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Marine Ecology Progress Series

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MEPS 641:195-208 (2020)  -  DOI:

Spatial trophic variability of a coastal apex predator, the giant trevally Caranx ignobilis, in the western Indian Ocean

Jessica R. Glass1,2,*, Ryan Daly2,3, Paul D. Cowley2, David M. Post1

1Yale University, Department of Ecology and Evolutionary Biology, New Haven, Connecticut 06520, USA
2South African Institute for Aquatic Biodiversity, Grahamstown 6140, South Africa
3Oceanographic Research Institute, Marine Parade, Durban 4056, South Africa
*Corresponding author:

ABSTRACT: Top predators have substantial downstream effects on the structure, function, and resilience of ecosystems. The influence of top predators on an ecosystem can vary if they occur within multiple habitat types and have a wide niche breadth due to spatiotemporal changes in diet. We examined spatial patterns in trophic position and niche width for an economically important reef-associated fishery species, the giant trevally Caranx ignobilis. We sampled 4 localities in the western Indian Ocean representing different habitats: coral atolls, coastal reefs, and granitic islands. We analyzed isotopic ratios of carbon (13C/12C) and nitrogen (15N/14N), and performed compound-specific amino acid stable isotope analysis (AA-CSIA) to control for baseline nitrogen variation. Our analysis of 12 juveniles and 43 adults revealed wide variation in trophic niche breadth between sampling sites and an offshore to coastal gradient in carbon that drove niche distinctiveness between localities. We observed niche width patterns suggestive of ontogenetic changes in diet and habitat utilization and larger niche sizes at the oceanic island sites than the coastal site. Trophic position estimates ranged from 3.5-5, expanding the trophic range of C. ignobilis relative to previous studies using AA-CSIA and placing it at the equivalent trophic level as many predatory sharks. Our study corroborates prior evidence that C. ignobilis is an important apex predator in reef and island ecosystems. Additionally, we show how evaluating spatiotemporal components of trophic ecology of marine predators is critical for characterizing their functional role and ecosystem influence, allowing for targeted conservation efforts.

KEY WORDS: Compound-specific stable isotope analysis · Amino acids · Reef fishes · Apex predators · Trophic position · Trevally

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Cite this article as: Glass JR, Daly R, Cowley PD, Post DM (2020) Spatial trophic variability of a coastal apex predator, the giant trevally Caranx ignobilis, in the western Indian Ocean. Mar Ecol Prog Ser 641:195-208.

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