Recovery of the critically endangered river pipefish, Syngnathus watermeyeri, in the Kariega Estuary, Eastern Cape province
- Vorwerk, Paul D, Froneman, P William, Paterson, Angus W
- Authors: Vorwerk, Paul D , Froneman, P William , Paterson, Angus W
- Date: 2007
- Language: English
- Type: text , Article
- Identifier: vital:6965 , http://hdl.handle.net/10962/d1012028
- Description: An intensive ichthyofaunal survey in the permanently open Kariega Estuary along the Eastern Cape coast has identified a breeding population of the critically endangered river pipefish, Syngnathus watermeyeri, within the middle and upper reaches of the system. This is the first recorded capture of this species in the estuary for over four decades. We suggest that the presence of S. watermeyeri is the result of the heavy rainfall within the region, which contributed to the establishment of optimum habitat requirements (mesohaline conditions and increased food availability) of the pipefish.
- Full Text:
- Date Issued: 2007
- Authors: Vorwerk, Paul D , Froneman, P William , Paterson, Angus W
- Date: 2007
- Language: English
- Type: text , Article
- Identifier: vital:6965 , http://hdl.handle.net/10962/d1012028
- Description: An intensive ichthyofaunal survey in the permanently open Kariega Estuary along the Eastern Cape coast has identified a breeding population of the critically endangered river pipefish, Syngnathus watermeyeri, within the middle and upper reaches of the system. This is the first recorded capture of this species in the estuary for over four decades. We suggest that the presence of S. watermeyeri is the result of the heavy rainfall within the region, which contributed to the establishment of optimum habitat requirements (mesohaline conditions and increased food availability) of the pipefish.
- Full Text:
- Date Issued: 2007
Effects of temperature and salinity on the standard metabolic rate (SMR) of the caridean shrimp Palaemon peringueyi
- Allan, E Louise, Froneman, P William, Hodgson, Alan N
- Authors: Allan, E Louise , Froneman, P William , Hodgson, Alan N
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6831 , http://hdl.handle.net/10962/d1007567
- Description: The standard metabolic rate (SMR) of the caridean shrimp Palaemon peringueyi to changes in temperature (15–30 °C), salinity (0–45‰) and a combination thereof was investigated. The rate of oxygen consumption of the shrimp was determined using a YSI oxygen meter. At a constant salinity of 35‰ the respiration rate of P. peringueyi increased with an increase in temperature and ranged between 0.260 and 0.982 μl O[subscript 2] mg wwt[superscript −1] h[superscript −1]. The Q[subscript 10] value over the temperature range 15–25 °C was estimated at 3.13. At a constant temperature of 15 °C the respiration rate of P. peringueyi also increased with an increase in salinity and ranged between 0.231 and 0.860 μl O[subscript 2] mg wwt[superscript −1] h[superscript −1]. For combination experiments the absence of any significant difference in the respiration rate of P. peringueyi at the four temperatures over the salinity range 15–35‰ suggests that the shrimp is well adapted to inhabiting environments characterised by variations in salinity and temperature such as those encountered within the middle and lower reaches of permanently open estuaries with substantial freshwater inflow. On the other hand, the total mortality of the shrimp recorded at salinities < 5‰ at all four temperatures suggests that the upper distribution of the shrimp may reflect physiological constraints. Similarly, the increase in the respiration rate of the shrimp at the four temperatures at salinities > 35‰ suggests that the shrimp may experience osmotic stress in freshwater deprived permanently open and intermittently open estuaries where hypersaline conditions may develop.
