Identification of non-indigenous and other fouling species on marine litter using DNA metabarcoding : A comparison of marine taxa found on plastic litter and settlement plates collected from beaches and a harbour in the Netherlands, and a comparison to taxa found on marine litter in Iceland

Summary

Plastics from consumers and economic activities enter the oceans in increasing numbers. The resulting debris can not only cause mortality for seabirds and marine mammals, but by means of winds and currents can also function as a floating vessel for algae and animals that transport these species to places where they do not naturally occur. Here, we studied fouling animals and algae on marine litter found along the Dutch coast (2019-2021). In addition, ‘settlement plates’ were used to be able to make a distinction between exotic species already present in the Netherlands and newly arrived exotics that come along with the plastic litter. To identify the animal and algal species, DNA metabarcoding was used. Combined application of two barcoding markers (18SV4 and COI) showed the potential to identify fouling in many cases to species level. In total, 46 non-indigenous algae and animals were detected, including mostly taxa that have already been recorded in the Netherlands before, but also twelve potential newcomers for the Netherlands and 6 not recorded before in the NE Atlantic region. Identification of fouling species can therefore help to 1) assess potential risks of floating marine litter as a vector for the introduction of non-indigenous species, and 2) to establish a minimum age and origin of the plastic that can help in determining and/or modelling where the plastic may have come from. Geographical origin assessment can be used to identify the sources and potential risks to the ecosystem of floating marine litter.