Understanding the relationship between mangrove composition, stand dynamics and resource use in the Ntafufu estuary, Eastern Cape, as basis for sustainable resource use
- Mvakade, Monica, Rajkaran, Anusha
- Authors: Mvakade, Monica , Rajkaran, Anusha
- Date: 2020
- Subjects: Estuarine ecology -- South Africa -- Eastern Cape , Aquatic ecology , Marine sciences , Fresh water
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49215 , vital:41611
- Description: Traditionally, coastal communities along the Wild Coast in the Eastern Cape, used mangrove forests for their livelihoods and socio-economic needs. Mangroves along the Eastern Cape coast are threatened by both natural and human factors. The wood obtained from the mangroves by rural households was used as poles for house and fence construction, firewood, and traditional medicine. This is a threat to the status of several mangrove species in this and surrounding areas. The harvesting of mangrove trees will have a direct and indirect effect on the other biotic and abiotic components of the mangrove ecosystems. The Department of Agriculture, Forestry and Fisheries (DAFF) (currently the Department of Environment, Forestry and Fisheries, or DEFF), through the National Forest Act no 84 of 1998, was directly responsible for the wellbeing of the national forests in South Africa. This also includes the mangroves as a specific national forest type. Several estuaries with mangroves occur within state forests. The harvesting and clear-felling of trees for timber and land conversion and associated waste of harvested mangrove poles and laths causes the many changes in mangrove forests. The aim of this study was to develop a framework for sustainable management of the mangroves for the Mtambalala forest management unit. This was done in relation to the requirements of the current legislation, policy guidelines and business plan of the management authority. The aim was pursued through two specific objectives. The first objective was to understand the variation in the composition in different parts of the Ntafufu Estuary, and the population dynamics of the main mangrove species, as basis for the development of sustainable resource use practices. Plots along transects were used to measure seedling to adult ratios, population structure and abiotic characteristics. The second objective was to understand the community use and requirements of mangrove wood from the Ntafufu Estuary. A participatory approach was followed to collect demographic data from each community, the requirements of mangrove poles and behaviour of harvesters. This was used to set up a framework to guide the sustainable management of mangroves based on the current status and stand dynamics of the mangrove communities. There are three mangrove species found in the Ntafufu Estuary: Bruguiera gymnorhiza (black mangrove) regenerates under the mangrove canopy and forms layers of even-aged stands. Avicennia marina (white mangrove) does not regenerate under a mangrove canopy i.e. the seedlings establish outside the canopy. A few Rhizophora mucronata (red mangrove) trees exist in the lower intertidal zone and form multiple stems on stilt roots. The mangrove associate, Hibiscus tiliaceus (wild cotton tree- mangrove associate), forms dense clusters of scrambling stems. Some of the Avicennia individuals show signs of mangrove bleeding and one individual of Bruguiera showed indications of disease. Mngazana and Ntafufu Estuaries had the highest tree densities of 2594 and 1402 trees ha-1 respectively, typical of riverine mangrove forest. The seedling to adult ratio was high in this study: 12.8 for B. gymnorrhiza and 24.3 for A. marina. Abandoned cut stems and laths were found during the study. Bark harvested for traditional medicine and cattle feeding in mangroves was also prevalent and expected to reduce the health of the forest. Mangroves in the Ntafufu Estuary are expanding, and the population structure of the three mangrove species showed a healthy balance between young and mature stems. The harvesting of Black mangrove (B. gymnorrhiza) poles for mainly roof construction is relatively limited. As part of the functions of the DAFF, the use of the mangrove resources has to be balanced with the resource availability from the mangroves, and this should result in a healthy functioning mangrove forest. Development of a participatory forest management (PFM) plan for a forest estate and its forest management unit, require an understanding of the mangrove communities and their dynamics, and the current level of resource use associated with the mangroves. The study recommended that a Mangrove Pole Harvesters Group is needed to practice silviculture through guidance of relevant governmental personnel.
- Full Text:
- Date Issued: 2020
- Authors: Mvakade, Monica , Rajkaran, Anusha
- Date: 2020
- Subjects: Estuarine ecology -- South Africa -- Eastern Cape , Aquatic ecology , Marine sciences , Fresh water
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49215 , vital:41611
- Description: Traditionally, coastal communities along the Wild Coast in the Eastern Cape, used mangrove forests for their livelihoods and socio-economic needs. Mangroves along the Eastern Cape coast are threatened by both natural and human factors. The wood obtained from the mangroves by rural households was used as poles for house and fence construction, firewood, and traditional medicine. This is a threat to the status of several mangrove species in this and surrounding areas. The harvesting of mangrove trees will have a direct and indirect effect on the other biotic and abiotic components of the mangrove ecosystems. The Department of Agriculture, Forestry and Fisheries (DAFF) (currently the Department of Environment, Forestry and Fisheries, or DEFF), through the National Forest Act no 84 of 1998, was directly responsible for the wellbeing of the national forests in South Africa. This also includes the mangroves as a specific national forest type. Several estuaries with mangroves occur within state forests. The harvesting and clear-felling of trees for timber and land conversion and associated waste of harvested mangrove poles and laths causes the many changes in mangrove forests. The aim of this study was to develop a framework for sustainable management of the mangroves for the Mtambalala forest management unit. This was done in relation to the requirements of the current legislation, policy guidelines and business plan of the management authority. The aim was pursued through two specific objectives. The first objective was to understand the variation in the composition in different parts of the Ntafufu Estuary, and the population dynamics of the main mangrove species, as basis for the development of sustainable resource use practices. Plots along transects were used to measure seedling to adult ratios, population structure and abiotic characteristics. The second objective was to understand the community use and requirements of mangrove wood from the Ntafufu Estuary. A participatory approach was followed to collect demographic data from each community, the requirements of mangrove poles and behaviour of harvesters. This was used to set up a framework to guide the sustainable management of mangroves based on the current status and stand dynamics of the mangrove communities. There are three mangrove species found in the Ntafufu Estuary: Bruguiera gymnorhiza (black mangrove) regenerates under the mangrove canopy and forms layers of even-aged stands. Avicennia marina (white mangrove) does not regenerate under a mangrove canopy i.e. the seedlings establish outside the canopy. A few Rhizophora mucronata (red mangrove) trees exist in the lower intertidal zone and form multiple stems on stilt roots. The mangrove associate, Hibiscus tiliaceus (wild cotton tree- mangrove associate), forms dense clusters of scrambling stems. Some of the Avicennia individuals show signs of mangrove bleeding and one individual of Bruguiera showed indications of disease. Mngazana and Ntafufu Estuaries had the highest tree densities of 2594 and 1402 trees ha-1 respectively, typical of riverine mangrove forest. The seedling to adult ratio was high in this study: 12.8 for B. gymnorrhiza and 24.3 for A. marina. Abandoned cut stems and laths were found during the study. Bark harvested for traditional medicine and cattle feeding in mangroves was also prevalent and expected to reduce the health of the forest. Mangroves in the Ntafufu Estuary are expanding, and the population structure of the three mangrove species showed a healthy balance between young and mature stems. The harvesting of Black mangrove (B. gymnorrhiza) poles for mainly roof construction is relatively limited. As part of the functions of the DAFF, the use of the mangrove resources has to be balanced with the resource availability from the mangroves, and this should result in a healthy functioning mangrove forest. Development of a participatory forest management (PFM) plan for a forest estate and its forest management unit, require an understanding of the mangrove communities and their dynamics, and the current level of resource use associated with the mangroves. The study recommended that a Mangrove Pole Harvesters Group is needed to practice silviculture through guidance of relevant governmental personnel.
- Full Text:
- Date Issued: 2020
Characterization and ecology of selected micro-estuaries and micro-outlets in the Eastern Cape province, South Africa
- Authors: Magoro, Mandla Leon
- Date: 2018
- Subjects: Estuarine ecology -- South Africa -- Eastern Cape , Estuaries -- Management Estuaries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/31644 , vital:31640
- Description: South Africa has more than 200 Temporarily Open/Closed Estuaries (TOCEs) along its approximately 3000 km coastline. In addition, there are approximately 200 micro-estuaries and micro-outlets on the subcontinent, many of which share some of the characteristics with TOCEs but differ in that they are supplied by localised coastal stream catchments with a more limited supply of freshwater and less connectivity to the marine environment. Between 2015 and 2016, this study endeavoured to investigate the physico-chemical properties, microalgal dynamics as well as the seasonal species abundance and composition of aquatic invertebrates and fishes in four micro-estuaries and four micro-outlets along the warm-temperate section of the Eastern Cape coast. The micro-outlets were dominated by oligohaline or freshwater conditions, while the micro-estuaries were mostly mesohaline. Microalgal biomass in these systems was influenced by temperature, nutrient conditions and light availability. Chironomidae and Ephemeroptera dominated benthic macro-invertebrate communities in the micro-outlets, while Amphipoda and Mysida were most dominant in micro-estuaries. Copepoda and Amphipoda dominated the zooplankton assemblages in both system types. Nekton communities in micro-outlets were dominated by juvenile Myxus capensis and tadpoles (mostly Xenopus laevis), while Oreochromis mossambicus, Gilchristella aestuaria, M. capensis and Mugil cephalus were the four most common species in the micro-estuaries. Seasonal variations in physico-chemical parameters and community composition of both the nekton and invertebrates were recorded during this study. Micro-estuaries and micro-outlets exhibited relatively lower diversity and abundances of biota than TOCEs. Furthermore, the micro-estuaries have a low estuarine function when compared to TOCEs, while the micro-outlets have very limited estuarine characteristics and were dominated by freshwater biota. The micro-systems are smaller in size and contain lower proportions of estuary-associated taxa when compared to larger estuarine systems such as TOCEs and permanently open estuaries. The results of this study confirm that there are distinctions between the biota of iv the two micro-system types, thus making biotic assemblages, together with physico-chemical parameters, a viable tool for differentiating between micro-estuaries and micro-outlets. This study represents the first investigation into the ecological functioning of micro-estuaries and micro-outlets. As a whole, micro-systems serve as nursery areas for freshwater-associated invertebrate taxa. Due to their limited periods of stability, micro-estuaries serve as intermediate nursery areas for 0+ juveniles of estuary-associated marine fish which, after less than a year, then migrate to larger estuarine systems located nearby. The small catchment size and short period of stability in these systems heightens their level of sensitivity to water flow alterations through dams, direct water abstraction, afforestation and watercourse diversion, while their lower buffering capacity makes them more susceptible to pollution and nutrient inputs from intensive agricultural activities and urban expansion.
