Some marine habitats show extraordinary high biological diversity and activity. Some of these biological hotspots are found on large, man-made infrastructures, such as wind parks. Others are created by organisms themselves such as mussels, oysters, corals and seagrasses. These ecosystem engineers modify the environment to their own needs, while at the same time providing a substrate for associated species. We are interested in the interaction of these organisms with their environment, and to what extent their presence affects other organisms and the functioning of the marine environment.