox. World War II, however, temporarily halted any further academic career, and during the war years he was an Experimental Officer for the Army Operational Research Group (Ministry of Supply) achieving the rank of Major. For his work, which included being a Scientific Advisor to the Chief, Air Defence Division, Supreme Headquarters Allied Expeditionary Force, he was awarded the M.B.E. (Member of the British Empire).
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- Date Issued: 2006
Re-deploying Parker, post-colonially: review essay
- Authors: Macleod, Catriona I , Wilbraham, Lindy
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6275 , http://hdl.handle.net/10962/d1008275
- Description: In this paper we review two of Ian Parker’s recent books: Critical discursive psychology and Qualitative psychology: Introducing radical research. Although the books address different audiences (academics versus students) and talk to different problematics (theory versus research), taken together they represent useful resources for those wishing to take a critical stance with regards to the standard fare of psychology, to use critical theory in understanding social and psychological phenomena, and to engage in progressive research. As such, both theory and research methods appear as “tools”, and we suggest reading Parker sideways, shifting his intellectual trajectory into directions that illuminate colonial and post-colonial issues through empirical/textual application to real South African contexts. By way of illustration, we offer a post-colonial reading of Parker’s work on post-modernism. Concluding comments on tactics for a “post-colonial analysis of discourses” are offered.
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- Date Issued: 2006
Recruitment behaviour in the ponerine ant, Plectroctena mandibularis F. Smith (Hymenoptera: Formicidae)
- Authors: Wilkins, K J , Harman, K , Villet, Martin H
- Date: 2006
- Language: English
- Type: text , Article
- Identifier: vital:6887 , http://hdl.handle.net/10962/d1011647
- Description: Although workers of Plectroctena mandibularis laid trails with their stings while foraging, the trails appeared to be for individual orientation, because they never recruited nestmates to prey. However, both workers and queens laid trails when recruiting nestmates of either caste to new nest sites. During trail-laying, fluted hairs on the posterior edge of tergite VI were dragged along the ground, presumably applying a pheromone to the substrate. Anatomical and behavioural evidence suggests that pygidial gland secretions moved from the intersegmental pygidial gland between tergites VI and VII into a fingerprint-like, lamellar cuticular reservoir on the pygidium, and from there via the hairs to the substrate. These results suggest that recruitment may be crucial to moving nests but of value only to certain types of foraging, and that recruitment might even have originated in the Formicidae in the context of colony relocation, and then secondarily evolved to assist foraging.
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- Date Issued: 2006
Regional calibration of the Pitman model for the Okavango River
- Authors: Hughes, Denis A , Andersson, L , Wilk, J , Savenije, H H G
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:7085 , http://hdl.handle.net/10962/d1012344
- Description: This paper reports on the application of a monthly rainfall-runoff model for the Okavango River Basin. Streamflow is mainly generated in Angola where the Cuito and Cubango rivers arise. They then join and cross the Namibia/Angola border, flowing into the Okavango wetland in Botswana. The model is a modified version of the Pitman model, including more explicit ground and surface water interactions. Significant limitations in access to climatological data, and lack of sufficiently long records of observed flow for the eastern sub-basins represent great challenges to model calibration. The majority of the runoff is generated in the wetter headwater tributaries, while the lower sub-basins are dominated by channel loss processes with very little incremental flow contributions, even during wet years. The western tributaries show significantly higher seasonal variation in flow, compared to the baseflow dominated eastern tributaries: observations that are consistent with their geological differences. The basin was sub-divided into 24 sub-basins, of which 18 have gauging stations at their outlet. Satisfactory simulations were achieved with sub-basin parameter value differences that correspond to the spatial variability in basin physiographic characteristics. The limited length of historical rainfall and river discharge data over Angola precluded the use of a split sample calibration/validation test. However, satellite generated rainfall data, revised to reflect the same frequency characteristics as the historical rainfall data, were used to validate the model against the available downstream flow data during the 1990s. The overall conclusion is that the model, in spite of the limited data access, adequately represents the hydrological response of the basin and that it can be used to assess the impact of future development scenarios.
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- Date Issued: 2006
Repositioning Renaissance studies in South Africa: strategic thinking or 'business-as-usual
- Authors: Wright, Laurence
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:7054 , http://hdl.handle.net/10962/d1007415
- Description: Increasingly, in many leading South African tertiary departments of literature, early modern studies have a fairly slim hold on the core curriculum. More and more, departmental offerings concentrate on nineteenth and twentieth century literature, perhaps in the belief either that today’s students are so poorly prepared that they will never be able to cope with the mental shifts necessary to appreciate pre-industrial literature and its language, or, worse, that nothing before the C19 colonial incursion into South Africa can really matter very much to undergraduates. Whatever the reason, in such departments, it is no longer possible to get to grips with the contribution of the renaissance to the formation of the modern world. The significance of the broader nomenclature, early modern studies, doesn’t appear to strike home, especially the point that, if students want to understand the world we live in, they have to know this period particularly well. Indeed, they need to have some idea of the interaction between early modern Europe and the literature and ideas of the ancient civilizations of Rome and Greece. If we fail them in this regard, as I believe we are doing to an increasing extent, the result will be generations of intellectual sleepwalkers, denizens of mental landscapes they are responding to, or ‘reading’, in terms of an inner life unaware of important historical continuities and disjunctions; cut off, moreover, from understanding essential features of modernity.
