‘Blue proteins’ can help clean coastal waters and they are a sustainable food source

Interview

Danish fjords and inlets offer favourable conditions for cultivating seaweed and mussels, says Professor Jens Kjerulf Petersen from the National Institute of Aquatic Resources at the Technical University of Denmark (DTU Aqua). Mussel production could be scaled up 20-30 times compared with today.

Almost all crops grown in Danish fields are not produced for human consumption but for animal feed. Putting the proteins we grow in crops through cows, pigs or other animals has a massive climate footprint.

But ‘blue proteins’ hold great potential. We can grow food in the sea, and send the proteins on a shorter, less climate-impacting route. For example, we can grow mussels and seaweed. Danish coastal waters are particularly well-suited for growing both of these. In this context, an unresolved environmental problem in agriculture and Denmark’s many, effective wastewater treatment plants play an important role.
So says Professor Jens Kjerulf Petersen from DTU Aqua. He has helped start the Danish Shellfish Centre, now part of DTU Aqua. He has more than 30 years’ experience in the field, and he is convinced that ‘blue biomass’, such as seaweed and mussels, has huge potential as a future sustainable food source.

In Denmark, almost two-thirds of our land area is under cultivation. Nutrient pollution from agriculture has particularly serious implications for the marine environment. Moreover, we treat our wastewater to meet high quality standards. This gives us unique conditions for growing seaweed and mussels, which absorb nutrients and therefore have a positive impact on the marine environment. We already have good experience growing mussels in Limfjorden, and conditions are good in all our east-facing inlets, he says.

Three crises

According to Jens Kjerulf Petersen we are facing three crises at the same time. The first two are the climate crisis and the biodiversity crisis. And with a growing global population, the third crisis is a global food crisis, which has become all the more evident with the war in Ukraine. Farming so-called low trophic marine (LTM) species in the sea addresses all three of these crises.

We can’t stop producing food on land, but terrestrial farming is causing several problems. For example, nutrient pollution of the sea and CO2 emissions, with Danish agriculture accounting for around 30 percent of Denmark’s climate footprint, depending on how you measure it, he says.

An obvious alternative would therefore be to focus on the opportunities offered at sea. Fish, for example, require less energy to farm than animals on land, because fish do not use energy to keep warm. But there are still issues with nutrient pollution.

Looking at wild fish populations and fisheries, we see that some species, for example cod, have migrated north because of rising sea temperatures, and stocks are dwindling. However, fishing of commercial fish stocks is generally at sustainable levels. The problem here is rather that Danes have picky eating habits, says Jens Kjerulf Petersen.

Take the greater weever, for example. The greater weever is abundant in Danish waters, and it’s actually an excellent food fish, but the greater weever just doesn’t feature on Danish dinner plates, he says. And there is potential in other species as well, he says.

But first of all, we should focus on the species at the bottom of the food chain, the low trophic species, because the benefits to be gained here are even greater, stresses Jens Kjerulf Petersen. If we focus on these species and on sourcing our food from the sea, we will also be able to offset the discharge of nutrients from agriculture.

Ripe for development

Over the last 15-20 years, the Danish Shellfish Centre has been a driving force in accelerating mussel farming in Limfjorden. Production is now at 10,000 tonnes annually.

Jens Kjerulf Petersen assesses the total mussel production potential in Danish waters to be between 200,000 and 300,000 tonnes annually.

So far, Danish production of seaweed is rather modest, with only 10-20 tonnes annually. Production at European level is around 375 tonnes. Jens Kjerulf Petersen believes the seaweed potential is as high as 1 million tonnes.

We have only exploited a small part of the potential, because we are still at a low level of maturity with regard to knowledge and technology. This means we can achieve an exponential development.

In some ways, we’re at the same place as Danish Agriculture was 100 years ago. We still have extensive technological development ahead of us. We could be facing a steep development curve. Most mussel production in Denmark today is by small companies with only a single or a few owners. And mussel farming still requires relatively hard physical labour, says Jens Kjerulf Petersen.

With the company Blå Biomasse (blue biomass), owned by environmental services company Hedeselskabet, the first crucial step has been taken towards increased efficiency and scale. Investments in Blå Biomasse are at another level than in the rest of the sector.

