Ecosystem services provided by the Baltic Sea ... - Naturvårdsverket

SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5873 • Ecosystem services provided by the Baltic Sea and Skagerrak
Economic Marine Information
invertebrates, lowered pH may disrupt fertilisation and larval development (chapter
R1).
Although there are no obvious threats to the filtering of nutrients by e.g. mussels,
the situation is more uncertain for other important exchange pools. For example,
anoxic conditions impairs storage of phosphorus in benthic sediments and loss of
sea-grass, reduces sediment retention (chapter R2) and consequently the potential
for nutrient storage.
Mussels and ecosystem services
Blue mussels hold a key regulating role in many marine ecosystems. Their value to society
is foremost manifested by the following ecosystem services:
Storage and recycling of nutrients (chapter S1)
Maintenance of habitat (chapter S5)
Food for harvest (chapter P1)
Fodder and fertilizer (chapter P2)
Mitigation of eutrophication (this chapter)
Pharmaceutical and biochemical products (chapter P4)
Biological control (chapter R4)
How to strengthen natural alleviation of
eutrophication
The Baltic Sea countries have committed to substantially reduce nutrient levels to
the Baltic Sea no later than 2016 (28). Although reducing high inputs of nutrients is
the foremost measure to combat eutrophication, preventive measures could be
complemented by increasing densities of filter feeders. To date, the overall potential
to strengthen this service by harvesting nutrient-storing organisms (e.g. algae
and bivalves) remains under-used, possibly as a result of poor economic incentives
and technical restrictions. In Skagerrak as well as in many areas of the Baltic Sea,
conditions for mussel farming are considered favourable. According to a number of
researchers, mussel farming is a “simple, flexible and cost-effective measure to
counter marine eutrophication” and “compared to other measures, the added
benefits of mussel farming for society are striking at the same time as the negative
effects for the environment are minor and acceptable” (115). The harvest of 1 ton
mussels contains approximately 8.5 kg N and 0.6 kg P. In an area large as a football
field, 150 tons of mussels can be harvested each year resulting in withdrawal
of 1275 kg N and 90 kg P. Two thirds of this harvest can be used for human consumption
and the rest can be used as fertilizer or fodder for e.g. poultry (115). Additional
benefits of mussel production include increased denitrification under mussel
farms, causing increased removal of nitrogen. Using Limfjorden, a shallow
Danish estuary as an example, it can be shown that even though realistic numbers
of mussel production and related nutrient removal are low compared to nutrient
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