The climatic debt of loggerhead sea turtle populations in a warming world

Abstract Phenologicalshifts, by initiating reproductive events earlier, in response to advanced seasonal warming is one of the most striking effects currently observed in wild populations. For sea turtles, phenologicaladjustment to warming conditions could be the most effective short-term adaptation option against climate change. We calculated future phenologicalchanges required in seven important loggerhead (Caretta caretta) nesting populations to continue achieving a high hatching success and a sex ratio that lies within current ranges. Considering temperature-mediated phenologicalchanges, we found that most populations (six out of seven) will not be able to keep pace with a warming climate. Under an optimistic climate warming scenario (RCP4.5), these populations will face a climatic debt, that is, a difference between required and expected phenologicalchanges, and warming will substantially reduce hatching success and induce a feminization of hatchlings, which may jeopardize their reproductive sustainability. Our approach offers the possibility to quantify the efficiency of phenologicalshifts in oviparousreptiles by considering physiological, developmental and phenologicalprocesses.