- Full Text:
- Date Issued: 2006
- Authors: Allan, E Louise , Froneman, P William , Hodgson, Alan N
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6831 , http://hdl.handle.net/10962/d1007567
- Description: The standard metabolic rate (SMR) of the caridean shrimp Palaemon peringueyi to changes in temperature (15–30 °C), salinity (0–45‰) and a combination thereof was investigated. The rate of oxygen consumption of the shrimp was determined using a YSI oxygen meter. At a constant salinity of 35‰ the respiration rate of P. peringueyi increased with an increase in temperature and ranged between 0.260 and 0.982 μl O[subscript 2] mg wwt[superscript −1] h[superscript −1]. The Q[subscript 10] value over the temperature range 15–25 °C was estimated at 3.13. At a constant temperature of 15 °C the respiration rate of P. peringueyi also increased with an increase in salinity and ranged between 0.231 and 0.860 μl O[subscript 2] mg wwt[superscript −1] h[superscript −1]. For combination experiments the absence of any significant difference in the respiration rate of P. peringueyi at the four temperatures over the salinity range 15–35‰ suggests that the shrimp is well adapted to inhabiting environments characterised by variations in salinity and temperature such as those encountered within the middle and lower reaches of permanently open estuaries with substantial freshwater inflow. On the other hand, the total mortality of the shrimp recorded at salinities < 5‰ at all four temperatures suggests that the upper distribution of the shrimp may reflect physiological constraints. Similarly, the increase in the respiration rate of the shrimp at the four temperatures at salinities > 35‰ suggests that the shrimp may experience osmotic stress in freshwater deprived permanently open and intermittently open estuaries where hypersaline conditions may develop.
- Full Text:
- Date Issued: 2006
Euphausiid population structure and grazing in the Antarctic Polar Frontal Zone—austral autumn 2004
- Bernard, Anthony T F, Froneman, P William
- Authors: Bernard, Anthony T F , Froneman, P William
- Date: 2006
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/480861 , vital:78488 , https://doi.org/10.2989/18142320609504207
- Description: The euphausiid community structure and grazing dynamics were investigated in the West Indian sector of the Polar Frontal Zone during the austral autumn 2004. Subsurface (200m) temperature profiles indicated that an intense frontal feature, formed by the convergence of the Subantarctic Front and the Antarctic Polar Front bisected the survey area into two distinct zones, the Subantarctic Zone (SAZ) and the Antarctic Zone (AAZ). Total integrated chlorophyll a (Chl a) biomass was typical for the region (below 25mg Chl a m−2), and was dominated by picophytoplankton.
- Full Text:
- Date Issued: 2006
- Authors: Bernard, Anthony T F , Froneman, P William
- Date: 2006
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/480861 , vital:78488 , https://doi.org/10.2989/18142320609504207
- Description: The euphausiid community structure and grazing dynamics were investigated in the West Indian sector of the Polar Frontal Zone during the austral autumn 2004. Subsurface (200m) temperature profiles indicated that an intense frontal feature, formed by the convergence of the Subantarctic Front and the Antarctic Polar Front bisected the survey area into two distinct zones, the Subantarctic Zone (SAZ) and the Antarctic Zone (AAZ). Total integrated chlorophyll a (Chl a) biomass was typical for the region (below 25mg Chl a m−2), and was dominated by picophytoplankton.
- Full Text:
- Date Issued: 2006
Impacts of marine biogeographic boundaries on phylogeographic patterns of three South African estuarine crustaceans
- Teske, Peter R, McQuaid, Christopher D, Froneman, P William, Barker, Nigel P
- Authors: Teske, Peter R , McQuaid, Christopher D , Froneman, P William , Barker, Nigel P
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6548 , http://hdl.handle.net/10962/d1006004 , http://dx.doi.org/10.3354/meps314283
- Description: The South African coastline comprises 3 main biogeographic provinces: (1) the cool-temperate west coast, (2) the warm-temperate south coast, and (3) the subtropical east coast. The boundaries between these regions are defined by changes in species compositions and hydrological conditions. It is possible that these affect phylogeographic patterns of coastal organisms differently, depending on the species’ ecologies and modes of dispersal. In the present study, genealogies of 3 estuarine crustaceans, each characterized by a different mode of passive dispersal and present in more than one biogeographic province, were reconstructed using mtDNA COI sequences, and the impacts of biogeographic boundaries on their phylogeographic patterns were compared. The species were (mode of dispersal in brackets): (1) the mudprawn Upogebia africana (planktonic larvae), (2) the isopod Exosphaeroma hylecoetes (adult rafting), and (3) the cumacean Iphinoe truncata (adult drifting). Two major mtDNA lineages with slightly overlapping distributions were identified in U. africana (the species with the highest dispersal potential). The other 2 species had 3 mtDNA lineages each, which were characterized by strict geographic segregation. Phylogeographic breaks in U. africana and E. hylecoetes coincided with biogeographic boundaries, whereas the phylogeographic patterns identified in I. truncata may reflect persistent palaeogeographic patterns. Ecological factors and modes of dispersal are likely to have played a role in both cladogenesis of the different lineages and in the establishment of their present-day distribution patterns.
