EFFECTS OF SCALLOP DREDGING ON A SOFT-SEDIMENT COMMUNITY - A LARGE-SCALE EXPERIMENTAL-STUDY

Changes to benthic infauna caused by scallop dredging at a site in Por t Phillip Bay, southeastern Australia, were examined experimentally us ing a BACI (before, after, control, impact) design. The experimental d redging was undertaken by commercial fishermen and was typical of norm al commercial operations in its spatial extent, intensity and duration . Changes to benthic community structure following dredging were monit ored using grab samples taken on 3 occasions pre-dredging and 6 occasi ons post-dredging. The significance of changes was assessed using ANOV A for the more abundant species and, for pooled groups of species, Bra y-Curtis community dissimilarities and multidimensional scaling (MDS). The abundance of 7 of the 10 most common species changed significantl y (ANOVA p < 0.10) after dredging; 6 species decreased in abundance wh ile 1 species increased. The size and persistence of dredging impacts varied between species, but most species decreased in abundance by 20 to 30%. Dredging impacts became undetectable for most species followin g their next recruitment. Most species recruited within 6 mo of the dr edging impact, but a small number of species still had not recruited a fter 14 mo. These latter species appeared to cause a persistent change in community structure which was still detectable after 14 mo using B ray-Curtis dissimilarities. MDS ordination indicated that changes to c ommunity structure caused by dredging were smaller than those that occ ur between seasons and years.