Archipelago Sea and Southern Bothnian Sea

Situational picture

Description of the planning area

The Archipelago Sea and souther Bothnian Sea planning area covers the marine areas in the regions of Southwest Finland and Satakunta and its surface area is approximately xxx km2. The planning area is bordered in the south by the northern Gotland basin, in the west to the Sea of Åland, and in the north it spans about halfway through the Bothnian Sea and its boundary lies at the border of the municipality of Merikarvia.

The most important factor in the Archipelago Sea that influences the structure and composition of biota communities are the archipelago conditions and its regional variations. The Archipelago Sea is a unique area worldwide. Finland’s marine areas have over 80,000 islands more than on hectare in size, nearly half of which are located in the Archipelago Sea. The Archipelago Sea is divided into the inner, middle and outer archipelago – they differ in their landscape, vegetation and fauna.

The southern part of the Bothnian Sea is characterised by a low lying and the small featured coastal zone, a narrow and rugged archipelago zone, as well as an open sea. The islands are usually quite small in size and the waters surrounding the archipelago are shallow. The sea deepens rapidly from the coastline of the Bothnian Sea, so the archipelago zone is narrow and predominantly less than 10 kilometres from the mainland. Due to the openness of the Bothnian Sea, the sea has a strong impact on the coast and even on inland areas far from the coast.

Land uplift continuously changes the archipelago and coastal areas of the planning area; new islands will gradually rise from the sea, the old will grow in size, the straits, bays and estuaries will become more shallow and the coastline will move further into the sea. As gulfs gradually separate from the sea, flads and saltwater lakes that are important to biota will be formed and gradually turn into mires. The earth rises approximately 3.5 to 6.5 mm per year in the planning area, and the phenomenon is the strongest in the northern parts of the area.

The Baltic Sea is permanently layered due to the water’s salinity and temperature fluctuations. The salinity of the water in the planning area is only 6‰ and salinity differences in the areas waters are small. The salinity of the sea water in Finland’s marine areas is highest in the Archipelago Sea. Strong winds in the autumn mix the waters in the planning area all the way to the seafloor, which means that the oxygen conditions in the water remain good and there is no significant oxygen depletion in the open sea or in the shallow archipelago areas. In places, the oxygen conditions are poor in the Archipelago Sea’s deepest areas. The Archipelago Sea has been understood to function as a filter of nutrients and organic matter, which means that relatively few nutrients are transported into the Bothnian Sea. Due to the direction of the current, the Bothnian Sea also balances loads from other Baltic Sea waters.

The Bothnian Sea is located in the transition zone for southern and northern species, and the abundance of several species, such as bladder wrack and blue mussel, is rapidly reduced in the Bothnian Sea of as a result of the decrease in salinity in the Baltic Sea. On the other hand, the species in the Bothnian Sea and the archipelago area also include several species that occur in the Bothnian at their southern-most boundary, and they increase in abundance towards the Bay of Bothnia. Both freshwater and marine fish inhabit the waters in the planning area. As a result of the decreasing salinity towards the north, some of the marine fish species live in the Sea of Bothnia at the northern boundary of the distribution area.

A rise in the water level and eutrophication are considered the key impacts of climate change in the planning area. Predicted temperature increases, increasing rainfall and nutrient leaching from the mainland may change the living conditions of species in the sea. The impacts of climate change to the Baltic Sea also affect human activities, such as shipping, fishing and the recreational use, in coastal and marine areas.

Almost 700,000 people live in the regions of Southwest Finland and Satakunta in the Archipelago Sea and the southern Bothnian Sea planning area. The largest cities in Southwest Finland are Turku and Salo. Approximately 87% of the region’s population lives in coastal or archipelago municipalities. The coastal and archipelago areas of Southwest Finland has been inhabited and under the influence of human activities throughout human history. However, the archipelago areas’ permanent population has moved increasingly to the coastal growth centres over the past fifty years, while the summer population in the archipelago areas has grown steadily. People staying in the area’s holiday homes are a significant user of local services.

