Distribution and habitat preferences of marine megafauna in Nosy Be, Madagascar
- Authors: Lubbé, Alicea
- Date: 2023-10-13
- Subjects: Marine animals Habitat Madagascar Nosy Be , Marine animals Geographical distribution Madagascar Nosy Be , Species distribution modelling , Maximum entropy method , Citizen science , Habitat preference
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424710 , vital:72177
- Description: Marine megafauna have important ecological roles including the top-down regulation of lower trophic levels and the transport of nutrients. They are also charismatic species of socioeconomic importance, due to their public appeal and focus for ecotourism. However, these taxa face numerous anthropogenic threats including bycatch, habitat-loss, noise disturbance, prey reductions, pollution, and vessel traffic. Northwest Madagascar has been identified as an important marine mammal area and whale shark aggregation site, yet limited information on megafauna within Madagascar exists. In this thesis, I investigated the community structure, distribution trends, related environmental factors (Chapter 2) and predicted habitat suitability (Chapter 3) using a species distribution modelling approach for marine megafauna around Nosy Be, North-west Madagascar. Data collection consisted of opportunistic boatbased surveys conducted while looking for whale sharks, mobulid rays and cetaceans. These activities were performed by dedicated ‘swim with whale shark’ tourism operators, Les Baleines Rand'eau and Safari Baleine during tourism activities directed by the Madagascar Whale Shark Project over four years (2016-2019). A total of 1792 sightings were reported with 13 identified species, including elasmobranchs: whale shark, Rhincodon typus; spinetail mobula ray, Mobula japonica; giant oceanic manta ray, Manta birostris; shortfin devil ray, Mobula kuhlii; balaenids: humpback whale, Megaptera novaeangliae; Omura's whale, Balaenoptera omurai, delphinids: Indo-Pacific bottlenose dolphin, Tursiops aduncus; spinner dolphin, Stenella longirostris; pantropical spotted dolphin, Stenella attenuata; Indian ocean humpback dolphin, Sousa plumbea; false killer whale, Pseudorca crassidens; melonheaded whale, Peponocephala electra and one cheloniid species: leatherback sea turtle, Dermochelys coriacea. Sightings were spatially analysed at a community level according to feeding guilds (i.e., filter feeders vs. predators), and distribution of the megafauna groups v were compared to selected remotely sensed physico-chemical data (sea surface temperature and chlorophyll-a concentration) and bathymetry charts (depth and slope) using generalized linear models (Chapter 2). All four variables had a significant effect on filter feeder distribution. Spatial distribution of filter feeder sightings peaked at an area of steep underwater topography (18-50m; x slope=0.5%) located on the west coast of Nosy Be, where foraging aggregations of large filter feeders (primarily R. typus and B. omurai) were frequently observed. Only SST had a significant effect on the relative abundance of animals in the predator feeding guild, which demonstrated a more longitudinal distribution along the continental shelf. The maximum entropy model (Maxent) was used for predicting habitat preference for the most frequently sighted species (Chapter 3). The distribution of whale sharks, mobulid rays and Omura’s whales were significantly overlapped as they were abundant in two main hotspots, Grand banc de l’entrée (~10 km of the west coast) and near Nosy Mitsio island, (~50 km northeast of Nosy Be). Suitable habitat for the dolphins was in relatively shallow waters in temperatures <28ºC near areas of steep changes in bathymetry. Bottlenose and spinner dolphins had a more widespread distribution across the continental shelf and humpback dolphin was closely associated with inshore reefs and occur in waters <10m. The coastal and inshore region of Nosy Be is an important habitat for a variety of megafaunal species, and the continental shelf provided essential areas for feeding and breeding. The results were similar to those presented for these species in other regions of the Indian Ocean (i.e., Eastern and Southern Africa; Western Australia; Seychelles) as well as outside of the Indian Ocean (i.e., Indonesia; Caribbean; North Atlantic). Thus the results from this thesis could be considered for management recommendations for marine conservation in the region. The value and limitations of data collected by citizen science were outlined (Chapter 4). , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Authors: Lubbé, Alicea
- Date: 2023-10-13
- Subjects: Marine animals Habitat Madagascar Nosy Be , Marine animals Geographical distribution Madagascar Nosy Be , Species distribution modelling , Maximum entropy method , Citizen science , Habitat preference
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424710 , vital:72177
- Description: Marine megafauna have important ecological roles including the top-down regulation of lower trophic levels and the transport of nutrients. They are also charismatic species of socioeconomic importance, due to their public appeal and focus for ecotourism. However, these taxa face numerous anthropogenic threats including bycatch, habitat-loss, noise disturbance, prey reductions, pollution, and vessel traffic. Northwest Madagascar has been identified as an important marine mammal area and whale shark aggregation site, yet limited information on megafauna within Madagascar exists. In this thesis, I investigated the community structure, distribution trends, related environmental factors (Chapter 2) and predicted habitat suitability (Chapter 3) using a species distribution modelling approach for marine megafauna around Nosy Be, North-west Madagascar. Data collection consisted of opportunistic boatbased surveys conducted while looking for whale sharks, mobulid rays and cetaceans. These activities were performed by dedicated ‘swim with whale shark’ tourism operators, Les Baleines Rand'eau and Safari Baleine during tourism activities directed by the Madagascar Whale Shark Project over four years (2016-2019). A total of 1792 sightings were reported with 13 identified species, including elasmobranchs: whale shark, Rhincodon typus; spinetail mobula ray, Mobula japonica; giant oceanic manta ray, Manta birostris; shortfin devil ray, Mobula kuhlii; balaenids: humpback whale, Megaptera novaeangliae; Omura's whale, Balaenoptera omurai, delphinids: Indo-Pacific bottlenose dolphin, Tursiops aduncus; spinner dolphin, Stenella longirostris; pantropical spotted dolphin, Stenella attenuata; Indian ocean humpback dolphin, Sousa plumbea; false killer whale, Pseudorca crassidens; melonheaded whale, Peponocephala electra and one cheloniid species: leatherback sea turtle, Dermochelys coriacea. Sightings were spatially analysed at a community level according to feeding guilds (i.e., filter feeders vs. predators), and distribution of the megafauna groups v were compared to selected remotely sensed physico-chemical data (sea surface temperature and chlorophyll-a concentration) and bathymetry charts (depth and slope) using generalized linear models (Chapter 2). All four variables had a significant effect on filter feeder distribution. Spatial distribution of filter feeder sightings peaked at an area of steep underwater topography (18-50m; x slope=0.5%) located on the west coast of Nosy Be, where foraging aggregations of large filter feeders (primarily R. typus and B. omurai) were frequently observed. Only SST had a significant effect on the relative abundance of animals in the predator feeding guild, which demonstrated a more longitudinal distribution along the continental shelf. The maximum entropy model (Maxent) was used for predicting habitat preference for the most frequently sighted species (Chapter 3). The distribution of whale sharks, mobulid rays and Omura’s whales were significantly overlapped as they were abundant in two main hotspots, Grand banc de l’entrée (~10 km of the west coast) and near Nosy Mitsio island, (~50 km northeast of Nosy Be). Suitable habitat for the dolphins was in relatively shallow waters in temperatures <28ºC near areas of steep changes in bathymetry. Bottlenose and spinner dolphins had a more widespread distribution across the continental shelf and humpback dolphin was closely associated with inshore reefs and occur in waters <10m. The coastal and inshore region of Nosy Be is an important habitat for a variety of megafaunal species, and the continental shelf provided essential areas for feeding and breeding. The results were similar to those presented for these species in other regions of the Indian Ocean (i.e., Eastern and Southern Africa; Western Australia; Seychelles) as well as outside of the Indian Ocean (i.e., Indonesia; Caribbean; North Atlantic). Thus the results from this thesis could be considered for management recommendations for marine conservation in the region. The value and limitations of data collected by citizen science were outlined (Chapter 4). , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
