Habitat use by Juvenile coastal fish in subtidal vegetated habitats of Algoa Bay;s shallow water seascape
- Authors: Mkhize,Thembani
- Date: 2022-12
- Subjects: Sailing ships -- South Africa -- Algoa Bay --History , Marine fishes -- Algoa Bay -- South Africa , Fish improvement habitat
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/59788 , vital:62429
- Description: Structurally complex habitats such as seagrass, mangroves, and seaweed are important as nurseries in estuaries and nearshore marine environments. While numerous studies have focussed on structurally complex vegetated habitats in estuaries, few studies have focussed on vegetated nursery habitats (particularly seaweed) in coastal areas and their importance. The main aim of this project is to examine the nature of shallow water vegetated habitat (Zostera capensis seagrass and Plocamium corallorhiza macroalga) usage by juvenile fish in the Algoa Bay shallow water seascape (Swartkops Estuary and Flat Rocks nearshore subtidal reef). This aim was achieved by quantifying and comparing complexity of these two habitat-forming species, and the fish assemblages (relative abundance, richness, size structure and behaviour) across the two habitats. To measure and compare complexity of Z. capensis and P. corallorhiza, canopy height, density and leaf/blade width were sampled. In addition to these structural complexity indices, Fractal D (dimensionless complexity indices) was also quantified using Image software. Zostera capensis (1553.3 Indiv/m2 ) had a slightly higher mean density compared to P. corallorhiza (1303.7 Indiv/m2 ) but the difference was not significant. When sites (within each habitat) were compared, density did not show any significant differences between sites. Canopy height of Z. capensis (56.9 cm) was significantly higher compared to P. corallorhiza (16.6 cm), with no significant differences between sites. On the other hand, P. corallorhiza (0.9 cm) blades were significantly wider than Z. capensis (0.2 cm) leaves. Fractal D values followed the same trend as leaf/blade width with, with P. corallorhiza (1.8) having significantly higher Fractal D values than Z. capensis (1.5). The last two indices also had a positive relationship as Fractal D increased with increasing leaf/blade width. These results show that overall P. corallorhiza is more structurally complex than Z. capensis. Calibrated mini stereo underwater remote video systems (mini stereo-RUVs) were optimised in these two studied habitats to ensure they were suitable to measure and identify juvenile fishes. A pilot optimization study found that a minimum of five deployments and a minimum of 45 minutes filming duration is required to study fish assemblages in these two habitats. For comparison of fish assemblages and assessment of habitat use by fish, mini stereo-RUVs were deployed in both habitats (three sites per habitat) and were left to record for 60 minutes for a v total of five sampling occasions in seagrass and seven sampling occasions in macroalga between 7 September 2020 and 9 April 2021. Collected videos were analysed, with relative abundance (MaxN), richness and fish length extracted. Fish behaviour was also analysed and compared between habitats. Mean fish MaxN was slightly higher in Z. capensis (3.4) than in P. corallorhiza (2.9), although this result was not significant. Species diversity was significantly higher in P. corallorhiza as shown by both richness (Z. capensis = 11 and P. corallorhiza = 18) and the Shannon diversity index (Z. capensis = 1.3 and P. corallorhiza = 1.7). Both habitats were dominated by species from the family Sparidae, with six estuary-associated marine species common between the two habitats. Both Z. capensis and P. corallorhiza were dominated by juvenile fish, with more than 70 % of measured fish being juveniles. Fish length was not significantly different in the two habitats. Juvenile fish assemblages were significantly distinct between the two habitats (ANOSIM). In terms of habitat use, fish behaviour analysis showed that fish use both habitats as nurseries. There was no significant difference in fish behaviour in the two habitats and fish behaviours associated with higher levels of habitat use (slow meandering and feeding) were the most common behaviours in both habitats. Although not significant, feeding behaviour (also associated with a high degree of habitat use) was observed more in macroalga than in the seagrass habitat. Although none of the studied complexity indices could be related to abundance, both leaf/blade width and Fractal Dimension showed a positive relationship with the number of species recorded, while canopy height showed a strong negative relationship with the number of species. Overall, this study shows that Plocamium corallorhiza red macroalga in the shallow marine environment may be as important in shallow marine environments as Zostera capensis seagrass in estuaries as nursery habitats for marine fi , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2022
