Browsing Faculty of Natural Sciences by Issue Date
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Gibbons, Mark J.; Stuart, V; Verheye, H M (NISC and Taylor & Francis, 1992)[more][less]
Abstract: Carnivorous zooplankton in the Benguela system have tended to be ignored by all but early taxonomists and a handful of recent researchers. An attempt is made here to address the importance of carnivores in this system but, because the database is poor, it was necessary to apply material from outside the region. The taxa covered include ctenophores, cnidarians (Scyphozoa and Hydrozoa, including Siphonophora), chaetognaths and hyperiid amphipods as well as such minor groups as pelagic gastropods and decapods. Most groups of carnivores within the Benguela are represented by only one or two "common" species. These tend to be epiplanktonic and generally concentrated inshore of the shelf-break, where their distributions are influenced by changes in local hydrography. Their densities frequently exceed those of herbivores. The dominant carnivores share a number of attributes: wide-ranging diets, high assimilation and growth efficiencies and mostly a Type I functional response to food concentration. They fall into two categories. The first is the gelatinous species, which have short lifespans and exhibit rapid growth and often massive reproductive response to high concentrations of food. They are patchily distributed and some appear to have behavioural traits that enable them to stay within localized patches of prey on which they may be dependent because of high metabolic costs. In the second category are crustacean predators and chaetognaths which have slower response times to the food environment but may have longer lifespans, lower daily maintenance needs and an ability to store lipids. They are less dependent on high densities of food organisms and can survive throughout winter, when gelatinous predators are rare. The effect of predation on abundance of copepods is estimated on the basis of both published and unpublished data. Should swarms of predators coincide with a critical gateway of zooplankton or larvae, then there may be total depletion. This applies especially to the nearshore zone of the West Coast and to semi-enclosed bays. The role of carnivorous zooplankton in the diets of commercially important fish species is stressed, but their importance in the regeneration of nutrients may be insignificant. URI: http://hdl.handle.net/10566/305 Files in this item: 1
GibbonsTrophicEcology1992.pdf (1.199Mb) -
Barange, M; Macpherson, E; Gibbons, Mark J. (NISC and Taylor & Francis, 1994)[more][less]
Abstract: Information on vertical and horizontal distribution patterns, abundance and morphology of the decapod Pasiphaea semispinosa in the Benguela upwelling system is presented. P. semispinosa is the dominant pelagic decapod in the system, occurring between 19 and 32°S along the mid and inner shelf in concentrations of 10-100•m-2• Although it is more abundant during abated than during active upwelling in the northern Benguela, it would appear to be equally abundant during both upwelling scenarios in the southern Benguela. In the southern Benguela, reproductive females are present during winter and juveniles dominate during active upwelling, but juveniles appear to be more common during abated upwelling in the northern Benguela. The estimates of abundance of P. semispinosa presented in this study are subject to sampling biases attributable to their vertical migratory behaviour and net avoidance capabilities. URI: http://hdl.handle.net/10566/307 Files in this item: 1
GibbonsPasiphaea1994.pdf (692.3Kb) -
Gibbons, Mark J.; Stuart, V (NISC and Taylor & Francis, 1994)[more][less]
