Abstract
Understanding the drivers of key interactions between marine vertebrates and plastic pollution is now considered a research priority. Sea turtles are primarily visual predators, with the ability to discriminate according to colour and shape; therefore these factors play a role in feeding choices. Classification methodologies of ingested plastic currently do not record these variables, however here, refined protocols allow us to test the hypothesis that plastic is selectively ingested when it resembles the food items of green turtles (Chelonia mydas). Turtles in the eastern Mediterranean displayed strong diet-related selectivity towards certain types (sheet and threadlike), colours (black, clear and green) and shapes (linear items strongly preferred) of plastic when compared to the environmental baseline of plastic beach debris. There was a significant negative relationship between size of turtle (curved carapace length) and number/mass of plastic pieces ingested, which may be explained through naivety and/or ontogenetic shifts in diet. Further investigation in other species and sites are needed to more fully ascertain the role of selectivity in plastic ingestion in this marine vertebrate group.
Highlights
The abundance and spatial distribution of plastic pollution in the world’s oceans is ever increasing, and thought to be emerging as one of the most ubiquitous and long-lasting changes in natural systems[1,2,3]
All green turtles, where whole GI tracts were available (n = 19), had ingested plastics with individuals having ingested an average of 61.8 ± 15.8 items; ranging from 3–183 pieces (Fig. 1a)
The current work suggests that green turtles foraging in coastal waters of Cyprus regularly encounter and ingest plastic, so much so that the vast majority of animals contain some plastic in their GI tract, at the time of their death
Summary
The abundance and spatial distribution of plastic pollution in the world’s oceans is ever increasing, and thought to be emerging as one of the most ubiquitous and long-lasting changes in natural systems[1,2,3]. Www.nature.com/scientificreports plastic bottle lids ingested by loggerhead turtles (Caretta caretta) is thought to be because their round shape and presence floating near the surface means they resemble organisms that are normally preyed upon[12]. Such studies have prompted investigations into possible selective plastic ingestion[11]. Sea turtles are primarily visual feeders and an ability to discriminate among colours and shapes has been shown to play a role in feeding choices[11,31] Monitoring these aspects may offer insight into whether turtles are selectively ingesting some plastics. Data from beach plastic surveys have been used to set environmental baselines to investigate differences and selectivity with benthically feeding green and hawksbill (Eretmochelys imbricata) turtles (Queensland, Australia), which show a strong preference for ingesting clear sheet or rope like plastics and avoiding harder coloured pieces[11]
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