An application of finite element analysis predicts unique temperatures and fates for flatback sea turtle embryos

Incubation temperatures within sea turtle nests are governed by complex abiotic and biotic interactions. Established methods for estimating these temperatures include deploying temperature loggers at standard nest depths or using models to predict sand temperature. While these approaches capture abiotic drivers of incubation temperatures, they often fail to fully account for biotic factors, including the heat produced by the metabolism of embryos, despite its potential impact on hatchling development and mortality. Here, we applied finite element analysis to predict incubation temperatures for all embryos in five flatback sea turtle (Natator depressus) nests. To parameterise the models, we measured clutch size, nest depth, temperatures at several locations around nests, and the physical properties of beach sand, including density and moisture. Next, we simulated within-nest temperatures with an energy balance model that accounted for metabolic heat by applying an hourly heat flux, based on modelled embryonic metabolic rates, to each egg. Each model was validated by comparing predicted temperatures with observed temperatures at the base, centre and top of each clutch. On average, finite element models achieved good accuracy to within 0.4°C of observed data (mean error over the entire incubation period). By incorporating individual clutch size, nest depth and the metabolic contributions of embryos, our approach enhances the realism of temperature estimates for predicting the embryonic development of sea turtles, which is of increasing importance under rapid climate change.