- Full Text:
- Date Issued: 2006
- Authors: Teske, Peter R , McQuaid, Christopher D , Froneman, P William , Barker, Nigel P
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6548 , http://hdl.handle.net/10962/d1006004 , http://dx.doi.org/10.3354/meps314283
- Description: The South African coastline comprises 3 main biogeographic provinces: (1) the cool-temperate west coast, (2) the warm-temperate south coast, and (3) the subtropical east coast. The boundaries between these regions are defined by changes in species compositions and hydrological conditions. It is possible that these affect phylogeographic patterns of coastal organisms differently, depending on the species’ ecologies and modes of dispersal. In the present study, genealogies of 3 estuarine crustaceans, each characterized by a different mode of passive dispersal and present in more than one biogeographic province, were reconstructed using mtDNA COI sequences, and the impacts of biogeographic boundaries on their phylogeographic patterns were compared. The species were (mode of dispersal in brackets): (1) the mudprawn Upogebia africana (planktonic larvae), (2) the isopod Exosphaeroma hylecoetes (adult rafting), and (3) the cumacean Iphinoe truncata (adult drifting). Two major mtDNA lineages with slightly overlapping distributions were identified in U. africana (the species with the highest dispersal potential). The other 2 species had 3 mtDNA lineages each, which were characterized by strict geographic segregation. Phylogeographic breaks in U. africana and E. hylecoetes coincided with biogeographic boundaries, whereas the phylogeographic patterns identified in I. truncata may reflect persistent palaeogeographic patterns. Ecological factors and modes of dispersal are likely to have played a role in both cladogenesis of the different lineages and in the establishment of their present-day distribution patterns.
- Full Text:
- Date Issued: 2006
Population demographics of Palaemon peringueyi (Macpherson 1990)(Decapoda: Palaemonidae) in a small intermittently open Eastern Cape estuary
- Authors: Froneman, P William
- Date: 2006
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/481908 , vital:78596 , https://doi.org/10.2989/16085910609503891
- Description: The population demographics of the caridean shrimp Palaemon peringueyi was investigated monthly at four sites over a period of one year in the small, intermittently-open Grants River Estuary situated on the south-east coastline of southern Africa. Mean total abundance and biomass of P. peringueyi ranged between 0 and 23.2 ind m−2 and 0 and 2.3mg wwt m−2, respectively.
- Full Text:
- Date Issued: 2006
- Authors: Froneman, P William
- Date: 2006
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/481908 , vital:78596 , https://doi.org/10.2989/16085910609503891
- Description: The population demographics of the caridean shrimp Palaemon peringueyi was investigated monthly at four sites over a period of one year in the small, intermittently-open Grants River Estuary situated on the south-east coastline of southern Africa. Mean total abundance and biomass of P. peringueyi ranged between 0 and 23.2 ind m−2 and 0 and 2.3mg wwt m−2, respectively.
