Ecologically or Biologically Significant Areas (EBSAs)
published:17 Jan 2019
Åland Sea, Åland Islands and the Archipelago Sea of Finland
The area contains some of the most geomorphologically, biologically and ecologically variable marine environments in the Baltic Sea, and perhaps in the world. The area is characterized by an extremely mosaic and extensive archipelago that ranges from shallow and sheltered inner archipelago areas, through middle archipelago, with larger islands, to wave-exposed outer archipelago consisting of thousands of small islands and skerries. The Åland Sea, in contrast, is an open sea area with almost oceanic conditions and the second-deepest trench in the Baltic Sea, at 300 m. The trench is also the deepest oxygenated area in the Baltic Sea. Due to its low salinity (0 to 7 psu), the species composition in the area is a mixture of freshwater, brackish and marine organisms, with a high diversity of aquatic vascular plants and charophytes, in particular. The area contains hundreds of lagoons, narrow inlets, shallow bays, estuaries and wetlands, which are important areas for fish and birdlife. The benthic biomass in the shallow areas is the highest in the northern Baltic Sea. The area also supports important populations of the ringed seal (Pusa hispida botnica) and grey seal (Halichoerus grypus). Harbour porpoise (Phocoena phocoena) visit the area regularly.
The area contains the most variable marine environments in the Baltic Sea, and perhaps in the world. It is characterized by an extremely mosaic and extensive archipelago, which ranges from sheltered inner archipelago areas with lagoons, shallow bays and boreal inlets, through middle archipelago, with larger islands, to wave-exposed outer archipelago consisting of a myriad of small islands and skerries facing the Northern Baltic proper. The water depth of the archipelagic areas is relatively low in the inner archipelago (mostly 0 to 30 m) and increases in the outer archipelago, where there are several elongated channels that are 80–120 m deep (Figure 2 DEPTH). The Åland Sea, in contrast, is an open-sea area with almost oceanic conditions and the second-deepest point in the Baltic Sea, 300 m. Notably, this “abyss” is the deepest oxygenated area in the Baltic Sea. All other deep areas south of the Åland Sea are hypoxic or anoxic. The area is geologically one of the most diverse seafloor environments of the Baltic Sea (Kaskela et al., 2012; Kaskela & Kotilainen, 2017). The Precambrian crystalline bedrock and fault tectonics, together with glacial erosion and deposition as well as post glacial processes, have formed a complex landscape with a mosaic of structures and substrates. Submarine geological features typical to the area include till, various moraines, eskers, Salpausselkä formations, postglacial clays and relict river valley continuations, and the sediments are very varied, containing granite, rocky bottoms, moraine, gravel, sand and mud (Kaskela et al 2012). The Precambrian basement rocks have suffered glacial scouring and over-deepening of pre-existing drainage channels and, at present, the most resistant materials stand out as elevated structures forming, for example, rocky reefs. The elongated deep-sea troughs characteristic of the area partly coincide with fault lines and thrust zones, and serve as important water passages connecting the Baltic proper with the Gulf of Bothnia (Winterhalter et al. 1981; Koistinen et al. 1996). The surface salinity in the open sea varies from 6 to 7 psu, but may be close to zero in the inner archipelagic estuaries. This enables the existence of both marine and freshwater species.
The area is situated in the northern Baltic Sea and forms the border between the Baltic proper and the Gulf of Bothnia. It extends from the Swedish coast in the west across the Åland Islands to the Finnish Archipelago Sea and Hanko Peninsula in the east. The area is about 375 km in width and 100 km long (in W-E and N-S direction, respectively). The area covers 18,524 km2 in total.
DISCLAIMER: The designations employed and the presentation of material in this map do not imply the expression of any opinion whatsoever on the part of the Secretariat concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.
