Using empirical and mechanistic models to assess global warming threats to leatherback sea turtles

Abstract

Global warming may pose a greater risk to species with unique thermal require- ments during each life stage than species with a similar thermal requirement throughout all life stages. The risk to the former is higher because their unique thermal ranges may become geo- graphically or temporally discontiguous. Additionally, modeling global warming's effects on these species is challenging due to their multiple thermal requirements. We explore these issues using leatherback sea turtles Dermochelys coriacea as a study species. The gigantothermy of adult leatherbacks and their subterranean egg incubation means global warming will differentially affect adults and eggs. To assess the unique thermal requirements in each life stage we used 2 dis- tinct modeling approaches: (1) a mechanistic biophysical/physiological model to assess threats to adult leatherbacks, and (2) Bayesian regression with a mechanistic microclimate model to assess threats to leatherback eggs. We combined these models with a comprehensive literature search and a global climate model to establish the future thermal threats to the egg and adult leatherback life stages at 3 major rookeries (Gabon, French Guiana, and West Papua). We found that adult internesting and nesting core temperatures will not rise above the critical thermal maximum; however, at 2 of the 3 sites, adult core body temperatures will rise above the point where hatch- lings experience uncoordinated movement. We also found that increased temperatures will greatly reduce success rates of egg clutches in West Papua and Gabon by the end of the 21st century.