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

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SWEDISH ENVIRONMENTAL PROTECTION AGENCY Report 5873 • Ecosystem services provided by the Baltic Sea and Skagerrak Economic Marine Information ity. Coastal areas are heavily affected by nutrient loadings, particularly sheltered water bodies with a small volume and restricted water exchange, which include fjords, bays, lagoons and archipelago areas. Anoxic bottoms are difficult to visualize. Eutrophication becomes more obviously detrimental in areas important for tourism, recreation and residential development. Nevertheless anoxic bottoms contribute to the degradation of most supporting services. Two infamous examples of eutrophication are the Archipelago Sea and Stockholm archipelago. Besides, there are particularly sensitive areas, where consequences of eutrophication are particularly harmful. These include the Straights, between Sweden and Denmark, which constitutes a gateway into the Baltic Sea. The impact of respective nutrient varies, depending on the time of the year and on which is limiting in the geographic region. In the northern Baltic Sea, phosphorus is generally limiting, while nitrogen is limiting in the Baltic proper and Skagerrak. In yet other areas, the extent and nature of nutrient limitation is predominantly seasonal. Although reductions of nutrient inputs are underway (28), the result may not become manifested within decades. Despite extensive research effort, no engineering method has emerged as a solution to the Baltic Sea eutrophication (26, 112). Improved water quality (in terms of transparency) is believed to infer enormous benefits for the production of food and to all aspects of ecosystem diversity and function. Worldwide, the economic value of natural mitigation of eutrophication is estimated to be enormous (5). In fact, environmental conditions in the Baltic Sea would deteriorate rapidly without this service. In regions of importance for tourism and recreation, and where property prices are related to proximity and condition of the sea, mitigation of eutrophication may be particularly important. “There are good reasons to believe that eutrophication will, in the near future become a common hazard in marine coastal areas in many parts of the world, with consequent potentially damaging effects on both inshore fisheries and recreational facilities” Professor R. Rosenberg 1985 Nutrients may be stored in sediments. By acting as sediment traps, sea-grass and algal beds remove organic pollutants from the water column and increase water transparency. Most importantly, filter feeders play an essential role in regard to this service. A small Baltic blue mussel (ca 3 cm) filters 2 - 3L/ h while a larger mussel from Skagerrak can filter 2 - 3 times as much. This impressive filtering capacity links plankton- and bottom communities through the recycling of nutrients. Through filtration, plankton are removed from the water column and deposited as detritus, providing energy for bottom-dwelling organisms. This process contributes to increased water transparency which is beneficial to many habitat-providing marine plants as well as to valued ecosystem services such as scenery and tourism. In a semi-enclosed area, like a fjord, mussels can filter all water down to approximately 10 m and above mussel banks water transparency is typically high and de- 79
SWEDISH ENVIRONMENTAL PROTECTION AGENCY Report 5873 • Ecosystem services provided by the Baltic Sea and Skagerrak Economic Marine Information void of phytoplankton. In the northern Baltic proper, blue mussels are known to consume about 35 % of the annual pelagic primary production, naturally dominated by phytoplankton (113). The importance of this service is likely to vary regionally, in relation to the presence of oxygenated sea floors and the distribution of filter feeders. However, the exact extent to which natural mitigation of eutrophication reduces nutrient levels in the Baltic Sea and Skagerrak remains unknown. Interaction with other ecosystem services Efficient cycling of nutrients is dependent on the presence of filter feeders, which in turn are dependent on all supporting ecosystem services. The uptake and storage of limiting nutrients from the water by animals and sediments (exchange pools) is part of the biogeochemical cycle and influences primary production and thus, indirectly, various other ecosystem services. Status, threats and consequences Status Sustainability of use Level of threat Expected consequences Good Sustainable Low Limited The status of natural eutrophication mitigation is good in the Baltic Sea and Skagerrak. We benefit greatly from this service though our use does not impact the service itself. Nor are the organisms responsible for this function currently threatened .However, it should be kept in mind that natural filtration or sedimentation of nutrients cannot solve the severe problem of eutrophication that Baltic Sea countries are currently faced with. In Skagerrak and Kattegat there are numerous filter feeders. In the Baltic Sea there is only one species with this function, the blue mussel. It occurs as far north as Kvarken, and is the most common species in the Baltic Sea. Constituting 70 % of coastal biomass, it contributes greatly to ecosystem structure and function (114). As expected, current nutrient conditions are favourable for blue mussels. In fact, they have expanded at the expense of algal beds, due to reduced water transparency. There are few threats to blue mussels. Being sturdy competitors, no invasive alien species have so far influenced them. In Skagerrak, however, the introduction of the giant oyster could potentially cause a shift from mussel beds to oyster, as has occurred in the Wadden Sea. Typically, bivalves are also relatively tolerant to hazardous substances (chapter R5). Potentially more threatening, and currently under investigation, is ongoing marine acidification. As demonstrated for other marine 80
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Ecosystem services provided by the Baltic Sea ... - Naturvårdsverket

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