Changes in benthic communities of Port Phillip Bay, Australia, between 1969 and 1995

Abstract

Changes in benthic communities in Port Phillip Bay, Australia, were assessed over a 25- year period by comparing an intense bay-wide survey carried out in the early 1970s, a 3-year study in the mid 1970s, a limited survey in the early 1990s, and a resurvey in the mid 1990s. A major division of benthic communities into those on deeper muddy sediments and those on marginal sandy sediments persisted was less well defined (by ordination methods) in the 1990s than in the 1970s. The densities of individuals and species declined significantly, but absolute numbers of taxa did not change noticeably. Nevertheless, temporal variability in all variables over 25 years was within the range reported for the 3- year study. Polychaetes have become relatively more abundant than crustaceans and molluscs, and the proportion of suspension-feeding organisms has increased at the expense of deposit feeders. The introduced Japanese bivalve Theora lubrica was the most abundant invertebrate in the 1970s. In the 1990s, this species, the European bivalve Corbula gibba and the polychaete Euchone limnicola were the most abundant. Decreasing abundances of macrobenthic invertebrates, and a decreasing proportion of deposit feeders, is consistent with a decrease in nutrient load from moderate to low levels—such as occurred with reduced discharge from Melbourne’s sewage treatment plant—but lack of contemporaneous data prevents further explanation.