Study says warmer temperatures will skew ratio of female to male loggerheads
Florida biologists say warmer temperatures in nesting areas drive an increase in the development of juvenile female sea turtles. Under a long-term global warming trend, that could have significant consequences for loggerhead reproduction.
“The shift in our climate is shifting turtles as well, because as the temperature of their nests change so do their reproduction patterns,” said Jeanette Wyneken, Ph.D., professor of biological sciences in Florida Atlantic University’s Charles E. Schmidt College of Science. “The nesting beaches along Florida’s coast are important, because they produce the majority of the loggerhead hatchlings entering the northwestern Atlantic Ocean.”
Sea turtle eggs, incubating in beach sands, are affected by environmental conditions, including rainfall, sun, shade and sand type, all factors in developmental rates, hatch and emergence success, and embryonic sex. Warmer conditions produce females and cooler conditions produce males.
The new study, published in the journal Endangered Species Research, focused on the effects of turtle nest temperatures and sand temperatures and on hatchling sex.
“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,” said Wyneken. “That’s why it’s critical to understand how environmental factors, specifically temperature and rainfall, influence hatchling sex ratios.”
Wyneken and her team closely matched temperature and rainfall records with loggerhead turtle reproduction at a nesting beach in Boca Raton, located in southeast Florida. Rainfall data collected concurrently with sand temperatures at different depths showed that light rainfall affected only the surface sand; effects of the heaviest rainfall events tended to lower sand temperatures, however, the temperature fluctuations were very small once the moisture reached upper 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,” said Wyneken. “However, in the early portion of the nesting and in wet years, nest temperatures were cooler, and significantly more males hatched.”
The work was supported, in part by the National Save the Sea Turtle Foundation, Save our Seas Foundation and donations to the Nelligan Sea Turtle Support Fund.