IMPACT OF DOMESTIC SEWAGE EFFLUENT VERSUS NATURAL BACKGROUND VARIABILITY - AN EXAMPLE FROM JERVIS BAY, NEW-SOUTH-WALES

The effects of an outfall of low-volume, tertiary-treated effluent were evaluated within Jervis Bay on the southern coast of New South Wales by using the macrofauna inhabiting kelp (Ecklonia radiata) holdfasts. A range of analytical methods was used to determine differences in faunistic patterns between six sites (three close to the outfall and three controls) in the winters of 1990 and 1991. The analyses indicated that community structure was highly variable over both the spatial and the temporal scales of the study. Although some of the methods provided results consistent with a perturbed environment on the first sampling occasion (ABC plots, log-normal plots), these patterns were not repeated on the second sampling occasion. In addition, the species primarily responsible for the 'perturbed' configuration with those methods were from taxa that have been highlighted as pollution-sensitive in other studies of holdfast fauna. Non-parametric multivariate statistical methods (MDS, ANOSIM) consistently showed significant differences among sites but also revealed highly significant differences within a site over time. There was no consistent difference between sites closest to the outfall and more distant sampling locations and so no outfall effect was suggested. The results indicate that natural environmental factors are more influential than the low-volume, tertiary-treated effluent from the outfall in determining patterns of community structure in the holdfast community within Jervis Bay.