Global review and inventory: how stable isotopes are helping us understand ecology and inform conservation of marine turtles

Stable isotope analysis (SIA) has become a powerful and widely utilised tool in ecological studies, and more specifically has been used to answer conservation questions regarding key marine indicator species including marine turtles. Undertaking an exhaustive review of peer-reviewed literature, we summarise the current knowledge of marine turtle spatial, foraging, and reproductive ecology gained through stable isotope studies and highlight the considerable flexibility and ecological complexities in the life histories of the six species that have been studied. We demonstrate how SIA can inform conservation initiatives, identify threats faced, and provide pre-and post-disaster information that is otherwise unavailable. We summarise isotope ratios at a global scale and demonstrate intraspecific regional differences and interspecific overlap. We identify the geographical gaps in the current knowledge and the bias in the species studied. To facilitate future research we identify a comprehensive list of recommendations including the need for standardised protocols for tissue collection and analysis; the use of a third forensic marker to provide greater power of inference; combining complementary techniques to enhance the information gained; conducting long-term research; and a need for meta-analytic approaches to combine research findings to better understand the complexities of marine turtle ecology. This review provides a complete list of all published marine turtle stable isotope studies which are summarised in an open access inventory to enable researchers to add new studies and target future work.