The largest population and workplace centres in Satakunta are located along the Bothnian Sea’s coastline and in Kokemäenjoki valley. The region’s largest cities are Pori and Rauma, where slightly more than half of the entire population lives. All in all, some 63% of the Satakunta population lives in the coastal municipalities. Holiday dwellings are primarily located along the coast.

The planning area has a strong and versatile economic structure in which industry is more significant player than average. For example, maritime industry and maritime logistics already account for a significant share of jobs in the region, and the number of jobs is expected to continue to increase. The increase in the number of industrial jobs will also cause in a rise to the number of jobs in the service sector.

State of the marine environment

Humans have had an impact on the marine environment for a long time and in many ways, as a result of which the state of the Baltic Sea has deteriorated. The state of the marine environment has deteriorated due to factors such as the loading of nutrients and harmful substances, dredging and piling of dredging spoils, underwater civil engineering, invasive species, fishing, littering and underwater noise pollution. In order to achieve a good state of the marine environment, pressures caused by humans must be reduced and new activities located in marine area must be located and designed to minimise adverse impacts.

The forms of the seabed in the Archipelago Sea vary greatly from its shallow waters to a depth of more than 100 metres. Lush bays and river mouths provide an excellent habitat for many waterfowl and coastal birds, and especially for young fish, such as pike-perch, European perch and northern pike. These sea bays produce a significant share of the Southwest Archipelago pike-perch, European perch and northern pike fingerlings. The waters in the outermost archipelago are in nearly constant movement. An abundance of water vegetation grows on the soft seafloor of the sheltered coves of the outer archipelago’s low islands. Seawrack meadows grow on underwater sandbanks and maintain the abundant benthic community. The shallow marine areas in the Bothnian Sea are characterised predominantly by hard moraine, rock and gravel seafloors as well as in many areas by their extensive bladder wrack growth. Due to the purity of the Bothnian Sea and the clarity of the water, the areas where many aquatic plants and algae occur extend deeper than in other marine areas. Yyteri’s sand-based esker formation and Preiviikinlahti Bay provide a habitat for many plant and animal species that favour sandy seafloors and slurry.

Due to the extensive and versatile archipelago, the planning area has a large bird population. The population of nesting birds is most diverse in the archipelago, in the low areas of the coast, in estuaries and in the lush coastal forests that surround them. An exceptional mixture of birds from the oceans, coasts and inland waters live around the Archipelago Sea, and it is the most central breeding area for several species of archipelago birds in Finland. The coastline of the Gulf of Bothnia is a significant migration route for many bird species migrating to the north, and the coastline of Satakunta is a significant resting point for migrating birds by Finnish standards.

In terms of marine mammals, there are regular sightings of grey seals and Baltic ringed seals in the Gulf of Bothnia. The Archipelago Sea is a key area for grey seals, more than 8,000 of which have been identified in the Southwest Archipelago. The number of ringed seals in the Archipelago Sea is estimated at 200–300.

Permanent populations of grey seals and Baltic ringed seals are present in the Gulf of Bothnia. Around one-third of all the grey seals in the Baltic Sea live in Finland’s territorial waters. The number of grey seals in the southern part of the Bothnian Sea is quite low in comparison with areas such as the southwestern parts of the Archipelago Sea; the annual calculated population was between 500 and 700 individuals in the 2010s. The population of Baltic ringed seals focuses mainly on the Bothnian Bay. In the future, the poorer ice conditions brought on by climate change are expected to have a particularly severe impact on the wellbeing of Baltic ringed seal populations.


