The role of suspension—feeders varies according to the spatial and temporal scales at which assessments are made. In this paper, biodiversity, productivity, and filtration capacity are used to assess the influences of suspension-feeders at scales ranging from individual mussels to biogeographic regions. Quantitative comparisons based on the ‘catchment areas’ of single mussels, mussel beds and entire bays are used to illustrate how the role of these organisms varies as a function of the unit of measurement. One key factor influencing the relative importance of suspension-feeders at different scales is the rate of water movement and, thus, the volume of water available to the consumers. The biodiversity within suspension-feeder guilds is important because of the way it can affect the amount and sizes of particles removed from the spectrum of available food items. Variations in the role of these animals are also observed at time scales. The complexity of the scaling problem is illustrated using examples from the suspension-feeder guild in a tidal basin of the Wadden Sea (North Sea) where experiments and field measurements have provided insights into processes and mechanisms accounting for spatial and temporal variations.