Larval assemblages in intertidal habitats: the use of artificial and natural microhabitats
- Authors: Reddy, Seshnee
- Date: 2022-10-14
- Subjects: Larvae Habitat , Niche (Ecology) , Intertidal ecology South Africa Eastern Cape , Light trap , DNA barcoding , Artificial habitat , Larvae Effect of human beings on South Africa Eastern Cape , Urbanization South Africa Eastern Cape
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/364992 , vital:65668
- Description: Coastal habitats, and more specifically, intertidal habitats, host a unique range of biodiversity and are key areas for many fish and invertebrate species across one or more of their life stages. This is due to the provision of microhabitats which offer an escape from harsh environmental stressors and predation as well as increased food supply, hence increasing chances of survival. Due to the growing human population however, coastal habitats are being replaced by artificial structures (jetties, seawalls, piers, breakwaters) which partially or heavily fragment the natural environment through urbanisation-related expansion processes. These coastal infrastructures also have different physical properties from the natural environment and therefore tend to support different biological assemblages and can potentially alter the existing biodiversity and its functionality. The overall aim of this project was therefore to evaluate the use of artificial and natural intertidal microhabitats by fish and invertebrate larvae along the South African, Eastern Cape coastline. As independent case studies, fieldwork was conducted at an urban (Port Alfred Marina) and rocky shore (Kenton-on-Sea) site. Within each of these study sites, two replicated sheltered subsites were selected, which represented microhabitats. Samples were collected from these replicated microhabitats from September 2019 to February 2020 using light traps which targeted phototactic larval species, as well as a portable pump, for photo-neutral/negative taxa. All samples were preserved onsite in 99% ethanol and specimens were later counted and identified in the laboratory to the lowest possible taxonomic level using a stereomicroscope. Additionally, DNA barcoding was conducted on selected larval taxa for verification of morphological identification as well as contributing to the field of larval taxonomy through development of public database records. The barcoding technique was effective in positively identifying 96% and 58% of fish and invertebrate larvae sampled, respectively (overall identification success of 86%), to either family, genus or species level. Results of microhabitat use indicate higher larval abundances associated with artificial structures as compared to natural structures, with significant differences between the selected microhabitats within the rocky shores and the marina respectively, across months. High numbers of several early stage taxa were observed within the selected microhabitats in the marina, with Pinnotheres sp. (zoea) (Family: Pinnotheridae) being the most abundant invertebrate larval taxon collected at the artificial microhabitats of jetties and vertical walls. Fish larvae of Omobranchus woodi (preflexion) and Etrumeus whiteheadi (postflexion) were the most dominant at the selected artificial microhabitats within the marina. The DNA barcoding tool used in the current study to verify morphological identification proved to be instrumental in the accuracy of the reliable data collection of the early life stages present in these habitats. These results suggest that artificial structures may provide refugia for the vulnerable very early life stages of species and, in turn, play a potential facilitative role in reproductive and population connectivity which could result in replenishment of natural populations. It is therefore possible that these urban habitats could be considered as hubs for maintenance of coastal biodiversity. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-10-14
- Authors: Reddy, Seshnee
- Date: 2022-10-14
- Subjects: Larvae Habitat , Niche (Ecology) , Intertidal ecology South Africa Eastern Cape , Light trap , DNA barcoding , Artificial habitat , Larvae Effect of human beings on South Africa Eastern Cape , Urbanization South Africa Eastern Cape
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/364992 , vital:65668
