Trophic ecology of juvenile green turtles in the Southwestern Atlantic Ocean: insights from stable isotope analysis and niche modelling

Abstract

Determining the diet and trophic status of endangered species can provide insights into their key habitats and predator-prey relationships, both essential for conservation. Integrating dietary information from live-captured and dead-stranded turtles from the same area can also shed light on their ecological diversity. Here, diet intake and prey diversity are determined for juvenile green turtles Chelonia mydas from a mixed stock foraging aggregation in the Southwestern Atlantic Ocean (SWAO) using stable carbon (δ13C) and nitrogen (δ15N) isotope analysis. Skin samples were collected from 117 live-captured (LC) turtles and 66 dead-stranded (DS) individuals along the Paraná coast, southern Brazil. Bayesian isotope ellipse space was determined using the program SIBER. A larger isotopic niche space was found among DS turtles, probably because it included long-term resident turtles and recently settled individuals, the latter of which presented low δ15N values compared to larger putative local turtles. The Bayesian stable isotope mixing model MixSIAR was used to determine dietary contributions, using isotopic values of putative prey. MixSIAR results indicated invertebrates and macroalgae as primary prey groups, showing the omnivorous strategy of green turtles in the SWAO. Moreover, many of the smallest DS turtles had δ15N values suggestive of seagrass consumption, which may reflect individual- and/or life-stage-based diet variability. These findings underscore the value of integrating stranding monitoring protocols with research on live green turtles to evaluate habitat use and diet intake assembled in a neritic foraging area. The data also further knowledge about green turtle foraging ecology and are relevant for species and habitat conservation throughout the SWAO.