A multidisciplinary study of a small, temporarily open/closed South African estuary, with particular emphasis on the influence of mouth state on the ecology of the system
- Whitfield, Alan K, Adams, Janine B, Bate, G C, Bezuidenhout, K, Bornman, Thomas G, Cowley, Paul D, Froneman, P William, Gama, P T, James, Nicola C, Mackenzie, B, Riddin, T, Snow, G C, Strydom, Nadine A, Taljaard, S, Terörde, A I, Theron, A K, Turpie, J K, Van Niekerk, L, Vorwerk, Paul D, Wooldridge, T H
- Authors: Whitfield, Alan K , Adams, Janine B , Bate, G C , Bezuidenhout, K , Bornman, Thomas G , Cowley, Paul D , Froneman, P William , Gama, P T , James, Nicola C , Mackenzie, B , Riddin, T , Snow, G C , Strydom, Nadine A , Taljaard, S , Terörde, A I , Theron, A K , Turpie, J K , Van Niekerk, L , Vorwerk, Paul D , Wooldridge, T H
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/480839 , vital:78481 , https://doi.org/10.2989/AJMS.2008.30.3.2.636
- Description: In 2005/2006 a multidisciplinary research programme that included studies on the hydrodynamics, sediment dynamics, macronutrients, microalgae, macrophytes, zoobenthos, hyperbenthos, zooplankton, ichthyoplankton, fish and birds of the temporarily open/closed East Kleinemonde Estuary was conducted. Particular attention was given to the responses of the different ecosystem components to the opening and closing of the estuary mouth and how this is driven by both riverine and marine events. Using a complementary dataset of daily estuary mouth conditions spanning a 14-year period, five distinct phases of the estuary were identified, including closed (average = 90% of the days), outflow (below1%), tidal (9%) and semi-closed (below1%). The open-mouth phase is critical for the movements of a number of estuary-associated fish (e.g. Rhabdosargus holubi) and invertebrates (e.g. Scylla serrata) between the estuary and sea.
- Full Text:
- Date Issued: 2008
- Authors: Whitfield, Alan K , Adams, Janine B , Bate, G C , Bezuidenhout, K , Bornman, Thomas G , Cowley, Paul D , Froneman, P William , Gama, P T , James, Nicola C , Mackenzie, B , Riddin, T , Snow, G C , Strydom, Nadine A , Taljaard, S , Terörde, A I , Theron, A K , Turpie, J K , Van Niekerk, L , Vorwerk, Paul D , Wooldridge, T H
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/480839 , vital:78481 , https://doi.org/10.2989/AJMS.2008.30.3.2.636
- Description: In 2005/2006 a multidisciplinary research programme that included studies on the hydrodynamics, sediment dynamics, macronutrients, microalgae, macrophytes, zoobenthos, hyperbenthos, zooplankton, ichthyoplankton, fish and birds of the temporarily open/closed East Kleinemonde Estuary was conducted. Particular attention was given to the responses of the different ecosystem components to the opening and closing of the estuary mouth and how this is driven by both riverine and marine events. Using a complementary dataset of daily estuary mouth conditions spanning a 14-year period, five distinct phases of the estuary were identified, including closed (average = 90% of the days), outflow (below1%), tidal (9%) and semi-closed (below1%). The open-mouth phase is critical for the movements of a number of estuary-associated fish (e.g. Rhabdosargus holubi) and invertebrates (e.g. Scylla serrata) between the estuary and sea.
- Full Text:
- Date Issued: 2008
Biological responses to a resumption in river flow in a freshwater-deprived, permanently open Southern African estuary
- Vorwerk, Paul D, Froneman, P William, Paterson, Angus W, Strydom, Nadine A, Whitfield, Alan K
- Authors: Vorwerk, Paul D , Froneman, P William , Paterson, Angus W , Strydom, Nadine A , Whitfield, Alan K
- Date: 2008
- Language: English
- Type: text , Article
- Identifier: vital:6886 , http://hdl.handle.net/10962/d1011645
- Description: The Kariega Estuary is a freshwater-deprived system due to numerous impoundments in the catchment. This system has had little or no horizontal salinity gradient over the last 15 years, with hypersaline conditions sometimes predominating in the upper reaches. Following high rainfall events in the catchment during the spring of 2006, including a flood event (approximate 1:10 year) in August 2006, a series of riverine pulses entered the estuary and a horizontal salinity gradient was established. This study examined the influence of this freshwater pulse on four components of the biota within the estuary, namely the zooplankton, and larval, littoral and demersal fishes. The study demonstrated that in three of these components elevated densities were recorded following the riverine input, with only the littoral fishes retaining an almost constant density. In addition, changes in the relative contributions of the estuarine utilisation classes for all three fish groups examined indicated that freshwater input into these systems positively influences the abundances. This has significant implications for water managers as it demonstrates the importance of an Ecological Reserve (defined as ‘the water required to protect the aquatic ecosystems of the water resource’) for this system.
