Coral Reefs

, Volume 35, Issue 2, pp 459–472

Reassessing the trophic role of reef sharks as apex predators on coral reefs

Authors

    • Australian Research Council Centre of Excellence for Coral Reef StudiesJames Cook University
  • Matthew Ireland
    • College of Marine and Environmental SciencesJames Cook University
  • Justin R. Rizzari
    • Australian Research Council Centre of Excellence for Coral Reef StudiesJames Cook University
    • College of Marine and Environmental SciencesJames Cook University
  • Oona M. Lönnstedt
    • College of Marine and Environmental SciencesJames Cook University
    • Department of Ecology and Genetics, LimnologyUppsala University
  • Katalin A. Magnenat
    • College of Marine and Environmental SciencesJames Cook University
  • Christopher E. Mirbach
    • College of Marine and Environmental SciencesJames Cook University
  • Jean-Paul A. Hobbs
    • Department of Environment and AgricultureCurtin University
Report

DOI: 10.1007/s00338-016-1415-2

Cite this article as:
Frisch, A.J., Ireland, M., Rizzari, J.R. et al. Coral Reefs (2016) 35: 459. doi:10.1007/s00338-016-1415-2

Abstract

Apex predators often have strong top-down effects on ecosystem components and are therefore a priority for conservation and management. Due to their large size and conspicuous predatory behaviour, reef sharks are typically assumed to be apex predators, but their functional role is yet to be confirmed. In this study, we used stomach contents and stable isotopes to estimate diet, trophic position and carbon sources for three common species of reef shark (Triaenodon obesus, Carcharhinus melanopterus and C. amblyrhynchos) from the Great Barrier Reef (Australia) and evaluated their assumed functional role as apex predators by qualitative and quantitative comparisons with other sharks and large predatory fishes. We found that reef sharks do not occupy the apex of coral reef food chains, but instead have functional roles similar to those of large predatory fishes such as snappers, emperors and groupers, which are typically regarded as high-level mesopredators. We hypothesise that a degree of functional redundancy exists within this guild of predators, potentially explaining why shark-induced trophic cascades are rare or subtle in coral reef ecosystems. We also found that reef sharks participate in multiple food webs (pelagic and benthic) and are sustained by multiple sources of primary production. We conclude that large conspicuous predators, be they elasmobranchs or any other taxon, should not axiomatically be regarded as apex predators without thorough analysis of their diet. In the case of reef sharks, our dietary analyses suggest they should be reassigned to an alternative trophic group such as high-level mesopredators. This change will facilitate improved understanding of how reef communities function and how removal of predators (e.g., via fishing) might affect ecosystem properties.

Keywords

Elasmobranch Food web Stable isotope analysis Top-down control Trophic ecology

Supplementary material

338_2016_1415_MOESM1_ESM.tif (11.9 mb)
Fig. S1 Relationship between δ13C (a–c), δ15N (d–f) and total length in (a, d) Triaenodon obesus, (b, e) Carcharhinus melanopterus and (c, f) C. amblyrhynchos. Other species are not included due to small sample sizes. Statistically significant relationships are depicted by regression lines (TIFF 12221 kb)

Copyright information

© Springer-Verlag Berlin Heidelberg 2016