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Reefs (Photo: Martynas Bucas)
Reefs are probably the most attractive and ecologically significant habitat types in the Eastern part of the Baltic Sea, real oases sustaining high biodiversity of fishes, birds, invertebrates and plants.

Reefs may be biological origin (e.g. coral reefs) or geological origin, like those in the Baltic Sea – formed on the stony bottoms and rocks, but depending on specific environmental conditions in each region they develop into unique formations with specific type of vegetation and animals living there.

The most typical species here are read, brown and green macroalgae, animal species attached to bottom, e.g. bivalves, ascidias, bryozoa, as well as molluscs (Modiolus modiolus, Mytilus sp., Dreissena polymorpha), crustaceans and benthic fish.

Reefs are also used as spawning grounds by most of the commercially important fish species, like sprat. Here are feeding areas of diving birds that feed on molluscs and crustaceans. Reefs attract also fish, followed by seals. Thus reefs take significant role in food chain.

An extensive zone of reefs including the moraine ridges as well as patches of stones, gravel and sandy bottoms is starting in Lithuanian waters a bit North from Klaipeda and continue up to Perkone in Latvia. Reefs and stony bottoms can be found also elsewhere in the Eastern part of the Baltic Sea, e.g. near Hiiumaa and Saarema islands, in the Gulf of Riga, etc., but mostly the sea bottom here is formed by the mixture of sand, gravel and stones.

Taken together, the reefs in the eastern Baltic Sea occupy the area of over 8000 km2 what is almost half the size of the Gulf of Riga. If the reefs are destroyed, the whole ecosystem may collapse.