Saltmarsh of the Parramatta-Sydney Harbour: determination of cover and species composition including comparison of API and pedestrian survey
Williams, R.J., Allen, C.B. and Kelleway, J., 2011. Saltmarsh of the Parramatta-Sydney Harbour: determination of cover and species composition including comparison of API and pedestrian survey. Cunninghamia, 12(1): 29–43.
The term “saltmarsh” covers a number of species of plants some of which grow in inland Australia whereas others grow on the coast. Species of saltmarsh growing on the coast were recently declared an Ecologically Endangered Community (EEC) under the NSW Threatened Species Conservation Act 2004. While not explicitly stated, compliance with the act would imply that the cover of saltmarsh in NSW estuaries be determined.
The first maps of coastal saltmarsh for NSW estuaries were provided by West et al. (1985). Maps for estuaries on the north and south coasts were upgraded as part of the recently completed Comprehensive Coastal Assessment (CCA). In both cases, aerial photographs were used as the input data. One deficiency of the CCA was that its terms of reference excluded the central coast of NSW, i.e., the estuaries from the Hunter River to Lake Illawarra, inclusive, were not part of the project. Subsequent efforts by the NSW Department of Primary Industries are attempting to fill this gap.
With the assistance of NSW Maritime, a map of the saltmarsh (as well as mangrove and seagrass) of the Parramatta River for the early 2000s was prepared (West et al. 2004). The latter map suggests there had been an increase in the number of patches, when compared to the earlier study. However, an increase in sophistication of mapping techniques over the intervening years suggests an alternative explanation – the resolution of aerial photos has been enhanced, and coupled with the application of geographic information systems (GIS), there is now better ability to detect small patches of saltmarsh.
Since the declaration of saltmarsh as an EEC, anecdotal reports have suggested there are even smaller patches than could be defined with the mapping technique used in the early 2000s. Aerial photos taken in 2005 and analysed using GIS initially indicated the presence of 417 patches of saltmarsh. However, field investigation revealed that 182 of these patches were spurious, being comprised of non-saltmarsh wetlands, terrestrial plant communities and anthropogenic materials. The remaining 235 patches were saltmarsh communities of various kinds, but the size of only seven patches was correctly estimated by the GIS technique. One reason for the discrepancy was that nearly 50% of all patches were under a canopy of mangrove or other type of tree and therefore not revealed in the aerial photos.
The field survey of the shoreline from Manly to Vaucluse located over 520 patches not identified in the aerial photographic investigation. All together, 757 patches were located, and 70% of these were less than 100 m2 in area. In total, they covered 36.8 ha. Species composition of each patch was determined and a geomorphic scheme was used to divide the estuary into readily definable subunits such that comparisons of distribution could be made. The cover of saltmarsh was found to be unevenly distributed, with most patches located in the upper and middle portions of the estuary. Rare species and the most important of the introduced species were also restricted to the upper and middle portions of the waterway.
Aerial photography is useful for generating broad indications of cover of saltmarsh, but ultimately pedestrian survey will be needed to determine the distribution of small patches, and identify species composition for NSW and for other estuaries in southeast Australia. This will be especially true for rare species.
West, R.J., C.A. Thorogood, T.R. Walford and R.J. Williams (1985). An estuarine inventory for New South Wales, Australia. Fisheries Bulletin 2. Department of Agriculture, New South Wales. 140 pp.