sixth mass extinction

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A Pacific green sea turtle. (Wikimedia Commons)

Want to know which species will go extinct in the near future? One way to predict the crash of a population is to take a headcount of a species’ latest arrivals. When researchers checked in on the endangered Pacific green sea turtle, which nests in only two places, on the northern and southern ends of Australia’s Great Barrier Reef, they were surprised to find that the next generation is almost entirely female. That’s not good news for future breeding activity.

The gender of many reptiles is determined by how warm the egg is when incubated. In the case of the sea turtles, the temperature of the sand the eggs are buried in triggers gender development. Very small temperature differences can tip male-female ratios in either direction, and researchers suspected that rising global temperatures might have an impact on this population. The area has already seen widespread coral bleaching due to rising sea temperatures around the Great Barrier Reef. "Within a few degrees Celsius you go from 100 percent males to 100 percent females," says marine biologist Michael Jensen, who was part of a team studying the turtles in a survey published in Current Biology. "A really narrow range, that transition."

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