Great Barrier Reef sea turtles turning female due to climate change

The sex of green turtle hatchlings, like that of some other reptiles, depends on the incubation temperature of the eggs, with warmer sand and sea temperatures favoring female offspring.
By Delila James | Jan 10, 2018
Warming global temperatures are having a strange effect on green sea turtles living around Australia's Great Barrier Reef: they are becoming almost entirely female.

The study, by researchers from the National Oceanic and Atmospheric Administration (NOAA) and the Worldwide Fun for Nature Australia, is published in the journal Current Biology.

The researchers looked at two genetically distinct populations of the reef's sea turtles. They found that while the southern population was 65-69 percent female, the vast majority as high as 99 percent of turtles in the northern group was female.

"This is extreme like capital letters extreme, exclamation point extreme," says co-author Camryn Allen, a turtle scientist with NOAA in Hawaii, in a report by National Geographic. "We're talking a handful of males to hundreds and hundreds of females. We were shocked."

The study's genetic test results combined with temperature data indicate that Great Barrier Reef turtles have been hatching mostly females for more than twenty years and that "complete feminization of this population is possible in the near future," the authors wrote.

The sex of green turtle hatchlings like that of some other reptiles depends on the incubation temperature of the eggs, with warmer sand and sea temperatures favoring female offspring.

The scientists also learned that the ratio of females to male sea turtles was highest in the northern region of the Great Barrier Reef where significant coral bleaching also thought to be a product of global warming has occurred.

Although marine turtles have survived many temperature fluctuations over the past 100 million years, the current global situation is different, says lead author Michael Jensen, a marine biologist with NOAA's Southwest Fisheries Science Center in La Jolla, California, in the National Geographic report.

"But what happens in 20 years when there are literally no more males coming up as adults?" asks Jensen, "Are there enough to sustain the population?"


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