Effects of Sabella spallanzanii physical structure on soft sediment macrofaunal assemblages: effects on existing assemblages

The introduced European polychaete Sabella spallanzani 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. The effects of S. spallanzanii on: i) existing macrofaunal assemblege; ii) distribution of larvae and iii) colonisation of macrofauna were tested in sub-tidal soft sediments at Clifton Springs, Bellarine Peninsula, Port Phillip Bay, Victoria. This dataset gives the macrofauna assemblege of soft sediment cores collected from five replicate plots, in each of four experimental treatments: i) Real Sabella, a clump of 15 S. spallanzanii individuals transplanted from the surrounding region; ii) Mimic Sabella, a clump of 15 S. spallanzanii mimics; iii) Control, undisturbed sediment without S. spallanzanii and iv) Disturbed Control, disturbed sediments without S. spallanzanii. Plots containing real and mimic Sabella were used to test if changes in the assemblage of macrofauna in the presence of Sabella could be attributed to physical effects alone. A comparison of control and disturbed sediments was used to test if the disturbance created when transplanting Sabella into experimental plots contributed to any observed changes in the macrofauna assemblage.

Comparisons between Real (RS) and Mimic Sabella (MS), and Control (C) and Disturbed Control (DC) treatments were found not to differ significantly for any of the individual taxa or combined groups. Consequently, data from RS and MS treatments were pooled and compared against pooled data from C and DC treatments. This analysis found that the presence of Sabella reduced the abundance of harpacticoid copepods, cumaceans and ostracods by more than 50% compared with numbers found in sediment without Sabella. Collectively these taxa made up 80% of the total numbers of individuals in soil cores; as such the total number of individuals was also significantly reduced by the presence of Sabella.