Diet composition of juvenile green turtles in the Southwestern Atlantic Ocean: long-term insights from a beach stranding program

Long-term diet studies provide information on the temporal variation in diet composition, habitat use, and foraging ecology of species. Assessment of dead-stranded sea turtles by stranding programs allows systematic diet sampling over a broad temporal scale, which can help elucidate potential ecological and environmental changes. Off the Southwestern Atlantic Ocean, the coast of Parana, Brazil, is an important foraging ground for juvenile green turtles Chelonia mydas. To determine seasonal and interannual diet variability, we analyzed the dietary contents of 351 dead-stranded individuals to the major taxa level from 2008 to 2020. We identified 13 major prey groups that made up green turtles' diets. A subset of turtles had diet identified to the lowest taxonomic level possible. Interannual differences were found, with the chlorophyte Ulva lactuca highly important in 2008 and 2011-2018, and Bivalvia and Gastropoda in 2016 and 2017. During La Nina events (2011, 2012, 2013, 2014, 2017, 2018, 2020), Chlorophyta, Mollusca, Crustacea, and Hydrozoa were the most frequently encountered diet items; during El Nino events (2015, 2016, 2019), Ochrophyta was the most consumed taxon. Seasonal differences were found, such that Echinodermata and Teleostei were important in autumn and winter, and Hydrozoa and Gastropoda in all seasons. Our results underscore individual dietary plasticity, including inter-seasonal and annual differences, which likely reflects the ability of green turtles to respond to changing prey availabilities and environmental characteristics driven by natural and perhaps anthropogenic influences. Understanding potential links between diet, habitat use, and the effects of a shifting diet and foraging grounds are key information for monitoring impacts and guiding conservation actions.