Temporal patterns of plastic contamination in surface waters at the SS Yongala shipwreck, Great Barrier Reef, Australia.

Plastic pollution is ubiquitous within the marine environment, including surface waters, water column and benthic sediments. Marine plastic contamination is expected to increase if future projections of increased plastic production eventuate. Conversely, national and international efforts are aiming to reduce marine plastic contamination. In this context, scientists, managers and the general public are increasingly interested in understanding the status and temporal trends of plastic contamination in the marine environment. Presented here is the first temporal assessment of plastic contamination in surface waters of the Great Barrier Reef (GBR), Australia. Specifically, duplicate surface seawater samples (n = 66) were collected at the SS Yongala shipwreck (Central GBR) monthly from September 2016 to September 2019 and analysed for plastic presence and abundance. The processing workflow involved density separation, followed by filtration, visual identification and sizing of putative plastics using stereomicroscopy, and chemical characterisation using Fourier transform infrared spectroscopy. A total of 533 plastic items were identified across all tows, consisting of macro-, meso- and microplastic fragments and fibres, with polypropylene and polyethylene being the most common polymers. Plastic contamination was detected in every replicate tow, bar one. Plastic concentrations fluctuated and spiked every three months, although contamination did not significantly alter across the three-year period. Wind speed, salinity and river discharge volume, but not surface current speed nor sea surface temperature, had a significant influence on the levels of plastic contamination. This study reveals, for the first time, the chronic presence of plastic debris in the surface waters of the GBR highlighting the need for long-term and on-going monitoring of the marine environment for plastic contamination.