Dietary success of a ‘new’ key fish in an overfished ecosystem: evidence from fatty acid and stable isotope signatures
- Van der Bank, M G, Utne-Palm, A C, Pittman, K, Sweetman, A K, Richoux, Nicole B, Brüchert, V, Gibbons, M J
- Authors: Van der Bank, M G , Utne-Palm, A C , Pittman, K , Sweetman, A K , Richoux, Nicole B , Brüchert, V , Gibbons, M J
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/478863 , vital:78233 , https://doi.org/10.3354/meps09078
- Description: The bearded goby Sufflogobius bibarbatus has become a key component of the pelagic food web off Namibia following the crash in pelagic fish populations during the 1970s, and its biomass is increasing despite significant predation pressure and apparent life-history constraints. The integrated feeding of the bearded goby was studied from samples collected during April 2008, using stable isotope ratios (δ 13 C, δ 15 N, δ 34 S) and fatty acids, to resolve conflict amongst previous dietary studies based on gut-content analysis and to understand how diet could influence its success within the region. Isotopes of carbon and nitrogen suggest that the now abundant jellyfish could contribute up to 74% of the diet, and δ 34 S signatures indicate that the diatom-and bacteria-rich sulphidic sediments on the central shelf may contribute around 15% to the diet. Fatty acid analyses provided support for sulphur bacterial and jellyfish-feeding amongst gobies, and further suggest that small gobies fed more on zooplankton while large gobies fed more on sedimented diatoms. Both data sets suggest that ontogenetic changes in diet were linked to changes in habitat: pelagic when small, more demersal when large. The study highlights the value of using multiple tracers in trophic studies and indicates that the dietary flexibility of the bearded goby, in conjunction with its behaviour and physiology, likely contributes to its success within the northern Benguela ecosystem.
- Full Text:
- Date Issued: 2011
- Authors: Van der Bank, M G , Utne-Palm, A C , Pittman, K , Sweetman, A K , Richoux, Nicole B , Brüchert, V , Gibbons, M J
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/478863 , vital:78233 , https://doi.org/10.3354/meps09078
- Description: The bearded goby Sufflogobius bibarbatus has become a key component of the pelagic food web off Namibia following the crash in pelagic fish populations during the 1970s, and its biomass is increasing despite significant predation pressure and apparent life-history constraints. The integrated feeding of the bearded goby was studied from samples collected during April 2008, using stable isotope ratios (δ 13 C, δ 15 N, δ 34 S) and fatty acids, to resolve conflict amongst previous dietary studies based on gut-content analysis and to understand how diet could influence its success within the region. Isotopes of carbon and nitrogen suggest that the now abundant jellyfish could contribute up to 74% of the diet, and δ 34 S signatures indicate that the diatom-and bacteria-rich sulphidic sediments on the central shelf may contribute around 15% to the diet. Fatty acid analyses provided support for sulphur bacterial and jellyfish-feeding amongst gobies, and further suggest that small gobies fed more on zooplankton while large gobies fed more on sedimented diatoms. Both data sets suggest that ontogenetic changes in diet were linked to changes in habitat: pelagic when small, more demersal when large. The study highlights the value of using multiple tracers in trophic studies and indicates that the dietary flexibility of the bearded goby, in conjunction with its behaviour and physiology, likely contributes to its success within the northern Benguela ecosystem.
- Full Text:
- Date Issued: 2011
Trophic ecology of zooplankton at a frontal transition zone: fatty acid signatures at the subtropical convergence, Southern Ocean
- Authors: Richoux, Nicole B
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/458033 , vital:75711 , xlink:href="https://doi.org/10.1093/plankt/fbq132"
- Description: Regional variations in fatty acid composition were assessed in zooplankton communities situated immediately north and south of the subtropical convergence (STC), where warm (maximum 21°C) nutrient-poor waters of the southwest Indian Ocean converge with cool (minimum 11°C) nutrient-rich subantarctic waters of the Southern Ocean. I hypothesized that food web structures differ from north to south based on average spatial differences in primary productivity, and that zooplankton in the more productive region show enhanced herbivorous feeding. Several taxonomic groups including euphausiids showed differences in their fatty acid signatures from north to south, indicating the existence of measurable within- and among-species differences in trophic relationships between the two communities, presumably stemming from variations in food quality and availability. The indices 22:6ω3/20:5ω3, 18:1ω9/18:1ω7 and Σω3/Σω6 indicated that carnivory was the dominant feeding mode in the north, whereas herbivory was more prevalent in the south, a pattern that was not detected in the same region using stable isotope ratios. Such conflicting results substantiate the importance of utilizing more than one method to investigate feeding relationships in aquatic systems. Fatty acid profiles of the amphipod Themisto gaudichaudii revealed some distinct herbivory markers, indicating more complex feeding habits by this important pelagic species than previously reported. My findings shed new light on the regional variations in zooplankton diet and food web dynamics in a poorly understood but critically important frontal zone bordering the Southern Ocean.
- Full Text:
- Date Issued: 2011
- Authors: Richoux, Nicole B
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/458033 , vital:75711 , xlink:href="https://doi.org/10.1093/plankt/fbq132"
- Description: Regional variations in fatty acid composition were assessed in zooplankton communities situated immediately north and south of the subtropical convergence (STC), where warm (maximum 21°C) nutrient-poor waters of the southwest Indian Ocean converge with cool (minimum 11°C) nutrient-rich subantarctic waters of the Southern Ocean. I hypothesized that food web structures differ from north to south based on average spatial differences in primary productivity, and that zooplankton in the more productive region show enhanced herbivorous feeding. Several taxonomic groups including euphausiids showed differences in their fatty acid signatures from north to south, indicating the existence of measurable within- and among-species differences in trophic relationships between the two communities, presumably stemming from variations in food quality and availability. The indices 22:6ω3/20:5ω3, 18:1ω9/18:1ω7 and Σω3/Σω6 indicated that carnivory was the dominant feeding mode in the north, whereas herbivory was more prevalent in the south, a pattern that was not detected in the same region using stable isotope ratios. Such conflicting results substantiate the importance of utilizing more than one method to investigate feeding relationships in aquatic systems. Fatty acid profiles of the amphipod Themisto gaudichaudii revealed some distinct herbivory markers, indicating more complex feeding habits by this important pelagic species than previously reported. My findings shed new light on the regional variations in zooplankton diet and food web dynamics in a poorly understood but critically important frontal zone bordering the Southern Ocean.
- Full Text:
- Date Issued: 2011
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