The Belgian part of the North Sea was once home to extensive offshore reefs of the European flat oyster Ostrea edulis. These reefs constituted an important habitat in the marine ecosystem, supporting a range of species and ecosystem functions. Belgium has ambitious plans to restore these lost reefs in the areas where they once occurred, the offshore gravel beds. The Institute of Natural Sciences monitors the success of these restoration efforts, by investigating both environmental (such as hydrodynamics, suspended matter, chlorophyll, sediment composition) and biological (such as survival, growth, reproduction, epifauna, predators, non-indigenous species) parameters.