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Final Report Summary - SEATURTLES (Climate change and sea turtles)

Climate Change and Sea Turtles

Summary Report. Climate change is impacting ecosystems and organisms around the world and can affect sea turtles in various ways. Sea level rise can result in loss of suitable nesting area, populations may become increasingly feminized because sea turtles have temperature-dependent sex determination (TSD), and reproductive output can be reduced because high temperature increase mortality of eggs and hatchlings. Past studies, showed that prevailing climatic conditions affected egg development and hatchling production in leatherback turtles (Dermochelys coriacea) in Pacific Costa Rica. In our research plan we proposed to expand the study done in Costa Rica to analyze the global effects of climatic conditions on several leatherback turtle populations and to test the effects of climate and climate change on other sea turtles that nest in the region.
During the two years of the fellowship we have contributed to make advances in the field of climate impacts on sea turtles and the role that some adaptations may play under climate change scenarios. We expanded the original research plan to explore evolutionary aspects related to TSD. In particular, we developed a theoretical framework to explain the adaptive significance of TSD under natural climate fluctuations.
1 - Development of a global leatherback hatchling output model. We obtained local climate and hatchling output data from different nesting sites located in the Pacific (Costa Rica), Atlantic (St. Croix and Costa Rica) and Indian (South Africa) Oceans. We obtained climate projections for each site under the IPCC SRES A2 emissions scenario throughout the 21st century. We found a heterogeneous effect of climate on the hatchling output of leatherback turtles. High levels of precipitation increased production of hatchlings in dry areas, but not in wet areas, and there was a detrimental effect of high temperature only in areas experiencing droughts. Air temperature was projected to increase at all sites by the end of the 21st century, but precipitation showed a mild decrease. Due to the heterogeneous effect of climate, some populations may become locally extinct by the end of the 21st century but others may survive. The results of this study were accepted for publication in Scientific Reports after minor changes were addressed and were presented at the International Sea Turtle Symposium in 2015.

2 - Development of hatchling output models for sea turtles in Central America
We obtained data on temperatures and hatching success from olive ridley (Lepidochelys olivacea), green (Chelonia mydas) and leatherback turtle nests from the same general area of Costa Rica. We compared the thermal conditions in the nest environment (daily fluctuation in temperature, seasonal fluctuation in temperature and mean temperature). Thermal conditions in the nest environment increased in stability with depth and affected hatching success and the Transitional Range of Temperature (TRT) over which both sexes are produced. The results of this study have been drafted in a manuscript.
3 - Projected sea turtle population response to climate change
We built a population model based on the characteristics of the leatherback population that nest in Costa Rica. We reconstructed historical nest temperatures based on the relationship between air temperature and nest temperature. We run simulations for a population that was stable under (1) current temperatures or (2) historical temperatures, and tested population responses to increasing nest temperatures. We tested the adaptive significance of temperature-dependent sex determination (TSD) by allowing sex ratios to change with temperature, or maintaining sex ratios fixed as if turtles had genotypic sex determination (GSD). Finally, we assessed the effectiveness of TSD as a mechanism to maintain populations under climate change scenarios. TSD provided an evolutionary advantage to sea turtles. TSD populations were more resilient to increased nest temperatures and mitigated the negative effects of high temperatures by increasing production of female offspring and future fecundity. TSD was an effective mechanism to counteract the negative effects of temperatures, but will become inefficient as these rise to levels projected by current climate change models. The results of this study were published in Global Change Biology and were highlighted in Nature Climate Change.
Some of the results obtained during the fellowship have been published or accepted for publication in Biological Conservations, Global Change Biology, PLoS ONE and Scientific Reports. Additionally, we will write a follow-up manuscript on the role that TSD can play in other sea turtle species under climate change scenarios. We have presented our results at two international symposiums, have facilitated the information to the local authorities in Costa Rica and have incorporated European students into our field projects.

Related information

Reported by

AGENCIA ESTATAL CONSEJO SUPERIOR DE INVESTIGACIONES CIENTIFICAS
Spain
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