One in three loggerhead turtles in the Adriatic Sea has plastic in its intestine, according to researchers studying the impact of debris on marine life.
The shallow waters of the Adriatic are important feeding grounds for the turtles as they develop into adults.
But the sea-floor is one of the most polluted in Europe.
The team studied the bodies of dead sea turtles that had been stranded or accidentally caught by fishing vessels.
The impacts of debris on marine creatures are not entirely clear. But scientists have found that animals ranging from invertebrates to large mammals consume plastic waste and are concerned that it could damage their health.
For a turtle, just a few grams of debris can be fatal if it obstructs the gut.
The researchers from the University of Zagreb found that more than a third of the 54 turtles they examined had ingested marine debris of some kind including plastic bags, wrapping foils, ropes, polystyrene foam and fishing line.
One turtle had consumed 15 pieces of plastic, which almost filled its stomach.
Although the plastic weighted just 0.71g in total, they said it was enough to “probably cause the death of this individual”.
Plastic can weaken the turtles by taking up space in the gut which would otherwise digest food.
The shallow coastal waters of the northern Adriatic are one of the most important feeding grounds for loggerhead turtles in the Mediterranean. Here they are able to progress to feeding on the sea floor at a young age.
The southern Adriatic is also important in their development into ocean-going animals.
“It is important to know more about the Adriatic Sea in order to help loggerhead turtles across the whole Mediterranean.” says Romana Gracan, one of the researchers involved in the study.
“The water temperature here suits them and because it is shallow they have the opportunity to feed on benthic [sea-floor] animals.”
The concentration of litter on the sea floor is among the highest along European coasts, after the northwestern Mediterranean and the Celtic Sea.
The waste comes from the dense population of four million people who live along the coast and are joined each summer by 18 million tourists.
The sea is small and largely cut off from the rest of the Mediterranean, only joined to the Ionian Sea by the 70km wide Strait of Otranto.
Loggerhead turtles (Caretta caretta) are omnivorous feeders that feed at a variety of different depths.
Where the Mediterranean is too deep for the turtles to reach the sea floor, they feed on floating animals.
But in shallower coastal waters of the Adriatic they take the opportunity to feast on larger sea-floor animals. This brings them into contact with large amounts of debris.
The researchers say their study, published in the journal Marine Pollution Bulletin, is the first to address the problems caused by solid debris in the Adriatic Sea.
Chemical pollution in the Adriatic has been studied for more than 30 years and is already central to marine conservation in the Mediterranean.
The researchers hope that, now they have shown that the turtles are particularly vulnerable to plastic debris, more will be done to reduce it.
“Loggerheads are opportunistic feeders which will eat almost anything that is in front of them and plastic stays around for a very long time in the sea,” says Dr Gracan.
“In the future we must think more carefully what we put in the sea.”