Marine litter in an important topic for the assessment of the environmental status of the seas. The Marine Strategy Framework Directive (MSFD) lists marine litter as one of eleven qualitative descriptors. Therefore marine litter is ranked as high in MSFD as e.g. eutrophication. To combat marine litter is addressed in the action plans developed by G-7 summit in 2015 and G-20 summit in 2017. Therefore marine litter has moved to the center of public attention. Before developing strategies for marine litter reduction, information is needed about number and distribution of litter in the seas.
The three Thünen fishery institutes collect data on marine litter at the sea floor since years. Litter items catched in bottom trawls are classified using the international standardized IBTS protocol . Most litter items are plastic such as sheets, fishing lines and fishing nets. Also glass and metal litter items were collected - sometimes even an old shoe. Plastic litter can be dangerous for marine organisms if they are entangled or swallow the litter blocking their digestive tract. Data on marine litter are part of the environmental assessment as demanded by MSFD.
Another research topic i is microplastic. It can arise from bigger plastic litter items by breakdown (secondary microplastic) or enter the sea directly e.g. as cosmetic ingredient via waster (primary microplastic). Fish can mistake microplastic for food and swallow it. How many microplastic can be found in commerially important fish species is currently under investigation. Effects of microplastic on fish are mostly unknown and are part of recent research in the Thünen Institute.