Microplastic consumption elevates fish oxidative stress but does not affect predator-driven mortality

The ubiquity and abundance of plastic debris is one of the most significant challenges facing marine environments. Recent research has demonstrated that microplastics are consumed by marine organisms from a wide variety of trophic levels. However, little is known about the sub-lethal effects of microplastic exposure on the health of coral reef fishes or their impacts on predator-prey interactions. To examine this, we exposed juvenile Ambon damselfish (Pomacentrus amboinensis) to one of two types of polystyrene plastic particles (virgin, or with the plasticizer di(2-ethylhexyl) phthalate - DEHP), and a control (no plastic). After 2 days (6 exposures), the initiation of antioxidant metabolism and oxidative defence was quantified. We also exposed the treated juvenile fish to a piscivorous fish (Pseudochromis fuscus) in mesocosms over a 22-h period to investigate whether microplastic exposure affected prey survival. Biomarkers associated with oxidative damage and antioxidant metabolism indicated that microplastic exposure had a negative effect on the health of P. amboinensis. Additionally, P. amboinensis exposed to DEHP microplastics showed the greatest levels of oxidative stress and damage, however the magnitude of this was dependent on the number of ingested particles. Interestingly, survival of P. amboinensis did not differ among plastic treatments during mesocosm survival trials. These results highlight that while studies may not find immediate lethal consequences to plastic ingestion, there may be more subtle sub-lethal costs that may have ecologically important consequences at later life stages, through energetic impacts on growth and energy allocation.