Several important marine habitat types exist in the area. These include, for example, estuaries, coastal lagoons, large shallow inlets and bays, boreal Baltic narrow inlets, underwater sandbanks, reefs, and Baltic esker islands with sublittoral vegetation (EU habitats directive classifications 1130, 1150, 1160, 1650, 110, 1170, 1610, respectively). All of these habitats host specific flora and fauna, which make the area biologically and ecologically very variable. Consequently, there are a large number of marine protected areas (both HELCOM and private) in addition to EU Natura 2000 sites and the large Archipelago Sea National Park (Finland) in the area. Due to the low salinity (0 to 6 psu, depending on area and proximity of estuaries; cf. VELMU data), the species composition is a mixture of freshwater and marine organisms, and the combined biodiversity of macroalgae and aquatic vascular plants in particular is high (Figures 3 and 4). Charophytes (e.g., Chara horrida, which is endangered in Finland and near threatened in the HELCOM area) form large meadows in sheltered lagoons and bays, and water mosses (Bryophyta), which normally are freshwater species, are found in some inner inlets and bays. Many marine species, including keystone and habitat-forming species such as bladderwrack (Fucus vesiculosus) and blue mussel (Mytilus trossulus), occur abundantly in the area, especially in the outer and middle archipelago, securing local microhabitats for a myriad of marine species, including algae, invertebrates and fish. The “Boreal Baltic narrow inlets” (habitat 1650, according to the EU Habitats Directive) and “large shallow inlets and bays” (habitat 1160) in the area form some of the most important breeding areas for pikeperch in the northern Baltic Sea (EC 1992). Also, marine fish species, such as Baltic herring and sprat, are common in the area, and flounder, cod and turbot occur regularly. This the northernmost area in the Baltic Sea where the eelgrass (Zostera marina) forms dense beds (Boström et al. 2014); certain underwater sand banks host the largest eelgrass meadows in Finland. Furthermore, the biomass of soft bottom benthic invertebrates in the Archipelago Sea is, after Kattegatt, the highest in the Baltic Sea (Gogina et al. 2016). This provides an abundant food supply for benthic feeding fish and birdlife. The area’s coastal lagoons and “Boreal Baltic narrow inlets” are very important feeding and nesting areas for coastal birds. Also the sea area surrounding the fringe of treeless skerries facing the northern Baltic proper includes an almost continuous series of Important Bird and Biodiversity Areas (IBAs). For example, common eider (Somateria mollissima) inhabits the outer archipelago where shallow rocky reefs provide feeding grounds with high densities of blue mussel (Mytilus trossulus). The outer archipelago is also an important breeding and feeding area for colonial alcids, such as razorbill (Alca torda) and black guillemot (Cepphus grylle), which feed on the small fish abundant in the area. In other sea areas they typically breed on cliffs, but in the Archipelago Sea they colonize shallow rocky islets in the extremities of the archipelago. The outer part of the archipelago is also an important wintering area for purple sandpipers (Calidris maritima), at least partially originating from Svalbard (Bioforsk). The western part of the area supports a population of the ringed seal (Pusa hispida botnica) (Halkka and Tolvanen 2017). Although the ringed seals are only classified as near-threatened in the Baltic Sea (Liukko et al 2015), the population in the Archipelago Sea needs special protection due to its small size (200-300 individuals) (Ministry of Agriculture and Forestry 2007; Ahola & Nordström 2017). The ringed seal is threatened by climate change, because its pups need crested sea ice for hiding places as they grow. Grey seals (Halichoerus grypus) are common in the outer and middle archipelagos and very common on the western side of the area. The high abundance of herring, salmon and cod is an important reason for the very high seal populations in the area, which is the most densely populated seal area in the Baltic Sea (Ministry of Agriculture and Forestry 2007). The Åland Sea abyss, which is a deep oxygenated area in the Baltic Sea, is a prerequisite for a healthy and species-rich macrofauna community. The abundance of cod and herring is high in the area. There are also indications that cod spawn in the area. However, it is not known if there has been successful spawning in the area or if it is a sink for the Southern Baltic cod (Bergström et al. 2015). The area also provides very important habitats for perch, pikeperch and pike (Bergström et al. 2007; Kraufvelin et al. 2018). The area also constitutes an important migration route for salmon and trout going up to the rivers in the Bothnian Bay to spawn (Michielsens et al. 2008). The area is also the northern distribution limit for Harbor porpoise (Phocoena phocoena) in the Baltic Sea (Figure 5) (ASCOBANS 2016, Sambah 2017). The harbour porpoise visits the southern part of the outer archipelago regularly. The harbour porpoise population of the Baltic Sea is critically endangered (HELCOM, 2013).
