In situ feeding rates of the copepods, Pseudodiaptomus hessei and Acartia longipatella, in a temperate, temporarily open/closed Eastern Cape estuary
- Authors: Froneman, P William
- Date: 2004
- Language: English
- Type: text , Article
- Identifier: vital:6901 , http://hdl.handle.net/10962/d1011754
- Description: Size-fractionated chlorophyll-a (chl-a) concentrations and the in situ grazing rates of the copepods, Pseudodiaptomus hessei and Acartia longipatella, were assessed seasonally at the temporarily open/closed Kasouga estuary situated along the southeast coast of southern Africa. Total integrated chl-a concentration ranged between 1.17 and 12.18 mg chl-a m^(–3) and was always dominated by small phytoplankton cells (<20 μm), which comprised up to 86% (range 64–86%) of the total pigment. Total zooplankton abundance ranged between 2676 and 62 043 individuals m^(–3). These copepods numerically dominated the zooplankton counts, accounting for between 79% and 91% of the total. Gut pigment concentrations of the two species at night were significantly higher than the daytime values (P<0.05 in all cases). The observed pattern could be related to the marked diurnal vertical migration patterns exhibited by the copepods. Gut evacuation rates of P. hessei during the study ranged between 0.29 and 0.77 h^(–1) and between 0.39 and 0.58 h^(–1) for A. longipatella. The rate of gut pigment destruction for P. hessei and A. longipatella ranged between 55% and 81% and between 88% and 92% of the total chl-a ingested, respectively. The combined grazing impact of the two copepods ranged between 0.65 and 4.37 mg chl-a m^(–3), or between 4.3% and 35.9% of the available chl-a in the water column. Variations in the grazing activity of the two species could be attributed largely to seasonality in water temperature and shifts in the phytoplankton community structure and zooplankton abundance.
- Full Text:
- Date Issued: 2004
- Authors: Froneman, P William
- Date: 2004
- Language: English
- Type: text , Article
- Identifier: vital:6901 , http://hdl.handle.net/10962/d1011754
- Description: Size-fractionated chlorophyll-a (chl-a) concentrations and the in situ grazing rates of the copepods, Pseudodiaptomus hessei and Acartia longipatella, were assessed seasonally at the temporarily open/closed Kasouga estuary situated along the southeast coast of southern Africa. Total integrated chl-a concentration ranged between 1.17 and 12.18 mg chl-a m^(–3) and was always dominated by small phytoplankton cells (<20 μm), which comprised up to 86% (range 64–86%) of the total pigment. Total zooplankton abundance ranged between 2676 and 62 043 individuals m^(–3). These copepods numerically dominated the zooplankton counts, accounting for between 79% and 91% of the total. Gut pigment concentrations of the two species at night were significantly higher than the daytime values (P<0.05 in all cases). The observed pattern could be related to the marked diurnal vertical migration patterns exhibited by the copepods. Gut evacuation rates of P. hessei during the study ranged between 0.29 and 0.77 h^(–1) and between 0.39 and 0.58 h^(–1) for A. longipatella. The rate of gut pigment destruction for P. hessei and A. longipatella ranged between 55% and 81% and between 88% and 92% of the total chl-a ingested, respectively. The combined grazing impact of the two copepods ranged between 0.65 and 4.37 mg chl-a m^(–3), or between 4.3% and 35.9% of the available chl-a in the water column. Variations in the grazing activity of the two species could be attributed largely to seasonality in water temperature and shifts in the phytoplankton community structure and zooplankton abundance.
