While plastic waste is a menacing presence on land, there are millions of tiny plastic particles currently floating in our oceans. Marine plastic debris has affected uncountable species, with research showing that plastic makes up 80% of all marine debris. Now, in a new study, published in the Frontiers in Marine Science journal, researchers show that small, juvenile marine turtles from the Indian Ocean and Pacific Ocean are at more risk of ingesting plastic due to their feeding preferences.
When turtles hatch, they adapt to enter the oceanic zone (for green, loggerhead, hawksbill, and olive ridley turtles) or neritic waters (flatback turtles), where they feed, mature and grow further. Normally, these habitats are ideal for their development, but the rapid influx of plastic debris has made these waters risky for juvenile turtles, a news release explains.
The researchers say plastic pollution has created a potential ‘evolutionary trap’ for young turtles. An evolutionary trap, the release explains, occurs when a previously adaptive behavior or habitat now has negative effects on the overall survival and reproduction of a species or organism.
How were the researchers able to determine what type of plastics, and in what quantity, were ingested by small juvenile turtles? They examined the contents of the stomach, intestines, cloaca and bladder of stranded or bycaught specimens from the Indian Ocean off western Australia and the Pacific Ocean off eastern Australia. They looked for plastics inside green (36 in the Pacific and 22 in the Indian Ocean), loggerhead (7 and 14), olive ridley (seven in the Pacific), hawksbill (five and two), and flatback turtles (10 and 18). Plastics were classified according to color and type (for instance, hard plastics, rope, or plastic bags) and the sources of plastic polymers found were also identified, the release adds.
Plastics were only found in the gastrointestinal tract and the amount of plastics (bigger than 1mm) that were ingested also varied by oceans and by species. The highest number of ingested plastic pieces occurred in green turtles: one animal in the Indian Ocean contained 343 pieces, and one animal in the Pacific Ocean contained 144. On the other hand, no plastic ingestion was found in sampled hawksbill turtles from either ocean, but this might have been due to the small sample size, the release explains.
Interestingly, the proportion of turtles that had ingested plastic was much higher in the Pacific Ocean than in the Indian Ocean. The types of plastic found also varied between the two study sites. “Plastic in the Pacific turtles was mostly hard fragments, which could come from a vast range of products used by humans, while Indian Ocean plastics were mostly fibers – possibly from fishing ropes or nets,” Dr Emily Duncan of the University of Exeter and lead author of the study explains in the release.
Duncan explains that the results show it is vital to mitigate and prevent plastic pollution. “The polymers most commonly ingested by turtles in both oceans were polyethylene and polypropylene,” she adds. “These polymers are so widely used in plastic products that it's impossible to pin down the likely sources of the fragments we found, so interventions are needed to stop plastic pollution from land-based sources.”