Spatial distribution of marine macro-litter on the seafloor in the northern Mediterranean Sea: the MEDITS initiative

Abstract

Marine litter is one of the main sources of anthropogenic pollution in the marine ecosystem, with plastic representing a global threat. This paper aims to assess the spatial distribution of plastic macro-litter on the seafloor, identifying accumulation hotspots at a northern Mediterranean scale. Density indices (items km–2) from the MEDITS trawl surveys (years 2013-2015) were modelled by generalized additive models using a Delta-type approach and several covariates: latitude, longitude, depth, seafloor slope, surface oceanographic currents and distances from main ports. To set thresholds for the identification of accumulation areas, the percentiles (85th, 90th and 95th) of the plastic spatial density distribution were computed on the raster data. In the northern Mediterranean marine macro-litter was widespread (90.13% of the 1279 surveyed stations), with plastic by far the most recurrent category. The prediction map of the plastic density highlighted accumulation areas (85th, 90th and 95th percentiles of the distribution, respectively, corresponding to 147, 196 and 316 items km–2) in the Gulf of Lions, eastern Corsica, the eastern Adriatic Sea, the Argo-Saronic region and waters around southern Cyprus. Maximum densities were predicted in correspondence to the shallower depths and in proximity to populated areas (distance from the ports). Surface currents and local water circulation with cyclonic and anticyclonic eddies were identified as drivers likely facilitating the sinking to the bottoms of floating debris.

Impacts of Marine Litter on Mediterranean Reef Systems: From Shallow to Deep Waters

“…Standardization of monitoring approaches and existing datasets is under development across European countries to generate comparable information about the temporal and spatial distribution of marine litter and its impact (Molina Jack et al, 2019). Since the MSFD included marine litter as one of the eleven descriptors to define the GES of European seas (Galgani et al, 2013), seafloor litter data collection has significantly increased in the last years, mainly through trawlsurveys (Maes et al, 2018;Spedicato et al, 2019). Litter items in fishery catches are now regularly recorded in many European countries as part of other environmental monitoring activities (e.g., the MEDITS program; Spedicato et al, 2019).…”

“…Since the MSFD included marine litter as one of the eleven descriptors to define the GES of European seas (Galgani et al, 2013), seafloor litter data collection has significantly increased in the last years, mainly through trawlsurveys (Maes et al, 2018;Spedicato et al, 2019). Litter items in fishery catches are now regularly recorded in many European countries as part of other environmental monitoring activities (e.g., the MEDITS program; Spedicato et al, 2019). Instead, no uniform programs exist to collect litter data on reefs/hard substrata and to assess/quantify litter harms on marine biota (as requested by D10C4 of the MSFD and Indicator 24 of the EcAp).…”

“…However, the most common method to study seafloor litter is still through trawling hauls (i.e., otter, beam, Agassiz trawl), mainly for its lower costs of operation in comparison with other methods and large scale evaluation (e.g., Galgani et al, 1996Galgani et al, , 2000Stefatos et al, 1999;Moore and Allen, 2000;Lee et al, 2006;Koutsodendris et al, 2008;Keller et al, 2010;Sánchez et al, 2013;Neves et al, 2015;Pasquini et al, 2016;Fortibuoni et al, 2019;Spedicato et al, 2019). In trawl surveys, litter is taken onboard and thus can be directly inspected, measured, counted, and weighed, allowing to obtain quantitative data.…”

How to Deal With Seafloor Marine Litter: An Overview of the State-of-the-Art and Future Perspectives

“…Gerigny et al 2019analyses a 24-year time series of data based on trawling for fish stock assessment of the MEDITS project in a large area of the French Mediterranean continental shelf. A similar approach has been recently adopted for other parts of the Mediterranean Sea (e.g., Galgani et al, 2013;Pasquini et al, 2016;Fortibuoni et al, 2019;Spedicato et al, 2019). However, bottom trawlers present several limitations: (1) they are invasive for the seafloor; (2) they cannot operate on rocky bottom where litter (such as ALDFG) is likely to accumulate; and (3) they do not give precise information about the spatial distribution of the litter on the seafloor.…”

Lessons learned from an intercalibration exercise on the quantification and characterisation of microplastic particles in sediment and water samples

“…pellets). These particles, highly persistent in the environment (Alimba and Faggio, 2019), are present in all marine matrices: water, sediment, biota, (Li et al, 2016;Peng et al, 2020;Sharma and Chatterjee, 2017) from the coastline to offshore areas, including deep sea submarine canyons (Alomar et al, 2017;Spedicato et al, 2019). An increasing number of studies are also investigating the consequences of chemical contamination of the marine ecosystem by substances such as bisphenol A and phthalates added during the manufacture of certain plastics (Vered et al, 2019).…”