- Full Text:
- Date Issued: 2018
- Authors: Magoro, Mandla Leon
- Date: 2018
- Subjects: Estuarine ecology -- South Africa -- Eastern Cape , Estuaries -- Management Estuaries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/31644 , vital:31640
- Description: South Africa has more than 200 Temporarily Open/Closed Estuaries (TOCEs) along its approximately 3000 km coastline. In addition, there are approximately 200 micro-estuaries and micro-outlets on the subcontinent, many of which share some of the characteristics with TOCEs but differ in that they are supplied by localised coastal stream catchments with a more limited supply of freshwater and less connectivity to the marine environment. Between 2015 and 2016, this study endeavoured to investigate the physico-chemical properties, microalgal dynamics as well as the seasonal species abundance and composition of aquatic invertebrates and fishes in four micro-estuaries and four micro-outlets along the warm-temperate section of the Eastern Cape coast. The micro-outlets were dominated by oligohaline or freshwater conditions, while the micro-estuaries were mostly mesohaline. Microalgal biomass in these systems was influenced by temperature, nutrient conditions and light availability. Chironomidae and Ephemeroptera dominated benthic macro-invertebrate communities in the micro-outlets, while Amphipoda and Mysida were most dominant in micro-estuaries. Copepoda and Amphipoda dominated the zooplankton assemblages in both system types. Nekton communities in micro-outlets were dominated by juvenile Myxus capensis and tadpoles (mostly Xenopus laevis), while Oreochromis mossambicus, Gilchristella aestuaria, M. capensis and Mugil cephalus were the four most common species in the micro-estuaries. Seasonal variations in physico-chemical parameters and community composition of both the nekton and invertebrates were recorded during this study. Micro-estuaries and micro-outlets exhibited relatively lower diversity and abundances of biota than TOCEs. Furthermore, the micro-estuaries have a low estuarine function when compared to TOCEs, while the micro-outlets have very limited estuarine characteristics and were dominated by freshwater biota. The micro-systems are smaller in size and contain lower proportions of estuary-associated taxa when compared to larger estuarine systems such as TOCEs and permanently open estuaries. The results of this study confirm that there are distinctions between the biota of iv the two micro-system types, thus making biotic assemblages, together with physico-chemical parameters, a viable tool for differentiating between micro-estuaries and micro-outlets. This study represents the first investigation into the ecological functioning of micro-estuaries and micro-outlets. As a whole, micro-systems serve as nursery areas for freshwater-associated invertebrate taxa. Due to their limited periods of stability, micro-estuaries serve as intermediate nursery areas for 0+ juveniles of estuary-associated marine fish which, after less than a year, then migrate to larger estuarine systems located nearby. The small catchment size and short period of stability in these systems heightens their level of sensitivity to water flow alterations through dams, direct water abstraction, afforestation and watercourse diversion, while their lower buffering capacity makes them more susceptible to pollution and nutrient inputs from intensive agricultural activities and urban expansion.
- Full Text:
- Date Issued: 2018
The response of microalgal biomass and community composition to the chemical and physical dynamics of two Eastern Cape estuaries
- Authors: Cotiyane, Phumlile L
- Date: 2017
- Subjects: Estuarine plants -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Phytoplankton -- South Africa -- Eastern Cape , Algal blooms -- South Africa -- Eastern Cape , Algal blooms -- Monitoring-- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/4999 , vital:20751
- Description: Water quality characteristics of estuaries are influenced by both natural and anthropogenic activities. Estuaries situated in coastal urban areas are exposed to more perturbations than those in rural settings. This study determined the drivers of phytoplankton biomass and community composition in two Eastern Cape estuaries and evaluated the anthropogenic activities that influence the overall health of each estuary. The estuaries were sampled in summer and winter (2014, 2015). The water quality of the estuaries was determined by measuring the variability in physico-chemical parameters (salinity, temperature, dissolved oxygen and pH), nutrients, phytoplankton biomass and composition and faecal bacteria. Results show that both Mngazana and Nahoon are well oxygenated (~ 6.0 mg l-¹) and are saline systems (~ 35 ppt) due to low freshwater inputs into both estuaries. Mngazana Estuary exhibited low nutrient inputs along the length of the estuary including Creeks 1 and 2 with low chlorophyll a (4.0 ± 0.2 µg Chl-a r¹) being recorded during this study while Nahoon Estuary had an overall chlorophyll a of 3.5 ± 0.3 µg Chl-a r¹. The two estuaries were dominated by flagellates with phytoplankton blooms recorded seasonally. Possible eutrophic conditions were evident along the upper reaches of Nahoon indicated by nutrient accumulation and by the presence of cyanobacteria. This also this reflected the possible anthropogenic nutrient inputs originating from the Nahoon catchment despite the low freshwater inflow. The presence of faecal bacteria counts along both estuaries indicates the need for further investigation into the source of faecal contamination. The use of nutrient analyses and phytoplankton composition during this study enabled a clear description of the water characteristics of the investigated estuaries. Furthermore, the need for the adherence to freshwater flow requirements of estuaries to limit the dominance of marine waters was clearly illustrated. Urban runoff due to impervious surfaces increases nutrient inputs into estuaries while rural use of estuarine waters introduces contaminants into the system; coupled with low freshwater inputs and eutrophic conditions, the deterioration of estuarine water quality over time demonstrates the need for effective monitoring of these systems.
- Full Text:
- Date Issued: 2017
- Authors: Cotiyane, Phumlile L
- Date: 2017
- Subjects: Estuarine plants -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Phytoplankton -- South Africa -- Eastern Cape , Algal blooms -- South Africa -- Eastern Cape , Algal blooms -- Monitoring-- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/4999 , vital:20751
- Description: Water quality characteristics of estuaries are influenced by both natural and anthropogenic activities. Estuaries situated in coastal urban areas are exposed to more perturbations than those in rural settings. This study determined the drivers of phytoplankton biomass and community composition in two Eastern Cape estuaries and evaluated the anthropogenic activities that influence the overall health of each estuary. The estuaries were sampled in summer and winter (2014, 2015). The water quality of the estuaries was determined by measuring the variability in physico-chemical parameters (salinity, temperature, dissolved oxygen and pH), nutrients, phytoplankton biomass and composition and faecal bacteria. Results show that both Mngazana and Nahoon are well oxygenated (~ 6.0 mg l-¹) and are saline systems (~ 35 ppt) due to low freshwater inputs into both estuaries. Mngazana Estuary exhibited low nutrient inputs along the length of the estuary including Creeks 1 and 2 with low chlorophyll a (4.0 ± 0.2 µg Chl-a r¹) being recorded during this study while Nahoon Estuary had an overall chlorophyll a of 3.5 ± 0.3 µg Chl-a r¹. The two estuaries were dominated by flagellates with phytoplankton blooms recorded seasonally. Possible eutrophic conditions were evident along the upper reaches of Nahoon indicated by nutrient accumulation and by the presence of cyanobacteria. This also this reflected the possible anthropogenic nutrient inputs originating from the Nahoon catchment despite the low freshwater inflow. The presence of faecal bacteria counts along both estuaries indicates the need for further investigation into the source of faecal contamination. The use of nutrient analyses and phytoplankton composition during this study enabled a clear description of the water characteristics of the investigated estuaries. Furthermore, the need for the adherence to freshwater flow requirements of estuaries to limit the dominance of marine waters was clearly illustrated. Urban runoff due to impervious surfaces increases nutrient inputs into estuaries while rural use of estuarine waters introduces contaminants into the system; coupled with low freshwater inputs and eutrophic conditions, the deterioration of estuarine water quality over time demonstrates the need for effective monitoring of these systems.
- Full Text:
- Date Issued: 2017
Spatial and temporal variability in water quality characteristics of the Swartkops Estuary
- Authors: Pretorius, Liaan Marié
- Date: 2015
- Subjects: Estuarine ecology -- South Africa -- Eastern Cape , Hydrology -- South Africa -- Eastern Cape , Water quality -- South Africa -- Swarkops River Estuary
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/4176 , vital:20563
- Description: Water quality characteristics of the heavily urbanised and industrialised Swartkops River catchment in the Eastern Cape has been the focus of several studies since the 1970s. Overloaded and poorly maintained wastewater treatment works (WWTW), polluted stormwater runoff and solid waste have had a negative impact on the water quality status of the Swartkops River and estuary. Past studies have revealed that a distinct relationship exists between land use activities and the water quality of the Swartkops Estuary, which in turn has raised concerns pertaining to the ecological, economic, recreational, and cultural value of the estuaryThe Swartkops Estuary has a Present Ecological State (PES) of Category D(1) and a Recommended Ecological Category (REC)(2) of a C (Van Niekerk et al., 2014). It is known that effective management of anthropogenic impacts on coastal systems requires a thorough understanding of the system’s biological responses to wastewater discharges and to hydrologic changes. For this reason, the objective of this study was to determine the current water quality status of the Swartkops Estuary, and to gain greater insight into factors controlling eutrophication. This was important as outdated water quality information was used in the Swartkops Integrated Environmental Management Plan (Enviro-Fish Africa, 2011) due to a lack of current data. To determine the current water quality status of the Swartkops Estuary the present study investigated spatial and temporal variability in physico-chemical parameters, nutrients, phytoplankton biomass and community composition, faecal bacteria, and “where possible” related this to historical water quality data. In general, points of entry into the estuary were investigated for their impact on nutrient enrichment and the bacteriological status of the estuary. Water quality surveys were completed in September 2012, November 2012, February 2013, May 2013 and August 2013The present study found evidence to suggest that water is not flushed as efficiently from the estuary as was previously the case, and that the natural hydrology of the estuary has been modified. These changes appear to be the effect of large volumes of wastewater discharges from the wastewater treatment works (WWTW), which has led to the additional stresses of increased vertical stratification and reduced vertical mixing. A build-up of dissolved inorganic nutrients has given rise to persistent eutrophic conditions and phytoplankton blooms occurring from the middle reaches to the tidal limit of the estuary. These findings were associated with a generally well oxygenated estuary; however, bottom water hypoxic conditions were recorded in the upper reaches of the estuary on two occasions and were generally associated with bloom.forming flagellates. Elevated concentrations of inorganic nutrients stimulated phytoplankton to attain high biomass ranging from 0 to 248 g l-1 (31.8 6.56 g l-1). All nutrients displayed positive linear gradients from the mouth to the tidal limit, showed significant (p < 0.05) temporal and spatial variability, and were significantly (p < 0.05) correlated with phytoplankton biomass. Phytoplankton blooms (> 10 000 cells ml-1) of several different groups were recorded from the middle reaches of the estuary to the tidal limit. Diatoms were the dominant group during increased freshwater inflow (at mean daily flow rate of 2.14 m3 s-1) and low DIP levels, whereas flagellates were generally the dominant group during reduced flow and under higher nutrient levels. Although the different tidal stages had no effect on phytoplankton biomass per se, it did support co-existance between phytoplankton groups. This was noted during the spring ebb tide in September 2012 (i.e. flagellates, diatoms and dinoflagellate) and in February 2013 (i.e. dinoflagellates, diatoms and chlorophytes). Phytoplankton blooms have become persistent in the middle to upper reaches of the estuary where chlorophyll-a was > 20 µg l-1 and cell density exceeded 10 000 cells ml-1; a situation not reported in previous studies. The Motherwell Canal was and still is the main source of nitrogen (generally in the form of ammonium) to the estuary, whereas the Swartkops River is still the primary source of phosphorus to the estuary. Since the stormwater canal services the large residential area of Motherwell where leaks in the sewer system, the dumping of night soil buckets, and faulty pumps are often reported, polluted discharges from the Motherwell Canal can enter the canal at any given point. In contrast to the canal, DIP loading from the Swartkops River to the estuary generally occurred under conditions of low flow, whereas nitrogen showed no apparent relationship. Faecal bacteria originating from the Motherwell Canal had the most profound effect on the bacteriological status in the middle reaches of the estuary, whereas the Swartkops River had an intermediate effect due to bacteria die-offs occurring between the point of release from the WWTW to the riverine reaches and the tidal limit of the estuary. Nevertheless, Escherichia coli and enterococci levels are still high, especially in the summer months rendering the estuary unsafe for recreation during this season. Historical data on trace metals in the water column were limited and thus observations from the present study could not be concluded with much confidence. However, preliminary data suggest that levels of copper, zinc, iron and cadmium have increased by at least 90% in the estuary, at the tidal limit of the estuary and in the Markman and Motherwell canals. High inputs of nutrients, trace metals and faecal bacteria to the estuary from land-use activities indicate the necessity for remedial actions with the main objective being to conserve and protect the estuary’s recreational, ecological and economic functions.