Much of the manual work has been replaced by mechanised work. It is expensive, but it allows for production at an entirely different scale.

The best small-scale producers will still be able to contribute if they deliver high quality, but we need a far more industrial approach, and this requires investment, says Jens Kjerulf Petersen.

Positive bottom line with regard to nutrients

But it is not either big farms or small farms. Small mussel farms can still develop slowly and co-exist alongside large industrial farms. Furthermore, Jens Kjerulf Petersen has a list of areas where more knowledge is required.

The environment aspect is one such area that needs our attention. Large scale production requires concrete analyses of the individual farm location.

More detailed studies are needed, Jens Kjerulf Petersen stresses. At the same time, he corrects those who fear mussel farms will put pressure on the marine environment.

It is a question of simple household accounts, according to the DTU professor. If you farm mussels, they will absorb some of the nutrients in the sea, and although the mussels also poop, leaving mussel poop on the seabed, it all balances out. In the final analysis, mussel farms help absorb some of the nutrients that create problems for the marine environment.

We don’t add anything; we remove something. And at the same time, mussel production helps to filtre the water and make it cleaner. Plants and organisms will settle on the mussels. This will help improve biodiversity. So, the bottom line is positive, says Jens Kjerulf Petersen. Having said this, naturally, there’ll be consequences from concentrating certain animals and plants at a density that doesn’t occur in nature. For example, seabed conditions will be affected. We need to look at the total capacity of the ecosystem, and I’m sure this will differ from one bay to the other. This is something we need to have a closer look at, when the time comes, he elaborates.

The Vikings ate seaweed

Another item on the to-do list is ‘research into different species’. In addition to mussels, seaweeds hold great potential, and sweet tangle is being studied in particular.

In one new project, DTU Aqua is examining the potential of the seaweed species dulse. Whereas five to ten years ago, the paleo diet was all the rage, with this project, DTU Aqua is focusing on another historical era.

Dulse is known from the Viking Age, when the Vikings gathered and dried dulse and took it with them on their raids, says Jens Kjerulf Petersen.

He recognises that there is still some way to go before seaweeds and mussels become regulars on Danish dinner tables. Today, most of the mussels produced in Denmark are exported to the Netherlands and Belgium.

Low trophic species are good for the climate as well as for your health. Their climate impact is low, because producing them does not involve producing animal feed, and they have a high content of proteins and healthy omega-3 fats, says Jens Kjerulf Petersen.

The shells from the mussels can be used for horse arenas, and they are also suitable as insulation material. If they are used in foundations and walls, they become carbon sinks, stresses Jens Kjerulf Petersen.

Food habits can be changed

He acknowledges that our meals are unlikely to be fully based on seaweeds in the future, but, in his experience, it is possible to change people’s eating habits. He provides an example from his own childhood, growing up in the Greater Copenhagen area.

An Italian restaurant opened in Fiolstræde – it was very exotic! Until then, not many of us knew what a pizza was. I also remember a fellow student from Lolland, who had never tasted curry before, says Jens Kjerulf Petersen.

Changing people’s eating habits will require developments on several fronts. Not only is there a need to change what Danes put on their plates, there is also a need to develop different species. Because growth conditions vary from location to location.

The types of mussel vary depending on local conditions. The same applies to seaweed. And there are many possible applications. Some seaweeds can be used directly as produce. Some can be used to enrich other products, and there are experiments with fermentation. Finally, some seaweed species could be suitable for animal feed, says the DTU researcher.

Co-existence with offshore wind farms

While there are obvious potentials for growing blue proteins in Danish inlets, DTU Aqua is also looking at offshore projects. The department recently received funding for a new multi-use project, in which they will examine the potential for mussel farms at offshore wind farms.

We are already establishing wind turbine foundations on the seabed in many places, so why not use some of these areas to grow mussels? We can’t grow mussels directly on the foundations, but perhaps we can use the area around the foundations, says Jens Kjerulf Petersen. But he also admits there is an obvious paradox.

Mussel farming usually requires calm wind conditions, so placing mussel farms near wind turbines might not be the obvious solution.

There are benefits to moving the farms away from the coast, where they can be a nuisance to some, but currently this is not a feasible option, although it may be in five to six years, he says.