Growth and longevity of Exosphaeroma hylocoetes (Isopoda) under varying conditions of salinity and temperature
- Henninger, Tony O, Froneman, P William, Booth, Anthony J, Hodgson, Alan N
- Authors: Henninger, Tony O , Froneman, P William , Booth, Anthony J , Hodgson, Alan N
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124571 , vital:35630 , https://doi.org/10.3377/004.045.0118
- Description: Numerous studies have documented the importance of both temperature and salinity in influencing aquatic crustacean metabolic processes such as respiration and growth. For example, increased water temperatures have been shown to increase respiration rates in various species of shrimp (Chen & Nan 1993; Spanonopoulos-Hernándeza et al. 2005; Allan et al. 2006), and copepods (Isla & Perissinotto 2004). The response of invertebrates to changes in salinity is more complex, largely reflecting their evolutionary origins (Kinne 1966). For example, juvenile blue swimming crabs, Portunus pelagicus, displayed significantly faster growth and higher survival in response to increasingsalinity (Romano & Zeng 2006). Additional factors that may influence the growth rates of crustaceans include photoperiod (Gambardella et al. 1997), food availability (Shuster & Guthrie 1999) and sex (Newman et al. 2007).
- Full Text:
- Date Issued: 2010
- Authors: Henninger, Tony O , Froneman, P William , Booth, Anthony J , Hodgson, Alan N
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124571 , vital:35630 , https://doi.org/10.3377/004.045.0118
- Description: Numerous studies have documented the importance of both temperature and salinity in influencing aquatic crustacean metabolic processes such as respiration and growth. For example, increased water temperatures have been shown to increase respiration rates in various species of shrimp (Chen & Nan 1993; Spanonopoulos-Hernándeza et al. 2005; Allan et al. 2006), and copepods (Isla & Perissinotto 2004). The response of invertebrates to changes in salinity is more complex, largely reflecting their evolutionary origins (Kinne 1966). For example, juvenile blue swimming crabs, Portunus pelagicus, displayed significantly faster growth and higher survival in response to increasingsalinity (Romano & Zeng 2006). Additional factors that may influence the growth rates of crustaceans include photoperiod (Gambardella et al. 1997), food availability (Shuster & Guthrie 1999) and sex (Newman et al. 2007).
- Full Text:
- Date Issued: 2010
Growth and longevity of Exosphaeroma hylocoetes (Isopoda) under varying conditions of salinity and temperature
- Henninger, Tony O, Froneman, P William, Booth, Anthony J, Hodgson, Alan N
- Authors: Henninger, Tony O , Froneman, P William , Booth, Anthony J , Hodgson, Alan N
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/446784 , vital:74560 , https://doi.org/10.1080/15627020.2010.11657253
- Description: The effect of temperature (15 and 25°C) and salinity (15 and 35 practical salinity units) combinations on the growth and longevity of the South African estuarine isopod Exosphaeroma hylocoetes was investigated and data analysed using the logistic growth model. No significant differences (P = 0.43 to 0.54) were obtained for the growth rates of male and female E. hylocoetes under the suite of temperature/salinity combinations. Among the variables considered, temperature was identified as the most important in influencing the growth rates of the isopod. Elevated temperatures promoted faster initial growth in both males and females. Salinity had no significant influence on the growth rates of males and females. Males (25.77 ± 3.40 weeks) lived significantly longer (P 0.001) than females (21.52 ± 3.00 weeks), allowing males (8.08 ± 0.25 mm mean body length) to attain a significantly larger size than females (6.59 ± 0.25 mm) under experimental conditions. Females, however, attained sexual maturity (at 2.5 mm body length) 2–4 weeks earlier than males (5.5 mm in length). It is suggested that the faster growth rates at the higher temperature/salinity combinations allow the isopod to reach sexual maturity at an earlier stage than those at the lower combinations.
