Comparing marine anthropogenic debris on inhabited mainland beaches, coastal islands, and uninhabited offshore islands: A case study from Queensland and the Coral Sea, Australia

Highlights: • Abundance and type of AD differed between mainland, coastal and remote islands. • Durable buoyant AD, especially hard plastic, dominated remote beaches. • AD on remote island beaches had a strong relationship with onshore forcing. • AD types found solely on visited/inhabited sites arrived mainly via direct deposition. • Islands likely act as sinks for floating plastic. Anthropogenic debris (AD) including plastics, foams and fishing debris, are an undesirable accompaniment to beaches worldwide, arriving through direct deposition (littering) and oceanic transport. We investigated the standing stocks of 12 types of AD on inhabited islands, uninhabited islands and mainland locations, and the potential factors relating to AD deposition. We undertook beach-transects and sea-surface trawl surveys; comparing 13 uninhabited offshore islands, four inhabited/touristed coastal islands and 81 mainland beaches in Queensland, Australia. The abundance and type of AD differed between sites. Geographic factors had stronger relationships with AD density on islands than mainland beaches. Hard plastic density was linked with forcing from wind and sea surface currents. Beach width and onshore/side-shore forcing were the most important factors affecting AD loads (predominantly hard plastics) on islands. We found an inverse relationship between the density of beached plastic and plastic floating at the sea surface nearby and suggest that islands may act as a local sink for buoyant plastic.