Colonization of new nesting areas could provide climate refuge to loggerhead turtles under climate change

Climate change can impact regional and global biodiversity for multiple reasons. In sea turtles, changes in local climate at nesting beaches can affect egg and hatchling survival and primary sex ratios. Sea turtles could respond to climate change by occupying new nesting areas. The recent increase in sporadic nesting in the western Mediterranean may indicate colonization of new nesting beaches. We assessed the suitability of a western area, the Balearic Islands (similar to 1500 km from current nesting grounds) as climate refuge for loggerhead turtles (Caretta caretta) under current (2015-2017) and climate change scenarios to the mid (+40 years) and end (+80 years) of the 21st century. Using a correlative approach based on air and sand temperatures, we predicted nest temperatures and sex ratios for 19 beaches. Most beaches could provide viable temperatures and predominantly produce male hatchlings under all scenarios. Sex ratio projections were male-biased but with an increasing female ratio throughout time. Although mean sex ratio under the +80 years scenario was still male-biased, the warmest beaches could provide female-biased ratios, which are similar to those estimated for current nesting sites. The Balearic Islands could function as climate refuge for loggerhead turtles in the Mediterranean because temperatures could favor embryo viability and a male sex ratio. However, a nesting population may not be established until the percentage of female hatchlings increases and turtles return to nest as adults. Conditions at sea should also favor survival of hatchlings and juveniles. Because western Mediterranean beaches are popular tourist destinations, active management may be needed to protect nesting populations.