- Full Text:
- Date Issued: 2015
- Authors: Pretorius, Liaan Marié
- Date: 2015
- Subjects: Estuarine ecology -- South Africa -- Eastern Cape , Hydrology -- South Africa -- Eastern Cape , Water quality -- South Africa -- Swarkops River Estuary
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/4176 , vital:20563
- Description: Water quality characteristics of the heavily urbanised and industrialised Swartkops River catchment in the Eastern Cape has been the focus of several studies since the 1970s. Overloaded and poorly maintained wastewater treatment works (WWTW), polluted stormwater runoff and solid waste have had a negative impact on the water quality status of the Swartkops River and estuary. Past studies have revealed that a distinct relationship exists between land use activities and the water quality of the Swartkops Estuary, which in turn has raised concerns pertaining to the ecological, economic, recreational, and cultural value of the estuaryThe Swartkops Estuary has a Present Ecological State (PES) of Category D(1) and a Recommended Ecological Category (REC)(2) of a C (Van Niekerk et al., 2014). It is known that effective management of anthropogenic impacts on coastal systems requires a thorough understanding of the system’s biological responses to wastewater discharges and to hydrologic changes. For this reason, the objective of this study was to determine the current water quality status of the Swartkops Estuary, and to gain greater insight into factors controlling eutrophication. This was important as outdated water quality information was used in the Swartkops Integrated Environmental Management Plan (Enviro-Fish Africa, 2011) due to a lack of current data. To determine the current water quality status of the Swartkops Estuary the present study investigated spatial and temporal variability in physico-chemical parameters, nutrients, phytoplankton biomass and community composition, faecal bacteria, and “where possible” related this to historical water quality data. In general, points of entry into the estuary were investigated for their impact on nutrient enrichment and the bacteriological status of the estuary. Water quality surveys were completed in September 2012, November 2012, February 2013, May 2013 and August 2013The present study found evidence to suggest that water is not flushed as efficiently from the estuary as was previously the case, and that the natural hydrology of the estuary has been modified. These changes appear to be the effect of large volumes of wastewater discharges from the wastewater treatment works (WWTW), which has led to the additional stresses of increased vertical stratification and reduced vertical mixing. A build-up of dissolved inorganic nutrients has given rise to persistent eutrophic conditions and phytoplankton blooms occurring from the middle reaches to the tidal limit of the estuary. These findings were associated with a generally well oxygenated estuary; however, bottom water hypoxic conditions were recorded in the upper reaches of the estuary on two occasions and were generally associated with bloom.forming flagellates. Elevated concentrations of inorganic nutrients stimulated phytoplankton to attain high biomass ranging from 0 to 248 g l-1 (31.8 6.56 g l-1). All nutrients displayed positive linear gradients from the mouth to the tidal limit, showed significant (p < 0.05) temporal and spatial variability, and were significantly (p < 0.05) correlated with phytoplankton biomass. Phytoplankton blooms (> 10 000 cells ml-1) of several different groups were recorded from the middle reaches of the estuary to the tidal limit. Diatoms were the dominant group during increased freshwater inflow (at mean daily flow rate of 2.14 m3 s-1) and low DIP levels, whereas flagellates were generally the dominant group during reduced flow and under higher nutrient levels. Although the different tidal stages had no effect on phytoplankton biomass per se, it did support co-existance between phytoplankton groups. This was noted during the spring ebb tide in September 2012 (i.e. flagellates, diatoms and dinoflagellate) and in February 2013 (i.e. dinoflagellates, diatoms and chlorophytes). Phytoplankton blooms have become persistent in the middle to upper reaches of the estuary where chlorophyll-a was > 20 µg l-1 and cell density exceeded 10 000 cells ml-1; a situation not reported in previous studies. The Motherwell Canal was and still is the main source of nitrogen (generally in the form of ammonium) to the estuary, whereas the Swartkops River is still the primary source of phosphorus to the estuary. Since the stormwater canal services the large residential area of Motherwell where leaks in the sewer system, the dumping of night soil buckets, and faulty pumps are often reported, polluted discharges from the Motherwell Canal can enter the canal at any given point. In contrast to the canal, DIP loading from the Swartkops River to the estuary generally occurred under conditions of low flow, whereas nitrogen showed no apparent relationship. Faecal bacteria originating from the Motherwell Canal had the most profound effect on the bacteriological status in the middle reaches of the estuary, whereas the Swartkops River had an intermediate effect due to bacteria die-offs occurring between the point of release from the WWTW to the riverine reaches and the tidal limit of the estuary. Nevertheless, Escherichia coli and enterococci levels are still high, especially in the summer months rendering the estuary unsafe for recreation during this season. Historical data on trace metals in the water column were limited and thus observations from the present study could not be concluded with much confidence. However, preliminary data suggest that levels of copper, zinc, iron and cadmium have increased by at least 90% in the estuary, at the tidal limit of the estuary and in the Markman and Motherwell canals. High inputs of nutrients, trace metals and faecal bacteria to the estuary from land-use activities indicate the necessity for remedial actions with the main objective being to conserve and protect the estuary’s recreational, ecological and economic functions.
- Full Text:
- Date Issued: 2015
The role of the sandprawn, Callichirus kraussi, as an ecosystem engineer in a temporarily open/closed Eastern Cape estuary, South Africa
- Authors: Njozela, Cuma
- Date: 2013
- Subjects: Estuarine biology -- South Africa -- Eastern Cape , Decapoda (Crustacea) -- South Africa -- Eastern Cape , Biotic communities -- South Africa -- Eastern Cape , Bioenergetics -- South Africa -- Eastern Cape , Shrimps -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5583 , http://hdl.handle.net/10962/d1001539 , Estuarine biology -- South Africa -- Eastern Cape , Decapoda (Crustacea) -- South Africa -- Eastern Cape , Biotic communities -- South Africa -- Eastern Cape , Bioenergetics -- South Africa -- Eastern Cape , Shrimps -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape
- Description: The role of the sandprawn, Callichirus (=Callianassa) kraussi (Stebbing), as an ecosystem engineer was assessed in the lower reach of the temporarily open/closed Kasouga Estuary situated along the Eastern Cape coastline of southern Africa over the period April 2010 to June 2011. The study comprised two distinct components, a field study and a caging experiment. The field study assessed the correlation between sand prawn densities and selected physico-chemical (organic content of the sediment and bioturbation) and biological (microphytobenthic algal concentrations and macrobenthic abundance and biomass) variables in 50 quadrants in the lower reach of the estuary. Densities of the sand prawn within the quadrants ranged from 0 to 156 ind m⁻² (mean = 37 ind m⁻²). There were no significant correlations between the densities of the sandprawn and the estimates of the organic content of the sediment and the abundance and biomass of the macrofauna (P > 0.05 in all cases). Numerical analyses failed to identify any effect of the sandprawn density on the macrofaunal community structure. The rate of bioturbation was, however, strongly correlated to the sand prawn density. Similarly, the microphytobenthic alga concentrations were significantly negatively correlated to the sand prawn densities ((P < 0.05). The absence of any distinct impact of the sandprawn on the macrobenthic community structure appeared to be related to their low densities in the lower reach of the estuary during the study. To better understand the role of the sandprawn as an ecosystem engineer, a caging experiment was conducted using inclusion and exclusion treatments (n= 5 for each treatment). Densities of the sandprawn in the inclusion treatments (80 ind m⁻²) were in the range of the natural densities within the estuary. The experiment was conducted over a period of 18 weeks in the lower reach of the estuary during summer. The presence of the sandprawn, C kraussi, contributed to a significant decrease in the microphytobenthic algal concentrations and the abundance and biomass of the macrofauna (P < 0.05 in all cases). The decrease in the microphytobenthic algal concentrations in the presence of the sandprawn appeared to be related to the res-suspension of the sediments (bioturbation) generated by the burrowing and feeding activities of the sandprawn. The observed decrease in macrofaunal abundances and biomass in the inclusion treatments appeared to be mediated by both the decreased food availability (mainly the microphytobenthic algae) and the burial of organisms within the sediments. Numerical analysis indicated that the sandprawn did, however, not contribute to a change in the species composition of the macrofauna. Results of the current study indicate that C.kraussi plays an important role in structuring the invertebrate community and energy flow within temporarily/open closed Kasouga Estuary.
