Characterisation of the dietary relationships of two sympatric hake species, Merluccius capensis and M. paradoxus, in the northern Benguela region using fatty acid profiles
- Iitembu, Johannes A, Richoux, Nicole B
- Authors: Iitembu, Johannes A , Richoux, Nicole B
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456010 , vital:75475 , xlink:href="https://doi.org/10.2989/1814232X.2015.1115778"
- Description: The two sympatric species of Cape hake, Merluccius capensis and M. paradoxus, have been the main targets of bottom-trawl fisheries off Namibia for several decades. The feeding ecology of these hakes has been studied mainly using stomach content analyses and thus there remain some gaps in our knowledge about food assimilated over the longer term. In this study, we used fatty acid (FA) profiles to characterise the dietary relationships of M. capensis and M. paradoxus. Muscle samples from hake (n=110) and their known prey (n=68) were collected during trawl surveys off Namibia during 2011. Significant differences between the neutral FA profiles of the hake populations were detected in December 2011 but not in January 2011, an indication of temporal variations in diet and resource partitioning. Comparisons of the neutral FAs in hake and the total FAs of potential prey showed no clear trophic connections, with the exception of flying squid Todarodes sagittatus, which had FA profiles very similar to those of M. paradoxus in December 2011. Our results highlight the complex and temporally shifting relationships that exist between hake and the large pool of prey available to them, and between the two hake species that overlap in their feeding habits and distribution within the highly productive Benguela Current region.
- Full Text:
- Date Issued: 2016
- Authors: Iitembu, Johannes A , Richoux, Nicole B
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456010 , vital:75475 , xlink:href="https://doi.org/10.2989/1814232X.2015.1115778"
- Description: The two sympatric species of Cape hake, Merluccius capensis and M. paradoxus, have been the main targets of bottom-trawl fisheries off Namibia for several decades. The feeding ecology of these hakes has been studied mainly using stomach content analyses and thus there remain some gaps in our knowledge about food assimilated over the longer term. In this study, we used fatty acid (FA) profiles to characterise the dietary relationships of M. capensis and M. paradoxus. Muscle samples from hake (n=110) and their known prey (n=68) were collected during trawl surveys off Namibia during 2011. Significant differences between the neutral FA profiles of the hake populations were detected in December 2011 but not in January 2011, an indication of temporal variations in diet and resource partitioning. Comparisons of the neutral FAs in hake and the total FAs of potential prey showed no clear trophic connections, with the exception of flying squid Todarodes sagittatus, which had FA profiles very similar to those of M. paradoxus in December 2011. Our results highlight the complex and temporally shifting relationships that exist between hake and the large pool of prey available to them, and between the two hake species that overlap in their feeding habits and distribution within the highly productive Benguela Current region.
- Full Text:
- Date Issued: 2016
Depth and habitat determine assemblage structure of South Africa’s warm-temperate reef fish
- Heyns-Veale, Elodie R, Bernard, Anthony T F, Richoux, Nicole B, Parker, Daniel M, Langlois, T J, Harvey, E S, Götz, Albrecht
- Authors: Heyns-Veale, Elodie R , Bernard, Anthony T F , Richoux, Nicole B , Parker, Daniel M , Langlois, T J , Harvey, E S , Götz, Albrecht
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456035 , vital:75477 , xlink:href="https://doi.org/10.1007/s00227-016-2933-8"
- Description: Depth and habitat are important predictors of fish assemblage structure, yet current no-take marine protected area (MPA) networks are generally limited to providing refuge for fish species that inhabit shallow waters and may exclude deep habitats essential to exploited populations. To ensure MPA efficacy at the design, uptake and management levels, baseline data on fish populations associated with deep nearshore reefs are needed. This study employed baited remote underwater stereo-video systems to investigate fish habitat associations at shallow (11–25 m) and deep (45–75 m) reef sites in the Tsitsikamma National Park MPA, South Africa. The compositions of fish assemblages at shallow and deep reef sites were significantly different. Specifically, rare species, juveniles and low trophic level species dominated the shallow reef, while deep reef assemblages were characterised by large, sexually mature and predatory fish. The body size of abundant species was also correlated with depth, with larger individuals being more abundant on deeper reefs. Habitat types were identified according to a habitat classification system established in a previous study, which resulted in four broad depth separated habitat types (defined by macrobenthos and environmental variables). Canonical analysis of principle coordinates (CAP) indicated that habitat type was a good categorical predictor of the observed fish assemblages. The CAP analysis determined that 86 % of the samples were correctly assigned to the habitat type from which they were collected, indicating that specific fish assemblages were associated with distinct habitat types. This study highlights the importance of protecting both shallow and deep reefs, not only to ensure the conservation of particular fish assemblages, but also to provide protection for all stages of the life cycle of fish species.
- Full Text:
- Date Issued: 2016
- Authors: Heyns-Veale, Elodie R , Bernard, Anthony T F , Richoux, Nicole B , Parker, Daniel M , Langlois, T J , Harvey, E S , Götz, Albrecht
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456035 , vital:75477 , xlink:href="https://doi.org/10.1007/s00227-016-2933-8"
- Description: Depth and habitat are important predictors of fish assemblage structure, yet current no-take marine protected area (MPA) networks are generally limited to providing refuge for fish species that inhabit shallow waters and may exclude deep habitats essential to exploited populations. To ensure MPA efficacy at the design, uptake and management levels, baseline data on fish populations associated with deep nearshore reefs are needed. This study employed baited remote underwater stereo-video systems to investigate fish habitat associations at shallow (11–25 m) and deep (45–75 m) reef sites in the Tsitsikamma National Park MPA, South Africa. The compositions of fish assemblages at shallow and deep reef sites were significantly different. Specifically, rare species, juveniles and low trophic level species dominated the shallow reef, while deep reef assemblages were characterised by large, sexually mature and predatory fish. The body size of abundant species was also correlated with depth, with larger individuals being more abundant on deeper reefs. Habitat types were identified according to a habitat classification system established in a previous study, which resulted in four broad depth separated habitat types (defined by macrobenthos and environmental variables). Canonical analysis of principle coordinates (CAP) indicated that habitat type was a good categorical predictor of the observed fish assemblages. The CAP analysis determined that 86 % of the samples were correctly assigned to the habitat type from which they were collected, indicating that specific fish assemblages were associated with distinct habitat types. This study highlights the importance of protecting both shallow and deep reefs, not only to ensure the conservation of particular fish assemblages, but also to provide protection for all stages of the life cycle of fish species.
