Detecting human mitigation intervention: Effects of sewage treatment upgrade on rocky macrofaunal assemblages

► This study represents one of the first attempts to apply a beyond-BACI design in environmental impact assessment. ► We examine the effectiveness of secondary vs primary wastewater treatment over nine years at four different tidal levels. ► Improvement of treatment changed structure, diversity, abundance or spatial heterogeneity depending on the tidal level. ► Powerful sampling designs, univariate and multivariate analytical approaches are fundamental in detecting human impacts.