Inter-annual and seasonal variability in the occurrence of floating¯o:debris in the Northern Ionian and Southern Adriatic Sea
Seasonal and inter-annual changes in the occurrence of floating anthropogenic (AMD) and natural (NMD) debris (>2 cm) were investigated during two visual surveys carried out in the Southern Adriatic and Northern Ionian Sea between May-June 2013 and March 2015. Despite a very similar geographic coverage and sampling effort (e.g. 328.8 km vs 300.5 km surveyed), three times more floating objects were sighted in 2015 and significant differences in the abundance and composition of floating debris were observed between the two surveys (Fig.1). Proportion of anthropogenic litter remained constant (80.1% vs 80.6% of all sighted items), even though less Styrofoam items were observed in 2015 (29.6% vs 11.8% of all litter items). Mean AMD and NMD densities increased four-fold in 2015 survey, going from 27.7± 29.0 AMD and 6.6±11.5 NMD items/km2 recorded in 2013 to 112.8±168.6 AMD and 26.5±28.0 NMD items/km2. Given that slightly lower average wind speed were recorded during the 2015 survey (10.5±7.0 kts vs 6.9±2.6 kts), such differences might be better explained, rather than by a detection bias, by other environmental drivers capable of affecting debris inputs to the basin, such as seasonal differences in rainfall rates and/or riverine discharge.