Australia State of the Environment Report 2001 (Theme Report)
Australian State of the Environment Committee, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06751 5
Saltmarshes [CO Indicator 2.8]
These intertidal saltwater wetlands habitats comprise low herbaceous shrubs and grasses, on mainly low energy shorelines, often behind mangroves.
Saltmarshes are an important ecosystem and provide nursery areas for a range of fish and invertebrate species, roosting sites for many migratory shorebirds, and habitat for endangered species such as the Orange-Bellied Parrot.
The diversity of saltmarsh species is greatest in the southern temperate areas of Australia; Victorian and Tasmanian saltmarshes may contain up to 50 species (Zann 1995). Tropical saltmarshes contain fewer than 10 species.
It is not possible to document either the extent of saltmarsh habitat or the extent of habitat loss as the data is not available on a continental scale. Although there has been loss of saltmarsh habitat in the past, there is no inventory at State or national levels and little new information since 1996. In 1996 the best estimate of areas of saltmarsh was 13 595 km2, based mainly on remote sensing data.
|State/Territory||Area (km 2 )|
Source: Bucher and Saenger (1991), cited in Zann (1995).
Saltmarshes are sensitive to a range of pressures, including land reclamation in urban areas, alteration of land management practices in catchments, regulation of freshwater and tidal flows, invasion by weeds, and drainage for mosquito and midge control.
Vegetation on saltmarshes is being damaged or removed by activities such as cattle grazing, the use of off-road vehicles, and changing drainage regimes to control pest insect populations (Thomas and Connolly 2001). Pressures on saltflats could, in the future, include the development of aquaculture sites on what may be seen as unproductive land. Saltflats are particularly vulnerable to sea-level rise.
Decline in saltmarsh habitat on a continental scale may appear to be quite small. However, because reductions are concentrated in the south-east of the continent where saltmarsh areas are smallest, but support the greatest diversity of species, their significance is disproportionate to their extent. Several researchers, such as Wilton (2001) and Saintilan & Williams (2000), reported landward expansion of mangroves into saltmarsh habitat. In some cases the rate of mangrove encroachment is high, for example between 10 and 17 metres per year over 30 years on the eastern shore of Gulf St Vincent. The trend is not universal, however, with mangrove-saltmarsh boundaries in many estuaries being stable.