- Full Text:
- Date Issued: 2013
- Authors: Njozela, Cuma
- Date: 2013
- Subjects: Estuarine biology -- South Africa -- Eastern Cape , Decapoda (Crustacea) -- South Africa -- Eastern Cape , Biotic communities -- South Africa -- Eastern Cape , Bioenergetics -- South Africa -- Eastern Cape , Shrimps -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5583 , http://hdl.handle.net/10962/d1001539 , Estuarine biology -- South Africa -- Eastern Cape , Decapoda (Crustacea) -- South Africa -- Eastern Cape , Biotic communities -- South Africa -- Eastern Cape , Bioenergetics -- South Africa -- Eastern Cape , Shrimps -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape
- Description: The role of the sandprawn, Callichirus (=Callianassa) kraussi (Stebbing), as an ecosystem engineer was assessed in the lower reach of the temporarily open/closed Kasouga Estuary situated along the Eastern Cape coastline of southern Africa over the period April 2010 to June 2011. The study comprised two distinct components, a field study and a caging experiment. The field study assessed the correlation between sand prawn densities and selected physico-chemical (organic content of the sediment and bioturbation) and biological (microphytobenthic algal concentrations and macrobenthic abundance and biomass) variables in 50 quadrants in the lower reach of the estuary. Densities of the sand prawn within the quadrants ranged from 0 to 156 ind m⁻² (mean = 37 ind m⁻²). There were no significant correlations between the densities of the sandprawn and the estimates of the organic content of the sediment and the abundance and biomass of the macrofauna (P > 0.05 in all cases). Numerical analyses failed to identify any effect of the sandprawn density on the macrofaunal community structure. The rate of bioturbation was, however, strongly correlated to the sand prawn density. Similarly, the microphytobenthic alga concentrations were significantly negatively correlated to the sand prawn densities ((P < 0.05). The absence of any distinct impact of the sandprawn on the macrobenthic community structure appeared to be related to their low densities in the lower reach of the estuary during the study. To better understand the role of the sandprawn as an ecosystem engineer, a caging experiment was conducted using inclusion and exclusion treatments (n= 5 for each treatment). Densities of the sandprawn in the inclusion treatments (80 ind m⁻²) were in the range of the natural densities within the estuary. The experiment was conducted over a period of 18 weeks in the lower reach of the estuary during summer. The presence of the sandprawn, C kraussi, contributed to a significant decrease in the microphytobenthic algal concentrations and the abundance and biomass of the macrofauna (P < 0.05 in all cases). The decrease in the microphytobenthic algal concentrations in the presence of the sandprawn appeared to be related to the res-suspension of the sediments (bioturbation) generated by the burrowing and feeding activities of the sandprawn. The observed decrease in macrofaunal abundances and biomass in the inclusion treatments appeared to be mediated by both the decreased food availability (mainly the microphytobenthic algae) and the burial of organisms within the sediments. Numerical analysis indicated that the sandprawn did, however, not contribute to a change in the species composition of the macrofauna. Results of the current study indicate that C.kraussi plays an important role in structuring the invertebrate community and energy flow within temporarily/open closed Kasouga Estuary.
- Full Text:
- Date Issued: 2013
The distribution and diversity of macroalgae in selected estuaries along the Eastern Cape coast of South Africa
- Authors: Prinsloo, Shireen
- Date: 2012
- Subjects: Estuarine ecology -- South Africa -- Eastern Cape , Algal communities -- South Africa -- Eastern Cape , Marine plants -- Economic aspects -- South Africa -- Eastern Cape , Estuarine area conservation -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10631 , http://hdl.handle.net/10948/d1012314 , Estuarine ecology -- South Africa -- Eastern Cape , Algal communities -- South Africa -- Eastern Cape , Marine plants -- Economic aspects -- South Africa -- Eastern Cape , Estuarine area conservation -- South Africa -- Eastern Cape
- Description: The growth and accumulation of macroalgae in estuaries are a common sight throughout the world (Boyer and Fong, 2005). Because macroalgae establish such complex but important links with other components within an estuary, it is essential to know which variables control and regulate their occurrences. The type of algae that will occur in an estuary depends however, on the physical and chemical features of the particular estuary (Lobban and Harrison, 1994). The focus of this study was to document and provide a listing of algae from estuaries around the Eastern Cape coast of South Africa and describe the communities which form within each estuarine habitat. The questions posed were: Do algae assemblages differ in estuaries with different environmental conditions? Are different plant communities inhabited by different algae communities? Also, are algae diverse in estuaries that are in a pristine condition? The estuaries were Mngazana, Ngqusi/Nxaxo, Mtati, Mpekweni, East Kleinemonde, West Kleinemonde, Kariega, Bushmans, Kowie and the Sundays estuary. Percentage cover surveys were conducted and environmental parameters recorded to determine community structure of algae and their environmental tolerances. A total of 49 different macroalgal species were identified from 11 estuaries, which were dominated by Chlorophytes (23 species) and Rhodophytes (17 species). The Ochrophytes consisted of 10 species. The highest number of species recorded was 29 at the Bushmans estuary (March 2009), while the lowest number (4 species) was recorded at Mtati (October 2008). Common Chlorophytes found included Ulva prolifera, Chaetomorpha linum and Codium tenue. In the Division Ochrophyta, species from the Genus Ectocarpus were the most common. Of the red algae filamentous reds, Polysiphonia incompta and Polysiphonia kowiensis were the common algae found at estuaries. Salinity (p= 0.029861; n= 49) and temperature (p= 0.037641; n= 49) were the driving environmental parameters of estuaries and significantly influenced richness of species. In ordination analyses, patterns of biogeographic distribution were noticeable and were described by salinity. Four gradients caused by salinity were therefore found – which is inversely correlated to water clarity. Moreover, a clear split between temporarily open/closed and the permanently open estuaries was observed. Samples grouped into four communities presumably based on the similarity in conditions of estuaries. Within each estuarine community and major type of estuary there was a range of environmental conditions. However, the macroalgae within each community may not have been colonists of or found in greatest abundances in the estuaries of these communities per se, but may have grouped together in this manner based on the optimum growing conditions for them. Also, specific algal groups were not directly determined by the type of estuary they were found in; they were driven by environmental ranges rather. The results therefore support hypothesis one which states species distribution and diversity differ and are influenced by environmental gradients of the estuary. Although close species and habitat relationships were apparent from the ordination analyses, providing support for hypothesis two which states “Different plant communities in estuaries will be inhabited by different macroalgae communities”, the evidence was not substantial enough to provide sufficient support for the hypothesis. Lastly, the hypothesis “Macroalgae are diverse in estuaries that are in a pristine condition” was not accepted as highest species numbers were found in estuaries of greatest anthropogenic disturbance (e.g. Bushmans estuary) and not in estuaries which where ecologically more natural (e.g. Mtati estuary). By doing monthly macroalgal sampling over a period of one year for example one would obtain greater information of biodiversity, and patterns of macroalgal seasonality may be uncovered as well. This is an area of reasearch which needs to be investigated in the future as it would greatly add to the understanding of the role macroalge have in an estuarine environment.
- Full Text:
- Date Issued: 2012
- Authors: Prinsloo, Shireen
- Date: 2012
- Subjects: Estuarine ecology -- South Africa -- Eastern Cape , Algal communities -- South Africa -- Eastern Cape , Marine plants -- Economic aspects -- South Africa -- Eastern Cape , Estuarine area conservation -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10631 , http://hdl.handle.net/10948/d1012314 , Estuarine ecology -- South Africa -- Eastern Cape , Algal communities -- South Africa -- Eastern Cape , Marine plants -- Economic aspects -- South Africa -- Eastern Cape , Estuarine area conservation -- South Africa -- Eastern Cape
- Description: The growth and accumulation of macroalgae in estuaries are a common sight throughout the world (Boyer and Fong, 2005). Because macroalgae establish such complex but important links with other components within an estuary, it is essential to know which variables control and regulate their occurrences. The type of algae that will occur in an estuary depends however, on the physical and chemical features of the particular estuary (Lobban and Harrison, 1994). The focus of this study was to document and provide a listing of algae from estuaries around the Eastern Cape coast of South Africa and describe the communities which form within each estuarine habitat. The questions posed were: Do algae assemblages differ in estuaries with different environmental conditions? Are different plant communities inhabited by different algae communities? Also, are algae diverse in estuaries that are in a pristine condition? The estuaries were Mngazana, Ngqusi/Nxaxo, Mtati, Mpekweni, East Kleinemonde, West Kleinemonde, Kariega, Bushmans, Kowie and the Sundays estuary. Percentage cover surveys were conducted and environmental parameters recorded to determine community structure of algae and their environmental tolerances. A total of 49 different macroalgal species were identified from 11 estuaries, which were dominated by Chlorophytes (23 species) and Rhodophytes (17 species). The Ochrophytes consisted of 10 species. The highest number of species recorded was 29 at the Bushmans estuary (March 2009), while the lowest number (4 species) was recorded at Mtati (October 2008). Common Chlorophytes found included Ulva prolifera, Chaetomorpha linum and Codium tenue. In the Division Ochrophyta, species from the Genus Ectocarpus were the most common. Of the red algae filamentous reds, Polysiphonia incompta and Polysiphonia kowiensis were the common algae found at estuaries. Salinity (p= 0.029861; n= 49) and temperature (p= 0.037641; n= 49) were the driving environmental parameters of estuaries and significantly influenced richness of species. In ordination analyses, patterns of biogeographic distribution were noticeable and were described by salinity. Four gradients caused by salinity were therefore found – which is inversely correlated to water clarity. Moreover, a clear split between temporarily open/closed and the permanently open estuaries was observed. Samples grouped into four communities presumably based on the similarity in conditions of estuaries. Within each estuarine community and major type of estuary there was a range of environmental conditions. However, the macroalgae within each community may not have been colonists of or found in greatest abundances in the estuaries of these communities per se, but may have grouped together in this manner based on the optimum growing conditions for them. Also, specific algal groups were not directly determined by the type of estuary they were found in; they were driven by environmental ranges rather. The results therefore support hypothesis one which states species distribution and diversity differ and are influenced by environmental gradients of the estuary. Although close species and habitat relationships were apparent from the ordination analyses, providing support for hypothesis two which states “Different plant communities in estuaries will be inhabited by different macroalgae communities”, the evidence was not substantial enough to provide sufficient support for the hypothesis. Lastly, the hypothesis “Macroalgae are diverse in estuaries that are in a pristine condition” was not accepted as highest species numbers were found in estuaries of greatest anthropogenic disturbance (e.g. Bushmans estuary) and not in estuaries which where ecologically more natural (e.g. Mtati estuary). By doing monthly macroalgal sampling over a period of one year for example one would obtain greater information of biodiversity, and patterns of macroalgal seasonality may be uncovered as well. This is an area of reasearch which needs to be investigated in the future as it would greatly add to the understanding of the role macroalge have in an estuarine environment.