Disentangling the role of prokaryotes in regulating export flux via suspended and sinking organic matter in the southern ocean
- Authors: Dithugoe, Choaro David
- Date: 2022-10-14
- Subjects: Microbial ecology , Bioinformatics , Biochemistry , Oceanography , Metagenomics , Carbon cycle (Biogeochemistry) , Prokaryotes
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/365745 , vital:65782 , DOI https://doi.org/10.21504/10962/365745
- Description: The role of phytoplankton in regulating atmospheric carbon dioxide in the marine environment has been the subject of extensive research. We lack, however, comparative insights regarding the functional contributions of bacteria, archaea, fungi, and viruses (the microbiota) to organic matter export especially in understudied polar marine environments such as the Southern Ocean. This knowledge deficit is in part due to the high levels of microbial diversity which obscures efforts to study the relationship between diversity and ecosystem functions including their roles in the sequestration of carbon and nitrogen. Elucidating their precise contributions to organic matter export may be central to potential ecosystems feedbacks to global climate change. We examined several factors which may influence organic matter export to depth including net primary production, phytoplankton biomass, temperature, and prokaryotic functional capacity in the Southern Ocean. A Marine Snow Catcher was used to collect suspended and sinking material 10 metres below mixed layer depth at Southern Ocean Time Series (SOTS) in autumn (March-April) and in the Atlantic sector of the Southern Ocean in winter (July-August) and spring (October-November) 2019. The suspended and sinking material was used to determine the particulate organic carbon and nitrogen concentrations which were then used to calculate fluxes and export ratio ((e-ratio) - particulate organic carbon flux divided by net primary production). Additionally, genomic DNA was extracted from the suspended and sinking material and sequenced to obtain Shotgun metagenomic data which was employed to reconstruct metagenome assembled genome (MAGs) and their functional capacity using bioinformatic tools such as DRAM. Data from the Atlantic sector of the Southern Ocean, demonstrate that net primary production and temperature were inversely related to the e-ratio which is consistent with previous findings from the northern region of the Southern Ocean. Genomic functional capacity from SOTS suggested that r-strategist (organisms adapted to live in unstable environments) bacteria (e.g., Gammaproteobacteria) were prominent in the suspended pool. By contrast, the sinking particle-pool appeared to be dominated by K- strategists (organisms adapted to stable environment). The opposite was true for the archaea. This finding (i.e., bacteria) differs from a previous study in the northern region of the Southern Ocean, showing that microbes with K-strategists were more abundant in the suspended fraction. K-strategists typically degrade sinking organic matter into suspended organic matter or dissolved organic matter reducing the organic carbon export efficiency. Furthermore, Data from the Atlantic sector of the Southern Ocean revealed that seasonal temperature changes might dictate the rate of regional prokaryotic degradation across the zones. Resulting in rapid degradation at the northerly warmer regions and slow degradation further south. The data further provide evidence of chemolithoautotrophic mechanisms, with prokaryotes harbouring key pathways, required to transform dissolved inorganic carbon into complex organic forms, including recalcitrant dissolved organic carbon. Collectively, the SOTS and Atlantic sector of the Southern Ocean data suggest that shifts in prokaryotic community structure and functional capacity may regulate (either degradation or synthesis of organic matter) carbon export to depth. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Authors: Dithugoe, Choaro David
- Date: 2022-10-14
- Subjects: Microbial ecology , Bioinformatics , Biochemistry , Oceanography , Metagenomics , Carbon cycle (Biogeochemistry) , Prokaryotes
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/365745 , vital:65782 , DOI https://doi.org/10.21504/10962/365745
- Description: The role of phytoplankton in regulating atmospheric carbon dioxide in the marine environment has been the subject of extensive research. We lack, however, comparative insights regarding the functional contributions of bacteria, archaea, fungi, and viruses (the microbiota) to organic matter export especially in understudied polar marine environments such as the Southern Ocean. This knowledge deficit is in part due to the high levels of microbial diversity which obscures efforts to study the relationship between diversity and ecosystem functions including their roles in the sequestration of carbon and nitrogen. Elucidating their precise contributions to organic matter export may be central to potential ecosystems feedbacks to global climate change. We examined several factors which may influence organic matter export to depth including net primary production, phytoplankton biomass, temperature, and prokaryotic functional capacity in the Southern Ocean. A Marine Snow Catcher was used to collect suspended and sinking material 10 metres below mixed layer depth at Southern Ocean Time Series (SOTS) in autumn (March-April) and in the Atlantic sector of the Southern Ocean in winter (July-August) and spring (October-November) 2019. The suspended and sinking material was used to determine the particulate organic carbon and nitrogen concentrations which were then used to calculate fluxes and export ratio ((e-ratio) - particulate organic carbon flux divided by net primary production). Additionally, genomic DNA was extracted from the suspended and sinking material and sequenced to obtain Shotgun metagenomic data which was employed to reconstruct metagenome assembled genome (MAGs) and their functional capacity using bioinformatic tools such as DRAM. Data from the Atlantic sector of the Southern Ocean, demonstrate that net primary production and temperature were inversely related to the e-ratio which is consistent with previous findings from the northern region of the Southern Ocean. Genomic functional capacity from SOTS suggested that r-strategist (organisms adapted to live in unstable environments) bacteria (e.g., Gammaproteobacteria) were prominent in the suspended pool. By contrast, the sinking particle-pool appeared to be dominated by K- strategists (organisms adapted to stable environment). The opposite was true for the archaea. This finding (i.e., bacteria) differs from a previous study in the northern region of the Southern Ocean, showing that microbes with K-strategists were more abundant in the suspended fraction. K-strategists typically degrade sinking organic matter into suspended organic matter or dissolved organic matter reducing the organic carbon export efficiency. Furthermore, Data from the Atlantic sector of the Southern Ocean revealed that seasonal temperature changes might dictate the rate of regional prokaryotic degradation across the zones. Resulting in rapid degradation at the northerly warmer regions and slow degradation further south. The data further provide evidence of chemolithoautotrophic mechanisms, with prokaryotes harbouring key pathways, required to transform dissolved inorganic carbon into complex organic forms, including recalcitrant dissolved organic carbon. Collectively, the SOTS and Atlantic sector of the Southern Ocean data suggest that shifts in prokaryotic community structure and functional capacity may regulate (either degradation or synthesis of organic matter) carbon export to depth. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
Ecological assessment of a temperate river system using biomonitoring techniques: a case study of the Bloukrans River system, South Africa
- Authors: Magadze, Tinotenda
- Date: 2020
- Subjects: Bloukrans River , Ecological assessment (Biology) -- South Africa , Stream ecology -- South Africa , Rivers -- Environmental aspects -- South Africa , Benthic animals -- Effect of human beings on -- South Africa , Water quality biological assessment -- South Africa , Diatoms -- South Africa -- Data processing
