Sea turtle hatchling bodies struggle in hotter sands

Every year, thousands of sea turtle hatchlings burst out of nests buried under warm sand and make a mad dash toward the ocean. It’s a brutal beginning. They face hungry predators, strong waves, and a planet that’s heating up fast.

For loggerhead turtles – already a threatened species – climate change is reshaping everything from their shells to their chances of survival.

We’ve known for a while that hotter sand leads to more female turtles, fewer males, and weaker hatchlings. What we didn’t know – until now – is whether that heat messes with their brains too.

Heat reshapes turtle survival

As the planet heats up, so do the beaches where sea turtles lay their eggs. Nest temperature matters a lot, because it decides whether hatchlings are born male or female. Warmer sand tips the balance heavily toward females. That may seem harmless at first, but too few males could push populations into real trouble.

Heat also messes with the body. Sea turtle hatchlings from hotter nests are usually smaller, slower growing, and more likely to have deformed shells. They’re also less likely to survive the journey from nest to sea – and beyond.

But researchers at Florida Atlantic University wanted to know if there was another, less obvious effect. Does the heat also change how these turtles think? Can it make them less able to learn, adapt, or make split-second decisions?

Inside a turtle’s mind

To find out, the team ran a unique experiment. They incubated loggerhead turtle eggs at two temperatures: 88°F and 91°F. Both of these are warm enough to produce mostly females – but 91°F is at the higher end, closer to what’s happening now on many nesting beaches.

Once the turtles hatched, researchers waited about four weeks before testing their brains. They placed the hatchlings in a Y-shaped maze with a food reward at one end. To get the food, the turtles had to recognize and remember visual cues – simple patterns like stripes or a bull’s-eye.

Then came the twist. The researchers switched the reward to the opposite side, forcing the turtles to “unlearn” what they knew and relearn a new pattern. This part tested what scientists call behavioral flexibility – the ability to adapt when things change.

Hatchling minds stay sharp

Here’s the kicker: hatchlings from both temperature groups learned just fine. In fact, in the 2020 trial, they actually did better on the second round of learning than they did on the first.

“Not only were the post-hatchlings capable of suppressing previously learned behaviors to form new, more advantageous associations, they were able to do so with remarkable speed – often requiring fewer trials than the initial learning phase,” said Sarah L. Milton, Ph.D., senior author of the study and chair of FAU’s Department of Biological Sciences.

So despite the stress of being born in hotter nests, the turtles were still sharp. They could figure out new rules and change their behavior – a good sign in a world that keeps shifting under their flippers.

Physical toll on sea turtle hatchlings

But the news isn’t all good. Even though their brains seemed fine, their bodies told a different story. Turtles from the 91°F nests had more problems.

They hatched sooner, were smaller, and had more defects in their scutes – the hard, bony plates that form their shells. Their growth was slower, and fewer of them survived the incubation process.

“The concern remains very real,” said Ivana J. Lezcano, corresponding author and a doctoral candidate at FAU. “Elevated incubation temperatures are known to produce smaller, less physically resilient hatchlings and cause a significant decline in overall hatching success.”

“Together, this can pose serious risks to population survival,” she said. “However, our finding that cognitive ability and learning may remain largely unaffected, at least in the short-term, by these higher temperatures offers a hopeful perspective.”

It suggests that, despite other developmental and physical challenges, these turtles may retain the mental flexibility needed to adapt to their changing environments.

“This resilience gives us one of the first glimpses of how incubation temperature may affect behavioral traits, though ongoing research is essential to fully understand the long-term implications,” said Lezcano.

The unknowns beyond 91 degrees

The study only went up to 91°F. That’s already hot – but it’s not the worst. On some beaches in South Florida, sand temperatures are hitting 93°F or even 96°F. At those levels, turtle nests can become almost entirely lethal.

Researchers warn that just because the hatchlings handled 91°F without major cognitive issues doesn’t mean they’ll be fine at even higher temperatures. Brains are sensitive, and heat stress could start to take a toll in ways we haven’t seen yet.

And there’s another twist: in conservation, success is usually measured by how many turtles make it out of the nest. But that alone may not guarantee survival. Hatchlings that are too weak or not ready to handle challenges in the water have far slimmer odds of making it.

Clever turtles, fragile bodies

“The hatchlings in our study were able to swiftly adjust to new information despite developmental stressors,” Milton said.

This behavioral adaptability is not just a survival mechanism – it’s a critical evolutionary advantage that may enable them to cope with the complex challenges posed by their shifting habitats.

Conservation efforts must prioritize not only the preservation of hatchling populations but also the environmental conditions that support their ongoing cognitive development and resilience.

The full study was published in the journal Endangered Species Research.

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