- Full Text:
- Date Issued: 2012
Structure and functioning of fish assemblages in two South African estuaries, with emphasis on the presence and absence of aquatic macrophyte beds
- Authors: Sheppard, Jill Nicole
- Date: 2010
- Subjects: Estuaries -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5321 , http://hdl.handle.net/10962/d1005166 , Estuaries -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape
- Description: Temporarily open/closed estuaries (TOCEs) are the dominant estuary type in South Africa. These systems are often characterized by extensive beds of submerged macrophytes, which form important foraging and shelter habitats for fishes, especially for estuary-dependent fish species such as the Cape stumpnose Rhabdosargus holubi and Cape moony Monodactylus falciformis that are commonly associated with them. A loss of submerged macrophytes from an estuary has been shown to affect the fish community as well as reducing overall system productivity. The TOC East Kleinemonde Estuary, situated in the warm-temperate biogeographic region of South Africa has been subject to an ongoing long-term fish monitoring project since 1995. During the period 1995 to 2002, this estuary contained large beds of the submerged macrophytes Ruppia cirrhosa and Potamogeton pectinatus. However, subsequent to a major flood event in 2003 these macrophytes have been largely absent from this system. The effect of the loss of submerged macrophytes on the East Kleinemonde fish assemblage was investigated through an analysis of seine and gill net catch data. Seine net catches for a 12 year period, encompassing six years of macrophyte presence and six years of macrophyte senescence, revealed changes in the relative abundance of certain fish species. Vegetation-associated species such as R. holubi and M. falciformis decreased in abundance whereas sediment-associated species, especially members of the family Mugilidae, increased in abundance following loss of the macrophytes in this estuary. The critically endangered pipefish Syngnathus watermeyeri was only recorded in catches during years in which macrophyte beds were present. In addition to the analysis of catch data, the importance of macrophytes as a primary energy source for selected estuarine fishes was explored through the analysis of carbon and nitrogen stable isotopes. Prior to conducting these analyses, common methodological practices to address the presence of carbonates and lipids within isotope samples were evaluated. A subset of samples were either acid washed to remove carbonates, or lipids were removed according to the method of Bligh and Dyer (1959) as both of these compounds have been shown to affect stable carbon and nitrogen isotope ratios. The suitability of the lipid normalization models of Fry (2002) and Post et al. (2007) for samples of estuarine fish muscle were also tested. Based on this evaluation both models are suitable for use with estuarine fish muscle tissue, however since neither carbonate nor lipid content of any of the samples used in this study was high all samples were left untreated in the following analysis. Carbon isotope ratios from a wide range of fish species collected from the East Kleinemonde Estuary during the macrophyte-senescent phase were compared with individuals of the same species from the neighbouring West Kleinemonde Estuary (where extensive beds of R. cirrhosa and P. pectinatus were present) and revealed the influence of submerged macrophyte material in the diet of fishes in the latter system. However, it was apparent that these plants are not directly consumed but rather contribute to the detrital pool that forms a food source for most invertebrate and some fish species. The most significant source of carbon for East Kleinemonde fishes during the macrophyte senescent phase appeared to have a more depleted origin; probably from benthic or pelagic microalgae. In conclusion, while the importance of macrophyte beds as shelter and foraging habitats for estuarine fishes are well documented, their role in terms of the structuring and functioning of fish assemblages in TOCEs remains somewhat uncertain. The findings of this study were possibly masked by the resilience of vegetation-associated species to the loss of this habitat, as well as by life history characteristics of species such as R. holubi that allow their numerical dominance despite habitat change. Nonetheless, macrophyte senescence in the East Kleinemonde Estuary resulted in the loss of at least one species and the reduced abundance of vegetation-associated species, probably reflective of reduced food resources and/or increased vulnerability to predation. As a result, beds of submerged macrophytes are an important habitat within TOCEs.
- Full Text:
- Date Issued: 2010
- Authors: Sheppard, Jill Nicole
- Date: 2010
- Subjects: Estuaries -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5321 , http://hdl.handle.net/10962/d1005166 , Estuaries -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape
- Description: Temporarily open/closed estuaries (TOCEs) are the dominant estuary type in South Africa. These systems are often characterized by extensive beds of submerged macrophytes, which form important foraging and shelter habitats for fishes, especially for estuary-dependent fish species such as the Cape stumpnose Rhabdosargus holubi and Cape moony Monodactylus falciformis that are commonly associated with them. A loss of submerged macrophytes from an estuary has been shown to affect the fish community as well as reducing overall system productivity. The TOC East Kleinemonde Estuary, situated in the warm-temperate biogeographic region of South Africa has been subject to an ongoing long-term fish monitoring project since 1995. During the period 1995 to 2002, this estuary contained large beds of the submerged macrophytes Ruppia cirrhosa and Potamogeton pectinatus. However, subsequent to a major flood event in 2003 these macrophytes have been largely absent from this system. The effect of the loss of submerged macrophytes on the East Kleinemonde fish assemblage was investigated through an analysis of seine and gill net catch data. Seine net catches for a 12 year period, encompassing six years of macrophyte presence and six years of macrophyte senescence, revealed changes in the relative abundance of certain fish species. Vegetation-associated species such as R. holubi and M. falciformis decreased in abundance whereas sediment-associated species, especially members of the family Mugilidae, increased in abundance following loss of the macrophytes in this estuary. The critically endangered pipefish Syngnathus watermeyeri was only recorded in catches during years in which macrophyte beds were present. In addition to the analysis of catch data, the importance of macrophytes as a primary energy source for selected estuarine fishes was explored through the analysis of carbon and nitrogen stable isotopes. Prior to conducting these analyses, common methodological practices to address the presence of carbonates and lipids within isotope samples were evaluated. A subset of samples were either acid washed to remove carbonates, or lipids were removed according to the method of Bligh and Dyer (1959) as both of these compounds have been shown to affect stable carbon and nitrogen isotope ratios. The suitability of the lipid normalization models of Fry (2002) and Post et al. (2007) for samples of estuarine fish muscle were also tested. Based on this evaluation both models are suitable for use with estuarine fish muscle tissue, however since neither carbonate nor lipid content of any of the samples used in this study was high all samples were left untreated in the following analysis. Carbon isotope ratios from a wide range of fish species collected from the East Kleinemonde Estuary during the macrophyte-senescent phase were compared with individuals of the same species from the neighbouring West Kleinemonde Estuary (where extensive beds of R. cirrhosa and P. pectinatus were present) and revealed the influence of submerged macrophyte material in the diet of fishes in the latter system. However, it was apparent that these plants are not directly consumed but rather contribute to the detrital pool that forms a food source for most invertebrate and some fish species. The most significant source of carbon for East Kleinemonde fishes during the macrophyte senescent phase appeared to have a more depleted origin; probably from benthic or pelagic microalgae. In conclusion, while the importance of macrophyte beds as shelter and foraging habitats for estuarine fishes are well documented, their role in terms of the structuring and functioning of fish assemblages in TOCEs remains somewhat uncertain. The findings of this study were possibly masked by the resilience of vegetation-associated species to the loss of this habitat, as well as by life history characteristics of species such as R. holubi that allow their numerical dominance despite habitat change. Nonetheless, macrophyte senescence in the East Kleinemonde Estuary resulted in the loss of at least one species and the reduced abundance of vegetation-associated species, probably reflective of reduced food resources and/or increased vulnerability to predation. As a result, beds of submerged macrophytes are an important habitat within TOCEs.
- Full Text:
- Date Issued: 2010
Valuing preferences for freshwater inflows into five Eastern Cape and Kwazulu-Natal estuaries
- Authors: Chege, Jedidah
- Date: 2009
- Subjects: Estuarine ecology -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Kwazulu-Natal , Freshwater ecology -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Estuaries -- Management -- South Africa
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: vital:8990 , http://hdl.handle.net/10948/932 , Estuarine ecology -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Kwazulu-Natal , Freshwater ecology -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Estuaries -- Management -- South Africa
- Description: An estuary, according to the National Water Act of 1998, is a partially or fully enclosed body of water which is open periodically or permanently to the sea within which the sea water can be diluted, to an extent that is measurable with freshwater from inland. Estuaries and the lands surrounding them are places of transition from land to sea, and from freshwater to saltwater. Although influenced by the tides, estuaries are protected from the full force of ocean waves, winds, and storms by the reefs, barrier islands, or fingers of land, mud, or sand that surround them. South Africa’s estuaries are important and irreplaceable habitats, especially for prawns, fish, wading birds and mangroves. They are home to numerous plants and animals that live in water that is partly fresh and partly salty. Estuaries are also homes to growing coastal communities as increasing number of people occupy watersheds. However, estuaries are also threatened. One of the threats is reduced river water inflow. This study applies the contingent valuation method (CVM) to elicit user’s willingness to pay to mitigate the negative impacts of reduced freshwater inflow into selected five Eastern Cape and Kwazulu-Natal estuaries: the Sundays, Gamtoos, Mdloti, Mgeni and Mvoti estuaries. In addition to the contingent valuation method, the travel cost method was used to generate comparative values. The contingent valuation method is a technique to establish the value of a good (or service) that is not bought or sold in an actual market. The CVM establishes the economic value of the good by asking the users of an environmental good to state their willingness to pay (WTP) for a hypothetical project to prevent, or bring about, a change in the current condition of the environmental good. The users’ WTP is aggregated to establish a total willingness to pay (TWTP) for the population of the users of the environmental good.
- Full Text:
- Date Issued: 2009
- Authors: Chege, Jedidah
- Date: 2009
- Subjects: Estuarine ecology -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Kwazulu-Natal , Freshwater ecology -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Estuaries -- Management -- South Africa
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: vital:8990 , http://hdl.handle.net/10948/932 , Estuarine ecology -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Kwazulu-Natal , Freshwater ecology -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Estuaries -- Management -- South Africa
- Description: An estuary, according to the National Water Act of 1998, is a partially or fully enclosed body of water which is open periodically or permanently to the sea within which the sea water can be diluted, to an extent that is measurable with freshwater from inland. Estuaries and the lands surrounding them are places of transition from land to sea, and from freshwater to saltwater. Although influenced by the tides, estuaries are protected from the full force of ocean waves, winds, and storms by the reefs, barrier islands, or fingers of land, mud, or sand that surround them. South Africa’s estuaries are important and irreplaceable habitats, especially for prawns, fish, wading birds and mangroves. They are home to numerous plants and animals that live in water that is partly fresh and partly salty. Estuaries are also homes to growing coastal communities as increasing number of people occupy watersheds. However, estuaries are also threatened. One of the threats is reduced river water inflow. This study applies the contingent valuation method (CVM) to elicit user’s willingness to pay to mitigate the negative impacts of reduced freshwater inflow into selected five Eastern Cape and Kwazulu-Natal estuaries: the Sundays, Gamtoos, Mdloti, Mgeni and Mvoti estuaries. In addition to the contingent valuation method, the travel cost method was used to generate comparative values. The contingent valuation method is a technique to establish the value of a good (or service) that is not bought or sold in an actual market. The CVM establishes the economic value of the good by asking the users of an environmental good to state their willingness to pay (WTP) for a hypothetical project to prevent, or bring about, a change in the current condition of the environmental good. The users’ WTP is aggregated to establish a total willingness to pay (TWTP) for the population of the users of the environmental good.
