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Diet and foraging niche flexibility in green and hawksbill turtles

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Abstract

We used stable isotopes to investigate isotopic niche size, overlap, and diet composition in green (black and yellow morphotype Chelonia mydas; 50.0 to 95.0 cm curved carapace length, CCL) and hawksbill turtles (Eretmochelys imbricata; 38.5 to 83.0 cm CCL) in a recently described foraging habitat in North Pacific Costa Rica. We measured whole blood stable carbon (δ13C) and nitrogen (δ15N) ratios in black (n = 39; mean ± SD, − 16.54 ± 0.66‰ and 14.39 ± 0.77‰), yellow (n = 13; − 15.74 ± 0.65‰ and 12.37 ± 0.55‰) and hawksbill turtles (n = 13; − 16.23 ± 1.34‰ and 12.63 ± 0.32‰) and skin δ13C and δ15N values in black (n = 36; − 15.32 ± 0.79‰ and 15.16 ± 0.72‰), yellow (n = 12; − 15.38 ± 0.91‰ and 13.78 ± 0.75‰) and hawksbill turtles (n = 10; − 14.33 ± 1.49‰ and 13.77 ± 0.29‰). Isotopic niche space revealed distinctly higher δ15N area in black turtles and significant overlap between yellow and hawksbill turtles, and a recent shift in diet in yellow turtles from omnivory to herbivory. In black turtles, isotopic niche suggests individual specialization during the non-upwelling season and generalization in diet during the upwelling season. Mixing model results suggest that black turtles forage at multiple trophic levels (fish: 34.8 ± 10.1% of diet and macroalgae: 51.8 ± 12.8% of diet), while yellow and hawksbill turtles primarily forage on macroalgae (85.0 ± 6.6% in yellow turtles and 85.1 ± 5.9% in hawksbill turtles). These results add to a growing understanding that diet in sea turtles is influenced by diet items present in the environment and suggest that black turtles are potential tertiary consumers.

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Availability of data and materials

Data are available through a data repository. Link: https://purr.purdue.edu/publications/3863/1. doi: 10. 4231/CDAK-5N56.

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Acknowledgements

We would like to thank K. Mora, R. Mora, M. Mora, A. Lara, M. Giry and all the volunteers with Equipo Tora Carey for their assistance in the field and support in Costa Rica, F. Albertazzi for facilitating laboratory assistance at the University of Costa Rica, Drs. P. Ruhl and J. Berl, and C. Kent-Dotson for their assistance with data analysis, and Drs. J. Spotila and R. Goforth for reviewing this manuscript. We would also like to thank the Stable Isotope Facility at the University of Wyoming for their assistance with sample analysis. This project was financially supported by The Leatherback Trust, Equipo Tora Carey and the USDA National Institute of Food and Agriculture, Hatch Project 1019737 (to EAF).

Funding

This project was funded by the Department of Forestry and Natural Resources at Purdue University, The Leatherback Trust, and by the USDA National Institute of Food and Agriculture Hatch Project 1019737 (to EAF).

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All the authors contributed to study design. Data collection was performed by CEC-B and MH. Sample processing and data analyses were performed by CEC-B and EAF. The first draft of the manuscript was written by CEC-B and all the authors commented on previous versions of the manuscript. All the authors read and approved the final manuscript.

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Correspondence to Chelsea E. Clyde-Brockway.

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The authors declare that they have no conflict of interest.

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This research was conducted under approval by the Guanacaste Conservation Areas (ACG) of the Ministry of Environment of Costa Rica (ACG-PI-PC-019, R-ACG-057-2016), USFWS (CITES permit 17US06369C/9) and the Purdue Animal Care and Use Committee (protocol #1510001309).

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Clyde-Brockway, C.E., Heidemeyer, M., Paladino, F.V. et al. Diet and foraging niche flexibility in green and hawksbill turtles. Mar Biol 169, 108 (2022). https://doi.org/10.1007/s00227-022-04092-1

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