- Full Text:
- Date Issued: 2010
- Authors: Henninger, Tony O , Froneman, P William , Booth, Anthony J , Hodgson, Alan N
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/446784 , vital:74560 , https://doi.org/10.1080/15627020.2010.11657253
- Description: The effect of temperature (15 and 25°C) and salinity (15 and 35 practical salinity units) combinations on the growth and longevity of the South African estuarine isopod Exosphaeroma hylocoetes was investigated and data analysed using the logistic growth model. No significant differences (P = 0.43 to 0.54) were obtained for the growth rates of male and female E. hylocoetes under the suite of temperature/salinity combinations. Among the variables considered, temperature was identified as the most important in influencing the growth rates of the isopod. Elevated temperatures promoted faster initial growth in both males and females. Salinity had no significant influence on the growth rates of males and females. Males (25.77 ± 3.40 weeks) lived significantly longer (P 0.001) than females (21.52 ± 3.00 weeks), allowing males (8.08 ± 0.25 mm mean body length) to attain a significantly larger size than females (6.59 ± 0.25 mm) under experimental conditions. Females, however, attained sexual maturity (at 2.5 mm body length) 2–4 weeks earlier than males (5.5 mm in length). It is suggested that the faster growth rates at the higher temperature/salinity combinations allow the isopod to reach sexual maturity at an earlier stage than those at the lower combinations.
- Full Text:
- Date Issued: 2010
Plankton trophodynamics at the subtropical convergence, Southern Ocean
- Richoux, Nicole B, Froneman, P William
- Authors: Richoux, Nicole B , Froneman, P William
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457967 , vital:75704 , xlink:href="https://doi.org/10.1093/plankt/fbp054"
- Description: Stable isotope signatures (δ13C, δ15N) in zooplankton tissues and particulate organic matter (POM) were determined to assess regional differences in the trophodynamics of zooplankton communities between 38 and 43°S, where the cool nutrient-rich subantarctic waters of the Southern Ocean meet the warm nutrient-poor subtropical waters of the southwest Indian Ocean at the subtropical convergence (STC). Significantly enriched values of δ15N were noted in populations of all major zooplankton groups inhabiting the warm and saline water mass north of the STC (maximum surface temperature 21°C), including the euphausiids, salps, amphipods, copepods, ostracods, pyrosomes, pteropods and chaetognaths, compared with those in the cool, less saline southern water mass (minimum surface temperature 11°C). Similar patterns of δ15N in POM collected throughout the region suggest that the large changes in zooplankton δ15N values across the frontal region are driven by variations in the phytoplankton communities. The differing trophodynamics in communities north and south of the STC provide compelling evidence of distinct bottom-up effects on planktonic food webs which have important implications in the determination of trophic positions and motility of plankton and higher consumers using δ15N signatures. Although expected, similar latitudinal variations in δ13C signatures were not found.
- Full Text:
- Date Issued: 2009
- Authors: Richoux, Nicole B , Froneman, P William
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457967 , vital:75704 , xlink:href="https://doi.org/10.1093/plankt/fbp054"
- Description: Stable isotope signatures (δ13C, δ15N) in zooplankton tissues and particulate organic matter (POM) were determined to assess regional differences in the trophodynamics of zooplankton communities between 38 and 43°S, where the cool nutrient-rich subantarctic waters of the Southern Ocean meet the warm nutrient-poor subtropical waters of the southwest Indian Ocean at the subtropical convergence (STC). Significantly enriched values of δ15N were noted in populations of all major zooplankton groups inhabiting the warm and saline water mass north of the STC (maximum surface temperature 21°C), including the euphausiids, salps, amphipods, copepods, ostracods, pyrosomes, pteropods and chaetognaths, compared with those in the cool, less saline southern water mass (minimum surface temperature 11°C). Similar patterns of δ15N in POM collected throughout the region suggest that the large changes in zooplankton δ15N values across the frontal region are driven by variations in the phytoplankton communities. The differing trophodynamics in communities north and south of the STC provide compelling evidence of distinct bottom-up effects on planktonic food webs which have important implications in the determination of trophic positions and motility of plankton and higher consumers using δ15N signatures. Although expected, similar latitudinal variations in δ13C signatures were not found.