- Full Text:
- Date Issued: 2016
Trophic dynamics of the cape stumpnose (Rhabdosargus holubi, Sparidae) across three adjacent aquatic habitats
- Carassou, Laure, Whitfield, Alan K, Bergamino, Leandro, Moyo, Sydney, Richoux, Nicole B
- Authors: Carassou, Laure , Whitfield, Alan K , Bergamino, Leandro , Moyo, Sydney , Richoux, Nicole B
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456362 , vital:75506 , xlink:href="https://doi.org/10.1007/s12237-016-0075-3"
- Description: Migratory fish species are major vectors of connectivity among aquatic habitats. In this study, conventional stomach contents and stable isotope methods (δ13C and δ15N) were combined to understand how fish of different sizes feed across contrasting aquatic habitats. The Cape stumpnose Rhabdosargus holubi (Sparidae, Perciformes) was selected as an abundant estuarine-dependent species in the permanently open Kowie system, South Africa. Three different habitats were sampled in the region, namely, river, estuary, and sea. Fish entered the estuary as post-larvae from the marine environment, resided in the estuary and lower part of the river as juveniles, and then returned to the sea as sub-adults. The diet varied among habitats, seasons, and fish sizes. “Stable Isotope Analysis with R” (SIAR) Bayesian mixing models mostly supported the results from the stomach content analyses, but also revealed the importance of some prey (e.g., insects) that were underestimated in the consumed diet. Rhabdosargus holubi δ13C values indicated a clear spatial gradient in the origin of food sources assimilated across the habitats, with increasing δ13C along the freshwater-marine continuum. The δ13C ranges of sources and fish also overlapped within each habitat along this continuum, thus illustrating the fidelity of R. holubi to specific habitats at different life stages. By consuming prey in a particular habitat before migrating, either permanently or temporarily to another habitat, R. holubi participates in allochthonous fluxes among riverine, estuarine, and coastal marine environments, with approximately 7 tonnes of Cape stumpnose productivity being exported from the 142-ha Kowie Estuary to the sea each year.
- Full Text:
- Date Issued: 2016
- Authors: Carassou, Laure , Whitfield, Alan K , Bergamino, Leandro , Moyo, Sydney , Richoux, Nicole B
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456362 , vital:75506 , xlink:href="https://doi.org/10.1007/s12237-016-0075-3"
- Description: Migratory fish species are major vectors of connectivity among aquatic habitats. In this study, conventional stomach contents and stable isotope methods (δ13C and δ15N) were combined to understand how fish of different sizes feed across contrasting aquatic habitats. The Cape stumpnose Rhabdosargus holubi (Sparidae, Perciformes) was selected as an abundant estuarine-dependent species in the permanently open Kowie system, South Africa. Three different habitats were sampled in the region, namely, river, estuary, and sea. Fish entered the estuary as post-larvae from the marine environment, resided in the estuary and lower part of the river as juveniles, and then returned to the sea as sub-adults. The diet varied among habitats, seasons, and fish sizes. “Stable Isotope Analysis with R” (SIAR) Bayesian mixing models mostly supported the results from the stomach content analyses, but also revealed the importance of some prey (e.g., insects) that were underestimated in the consumed diet. Rhabdosargus holubi δ13C values indicated a clear spatial gradient in the origin of food sources assimilated across the habitats, with increasing δ13C along the freshwater-marine continuum. The δ13C ranges of sources and fish also overlapped within each habitat along this continuum, thus illustrating the fidelity of R. holubi to specific habitats at different life stages. By consuming prey in a particular habitat before migrating, either permanently or temporarily to another habitat, R. holubi participates in allochthonous fluxes among riverine, estuarine, and coastal marine environments, with approximately 7 tonnes of Cape stumpnose productivity being exported from the 142-ha Kowie Estuary to the sea each year.
- Full Text:
- Date Issued: 2016
Effects of temperature and food quality on isotopic turnover and discrimination in a cladoceran
- Masclaux, Hélène, Richoux, Nicole B
- Authors: Masclaux, Hélène , Richoux, Nicole B
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456216 , vital:75494 , xlink:href="https://doi.org/10.1007/s10452-016-9592-1"
- Description: Our experimental study was designed to assess the effects of temperature on nitrogen isotope turnover and to measure the effects of temperature and food quality on the stable carbon and nitrogen isotope discrimination factors (Δ13C and Δ15N) in a cladoceran. For the first part of our study, Daphnia were fed with non-enriched or 15N-enriched Scenedesmus obliquus at 12, 15, 20, and 25 °C. For the second part, Daphnia were reared at 15, 20, and 25 °C on Scenedesmus or Cryptomonas sp. There were no clear effects of temperature on turnover rates of the nitrogen isotope of cladocerans. However, a general increase in Δ13C with increasing temperature was measured, regardless of the food source. Δ15N was also affected by temperature, but contrasting results were measured depending on the food source used. There were significant effects of food quality on Δ13C and Δ15N in Daphnia, as values obtained for Daphnia fed Scenedesmus were always higher than those obtained for Daphnia fed Cryptomonas. Our experiments produced discrimination factors that were very different from those usually considered in isotope studies and showed that the values used for isotope model implementation to analyze field data need to be adapted to environmental conditions.
