Summary of environmental impacts

SUBTIDAL MACROFAUNA  

Hard Substrate Communities

Community changes in hard substrate macrofauna have usually been identified using photographic quadrats. Depending on the treatment type, gross changes in hard substrate macrofauna can occur. Effluent discharged with a high level of particulates can change a benthic community from one that is algal dominated to one dominated by filter feeders (e.g. sponges and crinoids). This was particularly evident at the old Burwood Beach outfall and was suggested at the North Head deep ocean outfall. An increase in silt matrix (a mixture of fine silt, microscopic invertebrates, algae and hydrozoans) was also observed at North Head deep ocean outfall. The presumed mechanism for these changes are a reduction in light penetration and particulate deposition.

More recently, a study of hard substrate macrofauna was conducted at sites close to the new Boulder Bay extended ocean outfall (Roberts et al 1998). Within 3 months of the commissioning of the outfall, significant reductions in the cover of crustose and foliose algae were apparent at the outfall location when compared to control locations. The cover of several species of sponge, including Cymbastela concentrica, Geodinella sp. and Spongia sp., also underwent marked declines coincident with the commissioning of the extended outfall. However, the cover and number of species of sponges or total fauna did not change significantly. After commissioning of the outfall, the cover of a nondescript matrix comprising silt and microorganisms doubled its representation to almost 60%. The overall composition of the community at the outfall changed from one in which algae and sponges were well represented to an assemblage dominated by silt and ascidians.

In contrast, long term studies at sites close to First Point, Norah Head and other Central Coast outfalls have failed to find significant changes in hard substrate macrofauna. In fact, the major factor suggested to be affecting hard substrate macrofauna in shallower areas was storm activity (Laxton & Laxton 1979). The differences in these results may be influenced to some degree by experimental design problems, however, they suggest that this issue may require further research.

Soft Substrate Communities

Infaunal benthic invertebrate species have been one of the most widely studied communities in terms of impact assessment. However, the majority of this work has been conducted overseas with only a few studies conducted in NSW (e.g. Otway et al 1996, Krogh et al 1997). Demonstrated impacts on benthic invertebrate communities have been linked to nutrient enrichment and sewage pollution (Pearson & Rosenberg 1978, Swartz et al 1986), chemical pollution (Rygg 1985, Ahn et al 1995) and natural and man-made sources of oil pollution (Gray et al 1990, Agard et al 1993). In extreme cases, impacts may eliminate all macrofauna from an area. Where the effect is not so extreme, impacts generally produce a reduction in species diversity. The numbers of some individual species may increase in impacted areas to the point where one or a few opportunistic species can be present in large numbers. An example of this is the polychaete worm Capitella capitata which dominates areas close to some outfalls in the USA to the exclusion of nearly all other species. This species has been recorded from NSW (although the actual status of this species in NSW waters may require further investigation), however, this species has not yet been found to dominate any areas of NSW affected by sewage pollution. This may partly be due to the majority of sewage outfalls in NSW being located in coastal, rocky, high wave energy environments as opposed to areas which contain soft sediments. Recent investigations into the effects of Sydney’s deep ocean outfalls, which do discharge into waters characterised by soft sediment bottoms, have not identified any areas of obvious reduction in diversity that can be attributed to the outfalls.

ALGAL ASSOCIATED MACROFAUNA

1. Kelp Holdfasts

The invertebrate fauna inhabiting kelp holdfasts near sewage outfalls have been investigated by Smith and Simpson (1990, 1993), Saenger et al (1991), Smith (1994) and Roach et al (1995). The impact of sewage effluent disposal on these communities appears to be site specific. At Corambirra Point (Coffs Harbour) outfall the most sensitive indicators were bivalves (higher abundance adjacent to the outfall) and amphipod crustaceans (lower abundance adjacent to the outfall). In addition, there were consistent changes in the importance of different feeding strategies with a shift away from generalist feeders (omnivores) to suspension feeders at the closer outfall sites. At Skennars Head the sewage effluent altered the community structure of kelp holdfast fauna by increasing the number of polychaetes and decreasing the number of amphipods. At Plantation Point (Jervis Bay) outfall, however, natural environmental factors were more important in determining community structure than the effects of tertiary treated effluent (Smith 1994) and no changes in community structure could be attributed to the outfall. Similar results were obtained near Bellambi and Port Kembla outfalls, where Roach et al (1995) concluded that the effects of effluent discharge on the composition of kelp holdfast communities, if any, were small compared with natural variation.

2. Turfing Algae

The invertebrate fauna inhabiting subtidal turfing algae near Penguin Head outfall have been investigated by TEL (1996a). Invertebrates associated with subtidal turfing algae were abundant and diverse and trends in variability at Penguin Head were similar to those at the reference locations. There was no evidence of an effect due to the release of effluent.

(Impac_4) Last updated May 2000