Summary

Saltmarsh, mangrove and seagrass are known to provide important vegetated habitats for many species of fish and invertebrates, some of which are of commercial and/or recreational importance. The distribution of these plants in various New South Wales estuaries are reported to have changed over time. One place where change has been reported is the Parramatta River and its downstream extension, Sydney Harbour. It is possible to assess the degree of change as NSW Fisheries mapped the extent of the large estuarine plants in the early 1980s. Furthermore, it is desirable to know the current distribution of these plants to assist planning authorities with foreshore decision-making and response to the spill of oil or other toxic material.

To assess the present distribution of estuarine vegetation in the Parramatta River a series of aerial photographs taken in 2000 were obtained from the then Office of the Sydney Harbour Manager. The Office had commissioned a commercial consultant to fly and photograph much of the metropolitan area, and the photographs were obtained as electronic images. The images were examined with the assistance of specialised computer facilities known as a Geographic Information System (GIS) and draft maps were produced of the distribution of saltmarsh, mangrove and seagrass. Draft maps were taken into the field and checked against the actual distribution of the plants.

When compared to the maps produced in the 1980s, there would appear to have been a large net loss of seagrass from 129 ha to 52 ha, with large losses at some locations (Clontarf) and small gains at others (e.g., Iron Cove). In contrast, the area of mangrove has increased from 148 ha to 185 ha. Area of saltmarsh appears to have been steady at less than 10 ha. The validity of these comparisons is somewhat reduced given that the current measurements are considered more accurate given the application of GIS technology. A more rigorous determination of change would be obtained by analysing the older photos with the GIS technique. Nevertheless, the results show that seagrass has been lost to a large degree and is presumably susceptible to further loss. This situation needs to be immediately addressed due to the importance of seagrass as a fish habitat. The increase in amount of mangrove is also of concern as it confirms studies done elsewhere in the Parramatta River that show an expansion of mangrove that parallels human settlement and use of the river.