- Full Text:
- Date Issued: 2009
Ecological role of free-living bacteria in the microbial food web of the temporarily open/closed East Kleinemonde Estuary, South Africa
- Authors: Allan, Elizabeth Louise
- Date: 2008
- Subjects: Bacterial growth -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Microbial ecology -- South Africa -- Eastern Cape , Nutrient cycles -- South Africa -- Eastern Cape , Food chains (Ecology)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5666 , http://hdl.handle.net/10962/d1005351 , Bacterial growth -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Microbial ecology -- South Africa -- Eastern Cape , Nutrient cycles -- South Africa -- Eastern Cape , Food chains (Ecology)
- Description: The main aim of this study was to assess the “top-down” and “bottom-up” control of bacterial production in the small temporarily open/closed East Kleinemonde Estuary, situated on the south-eastern coastline of southern Africa. Spatial and temporal patterns in bacterial abundance, biomass and production and the importance of abiotic and biotic factors were investigated over the period May 2006 to April 2007. The trophic interactions between bacteria, phytoplankton, nanoflagellates (< 20 μm), microzooplankton (< 200 μm) and mesozooplankton (< 2 000 μm) were investigated during winter and summer. Bacterial abundance, biomass and production ranged between 1.00 × 10⁹ and 4.93 × 10⁹ cells 1⁻¹, 32.4 and 109 μg C 1⁻¹ and 0.01 and 1.99 μg C 1⁻¹ h⁻¹, respectively. With a few exceptions there were no spatial patterns in the values. Bacterial abundance, biomass and production, however, demonstrated a distinct temporal pattern with the lowest values consistently recorded during the winter months. Nanoflagellate and bacterial abundances were significantly correlated to one another (lower reaches: r = 0.818, p < 0.001; middle reaches: r = 0.628, p < 0.001; upper reaches: r = 0.484, p < 0.05) suggesting a strong predator-prey relationship. The frequency of visibly infected bacterial cells and the mean number of virus particles within each bacterial cell during this study demonstrated no temporal or spatial patterns and ranged from 0.5 to 6.1 % and 12.0 to 37.5 virus particles per bacterium, respectively. Viral infection and lysis was thus a constant source of bacterial mortality throughout the year. The estimated percentage of bacterial production removed by viral lysis ranged between 7.8 and 88.9% of the total which suggests that viral lysis represented a very important source of bacterial mortality during this study. The biological interactions between the selected components of the plankton community demonstrated that among the heterotrophic components of the plankton, the nanoflagellates were identified as the most important consumers of bacteria and small phytoplankton cells (< 20 μm). In the presence of microzooplankton the impact of the nanoflagellates on both the bacteria and phytoplankton was reduced, indicating that larger heterotrophs were preying upon the nanoflagellates. Mesozooplankton, however, appeared to exert the greatest impact on nanoflagellates. In the cascading experiments, the data suggest that mesozooplankton consume nanoflagellates, which resulted in a decrease in the predation impact of these organisms on the bacteria. This result is consistent with predator-prey cascades. The presence of the larger heterotrophs therefore, mediates the interactions between the primary bacterivores, the nanoflagellates, and the bacteria within the temporarily open/closed East Kleinemonde Estuary.
- Full Text:
- Date Issued: 2008
- Authors: Allan, Elizabeth Louise
- Date: 2008
- Subjects: Bacterial growth -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Microbial ecology -- South Africa -- Eastern Cape , Nutrient cycles -- South Africa -- Eastern Cape , Food chains (Ecology)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5666 , http://hdl.handle.net/10962/d1005351 , Bacterial growth -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Microbial ecology -- South Africa -- Eastern Cape , Nutrient cycles -- South Africa -- Eastern Cape , Food chains (Ecology)
- Description: The main aim of this study was to assess the “top-down” and “bottom-up” control of bacterial production in the small temporarily open/closed East Kleinemonde Estuary, situated on the south-eastern coastline of southern Africa. Spatial and temporal patterns in bacterial abundance, biomass and production and the importance of abiotic and biotic factors were investigated over the period May 2006 to April 2007. The trophic interactions between bacteria, phytoplankton, nanoflagellates (< 20 μm), microzooplankton (< 200 μm) and mesozooplankton (< 2 000 μm) were investigated during winter and summer. Bacterial abundance, biomass and production ranged between 1.00 × 10⁹ and 4.93 × 10⁹ cells 1⁻¹, 32.4 and 109 μg C 1⁻¹ and 0.01 and 1.99 μg C 1⁻¹ h⁻¹, respectively. With a few exceptions there were no spatial patterns in the values. Bacterial abundance, biomass and production, however, demonstrated a distinct temporal pattern with the lowest values consistently recorded during the winter months. Nanoflagellate and bacterial abundances were significantly correlated to one another (lower reaches: r = 0.818, p < 0.001; middle reaches: r = 0.628, p < 0.001; upper reaches: r = 0.484, p < 0.05) suggesting a strong predator-prey relationship. The frequency of visibly infected bacterial cells and the mean number of virus particles within each bacterial cell during this study demonstrated no temporal or spatial patterns and ranged from 0.5 to 6.1 % and 12.0 to 37.5 virus particles per bacterium, respectively. Viral infection and lysis was thus a constant source of bacterial mortality throughout the year. The estimated percentage of bacterial production removed by viral lysis ranged between 7.8 and 88.9% of the total which suggests that viral lysis represented a very important source of bacterial mortality during this study. The biological interactions between the selected components of the plankton community demonstrated that among the heterotrophic components of the plankton, the nanoflagellates were identified as the most important consumers of bacteria and small phytoplankton cells (< 20 μm). In the presence of microzooplankton the impact of the nanoflagellates on both the bacteria and phytoplankton was reduced, indicating that larger heterotrophs were preying upon the nanoflagellates. Mesozooplankton, however, appeared to exert the greatest impact on nanoflagellates. In the cascading experiments, the data suggest that mesozooplankton consume nanoflagellates, which resulted in a decrease in the predation impact of these organisms on the bacteria. This result is consistent with predator-prey cascades. The presence of the larger heterotrophs therefore, mediates the interactions between the primary bacterivores, the nanoflagellates, and the bacteria within the temporarily open/closed East Kleinemonde Estuary.
- Full Text:
- Date Issued: 2008
Spatial and temporal variations in metals in the sediment and water of selected Eastern Cape Estuaries, South Africa
- Authors: Orr, Kyla Kathleen
- Date: 2008
- Subjects: Marine sediments -- South Africa -- Eastern Cape , Metals -- South Africa -- Eastern Cape , Metals -- Environmental aspects , Estuaries -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Estuarine sediments -- South Africa -- Eastern Cape , Water quality -- South Africa -- Eastern Cape , Water pollution -- South Africa -- Eastern Cape , Environmental toxicology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5769 , http://hdl.handle.net/10962/d1005457 , Marine sediments -- South Africa -- Eastern Cape , Metals -- South Africa -- Eastern Cape , Metals -- Environmental aspects , Estuaries -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Estuarine sediments -- South Africa -- Eastern Cape , Water quality -- South Africa -- Eastern Cape , Water pollution -- South Africa -- Eastern Cape , Environmental toxicology -- South Africa -- Eastern Cape
- Description: The spatio-temporal patterns in concentrations of selected metals within the sediment (Cd, Co, Cu, Fe, Pb, Ni and Zn) and water (Cd and Pb) of three permanently open estuaries (Kariega, Kowie, Great Fish) and six temporary open-closed estuaries (Mpekweni, East Kleinemonde, West Kleinemonde, Riet, Kasouga, Boknes) were investigated. The concentrations of metals were influenced by size composition and total organic content of the sediments. Enrichment factors (EFs), using Fe as a reference element, and baseline linear regression models for metals vs. Fe were calculated to assess the extent of metal enrichment in the sediments. The mean concentrations of metals in the sediments(mg·kg⁻¹) showed ranges of 0.28 – 2.31 for Cd, 1.26 – 6.24 Co, 0.69 – 6.93 for Cu, 2119 – 14912 for Fe, 2.29 –14.01 for Ni, 4.81 – 22.20 for Pb and 5.77 – 21.75 for Zn. Mean normalized enrichment factors ranged between 0.75 – 6.19 for Cd, 0.53 – 2.71 for Co, 0.22 – 0.84 for Cu, 0.30 – 1.87 for Ni, 0.99 – 3.17 for Pb and 0.14 – 0.98 for Zn. All nine estuaries had average enrichment factors of greater than 1 for Cd. In general there was no enrichment of Cu and Zn in the sediments of any of the estuaries included in this study (EFs < 1). The Kariega, East Kleinemonde, West Kleinemonde, Riet and Great Fish Estuaries showed some degree of enrichment for Co (1 < EF < 4), Ni (1 < EF < 2) and Pb (1 < EF < 4), while the Mpekweni, Kasouga, Boknes and Kowie Estuaries were unenriched with these metals (EF < 1). Enrichment factors for Cd, Co and Pb typically followed the development gradient along the estuaries, suggesting anthropogenic enrichment. The concentrations of Cd and Pb in the water of the nine estuaries were also determined. The average concentrations of Cd and Pb in the water (μg·ℓ⁻¹) ranged between 0.05 – 3.32 and 0.75 – 34.13 respectively. On average the concentrations of Cd and Pb in the water of all the estuaries were below the South African recommended water quality guidelines for coastal marine waters. Variations in metal concentrations associated with changes in hydrology (wet vs. dry season) were determined in the water and sediment of the Kariega, East Kleinemonde and Riet Estuaries. Cobalt, Pb and Ni enrichment in the Kariega Estuary sediment was significantly higher during the dry season, and the mean concentrations of Pb and Cd in the water column were 19-fold and 66-fold higher in the dry season. The elevated concentration of metals during the dry season could be related to accumulation of diffuse pollution from human activities within the catchment area. Conversely, inflow of fresh water into the estuary had the net effect of reducing the concentration and enrichment of these metals within the Kariega Estuary due to scouring and outflow of estuarine water and sediment into the marine environment. The temporal variations in metal concentrations and enrichment factors were less pronounced in the temporary open-closed estuaries than the permanently open Kariega Estuary. The observed trend can probably be related to the low anthropogenic impact within the catchment areas of these systems, and the relatively smaller size of the catchments. Significant spatial variations existed in metal enrichment in the sediment of both the East Kleinemonde and Riet estuaries, with the highest degrees of enrichment occurring in the sediments from the marine environment and lower reaches.