- Full Text:
- Date Issued: 2017
- Authors: Masclaux, Hélène , Richoux, Nicole B
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456216 , vital:75494 , xlink:href="https://doi.org/10.1007/s10452-016-9592-1"
- Description: Our experimental study was designed to assess the effects of temperature on nitrogen isotope turnover and to measure the effects of temperature and food quality on the stable carbon and nitrogen isotope discrimination factors (Δ13C and Δ15N) in a cladoceran. For the first part of our study, Daphnia were fed with non-enriched or 15N-enriched Scenedesmus obliquus at 12, 15, 20, and 25 °C. For the second part, Daphnia were reared at 15, 20, and 25 °C on Scenedesmus or Cryptomonas sp. There were no clear effects of temperature on turnover rates of the nitrogen isotope of cladocerans. However, a general increase in Δ13C with increasing temperature was measured, regardless of the food source. Δ15N was also affected by temperature, but contrasting results were measured depending on the food source used. There were significant effects of food quality on Δ13C and Δ15N in Daphnia, as values obtained for Daphnia fed Scenedesmus were always higher than those obtained for Daphnia fed Cryptomonas. Our experiments produced discrimination factors that were very different from those usually considered in isotope studies and showed that the values used for isotope model implementation to analyze field data need to be adapted to environmental conditions.
- Full Text:
- Date Issued: 2017
Macroinvertebrate functional organisation along the longitudinal gradient of an austral temperate river
- Moyo, Sydney, Richoux, Nicole B
- Authors: Moyo, Sydney , Richoux, Nicole B
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456280 , vital:75499 , xlink:href=" https://doi.org/10.1080/15627020.2017.1354721"
- Description: The Kowie River, a relatively pristine system in South Africa, was sampled on four occasions over one year to determine if relative abundances of functional feeding groups (FFGs) of invertebrates changed along the longitudinal gradient, and if these changes matched predictions of the river continuum concept (RCC). The results revealed that gatherers and filterers dominated in the Kowie River, and together represented 50–83% of the invertebrate assemblages. There was a general paucity of shredders (relative abundance was less than 10% at all sites and times). The changes in relative abundances of the different FFGs did not always follow the predictions of the RCC, as there were no correlations of community structure with river width or canopy cover in some seasons; however, some predictions of the RCC were supported, as a dominance of filterers (with relatively small contributions from shredders and grazers) and a consistent presence of predators were recorded. The FFG abundances were correlated with water velocity and total dissolved solids. Broadly, shifts in relative abundances of FFGs along the river continuum could not be explained by physical attributes alone, and were probably influenced by the availability of food and the chemistry of the river. Our findings highlight the need for theoretical and field studies across a broad array of African systems to refine the applicability of the RCC and FFG classifications to further develop models of ecosystem function.
- Full Text:
- Date Issued: 2017
- Authors: Moyo, Sydney , Richoux, Nicole B
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456280 , vital:75499 , xlink:href=" https://doi.org/10.1080/15627020.2017.1354721"
- Description: The Kowie River, a relatively pristine system in South Africa, was sampled on four occasions over one year to determine if relative abundances of functional feeding groups (FFGs) of invertebrates changed along the longitudinal gradient, and if these changes matched predictions of the river continuum concept (RCC). The results revealed that gatherers and filterers dominated in the Kowie River, and together represented 50–83% of the invertebrate assemblages. There was a general paucity of shredders (relative abundance was less than 10% at all sites and times). The changes in relative abundances of the different FFGs did not always follow the predictions of the RCC, as there were no correlations of community structure with river width or canopy cover in some seasons; however, some predictions of the RCC were supported, as a dominance of filterers (with relatively small contributions from shredders and grazers) and a consistent presence of predators were recorded. The FFG abundances were correlated with water velocity and total dissolved solids. Broadly, shifts in relative abundances of FFGs along the river continuum could not be explained by physical attributes alone, and were probably influenced by the availability of food and the chemistry of the river. Our findings highlight the need for theoretical and field studies across a broad array of African systems to refine the applicability of the RCC and FFG classifications to further develop models of ecosystem function.
- Full Text:
- Date Issued: 2017
The effect of different dietary microalgae on the fatty acid profile, fecundity and population development of the calanoid copepod Pseudodiaptomus hessei (Copepoda: Calanoida)
- Siqwepu, Oyama, Richoux, Nicole B, Vine, Niall G
- Authors: Siqwepu, Oyama , Richoux, Nicole B , Vine, Niall G
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456318 , vital:75502 , xlink:href="https://doi.org/10.1016/j.aquaculture.2016.10.008"
- Description: We studied the effect of dietary microalgae on the fecundity, population development, and fatty acid profile [with focus on the essential fatty acids docosahexaenoic acid (DHA; 22:6ω3) and eicosapentaenoic acid (EPA; 20:5ω3)] of the calanoid copepod Pseudodiaptomus hessei, a potential live food for finfish larvae in aquaculture. Two mono-algal diets, the Tahitian strain of Isochrysis galbana and Rhodomonas salina, and a 50:50 binary diet of the two were fed to copepods. Wild caught copepods were used as a baseline reference point. Copepods fed I. galbana and the 50:50 binary diet had high DHA:EPA ratios and DHA content relative to those fed R. salina. The EPA content of the copepods was similar for all three diets. Copepods fed R. salina had the highest fecundity relative to those fed I. galbana and the 50:50 binary diet. The largest population was obtained when the copepods were fed I. galbana, which differed from those fed R. salina and the 50:50 binary diet. The results of this study showed that the fatty acid composition of P. hessei can be altered by changing its dietary microalgae, and that the copepod can accumulate fatty acids from its diet, especially DHA and EPA. Diet also affected fecundity and population development of P. hessei, so this species represents a potential live food candidate for marine finfish larvae as its nutritional composition and productivity can be manipulated to suit the needs of marine finfish larvae.