State of the marine environment Status
Pollutant concentrations and effects
Contamination in fish intended for human consumption
Energy and underwater noise
Hydrographic changes
Invasive species
Commercial fish
Food networks
Partly positive, partly negative

The state of Finland’s marine environment is assessed as part of Finland’s Marine Strategy, which is based on the Act on Water Resources Management (1299/2014). This summary on the state of the marine environment in the planning area is essentially based on the Status of Finland’s Marine Environment 2018 (PDF), which has been prepared as part of Finland’s Marine Strategy. The Status of Finland’s Marine Environment 2018 covers marine biodiversity, the state of commercial fish stocks and food networks, the current status of the spread of alien species, eutrophication, littering and the status of hazardous and harmful substances. The report classifies the state of the marine environment as either good or poor for all these factors. The marine strategy assessment will supplement the classification of surface waters, which includes coastal waters, carried out as part of water resources management The water management classification divides surface waters into five ecological categories: Poor, unsatisfactory, satisfactory, good and excellent.

The aim of water resource management is to achieve at least a marine classification of good, but on the basis of the third round assessment on the ecological classification of surface waters (2019) the condition of the waters has deteriorated in the planning area.

The ecological status of the Archipelago Sea is predominantly classified as satisfactory, but there are also water areas in unsatisfactory and even poor conditions near the coast. The Bothnian Sea has been one of Finland’s cleanest marine areas, which has been evident in the classification of the ecological condition of the area’s surface waters and in the depth to which one can see in the waters. In the most recent assessment, the marine area classified as good has shrunk considerably, and the Bothnian Sea is no longer classified as good in the sea area between Rauma and Pori. The condition of other coastal waters varies from satisfactory to unsatisfactory.

Blue growth

The Blue Economy refers to sea-based livelihoods. The blue economy includes activities that take place in the marine environment, exploit marine resources or are involved in the provision of goods or services that contribute to economic activity in the marine environment.

Blue Growth refers to the ecologically, economically, socially, and culturally sustainable use of marine resources.

Offshore wind power is the fastest growing source of energy production worldwide. This has been influenced by technological development, the constantly increasing size of turbines and the substantial increase in production volumes.

Offshore wind power is the fastest growing source of energy production worldwide. This has been influenced by technological development, the constantly increasing size of turbines and the substantial increase in production volumes. The Baltic Sea’s offshore wind power potential is estimated to be considerable, and the potential is greatest in Finland’s coastal areas compared to other Baltic Sea countries. The potential estimate is based on the Finnish coast’s shallow water depth, the short distance from the coast and the reasonable proximity of an electricity connection.

Finland’s first offshore wind farm and the world’s first offshore wind farm built for demanding ice conditions operates in the Bothnian Sea off the coast of Tahkoluoto in Pori. The offshore wind farm, which opened in 2017, comprises 10 wind turbines that produce 4,2MW each. The estimated annual output of the Tahkoluoto offshore wind farm is 155 GWh. Wind turbines have also been built on land at the Port of Pori. The overall regional plan for Satakunta includes a designated area for wind turbines off the coast of Tahkoluoto in Pori.

The seamless operation of maritime transport is particularly important for Finland, as 90% of Finnish exports and 80% of imports are transported by sea. Expertise in technology and sustainable development are particularly emphasised in maritime transport. The development of ports and port operations (e.g. deepening of routes, digitalisation) is seen as an important for the improvement of industry’s operating conditions.

A substantial share of Finland’s imports and exports, especially when measured by the value of goods, travel through Southwest Finland’s ports. The fast and frequent transport to Sweden provided by the region’s ports is particularly important for the entire country’s foreign trade. Turku is also the second largest passenger port in the country. In addition to road connections well-functioning cable ferries, passenger ferry and commuter vessels linked to these are prerequisites for maintaining the large archipelago area as a vibrant residential, enterprising and tourism area.

The coast of Satakunta is the location of two nationally important freight ports, Pori and Rauma, through which regular freight traffic travels year-round. The Port of Pori comprises Mäntyluoto harbour (12m) and deep harbour (15.3m) and chemical harbour in Tahkoluoto. The Port of Pori specialises in dry and liquid bulk products, large and heavy project loads and sawn timber. The Port of Pori is also in use during winters when the sea is covered by ice. The Port of Rauma is a significant export port for the forest industry and cereals and the largest container port on Finland’s west coast (depth 12m).

