Picky sea turtles have chosen to munch in this one spot for 3000 years

A blend of modern data and archaeological findings underscores the timeless importance of safeguarding North African seagrass meadows.
Sade Agard
Green Sea Turtle grazing on seagrass beds on Red Sea - Marsa Alam - Egypt
Green Sea Turtle grazing on seagrass beds on Red Sea - Marsa Alam - Egypt


For approximately 3,000 years, generations of green sea turtles have returned to the same seagrass meadows to eat, discovers a recent study published in PNAS on July 17.

The multi-generational nature of sea turtle migrations, as solidified by modern and archaeological data findings, emphasizes the value of preserving North African coastal seagrass meadows for their habitat.

Unearthing old sea turtle bones

When young green sea turtles hatch, they venture into the ocean while their parents embark on a long migration. After years of floating around, the young turtles eventually navigate their way to the same area where their parents went, where they feast on a herbivore's diet of seagrass.

"We currently spend a lot of effort protecting the babies but not the place where they spend most of their time: the seagrass meadows," emphasized the study's lead author Dr. Willemien de Kock, in a press release. 

Significantly, these seagrass meadows are being negatively impacted by the climate crisis.

In the attic of the Groningen Institute of Archaeology at the University of Groningen, researcher De Kock discovered boxes filled with sea turtle remains from ancient sites in the Mediterranean Sea region. Her supervisor, Dr. Canan Çakırlar, had previously conducted these excavations.

"All I had to do was dig in some boxes," said De Kock. By analyzing the bones, she was able to distinguish two species within the collection of bones: the green sea turtle and the loggerhead turtle. 

Picky sea turtles have chosen to munch in this one spot for 3000 years
The migration routes of green sea turtles (red and white stripes) between their nesting grounds (circles) and the seagrass meadows where they eat (triangles).

She then determined the sea turtles' diet by examining bone collagen. Using a mass spectrometer, De Kock analyzed the bone collagen to identify the specific plants the sea turtles consumed.

"For instance...one plant might contain more of the lighter carbon-12 than another plant, which contains more of the heavier carbon-13," she explained. 

"Because carbon does not change when it is digested, we can detect what ratio of carbon is present in the bones and infer the diet from that."

A dose of satellite tracking 

Using modern satellite tracking data, De Kock obtained valuable insights into the current migration patterns and destinations of sea turtles. Additionally, researchers from the University of Exeter collected small samples of sea turtle skin, which revealed dietary information similar to the findings from the bone analysis. 

By combining these sources, De Kock established connections between the diets of sea turtles from thousands of years ago and specific locations. 

Her research unveiled a fascinating discovery: for approximately 3,000 years, successive generations of green sea turtles have been feeding on seagrass meadows along the coasts of Egypt and West Libya. However, the dietary patterns of loggerhead turtles were less precise due to their more varied diet. 

"Even long-term data goes back only about 100 years,' said De Kock. "But tracing back further in time using archaeological data allows us to better see human-induced effects on the environment. And it allows us to predict a bit."

The authors highlighted that recent models indicate a significant threat of extensive seagrass decline in the very areas where green sea turtles have relied for thousands of years. 

The full study was published in PNAS on July 17.

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