by Sean Rossman, USA Today
Researchers suggest a generation of sea turtles in the Great Barrier Reef were born mostly female because they were nested in warmer areas, raising concerns global warming might threaten the species.
The study, published Monday in the journal Current Biology, found 99.8% of green sea turtles near adulthood and originating from the northern — and warmer — part of the Great Barrier Reef were born female. A slightly younger group of juvenile turtles was found to be 99.1.% female.
“It was surprising and we were not expecting it at all,” said co-author Camryn Allen of the Joint Institute for Marine and Atmospheric Research in Honolulu, Hawaii. “We didn’t expect it to be that extreme.”
The study analyzed more than 400 turtles and was conducted by researchers from the U.S. National Oceanic and Atmospheric Administration (NOAA), as well as the Queensland Department of Environment and Heritage Protection in Australia.
The lopsided gender split, the authors point out, could cause the population to collapse, or the species to go extinct, unless efforts are made to lower nesting temperatures.
In the southern part of the Great Barrier Reef, where sand temperatures are cooler, females still outpaced males, but by far less. The study found juvenile and subadult turtles were 67.8% and 64.5% female, respectively.
The northern Great Barrier Reef, the site of the overwhelming female population, has one of the largest populations of green sea turtles in the world, the study said. It has a population of about 200,000 nesting females.
A shift of just a few degrees can have big impacts on sex outcomes in sea turtles. Sea turtle gender is dependent on the incubation temperature while a turtle is an embryo, a characteristic common in some reptiles. Cooler temperatures produce more males in sea turtles, while warmer temperatures produce more females. The temperature which produces the perfect ratio of half females and half males serves as the “pivotal temperature” marker. Researchers found temperatures in nesting spots in the northern Great Barrier Reef consistently skewed higher than the pivotal temperature since the 1990s. The juvenile and subadult groups were born within the past two decades.
The study shows the female percentages have increased in the northern Great Barrier Reef. Of the older adult-sized turtles analyzed, 86.8% were female, the study said.
“These results suggest that increased sand temperatures affect the sex ratios of the (northern Great Barrier Reef) population such that virtually no male turtles are now being produced from these nesting beaches,” the study said. “Our findings add another dimension to the growing body of evidence that increasing temperatures are broadly affecting (Great Barrier Reef) ecosystems.”
The question now, said co-author Michael Jensen, a research scientist working for NOAA, is how the turtles adapt to the temperatures. Instead of nesting in the heat of summer, Jensen said, turtles could nest earlier or later in the year when it’s cooler. They also could find cooler places to store their eggs.
But it can take generations to adapt, and that could be a long time for this sampling of turtles, which reach maturity at roughly 25 years old. That means in just a few generations, temperatures might increase by several degrees.
“Our study raises new concerns over the immediate threats of climate change to sea turtle populations,” the study read. “We need to learn more about how (temperature-dependent sex determination) species cope with rapid climate change.”
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