Henrik Willem HofsResearcher Tjisse van der Heide
NOS Nieuws•vandaag, 18:12
Francien Intema
editor Domestic
Francien Intema
editor Domestic
Young mussels in the Wadden Sea cling to 3D-printed, biodegradable reefs. This is evident from a test on the mudflats near Texel. The researchers hope that the reefs can help the growth of mussel banks, because these banks are important for biodiversity. Nature manager Rijkswaterstaat wants to expand the mussel banks in the Wadden Sea, but not all experts think this makes sense.
“We are actually imitating adult mussel beds,” says researcher Tjisse van der Heide of the Netherlands Institute for Sea Research. “Existing mussel banks offer support and protection against predators such as shrimps, crabs and starfish. This means that young mussels survive more easily on such a bank than on a bare sandy bottom. Ultimately, the printed material must break down and a natural mussel bank remains.”
Counting and weighing
Last May, Van der Heide and his colleagues placed about thirty artificial reefs of about half a square meter on a tidal flat near Texel. The reefs are made of biopolymers; a type of biodegradable plastic. There are cavities in which young mussels can hide. The researchers used coconut rope in some of the reefs because its texture resembles the threads with which adult mussels hold each other.
In the laboratory in the coming months, the researchers will count how many mussels there are in the reefs and how heavy they are. “But we can also see with the naked eye that young mussels have succeeded in establishing themselves here,” says Van der Heide. “So the principle works, both for reefs that are permanently under water and for reefs that dried up at low tide.”
Reporter Henrik-Willem Hofs went out into the Wadden Sea to view the 3D-printed mussel beds:
3D-printed reefs offer mussels in the Wadden Sea something to hold on to
Mussels play an important role in the Wadden Sea. They filter seawater and are a food source for shrimp, crabs, starfish and birds. They also ensure diversity on the seabed. “In the sandy bottom you will find many worms and shellfish that burrow into the mudflats,” says Van der Heide. “Mussel beds build their own landscape, on which very different species grow, such as anemones and barnacles.”
For the mussel beds below the water surface, European legislation requires that we strive for “an increase in the share of old mussel beds”. As nature manager of the Wadden Sea, Rijkswaterstaat is looking for measures to create more perennial mussel banks underwater. On the one hand because of European legislation, on the other hand because Rijkswaterstaat strives for “a robust and climate-proof ecosystem”, says a spokesperson.
The mussel beds are not expanding at the moment. Some of the banks are still being worked on fished for young mussels and shellfish researcher Karin Troost of Wageningen Marine Research monitors the ‘submerged’ mussel banks twice a year on behalf of the mussel fishing sector. “The total weight of the mussels varies from year to yearbut the mussel beds have been relatively stable since monitoring started in 1992.”
Mussel seed fishing
In the Wadden Sea, mussel banks that are completely submerged are still fished for ‘mussel seed’: young mussels. The small shellfish are then raised for consumption in parts of the Wadden Sea and the Oosterschelde.
In 2008 it was agreed to phase out and ultimately stop bottom mussel seed fishing. In 2020 it is covenant renewed and it has been agreed to end this form of mussel fishing in 2029.
Rijkswaterstaat would prefer that the mussel banks continue to develop naturally. This would include ‘less soil disturbance’, says the spokesperson. In other words: less fishing on the bottom. Rijkswaterstaat only considers so-called ‘active recovery’ if natural development is not possible or if it is not happening fast enough. That is why the organization is following Van der Heide’s research with interest.
Shellfish researcher Troost is critical of the artificial reefs. “Why do you tinker with non-natural materials in a nature reserve? There is enough hard surface to which mussels can attach. Moreover, the mussel population below the water surface maintains itself. There is a legal task to allow mussel beds to age, but not to to create more mussel beds than there are now.”
Van der Heide is investigating whether natural processes can be accelerated and, as a coastal ecologist, he also believes it is important to expand the mussel beds. “Those banks are indeed stable, but that is in the current situation. Without fishing, the surface area would almost certainly be larger and you want to move towards mussel banks as they can occur naturally in the Wadden Sea.”
Next year he will test 3D-printed reefs in the sea again. “We now see that the reefs with coconut rope and small cavities are the most attractive for the mussels. On this basis we can refine the design.” Moreover, Van der Heide wants to apply the knowledge acquired worldwide for the restoration of endangered shovel reefs.
2023-10-02 16:12:01
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