For approximately 3,000 years, generations of green sea turtles have returned to the same sea pastures to feed.
It was discovered by Willemien de Kock, a historical ecologist at the University of Groningen, by combining modern data with archaeological findings.
Sea turtles migrate between specific breeding grounds and feeding grounds throughout their lives—this much is known. But the fact that it lasts for many generations highlights the importance of protecting the seagrass meadows along the coast of North Africa. The results were published in PNAS on July 17.
When the young green sea turtles hatch, their parents leave for the long journey. The little turtles naively emerge from the beach into the sea and, having never sailed the long migration of their parents, float for years. During this time, they are not very picky eaters, even omnivores. Then, at about five years old, they swim to the same place where their parents went, to eat a herbivore diet of seagrass.
On the shores of the eastern Mediterranean Sea, volunteers are active in protecting the nests of the endangered green turtle. But, as Willemien de Kock explains, “Today we spend a lot of effort to protect children but not in the place where they spend most of their time: the seaweed.” And most importantly, these seagrass meadows are suffering the effects of the climate crisis.
Analysis of turtle bones
In the attic of the Groningen Institute of Archeology at the University of Groningen, De Kock has access to boxes full of turtle remains from archaeological sites in the Mediterranean Sea area. The excavations were done by his supervisor, Dr. Canan Çakırlar. “All I had to do was dig through some boxes,” De Kock said. By analyzing the bones, De Kock was able to identify two species within the collection of bones: the green sea turtle and the loggerhead turtle.
De Kock also knows what turtles eat. It relies on a substance called bone collagen. By inspecting the bone collagen with a mass spectrometer, De Kock noted what kind of plants the turtles ate. “For example,” explains De Kock, “one plant may have much lighter carbon-12 than another plant, which has much heavier carbon-13. of carbon is in the bones and say the food from that.”
Combining the old and the new
Modern satellite tracking data from the University of Exeter then provided De Kock with information on the sea turtles’ current travel routes and destinations.
Researchers from Exeter also took small samples of turtle skins, which revealed similar dietary information as De Kock found in the bones. Therefore, De Kock was able to draw conclusions, connecting the diets of millennia ago to specific places. He found that for approximately 3,000 years, generations of green sea turtles have been feeding on sea grass meadows along the coasts of Egypt and West Libya. The results for loggerhead turtles are less specific because they have a different diet.
So, why is it important to know the eating habits of a species over many past generations? Because we collectively suffer from the shifting baseline syndrome: slow changes in a larger system, such as an animal population, go unnoticed because each generation of researchers changes the what was the natural state, as they saw it at the beginning of their careers.
“Even the long-term data only goes back about 100 years,” says De Kock. “But going back further in time with archaeological data allows us to better see human impacts on nature. And it allows us to predict, a little bit.” In fact, recent models show a high risk of widespread loss of seagrass precisely in these areas where the green sea turtle goes for millennia. This may harm the green turtle, precisely because of the high fidelity of these areas.
de Kock, Willemien, Threatened North African seagrass meadows have supported green turtle populations for millennia, Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2220747120
Provided by the University of Groningen
Citation: Green sea turtles have been traveling to the same place to feed for 3,000 years, ecologist discovers (2023, July 17) retrieved on July 17, 2023 from https://phys.org/news/2023-07- green-sea-turtles-years-ecologist.html
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