In Öresund, beneath the surface of the sea, hides northern Europe’s largest mussel bed. This 75 square kilometer area is covered with millions of mussels. However, the most impressive part isn’t the size of the bed, it’s the fact that the mussels act as natural filtering organisms, keeping the Öresund sea clean.
Mussels provide us with a fantastic ecosystem service as they combat eutrophication in a totally natural way. They filter out nitrogen and phosphorus from the water, two substances that cause serious problems in terms of marine eutrophication. However, as long as the mussel biomass remains in the water, they provide no net effect. The filtering benefits of the mussels can be increased if the mussels are consequently harvested.
For this reason, the City of Malmö and the organization SEAU Marint Kunskapscenter (an education center with a marine focus) created a joint development project that explores novel mussel farming methods and innovative ways of using the harvested mussels.
Exploring novel mussel farming methods
Initiated in 2010, this project is part of a larger project called Bucefalos, a collaborative venture between the City of Malmö, the region – Region Skåne – and a smaller town in Skåne – Trelleborg Municipality. The project was financed in part by LIFE+, the EU’s environmental protection fund.
During the pilot runs, several farming methods were tested in order to identify the methods most appropriate to the area’s unique conditions. The selected method, i.e., the method currently in use, cultivates the mussels on nets hanging from buoys beneath the water surface.
The project also has explored the possibilities of harvesting mussels in Öresund from other submerged installations. An example of this is the Öresund Bridge’s 54 piers, where mussels grow in layers up to several decimeters thick.
The benefits of mussels
Normally, measures are taken against eutrophication by establishing wetlands upstream in the rivers, but for that, agricultural land is needed, which means that it competes with food production. Mussel farming contributes to food production, while simultaneously having a cleansing effect that equals that of wetlands with the same surface area.
Although the primary environmental service is made when we pick up mussels from the sea, mussel cultivation may also be financially profitable. For example, mussel meal can be sold as fish feed. Mussel shells can also be ground to a calcium-rich powder for use as a soil conditioner or as calcium enrichment in lakes.
“Mussels are, after all, living creatures, so we should make an effort to make good use of the harvested mussels,” says project manager, Rasmus Fredriksson.
Rasmus Fredriksson, Project Manager, Environment Dept
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