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Marine Ecology Progress Series

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MEPS 428:219-233 (2011)  -  DOI:

Dietary success of a ‘new’ key fish in an overfished ecosystem: evidence from fatty acid and stable isotope signatures

M. G. van der Bank1, A. C. Utne-Palm2, K. Pittman2, A. K. Sweetman3, N. B. Richoux4, V. Brüchert5, M. J. Gibbons1,* 

1Department of Biodiversity and Conservation Biology, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa
2Department of Biology, University of Bergen, PO Box 7803, 5020 Bergen, Norway
3Norwegian Institute for Water Research, Regional Office Bergen, Thormøhlensgate 53D, 5006 Bergen, Norway
4Department of Zoology and Entomology, Rhodes University, Grahamstown 6140, South Africa
5Department of Geology and Geochemistry, Stockholm University, 10691 Stockholm, Sweden
*Corresponding author. Email:

ABSTRACT: 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 (δ13C, δ15N, δ34S) 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 δ34S 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.

KEY WORDS: Benthic–pelagic coupling · Keystone species · Disturbed ecosystem · Feeding · Aequorea forskalea · Chrysaora fulgida

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Cite this article as: van der Bank MG, Utne-Palm AC, Pittman K, Sweetman AK, Richoux NB, Brüchert V, Gibbons MJ (2011) Dietary success of a ‘new’ key fish in an overfished ecosystem: evidence from fatty acid and stable isotope signatures. Mar Ecol Prog Ser 428:219-233.

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