- Full Text:
- Date Issued: 2017
- Authors: Siqwepu, Oyama , Richoux, Nicole B , Vine, Niall G
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456318 , vital:75502 , xlink:href="https://doi.org/10.1016/j.aquaculture.2016.10.008"
- Description: We studied the effect of dietary microalgae on the fecundity, population development, and fatty acid profile [with focus on the essential fatty acids docosahexaenoic acid (DHA; 22:6ω3) and eicosapentaenoic acid (EPA; 20:5ω3)] of the calanoid copepod Pseudodiaptomus hessei, a potential live food for finfish larvae in aquaculture. Two mono-algal diets, the Tahitian strain of Isochrysis galbana and Rhodomonas salina, and a 50:50 binary diet of the two were fed to copepods. Wild caught copepods were used as a baseline reference point. Copepods fed I. galbana and the 50:50 binary diet had high DHA:EPA ratios and DHA content relative to those fed R. salina. The EPA content of the copepods was similar for all three diets. Copepods fed R. salina had the highest fecundity relative to those fed I. galbana and the 50:50 binary diet. The largest population was obtained when the copepods were fed I. galbana, which differed from those fed R. salina and the 50:50 binary diet. The results of this study showed that the fatty acid composition of P. hessei can be altered by changing its dietary microalgae, and that the copepod can accumulate fatty acids from its diet, especially DHA and EPA. Diet also affected fecundity and population development of P. hessei, so this species represents a potential live food candidate for marine finfish larvae as its nutritional composition and productivity can be manipulated to suit the needs of marine finfish larvae.
- Full Text:
- Date Issued: 2017
Trophic ecology of adult male O donata. II. D ietary contributions of aquatic food sources
- Chari, Lenin D, Moyo, Sydney, Richoux, Nicole B
- Authors: Chari, Lenin D , Moyo, Sydney , Richoux, Nicole B
- Date: 2018
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456403 , vital:75510 , xlink:href="https://doi.org/10.1111/een.12459"
- Description: 1. Insects that emerge from rivers provide nutritional subsidies to local riparian predators. Adult damselflies and dragonflies often benefit from aquatic resources, but their high mobility and evasiveness have made it difficult to monitor their diets. 2. A dual fatty acid and stable isotope analysis approach was used to investigate the links between Odonata size and behaviour with proportions of their aquatically derived nutri-tional sources. Additionally, the study investigated the variation in die-tary contributions of aquatic food sources to Odonata between two sec-tions of a river, each with different aquatic productivity rates. 3. Varia-tions in body size and foraging method of Odonata in the Kowie River (South Africa) contributed to differences in the contributions of aquatic food sources to their diets. Large Odonata that consumed prey in flight had smaller proportions of aquatic indicator fatty acids and stable iso-tope‐generated proportions of aquatic food sources than did the smaller Odonata that consumed prey from perches. 4. There was a considera-ble amount of interspecific variation in indicators of aquatic feeding, but Odonata at an upstream site had smaller proportions of aquatic indica-tors than those at a downstream site which had higher insect emer-gence rates. 5. The findings of this study contribute information on the dynamics of feeding ecology among adult Odonata, and the substantial contributions of aquatic prey (>80% of total diet in some cases) indicat-ed that cross‐boundary trophic linkages via odonates are strong in the Kowie River.
- Full Text:
- Date Issued: 2018
- Authors: Chari, Lenin D , Moyo, Sydney , Richoux, Nicole B
- Date: 2018
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456403 , vital:75510 , xlink:href="https://doi.org/10.1111/een.12459"
- Description: 1. Insects that emerge from rivers provide nutritional subsidies to local riparian predators. Adult damselflies and dragonflies often benefit from aquatic resources, but their high mobility and evasiveness have made it difficult to monitor their diets. 2. A dual fatty acid and stable isotope analysis approach was used to investigate the links between Odonata size and behaviour with proportions of their aquatically derived nutri-tional sources. Additionally, the study investigated the variation in die-tary contributions of aquatic food sources to Odonata between two sec-tions of a river, each with different aquatic productivity rates. 3. Varia-tions in body size and foraging method of Odonata in the Kowie River (South Africa) contributed to differences in the contributions of aquatic food sources to their diets. Large Odonata that consumed prey in flight had smaller proportions of aquatic indicator fatty acids and stable iso-tope‐generated proportions of aquatic food sources than did the smaller Odonata that consumed prey from perches. 4. There was a considera-ble amount of interspecific variation in indicators of aquatic feeding, but Odonata at an upstream site had smaller proportions of aquatic indica-tors than those at a downstream site which had higher insect emer-gence rates. 5. The findings of this study contribute information on the dynamics of feeding ecology among adult Odonata, and the substantial contributions of aquatic prey (>80% of total diet in some cases) indicat-ed that cross‐boundary trophic linkages via odonates are strong in the Kowie River.
- Full Text:
- Date Issued: 2018
Trophic ecology of adult male Odonata. I. Dietary niche metrics by foraging guild, species, body size, and location
- Chari, Lenin D, Moyo, Sydney, Richoux, Nicole B
- Authors: Chari, Lenin D , Moyo, Sydney , Richoux, Nicole B
- Date: 2018
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456379 , vital:75508 , xlink:href="https://doi.org/10.1111/een.12458"
- Description: 1. Information on the dietary niches of adult odonates is sparse, as they are highly mobile and evasive animals, which makes them difficult to observe in their natural habitat. Moreover, there is a lack of knowledge on how varying behavioural traits of odonates relate to phenomena like niche partitioning. 2. This study investigated niche partitioning amongst odonate species, foraging guilds and size classes in a riverine system in the Eastern Cape province of South Africa. A combination of stable isotope and fatty acid‐based niches was used to infer odonate feeding. 3. Both fatty acid and stable isotope‐based niches showed that there was niche separation amongst odonates that forage in flight (fliers) and those that forage from a perch (perchers), amongst odonates of different size classes (damselflies, medium‐ and large‐sized dragonflies), and amongst species, although varying levels of niche overlap were observed in each case. 4. Niche sizes of odonates varied between an upstream and a downstream site. Generally greater niche overlap was recorded at the narrow upstream site (associated with low insect emergence rates) than the wider downstream site (associated with high insect emergence rates), indicating that a greater degree of resource sharing occurred at the upstream site where aquatic food was less abundant. 5. The findings of this study suggest that dietary niches of odonates can be influenced by foraging guild, body size, and/or environmental conditions, and additional study in a variety of regions is recommended to determine the greater applicability of these findings.
