From coastal to oceanic micro-meso and macroplastics in the SE Bay of Biscay

Several numerical models predict that the SE Bay of Biscay is a critical area for oceanic litter accumulation because of its geography and metocean conditions; and yet, the knowledge of marine litter is limited in the region. This has led local authorities to seek scientific ad- vice to manage this new challenge. Here we show the results of 3 oceanographic surveys that cover different oceanic regions of the Bay of Biscay: BIOMAN (May 2017), ETOILE (August 2017) and LEMA (Sept-Nov 2017 and May-Sept 2018), where 210 water surface samples were taken with a 500 im mesh-size neuston net. Results map the spatio-temporal distribution of micro-mesoplastic abundance, from coastal to oceanic waters. Micro-mesoplastic abundance in general follows an expected gradient from coastal to oceanic waters, but also shows high variabil- ity within the same water mass. Some coastal water samples contained high abundance levels with almost 1500·103 items km-2 in coastal waters in contrast to low levels (16·103 items km-2) in deeper waters, while no plastic was found in others. Such variability highlights the importance of understanding how the meso and small-scale ocean features (e.g. eddies, fronts), which are frequent on coastal waters, may influence and help to predict micro-mesoplastic accumulation hotspots for management purposes. Micro-mesoplastic abundance and characterisation results are completed with macro-litter mapping obtained for the same region by: (i) fishing vessels devoted to collect marine litter from coastal waters (May- September 2018); and (ii) visual detection of macro-litter (JUVENA and BIOMAN ecosystemic surveys). We anticipate that our results have started to provide data of marine litter abundance and sources, and that they are currently being used as a baseline to work with relevant authorities, sectors and industries (such as the fishing sector) regarding their responsibility in the prevention and the development of management strategies to deal with marine litter locally.