- Full Text:
- Date Issued: 2022-12
Towards defining the tipping point of tolerance to CO2-induced ocean acidification for the growth, development and metabolism of larval dusky kob Argyrosomus japonicus (Pisces: Sciaenidae)
- Authors: Mpopetsi, Pule Peter
- Date: 2019
- Subjects: Argyrosomus japonicus , Argyrosomus , Argyrosomus japonicus -- Larvae , Argyrosomus -- Larvae -- Effect of water acidification on , Argyrosomus japonicus -- Larvae -- Nutrition , Argyrosomus -- Larvae -- Nutrition , Ocean acidification
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/71602 , vital:29924
- Description: Increased CO2 production and the consequent ocean acidification (OA) have been identified as one of the greatest threats to both calcifying and non-calcifying marine organisms. Traditionally, marine fishes, as non-calcifying organisms, were considered to have a higher tolerance to near-future OA conditions owing to their well-developed ion regulatory mechanisms. However, recent studies provide evidence to suggest that they may not be as resilient to near-future OA conditions as previously thought. In addition, earlier life stages of marine fishes are thought to be less tolerant than juveniles and adults of the same species as they lack well-developed ion regulatory mechanisms for maintaining homeostasis. This study follows up on previous studies examining the effects of near-future OA on larval Argyrosomus japonicus, an estuarine-dependent marine fish species, in order to identify the tipping point of tolerance for the larvae of this species. These previous studies showed that elevated pCO2, predicted for the year 2100, had negative effects on growth, development and metabolism and ultimately, survival of larval A. japonicus from post-flexion stage. Larval A. japonicus in the present study were reared from egg up to 22 DAH (days after hatching) under three treatments. The three treatments, (pCO2 353 μatm; pH 8.03), (pCO2 451 μatm; pH 7.93) and (pCO2 602 μatm; pH 7.83) corresponded to levels predicted to occur in year 2050, 2068 and 2090 respectively under the Intergovernmental Panel on Climate Change (IPCC) Representative Concentration Pathways (IPCC RCP) 8.5 model. Size-at-hatch, growth, development and metabolic responses (standard and active metabolic rates and metabolic scope) were assessed and compared between the three treatments throughout the rearing period. Five earlier larval life stages (hatchling – flexion/post-flexion) were identified by the end of the experiment. There were no significant differences in size-at-hatch (P > 0.05), development or the active metabolic (P > 0.05) or metabolic scope (P > 0.05) of fish in the three treatments throughout the study. However, the standard metabolic rate was significantly higher in the year 2068 treatment but only at the flexion/post-flexion stage which could be attributed to differences in developmental rates (including the development of the gills) between the 2068 and the other two treatments. Overall, the metabolic scope was narrowest in the 2090 treatment, but varied according to life stage. Although not significantly different, metabolic scope in the 2090 treatment was noticeably lower at the flexion stage compared to the other two treatments, and the development appeared slower, suggesting that this could be the stage most prone to OA. The study concluded that, in isolation, OA levels predicted to occur between 2050 and 2090 will not negatively affect size-at-hatch, growth, development, and metabolic responses of larval A. japonicus up to 22 DAH (flexion/post-flexion stage). Taken together with the previous studies of the same species, the tipping point of tolerance (where negative impacts will begin) in larvae of the species appears to be between the years 2090 and 2100.
