Estuaries and Coasts

, Volume 39, Issue 4, pp 1221–1233 | Cite as

Trophic Dynamics of the Cape Stumpnose (Rhabdosargus holubi, Sparidae) Across Three Adjacent Aquatic Habitats

  • L. CarassouEmail author
  • A. K. Whitfield
  • L. Bergamino
  • S. Moyo
  • N. B. Richoux


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.


Stomach contents Stable isotopes Connectivity SIAR Fish 



This study was funded by the Water Research Commission (WRC) of South Africa, the National Research Foundation (NRF) of South Africa, Rhodes University’s Sandisa Imbewu Initiative, and the South African Institute for Aquatic Biodiversity (SAIAB). This project received ethics clearance from Rhodes University (RU Ethics Clearance ZOOL-02-2012) and the South African Institute for Aquatic Biodiversity (SAIAB Ethics Clearance 2012/04). We thank Dr. Angus Paterson, Professor Paul Cowley, Mandla Magoro, Dr. Tatenda Dalu, and Bernadette Hubbart for their help with field and laboratory work. Dr. Bergamino is grateful to the CSIC-program “Contratación de Cientificos Provenientes del Exterior” for financial support.

Supplementary material

12237_2016_75_MOESM1_ESM.docx (26 kb)
ESM 1 (DOCX 25 kb)


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Copyright information

© Coastal and Estuarine Research Federation 2016

Authors and Affiliations

  • L. Carassou
    • 1
    • 2
    • 3
    Email author
  • A. K. Whitfield
    • 2
  • L. Bergamino
    • 1
    • 4
  • S. Moyo
    • 1
  • N. B. Richoux
    • 1
  1. 1.Department of Zoology and EntomologyRhodes UniversityGrahamstownSouth Africa
  2. 2.South African Institute for Aquatic BiodiversityGrahamstownSouth Africa
  3. 3.Labex COTE, Integrative and Theoretical Integrative Ecology ChairUniversity of BordeauxBordeauxFrance
  4. 4.Centro Universitario Regional Este (CURE)Universidad de la RepúblicaRochaUruguay

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