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

Marine plastic pollution is an identified contaminant of emerging concern, with expected increases in contamination levels if plastic production projections eventuate. Scientists, managers and the public are increasingly interested in understanding the status and temporal trends of plastic contamination in the marine environment and specifically the Great Barrier Reef (GBR). Presented in this study is the first temporal assessment of plastic contamination in the surface waters of the GBR, Australia. This was accomplished by conducting replicate surface seawater samples (n=66) adjacent to the SS Yongala shipwreck (central GBR), in Bindal sea country, between 2016 and 2019 using a neuston net. The processing workflow included a stringent protocol involving density flotation, filtration, visual identification and sizing of putative plastics using stereomicroscopy, and chemical characterisation using Fourier transform infrared spectroscopy (FTIR). Overall, a total of 533 plastic items were identified and confirmed as plastic, with plastics detected in every single replicate tow, bar one. Polyethylene and polypropylene were the most common polymers present, and were comprised of macro-, meso- and microplastic fragments and fibres. Concentrations of plastic fluctuated across the three years, with spikes related to wind-speed and extreme weather events. However, overall plastic trends did not significantly increase or alter throughout the study period. This study reveals the chronic presence of plastic debris in the surface waters of the central GBR and highlights the need for long-term monitoring of the marine environment for plastic contamination.