- Full Text:
- Date Issued: 2018
- Authors: Chari, Lenin D , Moyo, Sydney , Richoux, Nicole B
- Date: 2018
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456379 , vital:75508 , xlink:href="https://doi.org/10.1111/een.12458"
- Description: 1. Information on the dietary niches of adult odonates is sparse, as they are highly mobile and evasive animals, which makes them difficult to observe in their natural habitat. Moreover, there is a lack of knowledge on how varying behavioural traits of odonates relate to phenomena like niche partitioning. 2. This study investigated niche partitioning amongst odonate species, foraging guilds and size classes in a riverine system in the Eastern Cape province of South Africa. A combination of stable isotope and fatty acid‐based niches was used to infer odonate feeding. 3. Both fatty acid and stable isotope‐based niches showed that there was niche separation amongst odonates that forage in flight (fliers) and those that forage from a perch (perchers), amongst odonates of different size classes (damselflies, medium‐ and large‐sized dragonflies), and amongst species, although varying levels of niche overlap were observed in each case. 4. Niche sizes of odonates varied between an upstream and a downstream site. Generally greater niche overlap was recorded at the narrow upstream site (associated with low insect emergence rates) than the wider downstream site (associated with high insect emergence rates), indicating that a greater degree of resource sharing occurred at the upstream site where aquatic food was less abundant. 5. The findings of this study suggest that dietary niches of odonates can be influenced by foraging guild, body size, and/or environmental conditions, and additional study in a variety of regions is recommended to determine the greater applicability of these findings.
- Full Text:
- Date Issued: 2018
Dietary tracers and stomach contents reveal pronounced alimentary flexibility in the freshwater mullet (Myxus capensis, Mugilidae) concomitant with ontogenetic shifts in habitat use and seasonal food availability
- Carassou, Laure, Whitfield, Alan K, Moyo, Sydney, Richoux, Nicole B
- Authors: Carassou, Laure , Whitfield, Alan K , Moyo, Sydney , Richoux, Nicole B
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456201 , vital:75493 , xlink:href="https://doi.org/10.1007/s10750-017-3230-3"
- Description: We investigated ontogenetic and seasonal variations in the diet of the freshwater mullet (Myxus capensis) across a river–estuary interface using dietary tracer (stable isotopes and fatty acids) and stomach content analyses. Two hypotheses were tested: (A) the freshwater mullet diet shifts as individuals grow and migrate from the estuary to the river, and (B) the dominant food resources utilized by freshwater mullet vary through time, mainly as a function of the seasonal changes in the availability of preferred food items in each habitat. Both hypotheses were supported, as our results indicated broad dietary flexibility by M. capensis, with utilized food items ranging from benthic microalgae to insects depending on habitat and seasonal patterns in availability of resources. Given the unexpected importance of invertebrate-derived prey, including some of terrestrial origin (i.e. aerial or semi-aquatic insects), during the freshwater phase of the M. capensis life cycle, we also emphasize a need for a re-assessment of the trophic designation of this species (previously designated as a strict detritivore).
- Full Text:
- Date Issued: 2017
- Authors: Carassou, Laure , Whitfield, Alan K , Moyo, Sydney , Richoux, Nicole B
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456201 , vital:75493 , xlink:href="https://doi.org/10.1007/s10750-017-3230-3"
- Description: We investigated ontogenetic and seasonal variations in the diet of the freshwater mullet (Myxus capensis) across a river–estuary interface using dietary tracer (stable isotopes and fatty acids) and stomach content analyses. Two hypotheses were tested: (A) the freshwater mullet diet shifts as individuals grow and migrate from the estuary to the river, and (B) the dominant food resources utilized by freshwater mullet vary through time, mainly as a function of the seasonal changes in the availability of preferred food items in each habitat. Both hypotheses were supported, as our results indicated broad dietary flexibility by M. capensis, with utilized food items ranging from benthic microalgae to insects depending on habitat and seasonal patterns in availability of resources. Given the unexpected importance of invertebrate-derived prey, including some of terrestrial origin (i.e. aerial or semi-aquatic insects), during the freshwater phase of the M. capensis life cycle, we also emphasize a need for a re-assessment of the trophic designation of this species (previously designated as a strict detritivore).
- Full Text:
- Date Issued: 2017
Impact of an introduced predator (Micropterus salmoides, Centrarchidae) on native estuarine fish elucidated through fatty acid analyses
- Carassou, Laure, Magoro, Mandla L, Whitfield, Alan K, Richoux, Nicole B
- Authors: Carassou, Laure , Magoro, Mandla L , Whitfield, Alan K , Richoux, Nicole B
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456247 , vital:75496 , xlink:href="https://hal.inrae.fr/hal-04177984/document"
- Description: The introduction of alien fish species can have contrasting impacts on local aquatic communities. The largemouth bass Micropterus salmoides (Centrarchidae; Fig.1) was introduced in 1928 in South Africa for recreational anglers. Concerns about its impact on local indigenous freshwater and estuarine fish populations are raised (Gratwicke and Marshall, 2001; Weyl and Lewis, 2006; Wasserman et al., 2011). In particular, the predatory impact of M. salmoides on estuary-associated juveniles of marine fish species must be elucidated.
- Full Text:
- Date Issued: 2017
- Authors: Carassou, Laure , Magoro, Mandla L , Whitfield, Alan K , Richoux, Nicole B
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456247 , vital:75496 , xlink:href="https://hal.inrae.fr/hal-04177984/document"
- Description: The introduction of alien fish species can have contrasting impacts on local aquatic communities. The largemouth bass Micropterus salmoides (Centrarchidae; Fig.1) was introduced in 1928 in South Africa for recreational anglers. Concerns about its impact on local indigenous freshwater and estuarine fish populations are raised (Gratwicke and Marshall, 2001; Weyl and Lewis, 2006; Wasserman et al., 2011). In particular, the predatory impact of M. salmoides on estuary-associated juveniles of marine fish species must be elucidated.