- Full Text:
- Date Issued: 2006
The importance of phytoplankton size in mediating trophic interactions within the plankton of a southern African estuary
- Authors: Froneman, P William
- Date: 2006
- Language: English
- Type: text , Article
- Identifier: vital:6928 , http://hdl.handle.net/10962/d1011944
- Description: The influence of the phytoplankton size composition in mediating the trophic interactions between the bacteria, phytoplankton, microheterotrophs (<200 μm) and mesozooplankton (>200 μm) was investigated on three occasions in a warm temperate, temporarily open/closed estuary situated along the southern African coastline. Results of the investigation indicated that the microheterotrophs represented the most important consumers of bacteria and chlorophyll (chl)-a <5.0 μm. The low impact of the mesozooplankton on the bacteria and chl-a <5.0 μm during the study appeared to be related to the inability of the larger zooplankton to feed efficiently on small particles. During those periods when total chl-a concentration was dominated by picophytoplankton (<2.0 μm) and microphytoplankton (>20 μm), mesozooplankton were unable to feed efficiently on the chl-a due to feeding constraints. In response to the unfavorable size structure of the phytoplankton assemblages, mesozooplankton appeared to consume the microheterotrophs. The negative impact of the mesozooplankton on the microheterotrophs resulted in a decrease in the impact of these organisms on the bacteria and the chl-a <5.0 μm. This result is consistent with the predator-prey cascades. On the other hand, when the total chl-a was dominated by nanophytoplankton (2–20 μm), mesozooplankton were able to feed directly on the phytoplankton. Results of the study indicate that size structure of the phytoplankton assemblages within estuaries plays an important role in mediating the trophic interactions between the various components of the plankton food web.
- Full Text:
- Date Issued: 2006
- Authors: Froneman, P William
- Date: 2006
- Language: English
- Type: text , Article
- Identifier: vital:6928 , http://hdl.handle.net/10962/d1011944
- Description: The influence of the phytoplankton size composition in mediating the trophic interactions between the bacteria, phytoplankton, microheterotrophs (<200 μm) and mesozooplankton (>200 μm) was investigated on three occasions in a warm temperate, temporarily open/closed estuary situated along the southern African coastline. Results of the investigation indicated that the microheterotrophs represented the most important consumers of bacteria and chlorophyll (chl)-a <5.0 μm. The low impact of the mesozooplankton on the bacteria and chl-a <5.0 μm during the study appeared to be related to the inability of the larger zooplankton to feed efficiently on small particles. During those periods when total chl-a concentration was dominated by picophytoplankton (<2.0 μm) and microphytoplankton (>20 μm), mesozooplankton were unable to feed efficiently on the chl-a due to feeding constraints. In response to the unfavorable size structure of the phytoplankton assemblages, mesozooplankton appeared to consume the microheterotrophs. The negative impact of the mesozooplankton on the microheterotrophs resulted in a decrease in the impact of these organisms on the bacteria and the chl-a <5.0 μm. This result is consistent with the predator-prey cascades. On the other hand, when the total chl-a was dominated by nanophytoplankton (2–20 μm), mesozooplankton were able to feed directly on the phytoplankton. Results of the study indicate that size structure of the phytoplankton assemblages within estuaries plays an important role in mediating the trophic interactions between the various components of the plankton food web.
- Full Text:
- Date Issued: 2006
Anti-oesophageal cancer activity in extracts of deep-water Marion Island sponges
- Davies-Coleman, Michael T, Froneman, P William, Keyzers, Robert A, Whibley, Catherine, Hendricks, Denver T, Samaai, Toufiek, McQuaid, Christopher D
- Authors: Davies-Coleman, Michael T , Froneman, P William , Keyzers, Robert A , Whibley, Catherine , Hendricks, Denver T , Samaai, Toufiek , McQuaid, Christopher D
- Date: 2005
- Language: English
- Type: Article
- Identifier: vital:6569 , http://hdl.handle.net/10962/d1004132
- Description: Oesophageal cancer is one of the most common causes of cancer-related deaths in South African black males. The limited efficacy of chemotherapeutic agents to treat this disease has prompted a search for potential new chemical entities with anticancer properties. We report here on the evidence for anti-oesophageal cancer activity in the methanolic extracts of five species of sponges dredged from a depth of approximately 100 m in the vicinity of Marion Island in the Southern Ocean during the autumn of 2004.
