Female sea turtles lay their eggs, cover the nest with sand, and then return to the ocean, where they can develop and hatch on their own. From nest predators to rising temperatures, the odds for survival are bleak. Once hatched and released into the ocean, about one in a thousand reaches adulthood.
The size of the fry is important. Larger fry, which move faster, have a greater chance of survival because they spend less time on risky beach sand.
Research shows that both air and sand temperatures have a crucial influence on sea turtle hatchlings. Cooler temperatures produce larger, heavier hatchlings with more males, while warmer temperatures speed hatching and provide protection from predators. For endangered loggerhead turtle (Caretta caretta) and green (Chelonia mydas) sea turtles, cooler and moister conditions result in stronger hatchlings. However, rising temperatures can shorten incubation times, and erratic rainfall can disrupt growth, potentially affecting survival.
Balancing temperature and moisture is critical to the health of these delicate sea turtles. Too much moisture can be fatal for embryos.
An international joint study from Florida Atlantic University and led by the University of Tübingen in Germany examines how fluctuating rainfall affects the development of sea turtle hatchlings, showing that this has a more profound effect than changes in air temperature.
The study, which includes data from 37 beaches around the world – a longitudinal study in Florida and experimental studies in the Cape Verde Islands – shows that precipitation plays a crucial role in determining the body size of the young. Rainfall cools the beach surface and increases the moisture needed for egg development, making it a better predictor of body size than temperature.
Results of the study, published in BMC Ecology and Evolutionshow that the impact of rainfall varies between species. In loggerhead turtles, heavier rainfall results in hatchlings with smaller carapace (carapace) but greater weight, while green turtle hatchlings develop smaller shells with no change in body mass.
“The findings from our study highlight the need for more localized data on how regional weather affects incubation and hatchling development,” said Jeanette Wyneken, Ph.D., co-author and professor, Department of Biological Sciences, FAU Charles E. Schmidt College of Science. “These data are essential for refining conservation strategies to protect sea turtles amid global warming.”
The study started with data from Boca Raton, comparing hatchling size (length, width and mass) with local climate factors. Data were then collected from 19 beaches with loggerhead turtles and from 17 beaches with green turtle hatchlings. A third part of the study looked at hatchlings in Cape Verde after a few days of rain during the dry season to see how precipitation affected their size.
In the Mediterranean, especially on the beaches of Cyprus and Turkey, the dry season brings very little rain from the North Atlantic Ocean. For green turtles in these drier areas, the effects of precipitation only become noticeable after the dry season is over. However, in Florida, precipitation levels remain fairly constant throughout the breeding season due to local weather patterns, although droughts and heat waves typically occur in July and October.
“It is not exactly clear how rain affects the size of the young,” says Wyneken. ‘One idea is that rain cools the nests, which can change temperatures and affect the sex ratio of the young. This could lead to differences in the size and shape of the hatchlings, similar to how male and female hatchlings of other turtles, such as the giant river turtle, have different shell shapes.”
With climate change altering rainfall patterns – making wet areas wetter and dry areas drier – the impact on sea turtle nesting sites suggests that global conservation strategies for loggerhead and green sea turtles will likely need to be updated.
“Effective conservation management units should focus on regularly updating and recording important breeding sites, which emphasizes the importance of local conservation efforts,” Wyneken said. “Analyzing local data from different nesting sites is crucial for understanding sea turtle nesting patterns. These local databases need to be made more accessible and widely shared to improve our knowledge and support local conservation efforts.”
Co-authors of the study are first author Omar Rafael Regalado Fernández, Ph.D., University of Tübingen; Parima Parsi-Pour, Humboldt University of Berlin; John A. Nyakatura, Ph.D., Humboldt University of Berlin; and Ingmar Werneburg, Ph.D., University of Tubingen.
The research is supported by the German Research Foundation (Deutsche Forschungsgemeinschaft WE 5440/6-1).
