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
The growth and recovery of mangroves at three South African study sites
- Authors: Mbense, Sinegugu
- Date: 2017
- Subjects: Mangrove forests -- South Africa Mangrove ecology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/11931 , vital:27008
- Description: Mangroves in South Africa are prone to anthropogenic pressures such as browsing and trampling by livestock and by natural disturbances such as drought and floods. These mangroves exist at one of the most southerly limits in the world providing a unique opportunity to study recovery and resilience to change. This study used long term data at three South African study sites located in the subtropical (St Lucia Estuary) and warm temperate regions (Nxaxo and Kobonqaba estuaries) to compare mangrove growth rate, population structure and responses to disturbance. The first objective was investigated at St Lucia Estuary where site specific or microhabitat differences were measured to assess the influence of these on mangrove growth and population structure. It was suggested that site - specific variability would ensure mangrove survival and analysis showed that seedlings were present at different sites in different years. There was always some recruitment but often little survival to the next size class. Over time seedling numbers were quite variable and self – thinning of adults was evident. The second objective was to identify the environmental factors influencing population density and growth. Results showed that sediment moisture and salinity influenced seedling and adult density due to fluctuations in estuary water level. Mangrove growth rates for Avicennia marina in terms of height was faster (40 – 75 cm yr-1 ) at Site 1 where conditions were waterlogged and moderately saline and slower (5 – 25 cm yr1 ) in dry and hypersaline conditions at Site 4. Overall mangroves at St Lucia have shown persistence through drought and fluctuations in environmental conditions however resilience may be hindered at sites that are subjected to partially flooding and prolonged waterlogging. The second site was Nxaxo Estuary in the Eastern Cape where cattle exclusion plots (nonbrowsed) and control plots (browsed) were used to assess the recovery of A. marina trees from cattle browsing. Trees in the browsed plots showed no vertical growth while trees in the non-browsed plots grew significantly faster (5.4 ± 0.5 cm yr-1). When cattle were prevented from entering the mangrove area, the trees recovered fairly quickly and within 3 years growth was similar in both the non – browsed (17.9 ± 3.2 cm yr -1) and browsed plots (18 ± 1.6 cm yr -1). Lastly, mangrove recovery was investigated at Kobonqaba Estuary where long-term closure of the mouth to the sea resulted in high water levels, inundation of pneumatophores and die-back of the majority of the mangroves. This study measured the recovery of the mangroves by assessing changes in vegetation cover and sediment characteristics along transects. High initial porewater nutrient concentrations promoted salt marsh growth and plants increased average cover from 0% in 2011 to 18.9% (2013) and 50% in 2015. The total number of A. marina individuals increased from only seven to 27 individuals over four years. Salt marsh competition and facilitation will likely influence mangrove recovery in the future. Overall it was concluded that when a short term pressure (cattle browsing) is alleviated, mangrove forests even at warm temperate sites are able to recovery rapidly by increasing growth and seedling establishment. However, mangroves in the subtropical sites show more resilience and recovery potential to long term pressures such as fluctuating environmental conditions because of faster growth rates.
- Full Text:
- Date Issued: 2017
- Authors: Mbense, Sinegugu
- Date: 2017
- Subjects: Mangrove forests -- South Africa Mangrove ecology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/11931 , vital:27008
- Description: Mangroves in South Africa are prone to anthropogenic pressures such as browsing and trampling by livestock and by natural disturbances such as drought and floods. These mangroves exist at one of the most southerly limits in the world providing a unique opportunity to study recovery and resilience to change. This study used long term data at three South African study sites located in the subtropical (St Lucia Estuary) and warm temperate regions (Nxaxo and Kobonqaba estuaries) to compare mangrove growth rate, population structure and responses to disturbance. The first objective was investigated at St Lucia Estuary where site specific or microhabitat differences were measured to assess the influence of these on mangrove growth and population structure. It was suggested that site - specific variability would ensure mangrove survival and analysis showed that seedlings were present at different sites in different years. There was always some recruitment but often little survival to the next size class. Over time seedling numbers were quite variable and self – thinning of adults was evident. The second objective was to identify the environmental factors influencing population density and growth. Results showed that sediment moisture and salinity influenced seedling and adult density due to fluctuations in estuary water level. Mangrove growth rates for Avicennia marina in terms of height was faster (40 – 75 cm yr-1 ) at Site 1 where conditions were waterlogged and moderately saline and slower (5 – 25 cm yr1 ) in dry and hypersaline conditions at Site 4. Overall mangroves at St Lucia have shown persistence through drought and fluctuations in environmental conditions however resilience may be hindered at sites that are subjected to partially flooding and prolonged waterlogging. The second site was Nxaxo Estuary in the Eastern Cape where cattle exclusion plots (nonbrowsed) and control plots (browsed) were used to assess the recovery of A. marina trees from cattle browsing. Trees in the browsed plots showed no vertical growth while trees in the non-browsed plots grew significantly faster (5.4 ± 0.5 cm yr-1). When cattle were prevented from entering the mangrove area, the trees recovered fairly quickly and within 3 years growth was similar in both the non – browsed (17.9 ± 3.2 cm yr -1) and browsed plots (18 ± 1.6 cm yr -1). Lastly, mangrove recovery was investigated at Kobonqaba Estuary where long-term closure of the mouth to the sea resulted in high water levels, inundation of pneumatophores and die-back of the majority of the mangroves. This study measured the recovery of the mangroves by assessing changes in vegetation cover and sediment characteristics along transects. High initial porewater nutrient concentrations promoted salt marsh growth and plants increased average cover from 0% in 2011 to 18.9% (2013) and 50% in 2015. The total number of A. marina individuals increased from only seven to 27 individuals over four years. Salt marsh competition and facilitation will likely influence mangrove recovery in the future. Overall it was concluded that when a short term pressure (cattle browsing) is alleviated, mangrove forests even at warm temperate sites are able to recovery rapidly by increasing growth and seedling establishment. However, mangroves in the subtropical sites show more resilience and recovery potential to long term pressures such as fluctuating environmental conditions because of faster growth rates.