- Description: Coastal habitats, and more specifically, intertidal habitats, host a unique range of biodiversity and are key areas for many fish and invertebrate species across one or more of their life stages. This is due to the provision of microhabitats which offer an escape from harsh environmental stressors and predation as well as increased food supply, hence increasing chances of survival. Due to the growing human population however, coastal habitats are being replaced by artificial structures (jetties, seawalls, piers, breakwaters) which partially or heavily fragment the natural environment through urbanisation-related expansion processes. These coastal infrastructures also have different physical properties from the natural environment and therefore tend to support different biological assemblages and can potentially alter the existing biodiversity and its functionality. The overall aim of this project was therefore to evaluate the use of artificial and natural intertidal microhabitats by fish and invertebrate larvae along the South African, Eastern Cape coastline. As independent case studies, fieldwork was conducted at an urban (Port Alfred Marina) and rocky shore (Kenton-on-Sea) site. Within each of these study sites, two replicated sheltered subsites were selected, which represented microhabitats. Samples were collected from these replicated microhabitats from September 2019 to February 2020 using light traps which targeted phototactic larval species, as well as a portable pump, for photo-neutral/negative taxa. All samples were preserved onsite in 99% ethanol and specimens were later counted and identified in the laboratory to the lowest possible taxonomic level using a stereomicroscope. Additionally, DNA barcoding was conducted on selected larval taxa for verification of morphological identification as well as contributing to the field of larval taxonomy through development of public database records. The barcoding technique was effective in positively identifying 96% and 58% of fish and invertebrate larvae sampled, respectively (overall identification success of 86%), to either family, genus or species level. Results of microhabitat use indicate higher larval abundances associated with artificial structures as compared to natural structures, with significant differences between the selected microhabitats within the rocky shores and the marina respectively, across months. High numbers of several early stage taxa were observed within the selected microhabitats in the marina, with Pinnotheres sp. (zoea) (Family: Pinnotheridae) being the most abundant invertebrate larval taxon collected at the artificial microhabitats of jetties and vertical walls. Fish larvae of Omobranchus woodi (preflexion) and Etrumeus whiteheadi (postflexion) were the most dominant at the selected artificial microhabitats within the marina. The DNA barcoding tool used in the current study to verify morphological identification proved to be instrumental in the accuracy of the reliable data collection of the early life stages present in these habitats. These results suggest that artificial structures may provide refugia for the vulnerable very early life stages of species and, in turn, play a potential facilitative role in reproductive and population connectivity which could result in replenishment of natural populations. It is therefore possible that these urban habitats could be considered as hubs for maintenance of coastal biodiversity. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-10-14
Movement patterns of the iconic giant kingfish Caranx ignobilis from Southern Africa
- Authors: Dixon, Russell Bruce
- Date: 2022-10-14
- Subjects: Caranx Africa, Southern , Caranx Migration , Underwater acoustic telemetry , Carangidae Africa, Southern , Fish tagging
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/362797 , vital:65363
- Description: Giant kingfish Caranx ignobilis, the largest species in the family Carangidae, are global icons as apex marine predators. They are widespread in tropical to subtropical regions globally, where they are of high importance to ecosystems and fisheries. During summer, adults aggregate for spawning, making them vulnerable to overfishing. The world’s largest recorded C. ignobilis aggregation is in southern Mozambique. Some of these aggregating individuals (an unknown proportion) have been recorded passing into South African waters. Furthermore, a unique aggregation of adult C. ignobilis in South Africa’s Mtentu Estuary has attracted global attention but remains unexplained, hence warranting investigation. Research on C. ignobilis globally has shown relatively small home ranges. Research in southern Africa has been limited and inconclusive. Thus, the broad aim of this study is to describe the movement patterns of C. ignobilis from southern Africa. Long-term (36 years) mark-recapture data from the Oceanographic Research Institute’s Co-operative Fish Tagging Project, comprising 3 729 tagged C. ignobilis and 144 recaptures, were analysed. While 74% of recaptures were recorded < 1 km from the tagging location, long-distance movements of up to 419 km were also recorded (mean = 15 km). Although adults moved significantly (p < 0.01) greater distances than juveniles, they also displayed high levels of site fidelity. Seasonal trends included evidence of a summer migration; however, there was still considerable uncertainty regarding exact movements. Therefore, 43 C. ignobilis were acoustically tagged and subsequently monitored along the east coast for over five years with the Acoustic Tracking Array Platform’s passive receiver array. All acoustically tagged adult C. ignobilis migrated to southern Mozambique