The fishing industry depends on the good state of the aquatic environment and fish stocks. In 2019, some 500 commercial fishermen practiced their trade in the sections of the planning area comprising the Archipelago Sea and the southern Bothnian (138 Group I fishermen and 343 Group II fishermen). The area has abundant farming of fish intended for human consumption as well as fish processing companies. The network of fishing ports is comprehensive.

The Archipelago Sea is Finland’s most significant cluster in the fisheries industry. Important trawling areas are located in the southern Bothnian Sea both in the open sea and in the vicinity of the coast. The southern Bothnian Sea is Finland’s most significant Baltic herring fishing area. The largest fishing ports in the area are Reposaari in Pori, Uusikaupunki, and Kasnäs in Kimito.

Activity began in new fishery areas in accordance with the Fishing Act in 2019, and the areas are tasked with planning the sustainable use and management of fish stocks. The fishery areas will prepare a usage and management plan by the end of 2021. Each fishery area is responsible for implementing the plan and monitoring its impacts.

The majority of fish farming in Finland’s marine areas is located in the Archipelago Sea. Current activities are centred the inner archipelago, but the poor ecological status of the waters, water current conditions and other hydrological factors, extensive holiday home settlements and the environmental impacts of the activities have limited the wider use of existing areas.

The value of processing activities is significant, approx. EUR 358 million a year and the value of the fish wholesale business is approximately EUR 282 million a year. The most important species used by the domestic processing industry are rainbow trout, herring and whitefish.

The Archipelago Sea and the southern portion of the Sea of Bothnia are popular tourist and recreational areas with significant potential. The archipelago ring trail, Örö fortress island and other archipelago sites form the core of tourism and recreational activities in the Archipelago Sea. The action plan for tourism in Southwest Finland will highlight the development of services in Archipelago National Park and Bothnian Sea National Park, improving the accessibility of destinations, development of activities and accommodation options. Visit Finland has also highlighted Merellinen saaristo (marine wonders of the archipelago) as one of its key projects, as the archipelago is clearly attractive, but its development has been fragmented.

 The coastal and archipelago areas in the southern Bothnian Sea form a diverse entity that acts as a pull factor for tourism and recreational use due to its clean sea water, diverse archipelago nature and the area’s cultural historical values. For example, bird observation offers development opportunities for nature tourism. Bird sites, in particular Preiviikinlahti Bay and Kokemäenjokisuisto estuary, which waters in the Pori area favoured by birds as well as Yyteri’s sludge area attract birdwatchers year round. Efforts to strengthen cooperation related to tourism and to develop the general operating environment have been highlighted as key themes in the development of tourism in Satakunta.

Marine cultural heritage is tangible and intangible cultural heritage both above-ground and underwater, which is linked to man’s relationship with the sea and the resources found in the past by a community.

Maritime cultural heritage includes both concrete traces in the landscape and skills, customs and habits related to the marine landscape, such as practices, knowledge, stories and beliefs. These have been passed on from generation to generation helping to present, build and maintain the identities of different communities.

Marine cultural heritage is traces left by humans and elements produced by interaction between humans and nature in a marine environment. Marine cultural heritage is limited to the terrestrial and semi-waterborne areas of the coast, the archipelago and the outer sea, and is visible as the underwater landscape.

Marine cultural heritage is linked, among other things, to the settlement of the coast and the archipelago, maritime transport, fishing and other marine hunting culture, diving, and customs and beliefs that have linked humans to the marine environment.

With regard to cultural heritage the Archipelago Sea and southern Bothnian Sea planning area is reflected in very different ways in the areas municipalities: The culture of the archipelago is emphasised in the Archipelago Sea, and in Satakunta, cultural heritage is clearly more a combination of coastal culture related to fishing and shipping and the traditions, customs and characteristics of the farming community.

