The Impact of Plastic Pollution on Marine Turtles

Plastic debris is entering into the marine environment at an accelerating rate, now becoming one of the most ubiquitous and long-lasting changes in natural systems. Marine turtles are large marine vertebrates with complex life histories and highly mobile behaviour that may make them particularly vulnerable to its impacts. The main goals of this thesis were to i) evaluate the potential implications of the presence of plastic pollution in the environment to marine turtles by reviewing current literature ii) provide a global summary of the issue of entanglement in this taxon, utilising a global network of experts iii) explore the drivers of key interactions between marine turtles and plastic ingestion and develop novel additions classification methodologies to explore selective ingestion of plastics iv) develop a methodology for investigating and isolating the presence of microplastic ingestion in marine turtle gut content and v) examine plastic pollution on a key habitat for marine turtles e.g. nesting beaches. Major findings of the thesis include i) the issue of entanglement with plastic debris, the majority in ghost fishing gear, is both an under-reported and under-researched threat ii) a clear display of strong diet-related ingestion towards plastic debris that resemble natural food items, utilising a case study of green turtles in Northern Cyprus iii) a method development that allowed the identification and isolation of a suite synthetic particles in gut content residue samples, providing evidence of ingestion of synthetic debris at the microscopic size class iv) a more comprehensive viewpoint on plastic concentrations on nesting beaches, in the form of 3D sampling to investigate subsurface plastic densities, showing microplastics present down to turtle nesting depth of both loggerhead and green turtles in Northern Cyprus. In conclusion, this thesis forms the most detailed and comprehensive investigation to date on the impacts of this pollutant on the taxon of marine turtles; contributing to knowledge into macro and microplastic ingestion, entanglement and key habitats through method development and integration of marine turtle feeding ecology and developmental biology.