Other key species in the Baltic region are iconic species including salmon (Salmo salar), cod (Gadus morhua), great cormorant (Phalacrocorax carbo sinensis), white-tailed eagle (Haliaeetus albicilla), grey seal (Halichoerusgrypus), harbour seal (Phoca vitulina) and ringed seal (Phoca hispida). During the winter, approximately 90% of the sea ducks living in the Baltic Sea region gather in areas that constitute less than 5% of the Baltic Sea. Bladder wrack forms one of the most diverse Baltic Sea habitats down to 10-11 m depth. The lowest depth limit of bladder wrack (and other macroalgae) is widely used as one of the ecological quality indicators in the Water Framework Directive assessments in the Baltic Sea (Zettler et al., The mussels modify the environment and support a rich diversity of associated species (P. Norling & Kautsky, 2007, Ojaveer et al., Mussel beds uphold an important filter-feeding function: they regulate the availability and flow of resources such as nutrients and organic matter, thereby forming an important link between benthic and pelagic ecosystems.