Abstract: The feeding biology and the vertical migration of Sagitta friderici were examined over 24 h at two stations in the southern Benguela during spring (October) 1987. Together with studies conducted during summer (February 1991) and winter (May 1984), they serve to allow valuable generalizations of the biology and ecology of this abundant chaetognath. Populations migrate vertically and feed nocturnally, although the timing and the extent of migration vary between studies. S.friderici exhibits ontogenetic layering and the cross-shelf distribution of maturity stages differs, suggesting that it is able to take advantage of cross-shelf water movement in order to maintain populations in the nearshore waters of the West Coast. S.friderici prey almost exclusively on copepodg (cannibalism is rare), and there is a positive relationship between the lengths of predator and prey that is influenced by the size structure of the prey environment. This casts doubt on the validity of a chaetognath species-specific relationship between predator and prey size. S. friderici selects its prey on the basis of size, and not species. Daily ration is related linearly to prey density, so reflecting the low density of prey and providing support for theoretical predictions regarding ingestion rates under oceanic conditions. The impact of S. friderici predation on the copepod assemblage is generally less than 3% of the standing stock, although it could be much higher under conditions of low copepod biomass and poor secondary production. URI: http://hdl.handle.net/10566/306 Files in this item: 1
GibbonsFeeding1994.pdf (866.4Kb) -
Gibbons, Mark J. (NISC (Pty) Ltd and Taylor& Francis, 1995)[more][less]
Abstract: A total of 24 species of euphausiid was collected during a survey along the South African south coast during January 1992. Communities over the Agulhas Bank were of low diversity and abundance and were dominated by Nycliphanes capensis. Those at the shelf-edge were of high diversity and abundance and were dominated by Euphausia recurI'll and Thysalloessa gregaria. Such high diversity may be maintained by vertical scgregation at night. Few species displayed obvious diel vertical migration, although N. capen sis may be able to maintain itself on the shelf by means of this behaviour. E. recurl'Cl appeared to feed on phytoplankton throughout the water column at night, reflecting the distribution of food. URI: http://hdl.handle.net/10566/374 Files in this item: 1
GibbonsEuphausiid1995.pdf (584.2Kb) -
Tucker, William D.; Keats, Derek (Telkom, 1998)[more][less]
Abstract: Grafting an ATM network onto an existing Ethernet network is a non-trivial exercise in network configuration. The process of mating ATM technology to an Ethernet network without tampering the underlying backbone and network configuration gives rise to a variety of networking issues including addressing, compatibility, security, efficiency, administrative effort, and scalability. Examples of actual situations serve to illustrate these issues. We have designed several scenarios to tackle the topological problems of an ATM graft. A dual IP approach works but suffers from a lack of scalability. We expect an edge routing solution, with subnetting, will be the most elegant and scalable. URI: http://hdl.handle.net/10566/448 Files in this item: 1
TuckerKeatsATM1998.pdf (612.2Kb) -
Jeffries, Michael; Tucker, William D. (Telkom, 2000)[more][less]
Abstract: Current VoIP signaling protocols are interoperable with the PSTN SS7 via H.323-to-SS7 or SIP-to-SS7 gateways. As we move toward the Next Generation Network, the PSTN falls away and we work toward carrier-grade VoIP interoperability between H.323, SIP, and other future VoIP signaling protocols. This paper present a Work in Progress to design and implement a solution based on the Internet Protocol itself. URI: http://hdl.handle.net/10566/425 Files in this item: 1
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Naidoo, Vaughn; Tucker, William D. (Telkom, 2000)[more][less]
Abstract: With QoS available on IP-dominant NGNs, Policy-based Network Management (PBNM) is an effective mechanism for managing services as opposed to actual devices. IP is ubiquitous, and any NGN must contend with legacy devices that do not support emerging PBNM protocols. This Work in Progress uses the common Internet notion of a proxy to enforce policies on legacy equipment. We use VoIP as a mechanism to test the validity of our intended solution. URI: http://hdl.handle.net/10566/449 Files in this item: 1
NaidooTuckerVoIP2000.pdf (53.16Kb) -
Gibbons, Mark J.; Sulaiman, Amina; Hissman, K.; Schauer, J.; Wickens, Patti; McMillan, Ian (NISC and Taylor & Francis, 2000)[more][less]