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/142933 , vital:38177
- Description: Escalating pressures from growing human populations and environmental impacts increasingly imperil freshwater ecosystems. The Bloukrans River, which drains an urbanised and agricultural catchment in the Eastern Cape province of South Africa, is no exception. Detailed knowledge of the structure and function of the aquatic ecosystems is required in order to create models and matrices that predict, guide assessment and direct intervention on ecological integrity and water quality management in these systems. The main objectives of this research were to: examine the effects of urbanization on the benthic macroinvertebrate functional feeding guild structure among different stream orders; determine if benthic diatoms can be used as effective and reliable indicators of ionic composition and conductivity in different stream order categories and finally; to evaluate the applicability of the South African Diatom Index (SADI) and other indices in the Eastern Cape region of South Africa. Field studies were carried out to explore temporal patterns in community structure (macroinvertebrates and diatoms) and ecosystem function related to land-use patterns, instream habitat availability, and water quality parameters in the Bloukrans River system across four study periods: February (summer) and July (winter) 2016 and February (summer) and May/July (winter) 2018. The study was conducted along a gradient of impacts from less impacted agricultural headwaters to highly impacted urban sites located immediately downstream of the city of Makhanda. Macroinvertebrates were separated into functional feeding groups (FFGs) (i.e. collector-gatherer, collector-filterer, scraper, shredder, and predator) which were then used to assess the effects of selected physico-chemical variables and riparian zone condition on FFG organization. Collector-gatherers were the most abundant in the Bloukrans River and represented 71.3 % of the macroinvertebrate assemblages. Stream order 1species such as Nitzschia palea, Gomphonema parvulum, Tryblionella apiculata, Diploneis vulgaris and Staurosira elliptica. Multivariate analysis (Canonical correspondence analysis (CCA)) indicated that differences in diatom community assemblages were best explained by calcium, magnesium, pH, phosphate, nitrate, dissolved oxygen, sediment nitrate, conductivity and salinity. These results indicate that diatoms can be used as bioindicators for monitoring highly impacted river systems and to also further examine pollution gradients and impacts of specific/point pollution sources. In order to further test the application of diatom indices, nine sites with contrasting water quality were sampled along the length river system in February, May and July 2018. Diatom-based indices incorporated in OMNIDIA software were applied to assess the integrity of the water quality as indicated by diatom communities. For comparative purposes, several foreign indices (e.g. the trophic diatom index (TDI), the percentage pollution-tolerant valves (%PTV), biological diatom index (BDI)) and the South African Diatom Index (SADI) were used in the study. From the results, the Percentage Pollution-Tolerant Valves (%PTV) of most urban sites in the Bloukrans River was above the 20% limit indicating the presence of organic pollutants. Although the foreign diatom indices were applicable in the study, the SADI had significant correlations with most water quality variables (p < 0.05) compared to other indices such as Watanabe Index (WAT), Biological Index of Water Quality Trophic Index (BIWQ) and Trophic Index (TI)). These results support wider use of the SADI as an indicator of water quality conditions in South African river systems. Finally, the observed variations in diatom community structure and composition as a result of changes in water quality were broadly in agreement with the results of macroinvertebrate FFG structure indicating that the two biological indicators can, and should, be used as complementary techniques in the biomonitoring of rivers and streams in South Africa.
- Full Text:
- Authors: Magadze, Tinotenda
- Date: 2020
- Subjects: Bloukrans River , Ecological assessment (Biology) -- South Africa , Stream ecology -- South Africa , Rivers -- Environmental aspects -- South Africa , Benthic animals -- Effect of human beings on -- South Africa , Water quality biological assessment -- South Africa , Diatoms -- South Africa -- Data processing
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/142933 , vital:38177
- Description: Escalating pressures from growing human populations and environmental impacts increasingly imperil freshwater ecosystems. The Bloukrans River, which drains an urbanised and agricultural catchment in the Eastern Cape province of South Africa, is no exception. Detailed knowledge of the structure and function of the aquatic ecosystems is required in order to create models and matrices that predict, guide assessment and direct intervention on ecological integrity and water quality management in these systems. The main objectives of this research were to: examine the effects of urbanization on the benthic macroinvertebrate functional feeding guild structure among different stream orders; determine if benthic diatoms can be used as effective and reliable indicators of ionic composition and conductivity in different stream order categories and finally; to evaluate the applicability of the South African Diatom Index (SADI) and other indices in the Eastern Cape region of South Africa. Field studies were carried out to explore temporal patterns in community structure (macroinvertebrates and diatoms) and ecosystem function related to land-use patterns, instream habitat availability, and water quality parameters in the Bloukrans River system across four study periods: February (summer) and July (winter) 2016 and February (summer) and May/July (winter) 2018. The study was conducted along a gradient of impacts from less impacted agricultural headwaters to highly impacted urban sites located immediately downstream of the city of Makhanda. Macroinvertebrates were separated into functional feeding groups (FFGs) (i.e. collector-gatherer, collector-filterer, scraper, shredder, and predator) which were then used to assess the effects of selected physico-chemical variables and riparian zone condition on FFG organization. Collector-gatherers were the most abundant in the Bloukrans River and represented 71.3 % of the macroinvertebrate assemblages. Stream order 1species such as Nitzschia palea, Gomphonema parvulum, Tryblionella apiculata, Diploneis vulgaris and Staurosira elliptica. Multivariate analysis (Canonical correspondence analysis (CCA)) indicated that differences in diatom community assemblages were best explained by calcium, magnesium, pH, phosphate, nitrate, dissolved oxygen, sediment nitrate, conductivity and salinity. These results indicate that diatoms can be used as bioindicators for monitoring highly impacted river systems and to also further examine pollution gradients and impacts of specific/point pollution sources. In order to further test the application of diatom indices, nine sites with contrasting water quality were sampled along the length river system in February, May and July 2018. Diatom-based indices incorporated in OMNIDIA software were applied to assess the integrity of the water quality as indicated by diatom communities. For comparative purposes, several foreign indices (e.g. the trophic diatom index (TDI), the percentage pollution-tolerant valves (%PTV), biological diatom index (BDI)) and the South African Diatom Index (SADI) were used in the study. From the results, the Percentage Pollution-Tolerant Valves (%PTV) of most urban sites in the Bloukrans River was above the 20% limit indicating the presence of organic pollutants. Although the foreign diatom indices were applicable in the study, the SADI had significant correlations with most water quality variables (p < 0.05) compared to other indices such as Watanabe Index (WAT), Biological Index of Water Quality Trophic Index (BIWQ) and Trophic Index (TI)). These results support wider use of the SADI as an indicator of water quality conditions in South African river systems. Finally, the observed variations in diatom community structure and composition as a result of changes in water quality were broadly in agreement with the results of macroinvertebrate FFG structure indicating that the two biological indicators can, and should, be used as complementary techniques in the biomonitoring of rivers and streams in South Africa.
