Effects of moisture during incubation on green sea turtle (Chelonia mydas) development, morphology and performance

Abstract

While the effect of temperature on embryonic development in sea turtles has been well studied over recent years, our understanding of the effect of substrate moisture, another important environmental variable, is limited. High sand moisture decreases nest temperature through evaporative and direct cooling during rainfall, but its direct effect on hatchling development, morphology and performance is unclear. To address this knowledge gap, we incubated 40 green sea turtle Chelonia mydas clutches in a beach hatchery under either high (~8% v/v) or low (~5% v/v) sand moisture concentrations for the duration of embryonic development. In half of the clutches, temperature sensors were deployed to measure any effect of sand moisture on nest temperature. As hatchlings emerged, we measured body size and locomotory performance during the first 24 h, an important period of frenzied activity for sea turtles. We excavated clutches post-emergence to determine hatching success, emergence success and to determine the stage of embryonic death for unsuccessful eggs. High moisture concentrations increased incubation duration, decreased nest temperature and had marginal effects on hatchling morphology, but no effect on hatching success, stage of embryonic death, crawling speed or initial swimming performance. However, after 24 h of swimming, hatchlings from high-moisture clutches produced less mean swim thrust and spent less time powerstroking than hatchlings from low-moisture clutches, suggesting reduced swimming endurance and potentially impacting the ability of hatchlings to successfully disperse. The effect of moisture on nest temperature and hatchling endurance highlights the importance of considering rainfall patterns when predicting future impacts of climate change on sea turtle populations.

Evaluation of Reproductive Success of the Olive Ridley Turtle Lepidochelys olivacea (Testudinata: Cheloniidae) Using Different Incubation Treatments

“…We believe that the combination of the environmental conditions and the frequency of irrigation resulted in longer incubation periods. Our results agree with those of Matthews et al (2021), in the sense of that high humidity concentrations increase the duration of incubation, however, they do not affect hatching success.…”

Thermal conditions of green turtle (Chelonia mydas) nests in the largest rookery in the eastern Mediterranean

“…Many factors are likely to influence the temperatures of sea turtle nests. For example, the distance from the sea (Kılıç & Candan 2014), sand albedo (Hays et al 1995, 2001, nest moisture (Lolavar & Wyneken 2015, Matthews et al 2021) and sand grain particle size (Mortimer 1990, Ackerman 1997) could profoundly impact incubation conditions. In many conservation and monitoring studies, nests are consistently relocated to further distances from the high tide line.…”

“…Additional nest environmental parameters such as grain size, gas exchange and moisture also play an essential role in the thermal conditions of the nests and thus of hatchling sex ratios (Ackerman 1997). For instance, high rainfall and high-moisture concentrations in the nests decrease nest temperature and can indirectly alter hatchling sex ratios (Lolavar & Wyneken 2015, Matthews et al 2021.…”

Mitigating the effects of climate change on the nests of sea turtles with artificial irrigation

“…Unless water can be applied directly to eggs via pipes, irrigation generally involves watering the substrate surface so water percolates through the substrate to the nest (Matthews et al., 2021 ; Smith et al., 2021 ). As the water percolates, its temperature equilibrates to that of the surrounding substrate.…”

“…Frequency, duration, and when (timing) irrigation occurs are all part of irrigation timing (Figure 2 ). Frequency has been either a single application, daily irrigation, or targeted irrigation, where irrigation frequency or volume is varied to maintain predetermined incubation conditions (Matthews et al., 2021 ). All three frequencies produced cooling effects (Table 1 ).…”