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 R iver, Sydney Australia during 1997-1998. Natural sediment physicochemical d ifferences were assessed, along with low-level anthropogenic contaminants i ncluding copper, lead, zinc, phosphorus and nitrogen. Contaminant levels at all sites were below sediment guideline values for biological effects. Nat ural physicochemical sediment differences were the main determinants in spe cies 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 (and thus metals and nutrient s), higher in pH and lower in salinity, were similar in terms of contributi ons by the polychaetes Ceratoneresis aequisetis, Scoloplos normalis, the is opod Cyathura hakea and the bivalve mollusc Soletellina alba. Sites on uppe r Cowan Creek, higher in organic content, silt/clay (nutrients and metals) and lower in salinity, were similar and separated from other sites in terms of the polychaete Carazziella victoriensis and the gastropod mollusc Nassa rius jonasii. Sites lower in Cowan Creek, tended to be higher in sand conte nt, more saline and lower in organic content and thus nutrient and metal co ncentrations. These sites were similar in terms of contributions of the pol ychaete Sigalion bandaensis and the bivalve molluscs, Mysella vitrea and Te llina deltoidalis. The biotic assemblage patterns were not maintained tempo rally, suggesting the importance of monitoring over time to assess possible future impacts. Aggregating species data to the family level resulted in s imilar site discrimination. Site differences were less distinct at higher t axonomic levels and suggests future monitoring at the family level is suffi cient to detect assemblage differences among sites. The results obtained re present the difficulty in detecting responses to low-level contamination at the community level, and provide a sound anticipatory baseline for the ass essment of future possible anthropogenic disturbance in the Hawkesbury Rive r.