- Full Text:
- Date Issued: 2005
- Authors: Davies-Coleman, Michael T , Froneman, P William , Keyzers, Robert A , Whibley, Catherine , Hendricks, Denver T , Samaai, Toufiek , McQuaid, Christopher D
- Date: 2005
- Language: English
- Type: Article
- Identifier: vital:6569 , http://hdl.handle.net/10962/d1004132
- Description: Oesophageal cancer is one of the most common causes of cancer-related deaths in South African black males. The limited efficacy of chemotherapeutic agents to treat this disease has prompted a search for potential new chemical entities with anticancer properties. We report here on the evidence for anti-oesophageal cancer activity in the methanolic extracts of five species of sponges dredged from a depth of approximately 100 m in the vicinity of Marion Island in the Southern Ocean during the autumn of 2004.
- Full Text:
- Date Issued: 2005
Monitoring the oceanic flow between Africa and Antarctica: report of the first Good Hope cruise
- Ansorge, Isabelle J, Speich, S, Lutjeharms, Johan R E, Goni, G J, Rautenbach, C J de W, Froneman, P William, Rouault, M, Garzoli, S
- Authors: Ansorge, Isabelle J , Speich, S , Lutjeharms, Johan R E , Goni, G J , Rautenbach, C J de W , Froneman, P William , Rouault, M , Garzoli, S
- Date: 2005
- Language: English
- Type: Article
- Identifier: vital:6832 , http://hdl.handle.net/10962/d1007568
- Description: The Southern Ocean plays a major role in the global oceanic circulation, as a component of the Meridional Overturning Circulation, and it is postulated that it has a great influence on present-day climate. However, our understanding of its complex three-dimensional dynamics and of the impact of its variability on the climate system is rudimentary. The newly constituted, international GoodHope research venture aims to address this knowledge gap by establishing a programme of regular observations across the Southern Ocean between the African and Antarctic continents. The objectives of this programme are fivefold: (1) to improve understanding of Indo-Atlantic inter-ocean exchanges and their impact on the global thermohaline circulation and thus on global climate change; (2) to understand in more detail the influence these exchanges have on the climate variability of the southern African subcontinent; (3) to monitor the variability of the main Southern Ocean frontal systems associated with the Antarctic Circumpolar Current; (4) to study air-sea exchanges and their role on the global heat budget, with particular emphasis on the intense exchanges occurring within the Agulhas Retroflection region south of South Africa, and (5) to examine the role of major frontal systems as areas of elevated biological activity and as biogeographical barriers to the distribution of plankton. We present here preliminary results on the physical and biological structure of the frontal systems using the first GoodHope transect that was completed during February-March 2004.
- Full Text:
- Date Issued: 2005
- Authors: Ansorge, Isabelle J , Speich, S , Lutjeharms, Johan R E , Goni, G J , Rautenbach, C J de W , Froneman, P William , Rouault, M , Garzoli, S
- Date: 2005
- Language: English
- Type: Article
- Identifier: vital:6832 , http://hdl.handle.net/10962/d1007568
- Description: The Southern Ocean plays a major role in the global oceanic circulation, as a component of the Meridional Overturning Circulation, and it is postulated that it has a great influence on present-day climate. However, our understanding of its complex three-dimensional dynamics and of the impact of its variability on the climate system is rudimentary. The newly constituted, international GoodHope research venture aims to address this knowledge gap by establishing a programme of regular observations across the Southern Ocean between the African and Antarctic continents. The objectives of this programme are fivefold: (1) to improve understanding of Indo-Atlantic inter-ocean exchanges and their impact on the global thermohaline circulation and thus on global climate change; (2) to understand in more detail the influence these exchanges have on the climate variability of the southern African subcontinent; (3) to monitor the variability of the main Southern Ocean frontal systems associated with the Antarctic Circumpolar Current; (4) to study air-sea exchanges and their role on the global heat budget, with particular emphasis on the intense exchanges occurring within the Agulhas Retroflection region south of South Africa, and (5) to examine the role of major frontal systems as areas of elevated biological activity and as biogeographical barriers to the distribution of plankton. We present here preliminary results on the physical and biological structure of the frontal systems using the first GoodHope transect that was completed during February-March 2004.
