Abstract
Abstract In this study, multi-tissue (yolk and carapace) stable isotope analysis was used to assess individual isotopic niche trajectories of nesting green turtles on Rocas Atoll, off northeastern Brazil, and to reveal a diet shift in the temporal dimension. The diet trajectories of individual green turtles were highly directional, with a stronger component towards decreasing values of δ15N from carapace to yolk. When the green turtles are in their foraging sites (temporal window measured by the yolk samples), they are more herbivores. Conversely, in a broader temporal window, the green turtles demonstrate a carnivore-omnivore strategy, such as represented by heavier δ15N values in the carapace. This finding confirms a temporal diet shift. This is the first study that applies trophic niche trajectories for sea turtles, adding a new isotopic tool to understand the trophic ecology of these migrant animals.
Highlights
The green turtle (Chelonia mydas Linnaeus, 1758) is the only sea turtle species known to be herbivore after the individuals’ recruitment from oceanic to coastal waters (Bjorndal 1997)
Multi-tissue stable isotopes were used to assess the consistency of trophic niches of nesting green turtles over time
The stable isotope values used in this study, as well as the R script to calculate trajectory statistics and the randomization procedure are available as Supplementary material
Summary
The green turtle (Chelonia mydas Linnaeus, 1758) is the only sea turtle species known to be herbivore after the individuals’ recruitment from oceanic to coastal waters (Bjorndal 1997). Multi-tissue (yolk and carapace) stable isotopes were used to assess the consistency of trophic niches of nesting green turtles over time. This approach was adapted from Costa-Pereira et al (2019), whose study with dozens of populations and hundreds of individuals from tropical frogs’ species demonstrated the reliability of the trophic niche trajectories to measure the trophic consistency of individuals in a temporal scale. If the hypothesis of a consistent dietary pattern over time is supported, yolk and carapace isotope values will be similar, and variation in the individual trophic niche trajectories (lengths and angles) is not expected to differ from a random pattern of changes
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