Plastic pollution in the Belgian North Sea: no alarming amounts of microplastics in fish and shellfish, plastic fibers everywhere and a hotspot near Zeebrugge

More than three quarters of all waste in the Belgian North Sea consists of macroplastics (larger particles of plastic waste), and this is a major source of pollution, especially in the coastal zone. Plastic fibers, mostly from dolly rope (plastic fibers attached to trawling nets), can be found everywhere, even at a distance from the coast. Smaller plastic particles or microplastics of >50 µm (one-twentieth of a mm) also appear to turn up much more frequently along the coastal strip and in ports than further out to sea. This has all been shown by a systematic monitoring study in the Belgian North Sea. Through the MarinePlastics research project, scientists now have the necessary input to set up a macro- and microplastics monitoring plan for the Belgian part of the North Sea, a European obligation.

In the fishing grounds where Belgian fishermen are active, the researchers have also examined commercial fish species and crustaceans for microplastics. There, the numbers are very low to absent. On the basis of this study, the researchers are already calling the fish and crustaceans from Belgian fisheries a safe food source as far as microplastic pollution is concerned.

In addition to marine organisms (fish, crustaceans, etc.), Belgian fishermen also catch all kinds of plastics. © ILVO

The Flanders Research Institute for Agriculture, Fisheries and Food (ILVO) and the Royal Belgian Institute of Natural Sciences (RBINS), within the research project MarinePlastics, have mapped out how much and what types of plastic occur in Belgian fishing grounds. This involved both larger pieces of waste (macroplastics larger than 5 mm) and small to minuscule plastic particles (microplastics smaller than 5 mm). This research was not optional, but rather an obligation from Europe, which has been demanding since 2012 that every member state collect figures on macroplastics on the seabed. As of 2020, data must also be collected on microplastics in the sediment and in the water. The MarinePlastics project also examined the extent to which microplastics are present in the commercial fish and crustaceans from our fishing areas (North Sea, English Channel, Celtic Sea, Irish Sea). The researchers made a distinction between the plastic particles in the fish stomach (which people do not consume) and the fish fillet (which we do eat).

Belgian Fish Safe to Eat

The results of this research are reassuring: it was found that microplastics >50 µm (this is one-twentieth of a mm; contamination with nanoplastics, i.e. even smaller particles, was not investigated in this project) do not accumulate in commercial fish and crustaceans sampled in fishing areas where Belgian fishermen are active. In almost all fish and crustacean samples (both edible and non-edible parts), the numbers of microplastics were so low that the concentration could not be precisely determined. In only 5 out of 42 fish fillets, 2-6 microplastic particles per 100 g of fish fillet were found, which is not alarming. Thus, the public may be informed that fish and crustaceans from Belgian fisheries are currently a safe food source in terms of microplastic contamination.

Plastic fibres in water from the port of Zeebrugge, filtered through a 100 μm sieve (photographed by microscope). © RBINS/C. De Schrijver

More Microplastics Close to Ports and the Coast

Still, concentrations of microplastics in the seabed and in seawater can sometimes be quite high, albeit variable. In this study, the concentration of microplastics in coastal sediments (near Zeebrugge) was about nine times higher than further out to sea. In seawater, the difference was even more spectacular: water from the port of Zeebrugge and near the coast contained 48 and 10 times more microplastics, respectively, compared to more seaward locations. Currently, there is no monitoring program that follows the evolution of this type of pollution in Belgium. In order to meet the European obligations, a national monitoring program for microplastics must therefore be set up. To this end, the researchers also recommend that the transport of microplastics in the marine environment, possible hotspots and the link with the spread of macro-waste be further investigated (or commissioned).

Karien De Cauwer, KBIN researcher: “This study gives us a good picture of the degree of microplastic pollution near the coast and further out to sea. Based on a good detection methodology, the evolution can be followed up according to European standards. This will allow to evaluate if measures and actions taken are effective. With more knowledge about locations where microplastics might accumulate, more targeted measurements can be taken.”

Plastic Fibers from the Fisheries

Large pieces of waste – macroplastics – make up 77 to 88% of all marine waste in terms of numbers. One item is apparently present everywhere: plastic fibers. The very light monofilaments of dolly rope – the mat of loose threads that are supposed to protect the belly of a trawling net from damage – is the main plastic item that is spread evenly across our part of the North Sea, even further offshore. Heavier plastics (such as crates, bottles and containers) are mainly found near the coast. Important detail: in the Dutch part of the North Sea, there is more pollution from plastic fibers than in the Belgian part. The researchers ask the policy and sector to make it a top priority to find and implement a good biodegradable alternative to plastic dolly rope. Obviously, this not only concerns the Belgian fishing industry, but initiatives should be taken at the scale of the entire North Sea or even Europe.

‘Dolly ropes’, the mats of loose threads protecting the belly of a trawl net from damage, are an important source of synthetic fibres in the Belgian part of the North Sea. © ILVO

Route for Plastic Pollution?

