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 Status, threats and consequences Status Moderate Sustainability of use - Level of threat High Expected consequences Severe In all of the Baltic Sea and Skagerrak there are numerous habitats exhibiting different status and experiencing different threat. An attempt to characterise overall status and level of threat is therefore inherently difficult. The plethora of threats must be considered alarming, and status may deteriorate further. However, awareness is increasing and various steps towards protecting and restoring marine and coastal habitats around the Baltic Sea and Skagerrak have indeed been taken. According to the Millennium Assessment (13) many terrestrial species are stranded in small islands of nature, surrounded by human development. For long, the general belief has been that the vast appearance of the sea precludes a similar scenario. Defying this misconception, many marine habitats have become severely degraded in recent time. The extent of marine habitat destruction and fragmentation is approximating the situation on land, although causes are not always as apparent. A cocktail of threats, including eutrophication, over-fishing, pollution, development and atmospheric change is putting an ever increasing strain on marine ecosystems, sometimes acting in synergy and strengthened by positive feed-back mechanisms. Recovery from damage is typically slow and for most habitats, the potential for artificial restoration remains limited. The current states of some of our key marine habitats are described below, as well as the threats posed to them and their potential impacts. Sea-grass meadows Swedish sea-grass meadows are known to support a diverse and productive benthic fauna (61), providing essential nursery and feeding grounds for at least 40 species of fish (62). The loss of 60 % of all sea-grass meadows along the west coast of Sweden (63) is believed to be the result of coastal eutrophication and overfishing as well the result of development of road banks and harbours detrimental to marine environments (64). Moreover, concern has been raised that invasive nonindigenous algae may out-compete the Zostera sea-grass beds in a near future (65). For example, the invasive Gracilaria vermiculophylla often covers the sea-grass with a thick sheet, thereby decreasing its growth potential. The collapse of seagrass habitats is likely to bring about consequences for ecosystem diversity and functions. In terms of food provisioning (chapter P1), it should be noted that an almost 100 % reduction of juvenile cod has occurred where sea-grass has disappeared (64). The cost of artificially restoring sea-grass beds are estimated at approximately 5 300 €/ ha (50). 57
SWEDISH ENVIRONMENTAL PROTECTION AGENCY Report 5873 • Ecosystem services provided by the Baltic Sea and Skagerrak Economic Marine Information Algal beds Algal beds are important for marine biodiversity and primary production (66). Like sea-grass beds, they also act as a filter against high nutrient input from terrestrial sources. Algal beds are undoubtedly beneficial for the production of food by providing nursery and feeding habitat for juvenile fish of commercial importance (e.g. pike, perch and cod). In other parts of the world, and historically in Baltic Sea, large algae have been used as fertilizer and in food production. Finally, algal beds are popular sites for diving and sport fishing (chapter C1). Due to increased nutrient concentrations and reduced water transparency, erect macroalgae have in some areas been lost (67) and replaced by less productive and supportive habitats including soft bottoms, mussel beds or communities of red or filamentous algae (68). The latter often end up covering beaches, with reduced benefits and increased costs for recreational businesses (69). The effects vary with region; in the Bothnian Bay and in Skagerrak-Kattegat, macroalgae are primarily threatened in proximity to industrial discharges or sewage treatment plants (70-71). Algal beds may also become threatened by invasive alien species and climate change (72). In the Baltic Sea, Fucus algae are already stressed by the low salinity. To counteract loss, the restoration and replacement of algal beds have been initiated in e.g. Himmerfjärden, in the Stockholm archipelago (73) as well as in the Bay of Gdansk (74). In Himmerfjärden the majority of the plants survived transplantation and some even reproduced. In the latter region, the project failed and conditions were judged too poor to allow for continuous trials. Mussel beds The blue mussel is one of our most common marine species. It is a very tolerant habitat builder and considered suitable for cultivation. In Skagerrak and Kattegat mussel banks are restricted to shallow waters, whereas in the Baltic proper they dominate down to as much as 30 m depth. Blue mussels increase biodiversity (compared to bare substrate) by providing substrate for algae and refuge for small animals (75). There is a direct relationship between the size of mussel bank and species numbers. In addition to providing habitat structure to the benthic community, mussels continuously affect the habitat by increasing water transparency and removing toxic substances from the water (chapters R3-R5). The tolerance of mussels extends to most threats. Given a less saline future, they are still likely to persist, although perhaps smaller in size. How acidification may affect bivalves, however, remains largely unknown. How the development of blue mussels and oysters is affected by predicted changes in pH, is currently under scrutiny (76). Shallow soft bottoms Soft bottom seafloors occur along all coasts of the Baltic Sea and Skagerrak, although their extent and characteristics differ regionally and locally. These nutrientrich sediments are highly productive and diverse. Constituting a mosaic of different structures including sea-grass, sand and shells, they provide habitats and feeding grounds for numerous species, among which filter-feeders, sea birds and commer- 58
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Ecosystem services provided by the Baltic Sea ... - Naturvårdsverket

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