Reefs are considered to be underwater rocks and moraine or biological formations that rise considerably above the seabed that are sometimes exposed during low tide. The biota of the reefs is very diverse, the vegetation is mainly formed by brown and red algae communities. Bladder wrack communities are particularly rich in species.
There are no rocky reefs in Estonia, but here, this habitat type includes seabed ridges rich in boulders or basement rocks, which can extend above the water level during wind set-down. Such ridges can be found in the area of moraine seabed ridges: reefs are formed there from piles of granite boulders and rocks. The reefs also include carbonate rock embankments around some islands (Vaika, Pakri, Osmussaar), which gradually descend deeper.