Wageningen Marine Research is studying the long-term development of a number of individual intertidal mussel beds in the Dutch Wadden Sea to identify the characteristics that determine the survival of such beds. The study is being carried out as part of the WOT theme Nature Information Infrastructure. A large proportion of the mussel beds have been able to maintain themselves since the beginning of the study (1995). After formation of a new mussel bed they gradually decline in area, coverage and population density, and the proportion of empty shells, macroalgae and barnacles increases. The decline in size and coverage is occasionally reversed by a good mussel spatfall, after which the process starts again. Japanese oysters have settled in all beds, leading to higher shellfish coverage and a decline in mussel biomass.