Archipelago

Archipelago National Park is located in the Southwest Finland region, protecting a vast network of islands, islets, skerries, and open sea areas in the outer archipelago of the Turku Archipelago. Established in 1983, it is the largest national park in Finland by area, covering approximately 870 square kilometres, of which roughly half is marine and half is terrestrial across the approximately 1,800 islands and islets within its boundaries. The park forms part of one of the largest archipelago systems in the world, extending across the waters between the Finnish mainland and the Åland Islands. The outer archipelago landscape of bare exposed bedrock, windswept heath, and open sea contrasts dramatically with the sheltered inner archipelago of wooded islands and sheltered bays. The park supports exceptional breeding seabird colonies and protects important wintering and staging habitats for migratory waterbirds along the East Atlantic Flyway.

Archipelago National Park is one of the most important seabird breeding sites in the Baltic Sea region. The outer islets and skerries support internationally significant colonies of Arctic tern, common tern, little tern, razorbill, black guillemot, eider duck, and several species of gulls. The park is a stronghold for the white-tailed eagle, which has recovered dramatically in the Finnish archipelago following the DDT-related population crash of the mid-twentieth century. Grey seals and Baltic ringed seals haul out on the outer skerries, with the grey seal population recovering strongly following hunting protection. The sheltered inner bay and island habitats support breeding goldeneye, mergansers, and numerous wader species. The marine environment sustains diverse fish communities including populations of sea trout, pike, perch, and the increasingly rare whitefish. Harbour porpoise occurs in the outer sea areas, though populations are sparse due to the Baltic Sea's low salinity.

The flora of Archipelago National Park reflects the harsh conditions of the exposed outer archipelago and the more sheltered conditions of the inner islands. The outermost islets are dominated by littoral communities of bladder wrack and other algae at the water line, with sparse higher plant communities of sea rocket, orache, and cocklebur on storm-washed shores. Moving inward, heath communities dominated by heather, crowberry, and juniper cover the dry exposed island ridges, while sheltered depressions support peat bogs and sedge communities. The wooded inner islands support diverse deciduous and mixed forest communities including oak, birch, alder, and rowan. The transitional zone between the outer exposed archipelago and the inner sheltered zone is particularly diverse, with meadow communities developed on former grazing islands showing high plant species richness. Traditional management of island meadows through seasonal grazing by cattle is maintained on several islands as part of the park's cultural landscape management.

Archipelago National Park sits on the ancient Fennoscandian Shield, composed primarily of Precambrian granite and gneiss formed over 1.8 billion years ago. The archipelago landscape is a direct product of the glacial processes of the last ice age and subsequent isostatic rebound. Glacial erosion smoothed and rounded the bedrock into the characteristic whaleback forms of the Baltic coastal zone, while glacial deposition left a veneer of till and glaciofluvial sediment in sheltered locations. Following the retreat of the Scandinavian Ice Sheet approximately 10,000 years ago, the land has been rising steadily due to isostatic rebound at a rate of approximately 4 to 6 millimetres per year in this area, causing the archipelago to evolve continuously as new land emerges from the sea and shallow bays become marshes and eventually dry land. This ongoing geological process is fundamental to the dynamics of the archipelago ecosystem.

The southwestern Finnish archipelago experiences a maritime climate modified by the narrow Baltic Sea basin, with milder winters and cooler summers than the continental interior of Finland at comparable latitudes. The sea moderates temperature extremes, but the exposed outer archipelago is frequently subject to strong winds that can make small boat navigation dangerous. Annual precipitation is moderate at approximately 600 millimetres, distributed fairly evenly through the year. The Baltic Sea in this region freezes in most winters, typically from January through March or April, which significantly affects navigation and wildlife distribution. Ice fishing is a traditional winter activity on the frozen bays. Fog is common during spring and early summer as warm air moves over the still-cold sea. Summer days are long, with nearly 19 hours of daylight at midsummer, and the midnight sun creates a distinctive atmosphere for summer visitors.

The archipelago has been continuously settled since the Stone Age, with the earliest human communities exploiting the abundant marine resources of the Baltic Sea. By the Viking Age, the archipelago formed part of the trade and raiding networks connecting Scandinavia with the eastern Baltic and beyond. The Swedish-speaking population that has historically inhabited the outer archipelago has maintained a traditional maritime culture centred on fishing, seal hunting, small-scale farming on sheltered island meadows, and later, maritime trade and pilotage. Many islands within the park contain remains of historic fishing stations, pilot stations, fortifications, and farmsteads that document centuries of human presence and resource use. The gradual depopulation of the outer islands during the twentieth century, as traditional maritime livelihoods became economically unviable, preceded the park's establishment and contributed to the ecological recovery of the outer archipelago.

Archipelago National Park was established in 1983 by an act of the Finnish parliament, recognising the exceptional natural and cultural values of the outer archipelago zone and the importance of protecting the breeding seabird colonies and marine habitats from continued hunting, fishing, and development pressure. The park was initially controversial among the local fishing and maritime communities who feared restrictions on traditional livelihood activities. Management has evolved to accommodate traditional activities including fishing and the maintenance of historic island cultural landscapes through grazing and mowing. The park headquarters are located in Korppoo and the administration maintains a network of patrol and service vessels for management of this entirely maritime park. The park contributes to the broader Archipelago Sea Biosphere Reserve, designated by UNESCO in 1994.

Archipelago National Park is experienced primarily by boat, and independent navigation by kayak, sailing yacht, or motorboat allows exploration of the islands and waterways at one's own pace. The Jurmo island, accessible by scheduled ferry, is one of the most visited destinations within the park, offering exposed outer archipelago scenery, seabird colonies, and a traditional meadow landscape maintained by park grazing management. The island of Berghamn has a visitor centre and serves as a park gateway point. Designated nature trails on several of the larger islands lead through different vegetation zones from shore to forest interior. The open sea areas of the outer park offer exceptional sailing and sea kayaking in calm conditions. Winter ice conditions occasionally allow hiking or skiing across frozen sea ice between islands, an exceptional and atmospheric experience. Birdwatching from guided boats during spring migration or autumn staging is a popular organised activity.

Access to Archipelago National Park is exclusively by sea, with scheduled ferry services operating from Turku and several smaller mainland and island ports to destinations within and near the park during the summer season. The ferry network connects numerous islands in the archipelago and provides the primary means of reaching the park for visitors without their own boat. Kayak rental is available from operators in Turku and nearby coastal towns. Designated camping areas are available on several islands within the park, with simple facilities including dry toilets, firewood, and sometimes cooking shelters. Visitor facilities are intentionally minimal to preserve the wilderness character of the outer archipelago. Private boat anchoring is regulated within the park to protect sensitive habitats. The park is most accessible from May through September when scheduled ferries operate and weather is most favourable.

Archipelago National Park conservation priorities address the significant ecological challenges facing the Baltic Sea ecosystem, including eutrophication from agricultural and urban nutrient inputs, disturbance of sensitive seabird colonies by recreational boat traffic, and the recovery of grey seal populations. Nutrient enrichment of the Baltic Sea has driven increased algal growth and deterioration of water clarity, affecting seagrass and stonewort communities in sheltered bays. Management measures restrict boat navigation near sensitive seabird colonies during breeding season and regulate anchoring in protected habitats. White-tailed eagle monitoring and protection has contributed to the remarkable population recovery of this species across the Finnish archipelago. The maintenance of traditional island meadows and grazing on selected islands preserves an important cultural landscape element and supports the associated grassland biodiversity. Climate change is affecting sea ice conditions, seabird phenology, and the invasive round goby fish which is spreading northward into the park's marine habitats.