- Full Text:
- Date Issued: 2017
Tide-induced variations in the fatty acid composition of estuarine particulate organic matter
- Antonio, Emily S, Richoux, Nicole B
- Authors: Antonio, Emily S , Richoux, Nicole B
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456336 , vital:75504 , xlink:href="https://doi.org/10.1007/s12237-015-0049-x"
- Description: The particulate organic matter (POM) in hydrodynamically variable habitats such as the lower reaches of estuaries can change in its content and quality on very short time scales (example, hourly), and these changes can potentially influence higher-level consumers in river-estuary-marine systems. Estuarine water samples were collected hourly for 12 h downstream in a small river to evaluate the fatty acid composition of POM over a tidal cycle. Fatty acid constituents of POM collected during the flood tide were dominated by the saturated, higher plant and bacterial fatty acids, whereas unsaturated, polyunsaturated, essential, and diatom-associated fatty acids dominated the POM collected during the ebb tide. Elevated algal biomass (as indicated by high chlorophyll a concentrations), diatom, and freshness indices in the POM indicated enhanced fresh autochthonous-origin materials that dominated the mixed organic pool during the ebb tide compared to more degraded detritus during the flood tide. Tidal retention of organic matter and algal primary production were the most influential factors that differentiated the fatty acid composition of estuarine POM over the short time scale. The results of this study have important implications on the quality of POM at the time of sampling, especially in estuaries where mixed organic pools have multiple inputs and are strongly influenced by tidal cycles.
- Full Text:
- Date Issued: 2016
- Authors: Antonio, Emily S , Richoux, Nicole B
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456336 , vital:75504 , xlink:href="https://doi.org/10.1007/s12237-015-0049-x"
- Description: The particulate organic matter (POM) in hydrodynamically variable habitats such as the lower reaches of estuaries can change in its content and quality on very short time scales (example, hourly), and these changes can potentially influence higher-level consumers in river-estuary-marine systems. Estuarine water samples were collected hourly for 12 h downstream in a small river to evaluate the fatty acid composition of POM over a tidal cycle. Fatty acid constituents of POM collected during the flood tide were dominated by the saturated, higher plant and bacterial fatty acids, whereas unsaturated, polyunsaturated, essential, and diatom-associated fatty acids dominated the POM collected during the ebb tide. Elevated algal biomass (as indicated by high chlorophyll a concentrations), diatom, and freshness indices in the POM indicated enhanced fresh autochthonous-origin materials that dominated the mixed organic pool during the ebb tide compared to more degraded detritus during the flood tide. Tidal retention of organic matter and algal primary production were the most influential factors that differentiated the fatty acid composition of estuarine POM over the short time scale. The results of this study have important implications on the quality of POM at the time of sampling, especially in estuaries where mixed organic pools have multiple inputs and are strongly influenced by tidal cycles.
- Full Text:
- Date Issued: 2016
Fatty acids reveal the importance of autochthonous non-vascular plant inputs to an austral river food web
- Moyo, Sydney, Richoux, Nicole B
- Authors: Moyo, Sydney , Richoux, Nicole B
- Date: 2018
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456677 , vital:75542 , xlink:href="https://doi.org/10.1007/s10750-017-3347-4"
- Description: We hypothesised that the dominant organic source supporting macroinvertebrate consumers in a South African river is autochthonously produced non-vascular algae (regardless of season), and that the prevalence of autochthony increases with increasing distance from the headwaters. Fatty acid profiles of macroinvertebrates from six sites and four sample times were assessed to characterise the consumer diets and estimate the relative assimilation of autochthonous versus allochthonous-based sources in the food web. Fatty acid markers, ordination analyses and mixing models confirmed that the ultimate nutritional source for the invertebrate assemblages was autochthonous-produced carbon, with some contributions occurring from vascular plants (potentially of allochthonous and autochthonous origin, as some vascular plants were aquatic macrophytes). However, contrary to our second hypothesis, the prevalence of autochthony did not change predictably along the river. Such an autochthonous-based food web is consistent with many large rivers in well-researched regions of the world, although the complexity and variability that we observed in the fatty acid profiles of macroinvertebrate consumers in a small South African river should help stimulate renewed interest in investigations of carbon flow within small rivers from less-studied regions (particularly in arid climates).
- Full Text:
- Date Issued: 2018
- Authors: Moyo, Sydney , Richoux, Nicole B
- Date: 2018
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456677 , vital:75542 , xlink:href="https://doi.org/10.1007/s10750-017-3347-4"
- Description: We hypothesised that the dominant organic source supporting macroinvertebrate consumers in a South African river is autochthonously produced non-vascular algae (regardless of season), and that the prevalence of autochthony increases with increasing distance from the headwaters. Fatty acid profiles of macroinvertebrates from six sites and four sample times were assessed to characterise the consumer diets and estimate the relative assimilation of autochthonous versus allochthonous-based sources in the food web. Fatty acid markers, ordination analyses and mixing models confirmed that the ultimate nutritional source for the invertebrate assemblages was autochthonous-produced carbon, with some contributions occurring from vascular plants (potentially of allochthonous and autochthonous origin, as some vascular plants were aquatic macrophytes). However, contrary to our second hypothesis, the prevalence of autochthony did not change predictably along the river. Such an autochthonous-based food web is consistent with many large rivers in well-researched regions of the world, although the complexity and variability that we observed in the fatty acid profiles of macroinvertebrate consumers in a small South African river should help stimulate renewed interest in investigations of carbon flow within small rivers from less-studied regions (particularly in arid climates).
- Full Text:
- Date Issued: 2018
Seasonal population dynamics and energy consumption by waterbirds in a small temperate estuary
- Hean, Jeffrey W, Craig, Adrian J F K, Richoux, Nicole B
- Authors: Hean, Jeffrey W , Craig, Adrian J F K , Richoux, Nicole B
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456305 , vital:75501 , xlink:href="https://doi.org/10.2989/00306525.2016.1230897"
- Description: Simple measures of population dynamics and energy consumption can provide baseline information on the role of consumers in food webs, particularly for cryptic or highly-mobile species of waterbirds. We provide estimates of the seasonal population dynamics and energy consumption of waterbirds along the Kowie Estuary, South Africa. Ten census counts were conducted every month along the estuary from June 2013 to May 2014. Energy consumption and fresh-matter intake were calculated based on body-mass equations. Piscivorous birds dominated the waterbird assemblage during summer (up to 289 individuals), whereas non-migratory shorebirds were dominant at other times of the year. The total wet mass of prey items ingested by waterbirds ranged from 2.8 kg ha−1 during winter to 8.5 kg ha−1 during summer. The total energy consumption of waterbirds ranged from 12 543 kJ ha−1 during June to 33 104 kJ ha−1 during December. Shannon–Wiener diversity calculations revealed that the Kowie Estuary had a greater diversity of waterbirds than several other South African estuaries, but less diversity than many large European estuaries. Studies that incorporate census counts and energy consumption measures, although rudimentary, may provide valuable information on resource use by waterbirds in estuaries and may benefit conservation management schemes.