- Full Text:
- Date Issued: 2004
The Southern Ocean Group at Rhodes University: seventeen years of biological oceanography in the Southern Ocean reviewed
- McQuaid, Christopher D, Froneman, P William
- Authors: McQuaid, Christopher D , Froneman, P William
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6834 , http://hdl.handle.net/10962/d1010423
- Description: This paper reviews the main findings of the Southern Ocean Group at Rhodes University over the last 17 years. A primary contribution has been the development of conceptual models of the physical-biological driving mechanisms that support enormous seasonal populations of land-based top predators at the Prince Edward Islands. Collectively, these models are referred to as the life-support system of the islands. Near-shore subcomponents of the ecosystem, including inshore feeding predators, are largely supported by autochthonous primary production of kelps and localized diatom blooms. These energy sources feed indirectly into top predator populations via the benthic communities. A crucial link is formed by the bottom-dwelling shrimp, Nauticaris marionis, which feeds largely on benthic species and detritus and is eaten by a number of diving seabirds. The frontal systems that lie north and south of the islands are important feeding grounds for offshore feeding birds. A decadal-scale southward shift in the position of the Sub-antarctic Front towards the islands is reflected in increases in populations of these species. , Rhodes Centenary issue
- Full Text:
- Date Issued: 2004
- Authors: McQuaid, Christopher D , Froneman, P William
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6834 , http://hdl.handle.net/10962/d1010423
- Description: This paper reviews the main findings of the Southern Ocean Group at Rhodes University over the last 17 years. A primary contribution has been the development of conceptual models of the physical-biological driving mechanisms that support enormous seasonal populations of land-based top predators at the Prince Edward Islands. Collectively, these models are referred to as the life-support system of the islands. Near-shore subcomponents of the ecosystem, including inshore feeding predators, are largely supported by autochthonous primary production of kelps and localized diatom blooms. These energy sources feed indirectly into top predator populations via the benthic communities. A crucial link is formed by the bottom-dwelling shrimp, Nauticaris marionis, which feeds largely on benthic species and detritus and is eaten by a number of diving seabirds. The frontal systems that lie north and south of the islands are important feeding grounds for offshore feeding birds. A decadal-scale southward shift in the position of the Sub-antarctic Front towards the islands is reflected in increases in populations of these species. , Rhodes Centenary issue
- Full Text:
- Date Issued: 2004
Variability in pH, fCO2, oxygen and flux of CO2 in the surface water along a transect in the Atlantic sector of the Southern Ocean
- Chierici, M, Fransson, A, Turner, D R, Pakhomov, Evgeny A, Froneman, P William
- Authors: Chierici, M , Fransson, A , Turner, D R , Pakhomov, Evgeny A , Froneman, P William
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6847 , http://hdl.handle.net/10962/d1011105
- Description: Underway sampling and measurements of pH, fCO2, oxygen and Chlorophyll a (Chl a) were performed in the surface waters from Cape Town (South Africa) to Queen Maud Land (Antarctica) in the Atlantic sector of the Southern Ocean during the austral summer 1997/1998. From direct measurements of these parameters and from calculated fCO2 the oceanic carbon dioxide system was studied and related to hydrological and biological parameters. fCO2 was in general undersaturated relative to the atmosphere and showed a large variability with values ranging from 313 to 377 μatm with a mean value of 346±13 μatm. The undersaturation was more pronounced in areas associated with fronts where high Chl a and high pH in situ values were observed. Using shipboard wind speed data, estimates of the CO2 flux were made along the transect and during three mesoscale surveys on the northward return transect in the area of the Spring Ice Edge (SIE), the Winter Ice Edge (WIE) and in the Antarctic Polar Front (APF). The undersaturation observed during the transect caused the ocean to act as a sink for CO2 with a mean sea–air flux for the entire transect of −3±5 mmol m−2 d−1 with a large variability between −20 mmol m−2 d−1 (oceanic uptake) to 1.3 mmol m−2 d−1 (oceanic source). The lowest fCO2 values (largest oceanic uptake of CO2) were found at the southern boundary of the APF at 53°S, which coincided with a supersaturation in oxygen and high pH values. Oxygen concentrations were measured from 50°S to 63°S and varied between 324 and 359 μmol kg−1 with a mean value of 347±9 μmol kg−1. In general only small deviations from equilibrium oxygen saturation were observed (mean value=99±2%). However, in the SIE oxygen was clearly undersaturated, probably an effect of upwelling of oxygen poor deep water which had not yet been compensated for by biological production. Three weeks later, the ice edge had retreated in the SIE region and the Chl a concentration had increased three-fold, suggesting the start of a phytoplankton bloom. This was also seen in the oxygen concentration which had increased and showed supersaturation. This coincided with an increased oceanic uptake of CO2 in the SIE during the mesoscale survey.