- Full Text:
- Date Issued: 2008
- Authors: Orr, Kyla Kathleen
- Date: 2008
- Subjects: Marine sediments -- South Africa -- Eastern Cape , Metals -- South Africa -- Eastern Cape , Metals -- Environmental aspects , Estuaries -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Estuarine sediments -- South Africa -- Eastern Cape , Water quality -- South Africa -- Eastern Cape , Water pollution -- South Africa -- Eastern Cape , Environmental toxicology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5769 , http://hdl.handle.net/10962/d1005457 , Marine sediments -- South Africa -- Eastern Cape , Metals -- South Africa -- Eastern Cape , Metals -- Environmental aspects , Estuaries -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Estuarine sediments -- South Africa -- Eastern Cape , Water quality -- South Africa -- Eastern Cape , Water pollution -- South Africa -- Eastern Cape , Environmental toxicology -- South Africa -- Eastern Cape
- Description: The spatio-temporal patterns in concentrations of selected metals within the sediment (Cd, Co, Cu, Fe, Pb, Ni and Zn) and water (Cd and Pb) of three permanently open estuaries (Kariega, Kowie, Great Fish) and six temporary open-closed estuaries (Mpekweni, East Kleinemonde, West Kleinemonde, Riet, Kasouga, Boknes) were investigated. The concentrations of metals were influenced by size composition and total organic content of the sediments. Enrichment factors (EFs), using Fe as a reference element, and baseline linear regression models for metals vs. Fe were calculated to assess the extent of metal enrichment in the sediments. The mean concentrations of metals in the sediments(mg·kg⁻¹) showed ranges of 0.28 – 2.31 for Cd, 1.26 – 6.24 Co, 0.69 – 6.93 for Cu, 2119 – 14912 for Fe, 2.29 –14.01 for Ni, 4.81 – 22.20 for Pb and 5.77 – 21.75 for Zn. Mean normalized enrichment factors ranged between 0.75 – 6.19 for Cd, 0.53 – 2.71 for Co, 0.22 – 0.84 for Cu, 0.30 – 1.87 for Ni, 0.99 – 3.17 for Pb and 0.14 – 0.98 for Zn. All nine estuaries had average enrichment factors of greater than 1 for Cd. In general there was no enrichment of Cu and Zn in the sediments of any of the estuaries included in this study (EFs < 1). The Kariega, East Kleinemonde, West Kleinemonde, Riet and Great Fish Estuaries showed some degree of enrichment for Co (1 < EF < 4), Ni (1 < EF < 2) and Pb (1 < EF < 4), while the Mpekweni, Kasouga, Boknes and Kowie Estuaries were unenriched with these metals (EF < 1). Enrichment factors for Cd, Co and Pb typically followed the development gradient along the estuaries, suggesting anthropogenic enrichment. The concentrations of Cd and Pb in the water of the nine estuaries were also determined. The average concentrations of Cd and Pb in the water (μg·ℓ⁻¹) ranged between 0.05 – 3.32 and 0.75 – 34.13 respectively. On average the concentrations of Cd and Pb in the water of all the estuaries were below the South African recommended water quality guidelines for coastal marine waters. Variations in metal concentrations associated with changes in hydrology (wet vs. dry season) were determined in the water and sediment of the Kariega, East Kleinemonde and Riet Estuaries. Cobalt, Pb and Ni enrichment in the Kariega Estuary sediment was significantly higher during the dry season, and the mean concentrations of Pb and Cd in the water column were 19-fold and 66-fold higher in the dry season. The elevated concentration of metals during the dry season could be related to accumulation of diffuse pollution from human activities within the catchment area. Conversely, inflow of fresh water into the estuary had the net effect of reducing the concentration and enrichment of these metals within the Kariega Estuary due to scouring and outflow of estuarine water and sediment into the marine environment. The temporal variations in metal concentrations and enrichment factors were less pronounced in the temporary open-closed estuaries than the permanently open Kariega Estuary. The observed trend can probably be related to the low anthropogenic impact within the catchment areas of these systems, and the relatively smaller size of the catchments. Significant spatial variations existed in metal enrichment in the sediment of both the East Kleinemonde and Riet estuaries, with the highest degrees of enrichment occurring in the sediments from the marine environment and lower reaches.
- Full Text:
- Date Issued: 2008
Valuing preferences for freshwater inflows into the Bira, Bushmans, Kasouga, Keiskamma, Kleinemond East, Nahoon and Tyolomnqa estuaries
- Authors: Van der Westhuizen, Henri
- Date: 2007
- Subjects: Estuarine ecology -- South Africa -- Eastern Cape , Freshwater ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: vital:8998 , http://hdl.handle.net/10948/628 , Estuarine ecology -- South Africa -- Eastern Cape , Freshwater ecology -- South Africa -- Eastern Cape
- Description: There are about 259 estuaries in South Africa that can be classified as “functioning” and their “health” status is directly related to the quantity and quality of freshwater that flows into them. Many of South Africa’s estuaries have become smaller due to a steady decrease in the amount of freshwater that flows into them. This reduction in freshwater inflows decreases their ecological functioning and undermines the recreational activities and subsistence services available from them. The National Water Act (ACT No. 36 of 1998) recognises the right of the environment to water, but a large amount of data is still needed to make management decisions on the allocation of freshwater. The objective of this research was to contribute to the management of the allocation of freshwater in the catchment areas of the Bira, Bushmans, Kasouga, Keiskamma, Kleinemond East, Nahoon and Tyolomnqa rivers by determining the recreational value of the freshwater flowing into their estuaries. This recreational value was established using the contingent valuation method. The contingent valuation method (CVM) is a technique to establish the value of a good (or service) that is not bought or sold in an actual market. This technique is frequently applied in the valuation of environmental goods, e.g. the freshwater that flows into an estuary. The CVM establishes the economic value by asking the users of an environmental good to state their willingness to pay (WTP) for a hypothetical project to prevent or bring about a change in the current condition of the environmental good. The users’ WTP is then aggregated to establish a total willingness to pay (TWTP) for the population of the users of the environmental good. The hypothetical project presented in this study is that of an increase of freshwater inflows, that would prevent (bring about) predetermined changes in environmental services provided by the selected seven estuaries.
- Full Text:
- Date Issued: 2007
- Authors: Van der Westhuizen, Henri
- Date: 2007
- Subjects: Estuarine ecology -- South Africa -- Eastern Cape , Freshwater ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: vital:8998 , http://hdl.handle.net/10948/628 , Estuarine ecology -- South Africa -- Eastern Cape , Freshwater ecology -- South Africa -- Eastern Cape
- Description: There are about 259 estuaries in South Africa that can be classified as “functioning” and their “health” status is directly related to the quantity and quality of freshwater that flows into them. Many of South Africa’s estuaries have become smaller due to a steady decrease in the amount of freshwater that flows into them. This reduction in freshwater inflows decreases their ecological functioning and undermines the recreational activities and subsistence services available from them. The National Water Act (ACT No. 36 of 1998) recognises the right of the environment to water, but a large amount of data is still needed to make management decisions on the allocation of freshwater. The objective of this research was to contribute to the management of the allocation of freshwater in the catchment areas of the Bira, Bushmans, Kasouga, Keiskamma, Kleinemond East, Nahoon and Tyolomnqa rivers by determining the recreational value of the freshwater flowing into their estuaries. This recreational value was established using the contingent valuation method. The contingent valuation method (CVM) is a technique to establish the value of a good (or service) that is not bought or sold in an actual market. This technique is frequently applied in the valuation of environmental goods, e.g. the freshwater that flows into an estuary. The CVM establishes the economic value by asking the users of an environmental good to state their willingness to pay (WTP) for a hypothetical project to prevent or bring about a change in the current condition of the environmental good. The users’ WTP is then aggregated to establish a total willingness to pay (TWTP) for the population of the users of the environmental good. The hypothetical project presented in this study is that of an increase of freshwater inflows, that would prevent (bring about) predetermined changes in environmental services provided by the selected seven estuaries.
- Full Text:
- Date Issued: 2007
Population dynamics of selected ichthyofaunal components in the temperate, temporarily open/closed Kasouga Estuary, South Africa
- Authors: Tweddle, Gavin Paul
- Date: 2005
- Subjects: Estuaries -- South Africa -- Eastern Cape , Estuarine fishes -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5742 , http://hdl.handle.net/10962/d1005428 , Estuaries -- South Africa -- Eastern Cape , Estuarine fishes -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape
- Description: The spatial and temporal pattern of ichthyofaunal community composition in relation to selected physico-chemical (temperature and salinity) and biological variables (chlorophyll-a and zooplankton) was investigated at ten stations in the temperate temporarily open/closed Kasouga estuary. In addition, the food web structure in the estuary was investigated using stable carbon isotope analysis. Results of the 5 metre seine net survey indicated that ichthyofaunal composition and biomass in the Kasouga estuary was largely determined by seasonality and mouth condition. Maximum abundance and biomass of ichthyofauna was recorded during summer or during those periods when overtopping occurred. Overtopping coincided with the recruitment of marine estuarine dependant species, which dominated the catches both numerically and in biomass. The recruitment of these species resulted in an increase in diversity of the ichthyofaunal community. There were no significant spatial patterns in the distribution of smaller ichthyofauna (<50mm SL) identified in Bray-Curtis similarity matrices using cluster analysis (Primer 5 v5.2.4). Spearman’s correlation analysis revealed that there were no significant correlations between abundance and biomass of ichthyofauna and selected physico-chemical and biological variables other than salinity (P>0.05 in all other cases). There were two distinct spatial patterns in the distribution of the larger ichthyofauna (>50mm SL). These corresponded to a grouping associated with the mouth region and a grouping associated with the remaining regions of the estuary. Stable isotope analysis indicated that the primary source of carbon utilised by the ichthyofauna of the Kasouga estuary was derived from the channel, most likely microphytobenthic algae. The contributions of the riparian and salt marsh vegetation to the total carbon flow appear to be minimal.
- Full Text:
- Date Issued: 2005
- Authors: Tweddle, Gavin Paul
- Date: 2005
- Subjects: Estuaries -- South Africa -- Eastern Cape , Estuarine fishes -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5742 , http://hdl.handle.net/10962/d1005428 , Estuaries -- South Africa -- Eastern Cape , Estuarine fishes -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape
- Description: The spatial and temporal pattern of ichthyofaunal community composition in relation to selected physico-chemical (temperature and salinity) and biological variables (chlorophyll-a and zooplankton) was investigated at ten stations in the temperate temporarily open/closed Kasouga estuary. In addition, the food web structure in the estuary was investigated using stable carbon isotope analysis. Results of the 5 metre seine net survey indicated that ichthyofaunal composition and biomass in the Kasouga estuary was largely determined by seasonality and mouth condition. Maximum abundance and biomass of ichthyofauna was recorded during summer or during those periods when overtopping occurred. Overtopping coincided with the recruitment of marine estuarine dependant species, which dominated the catches both numerically and in biomass. The recruitment of these species resulted in an increase in diversity of the ichthyofaunal community. There were no significant spatial patterns in the distribution of smaller ichthyofauna (<50mm SL) identified in Bray-Curtis similarity matrices using cluster analysis (Primer 5 v5.2.4). Spearman’s correlation analysis revealed that there were no significant correlations between abundance and biomass of ichthyofauna and selected physico-chemical and biological variables other than salinity (P>0.05 in all other cases). There were two distinct spatial patterns in the distribution of the larger ichthyofauna (>50mm SL). These corresponded to a grouping associated with the mouth region and a grouping associated with the remaining regions of the estuary. Stable isotope analysis indicated that the primary source of carbon utilised by the ichthyofauna of the Kasouga estuary was derived from the channel, most likely microphytobenthic algae. The contributions of the riparian and salt marsh vegetation to the total carbon flow appear to be minimal.