- Full Text:
- Date Issued: 2017
- Authors: Hean, Jeffrey W , Craig, Adrian J F K , Richoux, Nicole B
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456305 , vital:75501 , xlink:href="https://doi.org/10.2989/00306525.2016.1230897"
- Description: Simple measures of population dynamics and energy consumption can provide baseline information on the role of consumers in food webs, particularly for cryptic or highly-mobile species of waterbirds. We provide estimates of the seasonal population dynamics and energy consumption of waterbirds along the Kowie Estuary, South Africa. Ten census counts were conducted every month along the estuary from June 2013 to May 2014. Energy consumption and fresh-matter intake were calculated based on body-mass equations. Piscivorous birds dominated the waterbird assemblage during summer (up to 289 individuals), whereas non-migratory shorebirds were dominant at other times of the year. The total wet mass of prey items ingested by waterbirds ranged from 2.8 kg ha−1 during winter to 8.5 kg ha−1 during summer. The total energy consumption of waterbirds ranged from 12 543 kJ ha−1 during June to 33 104 kJ ha−1 during December. Shannon–Wiener diversity calculations revealed that the Kowie Estuary had a greater diversity of waterbirds than several other South African estuaries, but less diversity than many large European estuaries. Studies that incorporate census counts and energy consumption measures, although rudimentary, may provide valuable information on resource use by waterbirds in estuaries and may benefit conservation management schemes.
- Full Text:
- Date Issued: 2017
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
Trophic relationships of hake (Merluccius capensis and M. paradoxus) and sharks (Centrophorus squamosus, Deania calcea and D. profundorum) in the Northern (Namibia) Benguela Current region
- Iitembu, J A, Richoux, Nicole B
- Authors: Iitembu, J A , Richoux, Nicole B
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457418 , vital:75636 , xlink:href="https://hdl.handle.net/10520/EJC183122"
- Description: The trophic relationships of two hake species (Merluccius capensis and M. paradoxus) and three shark species (Centrophorus squamosus, Deania calcea and D. profundorum) were investigated using nitrogen and carbon stable isotope signatures (15N and 13C) of their muscle tissues. The sharks were more enriched in 15N than the hake, an indication of the apex predator status of sharks. Among the sharks considered, C. squamosus occupied the highest trophic level and fed primarily on benthic prey. The two species of shark from the genus Deania were not different based on 15N or 13C, so they had similar diets. The 13C signatures indicated that M. capensis and sharks fed on prey derived from similar basal resources. However, there was a significant difference in 13C between M. paradoxus and all other species examined, suggesting that they occupied different feeding niches. Isotope-based populationmetrics showed narrower trophic ranges in sharks than M. capensis. Carbon and nitrogen ranges indicated that hake fed on a more diverse pool of carbon sources and had generally more enhanced trophic diversity in their feeding patterns than sharks. Among the species considered, C. squamosus occupied a unique isotopic space. Our results supported the hypothesis there are trophic overlaps among these species, but some interesting differentiation was revealed.
- Full Text:
- Date Issued: 2015
- Authors: Iitembu, J A , Richoux, Nicole B
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457418 , vital:75636 , xlink:href="https://hdl.handle.net/10520/EJC183122"
- Description: The trophic relationships of two hake species (Merluccius capensis and M. paradoxus) and three shark species (Centrophorus squamosus, Deania calcea and D. profundorum) were investigated using nitrogen and carbon stable isotope signatures (15N and 13C) of their muscle tissues. The sharks were more enriched in 15N than the hake, an indication of the apex predator status of sharks. Among the sharks considered, C. squamosus occupied the highest trophic level and fed primarily on benthic prey. The two species of shark from the genus Deania were not different based on 15N or 13C, so they had similar diets. The 13C signatures indicated that M. capensis and sharks fed on prey derived from similar basal resources. However, there was a significant difference in 13C between M. paradoxus and all other species examined, suggesting that they occupied different feeding niches. Isotope-based populationmetrics showed narrower trophic ranges in sharks than M. capensis. Carbon and nitrogen ranges indicated that hake fed on a more diverse pool of carbon sources and had generally more enhanced trophic diversity in their feeding patterns than sharks. Among the species considered, C. squamosus occupied a unique isotopic space. Our results supported the hypothesis there are trophic overlaps among these species, but some interesting differentiation was revealed.
- Full Text:
- Date Issued: 2015
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
Critical indirect effects of climate change on sub-A ntarctic ecosystem functioning
- Allan, E Louise, Froneman, P William, Durgadoo, Jonathan V, McQuaid, Christopher D, Ansorge, Isabelle J, Richoux, Nicole B
- Authors: Allan, E Louise , Froneman, P William , Durgadoo, Jonathan V , McQuaid, Christopher D , Ansorge, Isabelle J , Richoux, Nicole B
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457934 , vital:75696 , xlink:href="https://doi.org/10.1002/ece3.678"
- Description: Sub‐Antarctic islands represent critical breeding habitats for land‐based top predators that dominate Southern Ocean food webs. Reproduction and molting incur high energetic demands that are sustained at the sub‐Antarctic Prince Edward Islands (PEIs) by both inshore (phytoplankton blooms; “island mass effect”; autochthonous) and offshore (allochthonous) productivity. As the relative contributions of these sustenance pathways are, in turn, affected by oceanographic conditions around the PEIs, we address the consequences of climatically driven changes in the physical environment on this island ecosystem. We show that there has been a measurable long‐term shift in the carbon isotope signatures of the benthos inhabiting the shallow shelf region of the PEIs, most likely reflecting a long‐term decline in enhanced phytoplankton productivity at the islands in response to a climate‐driven shift in the position of the sub‐Antarctic Front. Our results indicate that regional climate change has affected the balance between allochthonous and autochthonous productivity at the PEIs. Over the last three decades, inshore‐feeding top predators at the islands have shown a marked decrease in their population sizes. Conversely, population sizes of offshore‐feeding predators that forage over great distances from the islands have remained stable or increased, with one exception. Population decline of predators that rely heavily on organisms inhabiting the inshore region strongly suggest changes in prey availability, which are likely driven by factors such as fisheries impacts on some prey populations and shifts in competitive interactions among predators. In addition to these local factors, our analysis indicates that changes in prey availability may also result indirectly through regional climate change effects on the islands' marine ecosystem. Most importantly, our results indicate that a fundamental shift in the balance between allochthonous and autochthonous trophic pathways within this island ecosystem may be detected throughout the food web, demonstrating that the most powerful effects of climate change on marine systems may be indirect.