- Full Text:
- Date Issued: 2009
The role of macrophytes as a refuge and food source for the estuarine isopod Exosphaeroma hylocoetes ()
- Henninger, Tony O, Froneman, P William, Richoux, Nicole B, Hodgson, Alan N
- Authors: Henninger, Tony O , Froneman, P William , Richoux, Nicole B , Hodgson, Alan N
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/458360 , vital:75735 , xlink:href="https://doi.org/10.1016/j.ecss.2009.01.01"
- Description: The role of submerged macrophytes as refugia from fish predation and as possible food sources for the estuarine isopod Exosphaeroma hylocoetes (Barnard, K.H., 1940) was investigated. Laboratory experiments tested the effectiveness of artificial vegetation, replicating submerged vegetation, in enabling isopods to elude selected fish predators Rhabdosargus holubi, Glossogobius callidus, Monodactylus falciformis and Clinus cottoides. Isopods preferentially hid in the vegetation (>90%), even in absence of fish. The predatory fish had varying success in finding isopods within the vegetation. Isopod mortality ranged from 2% (R. holubi) to a maximum of 87% (C. cottoides) within vegetation, depending on the fish predator present. Stable isotope and fatty acid analyses ruled out the submerged macrophyte Ruppia maritima and inundated fringing grasses as direct food sources, but highlighted the epiphytic biota (mainly diatoms) found on the submerged vegetation and sediments as more likely food sources. These findings are consistent with gut content analyses. The results suggest that the close association of E. hylocoetes with R. maritima is the result of the vegetation providing the isopod with a refuge against fish predation as well as areas of increased food availability.
- Full Text:
- Date Issued: 2009
- Authors: Henninger, Tony O , Froneman, P William , Richoux, Nicole B , Hodgson, Alan N
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/458360 , vital:75735 , xlink:href="https://doi.org/10.1016/j.ecss.2009.01.01"
- Description: The role of submerged macrophytes as refugia from fish predation and as possible food sources for the estuarine isopod Exosphaeroma hylocoetes (Barnard, K.H., 1940) was investigated. Laboratory experiments tested the effectiveness of artificial vegetation, replicating submerged vegetation, in enabling isopods to elude selected fish predators Rhabdosargus holubi, Glossogobius callidus, Monodactylus falciformis and Clinus cottoides. Isopods preferentially hid in the vegetation (>90%), even in absence of fish. The predatory fish had varying success in finding isopods within the vegetation. Isopod mortality ranged from 2% (R. holubi) to a maximum of 87% (C. cottoides) within vegetation, depending on the fish predator present. Stable isotope and fatty acid analyses ruled out the submerged macrophyte Ruppia maritima and inundated fringing grasses as direct food sources, but highlighted the epiphytic biota (mainly diatoms) found on the submerged vegetation and sediments as more likely food sources. These findings are consistent with gut content analyses. The results suggest that the close association of E. hylocoetes with R. maritima is the result of the vegetation providing the isopod with a refuge against fish predation as well as areas of increased food availability.
- Full Text:
- Date Issued: 2009
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 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
Assessment of spatial variation in carbon utilization by benthic and pelagic invertebrates in a temperate South African estuary using stable isotope signatures
- Richoux, Nicole B, Froneman, P William
- Authors: Richoux, Nicole B , Froneman, P William
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457923 , vital:75695 , xlink:href="https://doi.org/10.1016/j.ecss.2006.09.007 "
- Description: Stable isotope analyses (δ13C and δ15N) were used to evaluate the spatial variations in carbon flow from primary producers to consumers at two sites in the temperate and permanently open Kariega Estuary on the southeastern coast of South Africa during October 2005 and February 2006. One site was located opposite a salt marsh while the second was upstream of the marsh. Except for significantly enriched δ13C values of Zostera capensis and surface sediments near the salt marsh, the δ13C and δ15N signatures of the producers were similar between sites. The invertebrates were clustered into groups roughly corresponding to the predominant feeding modes. The suspension feeders showed δ13C values closest to the seston, whereas the deposit feeders, detritivores and scavengers/predators had more enriched δ13C values reflecting primary carbon sources that were likely a combination of seston, Spartina maritima and Z. capensis at the upstream site, with an increased influence of benthic algae and Z. capensis at the salt marsh site. The δ15N signatures of the consumers showed a stepwise continuum rather than distinct levels of fractionation, indicating highly complex trophic linkages and significant dietary overlap among the species. Consumers exhibited significantly enriched δ13C values at the salt marsh site, an effect that was attributed to enriched Z. capensis detritus in this region in addition to increased phytoplankton biomass in their diets compared with invertebrates living upstream. The data reinforce the concept that between-site variations in the stable isotope ratios of consumers can result not only from dietary shifts, but also from alterations in the isotope ratios of primary producers.
