Beneath the surface

The marine environment in Kvarken is very unique. In these waters, saltwater and freshwater species live side by side. The salinity of the brackish water is only 0.4 - 0.5% and it is very low compared to the great oceans, which have a salinity of about 3%. Due to the low salinity, many marine species have their northernmost distribution areas in the Kvarken archipelago. Not many species can live under these special conditions, and they are often very sensitive to changes in the aquatic environment. Therefore, there are not as many species in Kvarken compared to the great oceans. Overall, Kvarken is also very shallow with a maximum depth of about 25 meters.

Geological traces of the ice age can also be seen underwater. Moraine ridges of stones and boulders have also been formed on the seabed, which eventually form islands when they rise above the water surface. On these underwater moraine formations, or reefs, different algae and other plants are found. Further out in the archipelago, seaweed belts form favourable environments for both small animals and fish. These reefs can be found outside of the Norrskär islands, for example.

Image: Underwater moraine ridges covered with sea weed and algae, Gråsjälsgrynnorna

Sand or gravel banks can also form on the seafloor. They are important spawning grounds for fish, but seals usually feel at home here also. Underwater sandbanks are not so common in Kvarken, but they can be found at Norrskär, and probably also at Utgrynnan-Storkallan and Snipansgrund-Medelkallan.


Forststyrelsen. 2010. Skötsel- och användningsplan för Kvarkens yttre skärgård, förslag.

Rinkineva L., Bader P. 1998. Kvarkens natur. Kvarkenrådets publikationer 10, Vaasa

Airaksinen O., Karttunen K. (red.), 1999. Natura 2000 handbok över de finska naturtyperna, swedish translation (Åhman M. och Stenberg M.) of Finnish edition Natura 2000 – luontotyyppiopas, Finlands miljöcentral, Ympäristöopas 46, p. 194, 2001.