Hungry green sea turtles have eaten in the same seagrass meadows for about 3,000 years
'We currently spend a lot of effort protecting the babies, but not the place where they spend most of their time: the seagrass meadows.'
Green sea turtles could be putting even the pickiest eaters to shame. Generations of them have returned to the same seagrass meadows along the coasts of northern Africa to feast for roughly 3,000 years, according to a study published July 17 in the journal PNAS.
[Related: Endangered green turtles are bouncing back in the Seychelles.]
When baby green sea turtles hatch on the beaches of the Mediterranean Sea, they clumsily make their way into the ocean. Their parents have already left the shallows for a long migration, and baby sea turtles are not able to navigate this long trip, so they float around for a few years. During this awkward stage, they are typically not picky eaters. The youthful turtles are even considered omnivores, eating worms, insects, and crustaceans along with seagrasses. At about five years-old, they trek to the same areas where their parents traveled to eat the more seagrass-exclusive diet of herbivores.
While scientists have known that sea turtles migrate between specific eating and breeding locations, seeing how far back this activity stretches highlights the importance of conserving sea grass locations that are suffering the effects of climate change the same way that nesting habitats are protected.
“We currently spend a lot of effort protecting the babies, but not the place where they spend most of their time: the seagrass meadows,” study co-author and University of Groningen marine evolution and conservation PhD student Willemien de Kock said in a statement.
The study from the University of Groningen in the Netherlands combined archaeological findings with modern data. De Kock used boxes of sea turtle remains from archaeological sites in the Mediterranean Sea. By analyzing the bones, De Kock could distinguish two species within the collection: the green sea turtle and the loggerhead turtle.
From there, De Kock was also able to identify what both species had been eating and found that they relied on bone collagen in the plants. She used a mass spectrometer to inspect the bone collagen in the turtle remains and found what types of plants the sea turtles ate.
“For instance, one plant might contain more of the lighter carbon-12 than another plant, which contains more of the heavier carbon-13. 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,” De Kock said.
Satellite tracking data from the University of Exeter in the United Kingdom revealed the current traveling routes and destinations of sea turtles. The team from Exeter had also been taking tiny skin samples from the sea turtles, which revealed similar dietary information that was present in the ancient bone samples. De Kock could then draw conclusions by connecting the diets of turtles from thousands of years ago to specific locations. The study found that for about 3,000 years, numerous generations of green sea turtles have been feeding in the same seagrass meadows along the coasts of Egypt and West Libya.
[Related: Tiger sharks helped scientists map a vast underwater meadow in the Bahamas.]
Loggerhead turtles showed a more varied diet than the green sea turtles, so their results were less specific.
Understanding more about how a species eats over past generations can help counteract shifting baseline syndrome. This is when slow changes to a larger system, like animal populations, are unnoticed since each new generation of researchers may redefine what the natural state was based on how the environment was at the start of their careers.
“Even long-term data goes back only about 100 years. 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,” De Kock said.
Recent models have forecasted a high risk of widespread seagrass loss right where green sea turtles have been migrating for generations. Losing these food resources could be detrimental to the green sea turtle, and future conservation efforts can include supporting seagrass planting efforts, reducing greenhouse gas emissions, and building better signs and markers so that boats do not weigh anchor in seagrass meadows.