- Full Text:
Temporal patterns and seasonal variation in microplastic loads in the water column and in the tissues of consumers along the southern and south-eastern coasts of South Africa
- Authors: Redelinghuys, Suzanne
- Date: 2020
- Subjects: Microplastics -- South Africa -- Eastern Cape , Plastic marine debris -- South Africa -- Eastern Cape , Marine pollution -- South Africa -- Eastern Cape , Ocean circulation -- South Africa -- Eastern Cape , Marine invertebrates -- Effect of pollution on -- South Africa -- Eastern Cape , Marine animals -- Effect of pollution on -- South Africa -- Eastern Cape , Mexilhao mussel -- Effect of pollution on -- South Africa -- Eastern Cape , Mytilus galloprovincialis -- Effect of pollution on -- South Africa -- Eastern Cape , Barnacles -- Effect of pollution on -- South Africa -- Eastern Cape , Tetraclita -- Effect of pollution on -- South Africa -- Eastern Cape , Octomeris angulosa -- Effect of pollution on -- South Africa -- Eastern Cape
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/115623 , vital:34201
- Description: Plastic pollution in the marine environment has become an environmental concern and a subject of ecological research. The field of microplastic pollution in particular has expanded dramatically in the last few years. Though much data exists on the spatial variability of microplastics in the marine environment globally, little is known about temporal variability, especially on short-term time scales in the southern hemisphere. Similarly, virtually nothing is known about the temporal patterns in microplastic ingestion by marine invertebrates, despite the fact that numerous studies have demonstrated that vertebrates and invertebrates routinely ingest microplastics with varied physiological effects. This study aimed to, 1) provide base-line data for microplastic loads in the nearshore environment along the Eastern Cape Province of South Africa over four short-term time scales: daily, weekly, monthly, and yearly; and, 2) assess whether there are any seasonal patterns in microplastics ingested by selected filter-feeding consumers at two sites along the southern and south-eastern Cape coastlines of South Africa. Results for part one of this study demonstrate no temporal patterns over the different time scales considered (ANOVA, p > 0.05 in all cases). Microplastic counts ranged on average from 55 ± 289 to 930 ± 462 microplastic particles.m-3. With the exception of two instances, microfibres constituted > 50 % (range: 47 to 97 %) of the total microplastic counts. Part two of this study assessed the size range of, and seasonal and spatial patterns in ingested microplastic. No significant differences were found in the number of microplastics ingested within seasons between the mussels Perna perna (Linnaeus, 1758) and Mytilus galloprovincialis (Lamarck, 1819), and the barnacles, Octomeris angulosa (Sowerby, 1825) and Tetraclita serrata (Darwin 1954) (Student’s t-test; d.f = 18; p > 0.05 in all cases), or between the two sites sampled, Kenton-on-Sea, Eastern Cape, and Wilderness, Western Cape (ANOVA; d.f. = 18; p > 0.05 in all cases). The nitric acid digestion technique was used to determine the presence of ingested microplastics. Microplastic loads ranged from 2 ± 1 to 33 ± 19 microplastics.g-1 wwt across all consumers, and the size of ingested microplastics ranged from 1 to 16 μm. Though highly variable, the absence of statistically significant differences in ingestion rates points to a ubiquity in the availability of microplastics within the water column over time and space.
- Full Text:
- Authors: Redelinghuys, Suzanne
- Date: 2020
- Subjects: Microplastics -- South Africa -- Eastern Cape , Plastic marine debris -- South Africa -- Eastern Cape , Marine pollution -- South Africa -- Eastern Cape , Ocean circulation -- South Africa -- Eastern Cape , Marine invertebrates -- Effect of pollution on -- South Africa -- Eastern Cape , Marine animals -- Effect of pollution on -- South Africa -- Eastern Cape , Mexilhao mussel -- Effect of pollution on -- South Africa -- Eastern Cape , Mytilus galloprovincialis -- Effect of pollution on -- South Africa -- Eastern Cape , Barnacles -- Effect of pollution on -- South Africa -- Eastern Cape , Tetraclita -- Effect of pollution on -- South Africa -- Eastern Cape , Octomeris angulosa -- Effect of pollution on -- South Africa -- Eastern Cape
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/115623 , vital:34201
- Description: Plastic pollution in the marine environment has become an environmental concern and a subject of ecological research. The field of microplastic pollution in particular has expanded dramatically in the last few years. Though much data exists on the spatial variability of microplastics in the marine environment globally, little is known about temporal variability, especially on short-term time scales in the southern hemisphere. Similarly, virtually nothing is known about the temporal patterns in microplastic ingestion by marine invertebrates, despite the fact that numerous studies have demonstrated that vertebrates and invertebrates routinely ingest microplastics with varied physiological effects. This study aimed to, 1) provide base-line data for microplastic loads in the nearshore environment along the Eastern Cape Province of South Africa over four short-term time scales: daily, weekly, monthly, and yearly; and, 2) assess whether there are any seasonal patterns in microplastics ingested by selected filter-feeding consumers at two sites along the southern and south-eastern Cape coastlines of South Africa. Results for part one of this study demonstrate no temporal patterns over the different time scales considered (ANOVA, p > 0.05 in all cases). Microplastic counts ranged on average from 55 ± 289 to 930 ± 462 microplastic particles.m-3. With the exception of two instances, microfibres constituted > 50 % (range: 47 to 97 %) of the total microplastic counts. Part two of this study assessed the size range of, and seasonal and spatial patterns in ingested microplastic. No significant differences were found in the number of microplastics ingested within seasons between the mussels Perna perna (Linnaeus, 1758) and Mytilus galloprovincialis (Lamarck, 1819), and the barnacles, Octomeris angulosa (Sowerby, 1825) and Tetraclita serrata (Darwin 1954) (Student’s t-test; d.f = 18; p > 0.05 in all cases), or between the two sites sampled, Kenton-on-Sea, Eastern Cape, and Wilderness, Western Cape (ANOVA; d.f. = 18; p > 0.05 in all cases). The nitric acid digestion technique was used to determine the presence of ingested microplastics. Microplastic loads ranged from 2 ± 1 to 33 ± 19 microplastics.g-1 wwt across all consumers, and the size of ingested microplastics ranged from 1 to 16 μm. Though highly variable, the absence of statistically significant differences in ingestion rates points to a ubiquity in the availability of microplastics within the water column over time and space.
- Full Text:
A flight of fancy in the Chorister Robin-Chat (Cossypha dichroa) : an isotopic standpoint
- Wolmarans, Milena Helena Louise
- Authors: Wolmarans, Milena Helena Louise
- Date: 2015
- Subjects: Muscicapidae -- South Africa , Muscicapidae -- Food , Muscicapidae -- Habitat , Muscicapidae -- Habitat -- Conservation , Forest birds -- South Africa , Isotopes , Stable isotope tracers
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5920 , http://hdl.handle.net/10962/d1017207
- Description: Forested areas have been cited for their highly diverse floral and faunal assemblages, which are currently under threat from anthropogenic activities that restrict their range and deplete the resources produced within these naturally fragmented patches. Historically, up to 67 percent of avifaunal species associated with well-treed areas have undergone localised extinctions, consequentially affecting biodiversity as a measure of species richness and ecosystem functionality. To date, more than 900 of the bird species affiliated with forests are under threat and despite the theory surrounding functional redundancy, the mass extinction that is currently underway poses considerable limitations on the ecological integrity of these biomes. In South Africa, indigenous forest (one of the rarest biomes), occurs predominantly in small isolated patches along the eastern escarpment. With mountainous terrain emphasised as ‘prominent hotspots of extinction’, the limited dispersal and habitat sensitivity of montane forest fauna renders these species more prone to localised extinctions. BirdLife International, the IUCN and SABAP2 all indicate reductions in the range and abundance of the Chorister Robin-Chat (Cossypha dichroa) - an endemic forest specialist that is reported to move seasonally between high-altitude forest patches where they breed in summer, and lowland coastal forests where they overwinter. Beyond diet, body morphology and vocalisations, much of the information available on the altitudinal movements of C. dichroa is based on secondary sources and the assumptions therein. This study aimed to investigate the potential utilisation of δ13C and δ15N stable isotopes in determining the dietary niche width and altitudinal movements of C. dichroa. Feathers obtained in forested patches of the Limpopo, KwaZulu-Natal and Eastern Cape provinces exhibited a wide trophic niche width and generalised diet. Strong regional separation is apparent in the isotopic signatures suggesting little movement between provinces. A comparison of 13C-isotopes showed minimal variation that point to a uniformity in the carbon-base utilised by C. dichroa across their range. The 15N-signatures obtained in Limpopo, however, revealed a distinct trophic segregation between the northern-most Chorister populations and their southern counterparts. No altitudinal movements were detected in the isotopic signatures of recaptured Choristers, but more research is needed to investigate the long-term accuracy of these results and the breeding potential of resident Choristers in lowland coastal forests; especially when considering the reduced range and abundance reported for this endemic species.