- Full Text:
- Date Issued: 2019
Assessing estuarine nursery habitats for Cape Stumpnose (Rhabdosargus holubi), (Pisces: Sparidae) in a warm-temperate estuary in the Eastern Cape, South Africa
- Authors: Leslie, Timothy David
- Date: 2016
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3178 , vital:20381
- Description: The nursery role hypothesis provides an approach for assessing the nursery function of habitat types within estuaries. This study attempted to assess the nursery value of the dominant estuarine habitats in the Bushmans Estuary for Rhabdosargus holubi (Steindachner 1881) by analysing habitat complexity, relative abundance and behaviour of R. holubi and using stomach contents analysis and dietary diatom composition as indicative of feeding habitat. Structural habitat complexity was assessed in Zostera capensis (Setchell) seagrass and Spartina maritima (Curtis Fernald) salt marsh by sampling above-ground stem density and length, and total cover per unit area (Ct/At). Dimensionless habitat complexity indices such as the interstitial spatial index (ISI) at three magnifications and fractal geometry at two magnifications were used to further analyse habitat complexity. Above-ground biomass (P<0.05) in each season and canopy height (P<0.001) were significantly higher in salt marsh than in seagrass whilst stem density was significantly higher in seagrass than in salt marsh in each season (P<0.001). Each dimensionless index indicated that complexity is notably higher in seagrass than in the salt marsh. Using dimensionless indices that analyse complexity at different spatial scales provided a better analysis of habitat complexity than canopy height and biomass as it allowed for direct comparisons between habitat types. Underwater video cameras were deployed in seagrass, salt marsh and sand flat habitats to assess the relative abundance and behaviour of R. holubi. The relative abundance of R. holubi was significantly higher in seagrass than salt marsh and sand flats, whilst the behaviour of R. holubi indicated a high degree of habitat use in structured habitats and a low degree of habitat use in unstructured sand flat habitats. This indicated that not only are juvenile R. holubi a vegetation-associated species, but also a species that prefers seagrass to salt marsh.
- Full Text:
- Date Issued: 2016
Assessing the genetic diversity of catface rockcod epinephelus andersoni in the subtropical Western Indian Ocean and modelling the effects of climate change on their distribution
- Authors: Coppinger, Christine Rose
- Date: 2014
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/54499 , vital:26570
- Description: The catface rockcod Epinephelus andersoni is a range-restricted species that is endemic to the southeast coast of Africa from Quissico in Mozambique (subtropical) to Knysna in South Africa (warmtemperate). Its complex life-history, long-lived nature and high residency make E. andersoni potentially vulnerable to over-exploitation. Epinephelus andersoni is an important fishery species and has shown signs of depletion. Due to inadequate information necessary for management and conservation, further research is vital, particularly in the face of potentially significant climatic changes which could put further pressure on E. andersoni. The aim of the study was to provide information for the management of E. andersoni, with considerations for the possibly detrimental effects of future climate change. The objectives of this study were to describe the genetic structure and diversity of E. andersoni and to determine possible range shifts of E. andersoni with future changes in sea surface temperature. Genetic samples were collected throughout the distribution of E. andersoni. Standard DNA extraction and PCR using universal primers were conducted and nuclear (RPS7-1) and mitochondrial (cytochrome b) data were analysed to determine genetic diversity. A combination of nuclear and mitochondrial markers was used to ensure that the results were robust. RPS7-1 haplotype diversity was high (0.801) and an AMOVA on the RPS7-1 data showed significantly high among group variation (ΦCT = 0.204, p < 0.05) between five groups: 1. Quissico to Inhaca; 2. Cape Vidal to Port Edward; 3 Port St Johns to Coffee Bay; 4. Mbashe; 5. Port Alfred. This geographic structuring could be attributed to low gene flow across barriers such as the Port Alfred upwelling cell, the Mozambique Channel eddies and smaller more localised upwelling cells such as the Port St Johns cell. The cytochrome b results contrastingly indicate low haplotype diversity (0.309) and no differentiation (ΦCT = 0.265, p = 0.074) between groups and support the hypothesis of a historical population bottleneck. This may be due to an unusually slower mutation rate of the cytochrome b region than the RPS7-1 region, resulting in the RPS7-1 data showing a more recent picture of diversification. To complement the genetic results, niche modelling techniques were used to determine range shifts of E. andersoni with future temperature trends using species distribution and climatic data. The model illustrated a contraction of the E. andersoni distribution as well as future intensification of various upwelling cells along the south-east African coast including the Port Alfred upwelling cell. Due to the low gene flow across these barriers this intensification could decrease the resilience of E. andersoni, as its range becomes more limited with global change. The genetic data and modelling results combined provide useful information on which to base future fisheries management.
- Full Text:
- Date Issued: 2014