The area, especially its outer archipelago, has a high degree of naturalness, and biodiversity is high for a brackish-water sea area. While there are a lot of smaller buildings and summer cottages in the inner archipelago areas, the outer archipelago is almost completely uninhabited and undeveloped. Regular monitoring of the ecological state of the sea takes place in the area, implementing the EU directives and Finnish and Swedish national legislations. The Finnish Inventory Programme for Marine Underwater Environment (VELMU) has conducted extensive biodiversity inventories in the area. The inventories conducted from 2004 to 2017 included dive lines and drop videos, benthic sampling, fish larvae sampling, and echosoundings. Observation data for hundreds of species is available, and species distribution models (SDMs) have been made for 100+ species (below referred to as “VELMU data”; viewable in https://paikkatieto.ymparisto.fi/velmu). Habitat modelling activities were also conducted by the Swedish Board of Fisheries in the Archipelago Sea in 2006. The activities were part of the Interreg Baltic Sea Region Programme "Baltic Sea Management – Nature Conservation and Sustainable Development of the Ecosystem through Spatial Planning" (known as BALANCE). Habitat models were developed for four of the most ecologically and economically important fish species in the coastal ecosystem of the Baltic Sea (www.balance-eu.org). The ecological status of the water in the inner archipelago is presently not good, mainly because of anthropogenic nutrient loading. The water in the inner archipelago is turbid, especially in late summer, and anoxia is common in sheltered sea areas with poor water exchange. The exposed outer archipelago areas facing the northern Baltic Sea are in better condition, albeit blue-green algal blooms may occasionally make the water turbid during late summer. The European Union Marine Strategy Framework Directive (2008/56/EC), and the HELCOM Baltic Sea Action Plan (HELCOM 2007), oblige Sweden and Finland to improve the state of the marine environment by 2020 and 2021, respectively, e.g. by decreasing the amount of nutrient loading from land, so the water quality in area will probably gradually start improving.
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Bergström, U., Sandström, A, Sundblad G. (2007) Fish Habitat Modelling in the Archipelago Sea. BALANCE Interim Report No. 11. Bioforsk. The Purple Sandpiper in Finnmark. Information sheet for the project «Bird tourism in central and eastern Finnmark», a project part of «The natural heritage as a value creator (M)» http://www.bioforsk.no/ikbViewer/Content/109343/Fjareplytt_Engelsk.pdf. Accessed on 22.1.2018. Boström, C., Baden, S., Bockelmann, A. C., Dromph, K., Fredriksen, S., Gustafsson, C., ... & Olsen, J. (2014). Distribution, structure and function of Nordic eelgrass (Zostera marina) ecosystems: implications for coastal management and conservation. Aquatic Conservation: Marine and Freshwater Ecosystems, 24(3), 410-434. EC (1992): Council Directive 92/43/EEC of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora. OJ L 206: 7–50. Eriksson, Britas Klemens, et al. (2004): "Effects of boating activities on aquatic vegetation in the Stockholm archipelago, Baltic Sea." Estuarine, Coastal and Shelf Science 61.2. 339-349. Fauna Europaea https://fauna-eu.org/cdm_dataportal/taxon/1cd8581b-67c9-4455-a2f5-6629b84048c8 Finnish Bird Atlas. Suomen III Lintuatlaksen tulokset. Luonnontieteellinen keskusmuseo Luomus, Helsingin yliopisto. Creative Commons 4.0 (Finnish Bird Atlas III results.Natural History Museum Luomus, University of Helsinki. CC4.0.) Gogina, M., Nygård, H., Blomqvist, M., Daunys, D., Josefson, A. B., Kotta, J., ... & Zettler, M. L. (2016). The Baltic Sea scale inventory of benthic faunal communities. ICES Journal of Marine Science, 73(4), 1196-1213. https://academic.oup.com/icesjms/article/73/4/1196/2458890 Halkka, A., Tolvanen, P. (eds.) (2017). The Baltic Ringed Seal – An Arctic Seal in European Waters – WWF Finland report 36. https://wwf.fi/mediabank/9825.pdf Härkönen, T., Stenman, O., Jüssi, M., Jüssi, I., Sagitov, R., & Verevkin, M. (1998). Population