The effect of respiratory gases and incubation temperature on early stage embryonic development in sea turtles

Sea turtle embryos at high density nesting beaches experience relative high rates of early stage embryo death. One hypothesis to explain this high dead rate is that there is an increased probability that newly constructed nests are located close to maturing clutches whose metabolising embryos cause low oxygen levels, high carbon dioxide levels, and high temperatures. Although these altered environmental conditions are well tolerated by mature embryos, early stage embryos may not be as tolerant leading to an increase in their mortality. To test this hypothesis, we incubated newly laid sea turtle eggs for a week over a range of temperatures in different combinations of oxygen and carbon dioxide concentrations and assessed embryo development and death rates. We found that gas mixtures of decreased oxygen and increased carbon dioxide, similar to those found in natural sea turtle nest containing mature embryos, slowed embryonic development but did not influence embryo mortality of early stage embryos. In contrast, high incubation temperature not only decreased embryo development rate, but prolonged incubation at 34°C was fatal.