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- Date Issued: 2006
Restructuring manufacturing in South Africa's lagging regions : the case of the Free State
- Authors: Nel, Etienne L , Rogerson, C M , Marais, L
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6714 , http://hdl.handle.net/10962/d1006786
- Description: The manufacturing economy of the Free State reflects both historical dependence on locally available raw materials and high-levels of state intervention, in terms of support for import substitution and Homeland development. In the contemporary era, deindustrialization, the uncertain future of the clothing / textile industries and limited growth over the last ten years, suggests that, in terms of manufacturing, the Free State is a 'lagging' region. While there has been significant expansion in the number of small firms, this is not matched by employment growth and does not compensate for the loss of many large firms and economic downscaling in the Goldfields. Key sectors such as petro-chemicals and gold jewellery present certain opportunities for future growth.
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- Date Issued: 2006
Review of the African distribution of the brine shrimp genus Artemia
- Authors: Kaiser, Horst , Gordon, Andrew K , Paulet, T G
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6765 , http://hdl.handle.net/10962/d1007963
- Description: Brine shrimp (genus Artemia) are small (8 to 12 mm long) cosmopolitan crustaceans (Anostraca) found predominately in hypersaline water bodies such as inland salt lakes and pans, coastal lagoons, and salt works at salinity levels above 40 g(.)l[superscript(-1)]. They have been extensively studied due to their high monetary value as food for larval fish in aquaculture and their unique reproductive strategies. Brine shrimp occur as either bisexual species or as parthenogenetic populations. Despite published reviews of their world-wide distribution little is known about their occurrence in Africa. This review adds new information about 70 African Artemia sites and lists 26 potential sites and their coordinates. Sixteen sites in Southern Africa and Namibia were visited during a collecting trip, and new information on the reproductive mode of nine of these sites is given. Several South African populations exhibit bisexual reproduction. In Namibia there are two parthenogenetic populations (Walvis Bay and Swartkops) and an additional bisexual population (Hentie's Bay). A mixed population (bisexual and parthenogenetic reproduction at the same site) was found at Coega, South Africa.
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- Date Issued: 2006
Sand stress as a non-determinant of habitat segregation of indigenous (Perna perna) and invasive (Mytilus galloprovincialis) mussels in South Africa
- Authors: Zardi, Gerardo I , Nicastro, Katy R , Porri, Francesca , McQuaid, Christopher D
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6946 , http://hdl.handle.net/10962/d1011974
- Description: Periodical sand inundation influences diversity and distribution of intertidal species throughout the world. This study investigates the effect of sand stress on survival and on habitat segregation of the two dominant mussel species living in South Africa, the invasive Mytilus galloprovincialis and the indigenous Perna perna. P. perna occupies a lower intertidal zone which, monthly surveys over 1.5 years showed, is covered by sand for longer periods than the higher M. galloprovincialis zone. Despite this, when buried under sand, P. perna mortality rates were significantly higher than those of M. galloprovincialis in both laboratory and in field experiments. Under anoxic condition, P. perna mortality rates were still significantly higher than those for M. galloprovincialis, but both species died later than when exposed to sand burial, underlining the importance of the physical action of sand on mussel internal organs. When buried, both species accumulate sediments within the shell valves while still alive, but the quantities are much greater for P. perna. This suggests that P. perna gills are more severely damaged by sand abrasion and could explain its higher mortality rates. M. galloprovincialis has longer labial palps than P. perna, indicating a higher particle sorting ability and consequently explaining its lower mortality rates when exposed to sand in suspension. Habitat segregation is often explained by physiological tolerances, but in this case, such explanations fail. Although sand stress strongly affects the survival of the two species, it does not explain their vertical zonation. Contrary to our expectations, the species that is less well adapted to cope with sand stress maintains dominance in a habitat where such stress is high.
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- Date Issued: 2006
Seeing the wood for the trees: the role of woody resources for the construction of gender specific household cultural artefacts in non-traditional communities in the Eastern Cape, South Africa
- Authors: Cocks, Michelle L , Bangay, Lindsey , Wiersum, K Freerk , Dold, Anthony P
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6823 , http://hdl.handle.net/10962/d1003830
- Description: There is a growing wealth of data capturing the direct-use values of the environment and recognition of forests and wild resources as representing ‘‘the poor man’s overcoat’’. This focus has however resulted in an emphasis on the utilitarian values of wild resources for rural livelihoods and has for the most part overlooked their cultural values. In tangent to these developments within the field of anthropology there has been increased attention directed towards the relationship between biodiversity and human diversity over the past decade. This has resulted in the recognition of what the Declaration of Belem calls an ‘inextricable link’ between biological and cultural diversity. The term bio-cultural diversity has been introduced as a concept denoting this link. Consequently there is a need for more elaborate assessments of the various ways in which different groups of people find value in biodiversity. The aim of this paper is to demonstrate the cultural significance of wild harvested plant resources for the maintenance of two gender specific cultural artefacts for amaXhosa people in South Africa, to assess the persistence of these practices in rapidly modernizing communities. We demonstrate the endurance of these ancient cultural artefacts in present-day peri-urban communities and suggest that they point to the need for improved understanding of the significance of bio-cultural diversity. The findings of the study should not be interpreted as illustrating stagnation in the traditional past, but rather as pointing at the need for improved understanding of the significance of bio-cultural diversity in a dynamic sense.
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- Date Issued: 2006