- Full Text:
- Date Issued: 2007
- Authors: Richoux, Nicole B , Froneman, P William
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457923 , vital:75695 , xlink:href="https://doi.org/10.1016/j.ecss.2006.09.007 "
- Description: Stable isotope analyses (δ13C and δ15N) were used to evaluate the spatial variations in carbon flow from primary producers to consumers at two sites in the temperate and permanently open Kariega Estuary on the southeastern coast of South Africa during October 2005 and February 2006. One site was located opposite a salt marsh while the second was upstream of the marsh. Except for significantly enriched δ13C values of Zostera capensis and surface sediments near the salt marsh, the δ13C and δ15N signatures of the producers were similar between sites. The invertebrates were clustered into groups roughly corresponding to the predominant feeding modes. The suspension feeders showed δ13C values closest to the seston, whereas the deposit feeders, detritivores and scavengers/predators had more enriched δ13C values reflecting primary carbon sources that were likely a combination of seston, Spartina maritima and Z. capensis at the upstream site, with an increased influence of benthic algae and Z. capensis at the salt marsh site. The δ15N signatures of the consumers showed a stepwise continuum rather than distinct levels of fractionation, indicating highly complex trophic linkages and significant dietary overlap among the species. Consumers exhibited significantly enriched δ13C values at the salt marsh site, an effect that was attributed to enriched Z. capensis detritus in this region in addition to increased phytoplankton biomass in their diets compared with invertebrates living upstream. The data reinforce the concept that between-site variations in the stable isotope ratios of consumers can result not only from dietary shifts, but also from alterations in the isotope ratios of primary producers.
- Full Text:
- Date Issued: 2007
Conserving pattern and process in the Southern Ocean: designing a Marine Protected Area for the Prince Edward Islands
- Lombard, A T, Reyers, B, Schonegevel, L Y, Cooper, J, Smith-Adao, L B, Nel, D C, Froneman, P William, Ansorge, Isabelle J, Bester, M N, Tosh, C A, Strauss, T, Akkers, T, Gon, Ofer, Leslie, Rob W, Chown, S L
- Authors: Lombard, A T , Reyers, B , Schonegevel, L Y , Cooper, J , Smith-Adao, L B , Nel, D C , Froneman, P William , Ansorge, Isabelle J , Bester, M N , Tosh, C A , Strauss, T , Akkers, T , Gon, Ofer , Leslie, Rob W , Chown, S L
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6881 , http://hdl.handle.net/10962/d1011637
- Description: South Africa is currently proclaiming a Marine Protected Area (MPA) in the Exclusive Economic Zone (EEZ) of its sub-Antarctic Prince Edward Islands. The objectives of the MPA are to: 1) contribute to a national and global representative system of MPAs, 2) serve as a scientific reference point to inform future management, 3) contribute to the recovery of the Patagonian toothfish (Dissostichus eleginoides), and 4) reduce the bird bycatch of the toothfish fishery, particularly of albatrosses and petrels. This study employs systematic conservation planning methods to delineate a MPA within the EEZ that will conserve biodiversity patterns and processes within sensible management boundaries, while minimizing conflict with the legal toothfish fishery. After collating all available distributional data on species, benthic habitats and ecosystem processes, we used C-Plan software to delineate a MPA with three management zones: four IUCN Category Ia reserves (13% of EEZ); two Conservation Zones (21% of EEZ); and three Category IV reserves (remainder of EEZ). Compromises between conservation target achievement and the area required by the MPA are apparent in the final reserve design. The proposed MPA boundaries are expected to change over time as new data become available and as impacts of climate change become more evident.
