Assessing nutritional needs in green sea turtles (Chelonia mydas) using fatty acid and stable isotope analyses

Green sea turtles (Chelonia mydas) are unique because hatchlings and pelagic juveniles are omnivorous/carnivorous, while older juveniles and adults are primarily herbivorous. Nutritional requirements at each life stage are... [ view full abstract ]

Green sea turtles (Chelonia mydas) are unique because hatchlings and pelagic juveniles are omnivorous/carnivorous, while older juveniles and adults are primarily herbivorous. Nutritional requirements at each life stage are poorly understood, making diet selection during rehabilitation of sick and injured animals challenging. Food items high in animal protein are often offered early in rehabilitation to combat poor appetite and emaciation, however this may result in gastrointestinal pathologies and potential obesity. Fatty Acid (FAA) and Stable Isotope Analyses (SIA) were utilized to understand the impact of diet on health and recovery of turtles undergoing rehabilitation. These assays are often paired to elucidate dietary strategies of animals, as signatures in predators represent prey consumed. Green sea turtles at the Georgia Sea Turtle Center (GSTC) were compared to healthy, free-ranging turtles from St. Lucie County, Florida. Plasma samples for FAA were collected from wild turtles (N=30) at a single time-point and from rehabilitation animals (N=27) at three time-points: admission, mid-rehab, and recovery, to reflect diets fed during these time periods. At admission, animals are fed higher animal protein diets (e.g. fish). At mid-rehab and recovery, they consume at least 25% and 75% vegetation, respectively. Palmitic (16:0) and oleic (18:1n9C) acids were the most abundant in all samples. Levels of omega-3 fatty acids, docosahexaenoic (22:6n3) and eicosapentaenoic (20:5n3), were higher in rehabilitation animals, likely reflecting a larger amount of fish in their diet than that of wild turtles. Skin samples for SIA were collected from rehabilitation animals (N=25) at admission. Values reflected a marine-based diet (δ13C = -15‰ to -18‰) spanning several trophic levels (δ15N = 6‰ to 12‰). This information will help identify feeding strategies of turtles presenting to rehabilitation centers, and will be used to make dietary modifications and develop gel-based diets for centers to enhance recovery and ensure optimal survival.