An international collaborative research study explores how varying rainfall affects the growth of sea turtle hatchlings, indicating that rainfall has a more significant impact than fluctuations in air temperature. Local weather conditions influence both the incubation and development of hatchlings, and the effects of rainfall differ among turtle species. For loggerhead turtles, increased rainfall leads to hatchlings with smaller shells but heavier weights, while green turtle hatchlings also have smaller shells but maintain their overall weight. The size of hatchlings is crucial; larger ones tend to move more swiftly, which improves their chances of survival as they spend less time on perilous beach sands.
Female sea turtles create nests by laying their eggs and covering them with sand before returning to the ocean. This leaves the eggs to develop and hatch independently. Unfortunately, the survival rate is low due to threats from predators and rising temperatures. Once the hatchlings venture into the ocean, only about one in a thousand make it to adulthood.
Hatchling size is critical. Larger hatchlings can move quickly, which increases their survival chances since they spend less time on dangerous beach sands.
Research indicates that both air and sand temperatures significantly influence sea turtle hatchlings. Cooler conditions yield larger, heavier hatchlings with more males, while warmer temperatures speed up the hatching process and help protect against predators. For the endangered loggerhead (Caretta caretta) and green (Chelonia mydas) sea turtles, cooler and wetter conditions contribute to stronger hatchlings. Conversely, higher temperatures may reduce the incubation duration, and erratic rainfall can hinder their growth, potentially impacting survival rates.
Maintaining a balance between temperature and moisture is essential for the wellbeing of these at-risk sea turtles. Excess moisture can be lethal to embryos.
A study conducted by Florida Atlantic University in partnership with the University of Tübingen in Germany investigates the effects of fluctuating rainfall on the growth of sea turtle hatchlings, uncovering that it influences them more profoundly than shifts in air temperature.
The research, involving data from 37 beaches globally—including a longitudinal study in Florida and experimental studies on the Cape Verde Islands—reveals that rainfall is a critical factor in determining hatchling size. Rain decreases beach surface temperature and increases moisture essential for egg development, making it a better indicator of size than temperature alone.
Findings published in BMC Ecology and Evolution show that the effect of rainfall differs by species. For loggerhead turtles, increased rainfall leads to hatchlings with smaller shells but greater weight, whereas green turtle hatchlings develop smaller shells without a change in overall mass.
“Our study’s results emphasize the necessity for more localized research on how regional weather affects incubation and hatchling growth,” said Jeanette Wyneken, Ph.D., co-author and professor in the Department of Biological Sciences at FAU’s Charles E. Schmidt College of Science. “These findings are crucial for refining conservation tactics to safeguard sea turtles in the face of global warming.”
The study began by analyzing data from Boca Raton, comparing hatchling dimensions (length, width, and weight) with local climate variables. Next, data were collected from 19 beaches where loggerhead hatchlings were found and 17 beaches hosting green turtle hatchlings. A third component of the study examined hatchlings in Cabo Verde after rain during their dry season to assess how these conditions influenced their size.
In the Mediterranean region, particularly on the beaches of Cyprus and Turkey, the dry season typically has little rainfall from the North Atlantic. For green turtles in these drier areas, the influence of rainfall becomes evident only after the end of the dry season. However, in Florida, rainfall levels remain relatively stable throughout the nesting season due to local climatic patterns, despite occasional droughts and heatwaves in July and October.
“The precise effects of rain on hatchling size remain unclear,” mentioned Wyneken. “One possibility is that rain cools the nests, altering the temperature and affecting the sex ratio of hatchlings, which may lead to variations in size and form, similar to the different shell shapes seen in male and female giant river turtles.”
As climate change continues to alter rainfall patterns—making wet areas wetter and dry areas drier—the ramifications for sea turtle nesting sites could indicate that global conservation strategies for loggerhead and green sea turtles may need reconsideration.
“Efficient management strategies for conservation should prioritize the ongoing assessment and inclusion of key nesting sites, highlighting the importance of local conservation initiatives,” asserted Wyneken. “Studying local data from diverse nesting areas is vital for comprehending sea turtle nesting behaviors. Making these local databases more accessible and widely shared will enhance our understanding and bolster local conservation efforts.”
Co-authors of the study include Omar Rafael Regalado Fernández, Ph.D., from the University of Tübingen; Parima Parsi-Pour from the Humboldt University of Berlin; John A. Nyakatura, Ph.D., also from the Humboldt University of Berlin; and Ingmar Werneburg, Ph.D., from the University of Tübingen.
This research received support from the German Research Foundation (Deutsche Forschungsgemeinschaft WE 5440/6-1).