each year (with minor exceptions), from distances of up to 632 km. When not migrating, South African-based fish showed consistent inter-annual fidelity to individual home ranges. Although coastal home range length (excluding migrations) varied considerably between individuals, even the mean length (92 km) was greater than any previously recorded C. ignobilis home range, globally. In contrast to the southern Mozambique aggregation, the Mtentu Estuary aggregation seems to comprise of individuals showing fidelity to that region. The passive tracking of eight acoustically tagged individuals in the Mtentu Estuary revealed clear trends. Statistical modelling showed that estuarine presence was strongly associated with periods of cold coastal upwelling. Diel movement patterns showed that the utilisation of warm surface waters ~ 4 km upstream during the day was followed by nightly departures to the mouth or sea. Thus, it is likely that this majestic aggregation is for thermal refuge; specifically, for daily re-warming after feeding in cold waters at night. Findings from this study are of global ecological interest and have direct applications for local fisheries management and the development of sustainable eco-tourism. Protecting these vulnerable aggregations is of the utmost importance for the future of this species in southern Africa. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
- Full Text:
- Date Issued: 2022-10-14
- Authors: Dixon, Russell Bruce
- Date: 2022-10-14
- Subjects: Caranx Africa, Southern , Caranx Migration , Underwater acoustic telemetry , Carangidae Africa, Southern , Fish tagging
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/362797 , vital:65363
- Description: Giant kingfish Caranx ignobilis, the largest species in the family Carangidae, are global icons as apex marine predators. They are widespread in tropical to subtropical regions globally, where they are of high importance to ecosystems and fisheries. During summer, adults aggregate for spawning, making them vulnerable to overfishing. The world’s largest recorded C. ignobilis aggregation is in southern Mozambique. Some of these aggregating individuals (an unknown proportion) have been recorded passing into South African waters. Furthermore, a unique aggregation of adult C. ignobilis in South Africa’s Mtentu Estuary has attracted global attention but remains unexplained, hence warranting investigation. Research on C. ignobilis globally has shown relatively small home ranges. Research in southern Africa has been limited and inconclusive. Thus, the broad aim of this study is to describe the movement patterns of C. ignobilis from southern Africa. Long-term (36 years) mark-recapture data from the Oceanographic Research Institute’s Co-operative Fish Tagging Project, comprising 3 729 tagged C. ignobilis and 144 recaptures, were analysed. While 74% of recaptures were recorded < 1 km from the tagging location, long-distance movements of up to 419 km were also recorded (mean = 15 km). Although adults moved significantly (p < 0.01) greater distances than juveniles, they also displayed high levels of site fidelity. Seasonal trends included evidence of a summer migration; however, there was still considerable uncertainty regarding exact movements. Therefore, 43 C. ignobilis were acoustically tagged and subsequently monitored along the east coast for over five years with the Acoustic Tracking Array Platform’s passive receiver array. All acoustically tagged adult C. ignobilis migrated to southern Mozambique each year (with minor exceptions), from distances of up to 632 km. When not migrating, South African-based fish showed consistent inter-annual fidelity to individual home ranges. Although coastal home range length (excluding migrations) varied considerably between individuals, even the mean length (92 km) was greater than any previously recorded C. ignobilis home range, globally. In contrast to the southern Mozambique aggregation, the Mtentu Estuary aggregation seems to comprise of individuals showing fidelity to that region. The passive tracking of eight acoustically tagged individuals in the Mtentu Estuary revealed clear trends. Statistical modelling showed that estuarine presence was strongly associated with periods of cold coastal upwelling. Diel movement patterns showed that the utilisation of warm surface waters ~ 4 km upstream during the day was followed by nightly departures to the mouth or sea. Thus, it is likely that this majestic aggregation is for thermal refuge; specifically, for daily re-warming after feeding in cold waters at night. Findings from this study are of global ecological interest and have direct applications for local fisheries management and the development of sustainable eco-tourism. Protecting these vulnerable aggregations is of the utmost importance for the future of this species in southern Africa. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
- Full Text:
- Date Issued: 2022-10-14
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