size and distribution of the Baltic ringed seal (Phoca hispida botnica). NAMMCO Sci Publ, 1, 167-80. HELCOM (2012). Checklist of Baltic Sea Macro-species. Baltic Sea Environment Proceedings No. 130 HELCOM (2013). HELCOM Red List of Baltic Sea species in danger of becoming extinct. Baltic Sea Environment Proceedings 140: 1-106. HELCOM Depth. http://metadata.helcom.fi/geonetwork/srv/eng/catalog.search#/metadata/5dcf182a-517a-4599-be0d-626bea8e058d. Kaskela, A.M., Kotilainen, A.T., Al-Hamdani, Z., Leth, J. & Reker, J. (2012). Seabed geomorphic features in a glaciated shelf of the Baltic Sea. Estuarine Coastal and Shelf Science 100, 150–161. ISSN 0272-7714, http://dx.doi.org/10.1016/j.ecss.2012.01.008 Kaskela, A.M. & Kotilainen, A.T. (2017). Seabed geodiversity in a glaciated shelf area, the Baltic Sea. Geomorphology 295, 419-435. ISSN 0169-555X, http://dx.doi.org/10.1016/j.geomorph.2017.07.014 Koistinen, T., Klein, V., Koppelmaa, H., Korsman, K., Lahtinen, R., Nironen, M., Puura, V., Saltykova, T., Tikhomirov, S. & Yanovskiy, A. (1996). Paleoproterozoic Svecofennian orogenic belt in the surroundings of the Gulf of Finland. In: Koistinen, T. (ed) Explanation to the Map of Precambrian Basement of the Gulf of Finland and Surrounding Area 1: 1 000 000. Geological Survey of Finland Special Paper 21, 21–57. Kraufvelin, P., Pekcan-Hekim, Z., Bergström, U., et al. (2018). Essential coastal habitats for fish in the Baltic Sea. Estuarine, Coastal and Shelf Science 204: 14-30. Liukko, U-M., Henttonen, H., Hanski, I. K., Kauhala, K., Kojola, I., Kyheröinen, E-M. & Pitkänen, J. (2016). Suomen nisäkkäiden uhanalaisuus 2015 – The 2015 Red List of Finnish Mammal Species. Ympäristöministeriö & Suomen ympäristökeskus. 34 p Meier, H. E. M., Döscher, R., & Halkka, A. (2004). Simulated distributions of Baltic Sea-ice in warming climate and consequences for the winter habitat of the Baltic ringed seal. AMBIO: A Journal of the Human Environment, 33(4), 249-256. Michielsens, C.G., McAllister, M.K., Kuikka, S., et al. (2008). Combining multiple Bayesian data analyses in a sequential framework for quantitative fisheries stock assessment. Canadian Journal of Fisheries and Aquatic Sciences, 65(5): 962-974. Ministry of Agriculture and Forestry (2007). Itämeren hyljekantojen hoitosuunnitelma. Ministry of Agriculture and Forestry 4b/2007. ISBN 978-952-453-329-4. 93p. http://mmm.fi/documents/1410837/1721042/4b_Hylkeen_enkku_nettiin.pdf/aeb2abf7-d6f0-422e-8a6a-94ba8403df31 Munsterhjelm, Riggert. 2005. "Natural succession and human-induced changes in the soft-bottom macrovegetation of shallow brackish bays on the southern coast of Finland." Pitkänen, H., Peuraniemi, M., Westerbom, M., Kilpi, M., & Numers, M. V. (2013). Long-term changes in distribution and frequency of aquatic vascular plants and charophytes in an estuary in the Baltic Sea. In Annales Botanici Fennici (Vol. 50, No. SA, pp. 1-54). Finnish Zoological and Botanical Publishing Board. Rinne, H., Kaskela, A., Downie, A. L., Tolvanen, H., von Numers, M., & Mattila, J. (2014). Predicting the occurrence of rocky reefs in a heterogeneous archipelago area with limited data. Estuarine, Coastal and Shelf Science, 138, 90-100. Saari, S. (2007). Meriuposkuoriaisen, Macroplea pubipennis (Coleoptera: Chrysomelidae), levinneisyys ja elinympäristövaatimukset Espoonlahdessa. M.Sc thesis (in Finnish). University of Helsinki. https://helda.helsinki.fi/handle/10138/18928 Sambah. 2017. Sambah Final report. Figure 1a. http://www.sambah.org/SAMBAH-Final-Report-FINAL-for-website-April-2017.pdf Accessed 7.3.2018 Snickars, M., Sandström, A., Lappalainen, A., Mattila, J., Rosqvist, K. & Urho, L. (2009). Fish assemblages in coastal lagoons in land-uplift succession: the relative importance of local and regional environmental gradients. Estuarine, Coastal and Shelf Science, 81, 247–256. Snoeijs-Leijonmalm, P., Schubert, H., & Radziejewska, T. (Eds.). (2017). Biological oceanography of the Baltic Sea. Springer Science & Business Media. Stjernberg, T., Nuuja, I., Laaksonen, T., Koivusaari, J., Ollilal T., Keränen, S., Ekblom, H. lokki, H. & Saurola, P. 2016: Suomen merikotkat 2013-2015. - Linnut vuosikirja 2015: 20-29. Sundblad, G., U. Bergström, and A. Sandström (2010). Ecological Coherence of Marine Protected Area Networks: A Spatial Assessment Using Species Distribution Models. Journal of Applied Ecology 48: 112–20. Sundqvist, L., Harkonen, T. Svensson, C.J., Harding, K.C. (2012) Linking climate trends to population dynamics in the Baltic ringed seal - Impacts of historical and future winter temperatures. Ambio. DOI 10.1007/s13280-012-0334-x Toivanen, T., Mehtonen, T., Lehtiniemi, T. (2014). Lintujen päämuuttoreitit Suomessa (Main migration routes of birds in Finland; in Finnish). Birdlife 2014. 