Fish utilization of surf-zones. Are they changing? A case study of the sheltered, warm-temperate King’s Beach
- Rishworth, Gavin M, Strydom, Nadine A, Potts, Warren M
- Authors: Rishworth, Gavin M , Strydom, Nadine A , Potts, Warren M
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124504 , vital:35619 , https://doi.org/10.1080/15627020.2014.11407616
- Description: Surf-zone fish communities and their shifts over time are generally poorly understood. The aim of this study was to compare the current surf-zone fish assemblage at King’s Beach, South Africa, to a similar study conducted three decades ago, before the collapse of many exploited shore fishes in the region. Beach seine nets (mesh sizes of 10 and 50 mm) were used to target juvenile and adult fishes bimonthly from February to August 2011 over the high tide around sunset. A total of 14 species were recorded in both the 30mand 100mseine nets. The catch in these seine nets was dominated by Pomadasys olivaceus and Liza richardsonii, and this was significantly different to three decades ago, when P. olivaceus, Sarpa salpa and Diplodus capensis dominated the catch. Important linefish species belonging to the Sparidae and Sciaenidae families were significantly smaller and less abundant in this study. Two sparids, S. salpa and Lithognathus mormyrus, which made a large contribution to the surf-zone catch three decades ago were absent during this study. Reasons for the significant shifts in the surf-zone fish community, including overexploitation of the linefish and potential habitat modification, are discussed.
- Full Text:
- Date Issued: 2015
- Authors: Rishworth, Gavin M , Strydom, Nadine A , Potts, Warren M
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124504 , vital:35619 , https://doi.org/10.1080/15627020.2014.11407616
- Description: Surf-zone fish communities and their shifts over time are generally poorly understood. The aim of this study was to compare the current surf-zone fish assemblage at King’s Beach, South Africa, to a similar study conducted three decades ago, before the collapse of many exploited shore fishes in the region. Beach seine nets (mesh sizes of 10 and 50 mm) were used to target juvenile and adult fishes bimonthly from February to August 2011 over the high tide around sunset. A total of 14 species were recorded in both the 30mand 100mseine nets. The catch in these seine nets was dominated by Pomadasys olivaceus and Liza richardsonii, and this was significantly different to three decades ago, when P. olivaceus, Sarpa salpa and Diplodus capensis dominated the catch. Important linefish species belonging to the Sparidae and Sciaenidae families were significantly smaller and less abundant in this study. Two sparids, S. salpa and Lithognathus mormyrus, which made a large contribution to the surf-zone catch three decades ago were absent during this study. Reasons for the significant shifts in the surf-zone fish community, including overexploitation of the linefish and potential habitat modification, are discussed.
- Full Text:
- Date Issued: 2015
Micro-structures, mineralogy, and chemistry of peritidal tufa stromatolites along the Eastern Cape coast
- Edwards, Mark Joseph Kalahari, Rishworth, Gavin M
- Authors: Edwards, Mark Joseph Kalahari , Rishworth, Gavin M
- Date: 2019
- Subjects: Mineralogy -- Analysis -- South Africa , Environmental forensics Environmental chemistry Stromatolites
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/39896 , vital:35503
- Description: Peritidal tufa microbialites occurring along the coast near Port Elizabeth, South Africa have been investigated from multiple disciplines and are found to be similar to supratidal tufa deposits in South West Australia. Studies have been conducted on the biological factors, geomorphology, ecosystems, and associated water chemistry. However, to date no mineralogical, micro-fabric, or geochemical analyses have been reported on these tufa deposits. This work, carried out at a previously well-studied area, provides the first study of this kind on the tufa. Chapter 1 is a mineralogical and micro-fabric analysis of the tufa deposits near Port Elizabeth for the purpose of classification and contextualisation. Chapter 2 provides the first geochemical study of these peritidal microbialites. X-Ray diffraction (XRD) investigations reveal dominance of low-Mg calcite in the mineral make-up of the tufa. A micro-structure analysis via thin section exposes a number