Estuarine Macrobenthic Community Structure in the Hawkesbury River, Australia: Relationships with Sediment Physicochemical and Anthropogenic Parameters

Macrobenthic community assemblage diversity and abundance were monitored on both Cowan and Berowra Creeks in the estuarine reaches of the Hawkesbury River, Sydney Australiaduring 1997–1998. Natural sediment physicochemical differenceswere assessed, along with low-level anthropogenic contaminantsincluding copper, lead, zinc, phosphorus and nitrogen. Contaminant levels at all sites were below sediment guidelinevalues for biological effects. Natural physicochemical sedimentdifferences were the main determinants in species assemblage patterns among sites. Three groupings of sites with similar assemblages were observed during February 1998. Berowra Creek sites, which were higher in organic content and silt/clay (andthus metals and nutrients), higher in pH and lower in salinity,were similar in terms of contributions by the polychaetes Ceratoneresis aequisetis, Scoloplos normalis, the isopod Cyathura hakea and the bivalve mollusc Soletellina alba.Sites on upper Cowan Creek, higher in organic content, silt/clay(nutrients and metals) and lower in salinity, were similar andseparated from other sites in terms of the polychaete Carazziella victoriensis and the gastropod mollusc Nassarius jonasii. Sites lower in Cowan Creek, tended to be higher in sand content, more saline and lower in organic contentand thus nutrient and metal concentrations. These sites were similar in terms of contributions of the polychaete Sigalion bandaensis and the bivalve molluscs, Mysella vitrea and Tellina deltoidalis. The biotic assemblage patterns were not maintained temporally, suggesting the importance of monitoring over time to assess possible futureimpacts. Aggregating species data to the family level resultedin similar site discrimination. Site differences were less distinct at higher taxonomic levels and suggests future monitoring at the family level is sufficient to detect assemblage differences among sites. The results obtained represent the difficulty in detecting responses to low-levelcontamination at the community level, and provide a sound anticipatory baseline for the assessment of future possible anthropogenic disturbance in the Hawkesbury River.