Stable isotope analysis indicates a lack of inter- and intra-specific dietary redundancy among ecologically important coral reef fishes

Jeremiah Grahm Plass-Johnson, Christopher D. McQuaid, Jaclyn M. Hill

Research output: Contribution to journalJournal articleResearchpeer-review


Parrotfish are critical consumers on coral reefs, mediating the balance between algae and corals, and are often categorised into three functional groups based on adult morphology and feeding behaviour. We used stable isotope analysis (delta C-13, delta N-15) to investigate size-related ontogenetic dietary changes in multiple species of parrotfish on coral reefs around Zanzibar. We compared signatures among species and functional groups (scrapers, excavators and browsers) as well as ontogenetic stages (immature, initial and terminal phase) within species. Stable isotope analysis suggests that ontogenetic dietary shifts occurred in seven of the nine species examined; larger individuals had enriched delta C-13 values, with no relationship between size and delta N-15. The relationship between fish length and delta C-13 signature was maintained when species were categorised as scrapers and excavators, but was more pronounced for scrapers than excavators, indicating stronger ontogenetic changes. Isotopic mixing models classified the initial phase of both the most abundant excavator (Chlorurus sordidus) as a scraper and the immature stage of the scraper Scarus ghobban (the largest species) as an excavator, indicating that diet relates to size rather than taxonomy. The results indicate that parrotfish may show similar intra-group changes in diet with length, but that their trophic ecology is more complex than suggested by morphology alone. Stable isotope analyses indicate that feeding ecology may differ among species within functional groups, and according to ontogenetic stage within a species.
Original languageEnglish
JournalCoral Reefs
Issue number2
Pages (from-to)429-440
Publication statusPublished - 2013
Externally publishedYes


  • Aquatic Science
  • δ13C
  • δ15N
  • Diet
  • Indian Ocean
  • Parrotfish
  • Resource partitioning
  • Zanzibar
  • adult
  • alga
  • coral reef
  • dietary shift
  • feeding behavior
  • feeding ecology
  • fish
  • morphology
  • niche partitioning
  • stable isotope
  • taxonomy
  • Tanzania
  • Zanzibar Island
  • algae
  • Anthozoa
  • Chlorurus sordidus
  • Pisces
  • Scaridae
  • Scarus ghobban
  • Ecology: environmental biology - General and methods
  • Ecology: environmental biology - Animal
  • Ecology: environmental biology - Oceanography
  • Animals, Chordates, Fish, Nonhuman Vertebrates, Vertebrates
  • species abundance
  • ontogenetic dietary change
  • dietary redundancy
  • FOOD
  • delta C-13
  • delta N-15
  • Life Sciences
  • Freshwater & Marine Ecology
  • Oceanography
  • Biomedical and Life Sciences

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