21 pp. http://www.ymparisto.fi/download/noname/%7BFA98FD1F-987F-4546-84F7-93BDC1F0CE06%7D/100332 Tolvanen, H., Numminen, S., & Kalliola, R. (2004). Spatial distribution and dynamics of special shore-forms (tombolos, flads and glo-lakes) in an uplifting archipelago of the Baltic Sea. Journal of Coastal Research, 234-243. Vahteri, P., & Vuorinen, I. (2016). Continued decline of the bladderwrack, Fucus vesiculosus, in the Archipelago Sea, northern Baltic proper. Boreal Environment Research, 21(5-6), 373-386. VELMU data: VELMU Map Service: https://paikkatieto.ymparisto.fi/velmu VELMU. Data collected from VELMU database managed by Finnish Environment Institute (Markku Viitasalo, Juho Lappalainen. Email: email@example.com) Map service available online (https://paikkatieto.ymparisto.fi/velmu). Vösa, R., Högmander, J. Nordström, M. Kosonen, E. Laine, J. Rönkä, M. & Von Numers, M. 2017: Saaristolinnuston historia, kannankehitys ja nykytila Turun saaristossa. - Metsähallituksen luonnonsuojelujulkaisuja. Sarja A 226, 311 s. Winterhalter, B., Flodén, T., Ignatius, H., Axberg, S. & Niemistö, L. (1981). Geology of the Baltic Sea. In: Voipio, A. (ed) The Baltic Sea. 30. Elsevier Oceanography Series.
- Additional figures_Åland Sea, Åland Islands and the Archipelago Sea of Finland.pdf (/api/v2013/documents/AA389D58-1B5E-26BB-54BF-8F92F50D379D/attachments/Additional%20figures_%C3%85land%20Sea%2C%20%C3%85land%20Islands%20and%20the%20Archipelago%20Sea%20of%20Finland.pdf)
- BALT_3_EBSA.zip (/api/v2013/documents/AA389D58-1B5E-26BB-54BF-8F92F50D379D/attachments/BALT_3_EBSA.zip)
Areas described as meeting EBSA criteria that were considered by the Conference of the Parties
C1: Uniqueness or rarityHigh
The area is probably the most complex archipelago area in the world, with tens of thousands of islands and skerries, and a myriad of different types of waters, from enclosed lagoons to large open-sea areas. The area has unique geomorphological and habitat characteristics, with features formed by the last glaciation, such as the largest end moraines (Salpausselkä) in the Baltic Sea (Tolvanen et al. 2004, Kaskela et al. 2012, 2017, Rinne et al. 2014). Several deep (mostly 70 to 120 m) trenches exist in the area. Due to relatively strong currents they are oxygen-rich (unlike the deep Baltic basins, which are anoxic). The deepest of these is located in the Åland Sea—at 300m, it is the second-deepest in the Baltic Sea. Notably, the trench is the deepest oxygenated area in the Baltic Sea, creating unique conditions for benthic fauna (Snoeijs-Leijonmalm, Schubert & Radziejewska 2017). The unique combination of various types of habitats, from sheltered lagoons to extremely exposed outer skerries, provides ample opportunities for bird nesting and feeding, and the area displays a unique diversity of coastal and marine birds (Vösa et al. 2017). A number of rare species can be found in the area, including the charophyte Chara horrida (FIN: EN; HELCOM: NT) (Artportalen database, VELMU data–not visible in VELMU map service), Macroplea pubipennis (FIN: VU ; HELCOM: DD), a leaf beetle species of the subfamily Donaciinae that feeds on aquatic plants and is endemic to Finland, has viable populations in the area (VELMU data, not visible in Map Service). A population of endangered Baltic ringed seal (Pusa hispida botnica) lives in the area (Härkönen et al. 1998); their existence relies on good ice winters (Meier et al. 2004). Harbour porpoises (Phocoena phocoena) visit southern part of the outer archipelago regularly. The harbour porpoise population of the Baltic Sea is critically endangered (HELCOM, 2013).