While there may be a link between plastic pollution and fishing, there is no unequivocal causal relationship with fishing intensity. In other words, most litter is not necessarily found in places with most intensive fishing. Nor was a direct link found with sand mining or offshore wind farms. A hotspot of waste was identified at one dredging site, near the port of Zeebrugge. However, it remains unclear whether this is due to the dumping itself, or due to currents or other driving forces. A detailed study of marine litter hotspots is therefore needed, examining the impact of different sources and modeling the transport processes of litter.

Bavo De Witte, ILVO researcher: “In our turbulent North Sea, it is not surprising that sea currents can exert a strong influence on plastic pollution. Through modeling, it should be possible to learn even more about the origin of different waste types.”

The full reports can be downloaded via the following links:

Microplastics in seafood from Belgian fisheries areas – ILVO Vlaanderen

Distribution and sources of macrolitter on the seafloor of Belgian fisheries areas – ILVO Vlaanderen

Marine Plastics project synthesis and recommendations – ILVO Vlaanderen & RBINS

The MarinePlastics research project was funded by the European Fund for Maritime Affairs and Fisheries and the Funding Instrument for the Flemish Fisheries.

Wind farms as suppliers of energy and mussels

The cultivation of mussels in Belgian offshore wind farms is both biologically and technically feasible, according to research carried out by our scientists and their partners within the Edulis project. The economic feasibility depends on solving technical challenges.

After two years of experimentation and research, scientists and private companies present the results of the research project ‘Edulis: offshore mussel culture in wind farms‘, which looked at the possibilities for mussel farming in offshore wind farms 30 to 50 km off the Belgian coast. Edulis is a collaboration between Ghent University, the Research Institute for Agriculture, Fisheries and Food (ILVO), RBINS/OD Nature and 5 private partners (Belwind, Brevisco, C-Power, Colruyt Group and DEME Group). The ambitious pilot project is largely financed by private funding and facilitated by Flemish and European funding.

Quality Mussels

The project has demonstrated that it is both biologically and technically possible to cultivate mussels in the Belgian offshore wind farms, which means that these can serve more than one purpose at a time. The experiments resulted in a tasty quality mussel that is well stocked and meets all food safety requirements. The yield is equivalent to that of hanging mussels from the Netherlands and Ireland, and the mussels grow faster than mussels from bottom cultivation (mussels ready for market in 15 months instead of 24 months).

Technical Challenges

The big challenge is designing installations that can withstand the sometimes extreme North Sea environment. Investing in robust, easy to maintain and safe systems, including vessels, is a must, according to the researchers, although this will push up overall production costs. In addition, it turned out that the sizing and organisation of the wind farms is not optimal for food production, which is logical as they were not designed for that purpose. The distance from the coast also poses a challenge to technical, practical and economic feasibility. When designing future wind farms, this should be taken into account in order to be able to combine both activities.

Economic Feasibility

“Edulis has given us a clear picture of the costs and benefits of mussel farming in the North Sea” says Margriet Drouillon, Senior Business Developer Aquaculture and Blue Life Sciences at Ghent University. “If we really want mussel farming on a commercial scale, we will have to put a lot of effort into developing knowledge about the economic feasibility of mussel farming in the wind farms. We will also explore other paths for multiple use of space at sea, with due attention to sustainable production”.

Three Additional Challenges for Aquaculture in the North Sea

Ghent University and the Research Institute for Agriculture, Fisheries and Food (ILVO) launched the ‘North Sea Aquaculture’ project in 2017, with Edulis and Value@Sea as subsidiary projects. They joined forces with their partners RBINS/OD Nature, Belwind, Brevisco, C-Power, Colruyt Group, DEME Group, Lobster Fish, and Sioen Industries. North Sea Aquaculture tackled three challenges:

  • Innovative shellfish and seaweed farming techniques;
  • Efficient use of space in the Belgian North Sea;
  • The development of a market for new regional marine products.


More info on Edulis:
Margriet Drouillon, UGent, 0484 13 95 39,

Leatherback turtle caught and released

On the 28th of October, the crew of the fishing vessel O190 Renilde experienced a shocking moment. Around 19:30 they encountered nothing less than a Leatherback turtle in their nets along the coast of Middelkerke/Ostend! The crew reacted quickly and was able to let the living animal return to the sea (see video © Kevin Van Thomme/crew O190).

Seventh Record

The Leatherback turtle typically inhabits open and warm seas, where they mainly feed on jellyfish. They don’t easily show up In coastal areas (unless to lay eggs, but that is excluded on our beaches). Jan Haelters of the Royal Belgian Institute of Natural Sciences provides interpretation: “Leatherback turtles are very rare in the Belgian part of the North Sea: until now, only three strandings (1988, 1998 and 2000) and three sightings (2018 and 2 in 2019) were recorded. Although the list only counts seven specimens, an increase is noticeable in recent years.”

© Kevin Van Thomme/bemanning O190

Also in the Netherlands

Remarkably, some Leatherback turtles were also seen in the Netherlands recently: one roamed the Eastern Scheldt from 22 to 24 September, while one swam along the North Sea coast of Scheveningen on 7 and 11 October. Comparison of the shape and size of the scars on the heads of the two animals, and of the ‘ribs’ on their back shields, shows that in Belgium and the Eastern Scheldt different individuals were involved. The Eastern Scheldt animal was washed ashore dead on 3 November near the Danish Ballum (article tvs).

