Effects of In Situ Incubation Temperatures on Hatchling Loggerhead Sea Turtle (Caretta caretta) Morphology, Health Indices, and Locomotor Performance

Incubation temperatures, in addition to an embryo’s genetic makeup, play crucial roles in development and alter a variety of characteristics in sea turtle embryos. Atmospheric temperatures are currently predicted to rise at least 1.5°C above preindustrial levels by 2052, potentially impacting embryonic development. Most sea turtle temperature studies document the effects of “high” and “low” incubation temperatures in laboratory-reared nests. This study’s objective was to examine impacts of varying in situ incubation temperatures on loggerhead sea turtle (Caretta caretta) hatchling morphology, health, and locomotor performance. Temperature data loggers were deployed in 15 individual loggerhead nests on Juno Beach, Florida between June and August 2018. In total, 144 hatchlings were measured and sampled. Carapacial scute abnormalities, mass, and morphological measurements (straight carapace length (SCL), straight carapace width (SCW), body depth (BD), front flipper length (FFL), umbilical scar length, and umbilical scar width) were taken. Heart rate was measured using a portable ultrasound and blood was collected to analyze for glucose, packed cell volume, hemoglobin, total solids, and white blood cell estimates with differentials. Lastly, righting response in water was tested. After mass emergence, 14 nests were excavated to identify hatching success and developmental stage of unhatched eggs. Unsurprisingly, incubation temperatures were significantly lower in May compared to June and July. The results of the KruskalWallis and Pearson’s Chi-squared tests indicated that warmer months resulted in higher vi values in umbilical scar size and abnormal scutes present, slower righting time, increased levels of several blood health analytes, and a higher number of unhatched embryos at full-term. The results of the linear regression and Kruskal-Wallis tests corroborate previous studies on hatchlings in laboratory-reared nests, with increasing temperatures resulting in smaller hatchling size (SCL, SCW, BD, FFL) and slower righting time. I suggest possible lower survival rates in hatchlings from warmer nests due to increased risk of predation from smaller body sizes, decreased physical responses, altered hemodynamic balance (e.g., dehydration) and potential inflammation due to increased temperatures. Furthermore, the higher number of unhatched embryos at full-term in warmer nests may indicate nest temperatures that are exceeding their lethal limit resulting in egg mortality. This study adds novel health reference intervals for loggerhead hatchlings and demonstrates that even sublethal increases in sand temperatures will likely affect sea turtle hatchling health and have the potential to negatively impact hatchling survival