- Full Text:
- Date Issued: 2004
- Authors: Chierici, M , Fransson, A , Turner, D R , Pakhomov, Evgeny A , Froneman, P William
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6847 , http://hdl.handle.net/10962/d1011105
- Description: Underway sampling and measurements of pH, fCO2, oxygen and Chlorophyll a (Chl a) were performed in the surface waters from Cape Town (South Africa) to Queen Maud Land (Antarctica) in the Atlantic sector of the Southern Ocean during the austral summer 1997/1998. From direct measurements of these parameters and from calculated fCO2 the oceanic carbon dioxide system was studied and related to hydrological and biological parameters. fCO2 was in general undersaturated relative to the atmosphere and showed a large variability with values ranging from 313 to 377 μatm with a mean value of 346±13 μatm. The undersaturation was more pronounced in areas associated with fronts where high Chl a and high pH in situ values were observed. Using shipboard wind speed data, estimates of the CO2 flux were made along the transect and during three mesoscale surveys on the northward return transect in the area of the Spring Ice Edge (SIE), the Winter Ice Edge (WIE) and in the Antarctic Polar Front (APF). The undersaturation observed during the transect caused the ocean to act as a sink for CO2 with a mean sea–air flux for the entire transect of −3±5 mmol m−2 d−1 with a large variability between −20 mmol m−2 d−1 (oceanic uptake) to 1.3 mmol m−2 d−1 (oceanic source). The lowest fCO2 values (largest oceanic uptake of CO2) were found at the southern boundary of the APF at 53°S, which coincided with a supersaturation in oxygen and high pH values. Oxygen concentrations were measured from 50°S to 63°S and varied between 324 and 359 μmol kg−1 with a mean value of 347±9 μmol kg−1. In general only small deviations from equilibrium oxygen saturation were observed (mean value=99±2%). However, in the SIE oxygen was clearly undersaturated, probably an effect of upwelling of oxygen poor deep water which had not yet been compensated for by biological production. Three weeks later, the ice edge had retreated in the SIE region and the Chl a concentration had increased three-fold, suggesting the start of a phytoplankton bloom. This was also seen in the oxygen concentration which had increased and showed supersaturation. This coincided with an increased oceanic uptake of CO2 in the SIE during the mesoscale survey.
- Full Text:
- Date Issued: 2004
Physical and biological variability in the Antarctic Polar Frontal Zone: report on research cruise 103 of the MV SA Agulhas
- Froneman, P William, Ansorge, Isabelle J, Vumazonke, Lukhanyiso U, Gulekana, A, Bernard, Kim S, Webb, Arthur C M, Leukes, Winston D, Risien, C M, Thomalla, S, Hermes, Juliet, Knott, M, Anderson, D, Hargey, N, Jennings, Michael E, Veitch, J, Lutjeharms, Johan R E, McQuaid, Christopher D
- Authors: Froneman, P William , Ansorge, Isabelle J , Vumazonke, Lukhanyiso U , Gulekana, A , Bernard, Kim S , Webb, Arthur C M , Leukes, Winston D , Risien, C M , Thomalla, S , Hermes, Juliet , Knott, M , Anderson, D , Hargey, N , Jennings, Michael E , Veitch, J , Lutjeharms, Johan R E , McQuaid, Christopher D
- Date: 2002
- Language: English
- Type: Article
- Identifier: vital:6910 , http://hdl.handle.net/10962/d1011863
- Description: A detailed hydrographic and biological survey was carried out in the region of the South-west Indian Ridge during April 2002. Hydrographic data revealed that the Andrew Bain Fracture Zone, centred at 30oE, 50oS, functions as an important choke point to the flow of the Antarctic Circumpolar Current, resulting in the convergence of the Antarctic Polar Front (APF) and the southern branch of the Sub-Antarctic Front (SSAF). Total chlorophyll-a concentration and zooplankton biomass were highest at stations occupied in the vicinity of two frontal features represented by the APF and SSAF. These data suggest that the region of the South-west Indian Ridge is an area of elevated biological activity and probably acts as an important offshore feeding area for the top predators on the Prince Edward Islands.
