When sea turtles lay their eggs and bury them in the sand, the temperature they develop in will dictate whether the hatchlings are born male or female. Pretty cool, right? Well, not really: A new study shows that climate change may cause most sea turtles to be born female. The future of sea turtles depends on the coexistence of dudes and gals, so no, this is not cool at all.
The study, published in December in Global Change Biology, took a deep dive into how sea turtles in the João Vieira and Poilão Marine National Park in West Africa will fare in a warming world. In the worst-case climate scenario the Intergovernmental Panel on Climate Change lays out, more than 90 per cent of sea turtles in this region would be female. Even in the mildest scenario, where we begin employing solutions to stabilise greenhouse gas emissions in some 20 years, females would still make up nearly 80 per cent of the population.
Turns out that as depressing as this news is, this specific sea turtle population should be one of the more resilient ones under a worst-case high-emissions scenario, where greenhouse gas emissions don’t slow down come the turn of the century. That’s because these turtles have options as to where to lay their eggs.
“[The population] has this unique habitat where the turtles can go and nest,” said lead author Ana Rita Patrício, a marine ecologist and postdoctoral fellow at the University of Exeter. “And that will always, always, promote the growth of male turtles. So although climate change will contribute to feminisation, we think that in this population, there will always be room for male turtles to be preserved, not like other ones.”
The highly female future of sea turtles isn’t exactly news. Earlier this year, a team of scientists published its findings that the Pacific green sea turtles of the Great Barrier Reef had been turning up almost entirely female for at least the last 20 years. The Earth’s increased temperatures are already impacting the animals there – and things aren’t expected to look much better as we, humans, continue to drive cars, fly in jets, and, well, gobble up fossil fuels.
The population in West Africa, however, isn’t seeing such a definitive change, nor do the study authors think it will. See, these sea turtles can leave their eggs in the open sand, where they will incubate under warmer temperature and likely breed more females, or they can leave their eggs closer to the forest part of the islands that surround the marine park, where they are more likely to turn out male. The turtles who nest in the forest are more likely to repeat this behaviour, Patrício said.
“Amid the threat of climate change, I guess we can call it an optimistic finding,” she said.
The scientists came to this conclusion by placing more than 100 data loggers into egg nests to monitor their temperatures and then sexing five hatchlings in each nest – which requires sacrificing the babies to look at their internal genitals, as these turtles don’t display their sex until they’re mature, a process that takes decades. Sad as that is, five hatchlings is not a lot for this species. A hundred eggs can lie in a nest, so this small sample size is definitely a limitation of the study. Still, this is one of the few studies to take the extreme step of confirming the sex so certainly.
“It is among one of the more robust studies around because most studies, due to the ethical issues, and defendable ethical issues, of taking hatchlings from nests, in most places this is not possible,” Patrício said. “The fact that we actually have the population-specific sex ratio response makes the study more robust than many.”
And the study didn’t look only at the sex response to temperature. It included other criteria that are impacted by climate change: the impact of sea level rise on habitat, hatchling emergence success, responses to different microclimates and times of year, flexibility in foraging behaviours, and rookery size and trends. With all this, the population should have a “medium to high resistance to climate change impacts,” per the study. The population size is large; nest numbers have more than doubled in the last 10 years. And more than half of their current nesting habitat should remain suitable by 2100, in even the worst scenario despite rising costs and flooding.
Luckily, a femme future shouldn’t mean the end for this population. You’re welcome, fellas.
Featured image: Getty