- Full Text:
- Date Issued: 2013
- Authors: Allan, E Louise , Froneman, P William , Durgadoo, Jonathan V , McQuaid, Christopher D , Ansorge, Isabelle J , Richoux, Nicole B
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457934 , vital:75696 , xlink:href="https://doi.org/10.1002/ece3.678"
- Description: Sub‐Antarctic islands represent critical breeding habitats for land‐based top predators that dominate Southern Ocean food webs. Reproduction and molting incur high energetic demands that are sustained at the sub‐Antarctic Prince Edward Islands (PEIs) by both inshore (phytoplankton blooms; “island mass effect”; autochthonous) and offshore (allochthonous) productivity. As the relative contributions of these sustenance pathways are, in turn, affected by oceanographic conditions around the PEIs, we address the consequences of climatically driven changes in the physical environment on this island ecosystem. We show that there has been a measurable long‐term shift in the carbon isotope signatures of the benthos inhabiting the shallow shelf region of the PEIs, most likely reflecting a long‐term decline in enhanced phytoplankton productivity at the islands in response to a climate‐driven shift in the position of the sub‐Antarctic Front. Our results indicate that regional climate change has affected the balance between allochthonous and autochthonous productivity at the PEIs. Over the last three decades, inshore‐feeding top predators at the islands have shown a marked decrease in their population sizes. Conversely, population sizes of offshore‐feeding predators that forage over great distances from the islands have remained stable or increased, with one exception. Population decline of predators that rely heavily on organisms inhabiting the inshore region strongly suggest changes in prey availability, which are likely driven by factors such as fisheries impacts on some prey populations and shifts in competitive interactions among predators. In addition to these local factors, our analysis indicates that changes in prey availability may also result indirectly through regional climate change effects on the islands' marine ecosystem. Most importantly, our results indicate that a fundamental shift in the balance between allochthonous and autochthonous trophic pathways within this island ecosystem may be detected throughout the food web, demonstrating that the most powerful effects of climate change on marine systems may be indirect.
- Full Text:
- Date Issued: 2013
Determining spatial changes in the diet of nearshore suspension-feeders along the South African coastline: stable isotope and fatty acid signatures
- Allan, E Louise, Ambrose, Shan T, Richoux, Nicole B, Froneman, P William
- Authors: Allan, E Louise , Ambrose, Shan T , Richoux, Nicole B , Froneman, P William
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457945 , vital:75697 , xlink:href="https://doi.org/10.1016/j.ecss.2010.02.004"
- Description: Mesoscale oceanographic features, such as upwellings, are known to play an important role in regulating the structure and productivity of nearshore marine communities. Stable isotope (δ13C and δ15N) and fatty acid analyses were employed to assess the influence of an upwelling cell along the south-eastern coastline of southern Africa on the diet of the mussel, Perna perna. Eight sites were sampled: two upstream, three in the vicinity and three downstream of the upwelling cell. Stable isotope and fatty acid signatures indicated that the mussels consumed a diet of detritus derived mainly from macroalgae, diatoms and dinoflagellates. One-way ANOVA on the δ13C and δ15N signatures and the principal component analysis of the fatty acid profiles of the mussels identified distinct groups corresponding to the above mentioned regions. The proportion of diatom biomarkers in the fatty acid profiles decreased downstream of the upwelling region while the proportion of dinoflagellate biomarkers increased. Upwelling regions are typically associated with elevated levels of productivity; however, these systems usually become silicon depleted and result in the replacement of diatoms with dinoflagellates. The highest proportions of the dinoflagellate markers were recorded in the two furthest sites downstream of the upwelling cell. The spatial variation in the diet of the mussels, therefore, appears to reflect the presence of the upwelling cell in the nearshore biology of the region.
- Full Text:
- Date Issued: 2010
- Authors: Allan, E Louise , Ambrose, Shan T , Richoux, Nicole B , Froneman, P William
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457945 , vital:75697 , xlink:href="https://doi.org/10.1016/j.ecss.2010.02.004"
- Description: Mesoscale oceanographic features, such as upwellings, are known to play an important role in regulating the structure and productivity of nearshore marine communities. Stable isotope (δ13C and δ15N) and fatty acid analyses were employed to assess the influence of an upwelling cell along the south-eastern coastline of southern Africa on the diet of the mussel, Perna perna. Eight sites were sampled: two upstream, three in the vicinity and three downstream of the upwelling cell. Stable isotope and fatty acid signatures indicated that the mussels consumed a diet of detritus derived mainly from macroalgae, diatoms and dinoflagellates. One-way ANOVA on the δ13C and δ15N signatures and the principal component analysis of the fatty acid profiles of the mussels identified distinct groups corresponding to the above mentioned regions. The proportion of diatom biomarkers in the fatty acid profiles decreased downstream of the upwelling region while the proportion of dinoflagellate biomarkers increased. Upwelling regions are typically associated with elevated levels of productivity; however, these systems usually become silicon depleted and result in the replacement of diatoms with dinoflagellates. The highest proportions of the dinoflagellate markers were recorded in the two furthest sites downstream of the upwelling cell. The spatial variation in the diet of the mussels, therefore, appears to reflect the presence of the upwelling cell in the nearshore biology of the region.
- Full Text:
- Date Issued: 2010
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
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