of fabrics, suggesting various micro-facies: phytoherm boundstone (layered), phytoherm framestone (non-layered), lithoclast, and minor metazoan tufa. Scanning electron microscopy (SEM) images show micro- to nano- scale variation in calcite grains and epitaxial forms of needlefibre calcite (NFC). The elemental composition of the tufa deposits were examined by X-ray fluorescence (XRF), Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS), and Scanning Electron Microscopy / Energy Dispersive X-Ray Spectroscopy (SEM/EDS). XRF and LA-ICP-MS were used to analyse the bulk rock chemistry while SEM/EDS was used to scrutinize specific areas within the tufa. These observations suggest the deposits are better classified as tufa microbialites (rather than exclusively “stromatolites”) and outline similarities and disparities to the micro-fabrics of supratidal tufa deposits in South West Australia, and Cape Morgan, South Africa. Here the Port Elizabeth tufa is shown to be similar, in terms of the dominant elements (O, Ca and to a lesser extent, Mg and Sr), to the Australian deposits despite subtle dissimilarities in water chemistry. Increasing trends toward more marine tufa for many elements are also shown here and can be explained by the interaction with increased amounts of sedimentary products and/or interactions with more saline water that contains a higher TDS (Total Dissolved Salts). This is also the first study to report needle-fibre calcite formation in stromatolites and the first to geochemically analyse modern peritidal microbialites.
- Full Text:
- Date Issued: 2019
- Authors: Edwards, Mark Joseph Kalahari , Rishworth, Gavin M
- Date: 2019
- Subjects: Mineralogy -- Analysis -- South Africa , Environmental forensics Environmental chemistry Stromatolites
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/39896 , vital:35503
- Description: Peritidal tufa microbialites occurring along the coast near Port Elizabeth, South Africa have been investigated from multiple disciplines and are found to be similar to supratidal tufa deposits in South West Australia. Studies have been conducted on the biological factors, geomorphology, ecosystems, and associated water chemistry. However, to date no mineralogical, micro-fabric, or geochemical analyses have been reported on these tufa deposits. This work, carried out at a previously well-studied area, provides the first study of this kind on the tufa. Chapter 1 is a mineralogical and micro-fabric analysis of the tufa deposits near Port Elizabeth for the purpose of classification and contextualisation. Chapter 2 provides the first geochemical study of these peritidal microbialites. X-Ray diffraction (XRD) investigations reveal dominance of low-Mg calcite in the mineral make-up of the tufa. A micro-structure analysis via thin section exposes a number of fabrics, suggesting various micro-facies: phytoherm boundstone (layered), phytoherm framestone (non-layered), lithoclast, and minor metazoan tufa. Scanning electron microscopy (SEM) images show micro- to nano- scale variation in calcite grains and epitaxial forms of needlefibre calcite (NFC). The elemental composition of the tufa deposits were examined by X-ray fluorescence (XRF), Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS), and Scanning Electron Microscopy / Energy Dispersive X-Ray Spectroscopy (SEM/EDS). XRF and LA-ICP-MS were used to analyse the bulk rock chemistry while SEM/EDS was used to scrutinize specific areas within the tufa. These observations suggest the deposits are better classified as tufa microbialites (rather than exclusively “stromatolites”) and outline similarities and disparities to the micro-fabrics of supratidal tufa deposits in South West Australia, and Cape Morgan, South Africa. Here the Port Elizabeth tufa is shown to be similar, in terms of the dominant elements (O, Ca and to a lesser extent, Mg and Sr), to the Australian deposits despite subtle dissimilarities in water chemistry. Increasing trends toward more marine tufa for many elements are also shown here and can be explained by the interaction with increased amounts of sedimentary products and/or interactions with more saline water that contains a higher TDS (Total Dissolved Salts). This is also the first study to report needle-fibre calcite formation in stromatolites and the first to geochemically analyse modern peritidal microbialites.
- Full Text:
- Date Issued: 2019
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