Abstract: A semi-quantitative assessment is made of the animals observed in archived videotapes taken from the research submersible Jago, during diamond mining and exploratory surveys off the mouth of the Orange River on the west coast of southern Africa (28° IS'S, 29°11 'S) in November 1996. The seabed environment is described and nekton associations with substratum features are identified. The area is characterized by heterogeneity to its physical and biological struture. The variety of observed nekton is low, and communities are dominated by goby Sufflogobius bibarbatus, juvenile hake Merluccius spp. and cuttlefish Sepia spp. (on soft substrata), as well as false jacopever Sebastes capen sis and kingklip Genypterus capensis (on rocky substrata). URI: http://hdl.handle.net/10566/419 Files in this item: 1
GibbonsDemersalNekton2000.pdf (501.8Kb) -
Naidoo, Vaughn; Tucker, William D. (Telkom, 2001)[more][less]
Abstract: Next Generation Networks use policy-based network management and QoS protocols to provide voice services on IP networks. Large numbers of older equipment still push IP packets. We present several solutions that include legacy equipment into a PBNM and QoS system. A static design uses traffic shaping at the legacy edge. A dynamic solution uses a Quasi-PEP implemented over RSVP and COPS. Preliminary test results are presented for the static solution. Collected data shows that the solution decreases packet loss on the legacy side. URI: http://hdl.handle.net/10566/519 Files in this item: 1
NaidooTuckerNextGenNetworks2001.pdf (59.43Kb) -
Glaser, Meryl; Tucker, William D. (Telkom, 2001)[more][less]
Abstract: A Teldem provides text-based telephony services to the deaf. Despite an array of text-based communications mechanisms on the web, the Teldem is the only means of synchronous telecommunication available to a deaf person. We examine a human-assisted relay that provides a bridge between the deaf and the hearing, and then propose several additional bridges. These bridges take advantage of both standard and cutting edge technologies. We present each bridge's impact on the deaf with respect to synchrony, connectivity, independence, and the Digital Divide. It is hoped that by deploying trials for each bridge, we can eventually provide the deaf with equal access. URI: http://hdl.handle.net/10566/613 Files in this item: 1
GlaserTucker-SATNAC2001.pdf (146.9Kb) -
Brierley, Andrew S.; Axelson, Bjorn Erik; Buecher, Emmanuelle; Sparks, Conrad A.J.; Boyer, Helen; Gibbons, Mark J. (Inter-Research, 2001)[more][less]
Abstract: Multi-frequency acoustic data (18, 38 and 120 kHz) were collected in conjunction with pelagic trawl sampling for gelatinous macrozooplankton during a cruise to the Namibian Benguela in September 1999. Sampling focused specifically on the scyphozoan Chrysaora hysoscella and the hydrozoan Aequorea aequorea, both of which occur in large numbers, are probably of major ecological importance, and physically hamper pelagic fishing and diamond extraction activities. C. hysoscella was detected predominantly at an inshore station and A. aequorea was found in greatest abundance further offshore in deeper water. Echo-sounder observations were linked directly to net catches, and relationships between catch density (number of individuals m–3) and nautical area scattering coefficients (sA) at each frequency were determined for both species in order to estimate target strength (TS) using the comparison method. TS for C. hysoscella (mean umbrella diameter 26.8 cm) was –51.5 dB at 18 kHz, –46.6 dB at 38 kHz and –50.1 dB at 120 kHz; for A. aequorea (mean central umbrella diameter 7.4 cm) TS was –68.1 dB at 18 kHz, –66.3 dB at 38 kHz and –68.5 dB at 120 kHz. These TS values compared favourably with previously published estimates for related species. Jellyfish were caught at high numerical densities (maxima 3 C. hysoscella per 100 m3, 168 A. aequorea per 100 m3). These high densities, combined with the not unsubstantial TS at frequencies used for fisheries surveys, imply that jellyfish could potentially bias acoustic estimates of fish abundance. We suggest a simple multifrequency approach that could be used to discriminate between echoes from jellyfish and some commercially important pelagic fish in the northern Benguela ecosystem. URI: http://hdl.handle.net/10566/246 Files in this item: 1
BrierleyAcoustic 2001.pdf (799.2Kb) -
