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How many marine litter lay at the sea floor?


How many marine litter lies at the sea floor?

Lead Institute FI Institute of Fisheries Ecology
Beteiligte Institute SF Sea Fisheries OF Baltic Sea Fisheries

A soda can lying at the beach and a plastic bag floating at the surface are visible for everybody. But the major part of marine litter sinks to the sea floor someday and is concealed. How many and which kind of litter is lying there is investigated by the Thünen-Institute using litter in fishery catches.

Background and Objective

Marine litter has become a subject of major concern in recent times. Globally, huge amounts of man-made solid waste materials end up in the oceans coming from both land - and sea-based sources. Levels of marine litter at the seafloor are presumed to be rising with the increasing global population densities and industrial production.

Plastic waste materials are of special concern, as plastic items are highly persistent and compose the dominating category of marine litter. Plastic debris can pose a risk to the marine environment, by causing physical damage in marine organisms via ingestion or entanglement and also due to potential toxic effects .

In Europe marine litter was recognized as major risc factor for the marine environment and consequently included as one of eleven qualitative descriptors for the "good environmental status" in the Marine Strategy Framework Directive (MSFD). The MSFD schedules monitoring programmes for the assessing the status of the marine ecosysteme. Studies on marine litter are often based on an international agreed protocols (e.g. ICES International Bottom Trawl Survey IBTS), for standardized recording of marine macro litter (>2,5cm).


Macrolitter in bottom trawl fishery catches are regularly monitored and categorized according to IBTS.
The amount of litter is given in litter items per km² area covered by the trawl.

Data and Methods

Every litter item collected on board is weighed, photographed and categorized according to IBTS. Platic litter items were taken to the lab to determine polymer composition using FTIR spectroscopy.

Our Research Questions

  • How much litter is present at the sea floor of North Sea and Baltic Sea?
  • Are there regional differences in litter amount and composition?
  • How does the amount of marine litter changes in time?
  • Which polymers are present in plastic litter?
  • Which threats for fish and ecosystem are caused by marine litter?

Preliminary Results

How much litter is present at the sea floor of North Sea and Baltic Sea?
According to Int-Veen et al. (2021, Mar Pollut Bull 172:112876) 49 litter items /km² are present at the seafloor of the North Sea and 10 litter items/km² in the Baltic Sea. However, these numbers are hardly comparable due to different gears used.

Are there regional differences in litter amount and composition?
Yes, close to the coasline litter may consist of different materials like glas, metal or plastic. Off-shore we find plastic only in many cases.

How does the amount of marine litter changes in time?
This is subject of current research. We cannot answer the question yet.

Which polymers are present in plastic litter?
Polyethylen is the polymer we find most in plastic litter items. Polypropylene is the second most frequently polymer.

Which threats for fish and ecosystem are caused by marine litter?
In principle macro litter can be swallowed by organisms and clog their stomach. This may lead to starvation of marine mammals or marine birds. The second threat of macro plastic is entanglement. Fish can entangle e.g. in lost fishing gears. Further on macro plastic can decay to micro plastic which has a different effect on the environment as macro plastic.

Links and Downloads


  1. 0

    Canals M, Pham CK, Bergmann M, Gutow L, Hanke G, Sebille E van, Angiolillo M, Buhl-Mortensen L, Cau A, Ioakeimidis C, Kammann U, Lundsten L, Papatheodorou G, Purser A, Sanchez-Vidal A, Schulz M, Vinci M, Chiba S, Galgani F, Langenkämper D, et al (2021) The quest for seafloor macrolitter: a critical review of background knowledge, current methods and future prospects. Environ Res Lett 16(2):023001, DOI:10.1088/1748-9326/abc6d4

  2. 1

    Maes T, Booth A, Galgani F, Bakir A, Barry J, Buhl-Mortensen L, Clayton L, Devriese L, De Witte B, Gago J, Hall M, Int-Veen I, Kammann U, Noren K, Näkki P, Rindorf A, Russell M, Silburn B, Storr-Paulsen M, Wodzinowski T (2021) Working Group on Marine Litter (WGML; outputs from 2020 meeting). Copenhagen: ICES, 90 p, ICES Sci Rep 3(51), DOI:10.17895/

  3. 2

    Kammann U, Aust M-O, Bahl H, Lang T (2018) Marine litter at the seafloor - abundance and composition in the North Sea and the Baltic Sea. Mar Pollut Bull 127:774-780, DOI:10.1016/j.marpolbul.2017.09.051

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