- Full Text:
- Date Issued: 2017
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
Assessing estuarine nursery habitats for Cape Stumpnose (Rhabdosargus holubi), (Pisces: Sparidae) in a warm-temperate estuary in the Eastern Cape, South Africa
- Authors: Leslie, Timothy David
- Date: 2016
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3178 , vital:20381
- Description: The nursery role hypothesis provides an approach for assessing the nursery function of habitat types within estuaries. This study attempted to assess the nursery value of the dominant estuarine habitats in the Bushmans Estuary for Rhabdosargus holubi (Steindachner 1881) by analysing habitat complexity, relative abundance and behaviour of R. holubi and using stomach contents analysis and dietary diatom composition as indicative of feeding habitat. Structural habitat complexity was assessed in Zostera capensis (Setchell) seagrass and Spartina maritima (Curtis Fernald) salt marsh by sampling above-ground stem density and length, and total cover per unit area (Ct/At). Dimensionless habitat complexity indices such as the interstitial spatial index (ISI) at three magnifications and fractal geometry at two magnifications were used to further analyse habitat complexity. Above-ground biomass (P<0.05) in each season and canopy height (P<0.001) were significantly higher in salt marsh than in seagrass whilst stem density was significantly higher in seagrass than in salt marsh in each season (P<0.001). Each dimensionless index indicated that complexity is notably higher in seagrass than in the salt marsh. Using dimensionless indices that analyse complexity at different spatial scales provided a better analysis of habitat complexity than canopy height and biomass as it allowed for direct comparisons between habitat types. Underwater video cameras were deployed in seagrass, salt marsh and sand flat habitats to assess the relative abundance and behaviour of R. holubi. The relative abundance of R. holubi was significantly higher in seagrass than salt marsh and sand flats, whilst the behaviour of R. holubi indicated a high degree of habitat use in structured habitats and a low degree of habitat use in unstructured sand flat habitats. This indicated that not only are juvenile R. holubi a vegetation-associated species, but also a species that prefers seagrass to salt marsh.
- Full Text:
- Date Issued: 2016
- Authors: Leslie, Timothy David
- Date: 2016
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3178 , vital:20381
- Description: The nursery role hypothesis provides an approach for assessing the nursery function of habitat types within estuaries. This study attempted to assess the nursery value of the dominant estuarine habitats in the Bushmans Estuary for Rhabdosargus holubi (Steindachner 1881) by analysing habitat complexity, relative abundance and behaviour of R. holubi and using stomach contents analysis and dietary diatom composition as indicative of feeding habitat. Structural habitat complexity was assessed in Zostera capensis (Setchell) seagrass and Spartina maritima (Curtis Fernald) salt marsh by sampling above-ground stem density and length, and total cover per unit area (Ct/At). Dimensionless habitat complexity indices such as the interstitial spatial index (ISI) at three magnifications and fractal geometry at two magnifications were used to further analyse habitat complexity. Above-ground biomass (P<0.05) in each season and canopy height (P<0.001) were significantly higher in salt marsh than in seagrass whilst stem density was significantly higher in seagrass than in salt marsh in each season (P<0.001). Each dimensionless index indicated that complexity is notably higher in seagrass than in the salt marsh. Using dimensionless indices that analyse complexity at different spatial scales provided a better analysis of habitat complexity than canopy height and biomass as it allowed for direct comparisons between habitat types. Underwater video cameras were deployed in seagrass, salt marsh and sand flat habitats to assess the relative abundance and behaviour of R. holubi. The relative abundance of R. holubi was significantly higher in seagrass than salt marsh and sand flats, whilst the behaviour of R. holubi indicated a high degree of habitat use in structured habitats and a low degree of habitat use in unstructured sand flat habitats. This indicated that not only are juvenile R. holubi a vegetation-associated species, but also a species that prefers seagrass to salt marsh.
- Full Text:
- Date Issued: 2016
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