Jeffries, Michael; Tucker, William D. (Telkom, 2001)[more][less]
Abstract: The Session Initiation Protocol and H.323 dominate the Voice over IP world. These signaling protocols are responsible for call setup and call tear down by IP telephony solutions. This project analyses and discusses the underlying H.323 and SIP interoperability issues and intends to build a scalable solution for the interoperability of these protocols. The gateway maps the call sequences between the two protocols. A test scenario establishes a barrage of call setup and tear down requests to test the scalability of any H.323/SIP interoperability solution. URI: http://hdl.handle.net/10566/465 Files in this item: 1
JeffriesTuckerSIP2001.pdf (65.32Kb) -
Wilkinson, Dianne E.; Jaenicke, Thomas; Cowan, Donald A. (Kluwer Academic Publishers, 2002)[more][less]
Abstract: An efficient and simple method for constructing an environmental library using mechanically sheared DNA obtained directly from geothermal sediments is presented. The method is based on blunt-end modification of DNA fragments followed by 3' -adenylation using Vent DNA polymerase and Taq DNA polymerase, respectively. The prepared DNA fragments are then ligated into a TA cloning vector and used in the transformation of Escherichia coli. This method has been successfully applied to the cloning of ORFs derived from uncultivated prokaryotes present in geothermal sediment. URI: http://hdl.handle.net/10566/161 Files in this item: 1
WilkinsonEfficientMolecular2002.pdf (754.4Kb) -
Burton, Stephanie; Cowan, Donald A.; Woodley, John M. (Nature Publishing Group, 2002)[more][less]
Abstract: While the use of enzymes as biocatalysts to assist in the industrial manufacture of fine chemicals and pharmaceuticals has enormous potential, application is frequently limited by evolution-led catalyst traits. The advent of designer biocatalysts, produced by informed selection and mutation through recombinant DNA technology, enables production of process-compatible enzymes. However, to fully realize the potential of designer enzymes in industrial applications, it will be necessary to tailor catalyst properties so that they are optimal not only for a given reaction but also in the context of the industrial process in which the enzyme is applied. URI: http://hdl.handle.net/10566/150 Files in this item: 1
BurtonCowanWoodley2002.pdf (768Kb) -
Penton, Jason; Tucker, William D.; Glaser, Meryl (Telkom, 2002)[more][less]
Abstract: We have developed a prototype bridge that relays text and speech between Teldem, a text telephone for the Deaf, and a standard telephone or H.323 endpoint. Telgo323 uses modified H.323 media gateways and open source Text to Speech and Speech to Text software. The approach allows for easy integration of new tools as the technologies mature. This paper presents the design of the implementation prototype, discusses Teldem tone decoding, and suggests directions for future work. The Telgo323 provides evidence that an automated relay bridge is imminently viable for the Deaf Community, and further demonstrates an attractive approach for building bridges over the Digital Divide. URI: http://hdl.handle.net/10566/612 Files in this item: 1
PentonTuckerGlaser-SATNAC2002.pdf (99.60Kb) -
Lewis, John; Tucker, William D.; Blake, Edwin H. (Telkom, 2002)[more][less]
Abstract: Users and computing equipment have varying capabilities that include the abilities to exchange text and audio, engage in high bandwidth communication, etc. As the technological options increase, e ective communication between the di erent media has be able to bridge across these options: the bridges have to take into account network quality, end-user equipment capabilities as well as user preferences and capabilities. Our research proposes a Soft- Bridge, an abstracted communications platform for the construction of applications across disparate capabilities found in various Digital Divides. We outline the architecture and the requirements that the SoftBridge has to ful ll. An approach and some initial work is described. URI: http://hdl.handle.net/10566/606 Files in this item: 1
LewisTuckerBlake-SATNAC2002.pdf (126.3Kb) -
Cowan, Donald A.; Mamais, A.; Russell, Nick A.; Sheppard, Devon M. (Springer Verlag, 2002)[more][less]
