Determining suitable fish to monitor plastic ingestion trends in the Mediterranean Sea

Abstract The presence of marinelitter is a complex, yet persistent, threat to the health and biodiversity of the marineenvironment, and plastic is the most abundant, and ubiquitous type of marinelitter. To monitor the level of plastic waste in an area, and the prospect of it entering the food chain, bioindicatorspecies are used extensively throughout Northern European Seas, however due to their distribution ranges many are not applicable to the Mediterranean Sea. Guidance published for the Marine Strategy Framework Directivesuggests that the contents of fish stomachs may be analyzed to determine trends of marineplastic ingestion. In order to equate transnational trends in marineplastic ingestion, the use of standardized fish species that widely occur throughout the basin is favoured, however for the Mediterranean Sea, specific species are not listed. Here we propose a methodology to assess how effective Mediterraneanfish species, that are known to have ingested marineplastic, are as bioindicators. A new BioindicatorIndex (BI) was established by incorporating several parameters considered important for bioindicators. These parameters included species distribution throughout the Mediterranean basin, several life history traits, the commercial value of each species, and the occurrence of marinelitter in their gut contents. By collecting existing data for Mediterraneanfish, ranked scores were assigned to each trait and an average value (BI value) was calculated for each species. Based on their habitat preferences, Engraulis encrasicolus (pelagic), Boops boops(benthopelagic), three species of Myctophidae ( Hygophum benoiti, Myctophum punctatumand Electrona risso) (mesopelagic), Mullus barbatusbarbartus (demersal) and Chelidonichthys lucerna (benthic), were identified as currently, the most suitable fish for monitoring the ingestionof marineplastics throughout the Mediterranean basin. The use of standardized indicator specieswill ensure coherence in the reporting of marinelitter ingestiontrends throughout the Mediterranean Sea.