Effect of rainfall on loggerhead turtle nest temperatures, sand temperatures and hatchling sex

Marine turtles deposit their eggs in underground nests where they develop unattended and without parental care. Incubation temperature varies with environmental conditions, including rainfall, sun/shade and sand type, and affects developmental rates, hatch and emergence success, and embryonic sex. We documented (1) rainfall and sand temperature relationships and (2) rainfall, nest temperatures and hatchling sex ratios at a loggerhead turtle (Caretta caretta) nesting beach in Boca Raton, Florida, USA, across the 2010 to 2013 nesting seasons. Rainfall data collected concurrently with sand temperatures at different depths showed that light rainfall affected surface sand; effects of the heaviest rainfall events tended to lower sand temperatures but the temperature fluctuations were small once upper nest depths were reached. This is important in understanding the potential impacts of rainfall as a modifier of nest temperatures, as such changes can be quite small. Nest temperature profiles were synchronized with rainfall data from weather services to identify relationships with hatchling sex ratios. The sex of each turtle was verified laparoscopically to provide empirical measures of sex ratio for the nest and nesting beach. The majority of hatchlings in the samples were female, suggesting that across the 4 seasons most nest temperatures were not sufficiently cool to produce males. However, in the early portion of the nesting season and in wet years, nest temperatures were cooler, and significantly more males hatched.