Baby Sea Turtles Walk on Treadmills for Science

Baby sea turtles have to grow up fast. Granted, they don't actually reach adulthood until they're 10 to 50 years old, depending on the species, but their first 24 hours of life nonetheless require a ridiculous amount of grit for a newborn animal.

Those 24 hours are known as the "frenzy" period for baby sea turtles, during which they must: a) emerge from their nest, b) figure out where the ocean is and c) scramble there without being eaten. Plenty of predators are happy to disrupt that last step, but there is safety in numbers, since predators can only eat so much at once.

In recent decades, however, a newer danger has joined the threat of predators: light pollution. Baby sea turtles seem to have an innate attraction to light, which scientists believe is an evolutionary trigger for them to immediately hit the surf after hatching. (That's because, before electricity lit up so many beaches at night, the ocean was typically brighter than inland areas due to moonlight reflecting off seawater.)

This problem is well-known, and many coastal communities have adopted lighting ordinances, especially in nesting season, to stop electric lights from luring baby sea turtles inland. But while that's helpful, the widespread effects of light pollution remain a mortal danger to many newborn sea turtles around the world.

Baby sea turtles have a roughly 50 percent chance of reaching the ocean where electric lights pose a disorientation risk, according to researchers from Florida Atlantic University, and their odds drop further if they get separated from the crowd. Disoriented hatchlings that do eventually reach the ocean burn up lots of energy in the process, since they've spent much more time on land than necessary.

In hopes of helping these endangered turtles, the researchers conducted the first study of how extended crawling and swimming affects disoriented hatchlings.

Guiding lights

"What prompted our study was the desire to understand what happens to these hatchlings after they spend hours crawling on the beach because they are disoriented," says lead author Sarah Milton, a biologist at Florida Atlantic University, in a statement. "We wanted to know if they would even be able to swim after crawling 500 meters or more, which could take them as long as seven hours to complete."

The study involved 150 loggerhead and green sea turtle hatchlings, all collected as they emerged from 27 nests in Palm Beach County, Florida. (The hatchlings were released back into the ocean soon after they were collected from their nests, the authors note.) In a lab setting, the researchers simulated the effects of disorientation by placing hatchlings on tiny enclosed treadmills, using lights as a prompt for them to walk forward. Check out the video above to see what that looked like.

The hatchlings were then dressed in a special swimsuit and placed in a small tank, where researchers tested how the treadmill walk affected their swimming ability. They did this by measuring oxygen consumption and lactate buildup during the activity periods, and by measuring the rates at which turtles breathed and paddled their flippers. They did field work, too, watching the behavior and physiology of both normal and disoriented hatchlings, taking note of how far they crawled, how long it took them and how often they rested. The results from the lab and field studies matched, the researchers report — and were not what anyone expected.

Turtle power

"We were completely surprised by the results of this study," Milton says. "We were expecting that the hatchlings would be really tired from the extended crawling and that they would not be able to swim well. It turned out not to be the case and that they are in fact crawling machines. They crawl and rest, crawl and rest, and that's why they weren't too tired to swim."

This is good news, and a testament to the tenacity of these tiny survivors. At the same time, however, it doesn't mean light pollution isn't dangerous for baby turtles. Even if disorientation doesn't exhaust them as much as we thought, it still means they spend more time than necessary on dry land, where they're especially vulnerable to threats like predators or road traffic.

"There are some people who don't think that turning off the lights, really, is going to do any good," Milton tells the New York Times. "But I can say from being out on the beach doing the study, it's very clear that we would have one house that had a porch light on in the back or something like that, and the turtle would head straight for it. It made me want to leave a note on their door: 'Hi, you are personally responsible for the disorientation of 60 turtles last night.' So turning off the lights in the condominiums and in the houses really does make a difference."