- Full Text:
- Date Issued: 2002
- Authors: Froneman, P William , Ansorge, Isabelle J , Vumazonke, Lukhanyiso U , Gulekana, A , Bernard, Kim S , Webb, Arthur C M , Leukes, Winston D , Risien, C M , Thomalla, S , Hermes, Juliet , Knott, M , Anderson, D , Hargey, N , Jennings, Michael E , Veitch, J , Lutjeharms, Johan R E , McQuaid, Christopher D
- Date: 2002
- Language: English
- Type: Article
- Identifier: vital:6910 , http://hdl.handle.net/10962/d1011863
- Description: A detailed hydrographic and biological survey was carried out in the region of the South-west Indian Ridge during April 2002. Hydrographic data revealed that the Andrew Bain Fracture Zone, centred at 30oE, 50oS, functions as an important choke point to the flow of the Antarctic Circumpolar Current, resulting in the convergence of the Antarctic Polar Front (APF) and the southern branch of the Sub-Antarctic Front (SSAF). Total chlorophyll-a concentration and zooplankton biomass were highest at stations occupied in the vicinity of two frontal features represented by the APF and SSAF. These data suggest that the region of the South-west Indian Ridge is an area of elevated biological activity and probably acts as an important offshore feeding area for the top predators on the Prince Edward Islands.
- Full Text:
- Date Issued: 2002
Temporal variability in the effects of grazing by the territorial limpet Patella longicosta on the productivity of the crustose alga Ralfsia verrucosa
- Kaehler, Sven, Froneman, P William
- Authors: Kaehler, Sven , Froneman, P William
- Date: 1999
- Language: English
- Type: Article
- Identifier: vital:6935 , http://hdl.handle.net/10962/d1011956
- Description: This study reports the effects of grazing by the territorial limpet Patella longicosta on the productivity of the encrusting alga Ralfsia verrucosa. Grazing significantly increased algal growth during the first month of the study (August). Simulated grazing by brushing also enhanced productivity. However, the productivity of grazed and ungrazed algae did not differ significantly during the ensuing three months. As the growth of ungrazed plants remained the same throughout the study, the elevated productivity of grazed plants during August was attributed to increased limpet activity. The variation in grazer-induced algal growth was possibly associated with increased feeding when the limpets embark on energetically costly periods of reproduction.
- Full Text: false
- Date Issued: 1999
- Authors: Kaehler, Sven , Froneman, P William
- Date: 1999
- Language: English
- Type: Article
- Identifier: vital:6935 , http://hdl.handle.net/10962/d1011956
- Description: This study reports the effects of grazing by the territorial limpet Patella longicosta on the productivity of the encrusting alga Ralfsia verrucosa. Grazing significantly increased algal growth during the first month of the study (August). Simulated grazing by brushing also enhanced productivity. However, the productivity of grazed and ungrazed algae did not differ significantly during the ensuing three months. As the growth of ungrazed plants remained the same throughout the study, the elevated productivity of grazed plants during August was attributed to increased limpet activity. The variation in grazer-induced algal growth was possibly associated with increased feeding when the limpets embark on energetically costly periods of reproduction.