- Full Text:
- Date Issued: 2005
An interdisciplinary cruise dedicated to understanding ocean eddies upstream of the Prince Edward Islands
- Ansorge, Isabelle J, Froneman, P William, Lutjeharms, Johan R E, Bernard, Kim S, Lange, Louise, Lukáč, D, Backburg, B, Blake, Justin D, Bland, S, Burls, N, Davies-Coleman, Michael T, Gerber, R, Gildenhuys, S, Hayes-Foley, P, Ludford, A, Manzoni, T, Robertson, E, Southey, D, Swart, S, Van Rensburg, D, Wynne, S
- Authors: Ansorge, Isabelle J , Froneman, P William , Lutjeharms, Johan R E , Bernard, Kim S , Lange, Louise , Lukáč, D , Backburg, B , Blake, Justin D , Bland, S , Burls, N , Davies-Coleman, Michael T , Gerber, R , Gildenhuys, S , Hayes-Foley, P , Ludford, A , Manzoni, T , Robertson, E , Southey, D , Swart, S , Van Rensburg, D , Wynne, S
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6830 , http://hdl.handle.net/10962/d1007566
- Description: A detailed hydrographic and biological survey was carried out in the region of the South-West Indian Ridge during April 2004. Altimetry and hydrographic data have identified this region as an area of high flow variability. Hydrographic data revealed that here the Subantarctic Polar Front (SAF) and Antarctic Polar Front (APF) converge to form a highly intense frontal system. Water masses identified during the survey showed a distinct separation in properties between the northwestern and southeastern corners. In the north-west, water masses were distinctly Subantarctic (>8.5°C, salinity >34.2), suggesting that the SAF lay extremely far to the south. In the southeast corner water masses were typical of the Antarctic zone, showing a distinct subsurface temperature minimum of <2.5°C. Total integrated chl-a concentration during the survey ranged from 4.15 to 22.81 mg chl-a m[superscript (-2)], with the highest concentrations recorded at stations occupied in the frontal region. These data suggest that the region of the South-West Indian Ridge represents not only an area of elevated biological activity but also acts as a strong biogeographic barrier to the spatial distribution of zooplankton.
- Full Text:
- Date Issued: 2004
- Authors: Ansorge, Isabelle J , Froneman, P William , Lutjeharms, Johan R E , Bernard, Kim S , Lange, Louise , Lukáč, D , Backburg, B , Blake, Justin D , Bland, S , Burls, N , Davies-Coleman, Michael T , Gerber, R , Gildenhuys, S , Hayes-Foley, P , Ludford, A , Manzoni, T , Robertson, E , Southey, D , Swart, S , Van Rensburg, D , Wynne, S
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6830 , http://hdl.handle.net/10962/d1007566
- Description: A detailed hydrographic and biological survey was carried out in the region of the South-West Indian Ridge during April 2004. Altimetry and hydrographic data have identified this region as an area of high flow variability. Hydrographic data revealed that here the Subantarctic Polar Front (SAF) and Antarctic Polar Front (APF) converge to form a highly intense frontal system. Water masses identified during the survey showed a distinct separation in properties between the northwestern and southeastern corners. In the north-west, water masses were distinctly Subantarctic (>8.5°C, salinity >34.2), suggesting that the SAF lay extremely far to the south. In the southeast corner water masses were typical of the Antarctic zone, showing a distinct subsurface temperature minimum of <2.5°C. Total integrated chl-a concentration during the survey ranged from 4.15 to 22.81 mg chl-a m[superscript (-2)], with the highest concentrations recorded at stations occupied in the frontal region. These data suggest that the region of the South-West Indian Ridge represents not only an area of elevated biological activity but also acts as a strong biogeographic barrier to the spatial distribution of zooplankton.
