Baltic Sea Ecoregion – Ecosystem overview

The Baltic Sea is one of the largest brackish water bodies in the world, covering 420 000 km2. It is a semi-enclosed shallow sea with an average depth of 60 m, where one third of the area is less than 30 m deep (Figure 1). This ecoregion has many islands and a long and diverse coastline, especially in the northern areas. It is characterized by strong temperature and salinity gradients, from relatively warmer and saline waters in the southwestern part to cold and almost freshwater in the northernmost parts. In addition, there is strong permanent vertical stratification for much of the Baltic Sea. The northernmost parts are covered by ice in winter. Based on its bathymetry and hydrology, the Baltic Sea can be sub-divided into three main areas:

● The transition area, consisting of the Belt Sea and the Arkona Basin;

● The central Baltic Sea, consisting of the deep areas of the Bornholm Basin, Gdansk Deep, Gotland Basin and the Gulf of Riga; and

● The northern Baltic Sea, including the Gulf of Bothnia and the Gulf of Finland and the Archipelago Sea.