The thermal impacts of beach nourishment across a regionally important loggerhead sea turtle (Caretta caretta) rookery

Abstract

Beach nourishment is a common coastal management practice used to protect and maintain infrastructure, tourist revenue, and sandy beach habitats. Coastal erosion and increased development along the coast of North Carolina, USA, have resulted in increased use of beach nourishment as an environmentally friendly alternative to hard structures, such as groins and jetties. Despite its advantages, beach nourishment can alter the thermal properties of a beach, potentially impacting the incubation environment of species that utilize this habitat during reproduction. Importantly, in organisms with temperature-dependent sex determination, the incubation environment plays a key role in determining offspring sex ratios, hatchling survival, and fitness. Here we investigate how beach nourishment influences thermal properties and sand characteristics of eight beaches in the high-density loggerhead sea turtle (Caretta caretta) nesting region of North Carolina. We find that, despite considerable spatial and temporal variation, nourishment is a significant predictor of mean monthly sand temperatures in both univariate and multivariable predictive models. Across a season, nourished beach sections are, on average, 0.4°C (range 0.3–0.8°C) warmer than their unnourished counterparts. Nourishment is also a significant predictor of the mean and variance of sand grain size. Furthermore, variation in mean grain size, the relative percent of small, medium and large grain sizes and albedo are mainly responsible for differences in mean monthly sand temperatures. As such, the coarser and darker sand often used in nourishment projects may exacerbate climate driven increases in surface temperature.