Sea turtles are the ocean's "canaries in the coal mine" when it comes to climate change, according to researchers who are trying to find out how they are adapting to a warmer climate that may be leaving baby male turtles high and dry.
Recent studies have shown that warmer temperatures in sea turtle nests -- which lie buried under several feet of beach sand -- produce more female turtles. Since turtles have been around for more than 100 million years, biologists still don't know why a slight shift in temperature can mean more females than males.
They also don't know whether this "feminization" of turtle eggs will spell the end of sea turtle reproduction over the long term, or is just the turtle's way of adapting to natural cycles of warmer and cooler weather that happen each year.
A new study of nesting loggerhead turtles in South Florida has found that rainfall helps cool off the hot sand, but in recent years the females have been hatching more females because of hotter, drier weather.
"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," said Jeanette Wyneken, a marine biologist at Florida Atlantic University. "That's why it's critical to understand how environmental factors, specifically temperature and rainfall, influence hatchling sex ratios."
The four-year study examined the loggerhead nesting season, which runs from April through October, and buried instruments in the sand at three depths to measure both temperature and moisture.
"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."
Wyneken and her team published their study in the journal Endangered Species Research this month.
Wyneken says the effects of temperature and rainfall are still a bit of a mystery.
"The water is not just cooling the nest, it's modifying the sex ratios, but we don't know how," she said. "We don't know the mechanism that is temperature dependent. We know some proteins that are important in directing the formation of testosterone or estrogens (the male and female sex hormones), but, the first step, we don't know what that is."
Climate scientists say the Earth's tropical zones will likely become hotter and drier between now and 2100, as warming greenhouse gases like CO2 continue to increase from human activity. Much of Florida's coastline is likely to disappear under rising seas as well, according to the U.S. National Climate Assessment.
Given that sea turtles already face threats from drifting fishing nets, illegal poachers and loss of their beach habitat to human development, many researchers want to know whether climate change will push the turtles over the edge.
"Climate change is this big thing that is maybe going to sink us all in the long-term, but it's not driving down the population right now," said Peter Dutton, head of the marine turtle genetics program at National Oceanic and Atmospheric Administration's Southwest Fisheries Science Center in La Jolla, Calif.
"We can protect their habitat," Dutton said about conservation efforts throughout coastal regions of North and South America, "but how will the turtles adapt to climate change?"