Decoupled reciprocal subsidies of biomass and fatty acids in fluxes of invertebrates between a temperate river and the adjacent land:
- Moyo, Sydney, Chari, Lenin D, Villet, Martin H, Richoux, Nicole B
- Authors: Moyo, Sydney , Chari, Lenin D , Villet, Martin H , Richoux, Nicole B
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/140843 , vital:37923 , DOI: 10.1007/s00027-017-0529-0
- Description: Streams and riparian areas are tightly coupled through reciprocal trophic subsidies, and there is evidence that these subsidies affect consumers in connected ecosystems. Most studies of subsidies consider only their quantity and not their quality. We determined the bidirectional exchange of organisms between the Kowie River and its riparian zone in South Africa using floating pyramidal traps (to measure insect emergence) and pan traps (to capture infalling invertebrates).
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- Authors: Moyo, Sydney , Chari, Lenin D , Villet, Martin H , Richoux, Nicole B
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/140843 , vital:37923 , DOI: 10.1007/s00027-017-0529-0
- Description: Streams and riparian areas are tightly coupled through reciprocal trophic subsidies, and there is evidence that these subsidies affect consumers in connected ecosystems. Most studies of subsidies consider only their quantity and not their quality. We determined the bidirectional exchange of organisms between the Kowie River and its riparian zone in South Africa using floating pyramidal traps (to measure insect emergence) and pan traps (to capture infalling invertebrates).
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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).
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- 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).
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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.
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- 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.
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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.
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- 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.
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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/10962/443178 , vital:74086 , 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 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:
- Authors: Moyo, Sydney , Richoux, Nicole B
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443178 , vital:74086 , 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 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:
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:
- 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.
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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:
- 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.
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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:
- 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.
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