Extreme thermal conditions in sea turtle nests jeopardize reproductive output

The magnitude and frequency of extreme warming events over the last decades pose threats to biodiversity. In the near future, heatwaves will become even more frequent and longer-lasting. As ectothermic species, sea turtles are particularly vulnerable to climate change, with their reproductive success and offspring sex ratios dependent on in-nest conditions, particularly temperature. Here, we used field observations and climate model outputs (1) to examine impacts of extreme conditions on reproductive output and (2) to project thermal conditions within nest environments through the year 2100. Data were collected from 225 green turtle nests over 5 years (2009–2013) at Akyatan beach, Turkey, one of the most important nesting sites for this species in the Mediterranean. Our results suggest that green turtle eggs may demonstrate some resilience to rising temperatures if periods of temperature extremes are short. Declines in hatching success were observed only after conditions exceed the 33 °C thermal threshold for two-fifths of the incubation period. Under a moderate climate scenario (RCP 4.5), the number of days above lethal thresholds (i.e., 35 °C) would increase from 1% at the year that the study was conducted to 19.3% in 2100. Although sea turtles have survived through past climate changes, these projections raise concerns about future recruitment success and the persistence of sea turtle populations. Regular monitoring and determination of tipping points at local scales are required to inform conservation and management under global warming.