Brevetoxicosis in loggerhead (Caretta caretta) and Kemp's ridley (Lepidochelys kempii) sea turtles: Plasma proteomics for Florida red tide biomarkers.

Sea turtles are among the many wildlife species adversely affected by Florida red tide, Karenia brevis. This marine dinoflagellate blooms almost annually along Florida's west coast and produces brevetoxins, a suite of potent neurotoxins. Brevetoxins can reach carnivorous loggerhead and Kemp's ridley sea turtles via aerosols and marine food webs, leading to multi-system physiological effects. Sea turtles stranded during red tide can be rescued, transported to rehabilitation facilities, and given palliative care with the goal of return to the wild. However, there are no definitive diagnostic criteria for brevetoxicosis other than stranding in association with red tide. Often sea turtles experience delayed exposure due to the long temporal scale of trophic transfer of toxins. To identify exposure biomarkers and to better understand the mechanism of toxicity of brevetoxins, plasma samples from red-tide exposed and healthy loggerhead and Kemp's ridley sea turtles were analyzed via bottom-up TMT-labeled quantitative liquid chromatography tandem mass spectrometry-based proteomics. Multiple sea turtle plasma protein abundances were significantly altered in red tide exposed turtles, including several immune system proteins like serum amyloid A5 (SAA-5; loggerheads) and CD160 antigen (Kemp's ridley). Pro-inflammatory markers serum amyloid A (SAA) and myeloid-related protein 126 (MRP-126) were measured independently in plasma of loggerhead turtles, with significant increases in these markers with red tide toxin exposure. The two species also differed in their proteomic response to red tide, indicating distinct biomarker candidates. Amid intensifying red tide events and the endangered status of these species, our findings provide a foundation for biomarker-based diagnosis of brevetoxicosis in sea turtles.