Temporal patterns in the structure of macrobenthic communities of an Australian estuary

Abstract

The benthic fauna of a small estuary was examined to test hypotheses about community structure and environmental stress (foreign, or natural but excessive, perturbations in the environment). Quantitative samples were collected at approximately 2-month intervals over 18 months from Cabbage Tree Basin, Port Hacking, New South Wales. The sites sampled ranged from the intertidal to a central basin subject to deoxygenation of the bottom water. The species composition of the intertidal and shallow-water sites was more stable than that of the deeper sites, due to the presence of short-lived opportunistic species at the deeper sites after periods of deoxygenation. There were no obvious changes in species composition associated with temperature minima or maxima. No changes directly associated with reduced salinity after rainfall were found, although heavy rainfall prior to the sampling period may have reduced the number of species at some sites. The stable community structure and species composition at the intertidal and shallow-water sites indicated that greater environmental harshness does not necessarily imply less faunal stability. Differences in diversity among these sites were interpreted as evidence that biological accommodation was responsible for a reduction in diversity from values predicted by the neutral model. At a deeper site, diversity was close to neutral model predictions. It is suggested that the ecotone point in a stressed community may be characterized by diversity values that are in agreement with neutral model predictions. The statistical properties of the measures of diversity and evenness were not important for their interpretation. Biomass-based measures indicated patterns that were often different from frequency-based measures.