Sea Turtles, Reproduction and Climate Change: Warmer Temperatures Impact Hatchlings

Loggerhead sea turtles have been around for 60 million years and have survived through many changing environments. Now, however, hatchling sex ratios and future reproduction success are being threatened by climate change, a new study revealed. Sea turtles don't have an X or Y chromosome, so their sex is defined during embryo development, and can be greatly altered by changes in the environment. Researchers from Florida Atlantic University (FAU) discovered that warming temperatures during incubation yield more females, while more males develop under cooler conditions. 

During incubation, temperatures often vary with changes in temperature, sun, shade, sand types and rainfall. All of these environmental conditions play a key role in loggerhead sea turtle developmental rates, hatch and emergence success, and embryotic sex, the researches explained in their study. 

"The shift in our climate is shifting turtles as well, because as the temperature of their nests change so do their reproduction patterns," Dr. Jeanette Wyneken, a professor of biological sciences in FAU's Charles E. Schmidt College of Science, said in a news release. "The nesting beaches along Florida's coast are important, because they produce the majority of the loggerhead hatchlings entering the northwestern Atlantic Ocean."

Such environmental impacts could futher threaten loggerhead populations, which have been experiencing a decline in recent years. From their study, researchers estimate that roughly one in every 2,500 to 7,000 sea turtles make it to adulthood, the release noted. 

Generally, a loggerhead female produces about 105 eggs per nesting season, which runs from April through October each year. In that season, the turtles lay their eggs in underground nests; the eggs then mature without the care of a parent or grown turtle. Based on the aforementioned statistics on reproduction success, a loggerhead would have to nest for more than 10 nesting seasons over 20 to 30 years just to replace herself and possibly one mate, the researchers explained. However, since climate change is resulting in the development of fewer males, the species could be seriously impacted. 

"If climatic changes continue to force the sex ratio bias of loggerheads to even greater extremes, we are going to lose the diversity of sea turtles as well as their overall ability to reproduce effectively. Sex ratios are already strongly female biased," Wyneken said in the release. "That's why it's critical to understand how environmental factors, specifically temperature and rainfall, influence hatchling sex ratios."

For their study, researchers documented environmental conditions present along a loggerhead turtle nesting beach in Boca Raton, located in southeast Florida. Between 2010 and 2013 nesting seasons, researchers examined the relationship between rainfall and sand temperature, as well as rainfall, nest temperatures and hatchling sex ratios. They also made measurements at three separate depths of sand in order to see how temperature affected each of those, according to the release. 

Their data suggested that light rainfall only had an effect on surface sand, while heavier rainfalls ultimately lowered sand temperatures. However, fluctuations in temperature were very small when the moisture reached higher nest depths.

"The majority of hatchlings in the sampling were female, suggesting that across the four seasons most nest temperatures were not sufficiently cool to produce males," Wyneken explained in a statement. "However, in the early portion of the nesting and in wet years, nest temperatures were cooler, and significantly more males hatched."

Their study was recently published in the journal Endangered Species Research. 

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