Abstract: We have applied bioluminescent ATP detection methods to microbial enumeration in Antarctic Dry Valley mineral soils, and validated our ATP data by two independent methods. We have demonstrated that ATP measurement is a valid means of determining microbial biomass in such sites, and that the desiccated surface mineral soils of the Antarctic Dry Valleys contain cell numbers over four orders of magnitude higher than previously suggested URI: http://hdl.handle.net/10566/162 Files in this item: 1
CowanAntacticDryValleys2002.pdf (475.3Kb) -
Bustard, Mark T.; Whiting, Samantha; Cowan, Donald A.; Wright, Phillip C. (Springer Verlag, 2002)[more][less]
Abstract: The aerobic biodegradation of high-concentration, to 24 g l –1 , 2-propanol (IPA) by a thermophilic isolate ST3, identified as Bacillus pallidus , was successfully carried out for the first time. This solvent-tolerant B. pallidus utilized IPA as the sole carbon source within a minimal salts medium. Cultivation was carried out in 100-ml shake flasks at 60°C and compared with cultivation within a 1-l stirred tank reactor (STR). Specific growth rate () was about 0.2 h–1 for both systems, with a maximum cell density of 2.4 x 10 8 cells ml–1 obtained with STR cultivation. During exponential growth and stationary phase, IPA biodegradation rates were found to be 0.14 and 0.02 g l –1h–1, respectively, in shake-flask experiments, whereas corresponding values of 0.09 and 0.018 g l –1h–1 were achievable in the STR. Generation of acetone, the major intermediate in aerobic IPA biodegradation, was also monitored as an indicator of microbial IPA utilization. Acetone levels reached a maximum of 2.2–2.3 g l–1 after 72 and 58 h for 100-ml and 1-l systems, respectively. Both IPA and acetone were completely removed from the medium following 160 and 175 h, respectively, during STR growth, although this was not demonstrated within shake-flask reactions. Growth of B. pallidus on acetone or IPA alone demonstrated that the maximum growth rate () obtainable was 0.247 h–1 at 4 g l–1 acetone and 0.202 h–1 at 8 g l–1 IPA within shake-flask cultivation. These results indicate the potential of the solvent-tolerant thermophile B. pallidus ST3 in the bioremediation of hot solvent-containing industrial waste streams. URI: http://hdl.handle.net/10566/154 Files in this item: 1
BustardBiodegradation2002.pdf (453.9Kb) -
Buecher, Emmanuelle; Gibbons, Mark J. (NISC (Pty) Ltd and Taylor& Francis, 2003)[more][less]
Abstract: Diel vertical migration (DVM) of six common species of hydromedusae was investigated during two drogue studies conducted in St Helena Bay on the west coast of South Africa in February 1995. Clytia spp., Obelia spp. and Bougainvillia macloviana, were largely confined to surface waters and did not appear to display any DVM. By contrast, Leuckartiara octona and Euphysa aurata displayed clear DVM and, like Proboscidactyla menoni, were found at greater depths than the other species. The depth distribution and amplitude of migration varied between surveys for most species, so definitive interpretations of patterns could not be made. URI: http://hdl.handle.net/10566/377 Files in this item: 1
BuecherDielVerticalMigration2003.pdf (121.3Kb) -
Baker, Gillian; Ah Tow, Lemese; Cowan, Donald A. (Elsevier, 2003)[more][less]
Abstract: PCR-based technologies are widely employed for the detection of specific microorganisms, and may be applied to the identification of non-indigenous microorganisms in ‘pristine’ environments. For ‘pristine’ environments such as those found on the Antarctic continent, the application of these methods to the assessment of environmental contamination from human activities must be treated with caution. Issues such as the possibility of non-human dispersal of organisms, stability and survival of non-indigenous organisms in vivo, the sensitivity, reproducibility and specificity of the PCR process (and particularly primer design) and the sampling regime employed must all be considered in detail. We conclude that despite these limitations, PCR and related technologies offer enormous scope for assessment of both natural and non-indigenous microbial distributions. URI: http://hdl.handle.net/10566/149 Files in this item: 1
BakerPCRdetection2003.pdf (391.8Kb)
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