91 1. Abstract All sea turtles exhibit temperature-dependent sex determination, whereby warmer temperatures produce female-skewed primary sex ratios. This particular phenotypic plasticity jeopardizes their survival in a context of global warming, as temperature rises will increase the deficit of reproductive males, thus threatening the viability of populations in extreme cases. Nest temperature is affected by the geomorphology of nesting habitats, notably with a strong influence of substrate color. Yet, few studies have compared incubation conditions over a representative selection of nesting habitats found at the scale of nesting rookeries. Here, we investigate nest temperatures recorded in two nesting areas used by the same loggerhead turtle population in New Caledonia, South Pacific, yet showing contrasting nesting habitat characteristics. Coral-islet sites were significantly cooler than the coastal beach site (mean difference in temperature trends = 2.97°C). While the coastal site was predicted to produce almost exclusively female hatchlings, the sex ratios predicted in the coral-islet sites were relatively more balanced (12.5-52.3% depending on the model). As such, coral-islet habitats help sustain the production of males at the population scale, thus mitigating the deleterious effects of global warming on sex ratio. We therefore recommend a reinforcement of management and protective regulations for these insular nesting sites of high conservation priority. These results highlight the importance of comprehensive monitoring of nesting temperature conditions within sea turtle populations in order to inform conservation strategies. Keywords Sea turtles, global warming, sex ratio, TSD, feminization trend, nesting habitat, coral-islet, science-based conservation 2. Introduction Impacts of climate change on ecosystems and biodiversity is one of the most pressing ecological questions in recent decades (Malcolm et al. 2006; Bellard et al. 2012; Harnik et al. 2012; Rinawati et al. 2013; Legagneux et al. 2018; Malhi et al. 2020). Complex cascading effects have been highlighted in response to global warming, including species phenotypic plasticity and microevolution (Hulin et al. 2009; Richter et al. 2012; Oostra et al. 2018; Bonamour et al. 2019; Fuentes et al. 2024). These processes provide the potential for organisms to cope with environmental change, respectively through the production of distinct phenotypes to respond rapidly to short-term environmental variations (Przybylo et al. 2000; Réale et al. 2003; Charmantier et al. 2008), or through an adaptation occurring because of a genetic change in response to natural selection (Lane et al. 2018). For example, among vertebrates (Valenzuela and Lance 2004), sea turtles exhibit temperature-dependent sex determination (TSD), a mechanism by which the sex of the embryo is determined by immediate
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