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Stable isotope analysis reveals trophic diversity and partitioning in territorial damselfishes on a low-latitude coral reef


Investigating the niche overlap of ecologically similar species can reveal the mechanisms that drive spatial partitioning in high-diversity systems. Understanding how food resources are used and whether the diets of neighboring species are different are particularly important when considering the coexistence and functional role of species. Territorial damselfish on coral reefs are considered to be herbivores that defend algal mats from other food competitors. However, this guild contains numerous small species whose functional role and dietary diversification is poorly understood. Here, the relationships between diet and spatial distribution of seven intermediate-sized territorial damselfishes at Kimbe Bay, Papua New Guinea (5°30′S, 150°05′E) were investigated. These species partition habitat across three reef zones with distinct patterns of fine-scale distribution. It was predicted that neighboring species partition food resources with minimal dietary overlap. Examination of isotope ratios of carbon and nitrogen delineated three distinct feeding strategies: pelagic, reef-based, and an intermediate group feeding on both prey types. None of the species appear to be strict herbivores. Adjacent species exhibited high–intermediate trophic niche partitioning when examining pelagic versus reef-based production sources, with two species previously described as benthic herbivores exhibiting pelagic feeding. The study demonstrates that diet reinforces the patterns of spatial partitioning and coexistence among ecologically similar damselfishes. These findings add to a growing view that interspecific differences among similar species are lost when categorizing species into broad functional classifications, and that previous studies suggesting that territorial damselfish are strictly reef-based feeders may not be applicable in all systems or for all species.

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We are grateful to the traditional owners of the Tamare-Kilu reefs for allowing access to the reefs and welcoming us; S. Shomaker for her assistance in the field and laboratory; L. Boström-Einarsson, C. MacDonald, A. Paley, K. Mcmahon, T. Hempson, and D. Williamson for thoughtful discussions; and Mahonia Na Dari Research and Conservation Centre and Walindi Plantation Resort for logistical field support for the duration of the project. The manuscript greatly benefited from the input of two anonymous reviewers.


This project was funded by the Australian Research Council through the Centre of Excellence for Coral Reef Studies, and the College of Science and Engineering, James Cook University.

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JGE, RB, MIM, and GPJ conceptualized and designed the study. JGE conducted the field sampling, data collection, and sample preparation. JKM performed statistical analysis. JGE and JKM interpreted the data and prepared the figures. JGE wrote the manuscript text. All authors reviewed the manuscript and gave final approval of the submitted version.

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Correspondence to J. G. Eurich.

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All authors declare that they have no conflict of interest.

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All work carried out herein was in accordance with the James Cook University Animal Ethics Guidelines (JCU Animal Ethics approval A2106).

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Eurich, J.G., Matley, J.K., Baker, R. et al. Stable isotope analysis reveals trophic diversity and partitioning in territorial damselfishes on a low-latitude coral reef. Mar Biol 166, 17 (2019).

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