Submarine hard bottoms (e.g., boulders, outcropping strata) are of particular ecological importance. They were investigated in the Exclusive Economic Zones (EEZ) of the German North Sea and the Baltic Sea, using high-resolution seafloor imaging techniques (i.e., sidescan sonar and multibeam echosounder). Examples are shown from the research areas
Sylt Outer Reef (Sylter Außenriff
; North Sea),
Kadet Trench (Kadetrinne)
Adler Ground (Adlergrund)
(both in the Baltic Sea). There exist distinct differences between the two continental shelf seas regarding the distribution of boulders and the density (percent coverage) of boulders per unit seafloor. The observed differences are attributed to (a) different geological evolution of the seafloor, and (b) different forcing by waves, tides and currents, which are responsible for the redistribution of sediments.