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WaPo: ‘Climate change is turning 99% of these baby sea turtles female’

By Ben Guarino

Green sea turtles do not develop into males or females due to sex chromosomes, like humans and most other mammals do. Instead, the temperature outside a turtle egg influences the sex of the growing embryo. And this unusual biological quirk, scientists say, endangers their future in a warmer world.

Already, some sea turtle populations are so skewed by heat that the young reptiles are almost entirely female, according to a new report in the journal Current Biology.

“This is one of the most important conservation papers of the decade,” said biologist David Owens, a professor emeritus at the College of Charleston who was not a part of this research. It will not be long, perhaps within a few decades to a century, until “there will not be enough males in sea turtle populations,” he warned.

The sex of a green sea turtle is a result of its environment. “They have temperature-dependent sex determination,” said Camryn Allen, a National Oceanic and Atmospheric Administration endocrinology researcher and co-author of the new study. “It’s not genetics. It’s actually the temperature.”

At what biologists call the pivot temperature, turtles hatch as a mixture of males and females. For green sea turtles, this temperature is 29.3 degrees Celsius (85 Fahrenheit). A few degrees below 29.3 C, all the sea turtles are born male. Heat up the eggs and only females are born.

“That transitional range, from 100 percent males to 100 percent females, spans a very narrow band of only a couple of degrees,” said NOAA marine biologist and study co-author Michael Jensen.

Head toward the equator along Australia’s east coast and, near the continent’s tip, you will arrive at prime turtle nesting grounds. Some 200,000 turtles lay their eggs at the beaches of Raine Island and nearby cays. It is one of the largest gatherings of green sea turtles in the world.