Diversity but not abundance of ingested plastics changes with ontogenetic dietary shift: Stable isotope insights into plastic contamination in a mesopelagic predator longnose lancetfish Alepisaurus ferox.

We employed Fourier infrared spectroscopy, laser infrared technology, and stable isotope analysis to investigate the relationships between characteristics of ingested plastics and size-related feeding ecology of a mesopelagic predator, longnose lancetfish Alepisaurus ferox. Plastics were detected in 81.48 % of specimens, up to 8.81 ± 8.29 items/individual and 0.59 ± 0.66 items/g wet weight of intestine, and were sized 20.00 μm to 6.50 cm. The majority were granules and fragments in shape, and polystyrene and acrylate copolymer in polymer type. The diversity indices exhibited a correlation with trophic position and body size groups, emphasizing that the ontogenetic dietary shift of A. ferox may influence the diversity of plastics ingested. This study provides new insights into the plastic pathways linking epipelagic and mesopelagic food webs and demonstrates that biochemical ecological tracers can effectively indicate the bioavailability of plastic correlated with growth in mesopelagic predator.