The introduced European polychaete Sabella spallanzanii has become a dominant feature of sub-tidal habitats in south-eastern Australia. This study examines the physical effects of Sabella spallanzanii on macrofaunal assembleges of soft sediments. Macrofaunal assemblages were compared in the presence and absence of real and mimic S. spallanzanni clumps within sub-tidal experimental plots at Clifton Springs, Bellarine Peninsula, Port Phillip Bay, Victoria. The effects of S. spallanzanii on: i) existing macrofaunal assemblage; ii) distribution of larvae and iii) colonisation of macrofauna were tested. This dataset gives the colonisation of macrofauna in trays of sediments which had been defaunated and embedded in sediments within plots of undisturbed sediment (Control) and plots that contained a single clump of 15 S. spallanzanii individuals (Sabella). Sediment trays were colonised predominantly by crustaceans, representing 91% of all individuals found. The presence of Sabella clumps resulted in a significantly higher colonisation of Cylindroleberidid ostracods, but no other effects were detected.