Resolving the Diet of Nesting Green Turtles in the Northeastern Red Sea

Abstract Stable isotope analysis of green turtle ( Chelonia mydas ) scutes provides insights into long-term dietary patterns (~ 6.5 years). We analysed δ¹³C and δ¹⁵N values from nesting turtles in the Red Sea and combined these with macrophyte isotope data from the literature. Bayesian mixing models estimated dietary contributions by habitat and taxa. Seagrass meadows were the dominant inferred carbon source, contributing 90.1 ± 4.7%, with seagrass taxa contributing 92.3 ± 3.8%. Among available sources, Cymodocea sp and Enhalus acoroides showed the highest estimated contributions (43.5 ± 13.1% and 24.0 ± 8.6%, respectively), although source overlap and literature-derived baselines limit species-level resolution. These results should therefore be interpreted as consistent with, rather than definitive evidence of, species-specific dietary dominance. Gaussian mixture modelling identified two foraging clusters: “Close” and “Distant.” Distant foragers travelled farther ( F = 67.44, P < 0.001) and were smaller ( F = 36.63, P < 0.001). δ¹⁵N differed between clusters ( F = 4.82, P = 0.034), while δ¹³C showed a non-significant trend ( F = 3.71, P = 0.061). Because isotope baselines were derived from literature, temporal and spatial mismatch constrains inference about current ecosystem condition. These findings are therefore hypothesis-generating and provide a foundation for future field-validated studies of trophic ecology in the Red Sea.