- Full Text:
- Authors: Wolmarans, Milena Helena Louise
- Date: 2015
- Subjects: Muscicapidae -- South Africa , Muscicapidae -- Food , Muscicapidae -- Habitat , Muscicapidae -- Habitat -- Conservation , Forest birds -- South Africa , Isotopes , Stable isotope tracers
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5920 , http://hdl.handle.net/10962/d1017207
- Description: Forested areas have been cited for their highly diverse floral and faunal assemblages, which are currently under threat from anthropogenic activities that restrict their range and deplete the resources produced within these naturally fragmented patches. Historically, up to 67 percent of avifaunal species associated with well-treed areas have undergone localised extinctions, consequentially affecting biodiversity as a measure of species richness and ecosystem functionality. To date, more than 900 of the bird species affiliated with forests are under threat and despite the theory surrounding functional redundancy, the mass extinction that is currently underway poses considerable limitations on the ecological integrity of these biomes. In South Africa, indigenous forest (one of the rarest biomes), occurs predominantly in small isolated patches along the eastern escarpment. With mountainous terrain emphasised as ‘prominent hotspots of extinction’, the limited dispersal and habitat sensitivity of montane forest fauna renders these species more prone to localised extinctions. BirdLife International, the IUCN and SABAP2 all indicate reductions in the range and abundance of the Chorister Robin-Chat (Cossypha dichroa) - an endemic forest specialist that is reported to move seasonally between high-altitude forest patches where they breed in summer, and lowland coastal forests where they overwinter. Beyond diet, body morphology and vocalisations, much of the information available on the altitudinal movements of C. dichroa is based on secondary sources and the assumptions therein. This study aimed to investigate the potential utilisation of δ13C and δ15N stable isotopes in determining the dietary niche width and altitudinal movements of C. dichroa. Feathers obtained in forested patches of the Limpopo, KwaZulu-Natal and Eastern Cape provinces exhibited a wide trophic niche width and generalised diet. Strong regional separation is apparent in the isotopic signatures suggesting little movement between provinces. A comparison of 13C-isotopes showed minimal variation that point to a uniformity in the carbon-base utilised by C. dichroa across their range. The 15N-signatures obtained in Limpopo, however, revealed a distinct trophic segregation between the northern-most Chorister populations and their southern counterparts. No altitudinal movements were detected in the isotopic signatures of recaptured Choristers, but more research is needed to investigate the long-term accuracy of these results and the breeding potential of resident Choristers in lowland coastal forests; especially when considering the reduced range and abundance reported for this endemic species.
- Full Text:
Direct and indirect effects of zooplanktivorous predators on the estuarine plankton community
- Authors: Wasserman, Ryan John
- Date: 2014
- Subjects: Zooplankton -- Effect of predation on , Predation (Biology) , Zooplankton -- Predators of , Copepoda
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5870 , http://hdl.handle.net/10962/d1012938
- Description: Although predation has been identified as a potentially important driver in terrestrial and freshwater ecosystems, estuarine planktonic research has focused largely on the so-called "bottom-up" drivers of community assemblages. As such, this thesis focuses on the direct and indirect effects of zooplanktivorous predators on the planktonic community in an estuarine environment. By using a suite of in situ mesocosm experiments, a number of hypotheses, pertaining to the major research themes associated with predator-prey interactions, are tested. These themes included trophic cascading, risk effects associated with predation events and the importance of predator diversity in maintaining prey communities. The first experiment assessed the significance of apex predation pressure for the planktonic community through trophic cascades. Various treatments using in situ mesocosms were established in a closed oligotrophic estuary to highlight the importance of predation in stabilising estuarine plankton abundances. Through either the removal (filtration) or addition of certain planktonic groups, varied trophic scenarios were established. The experimental treatment containing apex zooplanktivores had consequences for multiple trophic levels, exerting a stabilising pressure throughout the food web (Chapter 3). Furthermore, pyrosequencing of filtered water samples revealed that when compared to the remaining treatments, the treatment containing stable apex predatory pressure experienced limited temporal deviation-from-initial in bacterial community structure (Chapter 4). These findings are consistent with trophic cascade theory whereby predators mediate interactions at multiple lower trophic levels with consequent repercussions for diversity. To assess the non-consumptive effects of predators on prey, two experiments were conducted. Firstly, using egg numbers per clutch as a measure of potential reproductive output, the non-lethal effects of predatory pressure on reproductive success in a key planktonic copepod was investigated. In this study, the average clutch size of fecund female copepods was found to be consistently lower in the presence of predators when compared to females not exposed to predation threat (Chapter 5). The second study assessed the effects of conspecific chemical alarm cues associated with predation, on population dynamics of a copepod species. This study revealed that the copepods appear to detect the presence of chemical alarm cues associated with predation events, with repercussions for population demographics over time. Furthermore, it showed that in the absence of actual predation, copepod prey responses to alarm cues were adjusted over time, consistent with the threat sensitive predator avoidance hypothesis (Chapter 6). The final data chapter dealt with predator diversity and its implications for zooplankton community structure. By experimentally monitoring the effects of two alternate model predators on the metazoan community over time, dissimilarities in community level control emerged. Alternate key prey populations were regulated by the different model predators, highlighting the importance of predator and prey behaviour in mediating predator-prey interactions (Chapter 7). These results highlight the potential importance of predators in maintaining community dynamics in estuarine planktonic communities under certain conditions. This study represents some of the first work to address these various aspects of predator-prey dynamics within the context of planktonic estuarine ecology.
- Full Text:
- Authors: Wasserman, Ryan John
- Date: 2014
- Subjects: Zooplankton -- Effect of predation on , Predation (Biology) , Zooplankton -- Predators of , Copepoda
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5870 , http://hdl.handle.net/10962/d1012938
- Description: Although predation has been identified as a potentially important driver in terrestrial and freshwater ecosystems, estuarine planktonic research has focused largely on the so-called "bottom-up" drivers of community assemblages. As such, this thesis focuses on the direct and indirect effects of zooplanktivorous predators on the planktonic community in an estuarine environment. By using a suite of in situ mesocosm experiments, a number of hypotheses, pertaining to the major research themes associated with predator-prey interactions, are tested. These themes included trophic cascading, risk effects associated with predation events and the importance of predator diversity in maintaining prey communities. The first experiment assessed the significance of apex predation pressure for the planktonic community through trophic cascades. Various treatments using in situ mesocosms were established in a closed oligotrophic estuary to highlight the importance of predation in stabilising estuarine plankton abundances. Through either the removal (filtration) or addition of certain planktonic groups, varied trophic scenarios were established. The experimental treatment containing apex zooplanktivores had consequences for multiple trophic levels, exerting a stabilising pressure throughout the food web (Chapter 3). Furthermore, pyrosequencing of filtered water samples revealed that when compared to the remaining treatments, the treatment containing stable apex predatory pressure experienced limited temporal deviation-from-initial in bacterial community structure (Chapter 4). These findings are consistent with trophic cascade theory whereby predators mediate interactions at multiple lower trophic levels with consequent repercussions for diversity. To assess the non-consumptive effects of predators on prey, two experiments were conducted. Firstly, using egg numbers per clutch as a measure of potential reproductive output, the non-lethal effects of predatory pressure on reproductive success in a key planktonic copepod was investigated. In this study, the average clutch size of fecund female copepods was found to be consistently lower in the presence of predators when compared to females not exposed to predation threat (Chapter 5). The second study assessed the effects of conspecific chemical alarm cues associated with predation, on population dynamics of a copepod species. This study revealed that the copepods appear to detect the presence of chemical alarm cues associated with predation events, with repercussions for population demographics over time. Furthermore, it showed that in the absence of actual predation, copepod prey responses to alarm cues were adjusted over time, consistent with the threat sensitive predator avoidance hypothesis (Chapter 6). The final data chapter dealt with predator diversity and its implications for zooplankton community structure. By experimentally monitoring the effects of two alternate model predators on the metazoan community over time, dissimilarities in community level control emerged. Alternate key prey populations were regulated by the different model predators, highlighting the importance of predator and prey behaviour in mediating predator-prey interactions (Chapter 7). These results highlight the potential importance of predators in maintaining community dynamics in estuarine planktonic communities under certain conditions. This study represents some of the first work to address these various aspects of predator-prey dynamics within the context of planktonic estuarine ecology.