Shipping, trade and early settlements are characteristic of the entire planning area. The conditions have been favourable for livestock farming and agriculture, and in addition to the old farming culture, the cultural history of the coastal area is characterised by fishing, trade and shipping. Lighthouses and fixed beacons are key signs of shipping. The most famous lighthouses in the Archipelago Sea are Bengtskär on Kimito Island, Utö in Parainen and Isokari in Kustavi. The most well-known lighthouses in the southern Bothnian Sea are the lighthouse of Kallo and Säppi, and the fixed beacons are Santkari in Rauma and Oura in Merikarvia.

Satakunta’s nationally valuable marine landscapes include the Yyteri beach landscape and the Ahlainen cultural landscape. In Southwest Finland, marine cultural heritage is closely linked to landscape areas of national value, such as Dragsfjärd, Nauvo and Korppoo. The Archipelago Sea is a national landscape that reflects the more representative features of nature and culture in Finland. Underwater cultural heritage is mainly made up traces of maritime transport, i.e. the wrecks of various vessels and anchors lying on the seafloor. The sawmill industry in the southern Bothnian Sea is an important part of the area’s underwater cultural heritage.

The situational picture of Finnish marine cultural heritage 2019 (link) prepared by the Finnish Heritage Agency has been used to support the construction and planning of the situational picture of regional cultural heritage.

The maritime industry consists of equipment manufacturers, turnkey suppliers, design agencies, software and system suppliers as well as shipbuilding, repair and offshore shipyards. In Southwest Finland, the maritime industry directly employs more than 5,000 people and produces a turnover of EUR 1.4 billion in approximately 400 companies. The sector’s indirect income and employment impacts are considerable, with a 1.3 coefficients, the employment impact of the sector is 6,500 people and a turnover of 1.8 billion euros. The sector’s employment impact will continue to grow substantially from 2018 onward.

The maritime industry’s turnover principally consists of installation and assembly services, industrial manufacturing, design, consulting and expert services as well as repair and maintenance services. In Southwest Finland, the sector’s focus is on the construction of cruise liners and passenger ships, but the repair of old ships and the construction of small special-purpose vessels are also part of the maritime industry. The Turku shipyard (Meyer Turku) is of considerable importance to the Finnish maritime industry cluster and continues to grow.

Satakunta is one of the most industrialised regions in Finland. In Satakunta, industry accounts for 25.4% of the value added, while the national average is 16.9% (2013). Industry accounts for 19.6 % of jobs in Satakunta while the national average is 12.9 % (2014). Industry accounts for 25% of value added and the investment level is high. In recent years, industrial investments amounting to approximately EUR 1 billion have been implemented in Satakunta, and more than one billion euros in investments are planned. The exchange ratio of foreign trade is double that of the rest of Finland. Satakunta is an open, export-driven and international region. There is a desire to renew existing industry, and new activities can also be built on existing expertise.

The major industrial hubs located on the Satakunta coast include the M20 Industrial Park in Pori and the Seaside Industry Park in Rauma. A significant industrial zone stretches via the Port of Pori along the Kokemäenjoki valley, main road 2 and the train track all the way to Industrial Park, Harjavalta. The LNG terminal located in Tahkoluoto, Pori, supports the area’s off-grid gas economy.

The seabed sediments in Finnish marine areas are, geologically speaking, very young. In practice, all sea sand and gravel reserves were formed at the end of the last Ice Age or after that over the past 13,000 years. The recoverable reserves are mainly located in the subsea extensions of the ridges and terminal moraine bodies created when the glacier melted. To a lesser extent, recoverable minerals can be found in other moraine or erosion-caused sand sediments.

The area’s iron manganese deposits are the most interesting seafloor reserves. These have been studied from the 1960s due to their iron, manganese, phosphorus and earth metal reserves. Iron manganese sediments are found in nearly all of Finland’s marine areas. The possibilities for utilising phosphorus bound to the seafloor have also been considered in recent years.

