Rest brings life

The underwater world has always really fascinated Oscar Bos. Not surprisingly, he chose to study Marine Biology in Groningen. Being an amateur diver also gave him a good impression of life below the surface of the North Sea. And now he is working to preserve and strengthen it. "It's a bit like combining work and hobby."

As a research associate, he works on several fronts. For example, he works for the Ministry of LVVN on background documents on biodiversity in conservation areas as well as on species protection plans. He is also active in the North Sea Nature Enhancement programme, which is working hard on nature restoration measures for important benthic animals and habitats, such as oyster reefs. As part of his involvement, he goes out to sea for monitoring purposes. All in collaboration with colleagues inside and outside Wageningen Marine Research. "It is very interesting to see what foreign colleagues are doing on nature restoration, such as in Germany, Denmark and England. That's why I always think international project groups and conferences are very important." 

Some parts of the North Sea are already fairly well mapped. However, there are still some gaps. Like the Borkumse Stenen, a conservation area in the sea, north of Schiermonnikoog. "More than a decade ago, we did an initial survey there to see what biodiversity exists on the seabed. And last year we returned with acoustic survey instruments, underwater drones and sampling equipment. "An area needs to be properly mapped before you can design a statistically robust long-term monitoring programme for it."

He is particularly interested in wind farms in the North Sea. Together with his colleagues, he looks through timelines at these parks, which are becoming increasingly large: "In areas where parks may be built from 2050, for example, we are mapping the conditions that must be met during construction to protect or enhance underwater nature values. At existing wind farms, we examine the effects of measures taken to enhance nature. Around each wind turbine foundation, there is a layer of stones to protect against erosion. We call that scour protection. A variety of things grow on and around those stones.  

As suppliers of green energy, wind farms are necessary to meet climate targets. "But they also offer nature conservation," says Bos. "For example, you can build rock reefs, dolmen-like structures with hiding places for species like cod and lobsters. You can also use those structures as a basis for oyster restoration projects. There are also underwater openings in the turbine pole for cables. If you make those openings a bit bigger, you can see seals swimming in and out." 

The European flat oyster is often cited as a species that is struggling in the North Sea. That used not to be the case, says Bos. "Before 1900, there were large oyster reefs all over the North Sea, all of which have been overfished or have disappeared due to disease. What remained in those places was mostly sand. I am now working on several recovery projects. These are currently small-scale, but the aim is to scale up."

An oyster reef was already found to exist in the Voordelta, a Natura 2000 site off the coast of Zeeland and South Holland. Bos: "It owes its existence to the oysters in the Grevelingen, through an opening in the dam through which water exchange with the North Sea takes place. So it’s not surprising to find flat oysters a few kilometres away. When the reef was mapped, it was found to be a mixed reef measuring about 30 hectares. Besides the dominant exotic species, the Pacific oyster, we also found the flat Zeeland oyster."

Experience in the Voordelta is fuelling approaches elsewhere. For example, in wind farms we are testing how oysters can survive: "You cannot put oysters in loose sand, because they will wash away. You need to provide substrate for larvae to attach to: structures made of clay or special reef tiles. That will enable the creation of a self-sustaining reef." 

Besides oysters, there are other habitat builders. Bos mentions the Ross worm, which lives in tubes made of coarse sand cemented with mucus. This can create large mounds among which other animals find hiding places. A very different interesting habitat is formed by burrowing crustaceans, which create burrows in the muddy deeper parts of the North Sea that aerate the bottom.

A major driver of biodiversity in the North Sea is the North Sea Nature Enhancement Programme, which formally started in 2024 and runs for seven years. The Dutch government launched this programme to complement already mandatory legal measures to prevent damage to nature. "The aim is to scale up successful small projects with the assistance of nature. You can’t fill the entire North Sea with concrete artificial reefs; that is very unnatural. We look at what is already there, for example an oyster reef, and what needs to be done to make it grow. The oyster reef in the Voordelta shows that it can be done."

Underwater drones and autonomous rockets are the new eyes of researchers. Bos: "Today, we can use autonomous vehicles, such as the Lobster Scout, to take pictures of the seabed. This 'rocket' systematically moves over the seabed, taking thousands of pictures. Pasted together, all those pictures produce a Google Earth-like image of the seabed of around 20 by 20 metres. You can then zoom in to the individual mussel or starfish. Divers used to do the same job with a small underwater camera, but such a large photo obviously provides really new insights."

"Not surprisingly, a lot of new technology also comes from the defence sector," says Bos. "For example, the Netherlands Organisation for Applied Scientific Research (TNO) is developing and testing underwater drones for the navy. We therefore worked with TNO to conduct market research to find small, affordable drones for ordinary citizens that you launch from a small boat. This summer, we organised test days with several manufacturers in the Voordelta and near Scheveningen to test their drones. This provides nice contacts and interesting opportunities for deployment in future projects." There is also a flipside to the success of new technology: NATO also needs it to protect underwater infrastructure, which is why it works with several companies: "That sometimes makes it difficult to rent equipment."

By 2030, 15% of the North Sea must be closed to the fishing industry. From a biodiversity perspective, this is a good development, argues Bos. "Rest areas really make a difference for nature. If you want to protect areas, you need to make sure there is no fishing, not even the occasional ship. Combined with active restoration projects, biodiversity can rebound."

Talking about the impact of climate change, he is realistic: as seawater warms and acidifies, some species will become less abundant in our waters. Others actually arrive with the warmer water, such as the common squid."

He is optimistic: "Wind farms attract new wildlife. There will be more closed areas. And if the restoration projects with oyster reefs and other structures are successful, biodiversity will continue to improve. We need to scale up what works, monitor smartly and learn. The North Sea will then once again become a sea brimming with life." 

• Deltares
• Ecoauthor
• ICES
• Lobster Robotics
• Ministry of LVVN
• North Sea Nature Enhancement
• NORA (Native Oyster Restoration Alliance)
• OSPAR
• Rijkswaterstaat
• SAS Consultancy
• Vattenfall
• Waardenburg Ecology