Factors Affecting Levels of Oxygen in Leatherback Turtle Nests
Eggs of the critically endangered leatherback turtle (Dermochelys coriacea) are incubated in beach sand up to 60 days, during which the embryos develop and finally hatch. Because the majority of leatherback turtle embryo development takes place within an incubation chamber dug almost a meter deep in moist sand, the gaseous microenvironment of leatherback nests must be studied to better understand the developmental physiology of the eggs. A three-dimension mathematical model of oxygen partial pressure within a sea turtle nest was derived and used to explore effects of nest characteristics on conditions to which eggs in nests would be exposed during incubation. The 3D model showed that as nest depth decreased, PO2 in the nest increased, in some cases significantly. The model also gave insight into which nest parameters - such as size, diffusion coefficient of oxygen in the sand, and clutch metabolism - have large influences on oxygen diffusion into the nest. Substituting the model into an equation for oxygen conductance of nests mathematically showed that nest conductance is independent of the total clutch metabolism. To test this model empirically, and thereby verify that nest conductance is independent of egg metabolism, oxygen-consuming batteries were connected to constant current circuits and buried in sand. The batteries were incrementally switched on to vary the metabolic rate within the nest and P02 inside the nest was measured. The ∆P02 from ambient increased proportionally with an increased metabolic rate. This suggests that nest oxygen conductance is independent of the total clutch metabolic rate.