- Full Text:
- Date Issued: 2007
- Authors: Lombard, A T , Reyers, B , Schonegevel, L Y , Cooper, J , Smith-Adao, L B , Nel, D C , Froneman, P William , Ansorge, Isabelle J , Bester, M N , Tosh, C A , Strauss, T , Akkers, T , Gon, Ofer , Leslie, Rob W , Chown, S L
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6881 , http://hdl.handle.net/10962/d1011637
- Description: South Africa is currently proclaiming a Marine Protected Area (MPA) in the Exclusive Economic Zone (EEZ) of its sub-Antarctic Prince Edward Islands. The objectives of the MPA are to: 1) contribute to a national and global representative system of MPAs, 2) serve as a scientific reference point to inform future management, 3) contribute to the recovery of the Patagonian toothfish (Dissostichus eleginoides), and 4) reduce the bird bycatch of the toothfish fishery, particularly of albatrosses and petrels. This study employs systematic conservation planning methods to delineate a MPA within the EEZ that will conserve biodiversity patterns and processes within sensible management boundaries, while minimizing conflict with the legal toothfish fishery. After collating all available distributional data on species, benthic habitats and ecosystem processes, we used C-Plan software to delineate a MPA with three management zones: four IUCN Category Ia reserves (13% of EEZ); two Conservation Zones (21% of EEZ); and three Category IV reserves (remainder of EEZ). Compromises between conservation target achievement and the area required by the MPA are apparent in the final reserve design. The proposed MPA boundaries are expected to change over time as new data become available and as impacts of climate change become more evident.
- Full Text:
- Date Issued: 2007
Exploring trophodynamics in the Southern Ocean: applications of fatty acid biomarkers and stable isotope ratios
- Richoux, Nicole B, Froneman, P William
- Authors: Richoux, Nicole B , Froneman, P William
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457956 , vital:75703 , xlink:href="http://hdl.handle.net/123456789/28541"
- Description: The dynamics of transfer of organic carbon among producers and consumers has interested trophic ecologists for several decades1. This field of research has proven to be particularly challenging for those investigating aquatic environments, as organisms of interest are often very small, remote and/or behaviourally complex. Furthermore, many species of plankton demonstrate a high degree of feeding plasticity, as the nature and availability of food can vary considerably both spatially and temporally. The diets of consumers are classically studied using gut contents and/or gut fluorescence analyses, approaches that are limited to freshly ingested prey, and in the latter case to herbivorous feeding2. Two methods that provide a time-integrated view of an organism's assimilated feeding history and incorporate both herbivorous and carnivorous pathways involve the determination of stable isotope ratios and fatty acid profiles3 4. Stable isotope ratios in animal tissues can be used as tracers to original sources of carbon at the base of a food chain as well as indicators of the trophic level of a population5, and fatty acids can provide information on the type and quality of resources assimilated by aquatic animals over ecologically meaningful time periods6,7. The aims of our current study are to determine trophodynamics among the numerically dominant zooplankton species and to assess regional differences in ecosystem fitness within the Subtropical Convergence zone (STC) using both stable isotope ratios and fatty acid profiles. As the STC can act as an effective biogeographical barrier8 food webs and the dynamics of energy transfer from primary producers to consumers on either side of this barrier are expected to differ. As global climate change has the potential to cause major shifts in the location, strength and physical and biological properties of the STC9 it is important to understand the potential effects on the biological communities inhabiting the region. Any changes in the food quality or availability for the dominant species or in the trophic relationships among producers and consumers may have serious implications for top consumers such as fish, birds and mammals. Successful characterization of food webs in the STC will provide an excellent framework for future studies in Southern Ocean trophic ecology.
- Full Text:
- Date Issued: 2007
- Authors: Richoux, Nicole B , Froneman, P William
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457956 , vital:75703 , xlink:href="http://hdl.handle.net/123456789/28541"
- Description: The dynamics of transfer of organic carbon among producers and consumers has interested trophic ecologists for several decades1. This field of research has proven to be particularly challenging for those investigating aquatic environments, as organisms of interest are often very small, remote and/or behaviourally complex. Furthermore, many species of plankton demonstrate a high degree of feeding plasticity, as the nature and availability of food can vary considerably both spatially and temporally. The diets of consumers are classically studied using gut contents and/or gut fluorescence analyses, approaches that are limited to freshly ingested prey, and in the latter case to herbivorous feeding2. Two methods that provide a time-integrated view of an organism's assimilated feeding history and incorporate both herbivorous and carnivorous pathways involve the determination of stable isotope ratios and fatty acid profiles3 4. Stable isotope ratios in animal tissues can be used as tracers to original sources of carbon at the base of a food chain as well as indicators of the trophic level of a population5, and fatty acids can provide information on the type and quality of resources assimilated by aquatic animals over ecologically meaningful time periods6,7. The aims of our current study are to determine trophodynamics among the numerically dominant zooplankton species and to assess regional differences in ecosystem fitness within the Subtropical Convergence zone (STC) using both stable isotope ratios and fatty acid profiles. As the STC can act as an effective biogeographical barrier8 food webs and the dynamics of energy transfer from primary producers to consumers on either side of this barrier are expected to differ. As global climate change has the potential to cause major shifts in the location, strength and physical and biological properties of the STC9 it is important to understand the potential effects on the biological communities inhabiting the region. Any changes in the food quality or availability for the dominant species or in the trophic relationships among producers and consumers may have serious implications for top consumers such as fish, birds and mammals. Successful characterization of food webs in the STC will provide an excellent framework for future studies in Southern Ocean trophic ecology.
