Ontogenetic diet shifts of green sea turtles (Chelonia mydas) in a mid-ocean developmental habitat
Green sea turtles (Chelonia mydas) arrive on the geographically isolated Bermuda platform as small juveniles and remain until they are approaching sexual maturity, at which point individuals depart for distant feeding and nesting sites. It has been reported that younger green turtles generally tend to carnivory or omnivory and that seagrasses become a significant food source as the turtles grow. Evidence indicates that grazing by green sea turtles in Bermuda is negatively impacting seagrass beds, thus understanding their diets is important to both conserving the turtles and their food. Stable isotope methods were used to investigate ontogenetic diet shifts of green sea turtles and to determine reliance on seagrass by larger turtles. Skin samples from 157 individual turtles and samples of known turtle foods, plants and animals, were collected for determination of consumer and food δ13C and δ15N values. A Bayesian stable isotope mixing model analysis indicated a wide range among individual turtles’ diets, with the greatest differences occurring between small and large turtles; larger turtles consumed seagrass almost exclusively. We also examined diet changes in 12 turtles captured in two successive years; these recapture data confirmed the changes in diet suggested by the relationship between size of turtles and diet composition. Very limited evidence was found of any diet variation among larger turtles that would indicate a shift away from declining seagrasses as their major food source.
We thank A.B. Meylan, P.A. Meylan, Jennifer Grey, and the rest of the Bermuda Turtle Project, for allowing us to join them in their turtle capturing trips and sharing data with us. Rachel Decker processed samples in the laboratory. The Department of Conservation Services (now the Department of Environment and Natural Resources) of the Government of Bermuda provided logistics and financial support for this work. This is contribution number 66 of the Marine Education Research Center in the Institute for Water and Environment at Florida International University and contribution number 264 of the BBP series at the Bermuda Department of Environment and Natural Resources library.
Compliance with ethical standards
Research involving human/animal participants
This work complied with all applicable national and international standards for the care and use of animals. Research was conducted with authorization from FIU’s IACUC #11-019, and importing and exporting of turtle samples was done under CITES permits 12BM0025 and 12US88774A/9.
Conflict of interest
The authors declare that they have no conflicts of interest.
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