Improving rehabilitation outcomes using metabolomics: Health, recovery and biomarkers of mortality in sick and injured green turtles (Chelonia mydas)

Sea turtles are listed in threatened categories at national and international levels. Hundreds of sick and injured turtles are admitted to rehabilitation clinics annually, where recovery and release are important aspects of their conservation and management. There is considerable interest in establishing biochemical markers to gauge the health of sea turtles, and as diagnostic tools to facilitate informed decision-making about overall care and specific treatment needs during rehabilitation. We applied untargeted metabolomics to monitor the health of 28 green turtles (Chelonia mydas) admitted to a rehabilitation clinic in eastern Australia between October 2018 and April 2019. Malnutrition and ketosis were identified as major physiological manifestations in sea turtles entering rehabilitation. Specifically, decreased branch-chain (leucine, isoleucine and valine) and aromatic amino acids (tyrosine, phenylalanine and tryptophan) were observed at admission, along with increases in the ketogenic metabolite 3-hydroxybutyric acid and metabolites associated with peroxisomal disorders (pipecolic acid and beta-alanine). Receiver Operating Characteristic (ROC) analysis comparing successfully rehabilitated animals with those that died identified a suite of metabolites that were predictive of mortality. Results suggest that, regardless the source of injury or illness, a major cause of sea turtle mortality during rehabilitation relates to severe malnutrition that ultimately manifests as sepsis-induced metabolic failure. This showcases the strength of metabolomics for monitoring sea turtle health and informing care and management during rehabilitation. More broadly, this serves as a compelling case-study highlighting that advanced molecular analytical techniques are well positioned to play an important role in various aspects of veterinary medicine and conservation science.