Mapping the habitats of NSW estuaries.
Creese RG, Glasby TM, West G and Gallen C (2009) Mapping the habitats of NSW estuaries. Industry & Investment NSW Fisheries Final Report Series 113. Port Stephens, NSW, Australia. ISSN 1837-2112. 95pp.
The health of the estuaries of NSW is something that needs constant consideration and attention. An important component of estuarine condition is the status of the key biogenic habitats in estuaries their seagrass, mangrove and saltmarsh communities, collectively known as macrophytes. Having comprehensive data about the extent of these habitat types is a fundamental first step to being able to assess trends through time, and hence assess whether condition is, in fact, improving. The primary objective of the estuarine component of the Seabed Mapping project, undertaken by DPI, was to complete a state-wide GIS inventory of these 3 habitats, a task that was started during the Comprehensive Coastal Assessment (CCA).
The CCA had adopted a rigorous protocol for recording the extent of estuarine macrophytes and had mapped them in estuaries north of Newcastle and south of Wollongong. However, this had left a significant knowledge gap along the central part of the NSW coast, a region that contained several very large drowned river systems (Hawkesbury River, Port Jackson) and the states largest coastal lake (Lake Macquarie). The task of finalising the state-wide inventory was completed using a combination of interpreted aerial photographs and field surveys. The inventory now contains a standardised GIS layer for the macrophytes in 54 estuaries. Having a comprehensive baseline for these habitats is an important first step in being able to manage them better to conserve estuarine biodiversity.
While macrophytes are acknowledged as being a major contributor to the habitat structure in estuaries, non-biogenic structures such as subtidal reefs, intertidal rocky shores and shallow sediment flats are also important as habitats for estuarine biodiversity. Further, many NSW estuaries contain increasing amounts of non-natural hard surfaces as a result of human activities in estuaries. Artificial rock walls, wharves, jetties, marinas, etc all provide structural habitat, especially in estuaries that are also major ports and/or are highly urbanised. Natural hard surfaces can increase the diversity of native plants and animals in estuaries, but artificial hard surfaces may also attract large numbers of introduced marine species. During this project, a protocol was developed for recording these hard surfaces. The technique uses a combination of aerial photograph interpretation (as for the macrophyte habitats), field surveys, side scan sonar and underwater video to delineate a set of foreshore features and rocky reef sub-habitats. This methodology is analogous to that used to map offshore habitats in deeper water, something that was done in the companion marine component of this Seabed Mapping project (undertaken by DECCW). The technique was piloted in 6 estuaries in the central and southern regions of the NSW coast where large amounts of hard surface habitat was known or suspected. Again, the information was recorded in a GIS and can therefore be readily used in conjunction with other GIS layers (including estuarine macrophytes) to assess the relative biodiversity values of an estuary or region.
Because the estuarine and marine habitat mapping work was done concurrently and because both components used complementary habitat classifications and recording standards, it is now possible to combine all the information in a common GIS. One of the key outputs from this project is a new set of maps (at 1:25000 scale) which show detailed bathymetrical, topographical and habitat information for the entire NSW coast from the upper tidal limit of estuaries out to the 3 nautical mile limit of state waters. These maps can continually be updated as new information is gathered and added into the underlying GIS. While these products are valuable in their own right in terms of providing a comprehensive description of the NSW coast, perhaps the greatest value of the GIS is that it provides a solid framework for making decisions about management actions needed to improve the condition of estuaries in NSW. This can now readily be done in an explicit spatial context by using the habitat maps generated during this project (and preceding ones), in conjunction with knowledge about how and where the threats operate, to generate vulnerability values for key estuarine habitats. When these values are considered in the risk assessment framework, it will be possible in the future to provide management agencies the means by which they can assign relative values to particular locations.