A contribution towards counteracting eutrophication
Despite being its most common macroorganism, the small size of Baltic Sea blue mussel – caused by slow growth due to low salinity – means that they can hardly be used in the world-wide thriving business of seafood. Mussel farming in the Baltic Sea can, however, serve as a possible measure to counteract eutrophication.
Evidence from the available pilot sites show that on average 100–150 tonnes per hectare mussel biomass can be harvested every second year containing 1.2–1.8 tonnes of nitrogen and 0.08–0.12 tonnes of phosphorous. The biomass itself can be used as organic fertilisers for gardens and greenhouses or be processed into chicken or fish feed with the added advantage of reducing pressure onto fish stocks. Ongoing trials and studies show promising results for all these products. Existing technologies are working sufficiently well with solutions already in place to avoid damage from ice drifts.
It is, however, difficult to give an estimate of the potential total area available for mussel farming throughout the Baltic Sea as sites have to fulfil a number of criteria in order to show a positive net effect on the environment. For instance, a small to moderate bottom water exchange is important, in order to avoid oxygen depletion and resulting decreases in abundance and biodiversity of benthic communities immediately beneath the cultivation site.
Overall mussel farming may in some parts of the Baltic Sea become a commercially promising area for small and medium sized private enterprises on the condition that environmental services rendered by them, such as nutrient removal, are also paid for. The Åland government (FI) is about to accept mussel farms as an environmental compensation for expansion of open net cage fish farms and in Sweden an appropriate regulatory framework is expected to come to force in 2014, but a Baltic Sea wide overall approach is missing so far.
In addition, zebra mussels have a relatively high abundance and distribution range throughout the shallow coastal lagoons and estuaries of the Baltic Sea. It can be assumed that they show similar qualities to the blue mussel, but so far no farming trials have been carried out and thus only very few data are available.