- Full Text:
- Date Issued: 2007
Phylogeographic structure of the caridean shrimp Palaemon peringueyi in South Africa: further evidence for intraspecific genetic units associated with marine biogeographic provinces
- Teske, Peter R, Froneman, P William, Barker, Nigel P, McQuaid, Christopher D
- Authors: Teske, Peter R , Froneman, P William , Barker, Nigel P , McQuaid, Christopher D
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/445486 , vital:74392 , https://doi.org/10.2989/AJMS.2007.29.2.9.192
- Description: Recent genetic studies have shown that most widely distributed, passively dispersing invertebrates in southern Africa have regional intraspecific units that are associated with the three main marine biogeographic provinces (cool-temperate, warm-temperate and subtropical). The caridean shrimp Palaemon peringueyi also occurs in all three provinces, but the fact that it can disperse both actively and passively (i.e. larval drifting, adult walking/swimming and potential adult rafting by means of floating objects) suggests that the amount of gene flow between regions may be too high for evolutionary divergence to have taken place. Samples of P. peringueyi were collected throughout South Africa and an intraspecific phylogeny was reconstructed using mitochondrial COI and 16S rRNA sequences. Three major clades were recovered, which were broadly associated with the three biogeographic regions. This suggests that, even though P. peringueyi can disperse actively, the fact that neither larvae nor adults are strong swimmers has resulted in genetic subdivisons comparable to those of passively dispersing coastal invertebrates in southern Africa.
- Full Text:
- Date Issued: 2007
- Authors: Teske, Peter R , Froneman, P William , Barker, Nigel P , McQuaid, Christopher D
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/445486 , vital:74392 , https://doi.org/10.2989/AJMS.2007.29.2.9.192
- Description: Recent genetic studies have shown that most widely distributed, passively dispersing invertebrates in southern Africa have regional intraspecific units that are associated with the three main marine biogeographic provinces (cool-temperate, warm-temperate and subtropical). The caridean shrimp Palaemon peringueyi also occurs in all three provinces, but the fact that it can disperse both actively and passively (i.e. larval drifting, adult walking/swimming and potential adult rafting by means of floating objects) suggests that the amount of gene flow between regions may be too high for evolutionary divergence to have taken place. Samples of P. peringueyi were collected throughout South Africa and an intraspecific phylogeny was reconstructed using mitochondrial COI and 16S rRNA sequences. Three major clades were recovered, which were broadly associated with the three biogeographic regions. This suggests that, even though P. peringueyi can disperse actively, the fact that neither larvae nor adults are strong swimmers has resulted in genetic subdivisons comparable to those of passively dispersing coastal invertebrates in southern Africa.
- Full Text:
- Date Issued: 2007
Physical and biological processes at the Subtropical Convergence in the South-west Indian Ocean
- Froneman, P William, Ansorge, Isabelle J, Richoux, Nicole B, Blake, Justin, Daly, Ryan, Sterley, Jessica A, Mostert, Bruce P, Heyns, Elodie R, Sheppard, Jill N, Kuyper, B, Hart, N, George, C, Howard, J, Mustafa, E, Pey, F, Lutjeharms, Johan R E
- Authors: Froneman, P William , Ansorge, Isabelle J , Richoux, Nicole B , Blake, Justin , Daly, Ryan , Sterley, Jessica A , Mostert, Bruce P , Heyns, Elodie R , Sheppard, Jill N , Kuyper, B , Hart, N , George, C , Howard, J , Mustafa, E , Pey, F , Lutjeharms, Johan R E
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6966 , http://hdl.handle.net/10962/d1012030
- Description: A detailed hydrographic and biological survey was conducted in the region of the Subtropical Convergence in the Indian sector of the Southern Ocean in April 2007. Hydrographic data revealed that the subsurface expression of the Subtropical Convergence (at 200 m), marked by the 10°C isotherm, appeared to meander considerably between 41°S and 42°15’S. Total surface chlorophyll- a concentration was low and ranged from 0.03 to 0.42 µg l–1 and was always dominated by the pico- (<2 µm) and nano- (2–120 µm) size classes, which contributed between 81% and 93% of the total pigment. The total chlorophyll-a integrated over the top 150m of the water column showed no distinct spatial trends, and ranged from 12.8 to 40.1mg chl-a m–2. There were no significant correlations between the total integrated chlorophyll- a concentration and temperature and salinity (P > 0.05). The zooplankton community was dominated, numerically and by biomass, by mesozooplankton comprising mainly copepods of the genera, Oithona,Paraeuchaeta, Pleuromamma, Calanus and Clausocalanus. An exception was recorded at those stations in the region of the front where the tunicate, Salpa thompsoni, dominated the total zooplankton biomass.
