Changes to benthic communities over 20 years in Port Phillip Bay, Victoria, Australia

Changes to the structure of benthic communities in Port Phillip Bay, Victoria, were determined by comparing results of a survey of 86 sites in 1969–72 with a survey of 13 sites in 1991–92. The species composition of communities differed significantly between surveys. Since the earlier study a further three exotic species (Sabella spallanzanii, Corbula gibba, Euchone limnicola) have become abundant and these are contributing to long-term and probably irreversible changes to the ecology of Port Phillip Bay. Other changes may reflect real change or differences between habitats sampled in both studies. The ambiguity of conclusions from comparisons between these studies emphasises the need for an adequate time-series of benthic monitoring to better define the extent of change and to identify their causes.