Improving stable isotope assessments of inter- and intra-species variation in coral reef fish trophic strategies
Jonathon D. Cybulski1,2, Christina Skinner3, Zhongyue Wan2, Carmen K. M. Wong4, Robert J. Toonen5, Michelle R. Gaither6, Keryea Soong7, Alex S.J. Wyatt3, David M. Baker1,2
1The Swire Institute of Marine Science, The University of Hong Kong, Shek O, Hong Kong. 2School of Biological Sciences, The University of Hong Kong, Pok Fu Lam, Hong Kong. 3Department of Ocean Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong. 4State Key Laboratory of Marine Pollution, City University of Hong Kong, Kowloon, Hong Kong. 5Hawaii Institute of Marine Biology, School of Ocean & Earth Sciences & Technology, University of Hawaii at Manoa, Kaneohe, Hawaii, USA. 6Department of Biology, University of Central Florida, Orlando, Florida, USA. 7Department of Oceanography, National Sun Yat-sen University, Kaohsiung, Taiwan.
Fish have one of the highest occurrences of individual specialization in trophic strategies among Eukaryotes. Yet, few studies characterize this variation during trophic niche analysis, limiting our understanding of aquatic food web dynamics. Stable isotope analysis (SIA) with advanced Bayesian statistics is one way to incorporate this individual trophic variation when quantifying niche size. However, studies using SIA to investigate trophodynamics have mostly focused on species- or guild-level (i.e., assumed similar trophic strategy) analyses in settings where source isotopes are well-resolved. These parameters are uncommon in an ecological context. Here, we use Stable Isotope Bayesian Ellipses in R (SIBER) to investigate cross-guild trophodynamics of 11 reef fish species within an oceanic atoll. We compared two- (δ15N and δ13C) versus three-dimensional (δ15N, δ13C, and δ34S) reconstructions of isotopic niche space for interpreting guild-, species-, and individual-level trophic strategies. Reef fish isotope compositions varied significantly among, but also within, guilds. Individuals of the same species did not cluster together based on their isotope values, suggesting within-species specializations. Furthermore, while two-dimensional isotopic niches helped differentiate reef fish resource use, niche overlap among species was exceptionally high. The addition of δ34S and the generation of three-dimensional isotopic niches were needed to further characterize their isotopic niches and better evaluate potential trophic strategies. These data suggest that δ34S may reveal fluctuations in resource availability, which are not detectable using only δ15N and δ13C. We recommend that researchers include δ34S in future aquatic food web studies.