- Full Text: false
- Date Issued: 1999
Prince Edward Islands' offshore oceanographic study: report of research cruise April-May 1997
- Pakhomov, Evgeny A, Froneman, P William, Ansorge, Isabelle J
- Authors: Pakhomov, Evgeny A , Froneman, P William , Ansorge, Isabelle J
- Date: 1998
- Language: English
- Type: text , article
- Identifier: vital:6939 , http://hdl.handle.net/10520/AJA00382353_9017 , https://journals.co.za/content/sajsci/94/4/AJA00382353_9017 , http://hdl.handle.net/10962/d1011962
- Description: preprint , Focuses on the preliminary results of the second cruise of the Marion Island Oceanographic Study designed to provide oceanological observations off Prince Edward Islands from April 25 to May 28, 1997. Physical and chemical oceanographic results; Surface seawater temperature; Total chlorophyll-a distribution.
- Full Text:
- Date Issued: 1998
- Authors: Pakhomov, Evgeny A , Froneman, P William , Ansorge, Isabelle J
- Date: 1998
- Language: English
- Type: text , article
- Identifier: vital:6939 , http://hdl.handle.net/10520/AJA00382353_9017 , https://journals.co.za/content/sajsci/94/4/AJA00382353_9017 , http://hdl.handle.net/10962/d1011962
- Description: preprint , Focuses on the preliminary results of the second cruise of the Marion Island Oceanographic Study designed to provide oceanological observations off Prince Edward Islands from April 25 to May 28, 1997. Physical and chemical oceanographic results; Surface seawater temperature; Total chlorophyll-a distribution.
- Full Text:
- Date Issued: 1998
Research cruise of the Scandinavian/South African Antarctic expedition, December 1997 to February 1998
- Froneman, P William, Pakhomov, E A, Turner, D, Abrahamson, K, Karlsson, B, Godhe, A, Bertilsson, S, Graneli, W, Carlsson, P, Wangberg, S, Wulff, A, Croot, P, Andersson, K, Balarin, Marianne G, Wedborg, M, Persson, T, Rasmus, K, Ozturk, M, David, R
- Authors: Froneman, P William , Pakhomov, E A , Turner, D , Abrahamson, K , Karlsson, B , Godhe, A , Bertilsson, S , Graneli, W , Carlsson, P , Wangberg, S , Wulff, A , Croot, P , Andersson, K , Balarin, Marianne G , Wedborg, M , Persson, T , Rasmus, K , Ozturk, M , David, R
- Date: 1998
- Language: English
- Type: Article
- Identifier: vital:6934 , http://hdl.handle.net/10962/d1011955
- Description: Focuses on the Scandinavian/South African Antarctic expedition conducted between December 4, 1997 to February 6, 1998 which determined the role of Southern Ocean in the global carbon cycle in physical and biological oceanographic studies. Aims of the expedition; Underway sampling conducted; Biological results of the expedition; Conclusions.
- Full Text: false
- Date Issued: 1998
- Authors: Froneman, P William , Pakhomov, E A , Turner, D , Abrahamson, K , Karlsson, B , Godhe, A , Bertilsson, S , Graneli, W , Carlsson, P , Wangberg, S , Wulff, A , Croot, P , Andersson, K , Balarin, Marianne G , Wedborg, M , Persson, T , Rasmus, K , Ozturk, M , David, R
- Date: 1998
- Language: English
- Type: Article
- Identifier: vital:6934 , http://hdl.handle.net/10962/d1011955
- Description: Focuses on the Scandinavian/South African Antarctic expedition conducted between December 4, 1997 to February 6, 1998 which determined the role of Southern Ocean in the global carbon cycle in physical and biological oceanographic studies. Aims of the expedition; Underway sampling conducted; Biological results of the expedition; Conclusions.