- Full Text:
The natural history of the humpback dolphin, Sousa chinensis, in KwaZulu-Natal, South Africa : age, growth and reproduction
- Authors: Nolte, Zianca
- Date: 2014
- Subjects: Sousa -- South Africa -- KwaZulu-Natal , Dolphins -- Behavior -- South Africa -- KwaZulu-Natal , Dolphins -- Age determination -- South Africa -- KwaZulu-Natal , Dolphins -- Development -- South Africa -- KwaZulu-Natal , Dolphins -- South Africa -- KwaZulu-Natal -- Reproduction , Dolphins -- Physiology -- South Africa -- KwaZulu-Natal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5878 , http://hdl.handle.net/10962/d1013178
- Description: Globally, inshore cetaceans are being threatened by a number of anthropogenic activities. The Indo-Pacific humpback dolphin, Sousa chinensis, is currently listed as ‘near threatened’ by the International Union for the Conservation of Nature (IUCN). In order to be able to advise on management and conservation strategies, knowledge on the life history of the species is required. To date very little is known about the biology of humpback dolphins. The aim of the present study was to determine basic life history parameters, including age, growth and reproduction of humpback dolphins incidentally caught in shark nets. Age was estimated by counting the growth layer groups (GLGs) in the dentine and cementum of sectioned and stained teeth. Both a Von Bertalanffy and a Gompertz growth curve fitted well to the data, but for comparison with previous studies on Sousa, the Gompertz growth function was adopted to describe the relationship between length and age for KwaZulu-Natal populations. Length at birth was estimated between 104.33 and 111.57 cm for males and females, respectively. Asymptotic length was reached at 266.48 cm and 239.29 cm for males and females, respectively. This corresponds to the attainment of physical maturity at 24 GLGs in males and 16 GLGs in females. Asymptotic mass for males could not be determined, while for females it occurred around 160 kg. The maximum age estimates and recorded lengths were 24 GLGs and 279 cm for males and 17.7 GLGs and 249 cm for females. Differences in length-at-age and mass-at-age for S. chinensis suggest sexual dimorphism. The attainment of sexual maturity in males occurred between 9 and 10 GLGs, corresponding to 230 cm total body length and 140 kg. The maximum combined testis mass of mature males comprised 0.42% of total body mass, and a roving male mating system was proposed. In females, sexual maturity occurred around 7.6 GLG, between 220 and 222 cm and 104 - 140 kg. The ovulation rate is estimated at 0.2 ovulations per annum, suggesting a calving interval of five years. It is evident from the results obtained in the present study that geographical differences exist in the life history parameters of S. chinensis. As a result, regional conservation and management strategies are imperative. Results from this study can therefore assist in assessing the status of existing population structures in the KwaZulu-Natal coastal waters, and the implementation of regional mitigation strategies to ensure the continued survival of humpback dolphins in the region.
- Full Text:
- Authors: Nolte, Zianca
- Date: 2014
- Subjects: Sousa -- South Africa -- KwaZulu-Natal , Dolphins -- Behavior -- South Africa -- KwaZulu-Natal , Dolphins -- Age determination -- South Africa -- KwaZulu-Natal , Dolphins -- Development -- South Africa -- KwaZulu-Natal , Dolphins -- South Africa -- KwaZulu-Natal -- Reproduction , Dolphins -- Physiology -- South Africa -- KwaZulu-Natal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5878 , http://hdl.handle.net/10962/d1013178
- Description: Globally, inshore cetaceans are being threatened by a number of anthropogenic activities. The Indo-Pacific humpback dolphin, Sousa chinensis, is currently listed as ‘near threatened’ by the International Union for the Conservation of Nature (IUCN). In order to be able to advise on management and conservation strategies, knowledge on the life history of the species is required. To date very little is known about the biology of humpback dolphins. The aim of the present study was to determine basic life history parameters, including age, growth and reproduction of humpback dolphins incidentally caught in shark nets. Age was estimated by counting the growth layer groups (GLGs) in the dentine and cementum of sectioned and stained teeth. Both a Von Bertalanffy and a Gompertz growth curve fitted well to the data, but for comparison with previous studies on Sousa, the Gompertz growth function was adopted to describe the relationship between length and age for KwaZulu-Natal populations. Length at birth was estimated between 104.33 and 111.57 cm for males and females, respectively. Asymptotic length was reached at 266.48 cm and 239.29 cm for males and females, respectively. This corresponds to the attainment of physical maturity at 24 GLGs in males and 16 GLGs in females. Asymptotic mass for males could not be determined, while for females it occurred around 160 kg. The maximum age estimates and recorded lengths were 24 GLGs and 279 cm for males and 17.7 GLGs and 249 cm for females. Differences in length-at-age and mass-at-age for S. chinensis suggest sexual dimorphism. The attainment of sexual maturity in males occurred between 9 and 10 GLGs, corresponding to 230 cm total body length and 140 kg. The maximum combined testis mass of mature males comprised 0.42% of total body mass, and a roving male mating system was proposed. In females, sexual maturity occurred around 7.6 GLG, between 220 and 222 cm and 104 - 140 kg. The ovulation rate is estimated at 0.2 ovulations per annum, suggesting a calving interval of five years. It is evident from the results obtained in the present study that geographical differences exist in the life history parameters of S. chinensis. As a result, regional conservation and management strategies are imperative. Results from this study can therefore assist in assessing the status of existing population structures in the KwaZulu-Natal coastal waters, and the implementation of regional mitigation strategies to ensure the continued survival of humpback dolphins in the region.