- Full Text:
- Date Issued: 2004
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
Food web structure in three contrasting estuaries determined using stable isotope (∂ 13C) analysis
- Authors: Froneman, P William
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/481897 , vital:78595 , https://doi.org/10.2989/16085914.2002.9626582
- Description: Food web structure in three contrasting estuaries, the freshwater-deprived Kariega, the freshwater-dominated Great Fish River and the temporarily open/closed Kasouga estuary, along the south-east coast of southern Africa was investigated in summer (1–4 November) 2000 by employing stable carbon (∂13C) isotope analysis.
- Full Text:
- Date Issued: 2002
- Authors: Froneman, P William
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/481897 , vital:78595 , https://doi.org/10.2989/16085914.2002.9626582
- Description: Food web structure in three contrasting estuaries, the freshwater-deprived Kariega, the freshwater-dominated Great Fish River and the temporarily open/closed Kasouga estuary, along the south-east coast of southern Africa was investigated in summer (1–4 November) 2000 by employing stable carbon (∂13C) isotope analysis.
- Full Text:
- Date Issued: 2002
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
Predation impact of carnivorous macrozooplankton and micronekton in the Atlantic sector of the Southern Ocean
- Pakhomov, Evgeny A, Perissinotto, Renzo, Froneman, P William
- Authors: Pakhomov, Evgeny A , Perissinotto, Renzo , Froneman, P William
- Date: 1999
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/480916 , vital:78493 , https://doi.org/10.1016/S0924-7963(98)00023-2
- Description: The composition, biomass, distribution and predation impact of carnivorous zooplankton were investigated along a transect from SANAE to Cape Town during the second cruise of the South African Antarctic Marine Ecosystem Study (SAAMES II) in January–February 1993.
- Full Text:
- Date Issued: 1999
- Authors: Pakhomov, Evgeny A , Perissinotto, Renzo , Froneman, P William
- Date: 1999
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/480916 , vital:78493 , https://doi.org/10.1016/S0924-7963(98)00023-2
- Description: The composition, biomass, distribution and predation impact of carnivorous zooplankton were investigated along a transect from SANAE to Cape Town during the second cruise of the South African Antarctic Marine Ecosystem Study (SAAMES II) in January–February 1993.
- Full Text:
- Date Issued: 1999
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
Abundance and trophodynamics of Euphausia crystallorophias in the shelf region of the Lazarev Sea during austral spring and summer
- Pakhomov, Evgeny A, Perissinotto, Renzo, Froneman, P William
- Authors: Pakhomov, Evgeny A , Perissinotto, Renzo , Froneman, P William
- Date: 1998
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/480895 , vital:78491 , https://doi.org/10.1016/S0924-7963(98)00046-3
- Description: An investigation to estimate the seasonal changes in feeding habits in relation to the energy budget of Euphausia crystallorophias was carried out during austral spring and summer 1994/95 in the shelf region of the Lazarev Sea.
- Full Text:
- Date Issued: 1998
- Authors: Pakhomov, Evgeny A , Perissinotto, Renzo , Froneman, P William
- Date: 1998
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/480895 , vital:78491 , https://doi.org/10.1016/S0924-7963(98)00046-3
- Description: An investigation to estimate the seasonal changes in feeding habits in relation to the energy budget of Euphausia crystallorophias was carried out during austral spring and summer 1994/95 in the shelf region of the Lazarev Sea.
- Full Text:
- Date Issued: 1998
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, Evgeny 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, Evgeny 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, Evgeny 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