- Full Text: false
- Date Issued: 1998
Surface distribution of microphytoplankton of the south-west Indian Ocean along a repeat transect between Cape Town and the Prince Edward Islands
- Froneman, P William, Pakhomov, Evgeny A, Meaton, V
- Authors: Froneman, P William , Pakhomov, Evgeny A , Meaton, V
- Date: 1998
- Language: English
- Type: text , Article
- Identifier: vital:6933 , http://hdl.handle.net/10962/d1011953
- Description: Surface chlorophyll-a (chl-a) concentrations, microphytoplankton (>20 μm) species composition and distribution along a repeat transect between Cape Town and the Prince Edward Islands were investigated in early austral autumn (April/May) 1996. Samples were collected at approximately 30 nautical mile intervals for the analysis of size-fractionated chl-a and the identification and enumeration of microphytoplankton species. Peaks in total chl-a (>1 μg 1 [superscript -1]) were recorded at the Subtropical Convergence (STC), at the Sub-Antarctic Front (SAF) and in the waters surrounding the Prince Edward Islands. In addition, a minor peak in chl-a concentration was recorded in the continental shelf waters. At stations where elevated chl-a concentrations were recorded, microphytoplankton generally formed a substantial contribution (-10%) to total chlorophyll. Outside these regions, total chlorophyll concentrations were lower (<0.9 μg 1 [superscript -1]) and almost entirely dominated by nano- and picophytoplankton, which contributed >95% of the total. Microphytoplankton species composition along both transects were dominated by chain-forming species of the genera Chaetoceros (mainly C. neglectum, C. peruvianus and C. constrictus), Nitzschia spp. and Pseudoeunotia doliolus. Cluster and ordination analysis based on species composition identified five distinct microphytoplankton assemblages, which were closely associated with the different water masses in the region between Cape Town and the Prince Edward Islands. The microphytoplankton species composition and biogeographic zones identified during this investigation are in general agreement with similar studies conducted in the south-west Indian Ocean during the austral summer, which suggests that there are little seasonal trends in both the microphytoplankton species composition and biogeographic zonation.
- Full Text:
- Date Issued: 1998
- Authors: Froneman, P William , Pakhomov, Evgeny A , Meaton, V
- Date: 1998
- Language: English
- Type: text , Article
- Identifier: vital:6933 , http://hdl.handle.net/10962/d1011953
- Description: Surface chlorophyll-a (chl-a) concentrations, microphytoplankton (>20 μm) species composition and distribution along a repeat transect between Cape Town and the Prince Edward Islands were investigated in early austral autumn (April/May) 1996. Samples were collected at approximately 30 nautical mile intervals for the analysis of size-fractionated chl-a and the identification and enumeration of microphytoplankton species. Peaks in total chl-a (>1 μg 1 [superscript -1]) were recorded at the Subtropical Convergence (STC), at the Sub-Antarctic Front (SAF) and in the waters surrounding the Prince Edward Islands. In addition, a minor peak in chl-a concentration was recorded in the continental shelf waters. At stations where elevated chl-a concentrations were recorded, microphytoplankton generally formed a substantial contribution (-10%) to total chlorophyll. Outside these regions, total chlorophyll concentrations were lower (<0.9 μg 1 [superscript -1]) and almost entirely dominated by nano- and picophytoplankton, which contributed >95% of the total. Microphytoplankton species composition along both transects were dominated by chain-forming species of the genera Chaetoceros (mainly C. neglectum, C. peruvianus and C. constrictus), Nitzschia spp. and Pseudoeunotia doliolus. Cluster and ordination analysis based on species composition identified five distinct microphytoplankton assemblages, which were closely associated with the different water masses in the region between Cape Town and the Prince Edward Islands. The microphytoplankton species composition and biogeographic zones identified during this investigation are in general agreement with similar studies conducted in the south-west Indian Ocean during the austral summer, which suggests that there are little seasonal trends in both the microphytoplankton species composition and biogeographic zonation.
- Full Text:
- Date Issued: 1998