Saving the Sea Turtles: How Climate Change Affects Loggerhead Populations
DeLorenzo, Lauren; Jackson, Samantha; Ring, Katherine; Sutton, Allison
An ample amount of research has been conducted on how nest temperatures affect the sex of sea turtle hatchlings, but little has been done on how heat transfer contributes to the temperature. For the purpose of determining if heat transfer could be modeled, Loggerhead sea turtles (Caretta caretta) in Southern Florida were examined. Further analysis of nest temperature under conditions associated with climate change can predict potential effects in the future on Loggerhead and other sea turtle populations. This paper assumes that research and modeling of the heating process can lead to a better understanding of what contributes to nest temperature. The nest was approximated as one spherical homologous domain with weighted egg and air properties, located at 0.35 m below the surface of the sand. Conditions affecting temperature of the nest include solar radiation on the sand, convective heat transfer at the surface of the sand, and metabolic heat generation in the eggs. Hourly weather data from locations in Southern Florida was collected and used to simulate a varying boundary condition at the sand surface from air temperature, wind speed, and solar radiation. Metabolic heat generation from the eggs was based on data from another species of sea turtle. Two-dimensional axisymmetric heat conduction through the sand and nest was modeled using the commercial analysis software COMSOL Multiphysics. The model was validated by comparing the resulting Loggerhead nest temperature over time with experimental data from another location in Florida. Analysis of parameter sensitivity was conducted by varying the density, specific heat, and thermal conductivity of both the egg mass and sand. Changes in all of these parameters by 20% produced negligible effects on nest temperature. Varying the heat transfer coefficient to reflect the minimum and maximum air temperatures found in Southern Florida did not have a noticeable impact on nest temperature. Sensitivity of solar radiation was considered in applying shading conditions. The model was also used to predict potential effects from climate change by varying the top boundary condition. The model was used to observe how variation of environmental conditions, especially the projected increase of temperature due to climate change, affects the model and destabilizes the ratio between males and females. The results indicated that average nests laid in peak nesting seasons tend to produce a female-dominated clutch. A 1 to 4 °C increase in air temperature, as predicted by global warming trends, could give rise to potentially dangerous nest temperatures and exclusively female clutches. Shading has a drastic effect on nest temperature and can act to stabilize the sex ratio in global warming scenarios. In a broad sense, any species with temperature dependent sex determination can feel the effects of climate change, making this model especially important for coming years. This study aims to examine the causes of nest temperature variation, and explore viable solutions to potentially harmful effects from climate change. More research and global attention on the harmful consequences of climate change impacting species is critical.
Temperature dependent sex determination, Loggerhead sea turtle, climate change, heat transfer, computational modeling