Coastal margins and backshores represent a major sink for marine debris: insights from a continental-scale analysis

Marine debris represents a major threat for the environment. Plastic production is increasing exponentially and causing an unprecedented growth of plastic pollution entering the marine environment. Hence, a thorough assessment of debris accumulation areas is required to address the longstanding question about where is all the missing plastic. Most research on marine debris sinks to date has focused on oceanic gyres, the water column, seabeds and wildlife. Relatively little has focused on the potential of coastal areas as debris sinks. To address this knowledge gap, the spatial distribution of debris from the waterline to the backshore was modelled from a continental-scale dataset of coastal debris distribution from 635 surveys across Australia. Results showed that the distribution of debris is significantly correlated with oceanic and atmospheric processes (i.e. onshore Stokes drift and wind), and coastal usage for recreational activities (i.e. regional population and distance to the nearest road). Debris density and size increased from the waterline to the backshore, indicating that the backshore area represents an important debris sink, especially for larger sized items.