Temporal and Spatial Variations of Marine Litter Scattered on the Soft Seabed in The Sea of Marmara

In this study, marine litter from the seafloor in the Sea of Marmara obtained through several trawl surveys between 1994 and 2021 is evaluated. When the levels of marine litter on the seabed of the Sea of Marmara are considered, there appears a significant increase in the quantity after the year 2000, with this increase particularly concentrating in the Gulf of Izmit and Gemlik, where the effect of current systems is prominent. In 2000, the quantity of plastic waste per unit area was approximately 40 items/km(2), while in 2016 it exceeded 800 items/km(2). Considering the total area for the 20-200 m in the Sea of Marmara, seafloor litter accumulation was calculated as 335 tons in 1994 but 5037 tons in 2021. In 2000, plastic waste accounted for 54% of the total, rising to 75% in 2016, 95% in 2019, and 67% in 2021. The L1 group, which represents plastic waste, is mainly contributed by plastic bags. In 2000, plastic bags accounted for 23% of the total, increasing to 83% in 2019. However, this value significantly decreased in 2021 whilst the "Packaging Plastic" subcategory also increased from 4% in 2000 to 48% in 2016 and 2021. Our analyses revealed that as the depth increases, the quantity and diversity of marine litter decrease, with plastic litter remaining dominant even in deeper waters.