While sea sand and gravel extraction has thus far been of a small scale in Finland, the need to exploit seafloor reserves is expected to grow as the availability of on-land gravel and sand resources declines, especially in the vicinity of growth centres. According to estimates produced in a background report produced by the Geological Survey of Finland, there are be approximately 2-3 billion m3 of sand and gravel in Finland’s marine areas, which is equal to approximately the amount of aggregates used in Finland over a period of 50 years. The estimate is based on the surface area of the surveyed sand and gravel deposits and a sediment thickness of five metres. However, efforts are being made to continuously reduce the use of virgin aggregates, and to transition increasingly to a circular economy in aggregate management.

There has been interest in the extraction of sea sand in Satakunta. The extraction of sea sand was studied in Pori sea area from 2007 to 2010. However, the projects have not been implemented, and no exploitation of sea sand or other extraction activities are currently carried out in the planning area.

The Bothnian Sea’s most substantial sand and gravel formations are located predominantly off the coast of Pori where a set of eskers stretching from Virttaankangas via Säkylä and Harjavalta to Pori continues for tens of kilometres from Yyteri Beach along the seafloor to the northwest. Another significant area is the sandy ridge on the island of Revel, to the north of Yyteri, in the Oura Archipelago.

The Archipelago Sea’s sand and gravel formations are mainly located in the Salpausselkä zone and in the Trollholm esker formation. The underwater formations on the seafloor are mainly covered by a thick layer of clay.

Blue biotechnology is a new sector, which from the perspective of the marine area’s use, refers to biomasses produced and harvested at sea and their production potential. In Finland, biomass potential has mainly been identified for common reed in lakes and less valuable fish. Growing algae in Finnish conditions is challenging due to the small amount of light and cold temperatures. Cultivation potential could be found in various waters containing waste heat and nutrients, which are formed for example by the pulp industry and in wastewaters. The low salinity and poor temperature conditions of Finland’s waters are a challenge in the cultivation of shellfish compared to other areas in the Baltic Sea. The potential for processing specialised products lies especially in the side-streams of the fisheries industry.

The special needs of national defence have been identified and taken into account in EU legislation in the Marine Strategy Framework Directive and in Finland’s national legislation in the Land Use and Building Act. Under the Land Use and Building Act, the needs of national defence must be secured and taken into account in land use planning and maritime spatial planning.

The Finnish Defence Forces carry out air and maritime surveillance in accordance with the Act on the Defence Forces (551/2007) and the Territorial Surveillance Act (755/2000) in all of Finland’s national territory and in its vicinity. National defence requires an active approach from the National Defence Forces in marine areas meaning comprehensive surveillance of air and sea. The Gulf of Finland and the southern parts of the Archipelago Sea are very important areas for Finland’s overall defence.

The implementation of the statutory tasks of the Finnish Defence Forces limits the other use of marine areas in some areas to the nature, location and timing of the activities. Finland’s marine areas include secured areas (18), shooting and training areas as well as their associated hazard and restriction areas. From the point of view of national defence, the usability of fairways, the needs of management systems under normal conditions and the underwater structures of the Defence Forces also play a key role. In addition, there may still be naval mines and other munitions during originating from the time Finland was at war and harmful substances from various activities in Finnish marine areas. These should be taken into account and examined on a case-by-case basis in more detailed planning.

Secured areas that are important to the arrangement of national security and territorial surveillance have been appointed in Finland’s marine areas and territorial waters. Their boundaries have be specified very carefully. Finland’s 18 secured areas are located in the Gulf of Finland and the Archipelago Sea. The Territorial Surveillance Act contains provisions on the secured areas and the operating restrictions in these secured areas, the purpose of which is to secure Finland’s territorial integrity.

There is usually a military area located within a secured area and these have a 100 metre buffer zone in which civilians are not permitted. The area is marked with signs prohibiting landing ashore and disembarkation. This limits anchoring in the area. Any activities in protected areas require a permit. The planning area’s secured areas in the Archipelago Sea and the southern part of the Bothnia Sea include Kimito, Örö, Utö, Gyltö, Houtskari and Pansio.