The results from the various investigations and monitoring programmes presented in this report demonstrate the continuous and widespread occurrence of litter in the Wadden Sea and adjacent offshore waters. Marine litter of different sizes and from diverse sources occurs on dunes and beaches, in and on inter- to subtidal sediments and in marine organisms, including protected seabirds and mammals. The OSPAR Beach Litter Monitoring and Monitoring on Litter in Fulmars’ Stomachs provide an evaluation of the temporal development of litter abundance in the southern North Sea. Both programmes clearly show that litter densities have not declined since the last Wadden Sea QSR in 2009, indicating that large amounts of litter are still entering the marine environment either directly within the Wadden Sea or from adjacent waters. The amount of litter entering the marine environment is continuously increasing
(Jambeck et al., 2015). This increase is, however, not apparent in the results of the two monitoring programmes. Litter degrades in the marine environment and breaks down into ever smaller fragments. The fragmentation of plastic objects produces microplastics, which are not sufficiently assessed by current monitoring programmes. Densities of microplastics are expected to increase substantially in the future in all marine habitats. Accordingly, scientifically sound monitoring of these synthetic particles with standardized methods that allow for the comparison of results from different programmes will be indispensable.
Marine litter is not restricted to specific habitats but occurs in all compartments of the marine environment with a constant exchange between them. Accordingly, monitoring litter densities in both coastal and offshore habitats is essential for a sound evaluation of litter pollution of the Wadden Sea. Many of the investigations presented in this report are on-off events, which do not provide information on temporal trends. However, they do demonstrate that the Wadden Sea is contaminated with marine litter and that litter densities in the Wadden Sea are not lower than in other coastal regions. The litter densities presented in this report provide a valuable baseline for future evaluations of temporal trends. The monitoring of litter in fulmars’ stomachs and the examinations of carcasses of harbour porpoise, harbour seals and eider ducks revealed that litter does not simply occur in the marine environment but actually interacts in a potentially harmful way with the marine biota. It is well established that the ingestion of litter can have deleterious and often lethal effects on marine organisms. It is yet unknown whether marine litter has demographically relevant implications for marine species. For evaluating this, the effects of marine litter must not be considered in isolation but always together with the effects of other environmental stressors such as ocean warming and acidification, eutrophication and the exploitation of natural stocks (see reports on climate change, geomorphology, eutrophication and fisheries). Several
Wadden Sea Plan targets are compromised by the continuous pollution of the North Sea with marine litter. A proper management of the marine litter problem will require appropriate reduction measures and extended and optimized monitoring programmes in order to evaluate future developments.