- Full Text:
- Date Issued: 2007
- Authors: Froneman, P William , Ansorge, Isabelle J , Richoux, Nicole B , Blake, Justin , Daly, Ryan , Sterley, Jessica A , Mostert, Bruce P , Heyns, Elodie R , Sheppard, Jill N , Kuyper, B , Hart, N , George, C , Howard, J , Mustafa, E , Pey, F , Lutjeharms, Johan R E
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6966 , http://hdl.handle.net/10962/d1012030
- Description: A detailed hydrographic and biological survey was conducted in the region of the Subtropical Convergence in the Indian sector of the Southern Ocean in April 2007. Hydrographic data revealed that the subsurface expression of the Subtropical Convergence (at 200 m), marked by the 10°C isotherm, appeared to meander considerably between 41°S and 42°15’S. Total surface chlorophyll- a concentration was low and ranged from 0.03 to 0.42 µg l–1 and was always dominated by the pico- (<2 µm) and nano- (2–120 µm) size classes, which contributed between 81% and 93% of the total pigment. The total chlorophyll-a integrated over the top 150m of the water column showed no distinct spatial trends, and ranged from 12.8 to 40.1mg chl-a m–2. There were no significant correlations between the total integrated chlorophyll- a concentration and temperature and salinity (P > 0.05). The zooplankton community was dominated, numerically and by biomass, by mesozooplankton comprising mainly copepods of the genera, Oithona,Paraeuchaeta, Pleuromamma, Calanus and Clausocalanus. An exception was recorded at those stations in the region of the front where the tunicate, Salpa thompsoni, dominated the total zooplankton biomass.
- Full Text:
- Date Issued: 2007
Preliminary survey of indigenous, non-indigenous and cryptogenic benthic invertebrates in Burrard Inlet, Vancover, British Columbia
- Richoux, Nicole B, Froneman, P William
- Authors: Richoux, Nicole B , Froneman, P William
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457981 , vital:75705 , xlink:href="https://doi.org/10.1016/j.ecss.2006.09.007"
- Description: In a preliminary investigation into the presence of non-indigenous invertebrates in Burrard Inlet, Vancouver, British Columbia, qualitative sampling on rocky shores, pilings and floating docks was conducted in July and August 2004. Twenty-nine sites were established, 34 samples were analysed, and 103 different taxa were identified. Data were also obtained on habitat characteristics including substrate type, salinity and temperature. Identification of polychaetes, mussels from four sites, all amphipods, isopods and patellogastropods have been confirmed by taxonomic specialists.
- Full Text:
- Date Issued: 2007
- Authors: Richoux, Nicole B , Froneman, P William
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457981 , vital:75705 , xlink:href="https://doi.org/10.1016/j.ecss.2006.09.007"
- Description: In a preliminary investigation into the presence of non-indigenous invertebrates in Burrard Inlet, Vancouver, British Columbia, qualitative sampling on rocky shores, pilings and floating docks was conducted in July and August 2004. Twenty-nine sites were established, 34 samples were analysed, and 103 different taxa were identified. Data were also obtained on habitat characteristics including substrate type, salinity and temperature. Identification of polychaetes, mussels from four sites, all amphipods, isopods and patellogastropods have been confirmed by taxonomic specialists.
- Full Text:
- Date Issued: 2007
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
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
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, 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 , 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 , 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