School of Biological Sciences, The University of Queensland, Qld, Australia.
Queensland Government Department of Environment and Science, Aquatic Threatened Species Unit, Dutton Park, Qld, Australia.
PLoS One. 2020 Dec 2;15(12):e0233580. doi: 10.1371/journal.pone.0233580. eCollection 2020.
Sea turtle embryos at high-density nesting beaches experience relative high rates of early stage embryo death. One hypothesis to explain this high mortality 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, i.e. embryos in eggs that have only been incubating for less than a week, may not be as tolerant leading to an increase in their mortality. To test this hypothesis, we incubated newly laid sea turtle eggs 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 nests containing mature embryos, slowed embryonic development but did not influence the mortality rate of early stage embryos. We found incubation temperature had no effect on early embryo mortality but growth rate at 27°C and 34°C was slower than at 30°C and 33°C. Our findings indicate that low oxygen and high carbon dioxide partial pressures are not the cause of the high early stage embryo mortality observed at high-density sea turtle nesting beaches, but there is evidence suggesting high incubation temperatures, particularly above 34°C are harmful. Any management strategies that can increase the spacing between nests or other strategies such as shading or irrigation that reduce sand temperature are likely to increase hatching success at high-density nesting beaches.
高密度筑巢海滩上的海龟胚胎经历相对较高的早期胚胎死亡率。有一种假说解释了这种高死亡率，即新筑巢的位置更有可能靠近正在成熟的卵堆，而这些卵堆代谢产生的胚胎会导致低氧、高二氧化碳和高温环境。虽然这些环境条件的改变对于成熟的胚胎来说是可以很好地耐受的，但早期胚胎（即在孵育不到一周的蛋中的胚胎）可能无法耐受，导致其死亡率增加。为了验证这一假说，我们在不同的氧气和二氧化碳浓度组合下，将新产下的海龟蛋在一系列温度下进行孵化，并评估胚胎的发育和死亡率。我们发现，类似于自然海龟巢中含有成熟胚胎的气体混合物，低氧和高二氧化碳的混合会减缓胚胎的发育，但不会影响早期胚胎的死亡率。我们发现孵化温度对早期胚胎的死亡率没有影响，但在 27°C 和 34°C 下的生长速度比在 30°C 和 33°C 下慢。我们的研究结果表明，低氧和高二氧化碳分压不是高密度海龟筑巢海滩上早期胚胎死亡率高的原因，但有证据表明，高温，特别是高于 34°C，对胚胎是有害的。任何可以增加巢穴之间间距的管理策略，或者通过遮蔽或灌溉来降低沙温的其他策略，都可能会提高高密度筑巢海滩的孵化成功率。