- Full Text:
- Date Issued: 2008
- Authors: Vorwerk, Paul D , Froneman, P William , Paterson, Angus W , Strydom, Nadine A , Whitfield, Alan K
- Date: 2008
- Language: English
- Type: text , Article
- Identifier: vital:6886 , http://hdl.handle.net/10962/d1011645
- Description: The Kariega Estuary is a freshwater-deprived system due to numerous impoundments in the catchment. This system has had little or no horizontal salinity gradient over the last 15 years, with hypersaline conditions sometimes predominating in the upper reaches. Following high rainfall events in the catchment during the spring of 2006, including a flood event (approximate 1:10 year) in August 2006, a series of riverine pulses entered the estuary and a horizontal salinity gradient was established. This study examined the influence of this freshwater pulse on four components of the biota within the estuary, namely the zooplankton, and larval, littoral and demersal fishes. The study demonstrated that in three of these components elevated densities were recorded following the riverine input, with only the littoral fishes retaining an almost constant density. In addition, changes in the relative contributions of the estuarine utilisation classes for all three fish groups examined indicated that freshwater input into these systems positively influences the abundances. This has significant implications for water managers as it demonstrates the importance of an Ecological Reserve (defined as ‘the water required to protect the aquatic ecosystems of the water resource’) for this system.
- Full Text:
- Date Issued: 2008
Fish community response to increased river flow in the Kariega Estuary, a freshwater-deprived, permanently open southern African system
- Vorwerk, Paul D, Froneman, P William, Paterson, Angus W, Whitfield, Alan K
- Authors: Vorwerk, Paul D , Froneman, P William , Paterson, Angus W , Whitfield, Alan K
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/481886 , vital:78594 , https://doi.org/10.2989/AJAS.2008.33.3.1.613
- Description: The littoral and demersal ichthyofaunal community structure in the freshwater-deprived, permanently open Kariega Estuary was investigated following heavy rain in November 2006 and was compared to low-flow condition data from 1991 and 1996. All surveys took place during the spring months and allowed for a comparison of a wet and a dry spring period.
- Full Text:
- Date Issued: 2008
- Authors: Vorwerk, Paul D , Froneman, P William , Paterson, Angus W , Whitfield, Alan K
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/481886 , vital:78594 , https://doi.org/10.2989/AJAS.2008.33.3.1.613
- Description: The littoral and demersal ichthyofaunal community structure in the freshwater-deprived, permanently open Kariega Estuary was investigated following heavy rain in November 2006 and was compared to low-flow condition data from 1991 and 1996. All surveys took place during the spring months and allowed for a comparison of a wet and a dry spring period.
- Full Text:
- Date Issued: 2008
The effects of increased freshwater inflow on metal enrichment in selected Eastern Cape estuaries, South Africa
- Orr, Kyla K, Burgess, Jo E, Froneman, P William
- Authors: Orr, Kyla K , Burgess, Jo E , Froneman, P William
- Date: 2008
- Language: English
- Type: Article
- Identifier: vital:6967 , http://hdl.handle.net/10962/d1012032
- Description: The concentrations of select metals (Cd, Co, Cu, Fe, Pb, Ni and Zn) within the water column and sediment of the permanently open Kariega Estuary and temporary open / closed Riet and East Kleinemonde Estuaries were investigated during a dry and a wet season. Enrichment factors (EFs), using Fe as a reference element, and baseline linear regression models for metals vs Fe were used to assess the extent of metal enrichment in the sediments. The results of the study indicate that Cd, Co Ni and Pb were enriched above baseline concentrations (1.0 < EF < 4.1) in the sediments of all three estuaries. Co, Pb and Ni enrichment in the Kariega Estuary sediments 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 freshwater 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 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 K , Burgess, Jo E , Froneman, P William
- Date: 2008
- Language: English
- Type: Article
- Identifier: vital:6967 , http://hdl.handle.net/10962/d1012032
- Description: The concentrations of select metals (Cd, Co, Cu, Fe, Pb, Ni and Zn) within the water column and sediment of the permanently open Kariega Estuary and temporary open / closed Riet and East Kleinemonde Estuaries were investigated during a dry and a wet season. Enrichment factors (EFs), using Fe as a reference element, and baseline linear regression models for metals vs Fe were used to assess the extent of metal enrichment in the sediments. The results of the study indicate that Cd, Co Ni and Pb were enriched above baseline concentrations (1.0 < EF < 4.1) in the sediments of all three estuaries. Co, Pb and Ni enrichment in the Kariega Estuary sediments 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 freshwater 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 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
The population dynamics of the estuarine isopod Exosphaeroma hylocoetes (Barnard, 1940) within three temporarily open/closed southern African estuaries
- Henninger, Tony O, Froneman, P William, Hodgson, Alan N
- Authors: Henninger, Tony O , Froneman, P William , Hodgson, Alan N
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/447627 , vital:74662 , https://doi.org/10.1080/15627020.2008.11657237
- Description: The population dynamics of the estuarine isopod, Exosphaeroma hylocoetes, was investigated monthly from February 2006 to August 2007 in three temporarily open/closed Eastern Cape estuaries, the East and West Kleinemonde and Kasouga Estuaries. Mean isopod abundances and biomasses ranged between 0 and 4791 ind/m2 and 0 and 9.65 mg/dwt/m2 in the West Kleinemonde Estuary and between 0 and 108 ind/m2 and 0 and 0.318 mg/dwt/m2 in the nearby East Kleinemonde Estuary. In the Kasouga Estuary, the values ranged between 0 and 3650 ind/m2 and 0 and 5.105 mg/dwt/m2. Temporal changes in the abundance and biomass of E. hylocoetes within the three systems was primarily linked to mouth phase, with populations crashing when the mouth was open and to a lesser extent, seasonality. In all three estuaries maximum abundance and biomass was recorded in the middle reaches, which could be ascribed to the presence of submerged macrophytes. E. hylocoetes demonstrates strong sexual dimorphism, with males being significantly larger than females (P 0.05). Sex ratios were skewed in favour of females in all three estuaries.