- Full Text:
Feeding dynamics of suspension-feeders in the nearshore marine environment adjacent to two contrasting estuaries in the Eastern Cape, South Africa
- Authors: Vermeulen, Ilke
- Date: 2012
- Subjects: Suspension feeders -- South Africa -- Eastern Cape , Suspension feeders -- Food -- South Africa -- Eastern Cape , Coastal organisms -- South Africa -- Eastern Cape , Streamflow -- South Africa -- Eastern Cape , Tetraclitidae -- South Africa -- Eastern Cape , Mexilhao mussel -- South Africa -- Eastern Cape , Polychaeta -- South Africa -- Eastern Cape , Estuarine health -- South Africa -- Eastern Cape , Estuaries -- Freshwater inflow -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5916 , http://hdl.handle.net/10962/d1016242
- Description: Coastal transition zones form important interlinking regions where marine ecosystems, rivers and estuarine environments significantly influence each other. Coastal rocky shores are key habitats that sustain a variety of primary producers and invertebrates and due to the dynamic nature of coastal ecosystems, suspension-feeders on rocky shores can be influenced by an array of autochthonous and allochthonous food sources. Fatty acid and stable isotope trophic markers were employed to distinguish between regional and temporal changes in the potential food sources to rocky shore suspension-feeders in the Eastern Cape Province of South Africa. The primary aim was to assess the spatial and temporal influences of contrasting river flows on the available food sources to three indigenous coastal suspensionfeeders, namely the volcano barnacle Tetraclita serrata, brown mussel Perna perna and tubebuilding polychaete Gunnarea capensis. This was done by examining the intra- and interspecific changes in the fatty acid and stable isotope signatures of the barnacles, mussels and polychaetes in the adjacent marine environment of a freshwater-restricted (Kariega) and freshwater-dominated (Great Fish) estuary during austral summer and winter. Multivariate and Kruskal-Wallis analyses of variance on the fatty acid and isotopic signatures, respectively, identified significant regional changes in the barnacles and mussels, while only stable isotopes distinguished between the Kariega and Great Fish polychaetes (P < 0.05). In addition, significant temporal changes were observed in consumer fatty acids and isotope values in both regions (P < 0.05). Bacterial sources, detritus and phytoplankton assemblages, which are influenced by hydrology and vegetation, differed between regions and were mainly responsible for the regional and temporal separations. Principal component analyses on the consumer fatty acid signatures distinguished between animals situated upstream (i.e. north) and downstream (i.e. south) of the Kariega Estuary mouth in summer. The north/south separation was mainly due to greater contributions of diatoms to northernlocated animals and dinoflagellates and detritus to southern-located consumers. In addition, the south-flowing Agulhas Current on the eastern shores of southern Africa appeared to influence the north/south separation in the Kariega region, as water leaving the estuary was probably entrained into the south-easterly flowing currents, thereby depositing estuarinederived detritus to southern populations. In general, diatoms and detritus were essential food sources to the filter-feeders in summer, and flagellates, diatoms, zooplankton and detritus were important in winter. Coastal macroalgae was a key food source in the Kariega and Great Fish regions during both seasons. Consistently large levels of diatom markers (16:1n-7 and 20:5n-3) and dinoflagellate markers (22:6n-3) in consumer tissues in the Kariega and Great Fish regions identified that phytoplankton was their dominant food source. The barnacles, mussels and polychaetes had similar fatty acid markers and a fairly narrow δ¹³C range (-16.5 to -14.4 ‰), suggesting that they probably consumed similar food. Carbon isotope analyses, however, separated the suspension-feeders into slightly depleted (barnacles; -16.5 to -16.1 ‰), intermediate (mussels; -15.8 to -15.0 ‰) and enriched (polychaetes; -15.0 to -14.4 ‰) consumers, but did not provide conclusive evidence of their preferences for specific phytoplankton. Conversely, fatty acid analyses highlighted that barnacles and mussels had greater proportions of dinoflagellate markers (22:6n-3; 7.0-15.3 % TFA), while polychaetes had larger diatom levels (20:5n-3; 15.1-22.2 % TFA). In addition, all three species had consistently large contributions from bacterial fatty acids (15:0, i-16:0, 17:0 and i-18:0; 4.2-13.6 % TFA) in summer and winter, and large proportions of saturated fatty acids (33.3-53.1 % TFA) including those with 14 to 18 carbons, indicating that bacterial and detritus food sources played an important role in their diets. Barnacles had small levels of terrestrial markers (18:2n-6 and 18:3n-3; <2.5 % TFA) and demonstrated increased omnivorous feeding compared with the other suspension-feeders [increased levels of 20:1n-11 and 20:1n-9, higher 18:1n-9/18:1n-7 ratios at ~2.1, enriched δ¹⁵N values at ~10.6 ‰; zooplankton (potentially including microzooplankton, larvae and protists) contribution of up to 61 % of the diet]. Mussels contained significant proportions of the terrestrial markers (18:2n-6 and 18:3n-3; >2.5 % TFA) and exhibited intermediate omnivory (intermediate levels of 20:1n-11 and 20:1n-9, intermediate 18:1n-9/18:1n-7 ratios at ~1.3, less enriched δ¹⁵N values at ~7.9 ‰; zooplankton contribution of 10-15 % of the diet). The more depleted nitrogen signatures in the mussels relative to the barnacles and polychaetes possibly illustrated a stronger preference for autotrophic food. Polychaetes mainly consumed plant food sources (i.e. microalgae, macroalgae and detritus; high levels of i-18:0, 18:1n-9, 18:4n-3 and 20:5n-3) and displayed little omnivory (low levels of 20:1n-11 and 20:1n-9, low 18:1n-9/18:1n-7 ratios at ~0.4, intermediate δ¹⁵N values at ~9.1 ‰; zooplankton contribution of <10 % of the diet). The barnacles, mussels and polychaetes are all suspension-feeders, originally presumed to consume the same food sources. The variations observed among the species, therefore, may result from differences in the proportional contributions of the various food sources to their diets as well as distinctions in metabolism. The distinct changes in the fatty acid and stable isotope signatures in all three filter-feeders in the Kariega and Great Fish regions are likely influenced by the diversity in regional vegetation and hydrology in the different systems, combined with interspecific differences in resource partitioning among the species.
- Full Text:
- Authors: Vermeulen, Ilke
- Date: 2012
- Subjects: Suspension feeders -- South Africa -- Eastern Cape , Suspension feeders -- Food -- South Africa -- Eastern Cape , Coastal organisms -- South Africa -- Eastern Cape , Streamflow -- South Africa -- Eastern Cape , Tetraclitidae -- South Africa -- Eastern Cape , Mexilhao mussel -- South Africa -- Eastern Cape , Polychaeta -- South Africa -- Eastern Cape , Estuarine health -- South Africa -- Eastern Cape , Estuaries -- Freshwater inflow -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5916 , http://hdl.handle.net/10962/d1016242
- Description: Coastal transition zones form important interlinking regions where marine ecosystems, rivers and estuarine environments significantly influence each other. Coastal rocky shores are key habitats that sustain a variety of primary producers and invertebrates and due to the dynamic nature of coastal ecosystems, suspension-feeders on rocky shores can be influenced by an array of autochthonous and allochthonous food sources. Fatty acid and stable isotope trophic markers were employed to distinguish between regional and temporal changes in the potential food sources to rocky shore suspension-feeders in the Eastern Cape Province of South Africa. The primary aim was to assess the spatial and temporal influences of contrasting river flows on the available food sources to three indigenous coastal suspensionfeeders, namely the volcano barnacle Tetraclita serrata, brown mussel Perna perna and tubebuilding polychaete Gunnarea capensis. This was done by examining the intra- and interspecific changes in the fatty acid and stable isotope signatures of the barnacles, mussels and polychaetes in the adjacent marine environment of a freshwater-restricted (Kariega) and freshwater-dominated (Great Fish) estuary during austral summer and winter. Multivariate and Kruskal-Wallis analyses of variance on the fatty acid and isotopic signatures, respectively, identified significant regional changes in the barnacles and mussels, while only stable isotopes distinguished between the Kariega and Great Fish polychaetes (P < 0.05). In addition, significant temporal changes were observed in consumer fatty acids and isotope values in both regions (P < 0.05). Bacterial sources, detritus and phytoplankton assemblages, which are influenced by hydrology and vegetation, differed between regions and were mainly responsible for the regional and temporal separations. Principal component analyses on the consumer fatty acid signatures distinguished between animals situated upstream (i.e. north) and downstream (i.e. south) of the Kariega Estuary mouth in summer. The north/south separation was mainly due to greater contributions of diatoms to northernlocated animals and dinoflagellates and detritus to southern-located consumers. In