Factors influencing variations of oxygen content in nests of green sea turtles during egg incubation with a comparison of two nesting environments

Several biotic and abiotic factors can influence nest oxygen content during embryogenesis of sea turtle eggs. These factors were evaluated during each stage of egg development on Lanyu Island, Taitung County, Taiwan. We measured oxygen content of 14 nests in 2010. Oxygen in the adjacent sand, total and viable clutch sizes, air, sand and nest temperatures and sand characters of each nest were also determined. The study found that the oxygen available to an egg differs within the clutch, resulted in this value being highest in the upper layer and decreased with depth. Metabolic heat increased with incubation and reached the peak value in the middle or late stage of incubation. This result in the oxygen content was highest in the early incubation stage and decreased afterwards. Clutch size is the major factor that influences the nest oxygen content during the incubation. Hatching success was found to decrease with decrease of average oxygen partial pressure in the nest. Comparison between Wan-an Island of Penghu Archipelago and Lanyu Island of Taitung County showed that the incubation microenvironment and the local weather pattern are the major factors responsible for differences in oxygen content during embryo development. It is possible that the nesting beach loyalty result in different adaptive morphological characters of hatchlings is produced from each island.