Recently published research from Australia shows that rising temperatures are affecting the nesting populations of green turtles on the Great Barrier Reef, causing them to produce offspring that are 99% female:

Rising temperatures are turning almost all green sea turtles in a Great Barrier Reef population female, new research has found.

The scientific paper warned the skewed ratio could threaten the population’s future.

Sea turtles are among species with temperature dependent sex-determination and the proportion of female hatchlings increases when nests are in warmer sands.

Tuesday’s paper, from the National Oceanic and Atmospheric Administration, California State University and Worldwide Fund for Nature Australia, is published in Current Biology. It examined two genetically distinct populations of turtles on the reef, finding the northern group of about 200,000 animals was overwhelmingly female.

While the southern population was 65%-69% female, females in the northern group accounted for 99.1% of juveniles, 99.8% of subadults and 86.8% of adults.

“Combining our results with temperature data show that the northern GBR green turtle rookeries have been producing primarily females for more than two decades and that the complete feminisation of this population is possible in the near future,” the paper said.

The temperature at which the turtles will produce male or female hatchlings is heritable, the paper said, but tipped to produce 100% male or 100% female hatchlings within a range of just a few degrees.

“Furthermore, extreme incubation temperatures not only produce female-only hatchlings but also cause high mortality of developing clutches,” it said. “With warming global temperatures and most sea turtle populations naturally producing offspring above the pivotal temperature, it is clear that climate change poses a serious threat to the persistence of these populations.”

Read more from The Guardian, the Washington Post and National Geographic.  The original research paper is open access, so you can read it online for free.

The green turtle nesting population in Australia is the world’s second largest; the largest green turtle nesting population is on the Caribbean coast of Costa Rica, and there are nesting beaches spread across the Caribbean. I’ll be looking for information about whether a similar sex imbalance has been observed in Caribbean green turtles.

[Image credit: Kris-Mikael Krister]