C2: Special importance for life-history stages of speciesHigh
The area is very important for several life history stages of a large number of taxa, including birds (Fig. 6), fish (Snickars et al. 2009, Sundblad et al. 2010, Kraufvelin et al. 2018) and seals (Halkka & Tolvanen 2017). The rocky islets of the outer archipelago are an important nesting and feeding area for colonial alcids, such as razorbill (Alca torda) and black guillemot (Cepphus grylle), which in other sea areas typically nest on cliffs. The outer part of the archipelago is an important wintering area for purple sandpipers (Calidris maritima), at least partially originating from Svalbard (Bioforsk). The middle and inner archipelagoes, in turn, are important nesting areas for common eider (Somateria mollissima), long-tailed duck (Clangula hyemalis), greylag goose (Anser anser), common tern (Sterna hirundo) and Arctic tern (Sterna paradisea), among others. Major bird migration routes also cross the area (Toivanen et al. 2014), which is therefore important as a resting and feeding area for various migrating birds. The numerous shallow bays and inlets of the area, which warm up early in spring, are important reproduction areas for many of these species, including pike (Esox lucius), perch (Perca fluviatilis), pikeperch (Sander fluviatilis) and roach (Rutilus rutilus) (Snickars et al. 2009; Kraufvelin et al. 2018). The sea ice habitat of the area is very important for ringed seal because its pups need ice lairs for shelter during their long lactation period (Meier et al. 2004).
C3: Importance for threatened, endangered or declining species and/or habitats Medium
A number of species that are Red Listed for the Baltic Sea region are found in the area (HELCOM 2013): the vulnerable ringed seal, critically endangered Anguilla anguilla, endangered Coregonus lavaretus, and the vulnerable Salmo salar and Salmo trutta. The area also has a high occurrence of a number of biotopes and habitats that are Red Listed for the Baltic Sea region (HELCOM 2013). This includes estuaries (critically endangered), coastal lagoons (endangered) and sandbanks (vulnerable) and rocky reefs (vulnerable). Zostera marina meadows (near threatened) are at their northerly distribution limit in the area, while charophyte meadows are relatively common throughout the area.
C4: Vulnerability, fragility, sensitivity, or slow recovery Medium
The coastal “Boreal Baltic narrow inlets” and semi-enclosed lagoons provide a habitat for a rich bird fauna and nursery areas for fish. Due to limited water exchange, such areas are especially vulnerable to human disturbance, especially nutrient loading, dredging, overfishing and excess boat traffic. This also makes the species in these habitats, such as freshwater fish and certain aquatic vascular plants and charophytes, vulnerable to the environmental change in the area (Eriksson et al. 2004, Pitkänen et al. 2013). Certain habitat-forming marine species, such as eelgrass (Zostera marina), live on the edge of their geographical range. This makes eelgrass meadows, and the species that live in them, particularly vulnerable to hydrographical and trophic changes caused by eutrophication and climate change (Baden et al. 2003, Boström et al. 2014). Many of the rare species, for example, ringed seal, waterfowl and charophytes, are slow to recover from disturbance (Meier, Döscher & Halkka 2004, Munsterhjelm 2005, Bäcklin et al. 2011, 2013, Sundqvist et al. 2012, Stjenberg et al. 2016).
C5: Biological productivityHigh
The entire archipelago has the highest zoobenthos productivity in the entire Baltic Sea inside the Danish and Swedish sounds (Gogina et al. 2016). The lagoons, inlets and bays, in particular, have high macrophyte, invertebrate, waterfowl and fish production.
C6: Biological diversity Medium
The area contains a high diversity of habitats that occur intermixed on a very fine spatial scale. The salinity gradient creates a mix of freshwater and brackish water species, but the species diversity is not particularly high from the Baltic Sea perspective (Table 1; HELCOM 2012). A high number of birds either nest or stop over in the area during migration.
C7: Naturalness Medium
The coast and the inner archipelago are intensively used for housing, agriculture and recreation, while the outer archipelago is, to large extent, unexploited for most part of the year.