- Full Text:
- Date Issued: 2005
Fishes in the Mngazi and Mngazana estuaries, with particular emphasis on the community structure and primary carbon sources
- Authors: Mbande, Sekiwe
- Date: 2004
- Subjects: Fishes -- South Africa -- Mngazi Estuary , Fishes -- South Africa -- Mngazana Estuary , Fishes -- Effect of habitat modification on -- South Africa -- Mngazi Estuary , Fishes -- Effect of habitat modification on -- South Africa -- Mngazana Estuary , Estuarine fishes -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Fishes -- Physiology , Fishes -- Effect of water quality on , Fishes -- Effect of temperature on , Fishes -- Food , Fishes -- Effect of turbidity on
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5700 , http://hdl.handle.net/10962/d1005386 , Fishes -- South Africa -- Mngazi Estuary , Fishes -- South Africa -- Mngazana Estuary , Fishes -- Effect of habitat modification on -- South Africa -- Mngazi Estuary , Fishes -- Effect of habitat modification on -- South Africa -- Mngazana Estuary , Estuarine fishes -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Fishes -- Physiology , Fishes -- Effect of water quality on , Fishes -- Effect of temperature on , Fishes -- Food , Fishes -- Effect of turbidity on
- Description: The fish community structure of two contrasting estuaries, one with a well developed mangrove forest (Mngazana) and the other without mangroves (Mngazi) was compared. Both the Mngazi and Mngazana estuary fish communities were dominated by marine species, reflecting the importance of these systems as nursery areas for marine fishes. The Mngazi Estuary contained 18% more estuarine fishes in terms of catch per unit effort (CPUE) than the Mngazana Estuary. The reduced tidal influence due to the narrow mouth opening is a possible reason for the heightened CPUE of estuarine species in the Mngazi estuary. The recorded higher diversity of fish species in the Mngazana Estuary when compared with the Mngazi Estuary was attributed to the greater influence of the marine environment due to the wide permanently open mouth, as well as the presence of a variety of habitats in this system. In both estuaries tropical and temperate species were captured, confirming the transitional nature of their biogeographic location which is situated close to the boundary between the subtropical and warm temperate regions of the Southern African coastline. Contrary to previous studies, which recorded seasonal changes in the proportions of tropical and temperate species, the proportions of tropical species remained unchanged at approximately 70% during the January and June sampling occasions. Global warming as a possible reason for the increased dominance of tropical species is discussed. Although several studies in southern Africa have investigated estuarine food web structure, none have compared mangrove and non-mangrove estuaries. In this study, the primary sources of carbon utilised by the fish fauna in the Mngazi and Mngazana estuaries was investigated. The carbon isotopic values of fishes in both estuaries displayed a continuum rather than a tight clustering around particular energy sources. Most detritus feeders of the family Mugilidae (mullets) from both estuaries were relatively more enriched than other fish taxa. The isotopic values of the mullet species suggest a diet derived from relatively enriched carbon sources such as benthic microalgae, the eelgrass Zostera capensis and associated epiphytes. Based on the isotopic values, piscivorous fishes from both estuaries could not be linked to specific prey fish taxa, but clearly the mullet species were not their main food source. The invertebrate feeders that were found in both estuaries showed greater isotopic variations in the Mngazana Estuary than in the Mngazi Estuary, probably reflecting the higher diversity of habitats (carbon sources) and invertebrate prey species in the Mngazana system. Generally the isotopic signatures of fishes from the Mngazi Estuary were more enriched than those from the Mngazana Estuary, thus indicating the possible effect of δ¹³C depleted mangrove derived carbon in the latter system.
- Full Text:
- Date Issued: 2004
- Authors: Mbande, Sekiwe
- Date: 2004
- Subjects: Fishes -- South Africa -- Mngazi Estuary , Fishes -- South Africa -- Mngazana Estuary , Fishes -- Effect of habitat modification on -- South Africa -- Mngazi Estuary , Fishes -- Effect of habitat modification on -- South Africa -- Mngazana Estuary , Estuarine fishes -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Fishes -- Physiology , Fishes -- Effect of water quality on , Fishes -- Effect of temperature on , Fishes -- Food , Fishes -- Effect of turbidity on
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5700 , http://hdl.handle.net/10962/d1005386 , Fishes -- South Africa -- Mngazi Estuary , Fishes -- South Africa -- Mngazana Estuary , Fishes -- Effect of habitat modification on -- South Africa -- Mngazi Estuary , Fishes -- Effect of habitat modification on -- South Africa -- Mngazana Estuary , Estuarine fishes -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Fishes -- Physiology , Fishes -- Effect of water quality on , Fishes -- Effect of temperature on , Fishes -- Food , Fishes -- Effect of turbidity on
- Description: The fish community structure of two contrasting estuaries, one with a well developed mangrove forest (Mngazana) and the other without mangroves (Mngazi) was compared. Both the Mngazi and Mngazana estuary fish communities were dominated by marine species, reflecting the importance of these systems as nursery areas for marine fishes. The Mngazi Estuary contained 18% more estuarine fishes in terms of catch per unit effort (CPUE) than the Mngazana Estuary. The reduced tidal influence due to the narrow mouth opening is a possible reason for the heightened CPUE of estuarine species in the Mngazi estuary. The recorded higher diversity of fish species in the Mngazana Estuary when compared with the Mngazi Estuary was attributed to the greater influence of the marine environment due to the wide permanently open mouth, as well as the presence of a variety of habitats in this system. In both estuaries tropical and temperate species were captured, confirming the transitional nature of their biogeographic location which is situated close to the boundary between the subtropical and warm temperate regions of the Southern African coastline. Contrary to previous studies, which recorded seasonal changes in the proportions of tropical and temperate species, the proportions of tropical species remained unchanged at approximately 70% during the January and June sampling occasions. Global warming as a possible reason for the increased dominance of tropical species is discussed. Although several studies in southern Africa have investigated estuarine food web structure, none have compared mangrove and non-mangrove estuaries. In this study, the primary sources of carbon utilised by the fish fauna in the Mngazi and Mngazana estuaries was investigated. The carbon isotopic values of fishes in both estuaries displayed a continuum rather than a tight clustering around particular energy sources. Most detritus feeders of the family Mugilidae (mullets) from both estuaries were relatively more enriched than other fish taxa. The isotopic values of the mullet species suggest a diet derived from relatively enriched carbon sources such as benthic microalgae, the eelgrass Zostera capensis and associated epiphytes. Based on the isotopic values, piscivorous fishes from both estuaries could not be linked to specific prey fish taxa, but clearly the mullet species were not their main food source. The invertebrate feeders that were found in both estuaries showed greater isotopic variations in the Mngazana Estuary than in the Mngazi Estuary, probably reflecting the higher diversity of habitats (carbon sources) and invertebrate prey species in the Mngazana system. Generally the isotopic signatures of fishes from the Mngazi Estuary were more enriched than those from the Mngazana Estuary, thus indicating the possible effect of δ¹³C depleted mangrove derived carbon in the latter system.
- Full Text:
- Date Issued: 2004
An assessment of bait availability, utilization and management guidelines in Eastern Cape estuaries
- Authors: Jooste, Jakobus Gerrit
- Date: 2003
- Subjects: Upogebia african -- Effects of sediments on -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Fishing baits -- Conservation -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:11073 , http://hdl.handle.net/10948/334 , Upogebia african -- Effects of sediments on -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Fishing baits -- Conservation -- South Africa -- Eastern Cape
- Description: Aspects around the management of benthic soft sediment bait organisms, with special focus on the mud prawn (Upogebia africana) of eastern Cape estuaries was investigated. The recreational linefishery of the Gamtoos estuary was described, and compared to previous studies. Target fish species was identified, and a large dependency on bait sourced from estuaries needed for the capture of these species was noted, especially for spotted grunter (Pomadasys commersonnii). A comparison between bait use, success and the natural diet of target fish species was also made. The structure and distribution of sediments in the old channel mud banks was described and compared with historical data. The influence of sediments on mud prawn distribution was investigated, but no significant interactions were found at the study site. The impacts of once-off pumping and digging events, and monthly trampling on the sediments and mud prawn population was studied over a 7-month period. Initial removal rates as well as recovery time varied significantly between the two collection methods, while the largest decline in prawn numbers (to zero) with no recovery visible after seven months was caused by trampling. All disturbances caused some alteration in sediment composition, but not to such an extent that the sediments became unfavorable for mud prawns. Trampling did, however, result in the compaction of sediments to such a degree that prawns could not construct burrows. Issues around current removal quotas of bait species as well as the creation of a small-scale commercial (SSC) bait selling operation at Swartkops estuary were critically evaluated, and suggestions for the future removal rates of mud prawns based on production export calculations were made. The distribution, size, sex ratios and number of gravid females occurring along a tidal gradient as well as along horizontal gradient of the mud bank during growth (January – March) and reproductive (September – October) periods was investigated. Changes in the distribution of females between the two study periods were significant, while the distribution of reproductively active females were closely linked to the low water mark (Lower tidal levels). Females occurring in this zone were also significantly larger than females occurring towards the back of the study site. Some minor changes along the horizontal gradient were also observed. The sediment compos ition of the mud bank was found not to play a role in this distribution, leading to the suggestion that exposure to ebb and flood tide currents could influence female prawn distributions. Management recommendations based on these observations were made.
- Full Text:
- Date Issued: 2003
- Authors: Jooste, Jakobus Gerrit
- Date: 2003
- Subjects: Upogebia african -- Effects of sediments on -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Fishing baits -- Conservation -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:11073 , http://hdl.handle.net/10948/334 , Upogebia african -- Effects of sediments on -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Fishing baits -- Conservation -- South Africa -- Eastern Cape
- Description: Aspects around the management of benthic soft sediment bait organisms, with special focus on the mud prawn (Upogebia africana) of eastern Cape estuaries was investigated. The recreational linefishery of the Gamtoos estuary was described, and compared to previous studies. Target fish species was identified, and a large dependency on bait sourced from estuaries needed for the capture of these species was noted, especially for spotted grunter (Pomadasys commersonnii). A comparison between bait use, success and the natural diet of target fish species was also made. The structure and distribution of sediments in the old channel mud banks was described and compared with historical data. The influence of sediments on mud prawn distribution was investigated, but no significant interactions were found at the study site. The impacts of once-off pumping and digging events, and monthly trampling on the sediments and mud prawn population was studied over a 7-month period. Initial removal rates as well as recovery time varied significantly between the two collection methods, while the largest decline in prawn numbers (to zero) with no recovery visible after seven months was caused by trampling. All disturbances caused some alteration in sediment composition, but not to such an extent that the sediments became unfavorable for mud prawns. Trampling did, however, result in the compaction of sediments to such a degree that prawns could not construct burrows. Issues around current removal quotas of bait species as well as the creation of a small-scale commercial (SSC) bait selling operation at Swartkops estuary were critically evaluated, and suggestions for the future removal rates of mud prawns based on production export calculations were made. The distribution, size, sex ratios and number of gravid females occurring along a tidal gradient as well as along horizontal gradient of the mud bank during growth (January – March) and reproductive (September – October) periods was investigated. Changes in the distribution of females between the two study periods were significant, while the distribution of reproductively active females were closely linked to the low water mark (Lower tidal levels). Females occurring in this zone were also significantly larger than females occurring towards the back of the study site. Some minor changes along the horizontal gradient were also observed. The sediment compos ition of the mud bank was found not to play a role in this distribution, leading to the suggestion that exposure to ebb and flood tide currents could influence female prawn distributions. Management recommendations based on these observations were made.
- Full Text:
- Date Issued: 2003
- «
- ‹
- 1
- ›
- »