More than just temperature: The effects of nest relocation on incubation environment and hatchling quality in green turtles (Chelonia mydas)

Published: 10 August 2026| Version 1 | DOI: 10.17632/8978mrvdbz.1
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Description

This study was conducted during the 2022 – 2023 and 2023 – 2024 nesting seasons on Heron Island, Queensland, Australia (S 23.44307°, E 151.91809°). Heron Island is a coral cay in the Southern Great Barrier Reef (sGBR) and a long-term Queensland Government monitoring site for the sGBR population of green turtles (Chelonia mydas). During nightly surveys, we identified nesting females that were laying nests within our study site on the east-facing side of the island at Shark Bay between 7th – 16th December 2022 and 3rd – 15th December 2023. Variables Nest_ID: Identifier for the nest (1–24). Treatment: Is the experimental treatment, i.e. In Situ (natural nest), Shaded, Unshaded. Year: Nesting season 2023 or 2024. ID: Unique identifier combining nest and year (e.g., 2320 = Nest 20, Year 2023). SCL: Straight carapace length (mm). SCW: Straight carapace width (mm). Mass: Hatchling mass (g). CSI: Carapace Size Index (SCL × SCW, mm²). Avg_Egg_Mass: Average egg mass for the nest (g). Meantemp: Mean incubation temperature (°C). Last_2_Week_Meantemp: Mean temperature during final 2 weeks of incubation (°C). Mean_Airtemp: Mean air temperature during incubation (°C). Last_2_Week_Mean_Airtemp: Mean air temperature during final 2 weeks of incubation (°C). Mean_Rainfall: Mean daily rainfall during incubation (mm). Last_2_Week_Mean_Rainfall: Mean rainfall during final 2 weeks of incubation (mm). Animal_ID: Unique ID for each hatchling tested. Clutch_Test_Time: Time of performance test (dd/mm/yyyy hh:mm:ss). Test_Order: Order in which hatchling was tested for performance within clutch. Time: Time to complete crawling raceway (seconds). Raceway_Temp: Hatchling temperature taken post-raceway test (°C). Speed: Crawling speed (cm/s) over 3m. Attempt_1 to Attempt_6: Times for up to 6 righting trials (seconds); NA if not attempted. Mean: Mean time across all successful righting attempts (seconds). Inverse_Time: Inverse of mean righting time (1 / seconds), used as performance proxy. Righting_Propensity: Number of successful righting attempts (0–6). Score: Composite righting score (mean time and success rate). Flip_Temp: Hatchling temperature taken post-righting test (°C). Hatch_Success: Hatching success of the nest (%). Emergence_Success: Emergence success of the nest (%). TCC: Total Clutch Count (number of eggs in clutch). Incubation: Incubation duration (days). Sex: Sex (if known); otherwise NA. Treatment.y: Repeated treatment columns from merges (identical to Treatment). Mass_Residuals: Residuals from regression of Mass ~ CSI. CTE: Constant Temperature Equivalent (°C), an estimate of developmental rate.

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R Statistical Software v. 4.3.1 was used to conduct statistical analyses. All continuous predictor variables were scaled prior to analysis. For categorical predictor variables, we calculated estimated marginal means (EMMs) using the emmeans *function from the *emmeans *package. We conducted post-hoc pairwise comparison using the *pairs function adjusted for Tukey’s HSD. To summarise nest temperatures, raw temperature data from the HOBO MX2307 Bluetooth temperature probes, HOBO MX2201 pendant temperature loggers and iButtons within each clutch were averaged to produce a single hourly temperature measurement. We removed temperature values that were considered logger hardware errors (i.e. spontaneous increases in temperature of up to 20°C+) and values that remained post hatching. We calculated the mean nest temperature for the entire duration of the incubation period, the mean nest temperature from the final two weeks of incubation (when nest temperatures rise greatly and sometimes reach sub-lethal levels), and the constant temperature equivalent (CTE) for each nest during the sex determining period (SDP). CTE was defined as the temperature at which 34% of development occurred within the window spanning 33 – 67% of total embryonic development, using a development rate model for sGBR green turtles. To examine the effects of relocation treatment and year on all three measures of nest temperature, we fitted separate linear models using the *lm *function with treatment and year as fixed factors and including their interaction. When examining nest outcomes, for each response variable, we investigated three models: (1) a treatment-only model including treatment, year, and their interaction; (2) a mean temperature model including treatment, year, mean nest temperature from the full incubation period, and (3) a two-week temperature model as above but using the mean nest temperature from only the final two weeks of incubation. For all models, post-hoc pairwise comparisons were conducted using Tukey-adjusted EMMs.

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Conservation Biology, Chelonia, Animal Morphology, Coastal Ecology, Animal Performance Testing

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