Structure of macrobenthic communities in relation to historical patterns of dredging in the Brisbane River estuary

Abstract

The composition of the benthic assemblages found along the margins of the Brisbane River estuary was examined to determine whether there were any relationships with the historical patterns of extractive dredging in the river. Three categories of treatment were used: control zones which had never been used for extractive dredging; recently dredged zones which had been dredged in the previous 2 years; and previously dredged zones which had been dredged within 3-5 years. A total of 3,113 animals was collected from 64 benthic grab samples, with the fauna dominated by spionid polychaetes (lower reaches) and tanaid crustaceans (upper reaches). The composition of the benthic assemblages in the up-and down-river sections was significantly different from each other, so analyses comparing the three treatments were done separately for the two sections. Multivariate and univariate analyses indicated that there were significant differences among the different zones in the numbers and types of animals found there, but these differences were not correlated with the dredge history for the zones. In each case, zones with a similar dredge history were as different from each other as they were from zones with a different historical pattern of dredging