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
The role of estuarine type in characterizing early stage fish assemblages in warm temperate estuaries, South Africa
- Strydom, Nadine A, Whitfield, Alan K, Wooldridge, T H
- Authors: Strydom, Nadine A , Whitfield, Alan K , Wooldridge, T H
- Date: 2003
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/447658 , vital:74664 , https://doi.org/10.1080/15627020.2003.11657192
- Description: Assemblages of early stage fishes (larval and early juvenile stages) were investigated and compared in seven permanently open and five intermittently open estuarine systems on the warm temperate Eastern Cape coast of South Africa. Estuarine type, by virtue of mouth state and prevailing physico chemical conditions, played a defining role in the structure of these fish assemblages. Clupeidae and Gobiidae were the dominant fish families in both estuarine types. Permanently open estuaries were characterized by the predominance of larvae and early juveniles of estuary dependent marine fish species while estuary resident fishes dominated intermittently open estuaries. Seasonal changes were observed in species density and diversity in both estuarine types. Species richness and diversity were highest in the permanently open Swartkops Estuary that is characterized by large nursery habitat availability. Species diversity was high in estuaries with a good supply of freshwater, that results in good recruitment of estuary dependent marine species. Similarly, freshwater deprived estuaries also displayed high species diversity and this was due to the higher incidence of marine straggler species in these systems. Salinity zones appeared to play a significant role in both species density and the presence or absence of species in both estuarine types. Mesohaline zones were found to be the most productive in terms of accumulator regions for larval stages.
- Full Text:
- Date Issued: 2003
- Authors: Strydom, Nadine A , Whitfield, Alan K , Wooldridge, T H
- Date: 2003
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/447658 , vital:74664 , https://doi.org/10.1080/15627020.2003.11657192
- Description: Assemblages of early stage fishes (larval and early juvenile stages) were investigated and compared in seven permanently open and five intermittently open estuarine systems on the warm temperate Eastern Cape coast of South Africa. Estuarine type, by virtue of mouth state and prevailing physico chemical conditions, played a defining role in the structure of these fish assemblages. Clupeidae and Gobiidae were the dominant fish families in both estuarine types. Permanently open estuaries were characterized by the predominance of larvae and early juveniles of estuary dependent marine fish species while estuary resident fishes dominated intermittently open estuaries. Seasonal changes were observed in species density and diversity in both estuarine types. Species richness and diversity were highest in the permanently open Swartkops Estuary that is characterized by large nursery habitat availability. Species diversity was high in estuaries with a good supply of freshwater, that results in good recruitment of estuary dependent marine species. Similarly, freshwater deprived estuaries also displayed high species diversity and this was due to the higher incidence of marine straggler species in these systems. Salinity zones appeared to play a significant role in both species density and the presence or absence of species in both estuarine types. Mesohaline zones were found to be the most productive in terms of accumulator regions for larval stages.
- Full Text:
- Date Issued: 2003
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