Benthos of the Port of Melbourne : The Yarra River and Hobsons Bay, Victoria

Abstract

The distribution of soft-bottom macrobenthos in the Yarra River and Hobsons Bay, Vic.,is examined in terms of temporal changes in abundance and diversity, and related to selected environmental variables.

Hierarchical classification was used to divide the stations into three zones: upstream river stations; downstream river stations with muddy bay stations; and sandy bay stations.

The faunas of the river and the central muddy basin of Port Phillip Bay are similar although several common Bay species were absent in the river, probably as a result of competition and lowered salinity and dissolved oxygen. Faunal diversity of the Yarra River was lower than that of Hobsons Bay and is lower than that of equivalent areas in the northern hemisphere. Seasonality in species composition or diversity was not observed.

The dominant river species, Theora fragilis (Bivalvia), was more abundant in the lower river than anywhere in Port Phillip Bay. Its life expectancy and density were lowest at stations further up the river.

Species diversity seems more predictable in highly diverse communities lacking dominant species than in communities of low diversity dominated at all times by one or two species.