Marine reptiles visit the same foraging grounds, millennium after millennium.

You might think you’re a creature of habit—but sea turtles have you beat. Green sea turtles in the Mediterranean Sea visit the same areas of seagrass meadows today that they did 3000 years ago, a new study reveals. The results, the authors say, spotlight ecologically critical and currently unprotected coasts in North Africa—and a new way for deep history to guide present-day conservation.

“It’s really, really thrilling,” says Cyler Conrad, a cultural resources environmental scientist at the Pacific Northwest National Laboratory who was not involved in the research. “Very few” studies, he says, have successfully traced such an ancient connection between animals and their environment.

Sea turtles like routine. Green sea turtles (Chelonia mydas) lay their eggs in the same place they themselves hatched. They also revisit hyperspecific spots—sometimes no more than 50 square meters large—to feed on seagrass, their favorite food. “They really have their little patch,” says Annette Broderick, a professor of marine conservation at the University of Exeter. “It makes sense—if you find somewhere good, you keep going back.”

Now, Broderick and others have found that this loyalty endures far beyond one turtle’s lifetime. The evidence comes from the rubbish bin. Sea turtles were a popular delicacy for thousands of years in the Mediterranean, and ancient dumpsites are filled with leftover bones and shells discarded from meals past. The researchers, in collaboration with the North Cyprus Society for the Protection of Turtles, gathered sea turtle bones found at three Bronze and Iron age sites, ranging from 4700 to 2700 years old, and identified the turtle species from the bone’s proteins.

Previous studies had shown the plants of different seagrass meadows each have unique chemical signatures. As sea turtles graze, those signatures eventually register in their body. The scientists sampled the bones to measure their chemical makeup, adjusting for atmospheric changes over the past few thousand years. Then, they created models to try to see how the signatures of modern meadows lined up with the skeletons.

Iron Age turtles fed in the same meadows as turtles today, the team reports today in the Proceedings of the National Academy of Sciences.

It “really surprised me,” says Willemien de Kock, the study’s first author and a postdoctoral researcher at the Groningen Institute of Archaeology. “We were able to look so far into the past, and still see the same behavior from the turtles.” The study shows animals have traditions, too, she says. “The question is, what happens if these areas go?”

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Most conservation focuses on where sea turtles breed, the authors note. “We see little baby turtles and we go, OK, we need to protect these,” says Alberto Taurozzi, a co-author of the study and paleobiologist at the University of Copenhagen. But turtles only breed once every few years. They spend most of their lives in these often-overlooked meadows on the North African coast.

De Kock, who studied seagrass meadows before her Ph.D., emphasizes that dependency goes both ways. For seagrasses to stay “lush,” de Kock says, the meadows need turtles to graze them.

But she says climate change threatens the future of these meadows, because they get less time to recover between record-setting heat waves. All of the foraging grounds her team identified do not have any governmental protections; many lie on the North African coast where conflict restricts research and oil developments are planned. Without protection from other stressors, Broderick says, green sea turtles may need a new place to go. Losing these seagrasses could also affect a host of other species and destroy an increasingly important buffer against climate change, she says.

Such historical, interdisciplinary research is critical for conservation, Conrad says. This combination of ancient chemistry and modern satellite techniques could be applied to understand other marine animals such as fish and whales, he says. “We have some responsibility to tell their story, a little bit more clearly, a little bit more fully to the rest of the world.”

Source:

Tanvi Dutta Gupta at Science

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