addition, the south-flowing Agulhas Current on the eastern shores of southern Africa appeared to influence the north/south separation in the Kariega region, as water leaving the estuary was probably entrained into the south-easterly flowing currents, thereby depositing estuarinederived detritus to southern populations. In general, diatoms and detritus were essential food sources to the filter-feeders in summer, and flagellates, diatoms, zooplankton and detritus were important in winter. Coastal macroalgae was a key food source in the Kariega and Great Fish regions during both seasons. Consistently large levels of diatom markers (16:1n-7 and 20:5n-3) and dinoflagellate markers (22:6n-3) in consumer tissues in the Kariega and Great Fish regions identified that phytoplankton was their dominant food source. The barnacles, mussels and polychaetes had similar fatty acid markers and a fairly narrow δ¹³C range (-16.5 to -14.4 ‰), suggesting that they probably consumed similar food. Carbon isotope analyses, however, separated the suspension-feeders into slightly depleted (barnacles; -16.5 to -16.1 ‰), intermediate (mussels; -15.8 to -15.0 ‰) and enriched (polychaetes; -15.0 to -14.4 ‰) consumers, but did not provide conclusive evidence of their preferences for specific phytoplankton. Conversely, fatty acid analyses highlighted that barnacles and mussels had greater proportions of dinoflagellate markers (22:6n-3; 7.0-15.3 % TFA), while polychaetes had larger diatom levels (20:5n-3; 15.1-22.2 % TFA). In addition, all three species had consistently large contributions from bacterial fatty acids (15:0, i-16:0, 17:0 and i-18:0; 4.2-13.6 % TFA) in summer and winter, and large proportions of saturated fatty acids (33.3-53.1 % TFA) including those with 14 to 18 carbons, indicating that bacterial and detritus food sources played an important role in their diets. Barnacles had small levels of terrestrial markers (18:2n-6 and 18:3n-3; <2.5 % TFA) and demonstrated increased omnivorous feeding compared with the other suspension-feeders [increased levels of 20:1n-11 and 20:1n-9, higher 18:1n-9/18:1n-7 ratios at ~2.1, enriched δ¹⁵N values at ~10.6 ‰; zooplankton (potentially including microzooplankton, larvae and protists) contribution of up to 61 % of the diet]. Mussels contained significant proportions of the terrestrial markers (18:2n-6 and 18:3n-3; >2.5 % TFA) and exhibited intermediate omnivory (intermediate levels of 20:1n-11 and 20:1n-9, intermediate 18:1n-9/18:1n-7 ratios at ~1.3, less enriched δ¹⁵N values at ~7.9 ‰; zooplankton contribution of 10-15 % of the diet). The more depleted nitrogen signatures in the mussels relative to the barnacles and polychaetes possibly illustrated a stronger preference for autotrophic food. Polychaetes mainly consumed plant food sources (i.e. microalgae, macroalgae and detritus; high levels of i-18:0, 18:1n-9, 18:4n-3 and 20:5n-3) and displayed little omnivory (low levels of 20:1n-11 and 20:1n-9, low 18:1n-9/18:1n-7 ratios at ~0.4, intermediate δ¹⁵N values at ~9.1 ‰; zooplankton contribution of <10 % of the diet). The barnacles, mussels and polychaetes are all suspension-feeders, originally presumed to consume the same food sources. The variations observed among the species, therefore, may result from differences in the proportional contributions of the various food sources to their diets as well as distinctions in metabolism. The distinct changes in the fatty acid and stable isotope signatures in all three filter-feeders in the Kariega and Great Fish regions are likely influenced by the diversity in regional vegetation and hydrology in the different systems, combined with interspecific differences in resource partitioning among the species.
- Full Text:
The population structure of two estuarine fish species, atherina breviceps (Pisces: Atherinidae) and gilchristella aestuaria (Pisces: Clupeidae), along the Southern African coastline
- Authors: Norton, Olivia Bridget
- Date: 2006
- Subjects: Estuarine fishes -- South Africa , Estuarine ecology -- South Africa , Clupeidae -- South Africa , Silversides -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5745 , http://hdl.handle.net/10962/d1005431 , Estuarine fishes -- South Africa , Estuarine ecology -- South Africa , Clupeidae -- South Africa , Silversides -- South Africa
- Description: Phylogeographic patterns of coastal organisms with different life histories and breeding strategies may reveal patterns not consistent with the current delineation of the biogeographic provinces around South Africa. The subdivision of the South African coastline into these three main climatological or biogeographic regions: namely the cool temperate west coast, the warm temperate south coast and the subtropical east coast, is based on average seawater temperatures and hydrological conditions. Genealogies of two estuarine fish species Atherina breviceps, a marine breeder, and Gilchristella aestuaria, an estuarine spawner, were reconstructed using mitochondrial DNA (mtDNA) control region sequences. The study comprised two components, an assessment of a small dataset of both fish species to compare their population structure along the South African coastline and a more comprehensive investigation of the phylogeography of G. aestuaria collected from 21 estuaries around the coast. The comparative study of A. breviceps and G. aestuaria indicate different population distribution patterns along the South African coastline. Results of the A. breviceps analysis demonstrate substantial gene flow due to the random mixing of alleles, while the comparative G. aestuaria dataset indicates a more structured population and considerably less gene flow. The G. aestuaria population demonstrates geographic separation into four groups, namely the west coast (Great Berg), Bot (south coast), Seekoei (south coast) and east coast (Bushmans, Kasouga and Cefane). Results from the larger G. aestuaria dataset indicate that the phylogeographic patterns observed during this study do not conform to existing biogeographic boundaries along the southern African coastline. The delineation identified during this study between the warm temperate and subtropical regions is further south than originally perceived and this southward extension can be ascribed to the prevailing hydrology. The life history patterns and ecology of these two estuarine fish species appears key to understanding their population structure. These factors interact with environmental characteristics such as physical oceanography and the distribution of estuaries (along the coastline) to explain the observed distribution patterns and population structure of A. breviceps and G. aestuaria.
- Full Text:
- Authors: Norton, Olivia Bridget
- Date: 2006
- Subjects: Estuarine fishes -- South Africa , Estuarine ecology -- South Africa , Clupeidae -- South Africa , Silversides -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5745 , http://hdl.handle.net/10962/d1005431 , Estuarine fishes -- South Africa , Estuarine ecology -- South Africa , Clupeidae -- South Africa , Silversides -- South Africa
- Description: Phylogeographic patterns of coastal organisms with different life histories and breeding strategies may reveal patterns not consistent with the current delineation of the biogeographic provinces around South Africa. The subdivision of the South African coastline into these three main climatological or biogeographic regions: namely the cool temperate west coast, the warm temperate south coast and the subtropical east coast, is based on average seawater temperatures and hydrological conditions. Genealogies of two estuarine fish species Atherina breviceps, a marine breeder, and Gilchristella aestuaria, an estuarine spawner, were reconstructed using mitochondrial DNA (mtDNA) control region sequences. The study comprised two components, an assessment of a small dataset of both fish species to compare their population structure along the South African coastline and a more comprehensive investigation of the phylogeography of G. aestuaria collected from 21 estuaries around the coast. The comparative study of A. breviceps and G. aestuaria indicate different population distribution patterns along the South African coastline. Results of the A. breviceps analysis demonstrate substantial gene flow due to the random mixing of alleles, while the comparative G. aestuaria dataset indicates a more structured population and considerably less gene flow. The G. aestuaria population demonstrates geographic separation into four groups, namely the west coast (Great Berg), Bot (south coast), Seekoei (south coast) and east coast (Bushmans, Kasouga and Cefane). Results from the larger G. aestuaria dataset indicate that the phylogeographic patterns observed during this study do not conform to existing biogeographic boundaries along the southern African coastline. The delineation identified during this study between the warm temperate and subtropical regions is further south than originally perceived and this southward extension can be ascribed to the prevailing hydrology. The life history patterns and ecology of these two estuarine fish species appears key to understanding their population structure. These factors interact with environmental characteristics such as physical oceanography and the distribution of estuaries (along the coastline) to explain the observed distribution patterns and population structure of A. breviceps and G. aestuaria.
- Full Text:
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