Comparison of the Leatherback turtle heads from Belgium (right, © Kevin Van Thomme) and the Eastern Scheldt (left, © Wageningen Marine Research)

Impressive Noctiluca (Sea Sparkle) bloom in the North Sea

On 15 August, striking orange spots and strings were observed in the Belgian part of the North Sea near the Buitenratel sandbank, that were reported to the Coast Guard as a possible pollution. After inspection by various services, it became clear that this was an unseen bloom of the single-celled plankton species ‘Sea Sparkle’. The warm and calm weather of the past few days is probably an important explanatory factor. The rotting mass could possibly lead to oxygen deficiency and fish mortality. It is also possible that the remains will be washed ashore on Belgian beaches during the next week.

Noctiluca bloom Buitenratel sandbank, 15 August 2020, documented from surveillance aircraft RBINS (© RBINS/MUMM)

In the morning of Saturday 15 August, the Belgian Coastguard Centre (MRCC – Maritime Rescue and Coordination Centre) received a report of a striking orange patch at sea, containing some dead birds. A sailor had noticed this at the ‘Buitenratel’ sandbank, one of the sandbanks in the ‘Vlaamse Banken’ complex. This sandbank is situated about 16 to 20 km from the shore of the Belgian West Coast, near the border with the French waters. The striking report raised eyebrows at the Coast Guard, because the reported colour did not match the typical colours of mineral oil, and because the dead birds may have hinted to a chemical product. However, an extensive natural algal bloom was also a possibility.

Control on Land, at Sea and in the Air

Following the report, the Shipping Police sent a patrol vessel to the Buitenratel. They found the reported patch and took some samples. Dead birds were no longer spotted. A rescue helicopter from the Coxyde air base also flew over the area, and the surveillance aircraft of the RBINS (MUMM, Royal Belgian Institute of Natural Sciences) was called upon to scan the wider sea areas off the Belgian coast for any further pollution. Both aircraft made images of the orangeish, kilometre-long patches and streaks.

Noctiluca bloom Buitenratel sandbank, 15 August 2020, documented from NH90 helicopter (© Geronimo/Rodrigo Vissers)

All the sailing and flying units involved came to the same conclusion: the patch probably indicated a large natural bloom, albeit on a very large scale. The sample taken by the Shipping Police was taken to the RBINS biological laboratories in Ostend where it could soon be confirmed that it was indeed a Noctiluca bloom.

Video: 2020_08_15 Noctiluca Buitenratel (c) Geronimo_Rodrigo Vissers NL

Sea Sparkle

The dinoflagellate Noctiluca scintillans or Sea Sparkle is a relatively large single-celled micro-algae (0.5 – 1 mm, so visible to the naked eye) that occurs in most seas of the world and belongs to the plankton. It looks like a gelatinous pellet with a tail (flagel), which catches food. In high concentrations – called blooms – Noctiluca forms highly visible orange-red spots that can occur in spring and summer. In case of turbulence, Sea Sparkle produces a bluish light that creates fairytale effects in the dark (‘lighting up’ of the sea). This bioluminescence is caused by luciferin, a pigment, and luciferase, an enzyme, when they come into contact with oxygen.

Samples of Noctiluca scintillans bloom at the Buitenratel sandbank, 15 August 2020, sample taken by Shipping Police (© RBINS/Francis Kerckhof)
Microscopic image of Noctiluca scintillans bloom at the Buitenratel sandbank, 15 August 2020, sample taken by Shipping Police (© RBINS/Francis Kerckhof)

Current Conditions

The high concentrations of Sea Sparkle that have now been observed are probably due to the very warm and calm weather of the past few days. The sampled Noctiluca was also already partly rotting, a process that consumes oxygen. Although it is essentially a harmless organism, mass extinction and rotting can locally lead to oxygen deficiency. At higher temperatures, less oxygen dissolves in water anyway, and the absence of strong winds and waves means that there was also little mixing that brought extra oxygen into the water. The resulting low oxygen tension due to the various phenomena can lead to the death of fish and other aquatic organisms, although under normal circumstances this is very unlikely in open sea conditions.

Modelling simulations by the RBINS, taking into account currents, meteorological conditions and the physical properties of the floating Noctiluca spots, illustrate that the remains of these spots could potentially wash ashore on Belgian beaches in the course of the next week.

In recent decades there has been a relative increase in the dinoflagellate community in the Belgian part of the North Sea. This increase could be related to the warming of the sea water (+ 1.6 ° C over the last thirty years). Noctiluca scintillans may also show an upward trend. In addition, blooms from other single-celled plankton organisms can also be expected, including some potentially dangerous species.

Noctiluca bloom Buitenratel sandbank, 15 August 2020, documented from surveillance aircraft RBINS (© RBINS/MUMM)


Noctiluca bloom Buitenratel sandbank, 15 August 2020, documented from surveillance aircraft RBINS (© RBINS/MUMM)