Effects of dredging on the macrobenthic infauna of Botany Bay

Abstract

The macrobenthic. infauna of dredged and undredged areas in Botany Bay were sampled. Data were analysed using tests of significance and computer classification.

While dredging has not significantly affected average species density per sample, the benthic fauna of dredged areas differs from that of nearby undredged areas with respect to species composition and richness. both of which appear to be strongly associated with sediment type. Species richness. in particular. is generally higher in areas characterized by sand than in those characterized by, mud. Thus, where dredging has brought about a change in sediment type from sand to mud, species richness has decreased. This has occurred in the dredged areas near the Kingsford-Smith Airport extension and Port Botany revetment. However, in the region of the entrance to the bay, where harsh conditions of high swell and current exposure apparently normally limit benthos. the deeply dredged entrance channel supports a particularly diverse and abundant fauna.

It is concluded that the major influence of dredging on the macrobenthos in Botany Bay has been indirect, through permanent modification of its physical environment. Extension of the present facilities at Port Botany are expected to lead to a significant decrease in the benthic species diversity of this area.