Green sea turtles have returned to the same place to eat for 3,000 years

It’s not uncommon to think of certain animals as creatures of habit, returning to their birthplace to mate or nesting in the same locations each year. However, a recent study reveals an unexpected level of continuity in the dining habits of green sea turtles, underscoring the need for habitat protection amidst a climate crisis.

For approximately 3,000 years, generations of green sea turtles have returned to the same seagrass meadows for meals. This fascinating discovery was made by Willemien de Kock, a historical ecologist at the University of Groningen. 

De Kock’s research opens up a new understanding of the endurance of sea turtles’ behavioral patterns, which extend well beyond previously known timeframes.

Multi-generational consistency 

The migratory patterns of sea turtles, from specific breeding locations to distinct feeding areas, are not a new revelation for the scientific community. But the multi-generational consistency in feeding locations underscores the necessity of safeguarding the seagrass meadows along the North African coastlines. 

Sea turtles begin life under challenging circumstances. When their parents embark on a long journey after hatching, these young sea turtles clumsily venture from the beach into the ocean. 

For the initial years of their lives, these turtles aren’t particularly discerning eaters and sustain themselves on an omnivorous diet. However, around the age of five, green sea turtles instinctively navigate toward the seagrass meadows that their parents used to frequent, adopting a more herbivorous dietary routine.

Many efforts have been made to safeguard the nests of endangered green sea turtles along the eastern Mediterranean coasts. The seagrass meadows, however, are bearing the brunt of the climate crisis. “We currently spend a lot of effort protecting the babies but not the place where they spend most of their time: the seagrass meadows,” said De Kock. 

Focus of the study

To investigate, De Kock delved into boxes of sea turtle remains from archaeological sites across the Mediterranean, housed in the attic of the Groningen Institute of Archaeology. With her supervisor Dr. Canan Çakırlar having previously conducted the excavations, De Kock’s task was to sift through these remains.

The meticulous examination of the sea turtle bones led De Kock to distinguish two species – the green sea turtle and the loggerhead turtle – and understand their diets. The key to this was bone collagen, a substance that preserves evidence of the creature’s diet. Using a mass spectrometer to examine the bone collagen, De Kock was able to identify the types of plants the 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,” explained De Kock. “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.”

How the research was conducted 

Collaborating with researchers at the University of Exeter, De Kock incorporated modern satellite tracking data that provided information about the present-day traveling routes and destinations of sea turtles. 

The team at Exeter had also been collecting tiny samples of sea turtle skin, which revealed dietary insights similar to what De Kock had discovered from the ancient bones.

Based on this data, De Kock managed to link the dietary preferences of green sea turtles from millennia ago to specific geographical locations. She discovered that for around 3,000 years, green sea turtle generations have been feeding on seagrass meadows along Egypt and West Libya’s coasts. The loggerhead turtles’ results were less specific, attributable to their more varied diet.

Implications of the study

Understanding the historical eating habits of a species over generations carries significant implications. It helps combat the “shifting baseline syndrome” – a phenomenon where slow changes in a larger system go unnoticed as each generation of researchers redefines the natural state based on their initial observations.

“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.”

Recent models project a concerning future, with high risks of widespread seagrass loss in the very regions that green sea turtles have frequented for thousands of years. Such a change could be devastating for these creatures, given their longstanding loyalty to these particular feeding locations. 

The research is published in the journal Proceedings of the National Academy of Sciences. 

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