- Full Text:
- Date Issued: 2008
- Authors: Henninger, Tony O , Froneman, P William , Hodgson, Alan N
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/447627 , vital:74662 , https://doi.org/10.1080/15627020.2008.11657237
- Description: The population dynamics of the estuarine isopod, Exosphaeroma hylocoetes, was investigated monthly from February 2006 to August 2007 in three temporarily open/closed Eastern Cape estuaries, the East and West Kleinemonde and Kasouga Estuaries. Mean isopod abundances and biomasses ranged between 0 and 4791 ind/m2 and 0 and 9.65 mg/dwt/m2 in the West Kleinemonde Estuary and between 0 and 108 ind/m2 and 0 and 0.318 mg/dwt/m2 in the nearby East Kleinemonde Estuary. In the Kasouga Estuary, the values ranged between 0 and 3650 ind/m2 and 0 and 5.105 mg/dwt/m2. Temporal changes in the abundance and biomass of E. hylocoetes within the three systems was primarily linked to mouth phase, with populations crashing when the mouth was open and to a lesser extent, seasonality. In all three estuaries maximum abundance and biomass was recorded in the middle reaches, which could be ascribed to the presence of submerged macrophytes. E. hylocoetes demonstrates strong sexual dimorphism, with males being significantly larger than females (P 0.05). Sex ratios were skewed in favour of females in all three estuaries.
- Full Text:
- Date Issued: 2008
Trophic ecology of dominant zooplankton and macrofauna in a temperate, oligotrophic South African estuary: a fatty acid approach
- Richoux, Nicole B, Froneman, P William
- Authors: Richoux, Nicole B , Froneman, P William
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/478883 , vital:78235 , https://doi.org/10.3354/meps07323
- Description: Fatty acid profiles of food sources, dominant zooplankton, macrofauna and a few small ichthyofauna in a temperate estuary on the southeastern coast of South Africa were used to trace the original carbon sources and the degree of feeding plasticity of consumers within an oligotrophic environment. Fatty acid analysis is seldom used to examine food web ecology in estuaries, as these systems are typically highly complex owing to the variety of potential food sources and the variable nature of detritus. We hypothesized that generalist consumers would exhibit similar and overlapping fatty acid compositions, whereas any specialist consumers would ‘stand out’as they may contain high proportions of fatty acids specific to their preferred food sources. Within-species variation was very small in the food sources, and Principal Component Analysis (PCA) allowed resolution of most species and sample types into distinct clusters. Variation of fatty acid composition was greater within the consumers, with PCA resolving several clusters by collection location within the site and feeding mode of the animals (suspension feeders, grazers and omnivores). We considered the fatty acid profiles (with particular reference to polyunsaturated fatty acids and essential fatty acids) of the consumers in relation to the food sources to determine which organisms played significant roles in the sequestration and cycling of high quality organic material within the estuary.
- Full Text:
- Date Issued: 2008
- Authors: Richoux, Nicole B , Froneman, P William
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/478883 , vital:78235 , https://doi.org/10.3354/meps07323
- Description: Fatty acid profiles of food sources, dominant zooplankton, macrofauna and a few small ichthyofauna in a temperate estuary on the southeastern coast of South Africa were used to trace the original carbon sources and the degree of feeding plasticity of consumers within an oligotrophic environment. Fatty acid analysis is seldom used to examine food web ecology in estuaries, as these systems are typically highly complex owing to the variety of potential food sources and the variable nature of detritus. We hypothesized that generalist consumers would exhibit similar and overlapping fatty acid compositions, whereas any specialist consumers would ‘stand out’as they may contain high proportions of fatty acids specific to their preferred food sources. Within-species variation was very small in the food sources, and Principal Component Analysis (PCA) allowed resolution of most species and sample types into distinct clusters. Variation of fatty acid composition was greater within the consumers, with PCA resolving several clusters by collection location within the site and feeding mode of the animals (suspension feeders, grazers and omnivores). We considered the fatty acid profiles (with particular reference to polyunsaturated fatty acids and essential fatty acids) of the consumers in relation to the food sources to determine which organisms played significant roles in the sequestration and cycling of high quality organic material within the estuary.
- Full Text:
- Date Issued: 2008
- «
- ‹
- 1
- ›
- »