Effects of incubation temperature on olive ridley sea turtle nest success at the Songor Ramsar Site, Ghana

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Abstract Incubation temperature plays a key role in sea turtle embryonic development through influencing developmental rate, hatchling phenotype, and temperature-dependent sex determination. We quantified nest and adjacent sand temperatures and examined their relationships with incubation duration, reproductive success, and hatchling performance in olive ridley sea turtles ( Lepidochelys olivacea ), during the 2020–2021 nesting season at the Songor Ramsar Site and UNESCO Biosphere Reserve in Ada Foah, Ghana. Temperature loggers were deployed within seven nests and in paired sand locations approximately 2 m from each nest at equivalent depth. Loggers were set to record temperatures at 15-min intervals throughout the incubation period. Nest and sand temperatures were similar during early incubation but diverged later in development, with nest temperatures becoming consistently higher than sand temperatures beginning around incubation day 17 and remaining elevated through hatching. Mean nest temperatures ranged from 30.7 to 33.3 °C (mean ± SD = 32.4 ± 0.8 °C) and were strongly negatively correlated with incubation duration ( r = − 0.88), indicating accelerated development in warmer nests. Relationships between nest temperature and hatching success or emergence success were weak and highly variable among nests. Nest temperature showed a moderate association with hatchling locomotor performance. Although hatchling sex ratios were not measured directly, nest temperatures exceeded pivotal thresholds for olive ridley turtles during a substantial portion of the thermosensitive period, suggesting a predicted female-biased hatchling sex ratio.

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