Fauna of Europe of the Baltic Sea has led to the evolution of many slightly divergent species, such as the Baltic Sea herring, which is a smaller variant of the Atlantic herring. The most frequent benthic species are "Saduria entomon" and "Monoporeia affinis", which is originally a freshwater species. A great part of its bottom is anoxic and without animal life. The Baltic Sea and North Sea are also home to a variety of marine mammals (common seals, grey seals). Europe contains several important freshwater ecoregions, including the heavily developed rivers of Europe, the rivers of Russia, which flow into the Arctic, Baltic,
Coastline of the North Sea have formed the Frisian Islands. In the micro tidal area, (a tidal range of up to , such as on the Dutch or Danish coasts, barrier beaches with dunes are formed. In the mesotidal area (a tidal range of between ), barrier islands are formed; in the macrotidal area (above tidal range), intertidal deposits raise the spring tide range . A soft rock coast is formed in the meso-macro tidal areas located in the southern North Sea. These soft rock coastal bedrock plains are interspersed with soft rock (shale and sandstone) cliffs. The small, historically strategic island of Heligoland was