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
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
Depth-related distribution patterns of subtidal macrobenthos in a well-established marine protected area
- Heyns, E R, Bernard, Anthony T F, Richoux, Nicole B, Götz, A
- Authors: Heyns, E R , Bernard, Anthony T F , Richoux, Nicole B , Götz, A
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457230 , vital:75618 , xlink:href="https://doi.org/10.1007/s00227-016-2816-z"
- Description: Effective marine resource management requires knowledge of the distribution of critical habitats that support resource populations and the processes that maintain them. Reefs that host diverse macrobenthic communities are important habitats for fish. However, detailed information on macrobenthic communities is rarely available and is usually limited to SCUBA diving depths. To establish depth-related distribution patterns and drivers that structure reef communities, the macrobenthos situated in a warm-temperate marine protected area (MPA; 34°01′24S; 23°54′09E) was sampled between 2009 and 2012. Comparison of shallow (11–25 m) and deep (45–75 m) sites revealed significantly different communities, sharing only 27.9 % of species. LINKTREE analysis revealed a changeover of species along the depth gradient, resulting in four significantly different assemblage clusters, each associated with particular environmental variables. High light intensity supported benthic algae at shallow depths, and as light availability decreased with depth, algal cover diminished and was eventually absent from the deep reef. Upright growth forms and settled particulate matter were positively related to depth and dominated the deep reef. Reduced wave action and currents on the deep reef can explain the increased settling of suspended particles. Under such conditions, clogging of feeding parts of the encrusting species is expected, and upright growth would be favoured. Considering that most MPAs are restricted to shallow coastal habitats and that macrobenthic communities change significantly with depth, it is probable that many unique deep reef habitats are currently afforded no protection.
- Full Text:
- Date Issued: 2016
- Authors: Heyns, E R , Bernard, Anthony T F , Richoux, Nicole B , Götz, A
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457230 , vital:75618 , xlink:href="https://doi.org/10.1007/s00227-016-2816-z"
- Description: Effective marine resource management requires knowledge of the distribution of critical habitats that support resource populations and the processes that maintain them. Reefs that host diverse macrobenthic communities are important habitats for fish. However, detailed information on macrobenthic communities is rarely available and is usually limited to SCUBA diving depths. To establish depth-related distribution patterns and drivers that structure reef communities, the macrobenthos situated in a warm-temperate marine protected area (MPA; 34°01′24S; 23°54′09E) was sampled between 2009 and 2012. Comparison of shallow (11–25 m) and deep (45–75 m) sites revealed significantly different communities, sharing only 27.9 % of species. LINKTREE analysis revealed a changeover of species along the depth gradient, resulting in four significantly different assemblage clusters, each associated with particular environmental variables. High light intensity supported benthic algae at shallow depths, and as light availability decreased with depth, algal cover diminished and was eventually absent from the deep reef. Upright growth forms and settled particulate matter were positively related to depth and dominated the deep reef. Reduced wave action and currents on the deep reef can explain the increased settling of suspended particles. Under such conditions, clogging of feeding parts of the encrusting species is expected, and upright growth would be favoured. Considering that most MPAs are restricted to shallow coastal habitats and that macrobenthic communities change significantly with depth, it is probable that many unique deep reef habitats are currently afforded no protection.
- Full Text:
- Date Issued: 2016
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